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CONTENTS
Volume 6, Number 6, June 2014
 

Abstract
Reinforced concrete (RC) structures are likely to experience damage when subjected to earthquakes. Damage index (DI) has been recognised as an advanced tool of quantitatively expressing the extent of damage in such structures. Last 30 years have seen many concepts for DI proposed in order to calibrate the observed levels of damage. The current research briefly reviews all available concepts and investigates their relative merits and limitations with a view to proposing a new concept based on residual deformation. Currently available DIs are classified into two broad categories – non-cumulative DI and cumulative DI. Non-cumulative DIs do not include the effects of cyclic loading, whilst the cumulative concepts produce more rational indication of the level of damage in case of earthquake excitations. Ideally, a DI should vary within a scale of 0 to 1 with 0 representing the state of elastic response, and 1 referring to the state of total collapse. Some of the available DIs do not satisfy these criteria. A new DI based on energy is proposed herein and its performances, both for static and for cyclic loadings, are compared with those obtained using the most widely accepted DI in literature. The proposed DI demonstrates a rational way to predict the extent of damage for a number of case studies. More research is encouraged to address some identified issues.

Key Words
cyclic loading, damage analysis, damage index, earthquake, hysteretic energy, reinforced concrete

Address
Vui V. Cao, Hamid R. Ronagh and Hassan Baji: School of Civil Engineering, The University of Queensland, St. Lucia, Australia

Mahmud Ashraf: School of Engineering and Information Technology UNSW Canberra at the Australian Defence Forces Academy Campbell, ACT 2610, Australia

Abstract
This paper presents a simple methodology that integrates an improved storey shear modelling, Incremental Dynamic Analysis and Monte Carlo Simulation in order to carryout vulnerability analysis towards development of fragility curves for Unreinforced Brick Masonry buildings. The methodology is demonstrated by developing fragility curves of a single storey Unreinforced Brick Masonry building for which results of experiment under lateral load is available in the literature. In the study presented, both uncertainties in mechanical properties of masonry and uncertainties in the characteristics of earthquake ground motion are included. The research significance of the methodology proposed is that, it accommodates a new method of damage grade classification which is based on „structural performance characteristics‟ instead of „fixed limiting values‟. The usefulness of such definition is discussed as against the existing practice.

Key Words
vulnerability analysis; fragility curve; capacity curve; capacity spectrum; improved storey shear modelling; incremental dynamic analysis; monte carlo simulation

Address
Balasubramanian S.R., Balaji Rao K. Anoop M.B.: CSIR-Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai-600113, Tamil Nadu, India

Meher Prasad A. and Rupen Goswami: Department of Civil Engineering, Indian Institute of Technology Madras, Chennai-600036, Tamil Nadu, India


Abstract
Adobe is one of the oldest construction materials that is still used in many seismic countries, and different construction techniques are found around the world. The adobe material is characterized as a brittle material; it has acceptable compression strength but it has poor performance under tensile and shear loading conditions. Numerical modelling is an alternative approach for studying the nonlinear behaviour of masonry structures such as adobe. The lack of a comprehensive experimental database on the adobe material properties motivated the study developed here. A set of a reference material parameters for the adobe were obtained from a calibration of numerical models based on a quasi-static cyclic in-plane test on full-scale adobe wall representative of the typical Peruvian adobe constructions. The numerical modelling, within the micro and macro modelling approach, lead to a good prediction of the in-plane seismic capacity and of the damage evolution in the adobe wall considered.

Key Words
adobe masonry; material properties; in-plane behaviour; seismic capacity; numerical modelling

Address
Tarque Nicola and Blondet Marcial: Department of Engineering, Division of Civil Engineering, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, Lima 32, Peru

Camata Guido and Spacone Enrico: Department of Engineering and Geology, University

Abstract
A reduction of the response of irregular structures subjected to earthquake excitation by control devices equipped by suitable control algorithm is proposed in this paper. The control algorithm, which is used, is the pole placement one. A requirement of successful application of pole placement algorithm is a definition-selection of suitable poles (eigen-values) of controlled irregular structures. Based on these poles, the required action is calculated and applied to the irregular structure by means of control devices. The selection of poles of controlled irregular structure, is a critical issue for the success of the algorithm. The calculation of suitable poles of controlled irregular structure is proposed herein by the following procedure: a fictitious symmetrical structure is considered from the irregular structure, adding vertical elements, such as columns or shear walls, at any location where is necessary. Then, the eigen-values of symmetrical structure are calculated, and are forced to be the poles of irregular controlled structure. Based on these poles and additional damping, the new poles of the controlled irregular structure are calculated. By pole placement algorithm, the feedback matrix is obtained. Using this feedback matrix, control forces are calculated at any time during the earthquake, and are applied to the irregular structure by the control devices. This procedure results in making the controlled irregular structure to behave like a symmetrical one. This control strategy can be applied to one storey or to multi-storey irregular buildings. Furthermore, the numerical results were shown that with small amount of control force, a sufficient reduction of the response of irregular buildings is achieved.

Key Words
structural control, pole placement, irregular structures, earthquake engineering

Address
Nikos G. Pnevmatikos: Department o Civil Engineering, Surveying and Geoinformatics, Technological Educational Institution of Athens, Ag. Spyridonos Str., P.O. 12210 Egaleo-Athens, Greece

George D. Hatzigeorgiou: Hellenic Open University, Director of Post-Graduate Program: Engineering Project Management, Parodos Aristotelous 18, GR-26335, Patras, Greece

Abstract
This paper presents a framework for analytical seismic vulnerability assessment of substandard reinforced concrete (RC) structures in developing countries. A modified capacity-demand diagram method is used to predict the response of RC structures with degrading behaviour. A damage index based on period change is used to quantify the evolution of damage. To demonstrate the framework, a class of substandard RC buildings is examined. Abrupt accumulation of damage is observed due to the brittle failure modes and this is reflected in the developed vulnerability curves, which differ substantially from the curves of ductile structures.

Key Words
seismic vulnerability; reinforced concrete; sub-standard construction; non-linear static, damage index; analytical; probabilistic, capacity-demand diagram methods

Address
Nicholas Kyriakides, Sohaib Ahmad, Kypros Pilakoutas, Kyriacos Neocleous: Department of Civil and Structural Engineering, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield S1 3JD, UK

Nicholas Kyriakides and Christis Chrysostomou: Present Address: Cyprus University of Technology, Department of Civil Engineering and Geomatics, P.O.Box 50329, 3603 Lemesos, Cyprus

Abstract
The seismic vulnerability of stone masonry buildings is studied on the basis of their fragility curves. In order to account for out-of-plane failure modes, normally disregarded in past studies, linear static Finite Element analysis in 3D of prototype regular buildings is performed using a nonlinear biaxial failure criterion for masonry. More than 1100 analyses are carried out, so as to cover the practical range of the most important parameters, namely the number of storeys, percentage of side length in exterior walls taken up by openings, wall thickness, plan dimensions and number of interior walls, type of floor and pier height-to-length ratio. Results are presented in the form of damage and fragility curves. The fragility curves correspond well to the damage observed in masonry buildings after strong earthquakes and are in good agreement with other fragility curves in the literature. They confirm what is already known, namely that buildings with stiff floors or higher percentage of load-bearing walls are less vulnerable, and that large openings, taller storeys, larger number of storeys, higher wall slenderness and higher ratio of clear height to horizontal length of walls increase the vulnerability, but show also by how much.

Key Words
fragility curves; masonry buildings; seismic fragility; seismic vulnerability; unreinforced masonry buildings

Address
Fillitsa Karantoni, Georgios Tsionis, Foteini Lyrantzaki and Michael N. Fardis: Department of Civil Engineering, University of Patras, 26504 Patras, Greece

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