Experimental Study on Seismic Retrofit Techniques for Cap Beams, Columns and their Connections of Highway Bridges

Status

Sequential Number

Matching Research Agency

Principal Investigator

Student Involvement

Project Objective

Project Abstract

Multiple column bridge bents are widely used in the construction of highway bridges. In many states including Missouri and Alaska, these substructures are often separated from the superstructure by steel bearings or rockers. Typically multiple column bridge bents are built with reinforced concrete materials and consist of one cap beam and several columns supported on spread footings or pile foundations. The current AASHTO Specifications adopt the modern seismic design concept that plastic hinges should form only at the top and bottom ends of the columns. Through the ductile response of the columns the earthquake energy is dissipated in the columns plastic hinge in the form of hysteretic damping. In addition, since the cap beam and joints are not conveniently used to provide energy dissipation, these members should be designed with sufficient overstrength factors to ensure that they are protected from any significant inelastic actions. This concept implies that the cap beams and the beam-column joints of a RC bridge bent must be stronger than the supporting columns and must be capable of transferring the seismic forces elastically. Contrary to this ideal design approach many bridge structures around the United States have been designed with major deficiencies that may lead to catastrophic failure of bridges in the event of an earthquake.

To effectively demonstrate the performance of various retrofitting techniques, large- or full-scale test specimens will be tested. The design of the specimens will follow the past practice of the Alaska Department of Transportation. To evaluate the performance of the test units under simulated seismic loading, each test unit will be monitored with LVDTs and strain gages. Testing of the test units will be conducted under quasi-static reversed cyclic loading to induce axial and shear forces as well as bending moments in the specimen, representing different loading conditions in field.

Task Description

Schedule

Anticipated Benefits

There is an urgent need to develop design guidelines for the retrofit of bridge beam-column joints. The application of the proposed experimental study will lead to retrofit schemes that will be both efficient and economically competitive. The proposed retrofit schemes will address the following requirements; (1) it is rather easy and simple to implement in the field, (2) traffic disruptions are maintained at minimum levels, and (3) it is durable.

The research results of this study can be used to effectively retrofit inadequate bridges along US60 and other emergency routes for enhanced performance. As a result, 76% of the bridges along US60 without seismic design can be upgraded to comply with the modern design codes; 24% of bridges will unlikely fail in a brittle manner during earthquakes. These efforts will ultimately reduce the potential loss of lives and property damage in Southeast Missouri in the event of a catastrophic earthquake event.

Modal Orientation

Bridge Assessment

After experiments are completed, the retrofit techniques used to retrofit the specimens will be compared and evaluated. The most effective technique will be used to retrofit an existing bridge in Missouri. UMR will provide practical design information and methodology that can be utilized by average practicing engineers or designers.

Milestones

Relationship to other Research/Projects

Technology Transfer Activities

Transportation Research Board Keywords