Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body

Abstract: Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.