Month: March 2019

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Values of shear strength factor for joints with discontinuous column effectively confined on four and three vertical faces proposed by ACI 352R-02 Code are based on the judgment of relevant committee. Moreover, CSA A23.3-14 used the same shear strength coefficients for joints with continuous and discontinuous column. Therefore, beam-column joints tested by the authors and their colleagues were modeled numerically. Parametric study was performed to define the proper values. Results showed joint shear strength factor could be relaxed for roof wide beam-column joints effectively confined on four or three vertical faces. For CSA A23.3, it was suggested to use different coefficients for joints with continuous and discontinuous column. Values of 1.3 and 1.1 were proposed for joints with discontinuous column effectively confined on four and three vertical faces with conventional beams, respectively. Moreover, for ACI 352, values of 12 and 10 were suggested for these joints.

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The shear loading applied to structures is resisted by implementation of hysteric dampers as structural seismic force resisting system. Recently, steel plates with engineered cut-outs are introduced to have controlled yielding. These structural elements behave as shear links are able to post pone brittle limit states, leading to resistance against early fracture. Among which, a promising type of link is butterfly-shaped link, for which the demand moment diagram aligns with capacity moment diagram to efficiently implement the steel. Previous studies show that these elements are used as appropriate choice for structural seismic fuse system since they are able to experience large drifts with sufficient ductility and full hysteric behavior. Therefore, the appropriate geometrical properties for these links are in need of further investigations. In this study, the finite element methodology is initially validated with experimental test. Then optimization criteria is introduced for set of 300 models to investigate the desired geometrical properties for having most energy dissipation with less fracture potential.  This paper represents optimization process with which the geometrical properties of butterfly shaped link is improved to have sufficient energy dissipation performance and less potential for fracture. The pushover curves and equivalent plastic strains are obtained from ABAQUS through an iterative process. The Grey Wolf Optimizer method is adopted for optimization methodology due to having strong capability in non-linear system. It can be found that by implementation of optimization methodology the links are designed to have a mode switch from flexural yielding limit state to shear yielding and are able to dissipate energy over a less equivalent plastic strain value.

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Great part of the existing buildings in seismic areas and in particular in developing countries is represented by masonry buildings, diffused also in the major part of historical centres in Europe. Damages due to seismic events have evidenced the large demand of rehabilitation together with suitable assessment methods for these structures. When out of plane mechanism can be avoided, the contribution of in-plane shear resistance of the masonry walls is a key aspect to consider in the vulnerability analysis of the whole structure. Based on this last consideration, this paper presents an approach to the analysis of in-plane behaviour of masonry walls, involving a minimum energy strategy. The results of the numerical analyses presented are compared with those obtained by laboratory tests on brick masonry panels.

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Several buildings located in earthquake-prone areas were conceived according to past design guidelines and do not comply with current seismic regulations. This requires effective seismic retrofitting interventions. After the collapse of the university hall of residence of L’Aquila, Italy, in 2009, several regional authorities in other Italian cities planned surveys for seismic assessments of similar student accommodation buildings, disclosing dramatic structural deficiencies in many cases. One of these buildings concerns the student hall of residence of Messina, Italy, a confined masonry-RC building analysed in this paper. This work summarizes the theoretical conception and underlying design philosophy of the seismic retrofitting of this building (through buckling restrained braces and pre-tensioned steel ribbons), describes the pushover analysis on the original and retrofitted structure, illustrates the acceptance tests on the hysteretic dampers performed at laboratory CERISI of Messina and discusses some construction issues that have arisen up to date during the installation phases.

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The aim of this work is to show an approach for both the retrofit of existing and the design of new industrial precast concrete buildings. This typology has been strongly hit in recent seismic events showing the inappropriate detailing of the typical claddings’ connections. The proposal made in this paper is to connect rigidly the panels to the internal framing creating a dual system where columns and claddings both contribute in terms of stiffness, resistance and energy dissipation. In order to provide an adequate ductility to the panels and to reduce the seismic demand, the inclusion of hysteretic dampers at the lower corners of the external walls is proposed. The methodology is validated in the paper through preliminary pushover analyses of an archetype building. The results show that considering the participation of the panels, the structure becomes stiffer, with a consequent benefit in terms of reduction of the lateral drifts, and its seismic response is improved, thanks to the high energy dissipation provided by the dampers placed at the base of the walls.

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