Rupture Of Reinforcement Research Articles

Comparison of copper-based composites fabricated by cross-accumulative roll bonding method for packaging design

Copper-based composites have interesting properties and they are widely used in electronics, packaging, and automotive applications. In the present work, the cross-accumulative roll bonding (CARB) process was used to fabricate Cu-based composites with Zn and Brass reinforcing layers. The experimental observations revealed a clear relationship between rolling strain and plastic instabilities including the necking and rupture of reinforcement. However, the grain refinement was observed on Cu, Zn, and Brass layers after seven CARB cycles, indicating the positive impact of rolling rotation on obtaining the ultrafine grains. Better ductility of Brass also resulted in finer grains. This also led to more significant improvement in mechanical properties. During the CARB process, the hardness of Zn and Brass increased from 59 HV and 250 HV to 89 HV and 310 HV, respectively.

Experimental investigation on the shear performance of hybrid structures comprising textile reinforced concrete stay-in-place formwork and reinforced concrete

Recently, the application of textile-reinforced concrete (TRC) in thin-walled precast structures has gained significant attention. Among these innovations, the combination of TRC and reinforced concrete (RC) has emerged as an effective method for creating hybrid structural systems. This paper presents the experimental results analyzing the shear behavior of a hybrid deck slab structure consisting of TRC stay-in-place (SiP) formwork and RC components. Shear performance was evaluated using 3-point bending tests on four large-scale specimens with aspect ratios (a/d) varying from 1.6 to 2.3. The average load carried by the TRC SiP formwork prior to failure—due to textile reinforcement rupture—was approximately 26.3 kN, with compressive strains at the top edge ranging from 2.8 to 3.4 ‰, just below the concrete's ultimate strain. The findings demonstrate the versatility of TRC SiP-formwork, highlighting its adaptable cross-section and substantial load-bearing capabilities, making it particularly suitable for composite bridge deck applications. The specimens experienced both shear compression and diagonal shear failures. Moreover, the TRC SiP-formwork effectively mitigated transverse cracking at the interface, enhancing bond strength and improving overall structural performance

Ultimate bearing capacity of geosynthetic reinforced soil abutment centrifuge model tests

Five centrifuge models of geosynthetic reinforced soil (GRS) abutments with segmental block facing were loaded in the acceleration field under plane strain condition. Influencing factors including reinforcement tensile strength, setback and bearing area width were considered and analysed. Results show that the abutment with stronger reinforcement remained stable under the maximum loading capacity. However, abutments with weaker reinforcement showed excessive vertical strain, local deformation or even collapse. The ultimate bearing capacity increased with the lengthening of setback but decreased due to a larger bearing area. The rupture of reinforcements was observed and considered as the cause of the failures. Compared with the measured ultimate bearing capacity, the values calculated by the semi-empirical formula of design guidelines were significantly conservative. The failure surface of failed abutment developed from the rear edge of the bearing area to the middle height of the abutment at an angle of nearly 45° + φ/2. The setback and the bearing area width affected the form and position of the failure surface. The difference between the potential failure surface predicted by available methods and the measured failure surfaces has been discussed, and suggestions for the design and ultimate bearing capacity prediction of GRS abutments with segmental block facing are provided.

Physical and Numerical Models of Mechanically Stabilized Earth Walls Using Self-Fabricated Steel Reinforcement Grids Applied to Cohesive Soil in Vietnam

Mechanically stabilized earth (MSE) walls have been widely applied in construction to maintain the stability of high embankments. In Vietnam, imported reinforcement materials are expensive; thus, finding locally available materials for MSE walls is beneficial. This study examines the behavior of an MSE wall using local reinforcement materials in Danang, Vietnam. The MSE was reinforced by self-fabricated galvanized steel grids using CB300V steel with 3 cm ribs. The backfill soil was sandy clay soil from the local area with a low cohesion. A full-scale model with full instrumentation was installed to investigate the distribution of tensile forces along the reinforcement layers. The highest load that caused the wall to collapse due to internal instability (reinforcement rupture) was 302 kN/m2, which is 15 times greater than the design load of 20 kN/m2. The failure surface within the reinforced soil had a parabolic sliding shape that was similar to the theoretical studies. At the failure load level, the maximum lateral displacement at the top of the wall facing was small (3.9 mm), significantly lower than the allowable displacement for a retaining wall. Furthermore, a numerical model using FLAC software 7.0 was applied to simulate the performance of the MSE wall. The modeling results were in good agreement with the physical model. Thus, self-fabricated galvanized steel grids could confidently be used in combination with the local backfill soil for MSE walls.

ПРИЧИНЫ ПОВРЕЖДЕНИЙ БАЛКОННЫХ ПЛИТ ЖИЛЫХ ДОМОВ

The main cause of defects and damage to balcony plates can be considered the so-called temporary factor, which has a far from positive effect on the general state of the structure - the impact of atmospheric-sphere precipitation, strong temperature differences. In addition to the temporary factor, the destruction of the balcony slab can be influenced by mistakes made during installation, no drains and overstrain of the balcony slab due to excessive load on it, which causes the formation of cracks. The basis for the survey was the check of the technical condition of the balcony slabs of a three-story multi-storey brick residential building in order to determine the degree of wear, possible defects and assess the possibility of further operation of the slab. A structural solution analysis was carried out to assess the technical condition of the building structures. Loads acting on the structures, impacts and operating conditions, the quality of structures, materials and connections were established. This also took into account factors such as the geometric dimensions of structures and their sections; presence of cracks, splits and destruction; condition of protective coatings; broken adhesion of reinforcement to concrete; presence of reinforcement rupture; condition of anchoring of longitudinal and transverse reinforcement; degree of corrosion of concrete and reinforcement. As a result of visual and measuring control, defects and damages having the requirements of operation and leading to a malfunction of the structure were revealed. The results set forth in the article may be of interest to specialists of expert organizations who are engaged in the examination of residential apartment buildings in order to assess the actual state of bearing structures, in particular balcony slabs

Fractographical Characterization of Jute Fibre Reinforced Paper Composite Subjected to Drop Test

Plastic bags are one of the most widely used packaging materials in industries. Lower production cost, lightweight and high strength envisage its use in food packaging, carrier, and transportation industries. However, these plastic bags are non-biodegradable and cause serious water and soil pollution. It is one of the most thrust areas of research to overcome this problem in the current world. In the present investigation, fabrication, and characterization of an environmentally friendly and biodegradable "jute fibre reinforced paper composite" and "reinforcement free paper laminate" subjected to drop test were done. The standard procedure of the "MIL-STD-810G 516.6" drop test was followed. The adhesion between the matrix (paper) and reinforcement (jute fibre) was produced by applying a chemical-free adhesive made of flour and water. There were four different types of samples: single paper (SP), reinforcement-free paper laminate (RFPL), single-layer jute fibre reinforced paper composite (SLJPC), and double-layer jute fibre reinforcement paper composite (DLJPC). The microstructural characterization of the fractured surface after the drop was done using a scanning electron microscope operated at a voltage of 20 kV. The DLJPC samples had the maximum density and envisage drop-strength of 7 times as compared to the SP samples having the lowest density. The drop-strength exhibited linear regression with density for all the samples. The microstructure of the as-received matrix showed a non-homogeneous distribution of fibres along with micro-voids which were susceptible sites for the fracture. Unlike as-received matrix fibres distribution, the reinforcement fibres were aligned in two mutually perpendicular directions which leads to its strengthening. Hence, it can be said that the non-uniform structural properties envisaged by the as-received matrix can be compensated by uniformly distributed structural properties of the as-received reinforcement when both come together as a composite. The primary fracture mechanism of SP samples exhibited fibre breaking along with a few fibres' delamination. However, in the case of the RFPL sample, the nature of adhesion applied was capable to hold both the interfaces and the primary fracture mechanism was fibre breaking. It is suggested that the adhesive applied transmitted load through the interfaces. Unlike SP sample, the RFPL sample exhibited some adhesive pull-off. The fractured surface of the SLJPC sample showed that the matrix did not subject to fracture, however, reinforcement did fracture hence the load was transferred from matrix to reinforcement followed by a rupture of the reinforcement. Therefore, the primary fracture mechanism for the SLJPC sample was reinforcement rupture. The DLJPC sample showed a delamination of matrix and reinforcement.

Post-Earthquake Strengthening of RC Coupling Beams with GFRP Wrapping: Experimental Investigation.

This research aims to address a post-earthquake urgent strengthening measure to enhance the residual seismic capacity of earthquake-damaged reinforced concrete wall structures with coupling beams. The study consists of a series of tests on half-scale prototype coupling beams with various detailing options, including confined with reduced confinement, partially confined, and unconfined bundles, under cyclic loading conditions. The methodology employed involved subjecting the specimens to displacement-controlled reversal tests, and carefully monitoring their response using strain gauges and potentiometers. The main results obtained reveal that GFRP wrapping significantly enhances the seismic performance of earthquake-damaged coupling beams, even in cases where specimens experienced strength loss and main reinforcement rupture. The strengthened beams exhibit commendable ductility, maintaining high levels of deformation capacity, and satisfying the requirements of relevant seismic design codes. The significance of the study lies in providing valuable insights into the behavior and performance of damaged coupling beams and assessing the effectiveness of GFRP wrapping as a rapid and practical post-earthquake strengthening technique. The findings can be particularly useful for developing urgent post-earthquake strengthening strategies for high-rise buildings with structural walls. The method may be particularly useful for mitigating potential further damage in aftershocks and eventual collapse. In conclusion, this study represents a significant advancement in understanding the post-earthquake behaviors of coupling beams and provides valuable guidance for practitioners in making informed decisions regarding post-earthquake strengthening projects. The findings contribute to the overall safety and resilience of structures in earthquake-prone regions.

Ductility evaluation and flexural failure mode recognition of reinforced Ultra-High performance concrete flexural members

Although ultra-high performance concrete (UHPC) exhibits material tensile ductility far in excess of that expected from conventional or high-strength concretes, structural UHPC members typically fail in flexure due to reinforcement rupture after crack localization, which may result in a low structural ductility. In the flexural design of reinforced UHPC (R-UHPC) members, attention should be paid to addressing the issue related to the low structural ductility due to crack localization. This study firstly develops a two-dimensional numerical model to simulate the flexural response of R-UHPC beams, and the numerical results agree well with the experimental results of the load–deflection curves as well as the failure modes. Parametric analyses are then carried out to examine the effect of the flexural reinforcement ratio, tensile strength of steel reinforcement, tensile behavior of UHPC and compressive strength of UHPC on the flexural failure mode and ductility behavior of R-UHPC members. The results indicate that when the failure is controlled by fracture of tensile steel bars after crack localization, higher reinforcing ratio, higher steel post-yield hardening strength, and lower steel fiber volume lead to more ductile behavior. When the failure is controlled by crushing of UHPC, however, higher reinforcing ratio and lower UHPC compressive strength lead to a lower ductility. In addition, a flexural failure mode recognition method is proposed for R-UHPC flexural members, whose accuracy is verified based on the available experimental results of 105 R-UHPC flexural members. Finally, a minimum flexural reinforcement ratio is proposed to avoid low structural ductility in R-UHPC flexural members.

Mesoscale simulation of compression-induced cracking and failure of ASR-damaged concrete with stirrup confinement

The alkali-silica reaction (ASR) is a durability concern that can lead to expansion and cracking of concrete structures. ASR damage affects the physical characteristics of the concrete itself, although the load-carrying capacity of an RC structure may be maintained because the reinforcement continues to confine the core concrete. However, if the combined effect of expansion damage and external loading were to result in reinforcement rupture, this would prejudice the safety of a structure. To study this phenomenon, the discrete numerical simulation method 3D RBSM is used to carry out a parametric study of the compressive failure of concrete with three ASR damage levels under confinement. Stirrups with normal yield strength and with elastic behavior are investigated. The ASR expansion and cracking behavior for concrete with different confinement scenarios are presented and discussed. Following that, the compressive failure of concrete with ASR damage and the effect of stirrup confinement are studied. The simulated stress–strain relationships for cases without ASR damage are well fitted by a theoretical prediction model. As for elastic modulus and compressive strength, it tends to decrease with increasing ASR expansion whatever the confinement conditions. For models confined by stirrups, the degradation of compressive strength is delayed. Visualizations of internal stress, concrete crack propagation and stirrup strain development are obtained from the simulations and these are discussed. It is found that the confinement effect of elastic stirrups is greater than that of stirrups with normal yield strength. Further, the strain distribution on inner and outer surfaces of stirrups which is hard to be monitored in experiments is extracted. Stress concentrations arise at the inner radius of the stirrup bends, which is consistent with observations of real structures and could lead to rupture at these locations.

Effect of fatigue loading on flexural performance of NSM CFRP-strengthened RC beams under different service temperatures

This paper presents an experimental work to investigate the effect of fatigue loading and high service temperature on the flexural performance of near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The experimental program included 11 beams, where the effect of the strengthening (CFRP) ratio (0.06 % and 0.18 %), fatigue load level (R1 = 0.57 and R2 = 0.38) and applied temperature (20 °C and 70 °C) have been considered. Experimental results on fatigue tests showed that high service temperature resulted in an increase in deflections and reduction in the stiffness of the specimens along the test. Moreover, the application of fatigue cycles with larger amplitude resulted in the failure of the specimens (by steel rupture), whilst specimens submitted to lower fatigue amplitude survived to the fatigue cycles. The NSM CFRP-strengthening helped to postpone the final failure of strengthened RC beams after steel reinforcement rupture during the fatigue test. Besides, damage due to fatigue derived in lower residual yielding and ultimate load in the post-fatigue test.

Pre‐ and post‐yield bond, tension‐stiffening, and cracking in ultra‐high performance fiber reinforced concrete

AbstractIn reinforced concrete elements, tension‐stiffening strongly influences deflections and crack‐widths at the serviceability limit, and plastic hinge rotation at the ultimate limit. Modeling has shown the impact of tension‐stiffening at the ultimate limit to be particularly important when ultimate failure is governed by reinforcement rupture, which has been is common in ultra‐high performance fiber reinforced concrete (UHPFRC) elements. It is further known that the magnitude of tension‐stiffening and crack opening is proportional to both the reinforcement ratio of the tension chord and the diameter of the reinforcing bar. Despite this understanding, very little testing has been undertaken to quantify the bond between larger diameter reinforcement and UHPFRC and also on the resulting impact to tension‐stiffening and concrete cracking. To address these issues, in this paper a series of bond and tension‐stiffening tests are undertaken on ultra‐high performance concretes both with and without steel fibers. The result of the experiments is used to develop a local bond stress slip relationship applicable to both pre‐ and post‐yield. When implemented in a partial‐interaction model, it is shown that the new bond model can be used to predict pre‐ and post‐yield tension‐stiffening and crack‐widths.

Nonlinear truss models for strain‐based seismic evaluation of planar RC walls

AbstractThis paper introduces a new approach for the seismic performance evaluation of planar RC walls. Compared to existing assessment guidelines, such as those in ASCE/SEI 41‐17, where performance limits are described by plastic rotation or lateral drift, the proposed method uses local (strain) quantities, obtained from computational models. The analyses rely on a user‐friendly implementation of the nonlinear truss model for RC structures, which eliminates the need to manually create a line‐element representation of a wall and includes a material law for steel accounting for buckling and rupture of reinforcement. The capability of the models to capture common failure patterns for planar walls is validated for a set of six previously tested wall components which experienced a variety of damage modes (bar rupture, boundary element failure, diagonal compression and tension failures). The analytical models accurately predict the lateral strength, deformation capacity and failure modes observed in the tests. A set of acceptance criteria, based on the analytically obtained concrete and steel strains, is then established for the immediate occupancy, life safety and collapse prevention levels, consistent with different levels and types of damage. An initial calibration of the limit values associated with these criteria is proposed and verified using the analytical results for the six walls considered. The results of the proposed assessment methodology applied to the six walls are compared to those obtained using the nonlinear procedures in ASCE/SEI 41‐17. The results indicate that ASCE/SEI 41‐17 may not accurately describe the deformability of walls exhibiting mixed flexure‐shear inelastic deformations.

Quantification of model uncertainties of the energy-based method for dynamic column removal scenarios

The Alternative Load Path (ALP) method is widely used to assess progressive collapse resistance of reinforced concrete (RC) structures by notional removal of one or more load-bearing elements. In general, a nonlinear time history analysis (NTHA) is needed to perform such an analysis if dynamic effects are explicitly taken into account. To avoid cumbersome nonlinear dynamic analyses, the energy-based method (EBM) is a promising technique to predict the maximum dynamic responses of a structural system. In this article, the accuracy and precision of the EBM is evaluated based on a validated finite element model of a tested RC slab subjected to a sudden column removal scenario, in particular in relation to the investigation of tensile membrane action (TMA). Influences of dynamic effects are evaluated, i.e. in relation to strain rate effects, damping, and the time duration of support removals. Strain rate effects are observed to have only slight influences on the dynamic responses. The strain rate dependency of reinforcement is found to have a more significant influence on the responses in TMA stage, although also to a limited extent. The magnitude of the load has a significant influence on the dynamic response, as do increasing damping ratios due to the corresponding significant energy dissipation. Finally, the dynamic response reduces with increasing time duration of the column removal. Based on the results of the stochastic analyses, the EBM is observed to perform well based on a comparison with the results of NTHA in both flexural and TMA stages. Furthermore, in relation to the analyzed case studies on reinforced concrete slabs, the model uncertainty of the responses obtained through the EBM compared with the NTHA is found to be represented well by a lognormal distribution with mean of 0.95 and a standard deviation of 0.20, for evaluating the loads of first rupture of reinforcement. Furthermore, a lognormal distribution with mean 0.96 and standard deviation 0.13 is found appropriate to represent the model uncertainty on ultimate load-bearing capacity predictions. Model uncertainties are also obtained with respect to the model predictions for displacements at the moment of the first rupture of reinforcement, displacements at the ultimate load-bearing capacities, and both loads and displacements at second load peaks.

Numerical Verification of the Use of GFRP Reinforcement in the Ceiling Slab of a Garage House

One of the major advantages of fibre reinforced polymers (FRPs) is their high tensile strength and low weight to strength ratio. Compared to steel reinforcement, this is one of the main and decisive features that could determine the choice of materials used in the design. Since there is no corrosion for this type of reinforcement, it is very suitable for concrete structures in aggressive environments. This point, along with others, gives concrete structures reinforced with FRPs significant advantages over conventional concrete structures with steel reinforcement. Different material properties and behaviour of FRP when compared to steel reinforcement result in the need of the modification of established design procedures, especially in the area of the ultimate strain, because FRP reinforcement has a different σ-ε diagram than the steel reinforcement. The experimental verification of the new design procedures is necessarily needed. This paper summarizes the results of practical design and calculations of the resistance of alternatively steel and GFRP reinforced concrete ceiling slab of a garage house and experimental results on the beam specimens reinforced with GFRP reinforcement tested under four-points test. It was necessary to adjust the conventional procedures in calculating the required area of GFRP reinforcement in order to avoid brittle failure of the cross-section (rupture of reinforcement). This is ensured by abiding the balance reinforcement level. Another fact to be considered is the creep rupture phenomenon causing immediate rupture of GFRP reinforcement under a high level of sustained loading. The reduction of GFRP strength according to the long-term loading results in rising required area of reinforcement. Finally, the serviceability limit state is checked. According to the low modulus of elasticity of GFRP reinforcement, the deflection should be the limiting factor for the amount of reinforcement designed.

Fatigue behavior of RC beams strengthened with FRP considering the influence of FRP-concrete interface

As an indispensable component of structure strengthened with FRP, the bond behavior of FRP-concrete interface is very important. In this paper, a theoretical model is established to analyze fatigue behavior of FRP-strengthened RC beam, and the bond-slip relationships are unified into one model. Two failure criteria are proposed according to steel reinforcement rupture and the intermediate crack-induced (IC) debonding. Through the theoretical model, the theoretical results show that the failure mode changes from the steel reinforcement rupture to the IC debonding as the peak loading increases. Therefore, the fatigue life prediction is more accurate by considering the corresponding failure modes.

On the dynamic response of reinforced concrete beams subjected to drop weight impact

To improve the impact resistance of reinforced concrete structures, a detailed understanding of the dynamic response is required. This study investigates this impact resistance using experiments in combination with 3D non-linear finite element (FE) simulations. The experiments made use of high-speed photography and digital image correlation (DIC), while a damage-plasticity constitutive model for concrete was used in the FE simulations. Drop weight impact tests of simply supported reinforced beams made of plain concrete and fibre reinforced concrete were made, and it was shown that the addition of fibres reduced crack spacing, crack widths and mid-point deflections. For the FE approach, tetrahedral elements were shown to be well suited for capturing inclined shear cracks and the structural response obtained in experiments and analyses agreed very well. The FE analyses showed that the reinforcement strains were more localised for concrete with fibres, and hence predicted an increased risk of reinforcement rupture.

Seismic Bearing Capacity of Strip Foundations on Fiber-Reinforced Granular Soil

The present study investigated the bearing capacity of strip footings on a bed of granular fiber-reinforced soils. Analyses were performed by the stress characteristics method (SCM). The failure criterion considers anisotropic distribution of fiber orientation and ignores the rupture of reinforcements. Seismic effects were included in the stress equilibrium equations as the horizontal and vertical pseudo-static coefficients. Stress equilibrium equations were solved by the finite difference method. A computer code was provided to solve the problem. Using the soil and reinforcement input parameters, the code determines the characteristics network and calculates the bearing capacity. The bearing capacity was expressed as the bearing capacity factors of the soil unit weight and surcharge. Parametric analysis was performed to investigate the effect of soil and reinforcement parameters on the bearing capacity and the shape of the failure zone. The outcomes indicated that the SCM results lower ultimate bearing capacity as compared with the upper bound method. Also, the depth of the failure zone increases with an increase in the amount of reinforcement or decrease in the horizontal seismic coefficient. Considering the anisotropic distribution of fiber orientations leads to more bearing capacity than the isotropic distribution.

Jute fabric as a reinforcement for rammed earth structures

This paper reports the results of an experimental campaign that aims at evaluating the capability of a composite made of jute fabric and stabilized earth matrix to act as a reinforcement of earth structures, and the analytical models able to interpret the results. Preliminary studies carried out in order to test adequate reinforcement systems for earthen structures, demonstrated that jute fabric applied with a stabilized earth plaster, among other natural fibers or systems, is able to develop exceptional adhesion and adequate stiffness. However, the collapse mechanisms observed seems to favor the rupture of reinforcement rather than the crisis of adhesion usually observed when dealing with artificial FRC reinforcements. It was necessary to step back to the theories of adhesion to plan the experimental analysis of the jute reinforcement for rammed earth structures. The poor material, the fact that adhesive and support are almost the same material (differing only for grain size, density and a small amount of gypsum), the difficulty in measuring fabric properties, strength and, most of all, local deformation and fracture energy in earthen materials, induced to define a specific procedure. The uncertainties connected to the determination of mechanical parameters were overcome both using statistical approach and numerical analysis of data, and reducing the number of parameters necessary to the analysis, that is turning to simple adhesion models.

Investigation of failure mechanisms and development of design recommendations for flexural reinforced concrete walls

For many mid- and high-rise concrete buildings in seismic regions, earthquake loads are resisted by reinforced concrete walls that respond primarily in flexure (i.e. yielding in flexure without exhibiting significant shear damage or shear failure). Under lateral loading, flexural walls may sustain compressive damage to concrete and reinforcing bars as well as tensile rupture of reinforcement, with the onset of lateral strength loss resulting from one or more of these damage mechanisms. Given the prevalence of concrete walls, there is interest in advancing numerical modeling to enable improved prediction of wall response as well as in advancing wall design and detailing to achieve enhanced performance. The research presented here does both. First, modeling recommendation for nonlinear finite element analyses were developed and validated using data from prior laboratory tests of large-scale structural walls. Second, the validated modeling approach was used to conduct a parametric study to investigate the impact of two critical design parameters, normalized shear stress demand and cross-sectional aspect ratio, on the deformation capacity corresponding to onset of lateral strength loss. Few tests have considered the larger cross-sectional aspect ratios and shear stress demands that are common in design of modern walls. Results of this study show that walls with large cross-sectional aspect ratios and moderate to high shear demands develop high minimum principal stresses within the web region of the wall at the web-boundary element interface; these high stresses can lead to lateral strength loss at relatively low drift levels due to concrete crushing and bar buckling within the web. This failure mode is termed a compression-shear failure. The third phase of the study used the validated modeling approach to conduct a parametric study to develop a mitigation strategy for walls susceptible to compression-shear failure, namely extension of the boundary element confinement into the web of the wall. The results of this study were combined with test data to determine the confined length required to suppress the compression-shear mode. This required confined length is a function of the shear stress demand and is conservatively estimated as c, where c is the depth of the compression region when the wall achieves nominal flexural strength.

Parameters affecting tensile membrane action of reinforced concrete floors subjected to elevated temperatures

This paper numerically investigates the mechanism and influencing factors of the tensile membrane action (TMA) developed in reinforced concrete slabs at large displacements and elevated temperatures. Explicit dynamic analyses are performed using LS-DYNA. The numerical model is first validated against ambient and fire tests on simply supported slabs. It shows that the slab responses are not sensitive to the mesh size. It is found that the 30min of heating in a standard fire can be scaled down to 1 s of computing time. Parametric studies are followed to demonstrate the influence of load ratio, boundary condition, slab thickness, reinforcement layout and aspect ratio on the occurrence and development of TMA. Five failure modes of slabs, initiated by the rupture of reinforcement, are found depending on the boundary condition, reinforcement layout and aspect ratio. As the aspect ratio increases, the location of the reinforcement rupture moves from the slab center to the intersections of longitudinal and diagonal yield lines, and further extends to the corners. For the presence of horizontal restraint at perimeter, the rupture of reinforcement occurs at the longer edges of slabs. Slabs with more reinforcement placed along the long span may fail by the rupture of reinforcement along the short span at the center of the slab. The reinforcement along the short span plays a key role in the load-bearing capacity of rectangular slabs. It is found that reinforced concrete slabs may have a fire resistance of 2 h at least due to the enhancement of TMA. The critical reinforcement temperature of 600 °C is necessary to ensure the efficiency of TMA. The deflection limit of span/20 reasonably predict the failure of slabs although a slab can resist loads at a deflection up to span/12 without collapse by means of TMA. It is recommended to increase the reinforcement ratio to enhance the effect of TMA.