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

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

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

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

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

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

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41 Table 33. Design guidance required. Grouted Ducts Seismic Guide Bar Couplers Technologies Specification Connections Connections Connections Connections Emerging Design Guidance Required Integral Hybrid Section Pocket Socket 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 4 X X X X X X capacity calculation methodology Plastic hinge length guidance 4 X X X X Ductility limits 4 X X X X System-specific displacement capacity 4 X X calculation methodology Dynamic demand analysis methodology for 5 X 3-D structures Material property guidance for modeling 5, 8 X X Strut-and-tie modeling guidance for force 5, 8 X X transfer Guidance for systems deforming biaxially, 5 X X including skews and curves Load distribution to girders 5 X Torsion modeling of cap beams 5 X Interface shear design for reinforced concrete 7, 8 X X X X X X columns, steel piles, and steel columns Guidance for development of moment- 8 X X X X X curvature relationship Reinforcing bar and strand strain limits 8 X X X X X X Development length of bars in ducts, pockets, 8 X X X X or sockets Lap splice requirements for adjacent bars 8 X transferring force to ducts Limitations on duct size relative to bar size 8 X Permissible materials and interface shape for 8 X X pocket/socket forms Proportioning of pocket/socket form relative to 8 X X adjacent member for force transfer and confinement Local detailing to avoid spalling near high force 8 X X X locations Shear capacity protection design for hybrid 8 X X columns Post-tensioning or pre-tensioning guidance, 5, 8 X X 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) Joint shear design requirements similar to those 8 X X X X for T and knee joints Anchorage detailing for development of precast 8 X girder strength in longitudinal direction Torsional steel detailing for cap beams, both 8 X flush soffit and two-stage cap beams

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