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CONTENTS
Volume 10, Number 6, June 2016
 

Abstract
For a nonlinear control system, there are many uncertainties, such as the structural model, controlled parameters and external loads. Although the significant progress has been achieved on the robust control of nonlinear systems through some researches on this issue, there are still some limitations, for instance, the complicated solving process, weak conservatism of system, involuted structures and high order of controllers. In this study, the computational structural mechanics and optimal control theory are adopted to address above problems. The induced norm is the eigenvalue problem in structural mechanics, i.e., the elastic stable Euler critical force or eigenfrequency of structural system. The segment mixed energy is introduced with a precise integration and an extended Wittrick-Williams (W-W) induced norm calculation method. This is then incorporated in the market-based control (MBC) theory and combined with the force analogy method (FAM) to solve the MBC robust strategy (R-MBC) of nonlinear systems. Finally, a singledegree- of-freedom (SDOF) system and a 9-stories steel frame structure are analyzed. The results are compared with those calculated by the H∞ -robust (R-H∞) algorithm, and show the induced norm leads to the infinite control output as soon as it reaches the critical value. The R-MBC strategy has a better control effect than the R-H∞ algorithm and has the advantage of strong strain capacity and short online computation time. Thus, it can be applied to large complex structures.

Key Words
market-based control; force analogy method; robustness; extended W-W algorithm; precise integration method

Address
Jian-Zhu Song, Hong-Nan Li and Gang Li: State Key Lab of Coastal and Offshore Engineering, Liaoning Collaborative Innovation Center for Engineering Disaster Prevention and Mitigation, Dalian University of Technology, Dalian 116024, China

Hong-Nan Li: School of Civil Engineering, Shenyang Jianzhu University, Shenyang 110168, China

Abstract
This paper addresses the concept of lateral overstrength; the ratio of actual lateral strength to design base shear force, for both SDOF and MDOF systems considering soil structure interaction. Overstrength factors are obtained with inelastic time history analysis for SDOF systems for period range of 0.1-3.0 s, five different aspect ratios (h/r=1, 2, 3, 4, 5) and five levels of ductility (µ=2, 3, 4, 5, 6) considering soil structure interaction. Structural overstrength for MDOF systems are obtained with inelastic time history collapse analysis for sample 1, 3, 6, 9, 12 and 15 storey RC frame systems. In analyses, 64 ground motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil are used. Also lateral overstrength ratios considering soil structure interaction are compared with those calculated for fixed-base cases.

Key Words
seismic design; overstrength; soil structure interaction; SDOF systems; multi-storey structures

Address
Department of Civil Engineering, Istanbul Aydin University, Istanbul, Turkey

Abstract
The paper presents the development of experimental fragility functions for exterior RC beamcolumn connections based on results obtained from extensive testing carried out in the present study. Three typical types of seismically deficient beam-column connections, which are commonly prevalent in Indian sub-continent, were considered. These specimens were tested under cyclic displacement histories with different characteristics to induce different damage states. Rehabilitation specific fragility functions for damaged specimens were developed considering drift angle as a demand parameter. Four probability distributions were fit to the data and suitability of each distribution was evaluated using standard statistical method. Specimens with different damage states were rehabilitated appropriately and rehabilitated specimens were tested under similar displacement histories. Fragility functions for rehabilitated specimens have also been developed following similar procedure. Comparison of fragility functions for both original and rehabilitated specimens for each rehabilitation method showed close agreement, which establishes the effectiveness of the adopted rehabilitation strategies and hence would provide confidence in field application.

Key Words
fragility functions; beam-column connections; damage states; demand parameter; rehabilitation; cyclic loading

Address
Comingstarful Marthong: Department of Civil Engineering, National Institute of Technology Meghalaya, India

Sajal K. Deb and Anjan Dutta: Department of Civil Engineering, Indian Institute of Technology Guwahati, India

Abstract
This study investigates ground motion parameters and their damage potential for building type structures. It focuses on low and mid-rise reinforced concrete buildings that are important portion of the existing building stock under seismic risk in many countries. Correlations of 19 parameters of 466 earthquake records with nonlinear displacement demands of 1056 Single Degree of Freedom (SDOF) systems are investigated. Properties of SDOF systems are established to represent RC building construction practice. The correlation of damage and ground motion characteristics is examined with respect to number of story and site classes. Equations for average nonlinear displacement demands of considered RC buildings are given for some of the ground motion parameters. Velocity related parameters are generally found to have better results than the acceleration, displacement and frequency related ones. Correlation of the parameters may be expected to decrease with increasing intensity of seismic event. Velocity Spectrum Intensity and Peak Ground Velocity have been found to have the highest correlation values for almost all site classes and number of story groups. Common parameter of Peak Ground Acceleration has lower correlation with damage when compared to them and some other parameters like Effective Design Acceleration and Characteristic Intensity.

Key Words
destructiveness; seismic evaluation; peak ground velocity; record characteristics; reinforced concrete

Address
Hayri Baytan Ozmen: Department of Civil Engineering, Usak University, 64200 Usak, Turkey

Mehmet Inel: Department Department of Civil Engineering, Pamukkale University, 20070 Denizli, Turkey

Abstract
Historical masonry structures have an important value for cultures and it is essential for every society to strengthen them and confidently transfer to the future. For this reason, determination of the seismic earthquake response, which is the most affecting factor to cause the damage at these structures, gain more importance. In this paper, the seismic earthquake behaviour of Kaya Çelebi Mosque, which is located in Turkey and the restoration process has still continued after 2011 Van earthquake, is determined. Firstly the dynamic modal analysis and subsequently the seismic spectral analysis are performed using the finite element model of the mosque constructed with restoration drawings in SAP2000 program. Maximum displacements, tensile, compressive and shear stresses are obtained and presented with contours diagrams. Turkish Earthquake Code and its general technical specifications are considered to evaluate the structural responses. After the analyses, it is seen that the displacements and compressive/shear stresses within the code limits. However, tension stresses exceeded the maximum values at some local regions. For this mosque, this is in tolerance limits considering the whole structure. But, it can be said that the tension stresses is very important for this type of the structures, especially between the stone and mortar. So, some additional strengthening solutions considering the originality of historical structures may be applicable on maximum tensile regions.

Key Words
historical masonry structures; Kaya Celebi mosque; restoration; seismic earthquake response; seismic spectral analysis; Turkish Earthquake Code

Address
Ahmet C. Altunisik, Alemdar Bayraktar: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Ali F. Genc: Department of Civil Engineering, Karadeniz Technical University, Of Technology Faculty, Trabzon, Turkey

Abstract
The purpose of this work is to investigate the seismic behavior of St. Titus Church in Heraklion, Crete, Greece as well as the need of its seismic retrofitting. A numerical model of the Church is constructed using shell finite elements and it is then seismically examined using response spectrum and linear timehistory analyses. Effects of soil-structure interaction have been also taken into account. The Church without retrofit is expected to exhibit extensive tensile failures and many compressive ones. Aiming to maintain the architectural character of the structure as well as to increase its seismic resistance, a retrofitting procedure involving injection of cement grout in conjunction with reinforced concrete jacketing to the internal side of the masonry walls is proposed. A numerical implementation of the proposed seismic retrofitting is performed and its effect is evaluated by response spectrum and linear time-history analyses. From the results of these analyses, it is shown that compressive failures are eliminated while only few tensile failures of local character take place.

Key Words
seismic response; masonry; retrofitting; response spectrum; time-history

Address
Michael J. Tzanakis: Engineer Consultant, Ag. Fanouriou 11, GR-71601 Heraklion, Crete, Greece

George A. Papagiannopoulos: Department of Civil Engineering, University of Patras, GR-26500 Patras, Greece

George D. Hatzigeorgiou: School of Science and Technology, Hellenic Open University, GR-26335 Patras, Greece

Abstract
The soil-structure interaction effect significantly influences the design of multi-storey buildings subjected to lateral seismic loads. The shear walls are often provided in such buildings to increase the lateral stability to resist seismic loads. In the present work, the nonlinear soil-structure analysis of a G+5 storey RC shear wall building frame having isolated column footings and founded on deformable soil is presented. The nonlinear seismic FE analysis is carried out using ANSYS software for the building with and without shear walls to investigate the effect of inclusion of shear wall on the moments in the footings due to differential settlement of soil mass. The frame is considered to behave in linear elastic manner, whereas, soil mass to behave in nonlinear manner. It is found that the interaction effect causes significant variation in the moments in the footings. The comparison of non-interaction and interaction analyses suggests that the presence of shear wall causes significant decrease in bending moments in most of the footings but the interaction effect causes restoration of the bending moments to a great extent. A comparison is made between linear and nonlinear analyses to draw some important conclusions.

Key Words
soil-structure interaction; ANSYS; space frame; shear wall; nonlinear analysis; foundation moments; isolated footings; seismic forces

Address
D.K. Jain and M.S. Hora: Department of Civil Engineering, Maulana Azad National Institute of Technology, Bhopal, India

Abstract
Peninsular Malaysia lying on the stable Sunda Plate has traditionally been considered safe with low to moderate seismicity. However, far field Sumatran mega-earthquakes have been shown to be capable of triggering ground motions felt in high rise structures in the major Malaysian cities while seismic impact from local earthquakes of moment magnitude 3.8 have reportedly induced nominal structural damages to nearby buildings. This paper presents an overview of the recent seismic activities in and around Peninsular Malaysia with reference to prominent earthquakes generated by far field interplate and local intraplate sources. Records of ground motion data and seismic hazard assessment (SHA) results available in the literature have been analyzed and discussed. The peak ground acceleration (PGA) values from historical records for few local intraplate events were observed to be higher than those for the events from Sumatran Subduction Zone. This clearly points to the need for a detailed and comprehensive SHA incorporating both far field and local sources. Such an analysis would contribute the knowledge required for secure and reliable infrastructure design and safeguard the Malaysian people and economy.

Key Words
seismic hazard; peak ground acceleration; far-field sources; intraplate source

Address
School of Engineering, Monash University Malaysia, Jalan Lagoon Selatan, Bandar Sunway, 47500 Subang Jaya, Selangor, Malaysia

Abstract
Besides the complex instructions of guidance documents for seismic rehabilitation of existing buildings, some institutions have provided simple criteria in terms of simplified rehabilitations. ASCE 41-06 is one of documents that introduced a simple method for assessment of certain buildings that do not require advanced analytical procedures. Furthermore the New Zealand guideline has presented a simple lateral mechanism analysis that is a hand static analysis for determining the probable collapse mechanism, lateral strength and displacement capacity of the structure. The present study is focused on verifying the results of the simplified methods which is used by NZSEE and ASCE 41-06 in assessment of existing buildings. For this, three different special steel moment and braced frames are assessed under these two guidelines and the accuracy of the results is checked with the results of nonlinear static and dynamic analysis. After comparison of obtained results, suggestions are presented to improve seismic retrofit criteria.

Key Words
pushover analysis; nonlinear dynamic analysis; moment frames; braced frames; peak ground acceleration failure (PGAf)

Address
Mohsen Tehranizadeh, Maryam Amirmojahedi: Department of Civil Engineering, Amirkabir University of Technology (Tehran Polytechnic), 474 Hafez Ave. Tehran, Iran

Amir Moshref: Department of Civil Engineering, Islamic Azad University-Tafresh Branch, Tafresh, Iran

Abstract
The effect of porosity on bending and free vibration behavior of simply supported functionally graded plate reposed on the Winkler-Pasternak foundation is investigated analytically in the present paper. The modified rule of mixture covering porosity phases is used to describe and approximate material properties of the FGM plates with porosity phases. The effect due to transverse shear is included by using a new refined shear deformation theory. The number of unknown functions involved in the present theory is only four as against five or more in case of other shear deformation theories. The Poisson ratio is held constant. Based on the sinusoidal shear deformation theory, the position of neutral surface is determined and the equation of motion for FG rectangular plates resting on elastic foundation based on neutral surface is obtained through the minimum total potential energy and Hamilton

Key Words
porosity coefficient; FGM plate; bending and free vibration behavior; elastic foundation

Address
Rabia Benferhat, Mohamed Said Mansour: Laboratoire de Géomateriaux, Departement de Génie Civil, Universite Hassiba Benbouali de Chlef, Algerie

Tahar Hassaine Daouadji, Lazreg Hadji: Departement de Genie Civil, Universite Ibn Khaldoun de Tiaret, Algerie

Abstract
The effectiveness of base isolation (BI) systems for mitigation of seismic vibration of bridges have been extensively studied in the past. It is well established in those studies that the performance of BI system is largely dependent on the characteristics of isolator yield strength. For optimum design of such systems, normally a standard nonlinear optimization problem is formulated to minimize the maximum response of the structure, referred as Stochastic Structural Optimization (SSO). The SSO of BI system is usually performed with reference to a problem of unconstrained optimization without imposing any restriction on the maximum isolator displacement. In this regard it is important to note that the isolator displacement should not be arbitrarily large to fulfil the serviceability requirements and to avoid the possibility of pounding to the adjacent units. The present study is intended to incorporate the effect of excessive isolator displacement in optimizing BI system to control seismic vibration effect of bridges. In doing so, the necessary stochastic response of the isolated bridge needs to be optimized is obtained in the framework of statistical linearization of the related nonlinear random vibration problem. A simply supported bridge is taken up to elucidate the effect of constraint condition on optimum design and overall performance of the isolated bridge compared to that of obtained by the conventional unconstrained optimization approach.

Key Words
seismic vibration; base isolation; bridges; stochastic structural optimisation; constrained optimisation

Address
Bijan K. Roy: Department of Civil Engineering, National Institute of Technology, Silchar, India

Subrata Chakraborty: Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, India

Sudib K. Mishra: Department of Civil Engineering, Indian Institute of Technology, Kanpur, India

Abstract
This research focuses on seismic performance of a class of single pier skewed bridges with three different pier-deck connections; skew angles vary from 0° to 60°. A well-documented four span continuous deck bridge has been modeled and verified. Seat-type connections with fixed and sliding bearings plus monolithic pier-deck connections are studied. Shear keys are considered either fully operational or ineffective. Seismic performances of the bridges and the structural components are investigated conducting bidirectional nonlinear time history analysis in OpenSees. Several global and intermediate engineering demand parameters (EDP) have been studied. On the basis of results, the values of demand parameters of skewed bridges, such as displacement and rotation of the deck plus plastic deformation and torsional demand of the piers, increase as the skew angle increases. In order to eliminate the deck collapse probability, the threshold skew angle is considered as 30° in seat-type bridges. For bridges with skew angles greater than 30°, monolithic pier-deck connections should be applied. The functionality of shear keys is critical in preventing large displacements in the bearings. Pinned piers experience considerable ductility demand at the bottom.

Key Words
skewed bridge; pier-deck connection; single pier; nonlinear time history; combined loading; torsion; fixed bearing; sliding bearing; shear key

Address
Intl Institute of Earthquake Eng. and Seismology (IIEES), No. 21, Arghavan St., North Dibajee, Farmanieh, Tehran, Iran


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