Bi-directional Loading Hybrid Test of Square Section Steel Piers

Bi-directionalloading test are carried out to examine response behavior of square section steel bridge piers under the prescribed ground accelerations in the Design Specification of Road Bridge in Japan. Each of these ground seismic motions has two horizontal components. Both uni-lateral and bi-lateral excitations are imposed to the 2.4m high pier models with the section of 450mm x 450mm. 1t is found from the test results that the bi-lateral excitation deteriorates the lateral bearing force of the piers compared to the uni-lateral loadin

Bidirectional loading hybrid tests of square cross-sections of steel bridge piers

Steel rectangular section columns with stiffened plates are commonly used for elevated highway bridges in the urban areas of Japan. The seismic design of bridge piers is usually performed by dynamic analysis in the horizontal direction using various independent directional seismic acceleration data. However，this simple treatment does not reflect the effect of bilateral loading as a structural response to inelastic interaction. In this study，unidirectional and bidirectional loading hybrid tests were conducted to examine the seismic response and performance of square cross-sections of steel bridge piers subjected to bidirectional seismic accelerations. Comparison of the results of unidirectional and bidirectional loading tests revealed that the maximum load is the same as the average of unidirectional loading in the NS and EW directions ; however， the maximum response displacement and residual displacement increase in proportion with hard to soft ground types. Moreover，a modified seismic design is proposed considering these bidirectional loading effects. Copyright @ 2012 John Wiley & Sons，Ltd

AN APPROXlMATED CURVE HYSTERETIC SIMULATION MODEL FOR SEISMIC RESPONSE OF STEEL BRIDGE PIERS

In this paper，an approximated curve hysteretic model is proposed to predict the seismic response of steel piers under strong ground motion. Instead of multiple stright lines，a series of curves are adopted to descript the complicated force-displacement hysteretic relationship of steel piers. P-δ effect，hardening effect in unloading-reloading hysteretic loops，deterioration characters of steel columns are considered in this model by introducing hysteretic rules and identifying free parameters. To verify the accuracy of the proposed model，six static cyclic tests and eleven hybrid tests using three types of steel pier specimens are conducted under the six strong ground motion records. By comparing the results due to the hybrid tests and the simulation，the average difference between these two is clarified as 5% in maximum response displacement，22% in residual displacement and 3% in energy absorption

The Cubic Curves Hysteresis Model of Steel Bridge Piers for Seismic Response Simulation

In this paper, a cubic type curve approximate hysteretic model for steel bridge pier is proposed. Simple equation curves are used to express restoring force-dislplacement relation of steel piers. The hysteretic rules introduved in this model are established based on the hysteretic characteristics not only observed from quasi-static tests in past, but also based on cunducted fybrid tests in thissyudy. A sesries quasi-static tests and hybrid tests are conducted using 3types of specimens and 6 accelerograms of strong ground motions. By conparing the results of tests and the simulation, it has been testified that this cubic curve type model can simulate the inelastic hysteresis behavior and earthquake response of steel piers in high precise, even in large displacement range where the piers experience local buckling near to collaps

AN APPROXIMATED CURVE HYSTERETIC SIMULATION MODEL FOR SEISMIC RESPONSE OF STEEL BRIDGE PIERS

In this paper，an approximated curve hysteretic model is proposed to predict the seismic response of steel piers under strong ground motion. Instead of multiple straight lines，a series of curves are adopted to descript the complicated force-displacement hysteretic relationship of steel piers. P-δ effect，hardening effect in unloading-reloading hysteretic loops，deterioration characters of steel columns are considered in this model by introducing hysteretic rules and identifying free parameters. To verify the accuracy of the proposed model, six static cyclic tests and eleven hybrid tests using three types of steel pier specimens are conducted under the six strong ground motion records. By comparing the results due to the hybrid tests and the simulation，t he average difference between these two is clarified as 5% in maximum response displacement，22% in residual displacement and 3% in energy absorption

A Curve Approximated Hysteresis Model for Steel Bridge Columns

In this paper，a curve approximated hysteresis model for SDF analysis is proposed to predict the nonlinear response of bridges supported by steel columns with suitable scope of severe damaged deterioration domain. Instead of multiple straight lines，a series of curves are adopted to precisely describe complicated force-displacement hysteresis behavior of the column. The P-δ effect, hardeing effect in unloading-reloading hysteresis loops, deterioration of strength and stiffness are taken into account. Parameters of proposed hysteresis model for three types of steel pier specimens used in this study are calibrated by six static cyclic tests. To verify the accuracy of the proposed model, eleven pseudo-dynamic tests are conducted. By comparing the simulation and the test results，the differences between the predicted nonlinear seismic response using the proposed model and pseudo-dynamic tests are found to be， averagely， 5% in maximum response displacement，22% in residual displacement and 4% in the amount of energy dissipation

STATIC AND DYNAMIC BEHAVIOR OF LENS-TYPE SHEAR PANEL DAMPERS FOR HIGHWAY BRIDGE BEARING

This paper describes a lens-type shear panel damper newly developed for highway bridge bearing. It has the form of concave lens shape made of low-yield steel LY 100. Both low yield strength and high ductility are the major requirements for damping devices. Response by static and dynamic shear tests results in rectangular sharpe of load-displacement hysteretic loops with high quality damping. Failure at the ultimate state highly depends on the cumulative deformation capacity of panel. Damage and life cycles can be estimated by Miner's rule. The analytical estimates agree well with the test findings. Large deformation of steel with high speed strain rate generates a lot of heat leading to high temperature of 300～400 ℃ on swface. Earthquake energy is converted to both strain and heate nergies wof hich results in large energy dissipation

Design and Experimental Performance Evaluation of Lens-type Shear Panel Dampers for Highway Bridge Bearings

This paper describes lins-type shear damper newly developed for highway bridge bearing. It utilizes low-yield steel LY100 and concave lins-shape panels. Both properties provide low strength and high ductility which are major requirements for damping devices, then contributes to high energy dissipation against seismic motion. Large deformation due to high speed strain velocity causes steel lens plate heating up to 400-500 centigrade in a moment. Earthquake energy is converted both to strain energy and heat energy. Cumulative deformation capacity of lens identity determines ultimate state of failures associated with strength and life time, dependent on time history of level-2 desibn earthquake(EQ). Fracture is roughly estimated by Miners rule esing damage index method. Prediction matches well with testing results. As case study with dampers, dynamic analysis on the existing continuous bridges has been conducted with some design parameters. The base shear acceleration due to livel-2 earthquake reduces down to 0.45g～0.5g from 0.8g of lead rubber bearing system. For planning of bridge system with dampers, 1-DOF model is simply useful to roughly know the base shear with dampers at the initial stage of planning onil when dead load is known. Design methods and experimental performance evaliation results are reported

RESIDUAL STRENGTH OF DAMAGED STEEL BRIDGE PIER WITH CIRCULAR CROSS SECTION AND ITS REPAIR METHOD

After HYOGOKEN-NANBU Earthquake in 1995 at Kobe，Ja pan，many researches for seismic resistance design have become actively. Especially seismic resistance design researches of steel bridge piers tend to how to strengthen them to against to severe earthquakes. For example，researches of improving the strength and the ductility by strengthen the cross section and proportion or by applying high performance materials，such as low yield steel，and so on. But，most of the above researches are only for new bridge piers or constructed by old design codes，and these piers are not experienced severe damages caused by earthquakes. Therefore there is no guideline about repairng methods for damaged steel bridge piers. And there is no assessment techniques retrofitted piers are established until now. In this study，firstly，we introduce repairing methods for local buckled of steel bridge piers after cyclic loading experiments. We prepared 6 damaged steel pier specimens，which had elephant foot bulge buckling at the bottom of pier，and repair them by filling concrete inside. After repairing，perform cyclic loading experiments are conducted under same load sequence，and by comparing the seismic resistance capacity between before and after repaired to discuss the reliability of repairing methods