Progressive collapse of structures means disproportion in size. Though the disproportion between cause and effect is a common feature, there are various differing mechanisms that produce such an outcome. The readiness to the theoretical treatment, approaches for quantifying indices, and possible or preferable alternate measures can vary accordingly. It is better to distinguish and describe the different types of progressive collapse. The term propagating action refers to the action that results from the failure of one element and leads to the failure of further similar elements.
A progressive collapse can be triggered by accident actions, including fire hazard, gas explosion, terrorist attack, vehicle collision, design and construction errors, and environmental corrosion. Due to industrialization, the buildings with multi-function and high complication become more common of which the safety and stability are far more concerned. Thus during the long-term use, the structure may suffer unexpected accidental actions, causing local damage or failure.
The progressive collapse of building structures is a complicated mechanical behaviour of the entire structural systems under large deformation. Problems such as large displacement, large rotation, contact and collision between specimens are inevitable during progressive collapse. Therefore, it is important to select the appropriate model for analysis to consider these features. Targeting at different objects, various progressive collapse models have been developed. The most representative models are the finite element model and the discrete element model. Before the failure of the entire structure the accurate mechanical behaviour can be calculated, but the following condition such as moving and collision between rigid bodies is hardly represented.
The progressive collapse of building structures can be analyzed using three finite models, they are the fine model, simplified model and multi-scale model. According to the mechanical behaviour of structural members the fine model can be established. This method is widely used for specimen because of its large calculations and large modelling process. Since the fine model is more time consuming and laborious simplified model is more preferred in the investigations on the progressive collapse. The ultimate mechanical behaviour of structures can be known by the simplified finite model. The finite element model can calculate the mechanical behaviour before the failure of the entire structure but the collision between the rigid bodies is not represented. The discrete element method brings out the mechanical behaviour of the structure. The dynamic effect can be known by comparing the internal forces and deformations in the dynamic and static analysis. The dynamic equation for structural progressive collapse is very complex hence is very difficult to obtain the simple mathematical expression of the dynamic effect. The structural ability to withstand the local damage due to accident is known as the robustness of the structure design courses in kerala. There are two classifications of the design methods for progressive collapse of building structures (1) the incident-dependent progressive collapse design; (2) incident-independent progressive collapse design. The first one is more accurate and mostly used with buildings with high safety requirement. The second method is all the more simpler.To put an end to the huge damage caused due to the progressive collapse several international designs and codes have been brought into effect.