13 results for Abu, A.K.

  • Parametric study of modelling structural timber in fire with different software packages

    Werther, N.; O'Neill, J.W.; Spellman, P.M.; Abu, A.K.; Moss, P.J.; Buchanan, A.H.; Winter, S. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    In a bid to accurately model structural behaviour of timber buildings in fire, a number of obstacles have been identified which must be fully understood before advanced computer modelling can accurately be used to represent physical behaviour. This paper discusses the obstacles, with suggestions on how to mitigate them, incorporating the challenges of using general purpose finite element software. The paper examines modelling with ANSYS, SAFIR and ABAQUS and the individual and collective challenges related to thermal analyses of timber structures in fire conditions. It considers the effects various model parameters (thermal and structural) may have on physical interpretation of experimental data in comparison with the accuracy of numerical solutions. In detail, the study looks at the effects of 1D and 2D heat transfer analyses, finite element mesh sizes, time steps and different thermal property approaches on thermal models of timber members in fires. It further recommends how best to model these structures using the different finite element software packages.

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  • Incremental fire analysis (IFA) for probabilistic fire risk assessment

    Moss, P.J.; Abu, A.K.; Dhakal, R.P. (2014)

    Conference Contributions - Published
    University of Canterbury Library

    In this paper, the concept of a probabilistic fire risk analysis method is presented in line with the seismic risk assessment approach. The probabilistic fire risk assessment approach runs through a series of probabilistic interrelationships between different variables representing the fire severity (called the Intensity Measure IM), structural response (called the Engineering Damage Parameter EDP) and damage/loss (called the Damage Measure DM). The paper explains the development of a probabilistic interrelationship between the IM and EDP through incremental fire analysis (IFA). For this purpose, a series of SAFIR analysis of a simple two span reinforced concrete beam subjected to different fire profiles have been conducted and are used to illustrate the required approach. Although a single EDP (maximum deflection) is considered in this investigation, two different IMs (maximum temperature and total radiant heat energy) are used. It is found that the radiant energy is more efficient than the maximum temperature in representing the fire severity.

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  • Design of post-tensioned timber beams for fire resistance

    Spellman, P.M.; Abu, A.K.; Carradine, D.M.; Moss, P.J.; Buchanan, A.H. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    This paper describes a series of three full-scale furnace tests on post-tensioned LVL box beams loaded with vertical loads, and presents a proposed fire design method for post-tensioned timber members. The design method is adapted from the calculation methods given in Eurocode 5 and NZS:3603 which includes the effects of changing geometry and several failure mechanisms specific to post-tensioned timber. The design procedures include an estimation of the heating of the tendons within the timber cavities, and relaxation of post-tensioning forces. Additionally, comparisons of the designs and assumptions used in the proposed fire design method and the results of the full-scale furnace tests are made. The experimental investigation and development of a design method have shown several areas which need to be addressed. It is important to calculate shear stresses in the timber section, as shear is much more likely to govern compared to solid timber. The investigation has shown that whilst tensile failures are less likely to govern the fire design of post-tensioned timber members, due to the axial compression of the post-tensioning, tensile stresses must still be calculated due to the changing centroid of the members as the fire progresses. Research has also highlighted the importance of monitoring additional deflections and moments caused by the high level of axial loads.

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  • The effect of edge support on tensile membrane action of compoiste slabs in fire

    Abu, A.K.; Burgess, I.W. (2010)

    Conference Contributions - Published
    University of Canterbury Library

    The Bailey-BRE Method is a simplified design approach that facilitates the use of a tensile membrane action design philosophy for composite floors under fire conditions. The method requires the division of a composite floor into rectangular slab panels, composed of parallel unprotected composite beams in their interior parts, supported vertically by protected composite edge beams. Enhanced slab capacities are obtained after the unprotected beams have lost significant strength, by allowing large deflections of the slab in biaxial bending. The use of tensile membrane action generates significant cost savings in composite structures, as a large number of floor beams can be left unprotected. However, the protected beams which provide vertical support to the edges of panels lose strength under the combined effects of thermal degradation and the increased loading due to biaxial bending, and this has the potential to cause panels to lose structural stability altogether. It is therefore imperative to investigate what constitutes adequate vertical support and the detrimental effects of inadequate vertical support on tensile membrane action of composite slabs in fire. This paper reports on a study of this effect, and puts forward some simple recommendations to avoid loss of stability of composite floors designed by this method.

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  • Modelling the fire performance of structural timber floors

    O'Neill, J.W.; Abu, A.K.; Carradine, D.M.; Moss, P.J.; Buchanan, A.H. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    This paper describes numerical modelling to predict the fire resistance of engineered timber floor systems. The floor systems under investigation are timber composite floors (various timber joist and box floor cross sections), and timber-concrete composite floors. 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 is also being undertaken to calibrate and validate the models, with a number of full scale tests to determine the failure mechanisms for each floor type and assess fire damage to the respective system components. The final outcome of this research will be simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems.

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  • Verification of code fire ratings of precast prestressed concrete slabs

    Min, J-K.; Abu, A.K.; Moss, P.J.; Dhakal, R.P.; Buchanan, A.H. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    In fire design for floors, the three criteria of stability, integrity and insulation are required for the specified fire resistance duration. Among these, stability is not easy to confirm. For solid prestressed concrete slabs of uniform thickness, Eurocode 2 provides tabulated data and specifies an axis distance to the centroid of strands to achieve particular fire resistance ratings, but it is not clear if this data can be used for a wide range of different prestressed slab profiles. In order to verify the current code-fire ratings for precast prestressed slabs, both simple and advanced calculation methods are investigated. This paper examines use of calculation methods, accounting for the real behaviour of unprotected simply supported prestressed concrete slabs exposed to the standard ISO 834 fire. The calculated fire resistance of each prestressed concrete slab is compared with tabulated data in Eurocode part 1.2, with detailed discussion.

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  • Post-earthquake structural design for fire - a New Zealand perspective

    Baker, G.B.; Collier, P.C.R.; Abu, A.K.; Houston, B. (2012)

    Conference Contributions - Published
    University of Canterbury Library

    On Tuesday 22 February 2011, a 6.3 magnitude earthquake struck Christchurch, New Zealand’s second largest city. The ‘earthquake’ was in fact an aftershock to an earlier 7.1 magnitude earthquake that had occurred on Saturday 4 September 2010. There were a number of key differences between the two events that meant they had dramatically different results for Christchurch and its inhabitants. The 22 February 2011 event resulted in one of New Zealand’s worst natural disasters on record, with 185 fatalities occurring and hundreds more being injured. In addition, a large number of buildings either collapsed or were damaged to the point where they needed to be totally demolished. Since the initial earthquake in September 2010, a large amount of building-related research has been initiated in New Zealand to investigate the impact of the series of seismic events – the major focus of these research projects has been on seismic, structural and geotechnical engineering matters. One project, however, conducted jointly by the University of Canterbury, the Fire Protection Association of New Zealand and BRANZ, has focused on the performance of fire protection systems in the earthquakes and the effectiveness of the systems in the event of post-earthquake fires occurring. Fortunately, very few fires actually broke out following the series of earthquake events in Christchurch, but fire after earthquakes still has significant implications for the built environment in New Zealand, and the collaborative research has provided some invaluable insight into the potential threat posed by post-earthquake fires in buildings. As well as summarising the damage caused to fire protection systems, this paper discusses the flow-on effect for designing structures to withstand post-earthquake fires. One of the underlying issues that will be explored is the existing regulatory framework in New Zealand whereby structural earthquake design and structural design for fire are treated as discrete design scenarios.

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  • Collapse Mechanisms of Composite Slab Panels in Fire

    Abu, A.K.; Ramanitrarivo, V.; Burgess, I.W. (2010)

    Conference Contributions - Published
    University of Canterbury Library

    The identification of tensile membrane action as a sustainable, high-capacity load-bearing mechanism of composite floors under fire conditions has led to the development of a number of simplified design solutions, because of the unsuitability of finite element analysis for routine design. Prominent amongst these is the Bailey-BRE method, which predicts composite slab capacity by calculating the enhancement of its traditional yield-line load capacity due to tensile membrane action. This method assumes that the two-way bending slab panel, composed internally of parallel unprotected composite beams, is supported on edges which resist vertical deflection. In practice, the protected composite beams which simulate this vertical edge support in fire deflect under the combination of heating and load, and this loss of vertical support induces single-curvature bending, which leads to an eventual structural failure by folding of the slab panel. A simple folding mechanism, which considers the contributions of the internal unprotected beams and the protected edge beams, has been developed for isolated slab panels. In the current study the mechanism has been extended to include the reinforcement in the slab as well as its 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 considered, the location of the slab panel and the severity of fire exposure. These factors are considered in developing a number of collapse mechanisms as an additional check within the Bailey-BRE design method. Comparisons are made with the finite element software Vulcan and other acceptance criteria.

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  • Effects of thermal gradients on membrane stresses in thin slabs

    Abu, A.K.; Burgess, I.W.; Plank, R.J. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    The Building Research Establishment (BRE) of the United Kingdom has developed a simple design method for the determination of the capacity of composite slabs in fire. The method, based on ambient temperature large-deflection plastic theory, predicts the capacity by calculating the enhancement added by tensile membrane action to the theoretical yield-line load of the slab. Tensile membrane action is a load-carrying mechanism experienced by thin slabs undergoing large vertical deflections, where stretching of the midplane produces a central area of tensile force balanced by a peripheral ring of compressive force. The use of this mechanism in structural fire engineering introduces safety and economy, as a large number of floor beams can be left unprotected. The method, developed on the assumption that the slabs are simply-supported, also assumes that the development of the tensile membrane mechanism is maintained at elevated temperatures. An analytical procedure for the determination of this membrane capacity has recently been developed by the University of Edinburgh. It argues that the development of tensile membrane action at elevated temperatures differs from that at ambient temperature, and that the tensile forces developed in the centre of the slab can only be balanced by sufficient anchorage along the slab’s boundaries. Experimental investigations on large-deflection behaviour of simply-supported slabs at ambient and elevated temperatures, conducted at the University of Sheffield, have confirmed the variation in the mechanism at ambient and elevated temperatures, but have identified that the load-carrying capacity can be effectively developed without the horizontal anchorage along the slab’s boundaries. These observations have led to the belief that thermal gradients, acting alone through the depth of the slab, can induce considerable amounts of tensile membrane action. This paper therefore investigates this phenomenon in simply-supported thin slabs. It examines displacements and stresses developed at ambient and elevated temperatures, using the Rayleigh-Ritz approach. Good comparisons are made with finite element analyses.

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  • Analysis of Tensile Membrane Action in Composite Slabs in Fire

    Abu, A.K.; Burgess, I.W.; Plank, R.J. (2007)

    Conference Contributions - Published
    University of Canterbury Library

    Tensile membrane action can have a major influence on the performance of composite floor structures, and a number of design tools have been developed to take account of this. These represent a major advance on previous design methods and generally compare well with available test data. However, uncertainties remain about suitable failure criteria and the relative importance of various assumptions. This paper reports on a project to study these issues, comparing results obtained using different design methods, and also with tests on model scale slabs.

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  • Structural fire engineering assessments of the FRACOF and Mokrsko fire tests, an engineering prediction

    Abu, A.K.; Block, F.M.; Butterworth, N.A.; Burgess, I.W. (2009)

    Conference Contributions - Published
    University of Canterbury Library

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  • Effects of edge support and reinforcement ratios on slab panel failure in fire

    Abu, A.K.; Burgess, I.W.; Plank, R.J. (2008)

    Conference Contributions - Published
    University of Canterbury Library

    The advancement in structural fire engineering towards more cost-effective solutions has necessitated the increasing use of performance-based approaches to the design of multistorey composite buildings. These methods consider the real behaviour of structures and provide economic solutions which optimise fire protection usage. Optimising structures to use tensile membrane action requires the structural use of slab panels. These are vertically supported lightly-reinforced composite floor systems, allowing biaxial bending at elevated temperatures. Vertical support is achieved, in practice, by protecting a panel’s perimeter beams to achieve temperatures of no more than 620°C at the required fire resistance time. The Bailey-BRE design method, which incorporates tensile membrane action, uses these vertically supported panels to establish composite slab capacities in fire. The slab panel resistance is determined by a combination of the residual composite beam strength and the large-deflection enhanced slab resistance. The simple calculations of the Bailey-BRE method imply improved performance with higher reinforcement ratios. However, proportional increases have not been observed in the modelling work reported here. The discrepancy may be due to the geometry, composition or support conditions of the slab panels. Also, with exposure to fire, a panel’s ‘vertical’ support can be lost. This will in turn affect the tensile membrane capacity, pre-empting a structural failure of the floor system. This paper presents the results of a finite element investigation into the effects of reinforcements and vertical support on slab panel failure. The study examines the effect of various degrees of protection on the development of the tensile membrane action mechanism. It examines the development and failure of this mechanism, considering various degrees of edge-beam protection, and makes comparisons with the predictions of the Bailey-BRE method and various design acceptance criteria.

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  • Effects of slab panel vertical support on tensile membrane action

    Abu, A.K.; Burgess, I.W.; Plank, R.J. (2007)

    Conference Contributions - Published
    University of Canterbury Library

    A recently-developed design method predicts composite slab capacities in fire, incorporating the effects of tensile membrane action. The method designs rectangular slab panels including unprotected beams within the panels, and are supported on edges that resist vertical deflection. In practice, vertical support is achieved by protecting the perimeter beams. Generic fire protection ensures that beam temperatures stay below critical temperatures of 550°C or 620°C within the required fire resistance time. However, large vertical displacements of the protected edge beams may cause a loss of the membrane mechanism, inducing single- curvature bending, which may lead to a catastrophic failure of the structure. A finite element investigation into the provision of adequate vertical support along slab panel boundaries has been conducted. The study has examined various degrees of protection relative to the development of the membrane mechanism. Comparisons are made with the membrane action design method and various acceptance criteria.

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