رفتار غیرخطی و پویای ساختارهای قاب فولادی سقف با قطعات خود محور تحت فشار گذرا و شدید باد

Collapse of roof could cause severe economic loss and poses safety risk to residents in the building. This paper presents a nonlinear dynamic analysis of steel framed roof structures with force limiting devices under combined static and transient wind loading. Two types of force limiting devices – one with self-centering behavior and the other exhibiting bilinear-like hysteresis are examined for roof collapse prevention. A nonlinear dynamic analysis that accounts for both material and geometrical nonlinearities was carried out for this simulation study. Two types of steel framed roof structures – a K-series steel joist and an arch truss are selected as the prototype roof frame in this study. It is found that installing force limiting devices at intentionally weakened zone of the prototype steel framed roof structures helps mitigating the displacement demand of the roof frame structure under transient up-lift wind pressure and thus reduce the dynamic collapse risk. Furthermore, the force limiting devices with self-centering behavior minimizes the residual deflection of the roof structures after the wind event.

Steel structural framings is a popular structural form to cover the large roof space of gymnasiums, industrial facilities and transportation terminals, with potential use as shelter structures for a disastrous event such as hurricanes. However, under high winds, either part of the roof enclosure or the entire roof structure can be lifted off a building, particularly for low sloped roofs subject to wind-induced suction force. Collapse of roof could cause severe economic loss and poses safety risk to residents in the building. Transient change in wind pressure may happen during a severe windstorm such as downburst and impose dynamic uplift load on low sloped roof structures. Such dynamic uplift load may cause failure of certain members in roof frames which may initiate the collapse of a steel framed roof structure as a result of load redistribution. The failure or rupture of members in a steel framed roof structure, may be dynamic in nature [31,14] and thus a nonlinear time history analysis is required to faithfully capture the dynamic collapse behavior of roof frames under transient wind loads. The collapse of a steel roof frame structure can be initiated by the buckling of a few members, as a result of load redistribution causing a subsequent progressive overstress condition in other members and thus its load carrying capacity is usually limited by the failure of first member or set of members to fail.

This research presents the results of nonlinear dynamic analysis of steel frame roof structures subjected to transient wind load. To accurately simulate the dynamic collapse of steel framed roof structure subjected to transient wind loading, dynamic effects associated with sudden loss of member capacity due to buckling and lateral inertial forces associated with mass lumped at the mid-length point of a buckled member are taken into account in this simulation study. In order to simulation member buckling and associated strength degradation and large deformation, a 2- dimensional force-based element with corotational formulation and fiber discretization of the cross section was adopted, which accounts for both material and geometric nonlinearities.