Open Access Open Access  Restricted Access Subscription Access

Scaling of Reaction Forces in a Displacement Controlled Steel Beam, Transitioning From Elastic to Plastic Behaviour



Fire resistance testing of structural elements and components is limited by the scale of fire resistance furnaces. Certification of long span or large structural systems may not be verified based on the results of full scale furnace tests but instead computer simulations. The response of structures exposed to fire depends on a number of different mechanisms which scale differently over different mechanical regimes. Consider the simple case of a fire exposed steel beam with a fixed point load, pinned at both ends. During the early period of fire exposure, it is the elastic behaviour which governs the flexural response. As the fire exposure increases, the beam starts to behave plastic and the axial response will be dominant. Dimensional analysis is applied to accurately create two different scale models of a prototype beam. The prototype and the models are modelled using Abaqus. We have shown that the total reaction force at displacements where a tensile mechanism is mobilised scales to the ratio of cross sectional areas of model to prototype. The total reaction force at low displacements under flexural behaviour scales with the ratio of the length of the model to the length of the prototype. Using a scale model to predict the response of a prototype exhibiting flexural and catenary mechanisms is therefore possible. There is a transition region between the elastic and the plastic region which does not scale with either length or area. It is our long term intention to develop scaling laws which could be used to help to 1) validate numerical models of structures exposed to fire; and 2) to better support extended application of test results.

Full Text: