Anthony K. Abu

Tensile Membrane Action of Thin Slabs Exposed to Thermal Gradients

AbstractA number of simplified design methods have been developed to predict composite slab capacities in fire. Most of these extend ambient-temperature large-deflection slab behavior to the elevated-temperature phase by reducing the strengths of fire-exposed concrete and reinforcement while neglecting the effects of thermal expansion and thermal bowing of the slab. Experiments have shown that there are significant differences between the predictions from these methods and the actual behavior and failure modes of ambient- and elevated-temperature concrete slabs in tensile membrane action. Therefore, this paper describes the development of a new analytical method that incorporates both thermal and mechanical effects into the prediction of slab behavior in fire conditions. It uses the variational Rayleigh-Ritz approach to classical large-deflection plate theory. The method is found to produce accurate predictions of deflections and membrane tractions; however, it requires further refinement for accuracy of ...

Collapse Mechanisms of Composite Slab Panels in Fire

A simple folding mechanism, which considers the contributions of internal unprotected beams and protected edge beams, has been proposed for isolated slab panels in fire conditions. The current study extends the mechanism to include the reinforcement in the slab as well as continuity across the protected edge beams. Structural failure of the panel depends on the applied loads, the relative beam sizes, their locations within the building, their arrangement in the slab panel, the panels location and the severity of fire exposure. These factors are considered in the development of a number of collapse mechanisms for verification so they may eventually serve as an additional check within the Bailey-BRE design method, to make it more robust for routine design of composite floors in fire. Comparisons are made with the finite element software Vulcan and other design acceptance criteria.

Modelling the fire performance of structural timber-concrete composite floors

This paper describes numerical modelling to predict the fire resistance of engineered timber-concrete composite floor systems. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies has also been undertaken to validate the models, with multiple full scale tests conducted to determine the failure mechanisms and assess fire damage to the system components. The final outcome of this research is the development of simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems, as part of a larger research project on multi-storey timber buildings.

Bidirectional Behaviour of Unstiffened and Stiffened Direct-Welded Connections for Square CFST Columns

This paper describes finite element analyses of two-way moment frame beam-column joint subassemblies constructed using steel I-shaped beams connected to square concrete filled steel tubular (CFST) columns. These are direct-welded connections with (i) no stiffeners, (ii) internal horizontal stiffener plates, (iii) vertical tube stiffeners, and (iv) the combination of (ii) and (iii). They were analyzed under one-way and two-way column lateral loading. It is shown that internal stiffeners increase the joint stiffness and strength by up to 80% and 60% respectively. The effect of bidirectional loading on the joint capacity is found to be minor. A design method is developed to predict the required stiffener capacity. The method is applicable for both one-way and two-way loading cases.

Comparison of Existing Time-Equivalence Methods and the Minimum Load Capacity Method

A fire resistance rating (FRR) is the minimum required ability of a building element to resist a fire. One way of determining FRR is the time-equivalence (TE) approach which relates the destructive potential of a post-flashover fire to an equivalent duration under the standard fire exposure. Many existing TE approaches use empirical correlations which account for fuel load, ventilation conditions, compartment size, lining materials, and structural materials. While they ease the determination of FRR, many parameters that also influence structural failure are not explicitly considered. These factors include load ratio, member size, and member capacity. A change in any of these will alter the survival duration of a member; this is not reflected in the existing TE methods.

Analytical Methods for Determining Fire Resistance of Concrete Members

Concrete structures have a reputation for excellent behavior in fires. Many reinforced concrete buildings that have experienced severe fires have been repaired and put back into use. Concrete is by nature noncombustible and has a low thermal conductivity. Concrete tends to remain in place during a fire, protecting the reinforcing steel, with the cool inner core continuing to carry the load. Catastrophic failures of reinforced concrete structures in fires are rare, but some occasionally occur [1].