Investigating the in-plane flexibility of steel-deck composite floors in steel structures

It is common practice in structural engineering to assume floor diaphragms infinitely stiff in their own plane. But, most of the code provisions lack clarity and unity in categorising floor diaphragms and discussing their behaviour based on the seismic response of the structures. Besides, although many of these code provisions have presented simple techniques and formulations for determining the level of flexibility in floor diaphragms, the implementation of these techniques on more complex floor systems such as the steel-deck composite floors is still under question. The paper aims to discuss these issues.

In this study, an equivalent concrete floor is employed as a representative of in-plane diaphragm action of steel-deck composite floor, using simple modelling techniques in SAP2000 and the results are validated by complex structural models developed in ABAQUS. Afterwards, the equivalent floor is inserted to 3, 5 and 7 storey steel structures with 2, 3 and 5 plan aspect ratios in two categories of structures with rigid diaphragms and analogous structures with flexible diaphragms and the responses are compared to each other.

The results show that the proposed technique is an effective method for evaluating the diaphragm action of steel-deck composite floors. Additionally, it is concluded that, the boundary values of plan aspect ratio equal to 3 and λ coefficient equal to 0.5 in steel-deck composite floors, mentioned in code provisions for categorising diaphragms, are not always conservative and need to be scrutinised.

The proposed methodology provides simple framework for assessing the effects of in-plane flexibility of steel-deck composite on seismic response of steel structures.