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CONTENTS
Volume 11, Number 2, August 2016
 

Abstract
Rehabilitation of historical unreinforced masonry (URM) buildings is a priority in many parts of the world, since those buildings are a living part of history and a testament of human achievement of the era of their construction. Many of these buildings are still operational; comprising brittle materials with no reinforcements, with spatially distributed mass and stiffness, they are not encompassed by current seismic assessment procedures that have been developed for other structural types. To facilitate the difficult task of selecting a proper rehabilitation strategy - often restricted by international treaties for non-invasiveness and reversibility of the intervention - and given the practical requirements for the buildings´ intended reuse, this paper presents a practical procedure for assessment of seismic demands of URM buildings - mainly historical constructions that lack a well-defined diaphragm action. A key ingredient of the method is approximation of the spatial shape of lateral translation, Φ, that the building assumes when subjected to a uniform field of lateral acceleration. Using Φ as a 3-D shape function, the dynamic response of the system is evaluated, using the concepts of SDOF approximation of continuous systems. This enables determination of the envelope of the developed deformations and the tendency for deformation and damage localization throughout the examined building for a given design earthquake scenario. Deformation demands are specified in terms of relative drift ratios referring to the in-plane and the out-of-plane seismic response of the building´s structural elements. Drift ratio demands are compared with drift capacities associated with predefined performance limits. The accuracy of the introduced procedure is evaluated through (a) comparison of the response profiles with those obtained from detailed time-history dynamic analysis using a suite of ten strong ground motion records, five of which with near-field characteristics, and (b) evaluation of the performance assessment results with observations reported in reconnaissance reports of the field performance of two neoclassical torsionally-sensitive historical buildings, located in Thessaloniki, Greece, which survived a major earthquake in the past.

Key Words
seismic assessment; historical and monumental buildings; unreinforced masonry structures (URM); pushover analysis; torsion

Address
tylianos I. Pardalopoulos, Stavroula J. Pantazopoulou: Department of Civil and Environmental Engineering, University of Cyprus, Nicosia, Cyprus

Stylianos I. Pardalopoulos: Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki, Greece

Stavroula J. Pantazopoulou: Department of Civil Engineering, Lassonde Faculty of Engineering, York University, Canada

Christos E. Ignatakis: Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece

Abstract
The linear and nonlinear seismic responses of steel buildings with perimeter moment resisting frames and welded connections (WC) are estimated and compared with those of buildings with posttensioned connections (PC). Two-dimensional (2D) and three-dimensional (3D) structural representations of the buildings as well as global and local response parameters are considered. The seismic responses and structural damage of steel buildings with PC may be significantly smaller than those of the buildings with typical WC. The reasons for this are that the PC buildings dissipate more hysteretic energy and attract smaller inertia forces. The response reduction is larger for global than for local response parameters. The reduction may significantly vary from one structural representation to another. One of the main reasons for this is that the energy dissipation characteristics are quite different for the 2D and 3D models. In addition, in the case of the 3D models, the contribution of each horizontal component to the axial load on an specific column may be in phase each other during some intervals of time, but for some others they may be out of phase. It is not possible to observe this effect on the 2D structural formulation. The implication of this is that 3D structural representation should be used while estimating the effect of the PC on the structural response. Thus, steel frames with post-tensioned bolted connections are a viable option in high seismicity areas due to the fact that brittle failure is prevented and also because of their reduced response and self-centering capacity.

Key Words
steel buildings; welded and post-tensioned connections; nonlinear analysis; seismic loading; 2D and 3D structural representation

Address
Alfredo Reyes-Salazar, Eden Bojorquez, Juan Bojorquez and Mario D. Llanes-Tizoc: Facultad de Ingenieria, Universidad Autonoma de Sinaloa, Ciudad Universitaria, Culiacan Sinaloa, Mexico

Sonia E. Ruiz: Instituto de Ingenieria, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico D.F., Mexico

Abstract
A suitable ground motion intensity measure (IM) plays a crucial role in the seismic performance assessment of a structure. In this paper, we introduce a scalar IM for use in evaluating the seismic response of single-layer reticulated domes. This IM is defined as the weighted geometric mean of the spectral acceleration ordinates at the periods of the dominant vibration modes of the structure considered, and the modal strain energy ratio of each dominant vibration mode is the corresponding weight. Its applicability and superiority to 11 other existing IMs are firstly investigated in terms of correlation with the nonlinear seismic response, efficiency and sufficiency using the results of incremental dynamic analyses which are performed for a typical single-layer reticulated dome. The hazard computability of this newly proposed IM is also briefly discussed and illustrated. A conclusion is drawn that this dominant vibration mode-based scalar IM has the characteristics of strong correlation, high efficiency, good sufficiency as well as hazard computability, and thereby is appropriate for use in the prediction of seismic response of single-layer reticulated domes.

Key Words
ground motion intensity measure; nonlinear seismic response; single-layer reticulated domes; incremental dynamic analysis; modal strain energy ratio

Address
Jie Zhong, Xudong Zhi and Feng Fan: Key Laboratory of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin 150090, China

Jie Zhong, Xudong Zhi and Feng Fan: School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

Abstract
Environmental and operational benefits of green roofs are manifolds; however, their main disadvantages are cost and weight. New technology enabled the use of plastics to reduce the weight of green roof systems to promote their installation. To maximize their potential benefits, green roofs can be installed on existing structures. This study evaluates the influence of green roofs on the seismic response of 3, 6, and 8 storey reinforced concrete ductile moment resisting frames, which were designed according to current seismic standards, however, not designed for green roofs. For each frame, three different types of roofs are considered: gravel flat roof, extensive green roof, and intensive green roof. Nonlinear dynamic time history analysis using an ensemble of twenty real earthquake records was performed to determine the inter-storey drift demand and roof drift demand for each frame. Eigenvalue analysis was also performed to determine the impact of green roofs weight on the elastic and cracked periods of the structure. Results from the analysis demonstrated that intensive and extensive green roofs do not affect the seismic performance of reinforced concrete frame structures.

Key Words
green roofs; RC frames; dynamic time history analysis; seismic response; base shear; drift

Address
Fabricio Bianchini, A.B.M. Rafiqul Haque, Kasun Hewage
and M. Shahria Alam: School of Engineering, University of British Columbia, Kelowna, Okanagan School of Engineering, EME 4225, 1137 Alumni Ave., Kelowna, BC, Canada

Abstract
This paper presents a study on a non-seismically designed reinforced concrete (RC) frame structure. The structure was a existing three-story office building constructed according to the 1990s practice in Vietnam. The 1/3 scaled down versions of structure was tested on a shake table to investigate the seismic performance of this type of construction. It was found that the inter-story drift and the overall behavior of structure meet the requirements of the actual seismic design codes. Then, nonlinear time history analyses are carried out using the fiber beam- column elements. The comparison between the experimental and simulation results shows the performance of the time history analysis models.

Key Words
seismic; reinforced concrete; non seismically designed; fiber beam; nonlinear; frame structure

Address
Xuan-Huy Nguyen and Huy Cuong Nguyen: Department of Civil Engineering, University of Transport and Communications, Vietnam

Xuan-Huy Nguyen and Huy Cuong Nguyen: Research and Application Center for Technology in Civil Engineering, University of Transport and Communications, Vietnam

Abstract
A virtual parameter is introduced into the formulation of the previously published integration method to improve its stability properties. It seems that the numerical properties of this integration method are almost unaffected by this parameter except for the stability property. As a result, it can have second order accuracy, explicit formulation and controllable numerical dissipation in addition to the enhanced stability property. In fact, it can have unconditional stability for the system with the instantaneous degree of nonlinearity less than or equal to the specified value of the virtual parameter for the modes of interest for each time step.

Key Words
unconditional stability; conditional stability; nonlinear dynamic analysis; virtual parameter; structure-dependent integration method

Address
Shuenn-Yih Chang: Department of Civil Engineering National Taipei University of Technology NTUT Box 2653, Taipei 106, Taiwan, Republic of China

Abstract
This paper presents the results of cyclic loading tests on concrete beams reinforced with various reinforcement, including ordinary steel bars, CFRP bars and CFRP prestressed concrete prisms(PCP). The main variable in the test program was the level of prestress and the cross section of PCP. The seismic performance indexes including hysteretic loops, skeleton curve, ductility, energy dissipation capacity and stiffness degradation were analyzed. The results show that the CFRP prestressed concrete prisms as flexural reinforcement of concrete beams has good seismic performance. And the ductility and the energy dissipation capacity were good, the hysteresis loops were full and had large area.

Key Words
CFRP; prism; cyclic loading; beam; seismic performance

Address
Jiongfeng Liang: State Key Laboratory Breeding Base of Nuclear Resources and Environment, Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, Nanchang, P.R. China

Jiongfeng Liang, Jianbao Wang, Pinghua Yi: Faculty of Civil&Architecture Engineering, East China Institute of Technology, Nanchang, P.R. China

Deng Yu: College of Civil and Architecture Engineering, Guangxi University of Science and Technology, Liuzhou, P.R. China

Abstract
The 2012 Emilia (Italy) earthquakes struck a highly industrialized area including several thousands of industrial prefabricated buildings. Due to the lack of specific design and detailing for earthquake resistance, precast reinforced concrete (RC) buildings suffered from severe damages and even partial or total collapses in many cases. The present study reports a data inventory of damages from field survey on prefabricated buildings. The damage database concerns more than 1400 buildings (about 30% of the total precast building stock in the struck region). Making use of the available shakemaps of the two mainshocks, damage distributions were related with distance from the nearest epicentre and corresponding Pseudo-Spectral Acceleration for a period of 1 second (PSA at 1 s) or Peak Ground Acceleration (PGA). It was found that about 90% of the severely damaged to collapsed buildings included into the database stay within 16 km from the epicentre and experienced a PSA larger than 0.12 g. Moreover, 90% of slightly to moderately damaged buildings are located at less than 25 km from the epicentre and were affected by a PSA larger than 0.06 g. Nevertheless, the undamaged buildings examined are almost uniformly distributed over the struck region and 10% of them suffered a PSA not lower than 0.19g. The damage distributions in terms of the maximum experienced PGA show a sudden increase for PGA

Key Words
precast RC buildings; damages; Emilia earthquake; seismic retrofitting; peak ground acceleration; pseudo-spectral acceleration

Address
Fabio Minghini, Nerio Tullini: Engineering Department - ENDIF, University of Ferrara, Via G. Saragat 1, 44122, Ferrara, Italy

Elena Ongaretto, Veronica Ligabue, Marco Savoia: Department of Civil, Chemical, Environmental, and Materials Engineering - DICAM, University of Bologna,
Viale Risorgimento 2, 40136, Bologna, Italy

Abstract
The main objective of this paper is the robust multi-objective optimization design of semi-active tuned mass damper (STMD) system using genetic algorithms and fuzzy logic. For optimal design of this system, it is required that the uncertainties which may exist in the system be taken into account. This consideration is performed through the robust design optimization (RDO) procedure. To evaluate the optimal values of the design parameters, three non-commensurable objective functions namely: normalized values of the maximum displacement, velocity, and acceleration of each story level are considered to minimize simultaneously. For this purpose, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) approach is used to find a set of Pareto-optimal solutions. The torsional effects due to irregularities of the building and/or unsymmetrical placements of the dampers are taken into account through the 3-D modeling of the building. Finally, the comparison of the results shows that the probabilistic robust STMD system is capable of providing a reduction of about 52%, 42.5%, and 37.24% on the maximum displacement, velocity, and acceleration of the building top story, respectively.

Key Words
semi-active control system; multi-objective optimization; robust design; genetic algorithm; fuzzy logic controller; earthquake excitation

Address
Saeid Pourzeynali, Meysam Yousefisefat: Department of Civil Engineering, Faculty of Engineering, University of Guilan, Rasht, I. R. Iran

Shide Salimi, Houshyar Eimani Kalesar: Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh-Ardebili, Ardebil, I. R. Iran

Abstract
During the last decades, many destructive earthquakes occurred in Algeria, particularly in the northern part of the country (Chlef (1980), Constantine (1985), Tipaza (1989), Mascara (1994), Ain-Benian (1996), Ain Temouchent (1999), Beni Ourtilane (2000), and recently Boumerdes (2003), causing enormous losses in human lives, buildings and equipments. In order to reduce this risk and avoid serious damages to the strategic existing buildings, the authorities of the country, aware of this risk and in order to have the necessary elements that let them to know and estimate the potential losses in advance, with an acceptable error, and to take the necessary countermeasures, decided to invest into seismic upgrade, strengthening and retrofitting of those buildings. To do so, seismic vulnerability study of this category of buildings has been considered. Structural analysis is performed based on the site investigation (inspection of the building, collecting data, materials characteristics, general conditions of the building, etc.), and existing drawings (architectural plans, structural design, etc.). The aim of these seismic vulnerability studies is to develop guidelines and a methodology for rehabilitation of existing buildings. This paper presents the methodology, based on non linear and seismic analysis of existing buildings, followed in this study and summarizes the vulnerability assessment and strengthening of one of the strategic buildings according to the new Algerian code RPA 99/version 2003. As a direct application of this methodology, both, static equivalent method and non linear dynamic analysis, of composite concrete masonry existing building in the city of "CONSTANTINE", located in the east side of ALGERIA, are presented in this paper.

Key Words
vulnerability; masonry; strategic building; capacity design; non linear dynamic analysis; strengthening

Address
Mustapha Remki, Fouad kehila, Hakim Bechtoula: Department of Civil Engineering, National Earthquake Engineering Research Center, CGS, Rue Kaddour Rahim, BP 252 Hussein Dey, Algiers, Algeria

Abdelkrim Bourzam: Faculty of Civil Engineering, University of Sce & Technology USTHB, Algiers, Algeria


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