Link to Latest: Quarterly Report Ending September 2017
ABC connections for prefabricated members are particularly critical in moderate and high seismic zones because earthquake forces place high demand on inelastic deformation of adjoining columns. Structural integrity of the bridge has to be maintained by capacity-protected connections that experience no or little damage.
Various ABC connections have been developed and investigated in the past few years. Because of the critical role of bridge columns, the majority of these connections have been for column ends at foundation and cap beams. In addition to column connections, superstructure to pier cap connections are also important to ensure that no plastic deformations are developed within the superstructure. Five types of ABC column connections have been developed, each with a variety of details:
- Grouted Duct (GD) Connections
- Mechanical Bar Splices
- Pocket Connections
- Pipe Pin Connections
- Rebar Hinge Connections
Superstructure precast concrete or steel girder to pier cap seismic connections are also of different types and details depending on the type of girder (steel or concrete) and the mechanism to provide positive moment capacity at the superstructure cap beam interface.
Nearly all the reported studies on ABC connections have been on components consisting of single or a sub-assembly of part of bridges. Component studies have been essential in understanding the local behavior of connections and have provided invaluable information that is beginning to help formulate seismic design guidelines for ABC connections. However, important questions remain on the total bridge seismic response when these connections are integrated in a bridge system. For example, it is not known how “simple for dead, continuous for live (SDCL)” connections behave under seismic loading when the girders are integrated with precast cap beams and column pocket connections. Additionally, some studies are on innovative concepts using advanced materials that are still emerging. Those studies do not directly address conventional reinforced concrete or steel materials and details.
There are three reasons for the lack of data on the seismic response of conventional ABC bridge systems:
- It has been essential to develop an understanding of ABC connection behavior at the component level before system studies can be undertaken,
- Seismic studies of bridge systems requires unique distributed shake table systems with sufficient capacity to test large-scale bridge models, and
- Bridge system tests are costly because of the number of components involved and the associated labor and laboratory fee costs.
The second barrier is addressed by the state-of-the-art shake table testing facility at UNR. The issue of cost can be addressed through allocating a portion of the ABC-UTC funds.
The overall objective of the proposed study is to investigate the seismic performance of a large-scale two-span bridge system that integrates some of the more promising ABC connections that have been proof tested. The selection of the connections will be based on the latest state-of-the-art review, a recently developed evaluation document, feedback from other ABC-UTC researches, the ABC-UTC-Seismic steering committee, and the AASHTO T-3 committee.
A two-span bridge model with concrete substructure, steel girders, and precast deck panels is envisioned. The bridge model will be supported on three shake tables at UNR and will be subjected to bidirectional horizontal seismic loading. Representative earthquake records will be simulated at the pier base and the abutments. The model will be tested under seismic loading of increasing amplitude until failure. Different limit states including the ultimate condition will be investigated. Specific objectives of the project are to determine:
- Any constructability issues related to assembling various bridge components and connections,
- Interaction among different bridge components,
- Effect of combined gravity and bidirectional seismic loading on ABC connections, the effectiveness of CFRP tendons in minimizing residual displacements under strong earthquakes, and
- Adequacy of emerging seismic design guidelines for ABC connections.
The following tasks will be performed to achieve the project goals:
- Task 1 – Update literature search on experimental and analytical studies of seismic performance of prefabricated bridge components, connections, and systems
- Task 2 – Evaluate and rank ABC connections and details
- Task 3 – Develop preliminary design for a two large-scale bridge models for shake table testing
- Task 4 – Finalize bridge model details, construct and instrument the bridge model, and conduct shake table tests
- Task 5 – Process and interpret shake table test data and assess seismic performance of bridge model
- Task 6 – Conduct analytical studies of the bridge model
- Task 7 – Summarize the investigation and the results in a draft final report
Principal Investigators: Dr. M. Saiid Saiidi (PI), Dr. Ahmad Itani (co-PI), and Dr. Mohammad Moustafa (senior personnel)