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CONTENTS
Volume 11, Number 1, July 2016
 

Abstract
Numerous buildings have been damaged or destroyed in previous earthquakes by developing soft storey. Almost all the seismic codes have provisions to prevent soft storey in structures, most of them have recommended the ratio of stiffness between adjacent storeys, but none of them has proposed the method to calculate the storey stiffness. On the other hand a great number of previous researches on stiffness have been focused on approximate methods and accurate methods by using analytical softwares have been almost neglected. In this study, six accurate methods for calculating the storey stiffness have been studied on 246 two-bay reinforced concrete frames. It is shown with the results of the statistical study and structural analysis that method 3 in which there is no modification of the original model and the forces with triangular distribution similar to seismic forces are applied to the center of mass of all storeys has acceptable accuracy and desirable efficiency for designing and controlling structures.

Key Words
storey stiffness; soft storey; calculation methods; earthquake; seismic codes

Address
Mohammad Reza Tabeshpour: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran

Azadeh Noorifard: Department of Architecture and Environmental Design, Iran University of Science and Technology,
Tehran, Iran

Abstract
The uneven distribution of rolling friction coefficient may lead to great uncertainty in the structural seismic isolation performance. This paper attempts to improve the isolation performance of a spring-damper-rolling isolation system by artificially making the uneven friction distribution to be concave. The rolling friction coefficient gradually increases when the isolator rolls away from the original position during an earthquake. After the spring-damper-rolling isolation system under different ground motions was calculated by a numerical analysis method, the system obtained more regular results than that of random uneven friction distributions. Results shows that the concave friction distribution can not only dissipate the earthquake energy, but also change the structural natural period. These functions improve the seismic isolation efficiency of the spring-damper-rolling isolation system in comparison with the random uneven distribution of rolling friction coefficient, and always lead to a relatively acceptable isolation state even if the actual earthquake significantly differs from the design earthquake.

Key Words
structure; isolation; concave friction distribution; spring; damper; seismic performance

Address
Biao Wei, Peng Wang, Xuhui He and Lizhong Jiang: School of Civil Engineering, Central South University, 22 Shaoshan South Road, Changsha, China

Biao Wei, Peng Wang, Xuhui He and Lizhong Jiang: National Engineering Laboratory for High Speed Railway Construction, 22 Shaoshan South Road, Changsha, China

Abstract
Structures with soft story irregularity have been seriously damaged in earthquakes. Therefore, the analysis of dynamic behavior of structures with soft story irregularity is of great value and relevance. In this study, a certain method will be used to discover the displacements and internal forces and to find out results about soft story irregularity. For this study, the multi-story frame-hinged shear wall system has been used as a model according to the continuous calculation system. The dynamic characteristics of the system have been obtained by analyzing the governing differential equation of the system. The dynamic characteristics have been calculated for a practical and quick analysis as indicated in tables. The suggested method is wholly based on manual calculation. A spectral analysis can be easily conducted with the help of Tables provided by this study. A sample has been solved and compared to the finite elements method to study the suitability of the method suggested at the end of this study.

Key Words
dynamic analysis; continuous system; multistory structure; hinged shear wall; frame

Address
Kanat Burak Bozdogan: Department of Civil Engineering, Canakkale Onsekiz Mart University, Canakkale, Turkey

Duygu Ozturk: Department of Civil Engineering, Ege University, Izmir, Turkey

Abstract
In this study, the bending and dynamic behaviors of laminated composite plates is examined by using a refined shear deformation theory and developed for a bending analysis of orthotropic laminated composite plates under various boundary conditions. The displacement field of the present theory is chosen based on nonlinear variations in the in-plane displacements through the thickness of the plate. By dividing the transverse displacement into the bending and shear parts and making further assumptions, the number of unknowns and equations of motion of the present theory is reduced and hence makes them simple to use. In the analysis, the equation of motion for simply supported thick laminated rectangular plates is obtained through the use of Hamilton´s principle. Numerical results for the bending and dynamic behaviors of antisymmetric cross-ply laminated plate under various boundary conditions are presented. The validity of the present solution is demonstrated by comparison with solutions available in the literature. Numerical results show that the present theory can archive accuracy comparable to the existing higher order shear deformation theories that contain more number of unknowns.

Key Words
higher-order theories; shear deformation theory of plates; laminated composite plate

Address
Belkacem Adim, Tahar Hassaine Daouadji, Lazreg Hadji: Departement de Genie Civil, Université Ibn Khaldoun Tiaret; BP 78 Zaaroura, 14000 Tiaret, Algerie

Belkacem Adim, Tahar Hassaine Daouadji, Lazreg Hadji: Laboratoire de Geomatique et Developpement Durable, Universite Ibn Khaldoun de Tiaret Algerie

Benferhat Rabia: Laboratoire de Geomateriaux , Departement de Genie Civil, Universite de Chlef, Algerie

Abstract
In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load applied on a footing resting on sandy soil at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into consideration include loading frequency, size of footing and different soil conditions. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used. The footings were tested by changing all parameters at the surface and at 50 mm depth below model surface. Meanwhile, the investigated parameters of the soil condition include dry and saturated sand for two relative densities; 30 % and 80 %. The dynamic loading was applied at different operating frequencies. The response of the footing was elaborated by measuring the amplitude of displacement using the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside soil media by using piezoelectric sensors. It was concluded that the final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it decreases with increasing the relative density of sand, modulus of elasticity and embedding inside soils. The maximum displacement amplitude exhibits its maximum value at the resonance frequency, which is found to be about 33.34 to 41.67 Hz. In general, embedment of footing in sandy soils leads to a beneficial reduction in dynamic response (displacement and excess pore water pressure) for all soil types in different percentages accompanied by an increase in soil strength.

Key Words
dynamic; saturated soil; machine foundation; displacement

Address
Mohammed Y. Fattah: Building and Construction Engineering Department, University of Technology, Baghdad, Iraq

Mosa J. Al-Mosawi and Abbas F.I. Al-Ameri: College of Engineering University of Baghdad, Iraq

Abstract
This paper examines the contribution of three sources of uncertainties to probabilistic seismic behaviour of wood frame buildings, including ground motions, intensity and seismic mass. This sensitivity analysis is performed using three methods, including the traditional method based on the conditional distributions of ground motions at given intensity measures, a method using the summation of conditional distributions at given ground motion records, and the Monte Carlo simulation. FEMA P-695 ground motions and its scaling methods are used in the analysis. Two archetype buildings are used in the sensitivity analysis, including a two-storey building and a four-storey building. The results of these analyses indicate that using data-fitting techniques to obtain probability distributions may cause some errors. Linear interpolation combined with data-fitting technique may be employed to improve the accuracy of the calculated exceeding probability. The procedures can be used to quantify the risk of wood frame buildings in seismic events and to calibrate seismic design provisions towards design code improvement.

Key Words
earthquake engineering; probability; reliability; wood frame structures; timber; seismic effect

Address
Jianzhong Gu: Architectural and Engineering Technology, Thompson Rivers University, 900 McGill Rd, Kamloops, BC, Canada

Abstract
This paper presents He´s Energy Balance Method (EBM) for solving nonlinear oscillatory differential equations. Three strong nonlinear cases have been studied analytically. Analytical results of the EBM are compared with numerical solutions using Runge-Kutta´s algorithm. The effects of different important parameters on the nonlinear response of the systems are studied. The results show the presented method is potentially to solve high nonlinear vibration equations.

Key Words
Energy Balance Method (EBM); Runge- Kutta´s Method (RKM); nonlinear vibrations

Address
Mahmoud Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran

Iman Pakar and Mahdi Bayat: Young Researchers and Elite club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
Fiber models have been developed and applied to various structural elements such as shear walls, beams and columns. Only scarcely have fiber models been applied to circular foundation systems such as cast in drilled holes shafts (CIDH). In pile foundations with constraint head boundary conditions, shear deformations can easily contribute to the lateral pile response. However, soil structure interaction formulations such as the p-y method, commonly used for lateral pile design, do not include structural shear deformations in its traditional derivation method. A fiber model that couples shear and axial-bending behavior, originally developed for wall elements was modified and validated on circular cross sections (columns) before being applied to a 0.61 m diameter reinforced concrete (RC) pile with fixed head boundary conditions. The analytical response was compared to measured test results of a fixed head test pile to investigate the possible impact of pile shear deformations on the displacement, shear, and moment profiles of the pile. Results showed that shear displacements and forces are not negligible and suggest that nonlinear shear deformations for RC piles should be considered for fixed-head or similar conditions. Appropriate sensor layout is recommended to capture shear deformation when deriving p-y curves from field measurements.

Key Words
piles; lateral loading; soil-pile interaction; shear deformations; reinforced concrete

Address
Anne Lemnitzer: Department of Civil Engineering, Univ. of California Irvine, 4135 Eng. Gateway, Irvine, CA, 92697, USA

Eduardo Nunez: Independent Structural Engineer, Santiago, Chile

Leonardo M. Massone: Department of Civil Engineering, University of Chile, Santiago, Blanco Encalada 2002, Santiago, Chile

Abstract
The goal of energy-based seismic design is to obtain a structural design with a higher energy dissipation capacity than the energy dissipation demands incurred under earthquake motions. Accurate estimation of the story hysteretic energy demand of a multi-story structure is the key to meeting this goal. Based on the assumption of a mode-equivalent single-degree-of-freedom system, the energy equilibrium relationship of a multi-story structure under seismic action is transformed into that of a multi-mode analysis of several single degree-of-freedom systems. A simplified equation for the estimation of the story seismic hysteretic energy demand was then derived according to the story shear force and deformation of multi-story buildings, and the deformation and energy relationships between the mode-equivalent single-degree-offreedom system and the original structure. Sites were categorized into three types based on soil hardness, namely, hard soil, intermediate hard (soft) soil, and soft soil. For each site type, a 5-story and 10-story reinforced concrete frame structure were designed and employed as calculation examples. Fifty-six earthquake acceleration records were used as horizontal excitations to validate the accuracy of the proposed method. The results verify the following. (1) The distribution of seismic hysteretic energy along the stories demonstrate a degree of regularity. (2) For the low rise buildings, use of only the first mode shape provides reasonably accurate results, whereas, for the medium or high rise buildings, several mode shapes should be included and superposed to achieve high precision. (3) The estimated hysteretic energy distribution of bottom stories tends to be underestimated, which should be modified in actual applications.

Key Words
hysteretic energy demand; nonlinear response history analysis; pushover analysis; equivalent SDOF system; earthquake excitation

Address
Feng Wang, Zhiyu Huang: College of Civil Engineering, Dalian Minzu University, Dalian, China

Ning Zhang: Dalian Polytechnic University, Dalian, China

Abstract
The effectiveness of 100/30, 100/40 and SRSS directional combination rules on the response of asymmetric setback buildings is examined. Because of the irregularity in setback buildings, the maximum seismic response would be correlative with the direction of earthquake. To verify the directional combination rules of mode superposition methods, the time history analyses of setback buildings to real earthquake records are carried out. Example analyses have been used to compare the validty and accuracy of SRSS and percentage methods for frame and dual frame-wall systems.

Key Words
combination rules; seismic analysis; multi-story buildings; asymmetric set-backs

Address
M. Gunhan Aksoylu, Yavuz Durguna and Kutlu Darilmaz: Istanbul Technical University, Civil Engineering Department, Maslak, Sariyer, 34469, Istanbul, Turkey


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