One-way Slabs Research Articles

Flexural performance of a new type of slightly curved arc HRB400 steel bars reinforced one-way concrete slabs

Abstract In the present study, a new type of slightly curved arc HRB400 steel bars (SCAHSs) was proposed to solve the problem of temperature-induced stress loss in mass concrete structures without cutting off steel bars. The flexural performance of SCAHSs and straight HRB400 steel bars reinforced one-way concrete slabs were first experimentally investigated. Then, the effects of the shape and dimension of SCAHSs on the distribution and width of concrete cracks were analyzed and discussed. Subsequently, the synergistic tensile work characteristics between SCAHSs and concrete were presented. Finally, equations for the bearing capacity and allowable crack widths for SCAHSs in hydraulic massive structures were proposed. The test results indicated that after replacing the straight steel bars in the concrete slab with SCAHSs, the crack width of the concrete slabs increased, with the maximum crack width at the bottom of the concrete slabs increasing by a factor of 1.2–1.4. As the rise-span ratio of SCAHSs increased, the flexural stiffness of SCAHSs reinforced concrete slab decreased slightly, but the deflection increased. The allowable crack widths of SCAHSs reinforced concrete slabs under environment categories I, II, and III were 0.20, 0.17, and 0.12 mm, respectively.

Experimental and Design Parametric Study of a Novel Grouted Square Steel Tube Upper Chord–Concrete Composite Floor

A novel composite floor consisting of an upper chord of a grouted square steel tube truss and a lower chord of a reinforced concrete slab is proposed to address existing problems with precast composite floors, such as a complex construction process, high cost, significant resource consumption, and severe environmental pollution. Sixteen-point loading tests were carried out on five simply supported one-way slabs to simulate the stress state of the floor under a uniform load and to investigate the stiffness, cracking moment, load-carrying capacity, and failure mode of the composite floor system. The results showed that the composite floor system exhibited ductile failure, with cracks uniformly distributed at the bottom of the slab; additionally, the grouted steel tube did not experience uplift or out-of-plane buckling, and the truss welds did not fracture, indicating that the composite floor system still had further deformation capacity and load-carrying capacity with satisfactory stress conditions. After unloading, the residual deformation of the composite floor accounted for 28% to 36% of the maximum deflection, demonstrating good deformation recovery ability. The bottom slab thickness and truss height are key parameters that influence the new composite floor, and increasing the two parameters enhances the cracking load, deformation resistance, and flexural capacity of the composite floor, with a significant improvement achieved by increasing the truss height. The floor slab should have a minimum thickness of 60 mm, as required by China’s Code for Design of Concrete Structures, and the truss height-to-span ratio should be 1:30, which meets the deformation and load-carrying requirements of the floor and conforms to the design concept of green buildings.

Performance of FRP-Upgraded RC One-Way Ribbed Slabs with an Opening in Flexure Zone

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings.

Experimental evaluation of flexural behavior of UHPFRC slabs utilizing local constituents

New ultra-high performance fiber reinforced concretes (UHPFRCs) are being developed throughout the world using locally-sourced materials to reduce financial and logistical burdens. Understanding force protection capabilities of these new materials requires experimental data that are useful for validating constitutive models or fast-running computational tools. Flexural performance of two UHPFRCs from different regions of the world are compared via one-way slabs subjected to uniform quasi-static loads. Results are also compared to a normal-strength concrete and two high-strength concretes from different regions. Results showed increased unconfined compressive strength of concrete leads to increased flexural resistance and stiffness. Furthermore, fiber reinforcement greatly increases flexural capacity in slabs but can cause brittle failure when combined with high reinforcement ratios of conventional reinforcement. While the UHPFRCs had different mechanical properties, both increased the maximum flexural capacity and showed potential for significantly improved performance for force protection applications.

Short-Term Efficiency of Using Sustainable BFRP Bars in Post-Tensioning Systems for One-Way RC Slab

Short-Term Efficiency of Using Sustainable BFRP Bars in Post-Tensioning Systems for One-Way RC Slab

Structural Performance of Reinforced Concrete One-Way Slabs Bubbled Using Hollow PET Balls

Structural Performance of Reinforced Concrete One-Way Slabs Bubbled Using Hollow PET Balls

Exploring Analytical Hierarchy Process for Multicriteria Assessment of Reinforced Concrete Slabs

The decision regarding which slab type should be used in a building is generally made by the structural engineer, considering structural efficiency and compatibility with the architectural design, as well as the costs related to the amount of material used in each option. Because of the technical responsibilities inherent to this specialty, the decision-making process neglects to encompass various other factors of consequence that influence the construction process. These considerations include productivity, the visual and aesthetic characteristics of the slab, waste generation, and thermal and acoustic comfort. This paper aims to develop a multicriteria method to assist stakeholders in selecting the most suitable structural system for slabs based on project needs and objectives. The study utilized the Analytic Hierarchy Process (AHP) and information from bibliographic research, expert opinion using the Delphi Method, and machine learning on a dataset of over 2000 previously constructed slabs to achieve this goal. The analysis showed that the conventional solid slab type was the top priority, followed by the two-way waffle slab, one-way waffle slab, solid flat slab, and waffle slab. Additionally, the proposed AHP method was effective in developing a decision-making model for companies and the construction sector.

NLFEA of one-way slabs in transition between shear and punching: Recommendations for modeling

Several studies investigated the precision of non-linear finite element analyses (NLFEA) to predict the shear capacity of beams or the punching capacity of slab-column connections. However, in the literature, there is little discussion regarding the results of NLFEA to predict the ultimate capacity and failure mechanism of slabs susceptible to different failure mechanisms. In this study, a set of tests from literature that developed different shear failure mechanisms was evaluated by NLFEA. A total of thirteen slabs were modeled, where slab’s width and shear span varied. A coupled damaged-plasticity model was employed to simulate the concrete behavior. The proposed model was calibrated to simulate specimens that failed as wide beams in one-way shear and specimens that failed by punching shear. Besides, the effect of different modeling choices was investigated: (i) the assumed stress–strain behavior in compression; (ii) tensile stress–strain behavior; (iii) the inclusion or not of damage parameters and (iv) the viscosity parameter. The results indicated that, on average, the proposed modeling strategy represented the failure mechanism and ultimate loads well. Also, the same calibrated model was found capable of representing one-way shear failure and punching shear failure or mixed modes. The sensitivity study demonstrated that the tensile stress–strain behavior and viscosity parameter influences the results of the numerical models more significantly than the assumed stress–strain behavior in compression or including/not including the damage parameters. This paper concludes that modeling strategies during the calibration process shall be checked carefully before performing any parametric analyses to identify the accuracy of the numerical models to represent the different failure mechanisms. Moreover, the validation step of the modeling strategy shall identify possible limits of the numerical model to be considered in the parametric analyses.

Practical flexural design approach for one-way hybrid fiber-reinforced concrete slabs based on a parametric study on slenderness limits

Fiber-reinforced concrete (FRC) is increasingly used for structural applications. Slabs are a particularly attractive use for FRC due to a potentially increased redistribution capacity, as well as the efficient cracking control that fibers provide. However, methods for reliably establishing slenderness limits of such elements are missing. Therefore, in this study, a previously developed closed-form solution for slenderness limits of hybrid FRC (HFRC) slabs (steel reinforcement bars and steel fibers) is presented and updated. Subsequently, a comprehensive parametric study on one-way solid slabs is performed, drawing clear conclusions on which parameters are the most influencing and offering a practical flexural design approach in the form of graphs and tables for determining minimum thicknesses of HFRC slabs that may be used as design aids for practitioners.

Shear Behavior of Prestressed Hollow Core One-Way Slabs with Openings: Experimental, Numerical, and Standard Formulation Verification

The use of prestressed precast hollow core slabs has intensified as technological advances. However, the knowledge of the structural behavior when openings are inserted into this element is still limited, mainly due to the shear force. Therefore, the present study aims to analyze the structural behavior of the shear test of prestressed hollow core slabs with openings. In this paper, three types of hollow core slabs were tested: no openings, a central opening and side openings; using experimental and numerical methodology. The experimental test was carried out in the Federal University of São Carlos, and the numerical analysis used the software ABAQUS. All results were compared with three standard formulations (i.e., NBR, ACI and Eurocode), in order to verify its accuracy. In the end, the numerical results demonstrated that the developed model (CDP) presented results close to the experimental results. For the hollow core slab with a central opening, a rupture occurred in the web adjacent to the opening. On the other hand, for the hollow core slab with side openings, the rupture occurred at the edge of the web. Therefore, it was possible to conclude that the openings influence the main web tensions, being responsible for the diagonal model stress rupture. Finally, the Brazilian and Eurocode standard formulations proved to be good estimators of the resistant shear force.

Strength, Ductility, and Collapse Response of UHPC Waffle Slabs

Waffle slabs made of ultra-high performance concrete (UHPC) are now being widely used in bridge deck construction. However, to date, no research has been conducted to study their failure behavior. Two one-way waffle slab strips made of UHPC were load-tested under four-point bending to investigate their strength, ductility, and failure patterns. An identical set made of high strength concrete (HSC) was also tested to provide a comparison to specimens made with traditional construction materials. The UHPC specimens exhibited multiple fine cracks prior to rebar yielding and failed by steel rebar rupture after a single crack localized. In contrast, the HSC slab strips exhibited several large cracks and substantially larger ductility than the UHPC slab strips, although their strength was about 40% less than the corresponding UHPC specimens. The experimental results were used to validate a three-dimensional finite element model, which was then employed to investigate the two-way response of UHPC waffle slabs. The simulation study revealed that the yield line design method is applicable to UHPC waffle slabs despite their markedly different behavior compared to concrete slabs. Like the HSC slabs, the UHPC slabs also exhibited displacements and load carrying capacities well in excess of those predicted by flexural theories, due to formation of membrane action.

Anchored CFRP ropes for flexural capacity recovering of thermally damaged RC one-way slabs

The effectiveness of utilizing near surface mounted (NSM) ropes of carbon fiber reinforced polymers (CFRP) in restoring the mechanical performance of heat-damaged RC slabs were studied using anchored and un-anchored techniques. The CFRP anchorage is supposed to increase the flexural behavior of the RC one-way slabs under investigation. To achieve this purpose, a total of (24) RC 1100 mm (long) × 500 mm (wide) slabs were devised. The experimental slabs were made in three heights; 60 mm, 80 mm, and 100 mm. Using an electric furnace for two hours each time, six of the slab were exposed to 200 °C, another six slabs were exposed to 400 °C, and the third group of six slabs was exposed to 600 °C, while the remaining six slabs were at room temperature. Twelve slabs were reinforced, in tension, with NSM-anchored ropes of CFRP. A test setup for 4-point loading was used to examine the slabs’ mechanical performance, while NSM CFRP ropes’ strain was measured. Also, the cracking patterns and failure modes were observed and documented. The slabs, with/without strengthening and damaged-by-heat/retrofitted, improved their toughness and load capacity up to 189% and 225%, respectively. In contrast, the slabs encountered a degradation in their displacement ductility with respect to the control slabs up to 2%, with the toughness ductility being increased up to 186% based on the slab’s rigidity and the exposed temperature. The present research demonstrated that the anchored NSM CFRP ropes to rehabilitate damaged-by-heat slabs was efficient in regaining the flexural behavior; the monitored behaviors indicated that. Lastly, it was observed that the improvement in the slabs was controlled by the transverse end-anchoring’s effectiveness, which permitted the prime ropes of CFRP to contribute more to the flexural performance without the possibility of the occurrence of un-expected de-bonding caused by cracking, even when the slabs reached their capacity. Based on the research findings, anchoring the utilized CFRP ropes and predicting its capacity using the proposed guidelines is recommended.

Experimental Study on the Structural Performance of Reinforced Truss Concrete Composite Slabs during and after Fire

Standard fire resistance tests and post-fire tests on residual mechanical properties were carried out on two four-edge simply supported reinforced truss concrete two-way composite slabs with wide seam splicing (“integral seam”) and close seam splicing (“separated seam”), and the effects of the different splicing forms on the mechanical properties of the reinforced truss concrete composite slabs during and after exposure to high temperatures were explored. The results indicate that there are significant differences in terms of crack developments, moisture loss times on the slab surface, spalling characteristics of the bottom of the slab and cross-section temperature gradients of concrete and steel reinforcement along the thickness direction between the wide seam spliced reinforced truss concrete composite two-way slab (referred to as “S1 composite slab”) and the close seam spliced reinforced truss concrete composite two-way slab (referred to as “S2 composite slab”) in the fire test. This is mainly due to differences in the splicing forms and structural measures of the prefabricated base slabs at joints, which led to changes in the heat transfer path at the joints. As the temperature at the close seam can be released quickly, the stiffness recovery of the S2 composite slab is significantly greater than the stiffness weakening due to the thermal hysteresis of the concrete, so the deflection of the S2 composite slab recovers immediately after the fire stops. Overall, both the S1 and S2 composite slabs exhibit two-way high temperature deformation characteristics. The post-fire residual static load tests show that the static load-carrying capacity of the S1 composite slab is 12.08% higher than that of the S2 composite slab and the ultimate displacement is 8.74% lower than that of the S2 composite slab. It is appropriate to calculate the residual load capacities of the S1 and S2 composite slabs after the fire as a one-way slab.

Structural performance of sandwich steel-concrete-steel composites utilising engineered cementitious composites

Due to the benefits of Steel-Concrete-Steel composites (SCS) and the improved mechanical characteristics of Engineered Cementitious Composites (ECC), utilising ECC as a core material for sandwich composite systems is expected to improve system performance. This paper investigates the ability to improve the flexural behaviour of composite structures by placing an ECC core sandwiched between two steel plates, which are interconnected by bolted connectors. An ECC core can sustain more flexural stresses and provide stronger lateral confinement to the bolts. Push-out tests confirm that the shear transfer capability of a bolted connector embedded in ECC is superior to those embedded in normal concrete (NC) in achieving composite action between the steel plate and the core. Four sandwiched one-way slabs were tested to evaluate their flexural performance when subjected to static point loads. The parameters investigated included the core material and the shear connector diameter. Using the analytical models available in Eurocode 4 and the literature for steel–concrete-steel sandwiches, theoretical analysis was conducted to predict the shear connector’s strength and the slab’s flexural behaviour, comparing them with the experimental results. The predicted capacities show general agreement with the test output, concluding that the available models for NC sandwiches can be followed for ECC. Test evidence also shows that the inclusion of ECC as a sandwich core significantly increases the flexural capacity, as well as its post-peak ductility.

Failure mechanism of one-way slabs under concentrated loads after local reinforcement yielding

One-way slabs under concentrated loads may fail by one-way shear such as wide beams, punching shear, flexure, or by combining two or more of these mechanisms. Nevertheless, most publications have only addressed shear and punching failures without flexural reinforcement yielding. This study investigates the ultimate shear capacity of one-way slabs under concentrated loads with local reinforcement yielding. In total, 12 tests were conducted on six reinforced concrete slabs. Simply supported slabs of 1.60 m × 3.40 m × 0.15 m were tested. Three parameters were varied: the load position, the span length and the reinforcement ratio. All slabs failed initially by punching with limited or extensive reinforcement yielding. Due to the relatively large amount of transverse reinforcement (0.44 %), most slabs underwent a large shear redistribution around the load, resulting in a wide beam shear failure after the local punching failure. The test results were compared to the theoretical predictions of shear, punching and flexure capacity using code expressions and the Extended Strip Model (ESM). The ESM resulted in the closest predictions of the experiments. These experiments confirm that a brittle shear and punching failure mechanism can occur even after extensive reinforcement yielding. Moreover, the results indicate that the ESM can be used to assess one-way slabs under concentrated loads with local reinforcement yielding.

Production Economical Reinforced Concrete Slabs using Eco-Friendly Material

Concrete is a material that is strong in compression but weak in tension. To overcome this issue, reinforcement must be used to improve the tensile strength of the concrete. However, it is acknowledged that steel has its drawbacks, such as the fact that it has a high cost and corrosion potential, and the rebar is heavy, non-renewable, and non-environmentally friendly. Thus, this experimental study investigates the potential product of economical reinforced concrete slabs using eco-friendly materials. Firstly, to enhance the concrete properties, a compressive, tensile, and flexural test, also a concrete with the addition of polypropylene fiber outlasted the control mix design in terms of strength and durability. The results included the control mix (CM), F1 0.25%, F2 0.50%, F3 0.75%, and F4 1%. The specimen with the highest compression and tensile strength was 24.28 MPa and 3.15 MPa, respectively, for the F1 specimen with 0.25% short fibers. Secondly, the bending test was carried out on ten slabs to check the structural behavior of these slabs reinforced with reed rods as the eco-friendly material. The good results of the bearing capacity of a partially reinforced concrete slab with a reed have been obtained at 23.8 kN. Meanwhile, to obtain better results, this research has enhanced the behavior of the concrete slab by improving the concrete's properties by adding polypropylene synthetic microfiber to the mixed concrete. In addition, giant reeds treated with epoxy increase the bonding strength with concrete, improve tensile strength properties, and reduce the absorption of reeds. Therefore, the bearing capacity results of the reed-reinforced concrete slab became the best, which were 35.83 kN. Thus, reinforcement of one-way slabs by reed partially with appropriate diameters could be substituted to obtain good performance in the reconstruction of low-cost buildings. As a result, economical reinforced concrete slabs have been produced using eco-friendly materials. Doi: 10.28991/CEJ-2023-09-06-010 Full Text: PDF

Parametric Study of Drilling Method Performed on One-Way Post-Tensioned Slabs

Abstract Determination of the stress state in concrete structures is a very important, but difficult task. In the case of new structures, it is possible to easily instal measurement instruments which can provide important data as a part of real-time monitoring. However, the evaluation of stresses in existing structures is much more challenging. Currently, stress relief methods are a well-established approach for the evaluation of the actual state of existing structures. The so-called Drilling method (also known as Stress-relief coring technique) is one of the possible techniques for such analysis. For practical use of this method, knowledge of pivotal factors which influence stress relief is crucial. Therefore, this paper presents a parametric study performed on a one-way post-tensioned slab which can help to understand the effect of the depth of the core and the distance from the edge of the hole (position of strain gauges) on the change in stress in the vicinity of the drilled core. Finally, based on the obtained data, the recommendations for the subsequent experimental program will be summarized. According to the study, it seems that the depth of drilled core does not significantly influence the stress relief and the main impact can be attributed to distance from the edge of the hole.

Influence of Supports on the Low-Velocity Impact Response of Square RC Slab of Standard Concrete and Ultra-High Performance Concrete: FEM-Based Computational Analysis

Structural members with low-flexural stiffness, such as slabs, are more susceptible to impulsive loadings induced by falling machines/tools during construction and installation, and also from rolling boulders/rocks triggered by wind/earthquake, especially in mountainous areas. The impact resistance of reinforced concrete (RC) slabs supported on two opposite edges (often called the one-way slab) and on all four edges (i.e., two-way slab) has been adequately studied experimentally as well as computationally, and is available in the literature. However, the slabs supported on three edges have not been studied under low-velocity impact for their impact response. For this purpose, a computational study is performed through finite elements by implementing ABAQUS software on the validated model, resulting in the slab, which is supported on (i) three edges and (ii) two opposite edges, to be subjected to low-velocity impact, induced by dropping a 105 kg non-deformable steel mass from a height of 2500 mm onto the slab centroid. Furthermore, the role of the material strength of the concrete of the slab is investigated via replacing the ultra-high performance concrete (UHPC) for standard or normal-strength concrete (NSC). The impact load is modeled by considering the explicit module of the software. Failure mechanism, stress/strain contour, displacement distribution, and crack pattern of the slabs are compared and discussed.

EVALUASI KINERJA STRUKTUR RANGKA BETON BERTULANG BALOK LEBAR DENGAN DISTRIBUSI BEBAN PELAT SATU DAN DUA ARAH

A reinforced concrete frame building system using wide beams is a solution for buildings with limited heights to get a larger number of stories, a higher distance between stories, and flexibility in installing architectural elements and MEP. This analytical study was conducted to evaluate the behavior and performance of open-frame structures with wide beams for one-way and two-way slab system conditions. This study was carried out using a structural analysis program by applying linear and nonlinear analyzes to four models of a five-story structure with square columns, which varied in beam dimensions and slab systems. The variations considered are normal beam with one-way slab system (1wSN), normal beam with two-way slab system (2wSN), wide beam with one-way slab system (1wSW), and wide beam with two-way slab system (2wSW). All structural elements are designed to follow and meet the criteria of the Indonesian Building Codes, which are then followed by a non-linear static pushover analysis to obtain the performance of each structural model. The results of the analysis show that a structure with wide beams has greater deformation than a structure with normal beams with a faster achievement of collapse conditions so that the ductility of the structure also becomes lower. This is caused by the stiffness of the wide beam-column joints is lower than that of the normal beam-column joints. The use of one-way or two-way slab systems on structures with wide beams does not have a significant effect

Partial factor for the shear resistance model in the 2nd generation of Eurocode 2 for GFRP reinforced concrete members

Fibre-reinforced polymer (FRP) bars provide a useable alternative to conventional steel reinforcement in concrete structures exposed to chlorides from de-icing salts and marine environments. Glass fibre-reinforced polymer (GFRP) bars have the widest practical applications in concrete structures all over the world. The lower modulus of elasticity and bond with concrete compared to steel rebars led to the development of new or modification of existing design models for predicting the shear capacity. The 2nd generation of Eurocode 2 (prEC2) introduces a new design provision for predicting the shear capacity of concrete members reinforced with FRP bars together with a new partial factor for shear γV. The paper deals with the statistical analysis of the accuracy and reliability of this design model. The analysis was carried out using a database of 288 experimental tests on beams and one-way slabs reinforced with GFRP bars. The correction factor bcor of a model and the coefficient of variation of the model error Vδ were evaluated according to Annex D of the EN 1990. Probabilistic properties of the random variables in the resistance function were assumed according to the recommendations of the JCSS Probabilistic Model Code and values introduced in Annex A of the prEC2. The analysis showed acceptable accuracy with Cov of model uncertainty Vθ = 0.190. However, the partial factor γV ranged within the interval of 1.62 to 1.65 which is a higher value than the proposed normative value of 1.50. The lower safety of the model also confirmed the comparison of the results with the performance of the design provisions in Canadian standard CSA S806-12 and in the ACI code of practice ACI 440.1R-15. An adjustment of the prEC2 design provision was proposed with the aim to increase the reliability of the model and maintain the normative value of the partial factor for shear on a proposed value of 1.50.