EXAMPLE 6. BUILDING VALUATION & REDESIGN STUDY

EXAMPLE 6: "STUDY FOR THE VALUATION AND REDESIGN OF A BUILDING ACCORDING TO THE CANC. 3 FOREWORD The analysis methodologies used to evaluate or redesign existing reinforced concrete structures for seismic loads are elastic analyses, static or dynamic, and inelastic analyses (i.e. non-linear due to material), also static or dynamic. The elastic methods adopt the classical linear stress-strain relationship for the structural elements of the structure, where in approximate ways (e.g. using global or local indices of behaviour or ductility) they indirectly take into account the inelastic behaviour of the structure. These methodologies are simpler to apply, but may lead to less accurate results than their inelastic counterparts. On the contrary, inelastic analysis methodologies help to better monitor and understand the actual response of the structures, demonstrating both the failure mechanisms and the potential for progressive collapse (it is therefore possible to control the deformations of the ends of the members, the overstrength reserves, as well as the way in which the plastic behaviour of the structure is triggered. In this way, inelastic analyses lead to a more rational and safer design. Inelastic dynamic analysis (i.e., time history analysis with direct numerical integration of nonlinear differential equations of motion) is the most complete and realistic methodology for the analysis of structures. In the inelastic dynamic analysis the seismic action is introduced in the form of a history of base accelerations, either from actual recordings or from synthetic accelerograms. However, this analysis encounters problems in simulating the meteoric recurrent behaviour of the members of the structure, which is currently under scientific investigation and experimental verification. In addition, there is also the issue of appropriate selection of seismic accelerations, where the above analysis method is particularly sensitive. Therefore, the design engineer conducting the assessment or redesign study of an existing structure using inelastic dynamic analysis should have considerable critical ability and experience. Thus, combined with its increased computational complexity, and the fact that the required analysis time even with modern computers is particularly high, especially in spatial analyses of high-rise buildings (note that because the analysis is non-linear, the principle of superposition does not apply), inelastic dynamic analysis is not considered practical for general use. In contrast, the static inelastic analysis gives results that lie between the elastic methods and the inelastic dynamic method. It should be noted that, in the case where the externally applied load is horizontal seismic loads, the inelastic static analysis is also known as pushover analysis. Thus, although Pushover analysis does not have the accuracy of inelastic dynamics, since the seismic loads (which are dynamic) are taken into account approximately as static, it nevertheless leads to a significantly more accurate estimation of the response of the structure than elastic methods, and its application is much simpler than the corresponding inelastic dynamics. It should be noted that inelastic static analysis is not a new methodology. However, in recent decades, extensive research has led to the development of simulations that allow the behaviour of reinforced concrete structural members after their theoretical failure to be estimated with reasonable accuracy, with the aid of appropriate