Shear Strength Of Concrete Slabs Research Articles

Enhancing machine learning models with metaheuristic Optimization techniques for accurate prediction of PSC in FRP-reinforced concrete slabs

The present research examines the utilization of metaheuristic optimization algorithms to enhance the predictive accuracy of the Extreme Gradient Boosting (XGBoost) machine learning model in predicting the capacity for punching shear of Fiber Reinforced Polymer (FRP) reinforced concrete slabs in the absence of shear reinforcement. A database including 610 experimental results is constructed, and the efficiency of twenty metaheuristic algorithms is assessed in optimizing the hyperparameters of the XGBoost model. The enhanced models undergo evaluation and comparison with existing prediction algorithms, showcasing their better accuracy. The study reveals that the DE, MVO, EOA, and VCS algorithms yield the highest precision among the investigated optimization techniques out of which VCS model performed better. Furthermore, the significance of input parameters on the punching shear capacity is analyzed by implementing the Shapley Additive Explanation (SHAP) method. The findings emphasize the potential of metaheuristic optimization in enhancing the estimating abilities of machine learning models for complex engineering problems and provide valuable insights into the key factors influencing the punching shear strength of concrete slabs reinforced with FRP.

Two-Way Shear Resistance of FRP Reinforced-Concrete Slabs: Data and a Comparative Study.

This study aims to investigate the two-way shear strength of concrete slabs with FRP reinforcements. Twenty-one strength models were briefly outlined and compared. In addition, information on a total of 248 concrete slabs with FRP reinforcements were collected from 50 different research studies. Moreover, behavior trends and correlations between their strength and various parameters were identified and discussed. Strength models were compared to each other with respect to the experimentally measured strength, which were conducted by comparing overall performance versus selected basic variables. Areas of future research were identified. Concluding remarks were outlined and discussed, which could help further the development of future design codes. The ACI is the least consistent model because it does not include the effects of size, dowel action, and depth-to-control perimeter ratio. While the EE-b is the most consistent model with respect to the size effect, concrete compressive strength, depth to control perimeter ratio, and the shear span-to-depth ratio. This is because of it using experimentally observed behavior as well as being based on mechanical bases.

Comparison of RCC and Post-Tensioned Flat Slabs Using ETABS

Flat slabs are widely used nowadays. The system’s insufficient punching shear capacity is a major and serious flaw. There are numerous approaches to increasing the punching shear strength of concrete slabs to solve the problem of punching failure. Increasing the thickness of the slab adjacent to the column, as well as the thickness of the column, contradicts the architectural intent. In developing countries such as India, the benefits of prestressing, particularly post-tensioning, have yet to be recognized. In this study, the technique of post-tensioning is used to strengthen a flat slab. RCC flat slabs are compared to post-tensioned flab slabs with different tendon profiles. Tendons are available in two forms: distributed and banded. The models were built as per ACI 318-14. These slab models were created using ETABS software, and the following parameters were compared: thickness, supporting reactions, punching shear, and deflection. When compared to traditional flat slabs. The results indicate that post-tensioned flat slabs have a higher punching shear capacity even at shallower depths, resulting in more cost-effective sections. The provision of tendons also results in lower deflection.

Punching shear behaviour of RC flat slabs incorporating recycled coarse aggregates and crumb rubber

This paper presents experimental, analytical and numerical investigations to evaluate the punching shear strength of concrete slabs incorporating a combination of recycled coarse aggregate (RCA) and crumb rubber (CR). Therefore, twelve different concrete mixes were designed with various substitution ratios of RCA and CR as a partial replacement of natural coarse aggregate (NCA) and fine aggregate (FA), respectively. Four substitution ratios of RCA (0%, 25%, 50% and 100%) by NCA and three substitution ratios of CR (0%, 10% and 20%) by FA were considered. Twelve simply supported two-way RC slabs with dimensions of 1000 × 1000 × 100 mm were cast and tested. The experimental programme was divided into two stages. The first and second stages were respectively conducted to evaluate the mechanical properties and the punching shear behaviour of concrete slabs incorporating a combination of RCA and CR. Experimental results show that the combination of RCA and CR negatively affects the mechanical properties of concrete. The substitution ratios of rubber content had a more significant effect on the reduction of the concrete strengths than the RCA content. The punching shear strength, stiffness and toughness of RC slabs incorporating RCA and CR decreased with increasing CR and RCA contents. Based on the experimental results, a combination of 25% RCA and 10% CR is the optimum substitution ratios that can be used on the concrete mixture, as it has a minor effect on the punching shear strength of concrete slab. The predictions of five approaches, namely ACI 318–2014, ECP 203, Euro −2, BS8110 and CSA A23.3, were compared with the experimental results. Finally, nonlinear element analysis (ANSYS) was conducted to verify the experimental results with numerical ones.

Experimental and numerical studies on punching shear strength of concrete slabs containing sintered fly ash aggregates

This paper presents experimental and numerical investigations on M30 Grade of concrete containing 40% of sintered fly ash aggregates (SFAs) on the punching behaviour of reinforced concrete (RC) slabs. Two 1000 x 1000 x 100 mm reinforced concrete slabs were cast and subjected to punching tests. The experimental results were compared with creating a nonlinear finite element programme using ABAQUS. This 3D Finite element analyses were performed with the appropriate modelling of element size and the constitutive modelling of concrete. The material parameters of the damaged plasticity model in ABAQUS were calibrated based on the test results of slab – plate connection. The comparison between experimental and numerical results indicates that the calibrated model correctly predicts the punching shear response of the slabs. A modification of 0.4 is introduced in MC2010 code.

Behaviour of Strengthened Flat Slab with Opening at Edge Column under Punching Shear Strength

Flat slab system is widely used because of its architectural flexibility Punching is one of the major and critical problems in flat slab especially for the edge column. There are many traditional ways to increase the punching shear strength of concrete slabs like increasing the slab thickness or column dimensions which is against the architectural desire Using FRP strengthening for the flat slabs against punching shear can be considered as a new application. Sometimes an opening is needed to be punched through existing slabs to install cables, elevators and ventilation systems, etc. This causes weakening due to the cutting of concrete and reinforcing steel and also increases the punching problems especially if the opening beside the edge columns. This research is aimed to evaluate the effects of strengthening with Glass Fiber Reinforced Polymer (GFRP) on the punching shear behaviour of flat slab with an opening varying in location with respect to the edge column. Bearing capacity, deflection, ductility, energy absorption and stiffness obtained from the tested slabs are compared to the control specimen, which was without opening and strengthening. It is observed that, the punching shear capacities of the strengthened specimens significantly increased compared to control specimen. Creating openings in flat slab beside the edge column should be approached with great caution and avoided if possible because of its bad effects. In case of openings are of extreme necessity, it is recommended to be created in the front of the edge column not in the side.

Enhancement of punching shear strength of flat slabs using shear-band reinforcement

Flat-slab system is widely used nowadays. Major and critical problem of this system is its sudden brittle failure is called punching shear failure. To overcome the punching failure problem, there are many ways to increase the punching shear strength of concrete slabs, increasing slab thickness in the area adjacent to the column, increasing column thickness which is against the architectural desire, and finally providing slab with shear reinforcement. Shear reinforcement is more advanced from both the structural and economical point of view.An experimental program includes seven full scale square flat slab interior column specimens tested under gravity loads. All slabs have same dimensions of 1700 mm × 1700 mm with thickness 160 mm and reinforcement ratio of 1.2%. Column was square of 200 mm length and 250 mm height. Elongated steel strips of 25 mm width and 1.5 mm thickness undulated into the slab in different ways to investigate punching shear resistance.The program is divided into five groups. First group investigates the effect of installing the shear-band reinforcement (hanged up on top mesh, knit the top and bottom mesh together). The second group investigates the effect of inclination of shear reinforcement (shear band with vertical leg, with bended leg 45°). The third group investigates the effect of concentrating the shear reinforcement by increasing the quantity around the column. The fourth group investigates effect of radial distribution of shear-band system around the column. Finally, the fifth group investigates the effect of box distribution of shear-band system around the column.

Influence of uniaxial tension and compression on shear strength of concrete slabs without shear reinforcement under concentrated loads

Under the shear load, reinforced concrete structures may be simultaneously subjected to the axial tensile or compressive forces due to shrinkage in restrained members, earthquake, tornado, and so on. Until now, no experiment addressing the effect of the uniaxial load on the shear resistance of reinforced concrete slab has been reported in the literature. All the experimental tests found in the literature were conducted on panel and beam (or wide beam) specimens. The current shear design provisions with axial load (ACI 318 and Eurocode 2) were developed based solely on panel and beam tests and not slab tests. Therefore, the current shear design codes applied to slab structures under the effect of axial forces urgently need revision. The present research studies the shear strength tests of slabs under the concentrated load simply supported on four sides. The effect of the tension/compression forces on the shear capacity was studied on full-scale slabs without shear reinforcement, a design similar to the slabs used in nuclear buildings, under a concentrated load near support. Experimental tests were conducted to quantify the shear capacity and the associated failure modes with the influence of axial forces. In this study, a series of seven tests on seven full-scale slabs measuring 4m×2.6m×0.3m is presented. The experiments were used to evaluate the pertinence of Eurocode 2 in terms of shear in reinforced concrete slabs with axial load, to compare these results to the AFCEN ETC-C code used for nuclear buildings, and to compare them to the ACI 318 code. The results showed that the axial tension forces equal to 0.28fctm (average concrete tensile capacity) reduced the shear capacity up to 30% in the concrete slab experiments conducted.

Influence of Clamping Stresses in the Shear Strength of Concrete Slabs Under Uniform Loads

Experimental results have shown shear capacities of concrete slabs under uniform loads sometimes considerably higher than those predicted by current concrete codes. Vertical compressive stresses transverse to the beam axis, or clamping stresses, are neglected in these analyses. The present study includes results from analytical and experimental research that was conducted to investigate the influence of clamping stresses on the shear strength of concrete slabs under uniform loads. Including clamping stresses in the Modified Compression Field Theory (MCFT) procedures was shown to considerably increase the shear prediction accuracy for members under uniformly distributed loads even for members with short shear spans. In addition, contrary to current sectional methods that give accurate results only in those regions where plane sections remain plane, results suggest that the MCFT with clamping stresses can provide reasonably accurate results in any region of a slab. Shear strength predictions from the MCFT with clamping were verified against 113 experiments from the literature and twelve tests designed and carried out during this work. Additional improvements in predicted shear capacities were achieved when tension stiffening was included in the calculations, an important issue for continuous members in which the shear critical region is close to the inflection point.

Strengthening Concrete Slabs for Punching Shear with Carbon Fiber-Reinforced Polymer Laminates

Although research into the application of externally bonded fiber-reinforced polymers (FRPs) to reinforce concrete slabs has concentrated on improving flexural capacity, FRP laminates also offer the potential to improve the shear capacity of reinforced concrete slabs. This paper describes an innovative approach for increasing the two-way shear strength of concrete slabs with carbon FRP laminates. A process analogous to stitching is used to retrofit concrete slabs with FRP strands. An experimental study was carried out on 28 square, isotropic two-way slab specimens simulating conditions in the vicinity of an interior square column in a continuous flat plate structure. Parameters such as the concrete strength, flexural capacity, and shear reinforcement arrangement were investigated, and the applicability of existing CSA A23.3-04 and ACI 318-05 standard specifications for punching shear resistance were examined. Results from the tests show that marked increases in the punching shear capacity and ductility (over 80 and 700%, respectively) can be achieved with CFRP retrofitting of slabs. The proposed procedure appears to be technically superior, easier to implement and produces more durable structures that traditional strengthening techniques. Although the procedure was tested for retrofitting of existing slabs, the results are equally applicable to new structures.

Punching shear strength of concrete slabs subjected to in-plane biaxial tension

Synopsis It has been found in three tests that in-plane biaxial tensile strains up to 0·0017 cause no reduction in the strength in punching shear of a reinforced concrete slab 90 mm thick. The test results are compared with the predictions of the recent Bridge Code (BS 5400) and of plastic theory.