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CHAPTER 3
Findings and Applications
Evaluation of Connection Types Bar Couplers
The description of the findings and the evaluation of con- Description
nection types in this section are organized by force transfer
A bar coupler is used to splice two bars together, end-to-
mechanism:
end. It allows axial force to be transferred from one bar to the
other and performs the same function as a welded butt splice.
· Bar Couplers In most cases, compression can be resisted by end bearing, and
· Grouted Ducts the transfer of tension is the more critical matter. A typical
· Pocket Connections arrangement is shown in Figure 6.
· Member Socket Connections Several styles of coupler (described in the following list and
· Hybrid Connections illustrated in Figure 7) are commercially available. Each
· Integral Connections depends on a different mechanical principle.
· Emerging Technologies
· Threaded sleeve. The bars are equipped with male thread,
Descriptions of individual connections or systems are con- and they screw into a sleeve with a female thread. The threads
tained in Appendices A through G, and those descriptions are may be tapered to reduce the number of turns necessary
then used in the more general discussions and evaluations of for full engagement. Such couplers permit little alignment
the connection types listed above. Appendix H provides the tolerance.
detailed evaluations of the connection types, and this chapter · Headed bars with separate sleeves. A head is formed on the
summarizes the information in Appendix H. As described in end of each bar and a threaded coupling piece draws the two
Chapter 2, each connection type is evaluated on the basis of together. To ensure contact for transferring compression, a
the following: shim may be placed between the bar ends.
· External clamping screws. A steel sleeve fits over the bar ends.
· Performance potential, which is a composite of construction Set screws are driven radially through the sleeve into the bar.
risk, seismic performance, durability, and post-earthquake The tension force is transferred from bar to sleeve to bar
inspectability through shear in the screws.
· Time savings potential · Grouted sleeves. A steel sleeve fits over the bar ends and is
· Technology readiness filled with grout. Tension is transferred by bond from bar to
grout, and grout to sleeve. A variant of the grouted sleeve
The reader is referred to Appendix H for detailed infor- uses a screw thread to connect one bar to the sleeve and
mation about each connection type. Additionally, the grout to connect the other. This adaptation allows the sleeve
appendix provides information on material requirements, to be shorter.
construction techniques, and detailed evaluation of labo-
ratory testing of representative specimens of the connec- The bar coupler connection type can be used in the follow-
tion type. ing locations:
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Threaded sleeve Headed bars with mating sleeves
External clamping screws Grouted splice sleeve
Figure 6. Bar coupler--typical
application. Figure 7. Bar coupler types.
· Footing to column because the test data for bar coupler connections is incom-
· Splices between column segments or cap beam segments plete. The post-earthquake inspectability is similar to CIP; so
· Column to cap beam a value of 0 is assigned. The durability is assigned a value of 0,
because the potential for local voids during grouting is offset
Performance and Time Savings Evaluation somewhat by the improvements in construction quality likely
with precast elements.
Performance scores were assigned for this connection The time savings for bar coupler connections was rated as
type based on the comments outlined in Appendix H regard- +2 (much better than CIP) (see Table 12). The estimated sav-
ing construction risk, seismic performance, inspectability, ings is approximately 11 days for a bent in which the columns
and durability (see Table 11). In the table, the shaded cells and cap beam are precast. The majority of that savings comes
indicate the composite performance expected as a group. from using such connections at the cap beam.
Additionally, the numbers indicate the scores of individual
connections, and the number corresponds to the identifying
Technology Readiness
number for the connection in the appendix. For instance, the
bar coupler type of connections include seven examples eval- Table 13 provides a summary of the TRL levels and of the
uated in Appendix A. In the appendix, the connections are estimated percentage of development that has been accom-
denoted by BC-1 through BC-7, but in Table 11 only the plished to date for the connection group. Because this rating
connection number appears. The numbers are provided in applies to the entire group, it is a composite of the status of the
the table simply to indicate the range of scores for the con- individual couplers.
nection type. The numbers also indicate how a particular
connection scored relative to other connections evaluated Summary
for the group.
The construction risk for bar coupler connections is less Bar coupler connections are being widely used in prac-
favorable than CIP construction because of the possibility that tice; however, their ability to sustain cyclic inelastic defor-
the bar and coupler might be misaligned relative to each other. mations is not well documented. Therefore, the connection
The coupler might also not be correctly or fully engaged, for type is considered constructible and promising for seismic
example, if a grouted splice sleeve was not filled properly. The use, but further experimental testing is suggested to verify its
seismic performance is rated lower than CIP construction performance.
Table 11. Performance potential of bar coupler connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better
+1 Slightly better
0 Equal 6 67 123456 123467
1 Slightly worse 12345 12345 7 5
2 Much worse 7
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Table 12. Time savings potential of Grouted Ducts
bar coupler connections.
Description
Time Savings Definition
Potential Relative to CIP Value In grouted duct connections, reinforcing bars extending
+2 Much better 1245 from one precast member are inserted into ducts cast into
+1 Slightly better 36 the second, and the ducts are then grouted. The hardened
0 Equal grout anchors the bar in the duct. The force from the bar is
1 Slightly worse 7
transferred into the surrounding concrete, and, possibly, to
2 Much worse
one or more bars lap-spliced to the outside of the duct. That
load transfer mechanism contrasts with the one found in
Areas in which additional research is needed include the bar couplers, in which the load is transferred from one bar
following: to another bar that is collinear with the first. A grouted duct
connection can be configured in many different ways, exam-
· Inelastic cyclic performance--drift capacity ples of which are shown in Appendix B. Application of column
· Influence of coupler on bar strain distribution to cap beam connections using grouted ducts are provided
· Influence of coupler location and orientation on inelastic in Figure 8 and Figure 9, and a sample connection is shown
performance in Figure 10.
Table 13. Technology readiness level evaluation of
bar coupler connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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 8. Grouted duct cap construction and cap placement (Matsumoto 2009b).
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Figure 9. Grouted duct lower stage cap erection
(Washington State DOT SR 520/SR 202).
Figure 10. Typical grouted duct.
This connection type can be used in the following locations:
ing (Matsumoto 2009b, Pang et al. 2010). Preliminary design
· Pile to pile cap guidelines have been formulated for seismic use (Restrepo
· Spread footing or pile cap to column et al. 2011; Matsumoto et al. 2001, 2008; PCI Design Handbook
· Column to cap beam 2004) and are in the process of refinement. The connection type
· Splice between column segments or cap beam segments has been deployed in non-seismic regions and a few times in
seismic regions (SR 520, Highways for LIFE). Thus, a TRL max-
Performance and Time Savings Evaluation imum value of 8 is assigned without any gaps (see Table 16).
Performance grades were assigned based on the comments
Summary
stated previously regarding construction risk, seismic per-
formance, inspectability, and durability. The construction risk Grouted duct connections have been used on projects in
was rated as less favorable than CIP construction because of both non-seismic and seismic regions. Additionally, significantly
the possibility of difficulties with grouting the ducts. All other more research has been conducted on grouted ducts than on
evaluations are similar to CIP, and they are shown in Table 14. other connection types.
The several -1 evaluations for inspectability reflect cases As noted in the seismic performance section, the use of fibers
where the grouted connection is deep within the member and, to reinforce the grout bedding layer needs to be confirmed. The
thus, difficult to inspect. question of strain distribution, which is affected by the rela-
The time savings potential was evaluated as much better tively rigid ducts, is similar to the one raised in the grouted
than CIP concrete, especially if the cap beam is precast (see splice sleeve evaluation and also merits further investigation.
Table 15). The corresponding group score was +2. Areas in which additional research is needed include the
following:
Technology Readiness
· Effect of duct size on anchorage length
Grouted ducts have been tested extensively under static load- · Influence of duct location on cyclic performance (e.g., in
ing, and a few tests have been conducted under cyclic load- plastic hinge zone versus adjacent)
Table 14. Performance potential evaluation for grouted duct connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better
+1 Slightly better
0 Equal 23 123456 1234567 2356
1 Slightly worse 14567 7 147
2 Much worse
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Table 15. Time savings potential evaluation
for grouted duct connections.
Time Savings Definition
Potential Relative to CIP Value
+2 Much better 1246
+1 Slightly better 57
0 Equal 3
1 Slightly worse
2 Much worse
Figure 11. Pocket connection concept.
· Implications of lap splicing column bars to connection bars
· Impact of additional bars on plastic hinge region cyclic
performance be adhered to the top and bottom of the steel duct to extend
· Influence of duct material, off-center bar, group pull-out the pocket form to the surface of the cap beam. The cardboard
effects, bedding layer reinforcement 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:
Pocket Connections
Description · Column to cap beam
· Footing to column
Pocket connections are constructed by extending reinforc- · Pile to pile cap
ing from the end of one precast structural member, typically a
column or pile, and inserting it into a single preformed pocket
Performance and Time Savings Evaluation
inside another member. The connection is secured by using
a grout or concrete closure pour in the pocket (Figure 11). A Performance grades were assigned based on the comments
grout/concrete bedding joint can be used to provide adjust- outlined in Appendix C regarding construction risk, seismic
ability. This connection differs from the member socket performance, inspectability, and durability (see Table 17). The
connection, in which the whole end of a member is embedded scores lower than CIP generally reflect the increase in difficulty
in the other. Pocket connection examples can be found in of constructing the connection and the potential for moisture
Appendix C. intrusion into the joint, which potentially reduces durability.
Special consideration must be given to the detailing of the The much lower seismic performance value for two connec-
pocket and how it will be formed. The transfer of forces between tions reflects designs not well-suited to seismic use.
the embedded member and the surrounding member occurs at The use of precast columns and cap beams connected with
the pocket perimeter. A steel duct can be used as a stay-in-place pockets is estimated to save 5.5 days, relative to CIP bridge bent
formwork that provides joint reinforcement and confinement construction (see the Time Savings section of Appendix H).
to the pocket concrete. This duct should be placed between the This is an approximately 25% reduction in construction time.
cap beam top and bottom reinforcing bars. An additional piece The majority of the savings was due to precasting the cap beam.
of formwork, such as a cardboard concrete form tube, must Little, if any, time is saved by using a pocket at the column to
Table 16. Technology readiness level evaluation for
grouted duct connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
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Table 17. Performance potential evaluation for pocket connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better
+1 Slightly better
0 Equal 125 12345
1 Slightly worse 12345 12345
2 Much worse 34
footing connection. Furthermore, if the pocket is formed in the needs to gain only enough strength to carry the beam's weight
footing, depositing the concrete into it would be difficult through compression.
because the precast column would block access from above.
Out of all the precast connection types, the time savings
Technology Readiness
associated with the pocket connection was the smallest, lead-
ing to a score of +1 (Table 18). Due to the large volume of Based on the level of seismic research, available design guid-
material required to fill the pocket, concrete would typically ance, and use in practice, the evaluated pocket connections
be used instead of grout. This choice reduces speed of the achieved TRL scores as shown in Table 19. The absence of test-
pocket connection because concrete typically requires more ing of seismic components (Level 5) is not regarded as negative
time to gain strength than grout. A pocket connection also because there are essentially no components, such as individ-
likely requires column jacks or other devices to support the ual couplers or grouted ducts, to test. Individual TRL values are
cap beam's weight until the concrete has gained sufficient given in Appendix C for different versions of the connection.
strength to transfer the loads by bond to the corrugated tube.
By contrast, in a cap beam equipped with grouted ducts or Summary
sleeves, no column jacks are needed and the grout in the bed
Given their good performance potential, pocket connections
are promising for use in high seismic regions, if sufficient joint
Table 18. Time savings potential for reinforcement is provided. However, the additional curing time
pocket connections. of concrete relative to grouted connections makes the pocket
less attractive for accelerated construction. This shortcoming
Time Savings Definition
Potential Relative to CIP Value
could be mitigated by using grout or concrete with high early
+2 Much better strength. To avoid the material's shrinking away from the cor-
+1 Slightly better 12345 rugated steel tube, grout with non-shrink properties would be
0 Equal the better choice.
1 Slightly worse Additional experimental and analytical efforts are necessary
2 Much worse to develop full design specifications for pocket connections.
Table 19. Technology readiness level evaluation for
pocket connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
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Figure 12. Member socket connection concepts.
Other areas that need to be further explored are the joint Table 20. Note that the range of evaluations is particularly
behavior and joint performance limit states. wide for this connection owing to complexity of the connec-
tion detailing and whether the connection's design considered
Member Socket Connections seismic loading.
Table 21 provides the time saving potential for socket con-
Description nections. The use of precast columns and cap beams con-
Member socket connections are constructed by embedding nected with sockets is estimated to save 10.5 days, relative to
a precast structural member inside another member. An exam- CIP bridge bent construction (see the Time Savings section
ple is shown in Figure 12. The connection is secured by either of Appendix H). This is an approximately 50% reduction in
casting the second member around the first or using a grout or construction time. The majority of the savings was due to
concrete closure pour in a preformed socket. The major types precasting the cap beam. For a column with a footing cast
described are connections involving precast concrete columns around it, time savings is limited by the strength required of
or concrete-filled steel tubes (CFST). Additional discussion the concrete before construction may proceed.
is provided on concrete filled fiber-reinforced plastic tubes
(CFFT) and on topics for which information was available. Technology Readiness
Socket connections have been used occasionally in the build-
ing industry, but few examples of their use in bridges were Based on the level of seismic research, available design
found. Connection examples are provided in Appendix D. guidance, and use in practice, the evaluated socket connec-
This connection type can be used in the following locations: tions achieved TRL scores as shown in Table 22. Individual
TRL values are given in Appendix D for different versions of
· Footing to column the connection type.
· Column to cap beam
· Pile to pile cap
Summary
Given their good performance potential and time savings,
Performance and Time Savings Evaluation
member socket connections are promising for use in ABC in
Performance scores were assigned based on the comments high seismic regions.
listed in Appendix D regarding construction risk, seismic per- For precast concrete column member sockets, the connec-
formance, inspectability, and durability and are given in tion needs to be tested for use with precast cap beams. A cap
Table 20. Performance potential evaluation for socket connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better 2 4
+1 Slightly better 1 124 4
0 Equal 4 123 356 12356
1 Slightly worse 356
2 Much worse 56
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Table 21. Time savings potential for Hybrid Connections
socket connections.
Description
Time Savings Definition
Potential Relative to CIP Value Hybrid systems and connections contain an unbonded
+2 Much better 12456 prestressing tendon and mild steel reinforcement or other
+1 Slightly better 3 energy-dissipating material in the plastic hinge region. The
0 Equal term "hybrid" denotes the use of two reinforcing materials,
1 Slightly worse prestressing, and mild steel, where each provides a benefit for
2 Much worse 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
beam is much narrower than a footing, and the effect of
accommodated by the concentrated rotation at the joint.
the reduced strength and stiffness on the connection has not
The body of the member undergoes no plastic deformation
been determined. The effect of different member surface
and damage to the member is thus minimized. Further-
roughnesses on required embedment, bond, and connection more, because the tendon is unbonded and able to elongate
performance should be explored. Also, models and design evenly along its full length, joint opening causes only a small
equations for transfer of forces in the joint region are needed, increase in strain in the tendon, which therefore remains
including the required embedment of column and required elastic. Consequently, the tendon provides an elastic restor-
footing depth. ing force to the system that minimizes residual drift after
Additional experimental and analytical efforts are neces- a seismic event. That system produces a nonlinear elastic
sary to develop design equations for CFST columns and foun- response with no energy dissipation. When it is coupled
dation connections. Areas that need to be addressed are the with yielding reinforcing bars, which do dissipate energy, it
ratio of diameter (D) to thickness (t) of the tube (D/t ratio), leads to hysteresis loops that are "flag-shaped," as shown in
steel strength, and models for the transfer of forces in the Figure 13. Ideally, the hysteresis loop passes through the ori-
joint. Those models are likely to be different from the ones for gin at each cycle thereby resulting in no displacement when
precast columns because CFSTs are typically embedded to a the load is removed.
smaller depth and are anchored by means of a flange on the Some building structures have been constructed using the
bottom of the tube. hybrid concept, but as yet no bridges. Examples of proposed
The monotonic loading tests of embedded CFFT connec- systems and summaries of laboratory tests on these systems
tions are a good start to understanding the connection behav- are given in Appendix E. In most cases, the column is post-
ior. Additional research is necessary to determine the cyclic tensioned, although pretensioned systems are being developed.
performance of embedded fiber-reinforced polymer (FRP)
connections. However, CFSTs are not considered a good can-
Performance and Time Savings Evaluation
didate for seismic zones because the cost is higher than steel
and FRP tubes are more susceptible to impact damage, more Performance scores were assigned based on the fore-
difficult to repair, and non-ductile. CFFTs are most beneficial going discussion regarding construction risk, seismic per-
for corrosive environments, where steel tubes could suffer formance, inspectability, and durability (see Table 23). The
from corrosion. values should be taken as indicative rather than definitive
Table 22. Technology readiness level evaluation for
socket connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
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Table 24. Time savings potential of
hybrid connections.
Time Savings Definition
Potential Relative to CIP Value
+2 Much better 8
+1 Slightly better 34
0 Equal 15
1 Slightly worse 67
2 Much worse 2
Technology Readiness
Figure 13. Hybrid connection-- The TRL evaluation is given in Table 25. Non-seismic field
diagram and generalized deployment is unlikely to occur because the unbonded tendon
hysteresis (Restrepo et al. 2011). 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
because of the many possible ways to implement a hybrid
that has been conducted on the system for buildings, much
system. The construction risk is rated as less favorable than
of which concerns the basic hybrid concept, rather than the
for a CIP system largely because of the additional site activ-
implementation in a particular structural type (bridges).
ities needed for post-tensioning and grouting. However,
This has not been done for the "deployment in seismic area"
those are not necessary in a pretensioned system. The seis-
category because that depends on particular details of construc-
mic performance is rated as potentially much better be-
cause of the reduced residual drift, and the consequently tion. However, it should be noted that a number of buildings,
high probability of being able to use the structure directly including the 39-story Paramount Building in San Francisco,
after an earthquake. The durability and post-earthquake California, (Englekirk 2002), have been constructed using the
inspectability are slightly worse than CIP due to concerns hybrid system.
about the post-tensioning tendons corroding and about
verification of remaining post-tensioning force after an Summary
earthquake.
The time savings for hybrid connections was rated as 0 Hybrid systems have been shown to have seismic perfor-
(equal to CIP) (see Table 24), due to the range of time sav- mance that is potentially better than that of conventional con-
ings estimated during the evaluations. As with the perform- struction because of the hybrid's re-centering properties. They
ance estimates, the expected time savings depend heavily have been used in buildings in high seismic zones in California,
on the details of the implementation. Use of precasting will but have not yet been used for bridges. One hybrid building in
reduce the time required, but post-tensioning will add to it, Santiago went through the recent Chile earthquake with no
most likely resulting in a modest net gain. A pretensioned damage (Stanton personal communication with Patricio
system, connected to both the foundation and cap beam Bonelli, the building's designer, October 26, 2010).
using socket connections, would be expected to offer the same Use of the technology in bridges differs from that in build-
time savings as a non-prestressed socket system, a type of ings because the columns, rather than the beams, are pre-
connection that represents the greatest time savings of all stressed. This is an advantage because, in building frames,
the systems considered. the "beam elongation" associated with rocking of the beams
Table 23. Performance potential of hybrid connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better 5
+1 Slightly better 4 123678 8
0 Equal 8 4 48
1 Slightly worse 13567 4 123567 123567
2 Much worse 2
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Table 25. Technology readiness level evaluation of
hybrid connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
against the columns creates detailing problems in the floor erected. This provides longitudinal positive and negative
system. In a bridge, the column elongates slightly as it rocks, moment continuity for seismic and other lateral loads. With
and it may do so freely, without concern about its attachment ABC, the lower stage of the cap beam may be precast and set
to adjacent members, if the bridge is designed for this effect. on the column using any of several connections described in
While the seismic performance benefits are not in doubt, previous sections. The erection of the girders and completion
connection details for bridges that allow good constructabil- of the integral connection would proceed as with CIP tech-
ity and durability are still being developed. The primary con- niques. The girders can be built with stay-in-place forms
cerns expressed by bridge engineers include the potential for attached for the upper stage of the cap beam, or forms could
higher cost to be weighed against the benefits of re-centering, be built on site. An example of a precast lower stage cap is
the additional time on site needed for post-tensioning, cor- shown in Figure 15 for the San Mateo (California) bridge
rosion of post-tensioning tendons, anchorage details, and project. This application used upper-stage forms that were
ease of inspection and repair. built on site.
Further research is needed on connection detailing that will Integrating the columns directly into a combined cap beam/
address the concerns of practicing bridge engineers. Engaging diaphragm, whose soffit is flush with the superstructure, allows
practitioners and contractors in such work would lead to ben- for a shallower construction height of the assembly and pro-
efits. The pretensioned system presently under development vides for both positive and negative moment resistance in the
appears to hold particular promise because it effectively longitudinal direction, with potential benefits to seismic per-
addresses many of the major practical concerns. formance. The stay-in-place formwork can be part of the
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 Figure 14. Two-stage cap beam with prestressed
to create the integral connection after the superstructure is girders.
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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.
Figure 15. Integral precast lower stage cap with pre- This connection type can also be used in the following
cast girders (Restrepo, Matsumoto, and Tobolski 2011). locations:
· Pile to pile cap
load-carrying system and can be equipped with dowels to · Spread footing or pile cap to column
integrate the structural formwork with the CIP concrete. A
structural formwork can be designed robust enough to allow
Performance and Time Savings Evaluation
carrying construction loads to enable the erection of the
superstructure to continue before the CIP concrete is cured. The performance ratings of integral connections are pro-
Typically, the stay-in-place formwork is already fully rein- vided in Table 26. The construction risk is seen generally as
forced before erection. Alternatively, the stay-in-place form- slightly lower than or equal to CIP connections because of the
work could be filled with fiber-reinforced concrete as the need to fit the girders to prefabricated cap beam elements. The
formwork provides confinement. seismic performance is seen as the same, because in both cases
Integral connections must develop the joint shear force the connection should be designed as capacity protected and
transfer mechanism that is required to "turn" the longitudinal should respond elastically. Several connections not well-suited
girder moments into the column moments. In the confined for seismic response scored poorly. Durability is, on average,
space between girders and the column, adequate force trans- the same, but is probably slightly better for precast concrete
fer can be difficult to achieve. systems because of the higher quality control available in a
Development of both positive and negative longitudinal plant and slightly worse for steel systems because of the risks of
bending capacities of the girders must be provided. Develop- water intrusion. Inspectability can be slightly worse, but, in
ment of negative bending is usually simple because the deck many cases, is equal to CIP. No damage should occur because
slab provides space for reinforcement. Positive (tension on of the expected elastic response but, if it does, detection of inte-
bottom) bending capacity is more difficult to provide. Strand rior problems in a steel system would be very difficult because
may be extended from the bottoms of the girders and may be the steel formwork masks the concrete inside.
terminated with strand chucks or other positive anchorage The time savings potential for integral connections is
devices. Older methods include bending the strand up into shown in Table 27. The high time savings potential is related
the cap beam, but this detail provides questionable anchorage. to the use of precast cap beam elements or prefabricated steel
Alternatively, deformed bars may be extended from the gird- sections. Both types can be filled with concrete after erection
ers and spliced, as shown in Figure 15. However, this requires of the key components of the connection. The use of precast
that sufficient room in the girder lower flange exists for the or prefabricated beam sections has the potential for excellent
bars. Often, this is not the case where straight strands have time savings because the construction of forms in the air and
been used. the time of curing for the cap beam concrete are removed
Longitudinal post-tensioning can be used to improve the from the schedule. However, depending on the scheme for
transfer of forces, and the post-tensioning force can potentially erecting the cap beam, the time savings may be nil, particu-
be used to compress vertical shear interfaces, simplifying the larly if shoring is required. For conventional girder bridge
fit-up of the girders to the cap for a flush-soffit arrangement. systems with either single- or multi-column bents, the use of
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Figure 16. Example for an integral connection, a pier cap on bearings made
as a steel/concrete composite (Florida DOT).
ABC techniques for the cap beam is the single most effective Summary
item in producing time savings.
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
Technology Readiness
significant history of construction experience. Among the
The TRL and the completeness of development for integral individual connections investigated, three have been tested
connections are given in Table 28. under seismic loading at a large scale (at least one-third of full
Table 26. Performance potential evaluation for integral connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better 5
+1 Slightly better 3 3
0 Equal 34689 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 10 124
2 Much worse 10
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Table 27. Time savings potential for they can be developed further. Two connection types are
integral connections. included, as follows:
Time Savings Definition
Potential Relative to CIP Value · Rotational Elastomeric Bearing
+2 Much better 1 2 4 10 · Special Energy-Dissipating Bar Systems
+1 Slightly better 789
0 Equal 3 5 6 11 Both have been proposed for use in the context of a hybrid
1 Slightly worse connection. However, they are not evaluated in the hybrid
2 Much worse
section of the report because their behavior is expected to be
characterized more by their special features than by the post-
scale). Limited design information is also available for the fol- tensioning. Because they differ significantly, they are described
lowing connections: and evaluated separately here.
· Integral connection of a steel superstructure with a steel/
Rotational Elastomeric Bearing
concrete composite cap beam and concrete pier per NCHRP
Report 527 (2004) Description. An elastomeric bearing can be used to
· Precast spliced-girder bridge with integral concrete col- provide a region of concentrated deformability at a struc-
umn (Holombo et al. 1998) tural joint. A possible use for such a connection might be to
· Integral connection of a steel superstructure with a post- reduce the moment entering the foundation for a given col-
tensioned concrete cap beam and concrete pier (Patty et al. umn drift. The California DOT (Caltrans) already uses a
2001) moment-reducing detail that has the same goal, although it
is achieved by forming a concrete hinge rather than an elas-
These connections were not specifically designed for tomeric one.
ABC and would have to be re-detailed in that regard. How- This connection type can be used in the following locations:
ever, their testing conclusions and design examples are
applicable to ABC because the philosophy for seismic · Foundation to column
design would be to avoid damage within the integral cap · Column to cap beam
beam.
An example is shown in Appendix G, where the connection
is shown as a footing to column connection. This connection
Emerging Technologies
is illustrated here in Figure 17 and Figure 18. Figure 19 shows
This section describes connections that use emerging photographs of the test specimen during construction.
materials and technologies in combination with prefabri- A steel reinforced elastomeric bearing assembly is cast into
cated bridge elements. The category is intended to contain both the top of a footing and a short segment of column
connection types that are at an early stage of development above. Precast column segments complete the column above,
but offer promise, on the basis of some novel feature, if with no mild steel reinforcement to connect the segments.
Table 28. Technology readiness level evaluation for
integral connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
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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). 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
Studs welded to the outer plates of the bearing connect the
prefabricated element in the footing and for the additional
assembly to the adjacent concrete. Longitudinal bars are cast
complexity of the construction of the bearing element and
into the footing and extend through holes in the bearing into
assembly (see Table 29). It is likely that the construction
the first cast-in-place column segment above the bearing. The
risk would be lowered (and the score would be higher) if
whole column is post-tensioned vertically by an unbonded
such construction were to become commonplace. The seis-
post-tensioned bar anchored at the footing and cap beam.
mic performance is given a +2, because the displacement
Shear deformation of the bearing is restrained by a steel pipe
capacity of this connection type is outstanding relative to
around the post-tensioned bar at the center of the bearing.
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.
Figure 18. Rotational elastomeric bearing Technology readiness. The TRL and the completeness of
(Motaref et al. 2010). development for the elastomeric bearing connection is shown
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Table 29. Performance potential evaluation for emerging
technology connections.
Seismic
Performance Definition Construction Performance Durability Inspectability
Potential Relative to CIP Risk Value Value Value Value
+2 Much better 1
+1 Slightly better 2
0 Equal
1 Slightly worse 12 12
2 Much worse 12
Table 30. Time savings potential for elasticity (stress-related) and shape memory (temperature-
elastomeric bearing connections. related). Both of these behaviors are related to phase
transformations of the material between austenite and
Time Savings Definition
Potential Relative to CIP Value martensite. A superelastic material can undergo very large
+2 Much better inelastic strains and recover them after the removal of the
+1 Slightly better applied stress. The superelastic behavior shown in Figure 20
0 Equal is described in Youssef et al. (2008). Structural engineering
1 Slightly worse researchers are interested in leveraging the superelastic
2 Much worse 12 properties of SMA bars to create low residual drift lateral
systems.
One example of these connections is shown in Appendix G.
in Table 31. The concept of installing an elastomeric bearing to
The details are not fully represented and the construction pro-
provide local rotational flexibility has been developed and ini-
cedure is not described by the researchers, but an attempt has
tial, proof-of-concept, testing has been conducted. The system
has not been deployed in the field, for either non-seismic or been made to describe a possible method of assembly. The
seismic applications. Many details require further develop- connection is part of a hybrid system that uses unbonded SMA
ment, particularly with regard to constructability. It is also bars for energy dissipation and unbonded post-tensioning
important to consider the system aspects of such a connection. strands for re-centering. The column consists of precast con-
For example, it is unlikely that it would be a suitable choice for crete segments with clamped steel plates at the joint to prevent
a single-column bent or other statically determinate structure. 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
Special Energy-Dissipating Bar Systems
height of the first column segment. The first column segment
Description. Nickel-titanium alloy bars have been is placed over the SMA bars. The top of each SMA bar is secured
explored for use in earthquake engineering applications. to the top of the first concrete segment or clamped to steel plates
This and other SMAs have the unusual properties of super- with a nut.
Table 31. Technology readiness level evaluation for
elastomeric bearing connections.
Technology Readiness Level (TRL) % of Development Complete
TRL Description 0-25 25-50 50-75 75-100
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
