One-way Slabs Research Articles

Research on the Residual Bearing Capacity of a Rib Beam Bridge Carriageway Slab Based on Fatigue Cumulative Damage

In order to study the residual bearing capacity of the carriageway slab of a reinforced concrete rib beam bridge after fatigue damage, a double T-beam carriageway slab model with a high degree of symmetry was designed and fatigue tests were carried out. Based on the fatigue cumulative damage theory, the fatigue residual strength equation of concrete was improved and a constitutive fatigue model of a steel bar and concrete with arbitrary loading times was established. Because the carriageway slabs are highly symmetrical, we used a ratio of length to width and a ratio of width to height to express the dimensional changes in the carriageway slabs. Abaqus general analysis program was used to create a symmetrical T-beams model and analyze the influence of the fatigue load level, the ratio of width to height of the roadway slab, and the ratio of length to width on the remaining bearing capacity of the roadway slab. Finally, the 1stOpt fitting software was employed to fit the roadway slab’s residual bearing capacity evaluation model. The fatigue test results show that the fatigue failure form of the roadway slab is punching failure, and the development law of fatigue damage can be divided into three stages, accounting for 6.25%, 56.25%, and 37.5% of the total fatigue life. The finite element analysis results showed that the length–width ratio of the roadway slab is positively correlated with its relative residual bearing capacity, and the residual bearing capacity of the two-way slab is higher than that of the one-way slab. The fatigue load level and the aspect ratio of width to height are negatively correlated with their relative residual bearing capacity.

Behavioral nonlinear modeling of prestressed concrete flexural members with internally unbonded steel strands

In this article, a nonlinear analysis was carried out to develop two different models able to estimate the performance of partially prestressed concrete flexural members with unbonded post-tensioned strands, mainly; a methodology proposed by the first author and programmed using FORTRAN language, and the commercial finite element software program ABAQUS. These models intend to investigate the entire load-strain behavior and the corresponding load-deformation status of the structural concrete members with unbonded steel up to failure. The results of these two models were verified with the outcomes of the experimental work conducted by the authors. The experimental part consisted of testing 22 different simply supported flexural members (beams and one-way concrete slabs) post-tensioned by internally unbonded steel strands that varied by the cylinder compressive strength of concrete (fc′); jacking stress (fpj); prestressing index (ω); and span to depth ratio (ℓ/dp). The main objective of this article is to develop a numerical model applicable to investigate the performance of concrete flexural members reinforced by a combination of unbonded and bonded steel at various load levels. Compared to experimental data, the two developed models have the ability, with a large degree of agreement, to predict the overall behavior of these types of members in terms of cracking load, ultimate flexural resistance, load-deflection response, strain evolution, and total stress in unbounded strands.

Flexural strength recovery of RC one-way slabs having cut-outs using NSM-SHCC plates

Creating a cut-out in an existing Reinforced Concrete (RC) slab became a common practice to allow passing facility services. This cut-out interrupts the loading trajectories resulting in the existence of weak points. Thus, the ultimate capacity of such slab including cut-out decreases with the increase of the size of the opening. In this paper, a new technique based on near-surface mounted has been employed using precast plates made of Strain-Hardening Cementitious Composites (SHCC). These SHCC plates were designed to compensate the cut reinforcement due to cut-out. The used plates had three different widths; 100, 200 and 300 mm, while their thickness was kept constant at 20 mm. One reference slab without cut-out, in addition to, nine damaged slabs with central cut-outs, were prepared and tested under incremental static loading. The tested slabs have the same dimensions; thickness = 140, effective depth = 120 mm, width = 1200 mm and span = 2200 mm. For the cut-out, a rectangular shape with constant width of 200 mm has been used, while the length parallel to the supporting line was varied considering three values; 200, 400, and 600 mm. All slabs were reinforced with a single bottom steel mesh with a longitudinal reinforcement ratio of 0.65%. The slabs having cut-outs were divided into three groups (I, II and III); each one included three different cut-outs. The slabs of group I were tested without strengthening. On the other hand, group II was strengthened at the tension side only, whereas, group III was strengthened at both tension and compression sides. Based on the experimental findings, the load-carrying capacities of group II raised by 15–57% compared to group I; however, this increase was accompanied by a significant decrease in the developed ductility where the displacement-based ductility index could be dropped by 58% for the slab having cut-out length of 600 mm. For group III, the application of SHCC plates at both tension and compression sides enabled the strengthened slabs to restore nearly the lost capacity resulting from providing the cut-out with a good ductility performance.

Enhancing the flexural load capacity of the reinforced concrete simply supported slabs using damaged tires strips (DTS)

Damaged tires or ended-life tires represent a difficult problem due to their ability to sustain for a long time which are not able to be dissolved easily. Present study focuses on the ability of using the damaged tires strips (DTS) in the field of structural engineering as an innovative reinforcing material used additionally with the main reinforcement. The adopted technique in the present work represents a clean solution to reuse and recycle DTS to increase the ultimate flexural capacity of the reinforced concrete one-way and two-way slabs used in structural systems satisfying clean environment and economic considerations. The tests were conducted upon eight specimens of reinforced concrete one-way slabs (RCOWS) and two specimens of reinforced concrete two-way slabs (RCTWS) reinforced by the DTS as an additional reinforcement. Experimentally obtained results exhibited enhancement for the ultimate flexural load capacity of the RCOWS and RCTWS models reinforced by the DTS in the range of 16–80 and 14.28% respectively, compared to the original reference specimens.

Flexural Behavior of One-way Concrete Slabs Reinforced with Combined Steel - CFRP bars

Flexural Behavior of One-way Concrete Slabs Reinforced with Combined Steel - CFRP bars

Predictive model for stress at ultimate in internally unbonded steel tendons based on genetic expression programming

Predicting the stress increment (Δfps) and in turn, the total stress (fps) in internally unbonded steel tendons at ultimate flexural strength of post-tensioned concrete members is one of the major challenges due to the lack of bond between the steel tendon and surrounding concrete. This article presents the development of a new predictive model to evaluate the stress increment (Δfps) and in turn, the total stress (fps) based on a genetic expression programming (GEP). GEP has the ability to collect all the influential parameters, among all the cross-sectional and the member's geometrical properties, the mechanical properties of materials, and the applied load, in one single closed-form expression for predicting (Δfps). The proposed model was developed based on a comprehensive experimental database of 196 concrete specimens that were collected from literature and the experimental outcomes of 22 beams and one-way post-tensioned concrete slabs which were previously prepared, fabricated, and tested by authors of the present study. A parametric study was conducted to obtain an idea of the relationship between the independent variables and their effect on the stress increment in unbonded tendons at ultimate (i.e., the target parameter (Δfps)). To inspect the potentiality of the proposed (GEP) model against 22 analytical models available in the literature, an extensive comparative study was carried out. The performance of the proposed model was checked according to the values of the coefficient of determination (R2) and different achieved statistical errors. In comparison to the experimental values of (Δfps) and (fps), the proposed model showed the highest coefficient of determination (R2) of 0.78 and 0.93, respectively, compared to the other 22 analytical models. While the values of mean absolute error, relative absolute error, root mean square error, and root-relative square error to determine (Δfps) and (fps) were found to be (60.98, 76.96, 0.45, and 0.47) and (60.98, 76.96, 0.25, and 0.26), respectively.

Effect of Pumice Stone and Sugar Molasses on the Behavior of Reinforced Concrete One-Way Ribbed Slabs

The world is currently heading towards sustainability by reducing the amount of concrete, thus reducing the total unit weight. Moreover, design construction requires materials with a higher strength-to-weight ratio. Ribbed slabs and lightweight concrete (LWC) are considered two leading sustainability facilities. This research developed an experimental study to evaluate the effects of concrete type, steel reinforcement ratio, the geometry of ribs, voiding ratio, and slab type on the structural behavior of one-way ribbed slabs. Eight of the one-way slabs were constructed using pumice stone and by-product material sugar molasses (SM), and one slab was constructed using gravel and SM. These slabs were tested under a static two-point load and simply supported until failure. The results showed that using SM with pumice stone instead of gravel led to high strength-lightweight concrete (HSLWC), with a cylinder compressive strength of 42.2 MPa and a density of 1943 kg/m3, which meets the requirements of HSLWC codes. Using HSLWC instead of high-strength normal-weight concrete (HSNWC) decreased the thermal conductivity by 43.55% and the unit weight by 19.31%. Moreover, the ultimate strength of the HSLWC one-way ribbed slab decreased by 17.70%. Overcoming this strength reduction necessitated increasing the steel reinforcement ratio of the ribs from 0.28 to 0.44% in the HSLWC ribbed slab. Changing the number of ribs at the same amount of HSLWC showed a minor effect on the strength capacity of slabs but showed an economic benefit. However, increasing the rib width to reduce the voiding ratio from 44 to 40% resulted in a greater improvement in structural efficiency (SE) of one-way ribbed slab than reducing it from 44 to 33%. Consequently, the optimum rib width was 120 mm. Moreover, using a ribbed slab instead of a solid slab of HSLWC at the same amount of concrete increased the ultimate strength by 130.37%, decreased deflection by 3.99%, and improved SE by 126.46%. Furthermore, experimental results of ultimate load were compared with the ACI 318-19 code design equation. Doi: 10.28991/CEJ-2022-08-02-011 Full Text: PDF

Probabilistic models of concrete compressive strength and elastic modulus with rubber aggregates

The disposal of waste rubber products is a significant issue globally and it poses a serious threat to the environment creating long-term ecological problems. The possible use of rubber aggregates in concrete is a valid alternative to obtain a green construction material. This paper develops probabilistic models for the concrete Strength Reduction Factor (SRF) and Elastic modulus Reduction Factor (ERF) accounting for the amount of rubber aggregates as well as several variables defining the mix design. Three different rubber aggregate types are considered, namely fine and coarse replaced individually and fine and coarse replaced simultaneously. A total of 644 sets of concrete compressive strength and elastic modulus tests are collected from the literature for the model calibration. The paper presents a discussion about the formulation of the models, variance stabilizing transformations, model calibration, and model selection. Once formulated, we calibrate the probabilistic models using data from experimental tests. The unknown model parameters are estimated using a Bayesian approach implemented using A Markov Chain Monte Carlo (MCMC) simulation method. The proposed probabilistic models are used to evaluate the reliability of rubberized concrete structures. As an illustration, the proposed probabilistic models are used to estimate the reliability of an example column made of rubberized concrete under compressive axial force and of an example one-way slab made of rubberized concrete under distributed load.

REINFORCED CONCRETE FLAT SLABS WITH COMMON ARRANGEMENTS OF FIBRE REINFORCED POLYMER SHEETS

Retrofitting of reinforced concrete (RC) flat slabs using fibre reinforced polymer (FRP) composites has become common in recent years. Flexural retrofitting of one-way and two-way RC flat slabs using five common arrays of carbon FRP (CFRP) strips has been investigated in this paper. A comparison of the obtained results provided optimum scheme. Finite element method has been used to conduct the study using a commercial computer program. Results from the numerical analyses suggest that the use of CFRP sheets leads to improved load bearing capacities of slabs, which depends on both the type of array and the widths of FRP strips. The most optimal array of the retrofitting material (considering the effects on both strength and deflection) is the cross-like condition, which increases the capacities for one- and two-way slabs, respectively, by thirty-four percent and thirty percent while decreasing their maximum deflection by ten percent and four percent, respectively.

Flexural behavior of concrete slabs strengthened with textile reinforced geopolymer mortar

This paper presents results from experimental and numerical studies on the flexural behavior of reinforced concrete (RC) one-way slabs strengthened with textile reinforced geopolymer mortar (TRGM). Eight one-way RC slabs, comprising of five TRGM strengthened slabs, two TRPM (textile reinforced polymer-modified cement mortar) strengthened slabs and one un-strengthened slab, were tested under static loading. The varied parameters in the experiments included the number of textile layers, spacing of the lateral textiles, presence of anchorage, and type of binder. Data from the tests is utilized to validate finite element models developed to simulate the flexural response of TRGM strengthened slabs. Then a set of parametric studies were conducted, to evaluate the effect of reinforcement ratio, slab thickness and the number of strengthening layers. Results from the tests and numerical studies clearly show that use of TRGM for strengthening delays the development and progression of cracks in slabs and enhances the post-cracking stiffness, as well as flexural capacity. In addition, the flexural capacity increases with increased number of strengthening layers, and decreased spacing of lateral textiles. Compared with TRPM strengthened slabs, TRGM strengthened slabs possess higher flexural capacity and better crack control. Finally, a calculation model for predicting the flexural capacity of TRGM strengthened slabs is proposed and the model predictions of flexural capacity is in good agreement with the results from tests and numerical simulations.

Static and Dynamic Behavior of High-strength Lightweight Reinforced Concrete One-way Ribbed Slabs

Nowadays, reducing the self-weight of structures and vibration problems is the primary goal for design requirements in most civil constructions. Two-point loading and harmonic loading tests were conducted to examine the strength and serviceability of high-strength reinforced concrete one-way ribbed slabs. Six slabs were cast and tested. The behavior of cracking, deflection, and vibration was investigated. The experimental results showed that using high strength-lightweight concrete (HSLWC) instead of high strength-normal weight concrete (HSNWC) in constructed one-way ribbed slab led to a decrease in the density by 19.31%, the strength by 17.70%, and ultimate deflection by 17.33%. Although the addition of steel fibers to HSLWC led to an increase in the density of concrete its addition enhances the load-deflection relationship and ultimate load for slab specimen which reduced the reduction in strength by 14.49%. Furthermore, ductility index, stiffness, and toughness index for ribbed slab specimens with steel fibers showed better behavior than those without steel fibers. The HSNWC gave a negative impact on the vibration of the one-way ribbed slab at both operation frequencies (25 and 50) Hz, while using HSLWC with and without steel fibers, led to reducing the vibration effect by (30.11and 30.68) % and (15.26 and 20.25) % at 25Hz and 50Hz, respectively.

Load deflection behaviour and properties of sustainable lightweight aggregate concrete slabs

This research has been conducted to investigate the effect of partial replacement of coarse aggregate by lightweight aggregate on different characteristics and load deflection behaviour of concrete. Natural aggregate was replaced once by waste walnut shell and then by porcelinate aggregate. And both types are considered lightweight aggregate. Percentages of replacement by volumetric rates ranging between 25% to 100% were adopted. In addition, cement was replaced by 10% waste glass powder. Compressive strength, splitting tensile strength, and dry density were made. Also, one-way slab was cast for 50% replacement and tested under four point flexural test. Results showed that replacement of natural aggregate with lightweight aggregate regardless of its source decrease density, compressive strength and splitting strength. While an increase in the deflection at failure was noticed for slabs incorporating lightweight aggregate compared to the reference one. Concrete containing 50% porcelinate demonstrated a slight increase in strength compared with the reference slab by 8.91% concrete containing 50% WA demonstrated a clear reduction in strength compared with the reference slab by 62.57%. The width of crack at failure for concrete incorporating walnut coarse aggregate was wider for the reference one. While concrete incorporating porcelinate failed with finer cracks than the reference one.

Strength of SIFCON- Ferrocement One-Way Ribbed Slabs Contain Steel Fibers

Slurry infiltrated fiber concrete” composites (SIFCON) are a novel type of concrete with improved strength, ductility, and crack resistance. In this study, infiltrating fibers (SIFCON) were used to reinforce of specimens of ferrocement one way ribbed slabs. The laboratory work consists of cast and testing of eight specimens with dimensions of 750 mm in length, 500 mm in width and 50 mm in depth. These samples have the same wire mesh reinforcement and the same shape as the ferrocement slabs. Two reference ferrocement slab without ribs contains SIFCON and six ferrocement slabs with ribs contains SIFCON. The variables were the volumetric ratio of fibers in the ribs, which were (2, 4 and 6)% and type of steel fiber (hook-end and hybrid fiber). Hybrid fibers contain two type of steel fiber (hook-end and micro steel fiber) with equal ratio. All samples were tested under line load up to failure with mid deflections for each test with simple supported. The results of the test showed that the presence of steel fibers in the ferrocement ribs, for both types of steel fibers, improves the resistance to the final loads and the ability to reduce deflection and increases the ductility and stiffness significantly.

Performance of Strengthened/Repaired Heat-Damaged One-Way Self-Compacted Concrete Slabs with Openings Using Nsm-Cfrp Strips

Performance of Strengthened/Repaired Heat-Damaged One-Way Self-Compacted Concrete Slabs with Openings Using Nsm-Cfrp Strips

Full-scale flexural testing of slabs made of modular structural concrete insulated panels

Structural concrete insulated panels (SCIPs) are an alternative construction technology to traditional wood framing and masonry units for use in residential homes and low-rise structures. SCIPs can be used to erect structurally sound buildings that are economi­cal, energy efficient, and durable while incorporating sandwich technology. This study presents a novel type of SCIP that can be fabricated using off-the-shelf components. A precasting technology for such modular SCIPs is proposed. Full-scale experimental testing of one-way SCIP slabs with three different span lengths (short, medium, and long) was carried out to investigate flexural behavior, strength, ductility, and failure mechanisms. Testing showed good performance of modular SCIPs under gravity loads. Appropriate splicing details for longer-span SCIPs are developed and tested. Results show that the SCIPs tested in this research can provide a moment capacity equal to 66% of the capacity of a fully composite section.

Behaviour of One-Way Reinforcement Concrete Cantilever Slabs with Openings

In some concrete structures, openings are placed because of the need for several utility requirements. These openings could affect the strength of the structural members. So the behavior of reinforcement concrete (RC) cantilever slab containing openings and its effect is the subject of the study. Opening shapes, numbers and sizes are the main variables that have been studied in this research. Five RC cantilever slabs were cast and tested; one is without openings and the other four slabs are with openings. It is found that there is a significant effect of openings on the behavior of these slabs. Where, the decrease in the ultimate load (from 39kN to 24.7kN), while the decrease in the deflection at ultimate load (from 67 mm to 35 mm).

A Design Method to Induce Ductile Failure of Flexural Strengthened One-Way RC Slabs.

Strengthening existing reinforced concrete (RC) slabs using externally bonded materials is increasingly popular due to its adaptability and versatility. Nevertheless, ductility reduction of the rehabilitated flexural members with these materials can lead to brittle shear failure. Therefore, a new approach for strengthening is necessary. This paper presents a methodology to induce ductile failure of flexural strengthened one-way RC slabs. Ultimate failure loads can be considered to develop the proposed design methodology. Different failure modes corresponding to ultimate failure loads for RC slabs are addressed. Flexural and shear failure regions of RC slabs can be established by considering the failure modes. The end span of the concrete slab is shown for a case study, and numerical examples are solved to prove the essentiality of this methodology.

Effect of concrete and reinforcement continuity on repairing mid-span zone in simply supported one-way slab

AbstractThe flexural strength of slabs may be reduced due to accidents and environmental effects. This study focuses on the rehabilitation of the one-way reinforced concrete slab. Experimental works include five simply supported one-way reinforced concrete slabs with width, depth, and length of 400, 120, and 2200 mm, respectively. Different configurations of steel continuity between old and new concrete have been tested. Moreover, in the control specimen (steel is continued overall, the specimen and concrete are cast in one stage over the entire slab). In the other four specimens, the concrete is cast in two stages, the left and right parts representing the old concrete are cast first, and the middle part representing a new concrete is cast after that. In these four specimens, new steel is connected to old one by different configuration (original steel remain to continue, new steel connected to old one by weld, new steel connected to old one by making 90° hooks, and new steel bars is put inside bores using epoxy). After testing, the welding method of connecting new to old steel is the best one.

Limitations of Flexural Crack Width in Simply Supported One-Way Ribbed Slab

The important consideration in design of multistory concrete buildings is reducing self-weight of the slabs. The system of one-way ribbed slab is one of the many systems chosen in order to reduce self-weight. This reduction occurs in concrete only for what causes high tensile stress in bottom fiber of concrete lead to cracking although the section is reinforced according to design specifications. Limitations of ACI 224R-01 2008 of maximum allowable crack width is 0.3 mm for members’ exposure to humidity, moist air, or soil. The experimental work in this research includes five simply supported reinforced concrete one-way ribbed slab with same dimensions and different in ratio of bottom steel reinforcement. The five specimens have reinforcement ratios of 0.0009, 0.0013, 0.0023, 0.0037, and 0.0059 respectively. The aim of this research is checking experimental crack width at design load with permissible limitations according to ACI 224R-01 2008. The experimental work and the theoretical calculations, for all the specimens, are cracked sections where the first crack appears at load less than design load. At design load the specimens with low and moderate reinforcement ratio 0.0009, 0.0013 and 0.0023 show crack width less than permissible value of 0.3 mm, while the specimens with high reinforcement ratio 0.0037 and 0.0059 show crack width more than permissible value of 0.3 mm, where the increases in width of crack causes reducing in the durability of members. At linear stage, the mid span deflection is decreasing as reinforcement ratio increase at same step of loading for all specimens. Finally, in the design of one-way ribbed slab, the emphasis is on checking the width of cracks according to codes permissible limitation and it is recommended to use low or moderate reinforcement ratio in this system of slabs.

Effects of grid-type shear connector arrangements used for insulated concrete sandwich wall panels with a low aspect ratio

Insulated concrete sandwich wall panels (ICSWPs), in which low thermal conductivity insulation is inserted between concrete wythes, can minimize the heat loss of building envelopes, and glass fiber-reinforced polymer (GFRP) grids are used to enhance both the structural and thermal performances of ICSWPs. For ICSWPs with low aspect ratios similar to a two-way slab, while bidirectional arrangements of shear grids may be considered based on two-way load transfers, unidirectional arrangements could be economically advantageous due to easier assembly of insulation and grids. This study aims to investigate the effects of grid-type shear connector arrangements on composite behaviors of ICSWPs. Bending tests were performed on four full-scale specimens to examine crack loads, stiffnesses, and strengths. Test variables consisted of GFRP grid arrangements and quantity of GFRP grids. The GFRP grid arrangements were divided into the unidirectional arrangement—installation of GFRP grids in only shorter span direction—and the bidirectional arrangement—installation of GFRP grids in both shorter and longer span directions. Major and minor axes were investigated by measuring radius of curvatures and slips in two perpendicular axes. The results revealed one-way slab behavior, with about nine times greater radius of curvature in minor axis than in major axis. As the result of quantifying degree of composite actions, the bidirectional arrangement in ICSWP demonstrated enhanced serviceability regarding crack loads and stiffness but had lower strength performance. Since the unidirectional arrangement in ICSWP exhibited acceptable composite actions conforming to the design criteria even with 11.4% less quantity of GFRP grid than the bidirectional arrangement, unidirectional installations of GFRP grid could be efficient design options of ICSWPs with low aspect ratios.