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CONTENTS
Volume 5, Number 4, October 2013
 

Abstract
Post-earthquake fire (PEF) can lead to a rapid collapse of buildings damaged partially as a result of prior earthquake. Almost all standards and codes for the design of structures against earthquake ignore the risk of PEF, and thus buildings designed using those codes could be too weak when subjected to a fire after an earthquake. An investigation based on sequential analysis inspired by FEMA356 is performed here on the Immediate Occupancy, Life Safety and Collapse Prevention performance levels of structures, designed to the ACI 318-08 code, after they are subjected to an earthquake level with PGA of 0.35g. This investigation is followed by a fire analysis of the damaged structures, examining the time taken for the damaged structures to collapse. As a point of reference, a fire analysis is also performed for undamaged structures and before the occurrence of earthquake. The results indicate that the vulnerability of structures increases dramatically when a previously damaged structure is exposed to PEF. The results also show that the damaging effects of post-earthquake fire are exacerbated when initiated from the second and third floor. Whilst the investigation is made for a certain class of structures (conventional buildings, intermediate reinforced structure, 3 stories), the results confirm the need for the incorporation of post-earthquake fire into the process of analysis and design, and provides some quantitative measures on the level of associated effects.

Key Words
post-earthquake fire; sequential analysis; fire resistance; reinforced concrete structures; performance-based design

Address
Behrouz Behnam and Hamid R. Ronagh: School of Civil Engineering, The University of Queensland, Australia

Abstract
The magneto-rheological (MR) damper contributes to the new technology of structural vibration control. Its developments and applications have been paid significant attentions in earthquake engineering in recent years. Due to the shortages, however, inherent in deterministic control schemes where only several observed seismic accelerations are used as the trivial input and in classical stochastic optimal control theory with assumption of white noise process, the derived control policy cannot effectively accommodate the performance of randomly base-excited engineering structures. In this paper, the experimental and analytical studies on stochastic seismic response control of structures with specifically designed MR dampers are carried out. The random ground motion, as the base excitation posing upon the shaking table and the design load used for structural control system, is represented by the physically based stochastic ground motion model. Stochastic response analysis and reliability assessment of the tested structure are performed using the probability density evolution method and the theory of extreme value distribution. It is shown that the seismic response of the controlled structure with MR dampers gain a significant reduction compared with that of the uncontrolled structure, and the structural reliability is obviously strengthened as well.

Key Words
shaking-table test; magneto-rheological damper; random ground motion; probability density evolution method; dynamic reliability

Address
Zhen Mei: School of Civil Engineering, Tongji University, Shanghai 200092, P.R.China; School of Civil Engineering, Huaqiao University, Xiamen 361021, P.R.China
Yongbo Peng: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, P.R.China; Shanghai Institute of Disaster Prevention and Relief, Tongji University, Shanghai 200092, P.R.China
Jie Li: School of Civil Engineering, Tongji University, Shanghai 200092, P.R.China; State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, P.R.China

Abstract
This study was concerned on the application of a hybrid approach for analyzing the buried pipelines deformations subjected to earthquakes. Nonlinear time-history analysis of Finite Element (FE) model of buried pipelines, which was modeled using laboratory data, has been performed via selected earthquakes. In order to verify the FE model with experiments, a statistical test was done which demonstrated a good conformity. Then, the FE model was developed and the optimum intersection angle of pipeline and fault was obtained via genetic algorithm. Transient seismic strain of buried pipeline in the optimum intersection angle of pipeline and fault was investigated considering the pipes diameter, the distance of pipes from fault, the soil friction angles and seismic response duration of buried pipelines. Also, a two-layer perceptron Artificial Neural Network (ANN) was trained using results of FE model, and a nonlinear relationship was obtained to predict the bending strain of buried pipelines based on the pipes diameter, intersection angles of the pipelines and fault, the soil friction angles, distance of pipes from the fault, and seismic response duration; whereas it contains a wide range of initial input data without any requirement to laboratory measurements.

Key Words
seismic strain analysis; buried pipelines; finite element method (FEM); genetic algorithm (GA); artificial neural network (ANN)

Address
Seyed Kazem Sadat Shokouhi: Department of Civil Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran
Azam Dolatshah:Department of Civil Engineering, Islamic Azad University, Dezful Branch, Dezful, Iran
Ehsan Ghobakhloo: Department of Civil Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran

Abstract
Main objective of the present study is to determine the statistical properties and suitable probability distribution functions of spectral displacements from nonlinear static and nonlinear dynamic analysis within the frame work of Monte Carlo simulation for typical low rise and high rise RC framed buildings located in zone III and zone V and designed as per Indian seismic codes. Probabilistic analysis of spectral displacement is useful for strength assessment and loss estimation. To the author

Key Words
nonlinear static analysis; nonlinear dynamic analysis; uncertainty modeling; statistical probability distribution functions; RC framed buildings

Address
P. Devandiran, P. Kamatchi, K. Balaji Rao, K. Ravisankar and Nagesh R. Iyer: CSIR-SERC, CSIR Campus, Taramani, Chennai-600 113, India

Abstract
A new experimental system of base-isolated structures is proposed. There are two kinds of dampers usually used in the base-isolated buildings, one is a viscous-type damper and the other is an elastic-plastic hysteretic-type damper. The base-isolated structure with a viscous damper and that with an elastic-plastic hysteretic damper are compared in this paper. The viscous damper is modeled by a mini piston and the elastic-plastic hysteretic damper is modeled by a low yield-point steel. The capacity of both dampers is determined so that the dissipated energies are equivalent at a specified deformation. When the capacity of both dampers is determined according to this criterion, it is shown that the response of the base-isolated structure with the elastic-plastic hysteretic damper is larger than that with the viscous damper. This characteristic is demonstrated through the comparison of the bound of the aspect ratio. It is shown that the bound of aspect ratio for the base-isolated structure with the elastic-plastic hysteretic damper is generally smaller than that with the viscous damper. When the base-isolated structure is subjected to long-duration input, the mechanical property of the elastic-plastic hysteretic damper deteriorates and the response of the base-isolated structure including that damper becomes larger than that with the viscous damper. The effect of this change of material properties on the response of the base-isolated structure is also investigated.

Key Words
base-isolated structure; experiment; viscous and hysteretic dampers; aspect ratio; long-duration input; dissipation energy

Address
I. Takewaki, M. Kanamori, S. Yoshitomia and M. Tsuji: Department of Architecture and Architectural Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan

Abstract
This paper reports extensive experimental study done to compare workability and bond strength of five different types of polymer-based bonding agents for reinforcing bars in pinning retrofit. In pinning retrofit, steel pins of 6 to 10 mm diameters are inserted into holes drilled diagonally from mortar joints. This technique is superior to other techniques especially in retrofitting historic masonry constructions because it does not change the appearance of constructions. With an ordinary cement paste as bonding agent, it is very difficult to insert reinforcing bars at larger open times due to poor workability and very thin clearance available. Here, open time represents the time interval between the injection of bonding agent and the insertion of reinforcing bars. Use of polymer-cement paste (PCP), as bonding agent, is proposed in this study, with investigation on workability and bond strengths of various PCPs in brick masonry, at open times up to 10 minutes, which is unavoidable in practice. Corresponding nonlinear finite element models are developed to simulate the experimental observations. From the experimental and analytical study,the Styrene-Butadiene Rubber polymer-cement paste (SBR-PCP) with prior pretreatments of drilled holes showed strong bond with minimum strength variation at larger open times.

Key Words
masonry retrofitting; pinning retrofit technique; polymer-cement paste; pretreatments; barrier impregnants; bonding agent; finite element modeling

Address
Kshitij C. Shrestha: Department of Architecture and Architectural Engineering, Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Japan
Sanjay Pareek: Department of Architecture, College of Engineering, Nihon University, Koriyama, Fukushima 963-8642, Japan
Yusuke Suzuki: International Research Institute of Disaster Science, Tohoku University, Aoba Sendai 980-8579, Japan
Yoshikazu Araki: Department of Architecture and Architectural Engineering, Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Japan


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