Abstract

The flexibility of floor diaphragms has a significant influence on the behavior of building structures. Commonly, in analyzing structures, floor diaphragms are considered rigid. This assumption distributes lateral loads between the resistant elements according to their rigidities, and decreases the degree of freedom that creates easier analysis. However, in steel structures with braced frames and long span floors, diaphragms usually behave flexibly. The seismic responses of such structures vary to the expected response of typical rigid floor structures. Ignoring the effects of diaphragm flexibility can lead to non-economic or unsafe structural design. In this paper, the nonlinear responses of braced steel buildings with flexible concrete block-joist floor diaphragms are investigated under both static lateral load and dynamic ground motion, and they are compared with the responses of structures with the assumption of rigid diaphragms. This study demonstrates that span ratio is an important parameter in the flexibility of floor diaphragms, and if this ratio exceeds three, the variation of results between the two assumptions of flexible and rigid diaphragms may not be ignored. In addition, results show that diaphragm flexibility changes the seismic response of the structures and linear analysis is not sufficient to explain this behavior.

Abstract

Slender lightweight structures have been earning more space in current Brazilian construction civil scenario, in especially steel structures. When in fire situations, these structures suffer a substantial decrease in their resistance and consequently an increase in the inelastic and geometric nonlinearity effects, and can anticipate structural failure. This paper presents the linear, nonlinear geometric and inelastic analyzes of steel reticulated structures under high temperatures based on the Finite Element Method (FEM). A beam-column element is used to model the structures, and the thermal effect is considered as a source of non-linearity by the displacements arising due to the stresses arising from the elevation of the temperature. The properties of the steel are changed according to the European standard EN 1994-1-2. The behavior of the material was adopted as perfectly plastic elastic, and the follow-up of the flow is done by the refined plastic hinge method. The solution of the nonlinear static problem is done through a modified Newton-Raphson incremental-iterative strategy. During the study, structures were evaluated considering the elevation of temperature.