• Earthquakes and Structures
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• v.3 no.2
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• pp.117-140
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• 2012

The proposed research includes a comprehensive study on the seismic vulnerability assessment of typical building types, representative of the structural materials, the seismic codes and the construction techniques of Southern Europe. A damage database is created after the elaboration of the results of the observational data obtained from post-earthquake surveys carried out in the area struck by the September 7, 1999 Athens earthquake, a near field seismic event in an extended urban region. The observational database comprises 180.945 buildings which developed damage of varying degree, type and extent. The dataset is elaborated in order to gather useful information about the structural parameters influence on the seismic vulnerability and their correlation to the type and degree of building damages in near field earthquakes. The damage calibration of the observational data was based on label - damage provided by Earthquake Planning and Protection Organization (EPPO) in Greece and referred to the qualitative characterization for the recording of damage in post-earthquake surveys. Important conclusions are drawn on the parameters that influence the seismic response based on the wide homogeneous database which adds to the reliability of the collected information and reduces the scatter on the produced results.

• Interaction and multiscale mechanics
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• v.3 no.1
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• pp.39-54
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• 2010

In this paper, a simple approach is presented for studying the dynamic response of multi-span steel bridges supported by pylons of different heights, subjected to earthquake motions acting along the axis of the bridge with spatial variations. The analysis is carried out using the modal analysis technique, while the solution of the integral-differential equations derived is obtained using the successive approximations technique. It was found that the height of piers and the quality of the foundation soil can affect significantly the dynamical behavior of the bridges studied. Illustrative examples are presented to highlight the points of concern and useful conclusions are gathered.

• Interaction and multiscale mechanics
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• v.2 no.4
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• pp.431-454
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• 2009

This paper presents a simple model for studying the dynamic response of multi-span bridges resting on piers with different heights and subjected to earthquake forces acting transversely to the bridge, but varying spatially along its length. The analysis is carried out using the modal superposition technique, while the solution of the resulting integral-differential equations is obtained via the Laplace transformation. It has been found that the piers' height and the quality of the foundation soil can affect significantly the dynamic behavior of such bridges. Typical examples showing the effectiveness of the method are presented with useful results listed.

• Smart Structures and Systems
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• v.8 no.5
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• pp.449-470
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• 2011

During the last thirty years many structural control concepts have been proposed for the reduction of the structural response caused by earthquake excitations. Their research and implementation in practice have shown that seismic control of structures has a lot of potential but also many limitations. In this paper the importance of two practical issues, time delay and saturation effect, on the performance of controlled structures, is discussed. Their influence, both separately and in interaction, on the response of structures controlled by a modified pole placement algorithm is investigated. Characteristic buildings controlled by this algorithm and subjected to dynamic loads, such as harmonic signals and actual seismic events, are analyzed for a range of levels of time delay and saturation capacity of the control devices. The response reduction surfaces for the combined influence of time delay and force saturation of the controlled buildings are obtained. Conclusions regarding the choice of the control system and the desired properties of the control devices are drawn.

• Steel and Composite Structures
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• v.1 no.4
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• pp.377-392
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• 2001

The response of multi-story building structures to lateral loads, mainly due to earthquake and wind, is investigated for preliminary design purposes. Emphasis is placed on structural systems consisting of rigid and braced steel frames. An attempt to gain a qualitative understanding of the influence of bending and shear stiffness distribution on the deformations of such structures is made. This is achieved by modeling the structure with a stiffness equivalent Timoshenko beam. It is observed that the conventional stiffness distribution, dictated by strength constraints, may not be the best to satisfy deflection criteria. This is particularly the case for slender structural systems with prevailing bending deformations, such as flexible braced frames. This suggests that a new approach to the design of such frames may be appropriate when serviceability governs. A pertinent strategy for preliminary design purposes is proposed.

• Smart Structures and Systems
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• v.5 no.3
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• pp.209-221
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• 2009

A control algorithm for seismic protection of building structures based on the theory of variable structural control or sliding mode control is presented. The paper focus in the design of sliding surface. A method for determining the sliding surface by pole assignment algorithm where the poles of the system in the sliding surface are obtained on-line, based on the frequency content of the incoming earthquake signal applied to the structure, is proposed. The proposed algorithm consists of the following steps: (i) On-line FFT process is applied to the incoming part of the signal and its frequency content is recognized. (ii) A transformation of the frequency content to the complex plane is performed and the desired location of poles of the controlled structure on the sliding surface is estimated. (iii) Based on the estimated poles the sliding surface is obtained. (iv) Then, the control force which will drive the response trajectory into the estimated sliding surface and force it to stay there all the subsequent time is obtained using Lyapunov stability theory. The above steps are repeated continuously for the entire duration of the incoming earthquake. The potential applications and the effectiveness of the improved control algorithm are demonstrated by numerical examples. The simulation results indicate that the response of a structure is reduced significantly compared to the response of the uncontrolled structure, while the required control demand is achievable.

• Earthquakes and Structures
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• v.6 no.3
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• pp.317-334
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• 2014

The work is concerned with an investigation of the advantages stemming from the use of lightweight aggregate concrete in earthquake-resistant reinforced concrete construction. As the aseismic clauses of current codes make no reference to lightweight aggregate concrete beams made of lightweight aggregate concrete but designed in accordance with the code specifications for normal weight aggregate concrete, together with beams made from the latter material, are tested under load mimicking seismic action. The results obtained show that beam behaviour is essentially independent of the design method adopted, with the use of lightweight aggregate concrete being found to slightly improve the post-peak structural behaviour. When considering the significant reduction in deadweight resulting from the use of lightweight aggregate concrete, the results demonstrate that the use of this material will lead to significant savings without compromising the structural performance requirements of current codes.

• Interaction and multiscale mechanics
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• v.5 no.3
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• pp.187-210
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• 2012

Cable-stayed bridges are commonly used in modern bridge engineering for covering long spans. In some special cases, the designer is obliged to build such a bridge over an existing fault. Activation of this fault is possible to bring about a relative displacement or separation movement between two neighboring pylons of the bridge built on opposite sides of the fault. In this work, the effect of such a fault-induced pylon displacement on bridge's deformations and on cables' strength is thoroughly studied for several types of cable-stayed bridges and useful conclusions are drawn aiming the design. The influence of a possible earthquake and traffic loads crossing the bridge when the pylons are moving away from each other is not examined.

• Interaction and multiscale mechanics
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• v.5 no.4
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• pp.317-345
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• 2012

Cable-stayed bridges are often used in modern bridge engineering for connecting two geographical points of long distance. A special load case to cable-stayed bridges is earthquake, which can produce horizontal as well as vertical movements on the pylons of the bridge. These movements may be transient in nature, i.e., only resulting in the transient vibration of the bridge, but causing no damage consequences. In some extreme cases, they may cause permanent subsidence on one or more pylons of the bridge. In this paper, the effect of pylons' subsidence on the dynamic deformations of the bridge and on the cables' strength is thoroughly studied. Conclusions useful to the design of cable-stayed bridges will be drawn from the numerical study.

• Smart Structures and Systems
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• v.2 no.4
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• pp.305-312
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• 2006

In the case of hospital buildings, where seismic design requirements are very high, existing structuresand especially those attacked by past earthquakes, appear, often, unable to fulfil the necessary safety prerequisites. In this paper, the retrofitting of hospital buildings is investigated, using alternative methods of repair and strengthening. Analysis of an existing hospital building in Patras, Greece, is performed. The load-bearing system is a reinforced concrete system. Two solutions are proposed: strengthening using concrete jackets around column and beam elements and application of viscoelastic dampers for the increase of the stability of the structure. Adequate finite element models are constructed for each case and conclusions are drawn on the efficiency of each rehabilitation method.