Report No.: CCEER-10-1
Title: Seismic Design of Pipe-Pin Connections in Concrete Bridges
Authors: Zaghi, A. E., and Saiidi, M.,
Date: January 2010
Sponsoring Agency: California Department of Transportation (Caltrans)
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
Telescopic pipe-pin two-way hinges are used in concrete bridges to eliminate moments while transferring shear and axial loads from integral bridge bent caps to reinforced concrete columns. The hinges consist of a steel pipe that is anchored in column with a protruded segment that extends into the bent cap. In the absence of experimental and analytical studies, design of pipe-pin hinges has been based on pure shear capacity of the steel pipe. The primary objective of this research was two-fold:
- To investigate the seismic performance of the current detail of pipe-pin hinges and propose necessary modifications
- To develop a reliable design method for pipe-pin hinges that reflects their actual behavior.
This research was comprised of comprehensive experimental and analytical studies of pipe-pin connections and their components including a shake table study of a two-column pier model.
The experimental component of the study included three sets of test models:
- Six push-off specimens to evaluate the bearing strength of concrete against the steel pipe
- Six pure shear specimens to determine the yielding and ultimate shear capacities
- A two-column 0.2-scale bridge pier model incorporating pipe-pin hinges that were designed based on the proposed guideline.
The pier model was used to evaluate the new design method under earthquake excitation. The experiments showed that the lateral failure mechanism is typically controlled by concrete diagonal tensile cracking of the column in combination with flexural yielding of the steel pipe as opposed to pure shear, although the pure shear failure mode should be considered when a large amount of lateral steel is used in the column. Another possible mode of failure is bearing failure of the concrete around the pipe in heavily reinforced columns. The shake table experiment of the pier model confirmed that t he proposed design method meets the safety and performance requirements under seismic loading.
The analytical studies consisted of:
- A stick model in SAP2000 that was developed for pipe shear key subassemblies
- Detailed nonlinear FE models using ABAQUS that were used to performed an extensive parametric study in order to shed light on different aspects of the behavior and generate the required data for the design guideline
- A model in OpenSees that utilized a macro model for the pipe-pin hinges
The experimental and analytical results helped identify the means to improve the performance of current pipe-pin hinge details. The pipe studs and spiral around the can proved to be unnecessary and were eliminated in the proposed standard detail. A thicker tapered hinge throat was suggested to solve the problem of local concrete damage to the throat and column edges. As a possible extension of pipe-pin application, a study was conducted on pipe-pins combined with isolation and damping systems. The analytical modeling of these details showed that modified connections can reduce the demands on the structure by dissipating a major portion of the earthquake energy.