Development of component-based connection modelling for steel framed structures subjected to blast or progressive collapse

Abstract

Predicting the behaviour of steel-framed structures subject to unexpected loading conditions is necessary to ensure integrity and prevent collapse during such an event. When analysing a structure of this type it is common to simplify the problem by assuming connections as simple, rigid or semi-rigid (using a rotational spring). Whilst these simplifications are suitable for static and wind loading conditions they are unsatisfactory for explosive and collapse conditions where other factors, such as axial load and strain-rate effects, alter the connection behaviour.

Moment-rotation and direct tension tests have been performed on a range of bare steel semi-rigid connections under static and dynamic loading conditions. Results indicate that when loaded rapidly to failure, in general the connections demonstrate increased rotational stiffness and reduced ductility. These factors could influence the global survivability of a frame structure and therefore need to be explicitly accounted for in problems of a dynamic nature.

Component-based methods are proposed as a technique to include this real connection behaviour in non-linear dynamic structural analysis without having to produce a full three-dimensional FE model of the connection. This method simplifies each deformable joint component as a non-linear spring which, once assembled into a connection model, is able to accurately represent joint behaviour under all conditions. Use of these methods to model the experimental tests indicates good prediction of the overall behaviour and the dynamic effects. These connection models were then incorporated into a series of structural problems to investigate their potential for global analysis of extreme loading events. Results highlighted the importance of including joint performance in problems where ultimate capacity is of interest as connection rotational stiffness and ductility supply can affect the global frame behaviour. Thus prescriptive design measures alone, such as tying force requirements, cannot always guarantee sufficient levels of robustness.

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ORCID for M.P. Byfield: orcid.org/0000-0002-9724-9472

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