SEISMIC SAFETY OF LOW DUCTILITY STRUCTURES USED IN SPAIN

The most important aspects of the design, seismic damage evaluation and safety assessment of structures with low ductility like waffle slabs buildings or flat beams framed buildings are examined in this work. These reinforced concrete structural typologies are the most used in Spain for new buildings but many seismic codes do not recommend them in seismic areas. Their expected seismic performance and safety are evaluated herein by means of incremental non linear structural analysis (pushover analysis) and incremental dynamic analysis which provides capacity curves allowing evaluating their seismic behaviour. The seismic hazard is described by means of the reduced 5% damped elastic response spectrum of the Spanish seismic design code. The most important results of the study are the fragility curves calculated for the mentioned building types, which allow obtaining the probability of different damage states of the structures as well as damage probability matrices. The results, which show high vulnerability of the studied low ductility building classes, are compared with those corresponding to ductile framed structures

Seismic performance of waffled-slab floor buildings

 The codes used in seismic design of waffled-slab floors buildings (WSFB), such as the Spanish NCSE-02 earthquake-resistant design code, assign them restricted ductility, utilise linear structural analysis based on modal analysis, but also consider the structural ductility concept. Uncertainties arise whenever these codes are applied to the special case of buildings with waffled-slab floors, the ductility of which is doubtful. In many cases, during earthquakes, buildings with restricted ductility are unable to reach the ductility values assumed in the design process, although they may exhibit adequate values of overstrength. This paper therefore studies typical WSFB by applying static incremental non-linear analysis procedures (pushover analysis) in order to calculate their actual structural ductility and overstrength values. Fragility curves corresponding to different damage states and damage probability matrices are also calculated and compared with those of moment-resisting frame buildings (MRFB) in order to obtain useful conclusions for earthquake resistant design. One of the most relevant conclusions of this article is that the use of a better confinement and of ductile steel can only improve the seismic behaviour of MRFB but not that of WSFB

NON LINEAR STRUCTURAL ANALYSIS. APPLICATION FOR EVALUATING SEISMIC SAFETY

Performance-Based Design is accepted commonly as the most advanced design and evaluation approach. However, its successful application depends on the ability to accurately estimate the parameters of structural response. The determination of these parameters requires applying analysis procedures where the non-linear behavior features of structures are included. This chapter presents and discusses these features of non-linear behavior and how they are incorporated in the process of static or dynamic structural analyses. Non-linear analysis allows obtaining from the seismic response significant structural response parameters such as ductility, overstrength, response reduction factor and damage thresholds. In order to illustrate the application of the non-linear analysis procedures, a set of concrete-reinforced moment-resisting framed buildings with various numbers of levels, was designed according to ACI-318 for high and very high level of seismic hazard. Their seismic safety is studied using both the static and dynamic non-linear analyses

Characterizations of upper and lower (α, β, θ, δ, I)-continuous multifunctions

Given a multifunction F : (X; _ ) ! (Y; _), _; _ oper-ators on (X; _ ), _; _ operators on (Y; _) and I a proper ideal on X. The purpose of the present paper is to introduce, study and characterize upper and lower (_; _; _; _; I)-continuous multifunctions, its relation with another class of continuous multifunctions. Also, we introduce a general decomposition form for this class of continuous multifunction

Computational simulation of the seismic response of buildings with energy dissipating devices

In this work, the nonlinear dynamic response of RC buildings with energy dissipating devices is studied using advanced computational techniques. A fully geometric and constitutive nonlinear model is used for describing the dynamic behavior of structures. The equations of motion are expressed in terms of cross sectional forces and strains and its weak form is solved using the displacement based finite element method. A suitable version of Newmark’s scheme is used in updating the kinematics variables in a classical Newton type iterative scheme. Material points of the cross section are assumed to be composed of several simple materials with their own constitutive laws. The mixing theory is used to treat the resulting composite. A specific finite element based on the beam theory is proposed for the dissipators including constitutive relations. Finally, several numerical tests are carried out to validate the proposed model

Seismic Evaluation of Low Rise RC Framed Building Designed According to Venezuelan Codes

This chapter uses a mechanical method that involves non-linear analysis with deterministic and probabilistic approaches, as well as procedures of analysis based on limits states defined by displacements, in order to evaluate the behavior of a low rise RC building with plan irregularity designed according to Venezuelan codes and subjected to seismic actions. By using adequate structural models and computational tools, the seismic behavior of the building is obtained in a suitable way. Among these tools, the quadrants method was chosen, which provides the rapid assessment of the seismic capacity of a structure through its non-linear response. The results of the research show that the current design of this kind of structures is not safe when they are designed for the maximum seismic actions prescribed by codes. Therefore, it is necessary to review the design procedures in order to fulfill the goals of the performance-based design

Seismic and structural response of a framed four level building with RC and steel structure designed according to current Venezuelan codes

This study determines the structural behavior of a four level framed building with composite RC and steel structure designed according Venezuelan seismic codes. The structural system consists of RC frames in the first three levels and steel frames in the fourth. It was performed linear analysis to design all structural elements. Capacity curves and performance points were obtained with pushover analysis. Results showed greater ductility in the X frames’ direction and greater resistance reserve in the external frames. Performing points showed adequate resistance values but low stiffness in two Y frames’ directions. Seismic action is carried on through synthetic accelerograms defined by the seismic codes used in this study. Dynamic analysis is used to compute parameters of ductility, over strength and displacements. In one case the collapse Limit State was reached, implying a general collapse of the building. Incremental dynamic analysis was performed to obtain fragility curves and damage probability matrix; a very high probability of significant lateral displacement and damage was evidenced from this despite a normative design of structural elements