Seismic Vulnerability Analysis for Optimum Design of Multistory Reinforced Concrete Buildings (original) (raw)
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This paper presents the general criteria and implementation of an automatic procedure to evaluate the seismic capacity of existing reinforced concrete (RC) regular buildings. The method represents a useful tool in the framework of mechanical based vulnerability assessment methods. In particular, the seismic capacity is retrieved via pushover analyses on a lumped plasticity model for the building. Unlike recent approaches that rely on a single representative structural model for an entire building population, the proposed method allows virtually all the buildings of the population to be analysed in an automatic loop. With the aim of expediting and automatizing the analysis process, a dedicated software was implemented, whose main functions are: identifying possible structural systems compatible with regular building shapes of assigned dimensions and designing its elements in terms of cross-section and reinforcement; constructing the related nonlinear model and performing pushover analyses in order to determine synthetic capacity parameters useful for preliminary vulnerability assessment at a large scale. The software application and potentialities are shown in an example for the generic building of a class.
Probabilistic seismic risk evaluation of reinforced concrete buildings
The main objective of this article is to propose a simplified methodology to assess the expected seismic damage in reinforced concrete buildings from a probabilistic point of view by using Monte Carlo simulation. In order to do so, the seismic behaviour of the building was studied by using random capacity obtained by considering the mechanical properties of the materials as random variables. From the capacity curves, the damage states and fragility curves can be obtained, and curves describing the expected seismic damage to the structure as a function of a seismic hazard characteristic can be developed. The latter can be calculated using the capacity spectrum and the demand spectrum according to the methodology proposed by the Risk-UE project. In order to define the seismic demand as a random variable, a set of real accelerograms were obtained from European and Spanish databases in such a way that the mean of their elastic response spectra was similar to an elastic response spectrum selected from Eurocode 8. In order to combine the uncertainties associated with the seismic action and the mechanical properties of materials, two procedures are considered to obtain functions relating the peak ground acceleration to the maximum spectral displacements. The first method is based on a series of non-linear dynamic analyses, while the second is based on the well-known ATC-40 procedure called equal displacement approximation. After applying both procedures, the probability density functions of the maximum displacement at the roof of the building are gathered and compared. The expected structural damage is finally obtained by replacing the spectral displacement calculated using ATC-40 and the incremental dynamic procedure. In the damage functions, the results obtained from incremental static and dynamic analyses are compared and discussed from a probabilistic point of view.
Considering the effects of earthquakes occurred during the last 15 years, this article focusses on finding solutions to minimize the human and economic losses. Several methodologies were developed in order to assess the vulnerability of the built environment with special reference to one of the most suitable structural systems in seismic areas for dwellings, offices or other functionalities, which is the reinforced concrete framed structure. Thus, the present article studies the influence on the vulnerability of reinforced concrete framed structures of geometric structural characteristics like the slab thickness, the building height and the plan configuration. Referring to the slab, it adds supplementary stiffness to the structure that can significantly influence upon its overall failure mechanism. 3D static nonlinear analyses are conducted by means of the SAP2000 computer program. The results are capacity curves which are used to develop the vulnerability curves. Three thicknesses are considered for the slab: 0.1 cm, 0.12 cm and 0.15 m. Medium and high rise structures are considered, with 4, and 8 levels, respectively, in order to determine the influence of the building height on the vulnerability index. Three plan configurations of the buildings are compared: a square one, a rectangular one and an L shaped one. For all the analyzed cases, the corresponding vulnerability curves are compared. The obtained results reveal that more realistic results for the behavior of the structure can be obtained if special attention is given to the structural characteristics, especially during the conceptual design process.
Seismic performance reliability analysis for reinforced concrete buildings
Journal of Civil Engineering and Construction Technology, 2011
Reliability analysis assessment of seismic performance for reinforced concrete buildings was investigated in this work. This was performed through the response surface methodology in order to derive explicit expression of the failure function. Two limit states defined in terms of the total building roof displacement and the maximum inter-story drift were considered. The seismic behaviour of the building was examined by using conventional pushover analysis through finite element computations conducted by means of ZeusNL software package. Three random variables characterizing material resistance variations of concrete and reinforcement steel as well as member's sections dimensions were introduced. A complete factorial design of experiment table having three levels was used to define a finite set of data points where the failure function was evaluated, before using these results to perform identification of the building response surface model via polynomial regression. An application of this procedure was illustrated on a five story building and analysis of reliability in terms of the actual ductility coefficient was performed. Discussion was carried out about the effect on reliability resulting from the distributions of probability modelling the uncertainties affecting parameters and from using the approximate methods: Monte Carlo based sampling analysis and FORM.
Seismic Reliability Assessment of Existing Reinforced Concrete Buildings
Journal of Earthquake Engineering, 1998
The RINTC research project (RINTC Workgroup, 2018), financed by the Italian Department of Civil Protection, is aimed at evaluating the seismic risk of buildings conforming to the Italian building code. Within the framework of this project, the attention has been recently focused on existing buildings, too. In this study, case-study structures, representative of the existing residential reinforced concrete (RC) building stock in Italy, are analyzed. These structures are three-storey buildings with compact rectangular plan, and they have been defined through a simulated design process, in order to represent two types of buildings, namely designed for gravity loads only during 1970s (gravity load designed, GLD) or for moderate seismic loads during 1990s (seismic load designed, SLD). GLD buildings are assumed to be located in three different sites, namely Milan, Naples and Catania, in increasing order of seismic hazard. SLD buildings are assumed to be located in L'Aquila. The assumed design typologies are consistent with the seismic classification of the sites at the assumed ages of construction. The presence of typical nonstructural masonry infill walls (uniformly distributed in plan as external enclosure walls) is taken into account, assuming three configurations along height, namely "bare" (without infills), uniformly infilled and "pilotis" (without infills at the bottom storey) buildings. Two 554 COMPDYN 2019 7 th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis (eds.
Reinforced concrete buildings represent major type of manmade structures all over the world. It is observed from the past major earthquakes in India, Turkey, China and other countries, numerous medium to high rise buildings suffered major damages including life and safety of people. This clearly implies that the design capacity of buildings designed as per codes was not enough to withstand earthquake demand. In the regions of high seismic activity, safety of these buildings occupying major population is of growing concern, as most of them are seismically deficient, as many low to medium rise buildings are designed only for gravity loading, or they are designed for earthquake forces by performing elastic analysis. When elastic analysis is performed, building structure is assumed as a linear system. This analysis is sufficed to withstand mild earthquakes but a major earthquake is expected to cause significant structural damage resulting in loss of structural stiffness. A linear elastic analysis is not applicable in this situation since these analyses do not account for change in structural properties nor they give any idea about the location and extent of damage or inelasticity. The true response is therefore determined only by non-linear analysis considering the changing stiffness of the various members and moment distribution, when structures are subjected to moderate or major earthquakes. Thus to mitigate the effects of future earthquake damages, the seismic design should be carried out incorporating non-linear analyses to calculate structural response in order to assess and design seismic retrofit solutions for existing buildings and design new buildings based on above approach. This paper emphasizes on the importance of carrying out performance based design of buildings and discusses nonlinear static procedures for performance evaluation of buildings and reviews recent investigations carried out by several researchers on performance evaluation using above methods and makes an attempt to identify suitability of each for ensuring safety of buildings. Based on the critical review of literature it is observed that current seismic design practice stops at demand estimation, analysis and design and consequently cannot guarantee that the designed structure meets the objectives set at the start. Therefore it is of paramount importance that the structural design community incorporates performance based seismic design concepts which attempts to quantitatively define performance objectives, define methods to calculate actual capacity of a designed structure and iteratively improve the design until the structure meets all design objectives, while designing all structures located in high seismic zone, high rise structures and structures with high importance factors for mitigating future disasters due to earthquakes.
Capacity, fragility and damage in reinforced concrete buildings: a probabilistic approach
The main goals of this article are the analysis of the use of simplified deterministic nonlinear static procedures to assess the seismic response of buildings, and to evaluate the influence that the uncertainties regarding the mechanical properties of the materials and of the features of the seismic actions have in the uncertainties of the structural response. A current reinforced concrete building is used as a guiding case study. In the calculation of the expected spectral displacement, deterministic static methods are simple and straightforward. In the case of non severe earthquakes, these approaches lead to somewhat conservative but adequate results when compared to more sophisticated procedures involving non-linear dynamic analyses. Concerning the probabilistic assessment, the strength properties of the materials, concrete and steel, and the seismic action are considered as random variables. The Monte Carlo method is then used to analyze the structural response of the building. The obtained results show that significant uncertainties are expected, as uncertainties in the structural response increase with the severity of the seismic actions. The major influence in the randomness of the structural response comes from the randomness of the seismic action. A useful example for selected earthquake scenarios is used to show the applicability of the probabilistic approach to assess the expected damage and risk analysis. An important conclusion of this work is the need to address the fragility of the buildings and expected damage assessment problem from a proba-bilistic perspective.
Controlling Parameters in the Assessment of the Seismic Vulnerability of Buildings
2016
The probabilistic seismic risk assessment in terms of economic losses for building portfolios requires the seismic hazard assessment, the definition and characterization of the building portfolio and the estimation of the expected economic losses of specific building typologies for increasing seismic intensities. The probability distribution function of economic losses for different seismic intensities can be estimated by integration of individual building component ́s repair costs. By means of Monte Carlo simulations, all relevant variables that influences the final repair cost can be introduced into the analysis. The results of the analysis are integrated and represented through specific vulnerability functions for each building typology, which relates the expected economic losses and its corresponding uncertainty measure with the seismic intensity level. The integration of losses considers the uncertainties associated with the hazard assessment, the dynamic response of the model,...
2015
This research deals with the assessment of the seismic behavior and capacity of a reinforced concrete building in order to examine the possibility of strengthening. This process is achieved by using the Nonlinear Static Analysis (Pushover Analysis) and is based also on performance criteria. In case of damages two different methods of strengthening are implemented: the reinforced concrete jacketing and the carbon fiber reinforced polymer wrapping (CFRP). Afterwards, the determination of the optimum strengthening design is performed, thanks to metaheuristic optimization algorithms, aiming at the minimization of the cost. Subsequently, the retrofitting measures are evaluated through a methodology defined by vulnerability criteria and fragility curves, produced either by the Incremental Dynamic Analysis (IDA) or by using Eurocode8 Regulations, the Method of Coefficients as well as the Hazus Methodology. The fragility curves refer to different earthquake performance levels and as a resul...
Buildings
The present paper deals with the influence of material variability on the seismic vulnerability assessment of reinforced concrete buildings. Existing r.c. buildings are affected by a strong dispersion of material strengths of both the base materials. This influences the seismic response in linear and nonlinear static analysis. For this reason, it is useful to define a geometrical parameter called "material eccentricity". As a reference model, an analysis of a two storey building is presented with a symmetrical plan but asymmetrical material distribution. Furthermore, an analysis of two real buildings with a similar issue is performed. Experimental data generate random material distributions to carry out a probabilistic analysis. By rotating the vector that defines the position of the center of strength it is possible to describe a strength domain that is characterized by equipotential lines in terms of the Risk Index. Material eccentricity is related to the Ultimate Shear of non-linear static analyses. This relevant uncertainty, referred to as the variation of the center of strength, is not considered in the current European and Italian Standards. The "material eccentricity" therefore reveals itself to be a relevant parameter to considering how material variability affects such a variation.