Abstract

One of the main concerns of specialists related to the built environment is related to the ability of structures to withstand exceptional actions. Among these actions are the effects of environmental and natural phenomena that impose extraordinary loads that unexpectedly can affect buildings, causing them a response that can lead to the damage of structural and nonstructural components or even to the collapse of the whole structure. Among these extraordinary actions that can affect structures within their lifetime, are those produced by wind and earthquake. Partial damage or collapse of buildings can injure or even kill people, also causing huge economic losses. In this context, many researches have been developed aiming to evaluate the seismic vulnerability of buildings, in order to improve their performance against the hypothetical action of future earthquakes. In this monograph, different recent contributions to this field are presented into nine chapters. In the first Chapter, entitled “Methodologies for the assessment of the seismic vulnerability of buildings”, a comprehensive state of the art review of the vulnerability assessment methods that have been developed and implemented worldwide is presented considering different structural typologies and seismic hazard levels. In the next chapter, “Vulnerability assessment using damage indices”, a new, objective, damage index, independent of the structural typology and of the damage level considered in the design, has been formulated, to establish a relationship between the evolution of damage and the global drift of the structure under the action of lateral loads. This objective damage index has been applied to study the behavior of structures with limited ductility, many of which are used in seismic-prone areas. The results of this study are presented in Chapter 3, entitled “Vulnerability of limited ductility buildings”. The results for buildings with flat beams and for buildings with waffled slabs are compared with the results obtained for moment-resisting framed buildings. Nonlinear analysis has become a tool of particular importance when estimating the seismic behaviour of structures. Its results allow formulating expressions relating the structural response parameters with indices describing damage. This topic is discussed in Chapter 4, “Damage thresholds for seismic limit states”, in which the authors propose damage thresholds formulated based of the results of incremental nonlinear static analysis (pushover analysis). Moment-resisting steel framed structures are widely used in areas of high seismic hazard, given the important structural advantages of structural steel. Nevertheless, they also have some disadvantages among which it can be mentioned the flexibility against lateral loads. To overcome this disadvantage, the framed structures are stiffened by means of eccentric and concentric braces. The concentric braces are perhaps the most popular; however, their use is limited by the lack of space within the structure. Additionally, the study of their effect on the different frames of the structure is necessary, because of the impossibility to locate these braces only within the inner frames. For this reason, this topic is developed in Chapter 5, “Vulnerability steel building with concentric braces”, in which results for both static and dynamic nonlinear analyses performed to buildings of different heights are presented. In Chapter 6, entitled “Vulnerability steel building with Chevron-type concentric braces”, the response of buildings stiffened with concentric braces which have received less attention than the structures shown in the previous Chapter, are studied. The results of both static and dynamic nonlinear analysis are shown obtaining these characteristic values of the seismic response, such as ductility and overstrength, which are essential in the assessment of the seismic vulnerability of these structures. The irregularity of buildings usually introduces significant changes in the seismic response. Seismic codes seek to establish limitations on plan and elevation irregularities, in order to control unwanted behaviors of structures. This topic is presented in Chapter 7, “Vulnerability of buildings with plan-irregularity”, which is based on recent studies on reinforced concrete buildings performed in Venezuela. In this chapter, in the vulnerability assessment process has been incorporated the effect of the amplification of the torsion moments in the columns located near the corners of the structures. The occurrence of recent strong earthquakes has given the opportunity to evaluate not only the damages of the structures in the affected areas, but also to calibrate design procedures contained in the earthquake-resistant design codes. In 2009, the North-Western coast of Venezuela was hit by a major earthquake (Mw 6,4), which caused damage especially in mid-rise buildings; thus, it was interesting to study the response of a reinforced concrete building located at 15 km from the epicenter. The building showed slight damage to nonstructural components and this state of damage was captured efficiently by nonlinear analysis. In Chapter 8, entitled “Numerical evaluation of the response of a building damaged by Tucacas earthquake”, are shown the most important results of this study. Finally, in Chapter 9 entitled “Procedure based on the dynamic incremental analysis to determine fragility curves”, a new method for obtaining fragility curves is disclosed, useful essentially in establishing the seismic vulnerability of buildings. It is based on the results of incremental dynamic analysis, IDA, that today is considered one of the most complete and efficient methods for analysis of nonlinear behaviour of the structures.