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Mengqi Zhu - One of the best experts on this subject based on the ideXlab platform.
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holographical description of bps wilson loops in flavored abjm theory
Journal of High Energy Physics, 2014Co-Authors: Bin Chen, Mengqi ZhuAbstract:As holographic description of BPS Wilson loops in $$ \mathcal{N}=3 $$ flavored ABJM theory with N f = k = 1, BPS M2-branes in AdS 4 × N (1, 1) are studied in details. Two 1/3-BPS Membrane configurations are found. One of them is dual to the 1/3-BPS Wilson loop of Gaiotto-Yin type. The regulated Membrane Action captures precisely the leading exponential behavior of the vacuum expectation values of 1/3-BPS Wilson loops in the strong coupling limit, which was computed before using supersymmetric localization technique. Moreover, there is no BPS Membrane with more supersymmetries in the background, under quite natural assumption on the Membrane worldvolume. This suggests that there is no Wilson loop preserving more than 1/3 supersymmetries in such flavored ABJM theory.
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holographical description of bps wilson loops in flavored abjm theory
arXiv: High Energy Physics - Theory, 2014Co-Authors: Bin Chen, Mengqi ZhuAbstract:As holographic description of BPS Wilson loops in ${\cal N}=3$ flavored ABJM theory with $N_f=k=1$, BPS M2-branes in $AdS_4\times N(1, 1)$ are studied in details. Two $1/3$-BPS Membrane configurations are found. One of them is dual to the $1/3$-BPS Wilson loop of Gaiotto-Yin type. The regulated Membrane Action captures precisely the leading exponential behavior of the vacuum expectation values of $1/3$-BPS Wilson loops in the strong coupling limit, which was computed before using supersymmetric localization technique. Moreover, there is no BPS Membrane with more supersymmetries in the background, under quite natural assumption on the Membrane worldvolume. This suggests that there is no Wilson loop preserving more than 1/3 supersymmetries in such flavored ABJM theory.
Colin Bailey - One of the best experts on this subject based on the ideXlab platform.
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large scale fire test of unprotected cellular beam acting in Membrane Action
Proceedings of the Institution of Civil Engineers: Structures and Buildings, 2012Co-Authors: Olivier Vassart, Colin Bailey, Mike Hawes, Ali Nadjai, W I Simms, Bin Zhao, Thomas Gernay, Jeanmarc FranssenAbstract:This paper describes a full-scale fire test performed recently on a composite floor for analysing the possibility for tensile Membrane Action to develop when unprotected steel beams in the central part of the floor are made of cellular beams. The natural fire was created by a wood crib fire load of 700 MJ/m2 and the 9 m × 15 m floor survived the fire, which peaked at 1000°C and lasted for about 90 min. Blind predictions of the air temperature development by the software ‘Ozone' and of the structural behaviour by the software ‘Safir', which proved quite satisfactory, are also described.
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large scale fire test of unprotected cellular beam acting in Membrane Action
Journal of Structural Fire Engineering, 2011Co-Authors: Olivier Vassart, Colin Bailey, Mike Hawes, Ali Nadjai, W I Simms, Bin Zhao, Thomas Gernay, Jeanmarc FranssenAbstract:This paper describes a full scale fire test performed the 27th of February 2010 on a composite floor for analysing the possibility of tensile Membrane Action to develop when the unprotected steel beams in the central part of the floor are made of cellular beams. The natural fire was created by a wood crib fire load of 700 MJ/m2 and the 9 × 15 m floor survived the fire that peaked at 1000°C and lasted for 90 minutes. Blind predictions of the air temperature development by the software OZone and of the structural behaviour by the software SAFIR which proved quite satisfactory are also described.
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simplified and advanced analysis of Membrane Action of concrete slabs
Aci Structural Journal, 2008Co-Authors: Colin Bailey, W S Toh, Bok M ChanAbstract:When assessing structures under accidental loads, it is important to understand the Membrane behavior of concrete slabs at large displacements. This study compares a simple analytical approach based on rigid-plastic behavior with a change of geometry, an advanced finite element model (FEM), and 14 tests on horizontally-unrestrained concrete slabs that reached vertical displacements up to 10 times the effective depth of the slab. Findings show that both analytical approaches predicted the Membrane behavior of the slabs, comprising compressive Membrane Action around the slab’s perimeter and tensile Membrane Action in the central span region of the slab. The simple approach produced good predictions of the load-displacement response toward the end of the test, while the FEM produced reasonable predictions over the full history of the test. By considering the magnitude and pattern of the stresses within the FEM, the assumptions adopted within the simple approach were investigated and are discussed. The overall findings suggest that the simple approach can safely be used for predicting the load-carrying capacity, due to Membrane Action, of concrete slabs under large displacements.
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Membrane Action of slab beam composite floor systems in fire
Engineering Structures, 2004Co-Authors: Colin BaileyAbstract:A structural performance-based design approach for steel beams supporting a composite floor system is presented allowing designers to specify fire protection to only a proportion of the steel beams within a given floor plate. The approach is a further development of a previous simplified design method where Membrane Action of the composite floor slab was included. The new method, presented in this paper, has been extended to incorporate the Membrane Action of the slab and beam system acting compositely, whereas the previous design method only considered the Membrane Action of the composite slab. In addition, the new method also includes the effect of the Membrane Action of the slab due to the variation in the deflected form, which is assumed to follow the changing yield-line patterns as the slab/beam system is heated in a fire. Previously, the Membrane Action of the composite slab was based on the lower-bound yield-line pattern assuming the slab and supporting beams acted independently. Comparison with the previous design approach shows that the simplifications, of ignoring the variation in the deflected form, and ignoring the contribution of the unprotected steel beams to the Membrane load-carrying capacity of the system, were conservative.
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Membrane Action of unrestrained lightly reinforced concrete slabs at large displacements
Engineering Structures, 2001Co-Authors: Colin BaileyAbstract:Following full-scale fire tests on a steel-framed building, together with observations from real fires, it has been shown that Membrane Action, at large displacements, of composite floors comprising steel deck, concrete, and anti-crack mesh, is extremely beneficial to the survival of the building. It was therefore decided to review previous research conducted on unrestrained concrete slabs, under large displacements, at normal temperatures. It was found that the assumptions used to develop previous theoretical predictions for the load-carrying capacity, for a given vertical displacement, are only valid for square slabs and do not conform to test observations for rectangular slabs. A new theoretical approach is therefore presented which is valid for both square and rectangular slabs and conforms to the mode of behaviour observed in tests. The design method is shown to give excellent correlation with published test data. A prediction for ultimate collapse of the slab due to fracture of the reinforcement is also presented, which limits the allowable mechanical strain in the reinforcement. Comparison with available test data shows that this prediction is always conservative.
I W Burgess - One of the best experts on this subject based on the ideXlab platform.
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yield line plasticity and tensile Membrane Action in lightly reinforced rectangular concrete slabs
Engineering Structures, 2017Co-Authors: I W BurgessAbstract:The paper provides the systematic derivation of a new analytical approach to tensile Membrane Action of lightly-reinforced thin concrete slabs at large deflections. The basic motivation for the work comes from the recent use of tensile Membrane Action as an enhancement, in the fire condition, of the capacity of the thin concrete slabs which are normally made composite with downstand steel beams, at temperatures which have substantially degraded the contribution of these steel beams. The method accepts as a premise that such slabs form a pattern of localized yield lines as an initial small-deflection failure mechanism, and that these yield lines retain their positions as subsequent deflection occurs. As the slab deflects, maintaining the correct kinematics of the articulation and displacement of the system of slab facets, interacting across the yield lines, is extremely important to the horizontal equilibrium of the slab. In this process it becomes necessary to re-think the basic assumption of traditional yield-line theory that any local cross-section of unit width along a yield line equilibrates the force of its concrete compression block with the yielded steel’s tension force, producing constant plastic moment capacities for the mesh in either direction along any yield line. In the approach set out in this paper only overall equilibrium of the system of facets needs to be maintained. As in normal rigid-plastic analysis, concrete acts only when compressed, and then at its compressive strength, and steel acts at its tensile yield strength whilst it remains intact. However, steel in either direction can fracture when the local crack-width causes its local strain to exceed its fracture ductility. When the rebar crossing the diagonal yield lines begins to fracture this generally indicates that the slab’s capacity is about to reduce with further deflection. The paper does not attempt to address how a rebar’s free length across a discrete crack is generated, or the limiting crack widths implied, but this is shown in a range of examples to be a major issue if tensile Membrane Action is to be used in practice to enhance the capacity of slabs, for example in hazard loading situations. It is important that principles be established in future to quantify this aspect of rebar ductility.
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a re examination of the mechanics of tensile Membrane Action in composite floor slabs in fire
2014Co-Authors: I W Burgess, Shanshan Huang, Savina StaikovaAbstract:This paper presents a re-examination from first principles of the mechanics of tensile Membrane Action (TMA) of thin rectangular concrete floor slabs, transversely supported around their edges. An existing simplified method of assessing the contribution of TMA to the fire resistance of a composite slab, including unprotected steel downstand beams in its interior area, appears to have some serious mechanical shortcomings in its fundamental assumptions. This paper describes, and presents results from, a re-examination of the mechanics of TMA of thin concrete floor slabs in fire conditions, starting from the same initial state of an optimal small-deflection yield-line hinge pattern. The basic formulation considers plain flat slabs, but is in no way limited to these, or to isotropic reinforcement. It is based on a large-deflection plastic analysis. The resulting formulation accounts for the plasticity and fracture of the reinforcing mesh, which is usually weaker in tension than the slab in which it is embedded, and the compressive strength of the concrete. It allows the changes in stress patterns around the yield lines to be monitored, from negligible deflection to complete failure of the slab, and provides a rational way of predicting when a through-depth tensile crack will occur; in fire conditions this is usually taken as an integrity failure of the separating function of the floor slab. If necessary the method can then follow the further development of this cracked mechanism up to full loss of structural load capacity. Like- against-like comparisons are made against the enhancements predicted by the existing method, and it can be seen that these are by no means identical; nor are the predictions by one method consistently conservative relative to the other.
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the influence of tensile Membrane Action on fire exposed composite concrete floor steel beams with web openings
Procedia Engineering, 2013Co-Authors: Bernice V Y Wong, I W BurgessAbstract:Abstract On the basis of a series of the full-scale fire tests carried out on the composite frame at Cardington, a design method is now well established to calculate the performance of composite flooring systems subject to fire. The method models in a simplified fashion the influence of tensile Membrane Action in composite floor slabs which are formed as an array of composite beams using solid-web steel downstand beams which are largely unprotected. The development of Membrane Action depends on the conditions of vertical support maintained around the boundaries of the fire-affected slab panels by protected beams. Cellular beams can achieve the same strength as unperforated I-beams of the same depth, with significantly reduced steel mass, and the ability to accommodate service ducts within the beam depth, and therefore the use of composite cellular beams as floor members is becoming increasingly popular in construction. Due to the general lack of research on perforated sections, the guidance about their design for fire conditions remains rather primitive. Moreover, tensile Membrane Action in composite floor slabs with cellular steel downstand beams could exhibit very different behaviour in fire from that when solid-web sections are used. A parametric study has been carried out as an initial investigation into the fire performance of cellular beams within composite slab systems, including the effects of tensile Membrane Action in enhancing the load-carrying capacity. The effects of changes to the edge support conditions are also investigated. The results show the protected perimeter beams maintained their load-carrying capacity and were subject only to small vertical displacements, although web-post buckling was observed to occur on the protected secondary beam near to a support. This suggests that maintenance of vertical support is not sufficient for a slab panel with cellular beams. Web-post buckling or the Vierendeel mechanism may govern the mode of structural failure, indicating that the sizes of openings and their positioning necessitate careful design.
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modeling Membrane Action of concrete slabs in composite buildings in fire ii validations
Journal of Structural Engineering-asce, 2003Co-Authors: Zhaohui Huang, I W Burgess, Roger J. PlankAbstract:A companion paper has documented a geometrically nonlinear layered procedure for modeling of the Membrane Actions in concrete slabs subject to very high deflections and in fire. The model is based on a layered procedure developed previously by the writers in which only material nonlinearities were taken into account. In this paper two solid reinforced concrete slabs with simply supported edges, tested by other writers at ambient temperature under uniform loading, are modeled. This is followed by a simulation of a full-scale fire test on a solid reinforced concrete slab floor. Finally very detailed simulations of two full-scale fire tests on the composite frame at the Cardington Laboratory are conducted. It is evident that the proposed model can predict structural behavior of reinforced concrete slabs and their influence on composite steel-framed buildings in fire with good accuracy, although the multiplicity of parameters which can affect a test result cannot always be controlled or measured. In all cases...
Caspeele Robby - One of the best experts on this subject based on the ideXlab platform.
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Additional load bearing capacity of prestressed hollow core slabs due to Membrane Action
2020Co-Authors: Thienpont Thomas, De Corte Wouter, Caspeele RobbyAbstract:Due to their efficient design, economic production process and quick installation, prestressed concrete hollow core slabs are frequently used in all kinds of constructions. These prefabricated units are typically installed as single span elements, which are at the joints tied to the neighbouring elements with additional rebars. In a final step, the joints at the edges and between the elements are filled with grout, or a second layer of cast in-situ concrete is added on top of the elements. Although the execution of the joints and the stiffness of the surrounding structure provide a certain level of rigidity, hollow core slabs are typically designed as simply supported single span elements. However, the stiffness of the surrounding structure might facilitate compressive Membrane Action, which can increase the bearing capacity of the elements. This additional load bearing capacity, which is usually not taken into account, can be beneficial in accidental loading situations. This paper evaluates the additional load bearing capacity of prestressed concrete hollow core slabs due to compressive Membrane Action using two detailed 3D non-linear finite element models in Abaqus. The influence of the longitudinal restraint forces on the load bearing capacity of a single hollow core element is evaluated and compared to a simply supported configuration. The influence of the element geometry and span to height ratio on the additional load bearing capacity is investigated for both reinforced and prestressed hollow sections
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Structural reliability calculations considering concrete tensile Membrane Action using the probability density evolution method
Seoul National University, 2019Co-Authors: Ding Luchuan, Botte Wouter, Droogné Didier, Van Coile Ruben, Caspeele RobbyAbstract:Based on experimental research on a real-scale one-way reinforced concrete slab with two spans for which the internal support was removed, a numerical model in ABAQUS was developed and validated. The model is subsequently used to investigate the uncertainty of the load bearing capacity of the damaged slab considering four key random variables. Further, the probability density evolution method (PDEM) is applied for the reliability assessment. Although PDEM has in general been applied to solve dynamic reliability problems, in this contribution this method was adapted and applied to a static problem. The PDF of the load bearing capacity is calculated considering the ultimate load bearing capacity of the slab in its damaged state, i.e. the load corresponding with the rupture of the reinforcement bars at the inner support due to the developed tensile Membrane Action (TMA). Taking into account the obtained PDF for the capacity of the damaged system, the reliability index of the damaged slab is assessed
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Reliability analysis of FRP strengthened RC beams considering compressive Membrane Action
'Elsevier BV', 2018Co-Authors: Zeng Yihua, Botte Wouter, Caspeele RobbyAbstract:Recent research has shown that the compressive Membrane Action (CMA) significantly enhances the load bearing capacity of FRP strengthened concrete beams. It is of great interest to investigate the effect of CMA on the structural reliability of such beams and how to incorporate the benefits of CMA into partial factor based design. Following a CMA model and the probabilistic models of its corresponding design variables, the effect of CMA on the reliability indices of FRP strengthened concrete beams was investigated. A parameter study as well as a sensitivity analysis were also conducted with parameters including properties of FRP and steel reinforcement, concrete properties and geometrical properties. The reliability indices with respect to load ratios i.e. ratios of the variable load to the total loads is selected to quantify the effect of CMA. The results show that the CMA effect significantly improves the structural reliability of FRP strengthened concrete beams. The parameter study indicates that an increase of the concrete strength and yield strain has positive effect on the structural reliability while an increase of FRP ratio, FRP modulus, steel ratio as well as the concrete ultimate strain has an adverse effect. Furthermore, it is found that the variations of the concrete strength, the FRP Young's modulus as well as the concrete cover have a significant influence on the reliability index; the variations of the ultimate strain of FRP, the yield strain of steel reinforcement and the ultimate strain of concrete have a moderate influence on the reliability index. Finally, an adjusted partial factor for the FRP strength is derived for cases where CMA would already be considered in the design stage
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Fire Resistance of Concrete Slabs Acting in Compressive Membrane Action
2017Co-Authors: Molkens Tom, Gernay Thomas, Caspeele RobbyAbstract:In building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive Membrane Action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive Membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature.status: publishe
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Fire resistance of concrete slabs acting in compressive Membrane Action
Doppiavoce, 2017Co-Authors: Molkens Tom, Gernay Thomas, Caspeele RobbyAbstract:peer reviewedaudience: researcher, professionalIn building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive Membrane Action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive Membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature
Gernay Thomas - One of the best experts on this subject based on the ideXlab platform.
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Fire Resistance of Concrete Slabs Acting in Compressive Membrane Action
2017Co-Authors: Molkens Tom, Gernay Thomas, Caspeele RobbyAbstract:In building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive Membrane Action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive Membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature.status: publishe
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Post-blast fire resistance of low-rise buildings through Membrane Action of composite floor slabs
2017Co-Authors: Haase Bryce, Elhami Khorasani Negar, Gernay ThomasAbstract:Sever fires in buildings can lead to local failures, instability, partial or total collapse of the structure. In majority of the times, fire is a secondary event, after blast or impact, while the building has experienced some damage. Examples of widely known events include the 1968 Ronan Point collapse in the UK, the 1995 Oklahoma City bombing, the World Trade Center Collapse in New York in 2001, the 2014 collapse of a building at New York’s Harlem neighborhood due to a gas explosion, and the recent 2015 collapse of a building at New York’s East Village also due to a gas explosion. The initial shock to the building can be conservatively modeled by removing an intermediate vertical supporting element (i.e. loss of load-carrying capacity in a critical element), leading to an increased span for composite floor slabs. In a lowrise building, if there is enough reinforcement throughout the slab and enough continuity and restraint, despite large deflections that will develop, the slab is capable of carrying the loads by Membrane Action. Fundamentally, the floor system behaves as an inverted dome structure with radial tensile forces and a compressive hoop stresses. This holds true at ambient temperature, yet a similar resisting mechanism forms during fire. Previous research and experimental work shows that fire performance of composite floor slabs can be used to reduce the fire protection requirement of the steel elements, i.e. the designer should take advantage of reserve capacity in the composite floor slab Membrane Action. The utilization of Membrane Action in the design of composite floor slabs has been used, to some extent, for mitigating collapse from single events (blast or fire only). Given that, often the initial blast is followed by a secondary fire event, this work investigates the system-level performance of low-rise damaged buildings subject to post-blast fires. The hypothesis is that, when incorporated in the design, low-rise buildings can withstand the post-blast fires through Membrane Action of composite floor slabs. Application of this concept, within a performance-based framework, can be used to avoid progressive collapse, or at the minimum increase fire resistance to allow for safe evacuation. This work investigates the design requirements for beam sizes, fire protection, concrete reinforcement and cover thickness to develop Membrane Action for a pre-defined fire resistance rating under cascading post-blast fires.Peer reviewe
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Post-blast fire resistance of low-rise buildings through Membrane Action of composite floor slabs
2017Co-Authors: Haase Bryce, Elhami Khorasani Negar, Gernay ThomasAbstract:peer reviewedaudience: researcher, professional, studentSever fires in buildings can lead to local failures, instability, partial or total collapse of the structure. In majority of the times, fire is a secondary event, after blast or impact, while the building has experienced some damage. Examples of widely known events include the 1968 Ronan Point collapse in the UK, the 1995 Oklahoma City bombing, the World Trade Center Collapse in New York in 2001, the 2014 collapse of a building at New York’s Harlem neighborhood due to a gas explosion, and the recent 2015 collapse of a building at New York’s East Village also due to a gas explosion. The initial shock to the building can be conservatively modeled by removing an intermediate vertical supporting element (i.e. loss of load-carrying capacity in a critical element), leading to an increased span for composite floor slabs. In a lowrise building, if there is enough reinforcement throughout the slab and enough continuity and restraint, despite large deflections that will develop, the slab is capable of carrying the loads by Membrane Action. Fundamentally, the floor system behaves as an inverted dome structure with radial tensile forces and a compressive hoop stresses. This holds true at ambient temperature, yet a similar resisting mechanism forms during fire. Previous research and experimental work shows that fire performance of composite floor slabs can be used to reduce the fire protection requirement of the steel elements, i.e. the designer should take advantage of reserve capacity in the composite floor slab Membrane Action. The utilization of Membrane Action in the design of composite floor slabs has been used, to some extent, for mitigating collapse from single events (blast or fire only). Given that, often the initial blast is followed by a secondary fire event, this work investigates the system-level performance of low-rise damaged buildings subject to post-blast fires. The hypothesis is that, when incorporated in the design, low-rise buildings can withstand the post-blast fires through Membrane Action of composite floor slabs. Application of this concept, within a performance-based framework, can be used to avoid progressive collapse, or at the minimum increase fire resistance to allow for safe evacuation. This work investigates the design requirements for beam sizes, fire protection, concrete reinforcement and cover thickness to develop Membrane Action for a pre-defined fire resistance rating under cascading post-blast fires
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Fire resistance of concrete slabs acting in compressive Membrane Action
Doppiavoce, 2017Co-Authors: Molkens Tom, Gernay Thomas, Caspeele RobbyAbstract:peer reviewedaudience: researcher, professionalIn building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive Membrane Action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive Membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature
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Fire resistance of concrete slabs acting in compressive Membrane Action
2017Co-Authors: Molkens Tom, Gernay Thomas, Caspeele RobbyAbstract:In building renovation, the real behaviour of reinforced concrete slabs cannot always be explained by the bending theory according to classical structural mechanics. Indeed, the bearing capacity, as assessed for instance by a loading test, sometimes appears to be much higher than what would be expected. This phenomenon may be caused by the activation of an arch-effect or so-called compressive Membrane Action (CMA) which can develop even with small vertical deformations. For a slab which is completely restrained, the presence of reinforcement becomes of lesser importance when this phenomenon is activated (except for end fields). Hence, for fire resistance purposes, it can be discussed whether reinforcement and concrete cover has a smaller influence on the bearing capacity for slabs subjected to fire which exhibit a significant concrete compressive Membrane behaviour. This paper presents a loading test performed on a real concrete building which highlighted the development of CMA as the load bearing mode. It then proposes a strategy to evaluate the behaviour resulting from the development of CMA in reinforced concrete slabs at ambient and at elevated temperature based on numerical modelling. The numerical analyses are performed with the finite element software SAFIR® using a strip of layered shell elements. A plastic-damage constitutive model with an explicit transient creep formulation is used to capture the concrete behaviour at elevated temperature