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7 with the more unusual non-emulative types, the connection technology's impact on the seismic system and perform- ance must be considered by the designer and kept consistent throughout. The building-block approach does have the advan- tage of permitting several types of connections to be used in a structure to solve various constructability or other problems, so long as the overall ERS is rational. Rational in this sense means capable of providing the expected performance of the entire bridge. Classification of Connection Types The information materials provided in the questionnaire Figure 5. Connection definition. responses and obtained from other sources were screened for details of connection intended to transfer seismic forces between bridge members. These details were classified in terms various pieces of a connection that must be considered when of their location within the bridge structure, their force trans- evaluating its suitability for seismic use. The connection fer mechanism, seismic performance, and method of instal- shown is between a column and a cap beam, and the seismic lation. The classifications are explained in more detail in the plastic hinging zone is indicated. The various reinforcing ele- following subsections. ments that constitute the connection are also indicated. On either side of the connection interface, or location where the Classification by Location members actually touch, the reinforcement must be devel- oped or anchored to provide continuity of internal force flow The connections were categorized according to the location for both seismic and permanent loads. Because the reinforce- for which they might be suitable. For the purpose of this proj- ment may need to extend well away from the interface and ect, only locations that are important for the seismic behavior plastic hinging zone, portions of an ED connection may of the bridge were considered. Starting from the ground up, the actually be in capacity-protected zones. In fact, they must be following location categories were defined: because only selected portions of the connection will typically be capable of sustaining the inelastic demands without deteri- Pile to Pile Cap Connections are typically completely below oration. This, of course, is highly dependent on the connec- grade and are very difficult to access for inspection or repair. tion configuration and concept. The connection might join the pile cap to straight or batter With respect to seismic performance, connections generally piles, driven or drilled piles, and concrete or steel piles. Dur- can be classified as "emulative" of CIP reinforced concrete or ing an earthquake, this location experiences a high shear, "non-emulative." The connection illustrated in Figure 5 might moment, tension, and compression demand. be an emulative connection because the configuration of con- Foundation to Substructure Connections are at grade and nection hardware, shown as the white boxes above the inter- may or may not be covered by overburden soil. The founda- face, is kept away from the plastic hinging zone and only tion may be a spread footing foundation, pile cap, or drilled conventional reinforcement is used in the plastic hinging zone. shaft. One or more elements of the substructure can be con- The non-emulative types are typically unique to each concept. nected to a foundation; typical elements include columns, Emulative behavior is desirable on one level because confi- piers, and walls. The location could be obscured by other dence in the connection performance, be it seismic or durabil- structural elements, such as barriers, pavement, and build- ity, is generally high due to the vast experience that exists with ings, or submerged in water, thereby making inspection CIP construction. difficult. The location could also be exposed to a harsh The use of ABC techniques with bridges designed for environment or be susceptible to damage from accidental seismic loading (seismic accelerated building construction impact. Under a seismic event, this location typically expe- [SABC]) will generally follow a building-block approach. This riences a high moment and shear demand in multiple direc- means that various types of connections may be used to assem- tions and may also be subjected to tension/compression in ble a bridge that is completely or partially built with ABC tech- the case of multiple-column bents. niques. The combination of connections, however, must result Connections between Column Segments are generally in a rational seismic load resisting system. This is generally a splices of prefabricated columns, piers, or walls. The con- simple thing to achieve with emulative connections. However, nections may be obscured in ways similar to those of the

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8 foundation to substructure connections, but are generally to fully develop the capacity of the bar or the length needed more accessible for inspection and repair. Under a seismic to transfer the bar force to the adjacent bars in the segment. event, these connections can experience loading that is sim- As the duct provides some confinement, the bar develop- ilar in nature to, but less intense than, the loads experienced ment length can be shorter than for typical CIP concrete by the foundation to substructure connection. In some design. However, the duct length can govern the size of a cases, connections between column segments may be specif- connection. Grouted ducts are nonproprietary and provide ically designed to accommodate earthquake displacements. larger construction tolerances than bar couplers, but they Substructure to Superstructure Connections join piles, require more space within the adjacent member's reinforce- columns, piers, or walls to a cap beam or diaphragm. The ment cage. Nevertheless, the general joint reinforcement lay- location is relatively easily accessible and is typically pro- out can still be similar to that of a CIP system. tected from environmental exposure by the bridge super- Pocket Connections involve forming a large opening, or structure above. In the longitudinal direction, this type of pocket, in one bridge member, such as a cap beam. Rein- connection can experience high seismic demands for both forcement projecting from another member, such as a col- moment and shear, and deformation demand may be high. umn, can be inserted into it, after which the pocket is filled Depending on how the connection is integrated with the with CIP concrete. The connection reinforcement is fully bridge diaphragm, the girder moments can have a signifi- developed in the CIP concrete within the pocket. The con- cant effect on the seismic behavior of the connection. In nection allows for ample construction tolerances as long multiple-column bents, the moment and shear demands as the joint region is not heavily reinforced. The pocket may also exist in the transverse direction. requires that all or part of the joint reinforcement be cast Connections between Precast Girders and Pier into the precast member. For example, if the longitudinal Diaphragms can be accessible in the same way as substruc- cap beam reinforcement in a column-to-cap-beam connec- ture to superstructure connections. Seismic loading can sub- tion penetrates the pocket, then the joint shear reinforce- ject this connection to reversing moments and high shear ment must exist in the precast cap beam, as it cannot be loads. The deformation demand on these connections is post-installed with the longitudinal column reinforcement. typically small by virtue of the capacity protection provided On the other hand, if the column connection reinforcement by the system geometry. includes longitudinal and spiral reinforcement, then the longitudinal cap beam reinforcement has to be placed out- side the pocket. The relocation of reinforcement plus the Classification by Force Transfer Mechanism requirement to provide full development length for the The connections were classified according to their force connection bars often leads to an increase of the member transfer mechanisms, which range from highly localized, such size compared with a CIP member. as bar couplers, to more global mechanisms involving large Member Socket Connections provide a socket in which an volumes of site-cast concrete. The categories used for this entire precast member can be inserted and grouted. A socket project are as follows: connection differs from a pocket connection in that no bare reinforcement crosses the interface between the two mem- Bar Couplers can be used to butt-splice reinforcing bars, bers; the connection bars are completely encased in the pre- allowing a continuous force flow in them across the inter- cast member. The inserted precast member is anchored by face between the adjacent members. The coupler type most the bond provided by the grout and by prying action. Both commonly used in bridges is a steel sleeve that is filled with interface surfaces are roughened to increase the bond resist- a high-strength grout after the members have been erected. ance. The connection offers ample installation tolerances, Several proprietary versions are available. These couplers particularly if the member with the socket is cast-in-place, as allow for some tolerance in field placement, but they are may be the case with a footing. If the member is precast, it inevitably larger than the bar itself, especially if oversize needs to be large enough to accommodate the socket with couplers are selected to provide extra placement tolerance. enough strength to resist the expected prying action. Bar couplers allow the connection reinforcement details Hybrid Connections are connections that contain un- to resemble those of CIP construction as long as there is bonded post-tensioning through the joint, which remains enough space to physically fit the coupler. elastic and renders the connection self-centering under lat- Grouted Ducts do not directly splice reinforcement bars eral cyclic loading. The hybrid connections also contain from adjacent bridge members, but rather allow individual bonded bar reinforcement that is either spliced by bar cou- reinforcement bars to be fully developed within the adjacent plers or anchored in grouted ducts. It yields alternately in member. A separate duct is provided for each connection tension and compression to dissipate energy under cyclic bar. The length of the duct is defined by the length needed loading.