Link To latest Report : Coming Soon.
Background :
A coupler is an alternative to traditional lap splicing to connect bars in RC structures. Even though it is feasible to incorporate mechanical bar splices in bridge bents as a precast detailing to expediate construction, the use of bar couplers in the plastic hinge region of bridge columns is prohibited in current US codes (AASHTO Seismic, 2023). This ban was mainly because the coupler performance and the effects of couplers on the seismic behavior of columns (including both capacity and demand) were not fully understood. To establish the seismic behavior of couplers, Dahal and Tazarv (2020) tested more than 160 mechanical bar splices under uniaxial monotonic and cyclic tensile loading to failure. Nine different products from six manufacturers were included. The study established the first-of-its-kind experimental database of coupler performance and defined “seismic splice” as: “A splice consisting of two bars and a coupler that is not longer than 15db (db is the bar diameter) and exhibits bar fracture outside the coupler region (Lcr, which is no more than the coupler length, Lsp, plus 4db) with a strength that is at least 95% of the tensile strength of a corresponding “unspliced specimen”. The “unspliced specimen” is a single-bar specimen used to determine benchmark mechanical properties of the two spliced bars.
Objectives :
past studies established the behavior of bar couplers and how they affect the structural performance (capacities) of columns built with these splices. Nevertheless, the dynamic behavior (seismic demands) of this ABC column type is largely unknown. The main objective of the proposed study is to understand the dynamic responses of mechanically spliced precast bridge columns through shake-table testing at the Earthquake Engineering Laboratory (EEL) at the University of Nevada, Reno (UNR) and to better understand the seismic demands on these columns.
Scope :
Task 1 – Contact Bar Coupler Manufactureres.
In the past, the PI worked with all major manufacturers of bar couplers in the US and abroad to perform capacity testing on couplers and columns. The PI will reach out to all major industry players inviting them to participate in this project by donating materials, time, and technical feedback. Furthermore, they will be invited to serve as the Research Advisory Panel (RAP). RAP will also include additional members from transportation agencies and academia. Only seismic couplers with an emphasis on grouted couplers (or hybrid couplers with a grout mechanism at one end) will be used in this project.
Task 2 – High-Strain Rate Tensile Testing of Sesmic Couplers.
The stress-strain model might be a viable option to simulate the dynamic behavior of seismic couplers. Seismic grouted couplers by all major US manufacturers will be tested under both static and dynamic tensile loading to understand the strain-rate effects on these devices and to explore if the current coupler material model is also valid for dynamic loading. The coupler design parameters (rigid length factor) will be empirically established.
Task 3 – Experimental Investigation on Mechanically Spliced Columns.
The findings of Task 2 will be discussed with RAP. Based on their feedback, at least two coupler products will be selected and then will be incorporated into two bridge column models for large-scale shake-table testing. Depending on the number of industry partners and their level of involvement, more products might be included in the column testing plan. A reference cast-in-place column from a previous UNR experiment will be used as the benchmark model. A local contractor or a precast plant will fabricate the columns. Subsequently, the columns will be assembled and tested at UNR-EEL. Each precast column will be tested under a near-fault ground motion based on a ramped-up testing method.
Task 4 – Post-Test Analytical Investigation.
The PI has performed extensive studies on the pushover response of mechanically spliced precast bridge columns (e.g., Tazarv et al., 2022). The column model, which was developed in OpenSees (2016). The accuracy of the column models has already been validated using slow-cyclic loading. Nevertheless, due to lack of shake-table test data, the accuracy of such models has not been evaluated for dynamic analyses. The research team will first evaluate the accuracy of existing models for mechanically spliced precast bridge columns under dynamic loading obtained from Task 3. Modifications will be proposed to improve the model’s performance. Subsequently, a comprehensive parametric dynamic analysis will be performed to further investigate the seismic demands of these columns. The study will include columns with different geometries, couplers, material properties, axial loads, single- and multi-column bents, and will utilize at least 10 near-fault ground motions.
Task 5 – Recommendations.
Based on the experimental and analytical findings at coupler and column levels, the proposed AASHTO design and construction guidelines for ABC columns (NCHRP 935) will be revisited and modifications will be proposed. RAP will review the document, and the guidelines will be updated based on their feedback.
Task 6 – Project Deliverables.
At the end of the project, a comprehensive final report will be prepared by the research team in conformance with the center guidelines. The final report will document all aspects of the project including details of the findings for each task. The final report will be reviewed by RAP and will be revised per their comments.
Research Team :
Principal Investigator : Mostafa Tazarv, Ph.D., P.E.