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Research Activities: 2003
Experimental Study on Seismic Retrofit Techniques for Cap Beams, Columns and Their Connections of Highway Bridges â€" Phase II
Matching Research Agency
|Alaska Department of Transportation|
|Ph. D student|
|This study is aimed at: (1) to experimentally investigate the shear and flexural capacity of cap beams and their corresponding columns that are typical in the states of Alaska, (2) to study the cyclic behavior of beam-column joints, and (3) to develop effective retrofit techniques for the seismic upgrading of the cap beams, columns, and their connections.|
|Multiple column bridge bents are widely used in the construction of highway bridges. In many states including 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.
|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 emergency routes for enhanced performance. As a result, bridges without seismic design consideration can be upgraded to comply with modern design codes; bridges without significant seismic design requirement will unlikely fail in a brittle manner during earthquakes. These efforts will ultimately reduce the potential loss of lives and property damage in Alaska in the event of a catastrophic earthquake event.
|(Example) 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 Alaska. UMR will provide practical design information and methodology that can be utilized by average practicing engineers or designers.
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. The complete investigation of this project includes the following tasks:
Sub-Task 3.2: Test Unit A2 will be identical to Test Unit A1, but the retrofit of the bent cap will consist of externally bonded pre-stressed carbon sheets along both sides of the bent cap for improved flexural and joint shear capacity. The remaining design/retrofit details are identical to Test Unit A1.
Sub-Task 3.3: In Test A3 the bent cap retrofit will be accomplished with other acceptable retrofit techniques, which will be determined later upon consideration by ADOT engineers. Two ADOT Engineers will visit UMR with full expenses paid under this research project funds. In this specimen, the prototype column longitudinal reinforcement will be selected within limit levels that will require cutting of the column longitudinal reinforcement in the column plastic hinge region. In addition the steel shell will also be removed within the first 4inches within the column plastic hinge 1.
Relationship to other Research/Projects
|This project is related to the FHWA project entitled Earthquake Mitigation Research Program of Highway Systems, which is part of the Natural Hazards Mitigation Institute.|
Technology Transfer Activities
|Workshops and meetings with DOT's officials.|
Transportation Research Board Keywords
|Seismic retrofit, FRP, capacity design, seismic evaluation|