Performance of steel-concrete composite floors subjected to blast loading

Abstract

This thesis investigates the behaviour and performance of steel-concrete composite floors with profiled decking subjected to uplift blast loading. In conventional composite floor design, primary actions are resisted by the capacity of the composite floors in sagging/positive bending moment. However, in the case of uplift blast loading, the same composite floors are subjected to a hogging/negative bending moment whose resistance is not generally considered in simple construction design.

According to a literature survey, numerous studies on steel and reinforced concrete (RC) structures subjected to blast can be found indisputably either in conference or journal papers. However, the survey concludes that there is a lack of experimental and numerical information or data on the behaviour and performance of steel-concrete composite floors subjected to blast loading, particularly in uplift blast loading. Furthermore, the survey investigated different modelling techniques with various complexity to model composite floors in finite element (FE) packages. The survey also investigated the constitutive materials models and properties of steel and concrete especially due to the influence of strain rates. In addition, a review has been conducted on an analytical method based on the rigid-plastic assumption in predicting maximum displacement of structures subjected to dynamic loading.

From these findings, an extensive and systematic validation process using FE analysis has been performed for quasi-static (composite floors) and blast loading cases (steel and RC structures). The FE results were validated against experimental results obtained from the open literature where the discrepancies between numerical and experimental results (static and dynamic) have been investigated and discussed. Various modelling techniques of composite floors were used in this investigation. As a result, a simplified FE model based on shell element for composite floors subjected to hogging bending moment was proposed and verified against detailed FE models.

In this thesis, the blast scenario for the composite floors prototype was considered based on packed explosives stored in luggage where the weight and standoff distances were varied. High fidelity FE models have been used in this study in order to investigate the uplift of the concrete slab, the behaviour of shear studs, the damage pattern in the concrete slab and the performance of the 3-bolts shear tab connection at the end-support of the composite floors. Moreover, the performance of the composite floors was compared against a set of response criteria where the results suggest the these selected criteria may not be appropriate for assessing the performance of composite floors under uplift blast loading. This study also performed investigations on the effect of various parameters such as the effect of strength (i.e. the number of rebars, steel beam and concrete strength), shear studs diameter and height, the influence of adjacent structural members and the influence of web stiffeners as well as the influence of strain rates in composite floors components.

This thesis proposes approximate solutions to estimate the maximum displacement of composite floors subjected to uplift blast loading. The proposed solutions were based on the rigid-plastic assumption. The influence of combined bending and membrane action were considered in the formulations. The results were compared against FE results where good agreements were achieved when the response of the composite floors is governed by plastic flow. The formulation considering the combined bending-membrane action provides more realistic values compared to membrane action only against FE results.