Steel chevron concentrically braced frames are expected to dissipate seismic energy by yielding of the brace under tension, while both beam and columns behave elastically. Besides the strength, also the stiffness of the brace-intercepted beam plays a key role to avoid unfavourable mechanisms. However, no codified requirements are provided to assure adequate beam rigidity. In order to examine this aspect, in the first part of this paper the main results of a numerical parametric study devoted to investigate the mutual interaction between the beam vertical deflection and the brace ductility demand are described. The second part of this article investigates the efficiency of both EC8 and AISC341-10 seismic provisions on the global performance of chevron bracings, particularly focusing on the design of the beam of the braced bays. The results of incremental dynamic analyses performed on several structures confirm the primary importance of the flexural stiffness of the beam.
stiffness
The influence of infill panels on the seismic behaviour of reinforced concrete buildings
As it is well known in literature, infills modify the behaviour of framed structures under lateral loads. Nevertheless, infills are generally neglected in structural analysis, and this, in many cases, may lead to unreliable evaluations of structural response. Although several theoretical and experimental researches express the necessity to take into account the infills, today reliable models of infilled structures do not exist, due to the difficult interpretation of experimental results. The aim of the proposed approach is to evaluate the effect of infills in the global and local response of a building under earthquake loads, identifying the most significant parameters that influence its behaviour. In this paper a convenient tool for the evaluation of the effects of the infills is suggested, in order to reach acceptable results in global and local analyses. The attention is focused on the most used typology in Italy: reinforced concrete structures infilled with masonry panels, realized in contact with the frame after its hardening and without connectors nor joints.