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CONTENTS
Volume 6, Number 2, February 2014
 

Abstract
Laminated rubber bearing is very popular base isolation of earthquake engineering pertaining to the passive structural vibration control technologies. Rubber used in fabricating NRB and LRB can be easily attacked by various environmental factors such as oxygen, heat, light, dynamic strain, and organic liquids. Among these factors, this study carried out thermal aging test to investigate the effect of thermal aging on the mechanical properties of laminated rubber bearings in accelerated exposure condition of 70⁰C temperature for 168 hours. The compressive-shear test was carried out to identify the variation of compressive and shear properties of the rubber bearings before and after thermal aging. In contrast to tensile strength and elongation tests, the hardness of rubber materials showed the increasing tendency dependent on exposure temperature and period. Based on the test results, the property changes of rubber bearing mainly aged by heat are quantitatively presented.

Key Words
laminated bearing; lead rubber bearing; natural rubber bearing; thermal aging

Address
Dookie Kim: Civil and Environmental Engineering, Kunsan National University, Kunsan 573-701, Korea
Ju Oh: Korean Intellectual Property Office, Daejeon, 302-701, Korea
Jeongyun Do: BK21 Plus Glocal Geo-Environmental Engineering Research Team, Kunsan National University, Kunsan 573-701, Korea
Jinyoung Park: Institute of R&D, UNISONeTech Co., Ltd., Cheonan, Choongnam, 330-882, Korea

Abstract
This article presents a new generation of empirical ground motion models for the prediction of response spectral accelerations in soil conditions, specifically developed for the Vrancea intermediate-depth seismic source. The strong ground motion database from which the ground motion prediction model is derived consists of over 800 horizontal components of acceleration recorded from nine Vrancea intermediate-depth seismic events as well as from other seventeen intermediate-depth earthquakes produced in other seismically active regions in the world. Among the main features of the new ground motion model are the prediction of spectral ordinates values (besides the prediction of the peak ground acceleration), the extension of the magnitudes range applicability, the use of consistent metrics (epicentral distance) for this type of seismic source, the extension of the distance range applicability to 300 km, the partition of total standard deviation in intra- and inter-event standard deviations and the use of a national strong ground motion database more than two times larger than in the previous studies. The results suggest that this model is an improvement of the previous generation of ground motion prediction models and can be properly employed in the analysis of the seismic hazard of Romania.

Key Words
ground motion prediction equation; strong ground motion database; seismic hazard; acceleration response spectra; peak ground acceleration

Address
Radu Vacareanu, Dan Lungu, Florin Pavel, Cristian Arion, Alexandru Aldea and Cristian Neagu: Department of Reinforced Concrete Structures, Technical University of Civil Engineering Bucharest, Bd. Lacul Tei no. 122-124, Sector 2, 020396, Bucharest, Romania
Sorin Demetriu and Mihail Iancovici: Department of Structural Mechanics, Technical University of Civil Engineering Bucharest, Bd. Lacul Tei no. 122-124, Sector 2, 020396, Bucharest, Romania

Abstract
Dynamic test with scaled model of a group of intake towers was performed to study the dynamic interaction between water and towers. The test model consists of intake tower or towers, massless foundation near the towers and part of water to simulate the dynamic interaction of tower-water-foundation system. Models with a single tower and 4 towers were tested to find the different influences of the water on the tower dynamic properties, seismic responses as well as dynamic water-tower interaction. It is found that the water has little influence on the resonant frequency in the direction perpendicular to flow due to the normal force transfer role of the water in the contraction joints between towers. By the same effect of the water, maximum accelerations in the same direction on 4 towers tend to close to each other as the water level increased from low to normal level. Moreover, the acceleration responses of the single tower model are larger than the group of towers model in both directions in general. Within 30m from the surface of water, hydrodynamic pressures were quite close for a single tower and group of towers model at two water levels. For points deeper than 30m, the pressures increased about 40 to 55% for the group of towers model than the single tower model at both water levels. In respect to the pressures at different towers, two mid towers experienced higher than two side towers, the deeper, the larger the difference. And the inside hydrodynamic pressures are more dependent on ground motions than the outside.

Key Words
dynamic interaction; intake tower; shaking table test; massless foundation; hydraulic structure

Address
Haibo Wang and Deyu Li: State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100048, China
Bihua Tang: Hydrochina Chengdu Engineering Corporation, Chengdu, 610072, China

Abstract
The infill walls, whose contribution to the earthquake resistance of a structure is generally ignored due to their limited lateral rigidities, constitute a part of the lateral load bearing system of an RC frame structure. A common method for improving the earthquake behavior of RC frame structures is increasing the contribution of the infill walls to the overall lateral rigidity by strengthening them through different techniques. The present study investigates the influence of externally bonded perforated steel plates on the load capacities, rigidities, and ductilities of hollow brick infill walls. For this purpose, a reference (unstrengthened) and twelve strengthened specimens were subjected to monotonic diagonal compression. The experiments indicated that the spacing of the bolts, connecting the plates to the wall, have a more profound effect on the behavior of a brick wall compared to the thickness of the strengthening plates. Furthermore, an increase in the plate thickness was shown to result in a considerable improvement in the behavior of the wall only if the plates are connected to the wall with closely-spaced bolts. This strengthening technique was found to increase the energy absorption capacities of the walls between 4 and 14 times the capacity of the reference wall. The strengthened walls reached ultimate loads 30-160% greater than the reference wall and all strengthened walls remained intact till the end of the test.

Key Words
perforated steel plate; hollow brick infill wall; structural strengthening; earthquake behavior; reinforced concrete frame

Address
Sabahattin Aykac: Civil Engineering Department, Gazi University, 06500 Ankara, Turkey
Ilker Kalkan: Department of Civil Engineering, Kirikkale University, 71450 Kirikkale, Turkey
Mahmut Seydanlioglu: Ministry of Environment and Urban Development, 06650 Ankara, Turkey

Abstract
Many building codes use the empirical equation to determine fundamental period of vibration where in effect of length, width and the stiffness of the building is not explicitly accounted for. Also the equation, estimates the fundamental period of vibration with large safety margin beyond certain height of the building. An attempt is made to arrive at the simple empirical equations for fundamental period of vibration with adequate safety margin, using soft computing technique of Genetic Programming (GP). In the present study, GP models are developed in four categories, varying the number of input parameters in each category. Input parameters are chosen to represent mass, stiffness and geometry of the buildings directly or indirectly. Total numbers of 206 buildings are analyzed out of which, data set of 142 buildings is used to develop these models. It is observed that GP models developed under B and C category yield the same equation for fundamental period of vibration along X direction as well as along Y direction whereas the equation of fundamental period of vibration along X direction and along Y direction is of the same form for category D. The equations obtained as an output of GP models clearly indicate the influence of mass, geometry and stiffness of the building over fundamental period of vibration. These equations are then compared with the equation recommended by other researcher.

Key Words
genetic programming; natural periods of vibrations; data driven tools

Address
Shardul G. Joshi and Shreenivas N. Londhe: Department of Civil Engineering, Vishwakarma Institute of Information Technology, Pune, MH 411048, India
Naveen Kwatra: Department of Civil Engineering, Thapar University, Patiala, Punjab, 147004, India

Abstract
In this paper, different feedback control strategies are presented for active seismic control using proportional–integral–derivative (PID) type controllers. The parameters of PID controller are found by using an numerical algorithm considering time delay, maximum allowed control force and time domain analyses of shear buildings under different earthquake excitations. The numerical algorithm scans combinations of different controller parameters such as proportional gain (Kp), integral time (Ti) and derivative time (Td) in order to minimize a defined response of the structure. The controllers for displacement, velocity and acceleration feedback control strategies are tuned for structures with active control at the first story and all stories. The performance and robustness of different feedback controls on time and frequency responses of structures are evaluated. All feedback controls are generally robust for the changing properties of the structure, but acceleration feedback control is the best one for efficiency and stability of control system.

Key Words
structural control; PID controller; feedback control; earthquake excitation

Address
Sinan Melih Nigdeli: Department of Civil Engineering, Faculty of Engineering, Istanbul University, 34320 Avcilar, Istanbul, Turkey

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