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CONTENTS
Volume 24, Number 3, October20 2006
 

Abstract
In this paper, the performance of a tuned liquid damper (TLD) in suppressing the seismic response of buildings is investigated with shake table testing of a four-story steel frame model that rests on pile foundation. The model tests were performed in three phases with the steel frame structure alone, the soil and pile foundation system, and the soil-foundation-structure system, respectively. The test results from different phases were compared to study the effect of soil-structure interaction on the efficiency of a TLD in reducing the peak response of the structure. The influence of a TLD on the dynamic response of the pile foundation was investigated as well. Three types of earthquake excitations were considered with different frequency characteristics. Test results indicated that TLD can suppress the peak response of the structure up to 20% regardless of the presence of soils. TLD is also effective in reducing the dynamic responses of pile foundation.

Key Words
tuned liquid damper; vibration control; soil-structure interaction; shaking table model test.

Address
Menglin Lou, Gang Zong and Weixin Niu; State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, P. R. China
Genda Chen; State Key Laboratory for Disaster Reduction in Civil Engineering,
Tongji University, Shanghai, P. R. China; Department of Civil, Architectural and Environmental Engineering, University of Missouri-Rolla, Rolla, MO, USA
Franklin Y. Cheng; Department of Civil, Architectural and Environmental Engineering, University of Missouri-Rolla, Rolla, MO, USA

Abstract
In order to improve the constructability and meanwhile ensure excellent seismic behavior, several innovative composite connection details were conceived and studied by the authors. This paper reports experimental results and observations on seismic behavior of steel beam bolted to reinforced concrete column connections (bolted RCS or BRCS). The proposed composite connection details involve post tensioning the end plates of the steel beams to the reinforced concrete or precast concrete columns using high-strength steel rods. A rational design procedure was proposed to assure a ductile behavior of the composite structure. Strut-and-tie model analysis indicates that a bolted composite connection has a favorable stress transfer mechanism. The excellent capacity and behavior were then validated through five full-scale beam to column connection model tests.

Key Words
beam-column connection; bolted end plate; hybrid structure; reinforced concrete column; steel beam; seismic design.

Address
Xian Li1, Yuntian Wu2, Weifeng Mao1, Yan Xiao1,2, J. C. Anderson2 and Yurong Guo1
1) College of Civil Engineering, CIPRES, Hunan University, Changsha, China
2) Department of Civil Engineering, University of Southern California, Los Angeles, USA

Abstract
This paper is concerned with the behaviour of steel and concrete composite joints subjected to reversal of loading. Three cruciform composite joint specimens and one bare steel joint specimen were tested so that one side of the beam-to-column connection was under negative moment and another side under positive moment. The steelwork beam-to-column connections were made of bolted end plate with an extended haunch section. Composite slabs employing metal decking were used for all the composite joint specimens. The moment-rotation relationships for the joints were obtained experimentally. Details of the experimental observations and results were reported.

Key Words
composite joints; cyclic loading; moment rotational response.

Address
College of Civil Engineering, Nanjing University of Technology, 210009, Nanjing, China

Abstract
In this paper, the hysteretic behaviors of channel and C-section cold-formed steel members (CFSMs) under cyclic axial loading were simulated with the finite element method. Geometric and material nonlinearities, Bauschinger effect, strain hardening and strength improvement at corner zones were taken into account. Extensive numerical results indicated that, as the width-to-thickness ratio increases, local buckling occurs prematurely. As a result, the hysteretic behavior of the CFSMs degrades and their energy dissipation capability decreases. Due to the presence of lips, the hysteretic behavior of a C-section steel member is superior to that of its corresponding channel section. The intermediate stiffeners in a C-section steel member postpone the occurrence of local buckling and change its shapes, which can greatly improve its hysteretic behavior and energy dissipation capability. Therefore, the CFSMs with a large width-to-thickness ratio can be improved by adding lips and intermediate stiffeners, and can be used more extensively in residential buildings located in seismic areas.

Key Words
hysteretic behavior; thin-wall cold-formed steel members; cyclic loading; finite element method; cold-formed steel framed residence.

Address
Jun Dong; Research Institute of Steel Structures, Nanjing University of Technology, Nanjing, 210009, China
Shiqi Wang; Metallurgical Design Institute of Shandong Province, Jinan, 250014, China
Xi Lu; Research Institute of Steel Structures, Nanjing University of Technology, Nanjing, 210009, China

Abstract
Hangzhou Bay Bridge spans the Hangzhou Bay and is located at Zhejiang province in the southeast seacoast of China. The total length of the bridge is 36 km. The bridge is composed of bridge approaches made up of multi-span prestressed concrete box girders and two cable-stayed bridges over the north and south navigable spans respectively. The seismic response analysis of the bridge model shows that if the navigable spans are designed as the routine earthquake-resistance system, the displacements and internal forces in pylons, piers and deckes are too large to satisfy the anti-seismic requirement of the structure. Therefore, the seismic reduction design was carried out by using viscous dampers to dissipate the kinetic energy of the structure both longitudinally and transversely. Using the vibration reduction system and aiming at the reasonable optimal goal, the purpose to reduce the seismic responses in south and north navigable spans has been achieved.

Key Words
Hangzhou Bay Bridge; cable-stayed bridge; earthquake response; seismic reduction; viscous damper; optimal design.

Address
Weiqing Liu; Nanjing University of Technology, Nanjing, China
Xiuli Xu; Southeast University, Nanjing, China; Nanjing University of Technology, Nanjing, China
Rengui Wang; China Highway Planning and Design Institute (HPDI), Beijing, China
Zijun Wang and Xiaolan Wu; Nanjing University of Technology, Nanjing, China

Abstract
Thin walled steel bridge-piers/columns are vulnerable to damage, when subjected to earthquake excitations. Local buckling, global buckling or interaction between local and global buckling usually is the cause of this damage, which results in significant strength reduction of the member. In this study new innovative design concepts,

Key Words
bridge pier; cyclic loading; seismic behavior; cellular columns; corrugated columns; pier ductility; pier strength.

Address
Department of Civil Engineering, Catholic University of America, Washington, DC, USA

Abstract
Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.

Key Words
semiactive structural control; sliding isolated structure; seismic response; variable MR dampers; variable stiffness device; nonlinear response spectra.

Address
Satish Nagarajaiah; Dept. of Civil & Env. Eng. and Mech. Eng. & Mat. Sci.,
Rice University, Houston, TX 77005, USA
Yuqing Mao; Mentor Subsea Engineering, Houston, TX 77079, USA
Sanjay Saharabudhe; J Ray McDermott Engineering LLC, Houston, TX 77079, USA


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