Ciro Faella

Cost-competitive Steel Devices for Seismic Retrofitting of RC Frames: Model Identification and Nonlinear Analysis

Seismic retrofitting of existing reinforced concrete (RC) buildings, designed in the last decades in seismic areas, is one of the most complex tasks for structural engineers: in fact, it includes several issues, such as quantifying the capacity of existing members, designing the supplemental ones and analysing the whole structure. This paper is intended as a contribution to clarifying some of those issues. First of all, a model based on using 1D finite elements with fiber section discretization is proposed for simulating the behaviour of a cost-competitive steel device that can be employed as a link in Y-shaped eccentric bracings (EB): particularly, the cyclic response and the low-cycle fatigue degradation is modelled, based on the results of obtained in a previous experimental research carried out at the University of Salerno. Secondly, the global response of an existing RC frame equipped with the aforementioned devices is investigated via Non Linear Time History (NLTH) analyses. Taking into account the lowcycle fatigue often leads to significantly more severe seismic displacement demand value on the retrofitted structure: a close correlation is unveiled between some specific features of the seismic signals adopted in the NLTH and the actual influence of low-cycle fatigue.

RATIONAL SEISMIC RETROFITTING OF RC STRUCTURES BASED ON GENETIC ALGORITHMS

This paper presents a rational strategy developed for optimizing seismic retrofitting of Reinforced Concrete (RC) frames. It is based on combing memberand structure-level techniques in order to achieve optimal design objectives within a multi-level PerformanceBased approach. On the one hand, in principle, confinement with composite materials, steel and/or concrete jacketing might be considered as a member-level technique capable to enhance the capacity of under-designed members and, consequently, of the structure as a whole. On the other hand, introducing steel bracing systems or shear walls might be taken into account as structure-level techniques. Generally, memberand structure-level techniques are not employed together in seismic retrofitting or, in the cases in which they are combined, no well-established rules are available for choosing their optimal combination. However, a synergistic use of such techniques by means of well-defined procedures could help designers obtain optimal seismic retrofitting performance. The latest progresses about a procedure developed by the authors for selecting the optimal retrofitting solution among the technically feasible ones, obtained by combining alternative configurations of steel bracing systems and FRP-confinement of critical members, are presented herein. Specifically, the main aspects about formulating a genetic algorithm capable to select the “fittest” retrofitting solution is implemented and summarised. The main assumptions about the representations of “individuals” as part of this genetic algorithm and the main information about the generic operations (i.e. selection, crossover and mutation) are outlined. Finally, the procedure is applied to a 3D frame with the aim to demonstrate its potential. 4194 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4194-4212

NONLINEAR STATIC ANALYSIS OF INFILLED RC FRAMES: A NOVEL SIMPLIFIED PROCEDURE

Abstract. Masonry walls are generally utilized in Reinforced Concrete (RC) structures, either as external infills or as internal partitions. Although the interaction between them and structural members significantly affects the seismic response of structures, infills are usually not included in the structural models and, hence, their mechanical contribution is neglected in seismic analysis and assessment of existing structures. However, additional strength provided by infills may either play a beneficial role or affect the resulting structural capacity. Although several proposals are currently available for simulating the nonlinear response of masonry infills in structural analysis, no well-established methods emerged so far for evaluating the global response of infilled RC frames. This paper proposes a simplified procedure based on Nonlinear Static (NLS) analysis and an extension of the well-known N2 Method. A statistical assessment and validation is also presented with the aim to confirm accuracy and reliability of the proposed analysis procedure.