An overview of the development of the hybrid method for seismic vulnerability assessment of buildings

The paper presents in a chronological and systematic way the development of the hybrid method for seismic vulnerability assessment of structures, which combines the use of empirical databases of earthquake damage with the results of nonlinear analysis of representative structural models. The key concepts and milestones in the development of the method are identified, and selected examples of its application are summarised. The first part of the paper focuses on the derivation of hybrid damage probability matrices and the second one with the derivation of fragility curves for reinforced concrete and masonry buildings. Finally, some general conclusions are drawn and directions of future research on the hybrid approach are suggested

Deformation-based seismic design of concrete bridges

A performance-based design (PBD) procedure, initially proposed for the seismic design of buildings, is tailored herein to the structural configurations commonly adopted in bridges. It aims at the efficient design of bridges for multiple performance levels (PLs), achieving control over a broad range of design parameters (i.e. strains, deformations, ductility factors) most of which are directly estimated at the design stage using advanced analysis tools (a special type of inelastic dynamic analysis). To evaluate the efficiency of the proposed design methodology, it is applied to an actual bridge that was previously designed using a different PBD method, namely displacement-based design accounting for higher mode effects, thus enabling comparison of the alternative PBD approaches. Assessment of the proposed method using nonlinear dynamic analysis for a set of spectrum-compatible motions, indicate that it results in satisfactory performance of the bridge. Comparison with the displacement-based method reveals significant cost reduction, albeit at the expense of increased computational effort

Semi-Active Control Systems in Bridge Engineering: A Review of the Current State of Practice

In view of the grave socioeconomic consequences of earthquake damage to bridge structures, along with their critical role in modern and older road and rail networks, this article attempts to identify and summarise the current trends in the use of semi-active control technology in bridge engineering, as an enhanced seismic response control solution, combining increased adaptability and reliability, compared to passive and active schemes. In this context, representative analytical and experimental studies, as well as some full-scale applications of semi-active control devices are first reviewed and a brief description of relevant benchmark studies is subsequently presented, with a view to serving as a point of reference for further research and development. A framework of performance-based control principles aiming at the aforementioned objectives is finally set forth

Derivation of fragility curves for traditional timber-framed masonry buildings using nonlinear static analysis

Recent earthquakes and two experimental campaigns on timber-framed masonry walls have shown that timber-framed masonry buildings possess a good displacement capacity and hence can withstand severe earthquakes without collapse. In the present paper, timber-framed masonry panels with diagonal braces are studied. Using a simplified model based on non-linear (NL) lumped plasticity strut elements, NL analyses are carried out of typical traditional buildings in Lefkas (Greece) with diagonally braced timber-framed masonry walls in their lateral load resisting system. Furthermore, an investigation is carried out regarding the foundation of the buildings. The key feature of the Lefkas buildings is their dual structural system. The primary system consists of a stone masonry ground floor and all upper floors are made of timber-framed masonry walls. Timber posts in the ground floor, a few centimetres apart from the stone masonry, constitute the secondary structural system which is connected to the upper floors. This latter system is activated once the ground floor stone masonry piers fail. Two different structural models are developed to simulate each system. Pushover curves are derived from the NL analyses of the buildings and are then converted into capacity curves assuming the fundamental mode dominates. On these curves four damage states (slight damage, moderate damage, heavy damage and collapse) are defined on the basis of criteria related to the actual response of the building. The first three damage states are defined on the capacity curve of the primary system, whilst the ultimate damage state is related to the response of the secondary system. Then, fragility curves in terms of spectral displacement are generated, adopting a log-normal statistical distribution of the probability of damage

A combined damage index for seismic assessment of non-ductile reinforced concrete structures

Existing seismic damage indices have been formulated and verified almost exclusively on the basis of flexural damage mechanisms. In this paper, a local damage index proposed previously by the authors for assessing existing reinforced concrete (RC) structures is described. According to its formulation, deterioration caused by all deformation mechanisms (flexure, shear, anchorage slip) is treated separately for each mechanism. Moreover, the additive character of damage arising from the three response mechanisms, as well as the increase in degradation rate caused by their interaction, are fully taken into consideration. The proposed local damage index is first calibrated against experimental recordings and then is applied to predict seismic damage response of one RC column and one frame test specimen with substandard detailing. It is concluded that in all cases and independently from the prevailing mode of failure, the new local damage index predicts well the damage pattern of the analysed specimens

Numerical study of confinement effectiveness in solid and hollow reinforced concrete bridge piers: Methodology

A consistent methodology is suggested for modelling confinement in both solid and hollow reinforced concrete bridge pier sections, within the computational framework of three-dimensional nonlinear finite element analysis. The ultimate goal is to suggest the most convenient transverse reinforcement arrangements in terms of enhanced strength and ductility, as well as ease of construction and cost-effectiveness. The present study is particularly relevant with respect to confinement of hollow sections, for which previous experimental and analytical research is limited. Constitutive laws, modelling techniques, post-processing issues and preliminary applications are first introduced, and a large parametric model setup for circular and rectangular bridge piers of solid and hollow section, is subsequently presented. A detailed discussion follows on various issues concerning confinement modelling, aiming to broaden the scope and applicability of the suggested methodology. The respective numerical results and their interpretation and evaluation will be presented in a companion paper

Seismic damage analysis including inelastic shear-flexure interaction

The paper focusses on seismic damage analysis of reinforced concrete (R/C) members, accounting for shear-flexure interaction in the inelastic range. A finite element of the beam-column type for the seismic analysis of R/C structures is first briefly described. The analytical model consists of two distributed flexibility sub-elements which interact throughout the analysis to simulate inelastic flexural and shear response. The finite element accounts for shear strength degradation with inelastic curvature demand, as well as coupling between inelastic flexural and shear deformations after flexural yielding. Based on this model, a seismic damage index is proposed taking into account both inelastic flexural and shear deformations, as well as their interaction. The finite element and the seismic damage index are used to analyse the response of R/C columns tested under cyclic loading and failing either in shear or in flexure. It is shown that the analytical model and damage index can predict and describe well the hysteretic response of R/C columns with different types of failure

Fragility curves and loss estimation for traditional timber-framed masonry buildings in Lefkas, Greece

The 2003 earthquake in the Greek island of Lefkas, has revived the interest for the local anti-seismic technique based on the use of timber-framed masonry, whose adequate performance during the earthquake revealed the merits of this rather sophisticated, albeit traditional, construction. A key feature of the Lefkas structures is their dual structural system. The secondary system is activated once the ground storey stone masonry piers of the primary system (which includes timber-framed masonry in all storeys) fail. In this regard, two different structural models are presented herein to simulate the response of each system. A macro-model based on nonlinear (NL) strut elements and point plastic hinges is intended to model the timber-framed masonry. NL analyses are carried out for one, two and three storey buildings, which represent the most common cases in Lefkas. Furthermore, an investigation is carried out regarding the foundation of the buildings resting on soft alluvial deposits. Pushover curves are derived from the NL analyses of the buildings and are then converted to capacity curves using the characteristics of the predominant mode. On these curves four damage states (slight damage, moderate damage, heavy damage, and collapse) are defined on the basis of criteria related to the actual response of the building. Then, fragility curves in terms of spectral displacement are generated, adopting a log-normal statistical distribution. These curves are converted into PGA values using a selected response spectrum. Utilising these fragility curves a seismic loss scenario for the 2003 Lefkas earthquake is developed for the timber-framed masonry stock of Lefkas city

Methodology for the development of bridge-specific fragility curves

A new methodology for the development of bridge-specific fragility curves is proposed with a view to improving the reliability of loss assessment in road networks and prioritising retrofit of the bridge stock. The key features of the proposed methodology are the explicit definition of critical limit state thresholds for individual bridge components, with consideration of the effect of varying geometry, material properties, reinforcement and loading patterns on the component capacity; the methodology also includes the quantification of uncertainty in capacity, demand and damage state definition. Advanced analysis methods and tools (nonlinear static analysis and incremental dynamic response history analysis) are used for bridge component capacity and demand estimation, while reduced sampling techniques are used for uncertainty treatment. Whereas uncertainty in both capacity and demand is estimated from nonlinear analysis of detailed inelastic models, in practical application to bridge stocks, the demand is estimated through a standard response spectrum analysis of a simplified elastic model of the bridge. The simplified methodology can be efficiently applied to a large number of bridges (with different characteristics) within a road network, by means of an ad hoc developed software involving the use of a generic (elastic) bridge model, which derives bridge-specific fragility curves