Application of Accelerated Bridge Construction Connections in Moderate-to-High Seismic Regions (2011)

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15 Evaluation of Connection Types The description of the findings and the evaluation of con- nection types in this section are organized by force transfer mechanism: • Bar Couplers • Grouted Ducts • Pocket Connections • Member Socket Connections • Hybrid Connections • Integral Connections • Emerging Technologies Descriptions of individual connections or systems are con- tained in Appendices A through G, and those descriptions are then used in the more general discussions and evaluations of the connection types listed above. Appendix H provides the detailed evaluations of the connection types, and this chapter summarizes the information in Appendix H. As described in Chapter 2, each connection type is evaluated on the basis of the following: • Performance potential, which is a composite of construction risk, seismic performance, durability, and post-earthquake inspectability • Time savings potential • Technology readiness The reader is referred to Appendix H for detailed infor- mation about each connection type. Additionally, the appendix provides information on material requirements, construction techniques, and detailed evaluation of labo- ratory testing of representative specimens of the connec- tion type. Bar Couplers Description A bar coupler is used to splice two bars together, end-to- end. It allows axial force to be transferred from one bar to the other and performs the same function as a welded butt splice. In most cases, compression can be resisted by end bearing, and the transfer of tension is the more critical matter. A typical arrangement is shown in Figure 6. Several styles of coupler (described in the following list and illustrated in Figure 7) are commercially available. Each depends on a different mechanical principle. • Threaded sleeve. The bars are equipped with male thread, and they screw into a sleeve with a female thread. The threads may be tapered to reduce the number of turns necessary for full engagement. Such couplers permit little alignment tolerance. • Headed bars with separate sleeves. A head is formed on the end of each bar and a threaded coupling piece draws the two together. To ensure contact for transferring compression, a shim may be placed between the bar ends. • External clamping screws. A steel sleeve fits over the bar ends. Set screws are driven radially through the sleeve into the bar. The tension force is transferred from bar to sleeve to bar through shear in the screws. • Grouted sleeves. A steel sleeve fits over the bar ends and is filled with grout. Tension is transferred by bond from bar to grout, and grout to sleeve. A variant of the grouted sleeve uses a screw thread to connect one bar to the sleeve and grout to connect the other. This adaptation allows the sleeve to be shorter. The bar coupler connection type can be used in the follow- ing locations: C H A P T E R 3 Findings and Applications

• Footing to column • Splices between column segments or cap beam segments • Column to cap beam Performance and Time Savings Evaluation Performance scores were assigned for this connection type based on the comments outlined in Appendix H regard- ing construction risk, seismic performance, inspectability, and durability (see Table 11). In the table, the shaded cells indicate the composite performance expected as a group. Additionally, the numbers indicate the scores of individual connections, and the number corresponds to the identifying number for the connection in the appendix. For instance, the bar coupler type of connections include seven examples eval- uated in Appendix A. In the appendix, the connections are denoted by BC-1 through BC-7, but in Table 11 only the connection number appears. The numbers are provided in the table simply to indicate the range of scores for the con- nection type. The numbers also indicate how a particular connection scored relative to other connections evaluated for the group. The construction risk for bar coupler connections is less favorable than CIP construction because of the possibility that the bar and coupler might be misaligned relative to each other. The coupler might also not be correctly or fully engaged, for example, if a grouted splice sleeve was not filled properly. The seismic performance is rated lower than CIP construction because the test data for bar coupler connections is incom- plete. The post-earthquake inspectability is similar to CIP; so a value of 0 is assigned. The durability is assigned a value of 0, because the potential for local voids during grouting is offset somewhat by the improvements in construction quality likely with precast elements. The time savings for bar coupler connections was rated as +2 (much better than CIP) (see Table 12). The estimated sav- ings is approximately 11 days for a bent in which the columns and cap beam are precast. The majority of that savings comes from using such connections at the cap beam. Technology Readiness Table 13 provides a summary of the TRL levels and of the estimated percentage of development that has been accom- plished to date for the connection group. Because this rating applies to the entire group, it is a composite of the status of the individual couplers. Summary Bar coupler connections are being widely used in prac- tice; however, their ability to sustain cyclic inelastic defor- mations is not well documented. Therefore, the connection type is considered constructible and promising for seismic use, but further experimental testing is suggested to verify its performance. 16 Figure 6. Bar coupler—typical application. Figure 7. Bar coupler types. Table 11. Performance potential of bar coupler connections. Threaded sleeve Headed bars with mating sleeves External clamping screws Grouted splice sleeve Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better +1 Slightly better 0 Equal 6 6 7 1 2 3 4 5 6 1 2 3 4 6 7 –1 Slightly worse 1 2 3 4 5 1 2 3 4 5 7 5 –2 Much worse 7

Areas in which additional research is needed include the following: • Inelastic cyclic performance—drift capacity • Influence of coupler on bar strain distribution • Influence of coupler location and orientation on inelastic performance 17 Table 12. Time savings potential of bar coupler connections. Time Savings Potential Definition Relative to CIP Value +2 Much better 1 2 4 5 +1 Slightly better 3 6 0 lauqE –1 Slightly worse 7 –2 Much worse Grouted Ducts Description In grouted duct connections, reinforcing bars extending from one precast member are inserted into ducts cast into the second, and the ducts are then grouted. The hardened grout anchors the bar in the duct. The force from the bar is transferred into the surrounding concrete, and, possibly, to one or more bars lap-spliced to the outside of the duct. That load transfer mechanism contrasts with the one found in bar couplers, in which the load is transferred from one bar to another bar that is collinear with the first. A grouted duct connection can be configured in many different ways, exam- ples of which are shown in Appendix B. Application of column to cap beam connections using grouted ducts are provided in Figure 8 and Figure 9, and a sample connection is shown in Figure 10. Figure 8. Grouted duct cap construction and cap placement (Matsumoto 2009b). Table 13. Technology readiness level evaluation of bar coupler connections. Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake

This connection type can be used in the following locations: • Pile to pile cap • Spread footing or pile cap to column • Column to cap beam • Splice between column segments or cap beam segments Performance and Time Savings Evaluation Performance grades were assigned based on the comments stated previously regarding construction risk, seismic per- formance, inspectability, and durability. The construction risk was rated as less favorable than CIP construction because of the possibility of difficulties with grouting the ducts. All other evaluations are similar to CIP, and they are shown in Table 14. The several −1 evaluations for inspectability reflect cases where the grouted connection is deep within the member and, thus, difficult to inspect. The time savings potential was evaluated as much better than CIP concrete, especially if the cap beam is precast (see Table 15). The corresponding group score was +2. Technology Readiness Grouted ducts have been tested extensively under static load- ing, and a few tests have been conducted under cyclic load- ing (Matsumoto 2009b, Pang et al. 2010). Preliminary design guidelines have been formulated for seismic use (Restrepo et al. 2011; Matsumoto et al. 2001, 2008; PCI Design Handbook 2004) and are in the process of refinement. The connection type has been deployed in non-seismic regions and a few times in seismic regions (SR 520, Highways for LIFE). Thus, a TRL max- imum value of 8 is assigned without any gaps (see Table 16). Summary Grouted duct connections have been used on projects in both non-seismic and seismic regions. Additionally, significantly more research has been conducted on grouted ducts than on other connection types. As noted in the seismic performance section, the use of fibers to reinforce the grout bedding layer needs to be confirmed. The question of strain distribution, which is affected by the rela- tively rigid ducts, is similar to the one raised in the grouted splice sleeve evaluation and also merits further investigation. Areas in which additional research is needed include the following: • Effect of duct size on anchorage length • Influence of duct location on cyclic performance (e.g., in plastic hinge zone versus adjacent) 18 Figure 10. Typical grouted duct. Figure 9. Grouted duct lower stage cap erection (Washington State DOT SR 520/SR 202). Table 14. Performance potential evaluation for grouted duct connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better +1 Slightly better 0 Equal 2 3 1 2 3 4 5 6 1 2 3 4 5 6 7 2 3 5 6 –1 Slightly worse 1 4 5 6 7 7 1 4 7 –2 Much worse

• Implications of lap splicing column bars to connection bars • Impact of additional bars on plastic hinge region cyclic performance • Influence of duct material, off-center bar, group pull-out effects, bedding layer reinforcement Pocket Connections Description Pocket connections are constructed by extending reinforc- ing from the end of one precast structural member, typically a column or pile, and inserting it into a single preformed pocket inside another member. The connection is secured by using a grout or concrete closure pour in the pocket (Figure 11). A grout/concrete bedding joint can be used to provide adjust- ability. This connection differs from the member socket connection, in which the whole end of a member is embedded in the other. Pocket connection examples can be found in Appendix C. Special consideration must be given to the detailing of the pocket and how it will be formed. The transfer of forces between the embedded member and the surrounding member occurs at the pocket perimeter. A steel duct can be used as a stay-in-place formwork that provides joint reinforcement and confinement to the pocket concrete. This duct should be placed between the cap beam top and bottom reinforcing bars. An additional piece of formwork, such as a cardboard concrete form tube, must be adhered to the top and bottom of the steel duct to extend the pocket form to the surface of the cap beam. The cardboard concrete form tube can be notched to fit over the reinforcing bars that cross through the pocket (Matsumoto 2009c). This connection type can be used in the following locations: • Column to cap beam • Footing to column • Pile to pile cap Performance and Time Savings Evaluation Performance grades were assigned based on the comments outlined in Appendix C regarding construction risk, seismic performance, inspectability, and durability (see Table 17). The scores lower than CIP generally reflect the increase in difficulty of constructing the connection and the potential for moisture intrusion into the joint, which potentially reduces durability. The much lower seismic performance value for two connec- tions reflects designs not well-suited to seismic use. The use of precast columns and cap beams connected with pockets is estimated to save 5.5 days, relative to CIP bridge bent construction (see the Time Savings section of Appendix H). This is an approximately 25% reduction in construction time. The majority of the savings was due to precasting the cap beam. Little, if any, time is saved by using a pocket at the column to 19 Table 15. Time savings potential evaluation for grouted duct connections. Time Savings Potential Definition Relative to CIP Value +2 Much better 1 2 4 6 +1 Slightly better 5 7 0 3lauqE –1 Slightly worse –2 Much worse Table 16. Technology readiness level evaluation for grouted duct connections. Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake Figure 11. Pocket connection concept.

footing connection. Furthermore, if the pocket is formed in the footing, depositing the concrete into it would be difficult because the precast column would block access from above. Out of all the precast connection types, the time savings associated with the pocket connection was the smallest, lead- ing to a score of +1 (Table 18). Due to the large volume of material required to fill the pocket, concrete would typically be used instead of grout. This choice reduces speed of the pocket connection because concrete typically requires more time to gain strength than grout. A pocket connection also likely requires column jacks or other devices to support the cap beam’s weight until the concrete has gained sufficient strength to transfer the loads by bond to the corrugated tube. By contrast, in a cap beam equipped with grouted ducts or sleeves, no column jacks are needed and the grout in the bed needs to gain only enough strength to carry the beam’s weight through compression. Technology Readiness Based on the level of seismic research, available design guid- ance, and use in practice, the evaluated pocket connections achieved TRL scores as shown in Table 19. The absence of test- ing of seismic components (Level 5) is not regarded as negative because there are essentially no components, such as individ- ual couplers or grouted ducts, to test. Individual TRL values are given in Appendix C for different versions of the connection. Summary Given their good performance potential, pocket connections are promising for use in high seismic regions, if sufficient joint reinforcement is provided. However, the additional curing time of concrete relative to grouted connections makes the pocket less attractive for accelerated construction. This shortcoming could be mitigated by using grout or concrete with high early strength. To avoid the material’s shrinking away from the cor- rugated steel tube, grout with non-shrink properties would be the better choice. Additional experimental and analytical efforts are necessary to develop full design specifications for pocket connections. 20 Table 18. Time savings potential for pocket connections. Time Savings Potential Definition Relative to CIP Value +2 Much better +1 Slightly better 1 2 3 4 5 0 lauqE –1 Slightly worse –2 Much worse Table 17. Performance potential evaluation for pocket connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better +1 Slightly better 0 Equal 1 2 5 1 2 3 4 5 –1 Slightly worse 1 2 3 4 5 1 2 3 4 5 –2 Much worse 3 4 Table 19. Technology readiness level evaluation for pocket connections. Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake

Other areas that need to be further explored are the joint behavior and joint performance limit states. Member Socket Connections Description Member socket connections are constructed by embedding a precast structural member inside another member. An exam- ple is shown in Figure 12. The connection is secured by either casting the second member around the first or using a grout or concrete closure pour in a preformed socket. The major types described are connections involving precast concrete columns or concrete-filled steel tubes (CFST). Additional discussion is provided on concrete filled fiber-reinforced plastic tubes (CFFT) and on topics for which information was available. Socket connections have been used occasionally in the build- ing industry, but few examples of their use in bridges were found. Connection examples are provided in Appendix D. This connection type can be used in the following locations: • Footing to column • Column to cap beam • Pile to pile cap Performance and Time Savings Evaluation Performance scores were assigned based on the comments listed in Appendix D regarding construction risk, seismic per- formance, inspectability, and durability and are given in Table 20. Note that the range of evaluations is particularly wide for this connection owing to complexity of the connec- tion detailing and whether the connection’s design considered seismic loading. Table 21 provides the time saving potential for socket con- nections. The use of precast columns and cap beams con- nected with sockets is estimated to save 10.5 days, relative to CIP bridge bent construction (see the Time Savings section of Appendix H). This is an approximately 50% reduction in construction time. The majority of the savings was due to precasting the cap beam. For a column with a footing cast around it, time savings is limited by the strength required of the concrete before construction may proceed. Technology Readiness Based on the level of seismic research, available design guidance, and use in practice, the evaluated socket connec- tions achieved TRL scores as shown in Table 22. Individual TRL values are given in Appendix D for different versions of the connection type. Summary Given their good performance potential and time savings, member socket connections are promising for use in ABC in high seismic regions. For precast concrete column member sockets, the connec- tion needs to be tested for use with precast cap beams. A cap 21 Figure 12. Member socket connection concepts. Table 20. Performance potential evaluation for socket connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better 2 4 +1 Slightly better 1 1 2 4 4 0 Equal 4 1 2 3 3 5 6 1 2 3 5 6 –1 Slightly worse 3 5 6 –2 Much worse 5 6

beam is much narrower than a footing, and the effect of the reduced strength and stiffness on the connection has not been determined. The effect of different member surface roughnesses on required embedment, bond, and connection performance should be explored. Also, models and design equations for transfer of forces in the joint region are needed, including the required embedment of column and required footing depth. Additional experimental and analytical efforts are neces- sary to develop design equations for CFST columns and foun- dation connections. Areas that need to be addressed are the ratio of diameter (D) to thickness (t) of the tube (D/t ratio), steel strength, and models for the transfer of forces in the joint. Those models are likely to be different from the ones for precast columns because CFSTs are typically embedded to a smaller depth and are anchored by means of a flange on the bottom of the tube. The monotonic loading tests of embedded CFFT connec- tions are a good start to understanding the connection behav- ior. Additional research is necessary to determine the cyclic performance of embedded fiber-reinforced polymer (FRP) connections. However, CFSTs are not considered a good can- didate for seismic zones because the cost is higher than steel and FRP tubes are more susceptible to impact damage, more difficult to repair, and non-ductile. CFFTs are most beneficial for corrosive environments, where steel tubes could suffer from corrosion. Hybrid Connections Description Hybrid systems and connections contain an unbonded prestressing tendon and mild steel reinforcement or other energy-dissipating material in the plastic hinge region. The term “hybrid” denotes the use of two reinforcing materials, prestressing, and mild steel, where each provides a benefit for seismic performance, as described below. The joints between precast members open when the seismic moment becomes large enough, and essentially all the member displacement is accommodated by the concentrated rotation at the joint. The body of the member undergoes no plastic deformation and damage to the member is thus minimized. Further- more, because the tendon is unbonded and able to elongate evenly along its full length, joint opening causes only a small increase in strain in the tendon, which therefore remains elastic. Consequently, the tendon provides an elastic restor- ing force to the system that minimizes residual drift after a seismic event. That system produces a nonlinear elastic response with no energy dissipation. When it is coupled with yielding reinforcing bars, which do dissipate energy, it leads to hysteresis loops that are “flag-shaped,” as shown in Figure 13. Ideally, the hysteresis loop passes through the ori- gin at each cycle thereby resulting in no displacement when the load is removed. Some building structures have been constructed using the hybrid concept, but as yet no bridges. Examples of proposed systems and summaries of laboratory tests on these systems are given in Appendix E. In most cases, the column is post- tensioned, although pretensioned systems are being developed. Performance and Time Savings Evaluation Performance scores were assigned based on the fore- going discussion regarding construction risk, seismic per- formance, inspectability, and durability (see Table 23). The values should be taken as indicative rather than definitive 22 Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake Table 22. Technology readiness level evaluation for socket connections. Table 21. Time savings potential for socket connections. Time Savings Potential Definition Relative to CIP Value +2 Much better 1 2 4 5 6 +1 Slightly better 3 0 lauqE –1 Slightly worse –2 Much worse

because of the many possible ways to implement a hybrid system. The construction risk is rated as less favorable than for a CIP system largely because of the additional site activ- ities needed for post-tensioning and grouting. However, those are not necessary in a pretensioned system. The seis- mic performance is rated as potentially much better be- cause of the reduced residual drift, and the consequently high probability of being able to use the structure directly after an earthquake. The durability and post-earthquake inspectability are slightly worse than CIP due to concerns about the post-tensioning tendons corroding and about verification of remaining post-tensioning force after an earthquake. The time savings for hybrid connections was rated as 0 (equal to CIP) (see Table 24), due to the range of time sav- ings estimated during the evaluations. As with the perform- ance estimates, the expected time savings depend heavily on the details of the implementation. Use of precasting will reduce the time required, but post-tensioning will add to it, most likely resulting in a modest net gain. A pretensioned system, connected to both the foundation and cap beam using socket connections, would be expected to offer the same time savings as a non-prestressed socket system, a type of connection that represents the greatest time savings of all the systems considered. Technology Readiness The TRL evaluation is given in Table 25. Non-seismic field deployment is unlikely to occur because the unbonded tendon system offers no advantage there. The analysis for seismic load- ing, seismic testing of components and subassemblies, and the design guidelines all take into account the extensive work that has been conducted on the system for buildings, much of which concerns the basic hybrid concept, rather than the implementation in a particular structural type (bridges). This has not been done for the “deployment in seismic area” category because that depends on particular details of construc- tion. However, it should be noted that a number of buildings, including the 39-story Paramount Building in San Francisco, California, (Englekirk 2002), have been constructed using the hybrid system. Summary Hybrid systems have been shown to have seismic perfor- mance that is potentially better than that of conventional con- struction because of the hybrid’s re-centering properties. They have been used in buildings in high seismic zones in California, but have not yet been used for bridges. One hybrid building in Santiago went through the recent Chile earthquake with no damage (Stanton personal communication with Patricio Bonelli, the building’s designer, October 26, 2010). Use of the technology in bridges differs from that in build- ings because the columns, rather than the beams, are pre- stressed. This is an advantage because, in building frames, the “beam elongation” associated with rocking of the beams 23 Figure 13. Hybrid connection— diagram and generalized hysteresis (Restrepo et al. 2011). Table 23. Performance potential of hybrid connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better 5 +1 Slightly better 4 1 2 3 6 7 8 8 0 Equal 8 4 4 8 –1 Slightly worse 1 3 5 6 7 4 1 2 3 5 6 7 1 2 3 5 6 7 –2 Much worse 2 Table 24. Time savings potential of hybrid connections. Time Savings Potential Definition Relative to CIP Value +2 Much better 8 +1 Slightly better 3 4 0 Equal 1 5 –1 Slightly worse 6 7 –2 Much worse 2

against the columns creates detailing problems in the floor system. In a bridge, the column elongates slightly as it rocks, and it may do so freely, without concern about its attachment to adjacent members, if the bridge is designed for this effect. While the seismic performance benefits are not in doubt, connection details for bridges that allow good constructabil- ity and durability are still being developed. The primary con- cerns expressed by bridge engineers include the potential for higher cost to be weighed against the benefits of re-centering, the additional time on site needed for post-tensioning, cor- rosion of post-tensioning tendons, anchorage details, and ease of inspection and repair. Further research is needed on connection detailing that will address the concerns of practicing bridge engineers. Engaging practitioners and contractors in such work would lead to ben- efits. The pretensioned system presently under development appears to hold particular promise because it effectively addresses many of the major practical concerns. Integral Connections Description Integral connections form joints between bridge elements that provide no articulation and transfer moment across the connection interface. The most typical application of integral connections is the integral cap beam/diaphragm to girder con- nection for a steel/concrete composite bridge. Such connec- tions have historically been constructed with CIP methods, but with ABC, these may use a steel or precast concrete stay- in-place formwork that is filled with reinforced concrete to integrate the bridge components in the joint area. An example of a CIP integral cap beam that supports con- crete girders with a lower stage cap beam is illustrated in Figure 14. The lower stage is constructed first then infilled to create the integral connection after the superstructure is erected. This provides longitudinal positive and negative moment continuity for seismic and other lateral loads. With ABC, the lower stage of the cap beam may be precast and set on the column using any of several connections described in previous sections. The erection of the girders and completion of the integral connection would proceed as with CIP tech- niques. The girders can be built with stay-in-place forms attached for the upper stage of the cap beam, or forms could be built on site. An example of a precast lower stage cap is shown in Figure 15 for the San Mateo (California) bridge project. This application used upper-stage forms that were built on site. Integrating the columns directly into a combined cap beam/ diaphragm, whose soffit is flush with the superstructure, allows for a shallower construction height of the assembly and pro- vides for both positive and negative moment resistance in the longitudinal direction, with potential benefits to seismic per- formance. The stay-in-place formwork can be part of the 24 Figure 14. Two-stage cap beam with prestressed girders. Table 25. Technology readiness level evaluation of hybrid connections. Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake

load-carrying system and can be equipped with dowels to integrate the structural formwork with the CIP concrete. A structural formwork can be designed robust enough to allow carrying construction loads to enable the erection of the superstructure to continue before the CIP concrete is cured. Typically, the stay-in-place formwork is already fully rein- forced before erection. Alternatively, the stay-in-place form- work could be filled with fiber-reinforced concrete as the formwork provides confinement. Integral connections must develop the joint shear force transfer mechanism that is required to “turn” the longitudinal girder moments into the column moments. In the confined space between girders and the column, adequate force trans- fer can be difficult to achieve. Development of both positive and negative longitudinal bending capacities of the girders must be provided. Develop- ment of negative bending is usually simple because the deck slab provides space for reinforcement. Positive (tension on bottom) bending capacity is more difficult to provide. Strand may be extended from the bottoms of the girders and may be terminated with strand chucks or other positive anchorage devices. Older methods include bending the strand up into the cap beam, but this detail provides questionable anchorage. Alternatively, deformed bars may be extended from the gird- ers and spliced, as shown in Figure 15. However, this requires that sufficient room in the girder lower flange exists for the bars. Often, this is not the case where straight strands have been used. Longitudinal post-tensioning can be used to improve the transfer of forces, and the post-tensioning force can potentially be used to compress vertical shear interfaces, simplifying the fit-up of the girders to the cap for a flush-soffit arrangement. Restrepo et al. (2011) have investigated one such configuration for ABC methods as part of the NCHRP Report 681. In the case of a composite steel and concrete bridge, the stay-in-place formwork may be steel and can provide flanges to which the steel girders can be bolted, as in Figure 16. Sim- ilarly, a stay-in-place formwork for concrete girders provides cut-outs through which the girders can be inserted and mono- lithically connected within the CIP concrete. The concrete col- umn is integrated by either inserting the entire concrete column with exposed connection reinforcement into a bottom open- ing of the steel form or by only extending connection steel through the bottom steel form and providing dowels for shear transfer. This principle is illustrated in Figure 15, although the form there is precast concrete rather than steel. Examples of integral connections can be found in Appendix F. This connection type can also be used in the following locations: • Pile to pile cap • Spread footing or pile cap to column Performance and Time Savings Evaluation The performance ratings of integral connections are pro- vided in Table 26. The construction risk is seen generally as slightly lower than or equal to CIP connections because of the need to fit the girders to prefabricated cap beam elements. The seismic performance is seen as the same, because in both cases the connection should be designed as capacity protected and should respond elastically. Several connections not well-suited for seismic response scored poorly. Durability is, on average, the same, but is probably slightly better for precast concrete systems because of the higher quality control available in a plant and slightly worse for steel systems because of the risks of water intrusion. Inspectability can be slightly worse, but, in many cases, is equal to CIP. No damage should occur because of the expected elastic response but, if it does, detection of inte- rior problems in a steel system would be very difficult because the steel formwork masks the concrete inside. The time savings potential for integral connections is shown in Table 27. The high time savings potential is related to the use of precast cap beam elements or prefabricated steel sections. Both types can be filled with concrete after erection of the key components of the connection. The use of precast or prefabricated beam sections has the potential for excellent time savings because the construction of forms in the air and the time of curing for the cap beam concrete are removed from the schedule. However, depending on the scheme for erecting the cap beam, the time savings may be nil, particu- larly if shoring is required. For conventional girder bridge systems with either single- or multi-column bents, the use of 25 Figure 15. Integral precast lower stage cap with pre- cast girders (Restrepo, Matsumoto, and Tobolski 2011).

ABC techniques for the cap beam is the single most effective item in producing time savings. Technology Readiness The TRL and the completeness of development for integral connections are given in Table 28. Summary Integral connections represent a promising detail that for connections of columns, cap beam, and bridge superstruc- ture provide a high TRL for seismic applications and have a significant history of construction experience. Among the individual connections investigated, three have been tested under seismic loading at a large scale (at least one-third of full 26 Figure 16. Example for an integral connection, a pier cap on bearings made as a steel/concrete composite (Florida DOT). Table 26. Performance potential evaluation for integral connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better 5 +1 Slightly better 3 3 0 Equal 3 4 6 8 9 1 2 4 5 6 8 9 11 1 2 4 5 6 7 8 9 11 3 5 6 7 8 9 10 11 –1 Slightly worse 1 2 7 10 11 7 10 1 2 4 –2 Much worse 10

scale). Limited design information is also available for the fol- lowing connections: • Integral connection of a steel superstructure with a steel/ concrete composite cap beam and concrete pier per NCHRP Report 527 (2004) • Precast spliced-girder bridge with integral concrete col- umn (Holombo et al. 1998) • Integral connection of a steel superstructure with a post- tensioned concrete cap beam and concrete pier (Patty et al. 2001) These connections were not specifically designed for ABC and would have to be re-detailed in that regard. How- ever, their testing conclusions and design examples are applicable to ABC because the philosophy for seismic design would be to avoid damage within the integral cap beam. Emerging Technologies This section describes connections that use emerging materials and technologies in combination with prefabri- cated bridge elements. The category is intended to contain connection types that are at an early stage of development but offer promise, on the basis of some novel feature, if they can be developed further. Two connection types are included, as follows: • Rotational Elastomeric Bearing • Special Energy-Dissipating Bar Systems Both have been proposed for use in the context of a hybrid connection. However, they are not evaluated in the hybrid section of the report because their behavior is expected to be characterized more by their special features than by the post- tensioning. Because they differ significantly, they are described and evaluated separately here. Rotational Elastomeric Bearing Description. An elastomeric bearing can be used to provide a region of concentrated deformability at a struc- tural joint. A possible use for such a connection might be to reduce the moment entering the foundation for a given col- umn drift. The California DOT (Caltrans) already uses a moment-reducing detail that has the same goal, although it is achieved by forming a concrete hinge rather than an elas- tomeric one. This connection type can be used in the following locations: • Foundation to column • Column to cap beam An example is shown in Appendix G, where the connection is shown as a footing to column connection. This connection is illustrated here in Figure 17 and Figure 18. Figure 19 shows photographs of the test specimen during construction. A steel reinforced elastomeric bearing assembly is cast into both the top of a footing and a short segment of column above. Precast column segments complete the column above, with no mild steel reinforcement to connect the segments. 27 Table 27. Time savings potential for integral connections. Table 28. Technology readiness level evaluation for integral connections. Time Savings Potential Definition Relative to CIP Value +2 Much better 1 2 4 10 +1 Slightly better 7 8 9 0 11653lauqE –1 Slightly worse –2 Much worse Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake

Studs welded to the outer plates of the bearing connect the assembly to the adjacent concrete. Longitudinal bars are cast into the footing and extend through holes in the bearing into the first cast-in-place column segment above the bearing. The whole column is post-tensioned vertically by an unbonded post-tensioned bar anchored at the footing and cap beam. Shear deformation of the bearing is restrained by a steel pipe around the post-tensioned bar at the center of the bearing. Performance and time savings evaluation. This con- nection, identified as connection 1, is given a −2 for con- struction risk due to the complexity of embedding a prefabricated element in the footing and for the additional complexity of the construction of the bearing element and assembly (see Table 29). It is likely that the construction risk would be lowered (and the score would be higher) if such construction were to become commonplace. The seis- mic performance is given a +2, because the displacement capacity of this connection type is outstanding relative to other considered connections. The durability of the con- nection is given a −1 due to the incorporated joints between the concrete and the elastomeric bearing. Such a joint can permit deleterious materials to intrude, leading to corro- sion problems. The times savings rating for this elastomeric bearing con- nection is given a −2 due to the complexity of construction and the fact that the assembly must be cast into the founda- tion (see Table 30). This could cause alignment problems if the placement of the lower segment is not controlled very carefully. Technology readiness. The TRL and the completeness of development for the elastomeric bearing connection is shown 28 Figure 18. Rotational elastomeric bearing (Motaref et al. 2010). Figure 19. Elastomeric bearing energy-dissipating bars at column base (Motaref et al. 2010). Figure 17. Rotational elastomeric bearing connection test specimen (Motaref et al. 2010).

in Table 31. The concept of installing an elastomeric bearing to provide local rotational flexibility has been developed and ini- tial, proof-of-concept, testing has been conducted. The system has not been deployed in the field, for either non-seismic or seismic applications. Many details require further develop- ment, particularly with regard to constructability. It is also important to consider the system aspects of such a connection. For example, it is unlikely that it would be a suitable choice for a single-column bent or other statically determinate structure. Special Energy-Dissipating Bar Systems Description. Nickel-titanium alloy bars have been explored for use in earthquake engineering applications. This and other SMAs have the unusual properties of super- elasticity (stress-related) and shape memory (temperature- related). Both of these behaviors are related to phase transformations of the material between austenite and martensite. A superelastic material can undergo very large inelastic strains and recover them after the removal of the applied stress. The superelastic behavior shown in Figure 20 is described in Youssef et al. (2008). Structural engineering researchers are interested in leveraging the superelastic properties of SMA bars to create low residual drift lateral systems. One example of these connections is shown in Appendix G. The details are not fully represented and the construction pro- cedure is not described by the researchers, but an attempt has been made to describe a possible method of assembly. The connection is part of a hybrid system that uses unbonded SMA bars for energy dissipation and unbonded post-tensioning strands for re-centering. The column consists of precast con- crete segments with clamped steel plates at the joint to prevent joint opening. Threaded studs and a post-tensioned tendon anchorage are cast into a concrete footing. Unbonded SMA bars are screwed into the threaded studs and extend to the height of the first column segment. The first column segment is placed over the SMA bars. The top of each SMA bar is secured to the top of the first concrete segment or clamped to steel plates with a nut. 29 Table 29. Performance potential evaluation for emerging technology connections. Table 30. Time savings potential for elastomeric bearing connections. Table 31. Technology readiness level evaluation for elastomeric bearing connections. Performance Potential Definition Relative to CIP Construction Risk Value Seismic Performance Value Durability Value Inspectability Value +2 Much better 1 +1 Slightly better 2 0 Equal –1 Slightly worse 1 2 1 2 –2 Much worse 1 2 Time Savings Potential Definition Relative to CIP Value +2 Much better +1 Slightly better 0 lauqE –1 Slightly worse –2 Much worse 1 2 Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake

Performance and time savings evaluation. At this point in their development, SMA bars have worse performance and take more construction time than conventional CIP con- struction with mild steel. From the seismic performance per- spective, the material behavior is very attractive: energy dissipation with minimal residual strains, high strain capacity, high corrosion resistance, and good low and high cycle fatigue properties. However, the difficulties with constructability, the high material cost, and the additional time required to splice SMA bars suggest that the technology is not ready for use in ABC. The scores for this connection type are shown in Table 29 and Table 30 as connection 2. Technology readiness. SMA bars are a relatively new technology in structural engineering. Only a handful of studies and tests have examined the material’s advantages and disadvantages for use in lateral force resisting systems. SMA bars have not been experimentally tested for use in precast bridge elements. Experimental testing of a con- structible SMA connection detail with prefabricated bridge substructure elements needs to be completed before consid- ering SMA technology for use in ABC. TRL values are given in Table 32. Self-Propelled Modular Transporters SPMTs are computer-controlled platform vehicles that can move prefabricated bridge superstructures weighing up to several thousand tons with precision to within a fraction of an inch. They consist of a load-bearing platform with many pairs of steered wheels, each pair with its own hydraulic jack. The platform may be raised or lowered as necessary to follow a certain travel path. This technology is used to lift and trans- port existing bridge superstructures from bridges requiring replacement. The technology can also be used to transport new bridge superstructures from temporary substructures at a bridge staging area along a designated travel path to be placed in the final bridge position, minimizing road closure time (Figure 21). SPMTs provide large amounts of flexibility, can move loads in multiple directions with a high degree of accuracy, all within a span of hours rather than months required by conventional bridge construction methods. The Utah DOT used SPMTs for their “Innovate 80” proj- ect to replace 13 bridge structures. UDOT is endeavoring to make ABC the standard for bridge construction, so SPMTs are being employed to assist in accomplishing that goal. See the UDOT website for the ABC SPMT Process Manual and Design Guide (2009a) for more information regarding engi- neering and construction using SPMTs. When SPMTs are used for rapid installation of bridge replacement projects, the traveling public experiences fewer hours interrupted by construction and spends less time in work zones. In addition, workers have less exposure to traffic hazards. Typically bridges requiring transport using SPMTs are simply supported beam and slab spans. Constructing the entire bridge superstructure away from the bridge site can allow longer cure times prior to loading for all concrete com- 30 Table 32. Technology readiness level evaluation for emerging technologies. Technology Readiness Level (TRL) % of Development Complete 001-5757-0505-5252-0noitpircseDLRT 1 Concept exists 2 Static strength predictable 3 Non-seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in seismic area 9 Adequate performance in earthquake Figure 20. Stress-strain behavior of SMA and steel.

ponents (because these are no longer on the critical path). Other advantages of SPMTs include better control by the contractor over the environment at the work site, lower life- cycle costs, and public favor for fewer disruptions to traffic. Constructing the entire span in a controlled environment adds benefits of reduced maintenance and improved quality. The technology should be considered for all bridge replace- ment projects where reduced onsite construction time is a priority and a nearby space is available for constructing the bridge. The SPMT process requires considerable coordination bet- ween the engineer of record, the contractor, a heavy lift con- tractor, and multiple disciplines, including traffic control, roadway and geotechnical engineering, as well as utilities and right of way. SPMTs are versatile devices that can be used to transport either a complete bridge or parts of one, depending on which approach is the most efficient and what equipment is avail- able. For example, the interior bridge piers and end abutments can be constructed at the final bridge site, without blocking traffic, while the superstructure is constructed off site at the bridge staging area and brought in on SPMTs when the sup- porting structure is ready. Seismic isolation techniques can be integrated fairly simply with bridges where the entire superstructure is moved into place. Isolation bearings may be used to support the superstruc- ture, thereby providing a place to attach the superstructure, although connections that are appropriate to the ABC construc- tion would need to be developed for each application. SPMTs provide additional means for handling large weights of precast and/or preassembled bridge elements. This advan- tage has great potential for SABC because seismic connectivity requirements lead to larger and heavier elements. For more information regarding SPMTs, refer to the FHWA Manual on Use of Self-Propelled Modular Transporters to Remove and Replace Bridges (2007). Note that simpler means than SPMTs can be used to trans- port whole spans where space and conditions permit. These include sliding, skidding, launching, and crane placement. Such schemes have been used in a number of applications, including bridges in Utah, Washington State, and California. These approaches work best with a partnering arrangement between the designer and contractor to ensure that the sys- tem is designed to handle the erection stresses and deforma- tions. The same design considerations apply for SPMT use (Park 2011, Khaleghi 2011). Time Savings The distinguishing characteristic of the bridge bent systems considered in this study is speed of construction, so some way of measuring it was necessary to evaluate the systems. Because of the wide variety of systems reviewed, a sophisticated method for evaluating the required construction time was deemed impractical. The method chosen is described in Chapter 2, and consisted of comparing the construction time of the precast system with that needed for a conventional CIP system. A mini-workshop was arranged to obtain estimates of construction time from professional design and construction personnel. As the project developed, it became clear that most of the connection technologies could be applied in several locations within the bridge. Thus, the decision was made to base the evaluations of performance, TRL, and so forth on connection technology rather than on connection location. A test bed structure was needed to make comparisons between the connection technologies. For that purpose, a bridge bent was selected that had dimensions typical of a free- way overpass in Washington State. The bent is shown in Figure 22. The results of the time savings workshop are pre- sented in Appendix H. The major conclusions from the time savings study are as follows: • The required curing time before construction may progress has an important influence on the total construction time. • In the precast systems, the majority of the time savings arises from precasting the cap beam, leading to 9 to 10 days savings for bar coupler, grouted duct, and socket-type con- nections used to facilitate the placement of a cap beam. Pocket-type connections saved about half that time due to the curing time of concrete in the pocket. • Precast columns provide significant time savings only under special circumstances, such as a bridge with a large number of columns. 31 Figure 21. Prefabricated superstructure installed using SPMTs (Utah DOT).

• Most precast connection types have the potential to reduce bridge bent construction time by 50% relative to CIP, although pocket connections only provided about a 25% time savings. The discussion at the workshop on time requirements showed that the potential time savings were more closely related to the characteristics of the bridge bent system as a whole rather than to any particular connection technology. In particular, the choice of precasting the cap beam rather than casting it in place made the dominant contribution to time savings. Evaluation of ABC Bent and Bridge Systems The connections summarized above each may be used to construct a bridge system. Overall the bridge system includes superstructure, deck, piers or bents, foundations, and abut- ments. Almost any of the bridge elements may be made up of precast or steel members connected with various forms of connection technologies. These are called Prefabricated Bridge Elements and Systems (PBES). Not all the connections used to connect such elements require the same ability to tolerate inelastic deformations in moderate or high seismic zones, and accordingly connection types have been catego- rized as energy-dissipating, capacity-protected, or deformation elements. The connections requiring the most rigorous seismic testing and the most thorough understanding of their behav- ior are the energy-dissipating and deformation elements con- nections. These connections typically occur in the substructure at pier locations. Thus, pier or bent systems are a primary focus for seismic use of ABC. Seismic Design A key point to understanding ABC in seismic regions is that it is essential that the designer understand and control the seismic design to ensure appropriate seismic behavior. This statement applies even more to ABC than it does to the more conventional construction types, because the seismic bridge design codes for conventional construction are set up to ensure appropriate behavior, even if the designer does not fully understand how all the provisions actually work. Such is not the case with ABC, in part because the connection tech- nologies vary widely and because specifications for design of such systems have not progressed to the same point as for conventional bridges. As has been pointed out several times, energy-dissipating and deformation elements connections must be able to endure multiple inelastic or large deformation cycles without losing their integrity. In contrast, capacity-protected connections only need to be capable of developing adequate elastic resistance, although such resistance is required under cyclic loading. This classification tool then is useful for focusing the designer’s attention on the elements and connections that require the most attention in seismic design. Bent Systems The approach for considering ABC in seismic regions has been one using “building blocks” of connection types. To a 32 Figure 22. Bridge bent considered for time savings evaluation. 6’ wide x 3’ deep pc cap beam. 4’-0” dia. x 25’ high pc column. WF74G pc girders @ 6’ c/c Four traffic lanes @ 12’ and sidewalks on each side. 66’-0” 27’-0” 6’-0” 18’-0” x 18’-0” x 4’-9” CIP footing.

great extent, systems (for example, pier or bent systems) can be constructed using one or more of the connection types previously reviewed. Ultimately, different DOTs or regions of the country might prefer different connection technologies for any of a number of reasons. It is certainly clear that differ- ent bridge construction technologies have been adopted for reasons of regional preference, success with systems, or other reasons. For instance, precast, prestressed girder bridges are often preferred in the Pacific Northwest while other types, such as steel girder bridges or CIP concrete boxes, may dom- inate the market in other states, each being considered the most cost-effective in its own region. A typical prestressed girder bridge is shown in Figure 23. In this bridge, only the gird- ers are precast; however, research sponsored by the Highways for LIFE program is under way to produce a precast bent sys- tem for these bridges that can be used in high seismic regions. As ABC technologies develop, it would be expected that regional preferences might still prevail. This trend can be seen in the emergence of several ABC bent technologies that have been conceived or even deployed to date. For example, the Utah DOT has probably constructed more full ABC bridges in seismic zones than any other agency. An example of one of the bents used along the Interstate-15 corridor near Salt Lake City is shown in Figure 24, where precast columns are con- nected to foundations and cap beams using grout-filled bar couplers (splice sleeves). Other types of PBES substructure systems or elements are shown below. Figure 24 illustrates a bent system constructed using grouted splice bar couplers between the base of the column and footing and between the top of the column and cap beam (Culmo 2009). Such connections have been widely used in the non- seismic applications of ABC, but as indicated in the bar coupler summaries, such connections may require special constraints for use in seismic regions. Figure 25 illustrates the construction of two column pile bents where steel pipe piles passed through sockets formed by corrugated metal pipe similar to that used for the “pocket connections” described previously. The pipes had steel rings 33 Figure 23. Typical precast, prestressed girder bridge in Washington State. Figure 24. Utah DOT bridge bent system (Culmo 2009). Figure 25. Steel pipe pile bent with socket connections (BergerABAM).

welded to them to create roughness that would improve ver- tical shear transfer, then the precast cap was lowered over the pipe piles and the annular space was grouted to form a full socket connection. The tops of the piles extended into the upper stage cap. Only the lower stage, as shown in the photo, was precast. Pile or trestle bents are common construction types used in many parts of the United States, and this marine application illustrates a viable configuration for use in seismic zones. The use of precast piling is also prevalent in pile bent construction, and marine applications of grouted duct con- nections to cap beams can be adapted for ABC use in land- based environments as well. Figure 26 illustrates another form of making the pier to superstructure connection using a precast pier segment of a spliced girder bridge. The bridge pictured used a CIP lower stage cap beam; however, a precast cap could have been made to work in this application. The longitudinal force transfer is made via interface shear/torsion similar to connection IC-9 of Appendix F. Figure 27 illustrates the concept under development in Washington State to develop PBES bent systems for ABC use in high seismic regions. This project is supported by the FHWA’s Highways for LIFE Technology Transfer Program and a demonstration project is currently under contract to construct this system. Precast columns along with precast lower-stage cap beams are used in this project, thus, making use of grouted duct, member socket, and integral connection types. The demonstration project also uses precast, prestressed decked-bulb tees as superstructure. These will be delivered to the site with “ears” at the ends to form stay-in-place forms for the upper stage of the CIP diaphragm. The objective is to use as many precast elements as is reasonable. The examples described above serve to illustrate the range of ABC connections and PBES that have been used previously in bridge bent construction. Much of the research work to date has focused on this type of bent system. PBES elements have also been constructed in the field, and the experience serves to provide data on constructability, durability, and time savings. Often the use of precast elements arises out of value engineering or contractor-proposed alternatives. A side benefit of such proposals is that, when a contractor chooses to use ABC technologies, the problems of tolerances and complex erection procedures can largely disappear, because the contractor “owns” the tight tolerances and can develop a casting and erection procedure that will work well. For low-bid work conditions, this may not be so positive. Much depends on the contractor’s attitude and willingness to work with unusual substructure configurations or connections, and much depends on the spirit of collaboration between the contractor, engineer, and owner. As described in the Time Savings section, the time savings expected for a bent system may not be directly attributable to a certain type of connection, but rather to the elements that are used. For example, it has been demonstrated that more time is saved by precasting the cap beams than by precasting columns, even if the connections at the base and top of the columns are the same. This illustrates a point that time savings are prima- rily a system attribute and not a connection attribute. This also means that savings may be bridge- or job-dependent. Other bent systems have been proposed that make use of ABC technologies. For example, the hybrid systems, contain- ing either a basic combination of prestressed and deformed bar steel, or more elaborate systems that provide further enhanced performance, were discussed earlier in this chapter and in the appendices. Such systems have been developed to the same point as the bent systems using the individual con- nection technologies. The hybrid systems are just that, a sys- tem for the entire bent, rather than a single connection. Various versions of hybrid systems have the potential for pro- viding significantly enhanced seismic performance, as well as potentially providing benefits for ABC. However, the two attributes may not always go together. Some systems may be more complex and take longer to construct than ABC systems optimized just to save construction time. Additionally, the hybrid systems are more appropriate for high seismic zones 34 Figure 26. Spliced girder bridge with precast pier segment (BergerABAM). Figure 27. Highways for LIFE precast bent for seismic regions. Precast Cap Beam CIP Diaphragm Precast Segmental Column (to demonstrate feasibility) CIP Footing Grouted Duct Connections Socket Connection

than for the lower to moderate zones. In a high seismic zone, the additional performance may be judged worthwhile despite possibly higher costs or construction times longer than those for the basic ABC bent systems. One system that has been considered by MCEER (Aref 2010) that could potentially have use in lower seismic regions is a pier that uses isolation bearings between the superstructure and substructure with precast column segments stacked with- out reinforcement between the segments. This type of system has features in common with the use of isolation to protect older masonry piers. A high confidence in the response of the system would need to be developed, through analytical and shake table testing, before such a system could be deployed. In summary, the non-prestressed bent systems have, in general, progressed to a more complete development than the hybrid systems. Design specifications have been developed for some connection systems and are under development for others. Field experience with construction of the basic con- nection systems also provides a higher comfort level both for constructability and durability of the basic connection sys- tems. While hybrid systems and some of the emerging tech- nologies may ultimately provide greater seismic performance, they are not currently at the same level of development as are the more basic systems, particularly with respect to their implementation details and their ease of construction. Bridge Systems At the full bridge level, many of the connections that can be used to produce a complete bridge system are capacity- protected type connections, and therefore, if reliable methods can be developed for predicting their cyclic first-yield strength, they may be deployed. Examples of such connections are pre- cast deck panel connections, internal diaphragm connections, connections used to assemble abutments from smaller pieces, and connections for attaching barriers. Connections that are still very much capacity-protected types but are adjacent to energy-dissipating regions, such as the integral class of connections summarized, represent a bit more complexity. Due to the proximity of the energy- dissipating regions and the local force-distribution attributes of these connections, more scrutiny of these connections is required. This is evident from the work that has been ongoing over the last 10 years to quantify the efficacy of integral con- nections. Such work includes consideration of both deformed bar and post-tensioning force transfer mechanisms from columns into the superstructure. To some extent, the work underway on integral connections seeks to fill in gaps in knowledge that may exist for non-ABC or partial-ABC appli- cations, for example, precast girder superstructures with CIP substructure. Nonetheless, quantification of performance lev- els for integral connections is, and will continue to be, an important area of research for ABC in seismic regions. An interesting emerging area of full bridge response that shows some promise is the use of the flexibility of partial opening of segmental or splice-girder superstructures under lateral loading (Aref 2009). When coupled with a hybrid-type substructure, such response, which provides deformability more than energy dissipation, may provide a viable seismic earthquake-resisting system in the future. Seismic isolation systems may also be used to facilitate ABC in bridge systems. Such systems may be particularly use- ful where large subassemblages of superstructure can be built and moved into place using such methods as the SMPTs. Isolation bearings could be used both to reduce the seismic demands that the bridge would experience in a design earth- quake and to provide an interface between the substructure and superstructure that would permit rapid erection. The reduced inertial force demands inherent in isolation systems could permit lighter connections between PBES, thereby sim- plifying design and potentially reducing costs. The associated improvements in seismic performance would also be a bene- fit of using isolation systems. While not discussed in detail in this report, seismic isolation is another tool or building block that can be used with ABC construction. Shear keys for abutments represent another location in a bridge system that may not be entirely rationalized with capacity-protected connections alone. Fusible shear keys are used by Caltrans and represent a rational means to limit in- ternal seismic forces in superstructures. Often shear keys at abutments are designed to be very strong such that they per- form elastically under the design earthquake. Such behavior may be acceptable in the design event, provided that all induced forces can be handled. But, there is no fusing mechanism to limit and control forces. Thus, adding fusible shear keys does provide a force-limiting feature that can be beneficial for bridge performance. The fusible shear keys developed for Caltrans by University of California, San Diego (Megally et al. 2002, Bozorgzadeh et al. 2007) could be used in combination with PBES abutment elements. Identification of Knowledge Gaps and Research Priorities for Connections for Seismic Performance Introduction Two of the primary goals of the study were to identify gaps in validation of the findings in the properties of each ABC sys- tem and to rank them in such a way as to facilitate selection for funding future research. The evaluations of connections were organized primarily according to the operational prin- ciple, rather than to the location of the connection, because it was found that many of the technologies could be used in sev- eral places in the bridge. Hence, a “building blocks” approach would be the most effective way of covering the range of pos- 35

sible ABC developments. For the same reasons, the identifica- tion of knowledge gaps and the ranking of the relative status of the connections considered are presented here using the same organizational structure. Prior to addressing each connection group, certain overarching observations are made. First, it is emphasized that the most important feature of each technology under evaluation should be its contribution to speed of construction. Thus, a system with seismic per- formance that is, or has the potential to be, better than that of conventional seismic designs was not considered unless it offered the possibility of accelerating construction. Further- more, performance (i.e., seismic performance, durability, etc.) was judged according to whether it was good enough. No more was required. By contrast, the speed of construction was judged against an unlimited scale. This approach was adopted because it reflected the focus of the project, and because many other research programs have the goal of improving the other characteristics, such as seismic resistance. Second, connections that have the potential to be used in the context of energy dissipation or deformability were viewed more favorably than those that would have to be restricted to capacity-protected roles. This was done because such connec- tions are more versatile and offer more possibilities for use in the building blocks approach. One of the findings of the study was that large variations exist in approaches to design and construction, both due to regional differences in construction culture and to variations among contractors’ preferences within a region. Consequently, provision of a range of versa- tile technologies would allow the designer and contractor the greatest freedom in selecting the system best suited to the cir- cumstances. It should be noted that any connection that will perform well in an energy-dissipating context will also perform well in a capacity-protected one; capacity-protected elements are a subset of energy-dissipating elements in which the ductil- ity demands are low. Third, some construction approaches, such as use of SPMTs, do not fit well into this building blocks approach. They clearly offer huge advantages in terms of site erection time, but they are also subject to certain restrictions, such as the need for space close to the site for prefabrication of the structure. They are highly project-specific and, thus, considered separately. Fourth, some time advantages were found that accrue to the system, rather than the local connection technology. The most important finding was that the greatest potential for time savings in the construction of a bridge bent is generally associated with precasting the cap beam. This was found to be true almost regardless of the nature of the individual connec- tions used because of the time needed in a CIP system to erect shoring, formwork, and a reinforcing cage, and then to wait for the concrete to gain strength before girders could be set. Precasting the columns can offer significant advantages, pri- marily when some special circumstances exist or when the local building culture has embraced the technology and con- tractors are comfortable with it. In the cases where special cir- cumstances prevailed, it was noteworthy that the option of precasting the columns was proposed by the contractor, who had detected a schedule advantage in so doing. Bar Coupler Connection Systems Bar coupling systems permit adjacent elements to be joined by connecting the reinforcing bars to create a continuous load path. The role of the couplers is typically to transfer tension forces, because the compression component of a coupler can readily be transferred by concrete-to-concrete bearing. There- fore, bar couplers function in much the same way as a welded butt splice between two bars, but they are faster to complete and avoid the material disadvantages of welding, such as loss of ductility. Bar couplers can be further subdivided into “hard” and “soft” couplers; in the former, the bars are joined using steel threads or locking devices, whereas the latter use a grouted sleeve to transfer the tension force. The sleeves are more forgiving of slight misalignment of the bars, but are typ- ically more bulky, heavier, and create a relatively rigid region along the tension load path. Bar couplers are quite widely used already, largely because of their convenience and the fact that they open the door to precasting. The major finding with respect to bar couplers is the paucity of comprehensive test data available to support their use in high seismic zones. It contrasts with their relatively widespread deployment in the field. For example, grouted splice sleeves have been adopted for wide use in Utah, but only one study, conducted in Japan in the 1970s, could be found that addressed inelastic cyclic loading of a connection that contained sleeves. (Other studies were found in which the sleeves had been tested, but they typically contained only a small number of tests and were used to compare various technologies rather than focus- ing on splice sleeves). Both the AASHTO LRFD design specifications and ACI 318-08 contain requirements for mechanical splices, but they address only strength. Acceptance is based on a static test criterion. Comprehensive test data is urgently needed for these cou- plers. Some of the questions or needs that should be addressed are as follows. These are organized in terms of priority— ranked from 1 to 3—as shown. Priority 1—Fundamental to Successful Seismic Application Cyclic performance. Is the performance of the coupler satisfactory under cyclic loading with bar stresses in the inelastic range? 36

Cyclic strain concentrations within the coupler. Does the coupler cause strain concentrations at hard contact points that could lead to low-cycle fatigue? Again, this question applies most readily to hard coupling systems. Buckling. Do certain types of couplers promote bar buck- ling by virtue of the discontinuity in the bar? This is more likely to affect hard couplers versus grouted couplers and may be sen- sitive to how well the coupler is tightened. It is worth noting that bar buckling is an important milestone on the road to bar failure by tension fracture, so premature buckling would be a serious shortcoming. Strain distribution in the bar. Does the presence of a coupler adversely affect the distribution of strain along the bar by creating strain concentrations? This question applies most urgently to grouted sleeve couplers because they are large and rigid and, consequently, force the inelastic defor- mations into the regions of the bar outside the coupler. For example, if a coupler is placed in the bottom of a precast col- umn, the moment gradient in the column may be such that the bar does not yield in the column above the coupler. Little inelastic deformation may occur in the coupler region, so most of the necessary deformation must occur in the footing. However, the footing is typically bulky and, therefore, con- fines the bar well, leading to a short anchorage length and potentially high strains. This is a deformation problem, but attention has mostly been focused on strength of bar couplers. Related questions include the selection of bar size. Small bars have shorter anchorage lengths and, if the system deformation is concentrated at a single crack, small bars are likely to suffer higher strain concentrations than big bars. This exacerbates the strain concentration effect of the coupler. What limits, if any, should be applied? Should such bars be locally debonded to reduce the strain concentrations? Priority 2—Highly Desirable Refinement for Seismic Use Strength details. Can the coupler develop the full strength of any bar that may legally be used with it? For example, AASHTO requires that a mechanical splice develop 125% of the specified yield strength of the bar. An ASTM A706 bar has a specified (minimum) yield strength of 60 ksi, but fy may legally be as much as 78 ksi. Thus, the strength of the coupler may satisfy the formal requirement, but may, in fact, not even develop the yield strength, much less the ultimate strength of the bar. In most bars, the tensile strength is at least 1.25 times the yield strength, in which case the real tensile strength of the bar could be 1.25* 78 ksi, or close to 100 ksi. Location of splice. Should the coupler be placed in the column or the adjoining element (typically footing or cap beam)? Many arguments can be applied and should include consideration of both seismic performance (including defor- mation capacity) and ease and reliability of assembly. The seismic performance of connections using couplers that may alter the strain distribution over long lengths may also be more sensitive to coupler location (for example, grouted- sleeve couplers). Priority 3—Further Refinement Role of surrounding concrete. In one test series, a grouted sleeve fractured before the bar broke. The test was conducted in air. Does the concrete that normally surrounds the bar have a beneficial effect? If so, how much is the benefit, and should designers rely on it? This effect may only be relevant to grouted sleeve couplers, and not to the other types of bar couplers. However, due to the widespread use of grouted sleeve couplers by some owners, the impact of surrounding concrete on cou- pler efficacy should be clearly understood. Other questions are also relevant, but are less amenable to solution through research. They involve such matters as the reliability with which a contractor will completely fill a grout sleeve, the ease with which a threaded coupler can be assem- bled and tightened even when the bars are not perfectly aligned, and so forth. In addition to physical testing, work also needs to be done to develop formal guidelines for use of bar couplers and suit- able specification language to regulate design of not only the coupler itself but also the connection region immediately sur- rounding it. Examples are included in the Required Design Specifications section that follows the individual connection knowledge gap summaries. Grouted Duct Connection Systems Grouted ducts share some characteristics with grouted splice sleeve bar couplers, but their use differs. A grouted duct is generally used to transfer tension force in a bar to the sur- rounding concrete, rather than to another collinear bar. For example, they have been considered for connecting bars pro- jecting from a column to a cap beam, but they can be used anywhere in the structure. In a grouted duct, the variety of available duct sizes allows the possibility of generous tolerances on bar location, pro- vided that the space is available. Thus, they offer a versatile means of connecting bars to concrete. More studies have been conducted on grouted ducts than on grouted splice sleeves, perhaps because splice sleeves are generally proprietary products. Thus, the behavior of grouted 37

ducts is, in general, better understood. Several studies have demonstrated that the anchorage length of the bar in the ducts is much shorter than the development length required in con- crete without a duct. Further testing is desirable because several features of behavior are not yet fully understood. Examples include the following. Priority 1—Fundamental to Successful Seismic Application Transfer of force into the surrounding concrete and bars. What are the anchorage requirements for the duct in the concrete? In some tests, especially with groups of ducts, the duct pulled out of the concrete. What are the require- ments for lap splicing bars to the outside of the duct, for example, in a column? How does the amount of concrete and/or spiral reinforcement surrounding the duct affect the seismic performance? Priority 2—Highly Desirable Refinement for Seismic Use Strain distribution. Does the presence of a grouted duct adversely affect the distribution of strain along the bar by cre- ating strain concentrations? The questions are similar to those for grouted splice sleeves. Shear strength of interface. Are shear keys required and what shape should they be? Should the grout contain fiber reinforcement to prevent loss of material from the joint after large cyclic forces are applied? What grout properties are best? Priority 3—Further Refinement Grout properties. Can the pullout strength of the bar be related to the cube strength of the grout alone or are other parameters, such as age, also important? This is important for determining when load can be placed on a grouted duct connection. Eccentricity of the bar in the duct. Does bar eccentricity in the duct detract from the anchorage strength? A small sam- ple of information is available, but a more comprehensive study is desirable. Role of surrounding concrete. Does the mass or amount of surrounding concrete affect the efficacy of the grouted duct connection? Is a specific amount of confinement transverse steel required to ensure proper performance? Shear strength of interface. Are keys required? How thick can the grout be? Should local/fiber reinforcement be used? What are the limits for grout material properties? Design guidance and specification requirements are included in the Required Design Specifications section. Pocket Connection Systems Pocket details are likely to be restricted to connections bet- ween a column and precast cap beam because the geometry of the connection at a footing makes casting the pocket concrete difficult. However, precast cap beams are an important ele- ment in saving onsite construction time, so the connection is likely to be useful. The cap beam should be as narrow as possible, to minimize its weight. However the presence of a pocket reduces the local bending and shear strength of the cap beam, so stresses dur- ing handling need to be checked on a case-by-case basis. The major outstanding issues requiring testing are associated with the mechanics of force and moment transfer from the col- umn to the cap beam. Specific questions include the following. Priority—Fundamental to Successful Seismic Application Pocket form material. What material, shape, and thick- ness of pocket form is required? Joint shear. What is the mechanism of joint shear trans- fer, and how do the steel pocket former and the stirrups con- tribute to joint shear strength? Priority 2—Highly Desirable Refinement for Seismic Use Stirrups outside pocket. What are the shear strength requirements in the parts of the cap beam that lie on either side of the pocket? What stirrups or other reinforcement are needed outside the pocket? Priority 3—Further Refinement Bar size. Can large column bars (and, therefore, a small number of them) be used in a pocket connection? Does the pocket provide enough confinement that the anchorage length of such large column bars would be reduced substantially below the length required for unconfined bars cast directly in concrete? If reduced development or anchorage lengths are used, how does this relate to joint shear performance? Design guidance and specification requirements are included in the Required Design Specifications section. Member Socket Connection Systems Member socket connections offer simplicity of construc- tion and generous tolerances. They appear to be best suited 38

for footing to column connections; tests on socket connec- tions to spread footings have proved successful and connec- tions to drilled shafts are in process. The simplest approach seems to be to cast the footing in place around the precast col- umn. This approach is less likely to be used at the top of the column, because it would mean casting the cap beam in place. The socket connection has the added advantage that it pro- vides a simple way of connecting a pretensioned column to the footing and cap beam. (In those tests, the column diam- eter was stepped down just below the cap beam to minimize the size of the opening). The tests to date have established that the socket concept works. Further experimental research is needed to determine design details. Examples include the following. Priority 1—Fundamental to Successful Seismic Application Joint shear. What is the mechanism of force and moment transfer in the joint region? Column surface roughness. What surface roughness is needed to transfer the vertical/gravity shear stresses across the interface? Priority 2—Highly Desirable Refinement for Seismic Use Use with drilled shafts. Can the detail be used to connect a column to a drilled shaft so the connection zone remains elastic? Priority 3—Further Refinement Element size ratio. What limits the ratio of column diam- eter to footing or cap beam depth? Footing and cap beam transverse steel (ties). What are the tie requirements in the footing (and to a lesser extent, the cap beam)? Note that straight, headed, longitudinal column bars have been used to date in place of bars bent out into the footing. Design guidance and specification requirements are included in the Required Design Specifications section. Hybrid Connection Systems Hybrid connections hold the promise of superior seismic performance, but are not inherently rapid to construct. Thus, it is their ABC features, rather than their seismic perform- ance, that needs attention in the present context. Furthermore, while hybrid systems could be used in low-to-moderate seis- mic zones, they are unlikely to provide a significant advantage there because the displacements are small enough that non- prestressed systems already offer a modicum of re-centering. In this report, attention was focused on solid hybrid columns suitable for a typical freeway overpass, on the basis that large hollow columns would be used for large structures with special features. Such columns would be feasible, but would require custom designs. The tests conducted for bridge columns, as well as those previously conducted for the building industry, show that the hybrid concept works. However, further studies are needed to develop details that are readily and rapidly constructible. The primary impediments lie with the prestressing tendon. If it is post-tensioned, it constitutes an extra operation to be conducted on site, probably by a separate subcontractor. This inevitably slows down construction. It also raises questions about installing the anchorages, especially at the footing, and about corrosion protection. Although a number of tests have been conducted by several researchers, these matters have not yet been resolved. Possible solutions lie in using a U-shaped tendon, with two post-tensioning anchors at the top, or in pretensioning the tendon. Both designs solve the corrosion and the bottom anchorage questions. Pretensioning would also eliminate the need to post-tension on site. Further experimental research is needed to develop appro- priate design details. Examples include the following. Priority 1—Fundamental to Successful Seismic Application Corrosion protection. How can a post-tensioned system be protected against corrosion? Stainless steel, epoxy-coated, or greased and sheathed strand? Is corrosion really a problem? Priority 2—Highly Desirable Refinement for Seismic Use Anchorage details. Development is needed of con- structible post-tensioning anchorage details, especially at the footing. Anchorage slip-back. What procedures should be used to avoid loss of prestress through slip-back at the post-tensioning anchor? The tendon length might be on the order of 25 feet, in which case slip-back, which can be especially large with epoxy- coated strands, could lead to the loss of a substantial and some- what variable proportion of the jacking stress. What details are best suited for past earthquake assessment of remaining post- tensioning force? Priority 3—Further Refinement Damage at the rocking interface. What details are needed to minimize crushing at the rocking interface? 39

Hybrid systems have force-displacement relationships that differ significantly from those of conventional, yielding, rein- forced concrete systems. This is true for both bending and shear. Some modeling needs, therefore, exist in addition to the experimental ones outlined. The primary design and specifi- cation guidance that is needed is included in the Required Design Specifications section. Integral Connection Systems Integral systems represent whole bent cap systems rather than individual connections. Thus, any laboratory experi- ments are likely to be larger, more complex, and more expen- sive than those conducted for other connection types. The primary needs are for improved understanding of the behavior under earthquake loading parallel to the longitudi- nal axis of the bridge, or longitudinal loading. Then, the end moments from the girders must be transferred to the cap beam, which carries them in torsion to the columns, where they are resisted by bending and shear. That complete load path needs to be studied, preferably in a test of a complete bent system. Several different bent cap systems are in use in different parts of the country (drop caps, flush caps, etc.) and each presents its own detailed questions in addition to the more global ones. Further experimental research on integral connection sys- tems should be undertaken to answer the following questions. Priority 1—Fundamental to Successful Seismic Application Positive moment capacity of precast, prestressed girders anchored to cap beams. What anchorage details of deformed bar and extended strand provide acceptable positive moment capacities? Priority 2—Highly Desirable Refinement for Seismic Use Joint shear. What joint shear geometry/requirements are necessary for two-stage cap beam construction? What are the analytical or effective limits of the joint? What strut-and-tie models are recommended for quantifying strength? Anchorage requirements of column steel into two-stage cap beams. How are the column forces distributed to the joint area in the upper stage of a two-stage cap beam? Priority 3—Further Refinement Torsional stiffness and strength of two-stage cap beams. How are superstructure longitudinal moments transferred to the columns through the cap beam? What is the effective width of superstructure? What torsional steel requirements are necessary in addition to shear steel? Where interruptions in stirrups occur to permit girders to be placed, what details will provide adequate performance? For the commonly used drop cap bents, the primary out- standing design guidance and specification requirements are included in the Required Design Specifications section. Emerging Technology Connection Systems The two systems classed as emerging technologies are both based on the hybrid concept, but they are not grouped with the other hybrid connections because they include an additional component. In one case, the column contains an elastomeric bearing that is intended to provide rotational flexibility and to reduce damage in the highly strained region. In the other, the mild steel energy-dissipating bars are replaced by SMA bars, which have special load-displacement properties that produce flag-shaped hysteresis loops. The development of these com- ponents is less advanced than for other connection types, so they are categorized separately. Both offer the possibility of superior seismic performance, but both would likely be slower to construct than a conventional CIP concrete system. The elastomeric bearing system could be used at the bottom of the column to reduce the end moments, thereby reducing the size of the footing. However, that design requires the top connection to carry more moment if the design base shear is to remain unchanged. Placing a bearing at both top and bot- tom would likely lead to a long period and excessive drift. As shown in Appendix G, the bearing is built integrally into the column system and replacement would likely be difficult. Because the bearing is the critical element that accommodates most of the deformation, the ability to replace it would be desirable. The hybrid system with SMA bars was not tested physi- cally, but was studied analytically. Yet many of the problems with implementation of SMAs are practical ones: the material is expensive, not widely available, and hard to machine. Forming upset ends on the bars and then threading them is likely to be difficult. Aligning the threads on site with those on the bars embedded in the column and foundation might also be difficult and cost time. Furthermore, because the sys- tem contains a post-tensioning tendon, flag-shaped hystere- sis loops can already be generated by combining the tendon with mild steel bars. Thus, the benefits of using the SMA are unclear. In each case, considerable development would be necessary to bring a system to a buildable stage, particularly to meet the demands of ABC. The needed design guidance, at both the connection and system level, should be addressed through the requirements outlined in the next section. 40

41 Design Guidance Required Se ism ic G ui de Sp ec ifi ca tio n Se ct io n Ba r C ou pl er s G ro ut ed D uc ts Po ck et C on ne ct io ns So ck et C on ne ct io ns H yb ri d C on ne ct io ns In te gr al C on ne ct io ns Em er gi ng Te ch no lo gi es Earthquake resisting element definitions 3 X X X X X X X Restrictions on location in structure 3 X X X X X X X Modification or confirmation of displacement capacity calculation methodology 4 X X X X X X Plastic hinge length guidance 4 X X X X 4stimilytilitcuD X X X X System-specific displacement capacity calculation methodology 4 X X Dynamic demand analysis methodology for 3-D structures 5 X Material property guidance for modeling 5, 8 X X Strut-and-tie modeling guidance for force transfer 5, 8 X X Guidance for systems deforming biaxially, including skews and curves 5 X X 5sredrigotnoitubirtsiddaoL X Torsion modeling of cap beams 5 X Interface shear design for reinforced concrete columns, steel piles, and steel columns 7, 8 X X X X X X Guidance for development of moment- curvature relationship 8 X X X X X Reinforcing bar and strand strain limits 8 X X X X X X Development length of bars in ducts, pockets, or sockets 8 X X X X Lap splice requirements for adjacent bars transferring force to ducts 8 X Limitations on duct size relative to bar size 8 X Permissible materials and interface shape for pocket/socket forms 8 X X Proportioning of pocket/socket form relative to adjacent member for force transfer and confinement 8 X X Local detailing to avoid spalling near high force locations 8 X X X Shear capacity protection design for hybrid columns 8 X X Post-tensioning or pre-tensioning guidance, including installation force and debonding lengths, if any (note that these have been worked out for buildings, but similar requirements need to be developed for bridges) 5, 8 X X Joint shear design requirements similar to those for T and knee joints 8 X X X X Anchorage detailing for development of precast girder strength in longitudinal direction 8 X Torsional steel detailing for cap beams, both flush soffit and two-stage cap beams 8 X Table 33. Design guidance required.

42 Required Design Specifications For each of the connection types that have been summa- rized, design specifications need to be developed that address the specific performance, material, and configuration of the connection. Many of the required design specification provi- sions are similar to one another and, for that reason, the spec- ification requirements are summarized in this section for all connections. This permits one to review the requirements for all connections at one time. The design specification require- ments are focused on the AASHTO Guide Specifications for LRFD Seismic Bridge Design (2009) because this document, with its displacement design approach, has a framework that can support all the different connection types, including the hybrid connections and emerging technologies. The suggested design specification additions or modifications are listed in Table 33. These are listed in order of the specification sec- tion that requires modification. Knowledge Gaps for Bridge Systems There are several knowledge gaps that exist for bridge sys- tems and they include, but are not limited to, the following: • Adequate design and construction specifications for bent systems addressing: – Design of column bottom, top, and intermediate connections – Design of capacity-protected connections with super- structure elements Laboratory testing will be necessary to fill these knowledge gaps. Suggested testing includes the following: • Subassemblage test for flush-soffit integral connections with precast cap beams • Subassemblage testing of commonly used integral connec- tions with two-stage cap beams (dropped cap beams) • Shake table concept validation testing of large-scale bent systems Much experience remains to be gained before owners and engineers will be satisfied with the actual field performance of ABC bridge systems. Significant experience gaps that exist for bridge systems include the following: • Durability experience for unbonded, post-tensioned, hybrid systems • Durability of grouted bed joints for connections in energy- dissipating and hybrid regions, both environmentally and under cyclic loading • Performance of systems in design level earthquakes • Performance of systems in skew or curved bridges • Demonstration projects for all types of ABC bridge systems in high seismic regions These knowledge and experience gaps serve to identify the development activities that should be undertaken in the near future to advance the use of ABC in seismic regions. The development of all information that will be needed for use of ABC in seismic regions will likely take a number of years. To that end, the first priority should be to ensure deployment as soon as reasonably possible of those bent systems that are presently at the most advanced stage of development. This would be the easiest route to implementing ABC substruc- tures in seismic regions and would also serve the greatest number of bridges. The second priority would be further development of those hybrid and emerging technology systems that have the potential for not only significantly enhancing seismic performance but also serving the ABC needs of the country.