Behavior Of Slabs Research Articles

Experimental Study on Flexural Behavior of the Composite Bottom Slab of the Stiffened Steel Truss

In order to study the influence of rib size on the flexural performance of the new reinforced truss concrete composite floor slab, two precast reinforced concrete floor slabs and one ordinary reinforced truss composite floor slab were designed and manufactured for flexural performance tests. The failure mode of the concrete slab under uniform load was analyzed, and the influence of rib size on the flexural capacity of the floor slab was studied. The results show that the stiffening of the steel truss composite slab can significantly improve the stiffness of the precast slab and effectively solve the problem of excessive deflection of the precast slab during construction. On the basis of the experimental study, the influence of the top chord steel bar diameter, concrete rib height and rib width on the short-term stiffness of the floor is deeply analyzed by using the finite element refined modeling. The results show that the diameter of the top chord reinforcement and the width of the concrete rib are positively related to the stiffness of the composite slab, and the height of the concrete rib has little effect on the initial stiffness of the precast slab, which mainly plays a role in the later stage.

Assessment of the torsional behaviour of hollow core slabs

There are many applications in buildings in which precast pre-stressed hollow-core (HC) slabs are subjected to shear, torsion, or combined shear and torsion. Nonetheless, extruded HC units contain no transverse reinforcement, being inherently vulnerable to brittle failure modes due to shear and torsional actions. In previous work by the authors, a finite element (FE) modelling approach for HC units failing in shear was developed and validated against experimental test data. This paper aims to extend the applicability of the proposed FE approach to help improve the understanding of the torsional behavior of HC units. For this purpose, the developed model is further validated against experimental data available in the literature and then used to predict the torsional capacity of New Zealand-specific 200 mm deep HC units. Results suggest that the FE model is capable of predicting the capacity of HC slabs with and without eccentricity of the applied vertical load. Finally, the numerical results are used to evaluate the performance of available simplified analysis approaches for assessing the torsional capacity of HC units, which are found to be non-conservative if used with expected material properties.

Experimental Study on Flexural Behavior of RC–UHPC Slabs with EPS Lightweight Concrete Core

This paper presents an experimental investigation that focuses on the flexural behavior of an innovative reinforced concrete–ultra-high performance concrete slab with an expanded polystyrene lightweight concrete core. This type of slab is proposed to serve the semi-precast solution, in which the bottom layer is ultra-high performance concrete working as a formwork during the construction of semi-precast slab, the expanded polystyrene lightweight concrete layer is used for the reduction of structure self-weight, and the top layer is normal concrete designed to withstand compressive stress when the slab is loaded. Two similar large-scale specimens with dimensions of 6200 mm × 1000 mm × 210 mm were fabricated and tested under four-point bending conditions to investigate the flexural behavior of composite slab. Test results indicated that three different layers of materials can work effectively together without separation. The bottom ultra-high performance concrete layer leads to the high ductility of the slab and has a good effect in limiting the widening of the crack width by forming other cracks. According to design code ACI 544.4R, a modified distribution stress diagram on the composite section was proposed and proven to be suitable for the prediction of flexural strength of the composite section with an error of 3.4% compared to the experimental result. The effect of the ultra-high performance concrete layer on the flexural strength of the composite slab was clearly demonstrated, and for the case in this study, the ultra-high performance concrete layer improves the flexural strength of the slab by about 11.5%.

Experimental and numerical investigation on the flexural performance of RC slabs strengthened with EB/NSM CFRP reinforcement and bonded reinforced HSC layers

In this paper, one-way reinforced concrete (RC) slabs were strengthened using External Bonding (EB) and Near Surface Mounted (NSM) techniques and tested under flexural loading until failure. The area of internal and external reinforcement, shape of strengthening elements (bars, strips, and reinforced high strength concrete (HSC) layers) and strengthening method (EB and NSM) were the experimental tested variables. The experimental results showed significant increases in the load capacities of the upgraded slabs ranging between 133.8% and 264.5% compared to their corresponding un-strengthened slabs. Consequently, the NSM technique showed higher load efficiency than the EB, even though they had nearly the same strengthening properties and area. Compared to the control slab, using NSM strips instead of EB strips or NSM bars amplified the slab load capacity by about 51.7% and 33.2%, respectively, while using NSM HSC layer instead of EB HSC layer increased slab load capacity by 74.7%. Moreover, doubling the area of EB strips improved the load capacity by 10.3%, while increasing the internal steel area by 195% enhanced the slab load capacity by 21% to 48 %, depending on the strengthening method. However, depending on the distance between internal and external strengthening elements the cracks were initiated at the ends of the strengthening element causing the slab shear failure at dissimilar loads. Finally, a verified finite element (FE) model was built to study the effect of bond length, material, and area of the strengthening element on the slab behavior.

Design Procedures for Predicting Long-Term Responses of Continuous Steel–Concrete Composite Slabs

Although the effect of nonuniform shrinkage on the time-dependent behavior of simply supported composite slabs has been extensively investigated, continuous composite slabs have not garnered enough attention. This paper aims to propose the routine design procedures for continuous composite slabs, including the hogging moment over the interior support and the mid-span deflection. Thus, the long-term test data on two-span continuous composite slabs provided by the authors and the related literature were collected to benchmark the current design methods in international specifications. The routine design procedures for calculating the long-term moment distribution and the mid-span deflection of two-span composite slabs were proposed considering the time-dependent range of hogging moment zones. Moreover, the effects of different shrinkage distributions and hogging moment ranges on the long-term performance of these slabs were further quantified. The results showed that the mid-span deflection and the hogging moment over the interior support increased significantly over time; both could not be accurately predicted using the typical design methods described in international specifications. The hogging moment declined by 28.0% when a uniform shrinkage profile was adopted for the design of composite slabs, and the mid-span deflection decreased by 15.0% when a constant range of the hogging moment zones was used. The design procedures proposed herein well described the long-term behavior of continuous composite slabs by accounting for the combined effects of the nonuniform shrinkage and time-dependent hogging moment range. The calculated hogging moment and mid-span deflection differed from the measured ones on average by 2.0% and 9.0%.

Behavior and Load Capacity of Concrete Slab Reinforced by CFRP Bar and Strengthening by CFRP Laminates

Abstract The most common FRP materials used are carbon fiber reinforced polymers (CFRPs), and glass fiber reinforced polymers (GFRPs). The use of CFRPs has grown rapidly in the construction industry, specifically in structural retrofitting, due to their strengthening property of CFRP. CFRPs are moreover high strength, lightweight, noncorrosive, and easy-to-install materials. In the present study, six reinforced concrete slab specimens included two control specimens reinforced by traditional steel reinforcements and the other reinforced by carbon fiber reinforced polymer CFRP bars without strengthening by laminated CFRP strips. The remaining four specimens are interiorly reinforced by CFRP bars and strengthened by CFRP laminates strips with different scheme layouts named Type 1 and Type 2. The specimens were tested under a uniformly distributed load applied at the top surface area of each specimen up to failure. The parameters considered in the present study are the amount of CFRP bars and CFRP laminates layout. Test results indicated that the strength carrying capacity and failure mode of tested specimens differ based on the steel reinforcement type and the presence of CFRP laminates layout.

The oedometric EOS of equal strength and different mix compositions concrete specimens

The uniaxial compressive strength of concrete is commonly used to characterize concrete properties. The three-dimensional behavior of concrete structures is modelled by the hydrostatic and deviatoric relationships. These relationships are assigned to a given concrete according to its uniaxial compressive strength. Based on high velocity penetration test results at targets with identical concrete strength, that were prepared from different mix designs, the authors conjectured that the slab behavior is not governed by the uniaxial compressive strength but by the concrete composition.This paper presents an experimental investigation of concrete specimens of equal uniaxial compressive strength, that are made from different mix compositions, aiming at examining the equation of state (EOS) and its relationship to the uniaxial compressive strength and to several mix components, in attempt to validate the above conjecture.A set of specimens was prepared characterized by equal uniaxial compressive strength (fc = 56 MPa) measured on 100 mm sided cubes. Several specimen groups were tested, each of them made from a different composition. The mix variables were the weight of water (and the corresponding weight of cement), the aggregates weight and the maximum aggregate size. The specimens were tested in a special triaxial apparatus, to high load-levels (up to 5000 kN), at a quasi-static rate of ∼ 5 kN/sec. Test results show a wide scatter of the EOS curves, depending on the different mix parameters. These results refute the commonly assumed correlation between the uniaxial compression strength and the EOS and validates the conjecture that the EOS depends on the specific concrete mix composition.

Capacity and failure modes of restrained hollow core slabs taking into account compressive membrane action

AbstractThe formation of compressive membrane action in restrained precast concrete hollow core slabs is investigated, and how it affects the load bearing capacity and failure mode under excessive loading. To this end, attention is oriented to a recently completed experimental campaign specifically aimed at quantifying this phenomenon in real‐scale hollow core slabs. The outcomes of this experimental campaign are then analyzed using a validated finite element model, to further study the effects of compressive membrane action on the structural behavior of hollow core slabs. From the numerical evaluations, it can be concluded that the ultimate capacity and failure mode of restrained hollow core slabs strongly depend on the restraint conditions, as well as the span‐to‐depth ratio. The results also indicate that in some cases the failure is caused by crushing of concrete in the top flange, which is typically not observed in case of simply supported boundary conditions. Additionally, the influence of the inherent uncertainties associated with material properties and geometry on the ultimate capacity and failure mode of restrained hollow core slabs is investigated. Probabilistic model evaluations are performed for a wide range of boundary conditions. The results indicate a very high influence of the uncertainty on the concrete tensile strength on the membrane action in precast hollow core slabs.

Seismic Analysis of a Multi-Storey Building with Different Types of Slabs

Earthquake plays an influential role in the analysis and design of structures. Unless the structures are designed and constructed to withstand seismic forces, failure cannot be avoided. Buildings can be made seismically sound with proper structure design, detailing and construction practice. The configuration of a building is very much important for the seismic performance of buildings. The important aspects that affect the seismic configuration of a building are overall geometry and structural system. This parameter varies in their behaviour in the flat slab, waffle slab and conventional slab. Therefore introducing different types of slabs becomes very crucial for a structural engineer when it comes to better performance of RC structure. The objective of this paper is to study the seismic behaviour of multi-storeyed buildings with different types of slab systems. The study is done by considering the varying number of stories i.e. low-rise, mid-rise and high-rise buildings. The study aims to find an effective slab system for both regular and irregular structures. The different types of slabs considered are flat plate system, flat slab with drop system and waffle slab system which is compared with the conventional slab system. Seismic assessment using response spectrum analysis is done. For low-rise to high-rise buildings, the seismic behaviour of the waffle slab is more effective.

Behavior of Unbonded Post-Tensioned Concrete Slabs Exposed to Fire

Behavior of Unbonded Post-Tensioned Concrete Slabs Exposed to Fire

Numerical and Experimental Behavior Analysis of Slabs Strengthened Using Steel Plates and Slurry-Infiltrated Mat Concrete (SIMCON) Laminates

This study has two main aims; firstly, investigating the behavior of slabs that are strengthened with different types of reinforcements and with Slurry-Infiltrated Mat Concrete (SIMCON) laminates, having different dimensions and thicknesses and subjected to static and dynamic (impact) loads. Secondly, the development of a non-linear finite element (FE) model to simulate the behavior of the tested slabs utilizing the ABAQUS/Standard package. The modeling of the NSC slabs strengthened with either SIMCON or steel plates involves using three-dimensional solid elements that are partially integrated with the modeling of concretes using the 8-node brick element (C3D8R). The results of the experimental and numerical investigations are compared to examine whether the slab modeling is sufficient. The comparison includes the element type, material characteristics, real constants, and convergence study. The predicted ultimate load-carrying capacity versus vertical deformation response is compared with the lab results that correspond with it, as obtained via the FE analysis of all tested slabs. In addition, the results of the FE analysis of slab specimens that are strengthened with steel plates were compared to the results of the ones strengthened using SIMCON laminates. The obtained results have led to a number of significant observations. Considering the punching shear strength, it was found that using SIMCON strengthening in different dimensions increased the slab’s punching shear capacity and outperformed steel-strengthened slabs. As for the plate stiffness, SIMCON-strengthened slabs presented higher stiffness rates than steel-strengthened slabs, to the extent that even 20 mm SIMCON strengthening outperformed the steel plate-strengthened slabs of any thickness or dimensions. The axial load-displacement relationships indicate that all the numerical models show a stiffer behavior when compared with the experimental axial load-displacement relationships. The slab thickness of SIMCON significantly affects the load-carrying capacity, and it increases with the increase in thickness. Likewise, using strengthening from steel plates gives a higher load-carrying capacity. Finally, since the results of the yield line analyses for these slabs are found to match the experimental results closely, this method is considered to be suitable for practical use in determining the strength of plated slabs. Therefore, the conclusion is drawn that the proposed FE model can be sufficiently used in evaluating the dynamic responses of slabs strengthened with SIMCON or steel plates and subjected to cyclic and impact load.

Insulation effect on post-earthquake fire punching shear behavior of slab–column connections

Insulation effect on post-earthquake fire punching shear behavior of slab–column connections

Development and investigation of an innovative, light-weight, two-way spanning timber-concrete composite slab

Timber-concrete composite (TCC) slabs play an essential role in modern timber construction. Consisting of a timber member in the tension zone, a concrete layer in the compression zone and a shear connection between the two parts, TCC slabs feature a number of advantages that make them ideally suitable for use in both office and residential buildings. However, currently used TCC slab systems carry loads only in one direction. In the frame of a large research project in cooperation with the industry, an innovative, light-weight, two-way spanning timber-concrete composite slab using beech laminated veneer lumber with steel tubes as connectors was developed. This paper presents the main results of the research project. First, the structural behaviour of the connection is characterised and discussed based on extensive experimental and analytical analysis. Second, the load-bearing behaviour of the TCC slab investigated in uniaxial bending tests is presented. The uniaxial bending tests showed a remarkably ductile global load-bearing behaviour due to the ductile failure mode in the connectors. A developed analytical model can describe the observed load-bearing behaviour of the tested TCC members accurately. Finally, the biaxial load-bearing behaviour of the TCC slab is characterised and discussed based on a large-scale experiment that allowed to perform static and dynamic tests on the same specimen in different support conditions. A substantial increase in stiffness and fundamental frequency in biaxial versus uniaxial support conditions was observed and accurately modelled, showing the great potential of the novel TCC slab.

Experimental and simulation analysis of thermal behavior of large‐span roof system under solar radiation

SummaryThe large‐span metal roof systems can produce a significant nonuniform temperature effect under solar radiation, leading to potential safety hazards. An experiment is conducted to study the nonuniform thermal behavior of a small‐scale continuous welded stainless steel roof (CWSSR) system under solar radiation. The small‐scale CWSSR system considered different roof slopes and sunward side and nightside. The efficiency of the numerical analysis of the thermal behavior of the roof slab is verified in comparison with the experimental results. Based on the numerical and experimental results, the thermal effect of a full‐scale CWSSR system is studied under different orientations, wind speeds, and atmospheric temperature. Through the analysis of research results, the nonuniform thermal features of the CWSSR system are significant and cannot be overlooked. The temperature difference between the sunward side and nightside roof slab is positively correlated with the roof slope. The thermal behavior of the CWSSR system is greatly influenced by wind speeds but is less affected by orientations and atmospheric temperature.

A comparative review on bubble-voided reinforced concrete slab – An innovative concept for lightweight concreting

The bubble-voided reinforced concrete (RC) slab is a relatively new concept of light-weight concreting, introduced to the industry. In this concept, the consumption of unnecessary concrete between the tension zone and the neutral axis, inside a RC slab (one-way or two-way), can be avoided by the introduction of voids at that very zone in the form of hollow plastic bubbles. The bubble-voided slab is lightweight in comparison to the solid slab, and self-weight can effectively decrease upto 30% to 40%, through the application of spherical voided-formers. Although, the bubble-voided slab’s load capacity is slightly less, compared to the equivalent solid slab. But, unlike the hollow-core slab, bubble-voided slab performs well against bi-axial loading. As, the concrete consumption is less in bubble-voided slabs, so less amount of cement needs to be manufactured, and, this way, the bubble-voided concreting method can indirectly be beneficial in reducing the Carbon-Di-Oxide (CO2) emission in the atmosphere. The bubbles can be made of plastic waste, which is an innovative way to recycle that waste plastic to use in industry, and, also reduce plastic wastage from the nature. So, it can be understood that bubble-voided concreting is very much eco-friendly. The present authors have explored through the evolution in the researches on the bubble-voided concrete slab, and, discussed about the critical findings of previous researchers. A comparative discussion is also, presented in this study on various input parameters and load vs deflection curves presented in previous studies. The comparisons showcase that the depth of slab (DS), grade of concrete, and, percentage of void, are the key factors which influence the load vs deflection behaviour of bubble-voided RC slabs. Future scopes in this field of study are identified, such as, studies on the effect of thermal loading, impact loading, and, cyclic loading on the bubble-voided RC slabs.

Efficiency of shear studs manufactured from threaded bars on the punching behavior of flat slabs

Punching resistance in flat slab systems in reinforced concrete structures is often provided with drop panels or shear reinforcement around columns. Shear studs are effectively used in these structures as shear reinforcement. However, factory-made shear studs may not be available in all locations and small quantities for small projects. Therefore, cheap shear studs that can be manufactured from widely available materials in small quantities can be very useful in certain cases. In this study, shear studs manufactured from threaded bars, widely available in hardware stores, are used for providing punching resistance to flat slabs. Stud heads were formed with T-section nuts. Four slab specimens, two with shear studs and two without, were cast and tested under concentrated loads at their mid-point. The slabs had 2150×2150×150 mm dimensions and they were cast with two different longitudinal reinforcement ratios. Test results showed that manufactured shear studs significantly increased the load and deformation capacities of the slabs. Slabs with shear studs were able to show up to three times higher bending deformations and they were able to sustain up to 50% higher loads. The study has shown that these studs can be effectively used for punching strengthening purposes in flat plate systems or in other cases where punching resistance is needed.

Experimental and numerical investigations of the effects of various tensile reinforcement types on the structural behavior of concrete bridge deck slabs

Fiber-reinforced polymers (FRPs) have attracted attention owing to their ability to solve steel corrosion problems. However, FRP-reinforced concrete (RC) deck slabs were found to fail in a brittle shear manner due to the low stiffness of the FRP bars. In contrast, steel-RC deck slabs failed in ductile flexural failure by yielding of steel reinforcement. This study attempts to avoid such brittle failure in FRP-RC slabs by using hybrid steel/FRP bars that can provide serviceability, high strength, and durability. Seven full-scale reinforced concrete bridge deck slabs were cast and tested under four-point loading up to failure. The slabs were 3100mm length × 1000mm width × 200mm thickness. The investigated parameters were the reinforcement type and ratio and different patterns of the hybrid system. Subsequently, a finite element model was constructed, and the model results were compared to the experimental test results. Moreover, a numerical study was carried out by studying the different parameters affecting the shear behavior of RC members, such as the reinforcement ratio, FRP-to-steel ratio and wide range of the shear span-to-depth ratio. Based on the test results, Hybrid-RC slabs showed flexural-shear or compression-shear failure with ample warning than that reinforced with pure BFRP bars. Increasing the reinforcement ratio enhanced the overall slab performance at serviceability limit state. Furthermore, the numerical study indicated that the FRP-to-steel ratio should be Af/As ≤ 1.0 for achieving favorable ductile failure.

Serviceability behaviour of FRP-reinforced slatted slabs made of high-content recycled aggregate concrete

At service load levels, shear-induced deflections of reinforced concrete (RC) slabs are small and therefore they are usually ignored in deflection calculations. However, shear-induced deflections can be large in RC slabs reinforced with Fibre Reinforced Polymer (FRP) bars, especially after the development of diagonal cracks. This article investigates the serviceability behaviour (deflections and crack widths) of FRP-reinforced slatted slabs cast with recycled aggregate concrete (RAC). Fifteen slabs were tested in flexure, including five slabs cast with normal concrete (NC), five slabs cast with RAC made with 50% recycled concrete aggregate, and five slabs cast with RAC made with 100% recycled concrete aggregate. The test results are compared to crack widths and deflection predictions given by current guidelines and Nonlinear Finite Element Analysis (FEA). The results show that, for the tested slabs with 100% recycled concrete aggregates, the predictions given by ACI 440.1R underestimate the experimental deflections by up to 30% at maximum load levels. Conversely, the sum of the flexural deflections given by Eurocode 2 and of the shear crack-induced deflections (calculated using a model proposed recently by the authors) match better the experimental deflections at both the onset of diagonal shear cracking load, and at the maximum load. The Concrete Damage Plasticity (CDP) model adopted in the FEA was found suitable to predict accurately the deformations of FRP RAC slabs. This study contributes towards the development of new more sustainable structural solutions for FRP RAC elements, as well as towards more accurate models to calculate their deflections.

Effect of hybrid steel-polypropylene fiber on punching shear behavior of flat slab with an opening

This research aimed to gain a better understanding of how the addition of fiber influences the punching shear capacity of two-way slabs by conducting an experiment into the structural behavior of flat slabs with and without a square opening using different volume fractions of hybrid steel-polypropylene fiber (0%, 0.9%, 1.05% and 1.8%). Ten 700 × 700 × 70 mm slabs were divided into five pairs, with two samples used as control samples (with and without openings), and eight other samples with different volume fraction of fibers. Results showed that an increase in fiber content enhanced the shear strength of the slabs. For example, as the volume fraction of hybrid fiber increased from 0.0 to 1.8%, the ultimate load increased by 52% for slabs without an opening and up to 42% for slabs with an opening.

Behavior of GFRP reinforced concrete slabs with openings strengthened by CFRP strips

The utilization of fiber-reinforced polymer (FRP), can be an efficient, and long-lasting solution for increasing the durability of reinforced concrete (RC) structures in hostile environments. FRP can be used as a reinforcement or as a strengthening technique that may recover the load capacity of a structure. This paper aims to investigate the flexural behavior of one-way concrete slabs with openings reinforced by glass fiber-reinforced polymers (GFRP) bars and strengthening using carbon fiber-reinforced polymer (CFRP) sheets. The experimental work consists of five one-way concrete slabs that were tested up to failure. All slabs had the same dimension, 750*2650 mm, with a thickness of 150 mm, and were reinforced with the same reinforcement ratio. The experimental work included one specimen without openings and without strengthening as a solid slab. While, the remaining slabs were fabricated with two different openings, rectangular and square 250*500 mm, and 250*250 mm respectively, and strengthened by CFRP sheets. The test results show that the failure load of existing slabs with mid-span openings is decreased by around 41% and 43%, for one and two openings respectively, compared to the solid slab. The utilization of CFRP sheets enhances the flexural load-carrying capacities by about 52% and 44% and improves the stiffness at the ultimate load by about 101%, and 95%, and decreases the deflection at a service load by about 56% and 54%, respectively compared with the un-strengthened slabs. Furthermore, the experimental data were used to validate a finite element (FE) model along with an additional parametric study.