Numerical Analysis of Voided Flat Slab

Reinforced concrete (RC) flat slabs, a popular choice in construction due to their flexibility, are susceptible to sudden and brittle punching shear failure. Existing design methods often exhibit significant bias and variability. Accurate estimation of punching shear strength in RC flat slabs is crucial for effective concrete structure design and management. This study introduces a novel computation method, the jellyfish-least square support vector machine (JS-LSSVR) hybrid model, to predict punching shear strength. By combining machine learning (LSSVR) with jellyfish swarm (JS) intelligence, this hybrid model ensures precise and reliable predictions. The model’s development utilizes a real-world experimental data set. Comparison with seven established optimizers, including artificial bee colony (ABC), differential evolution (DE), genetic algorithm (GA), and others, as well as existing machine learning (ML)-based models and design codes, validates the superiority of the JS-LSSVR hybrid model. This innovative approach significantly enhances prediction accuracy, providing valuable support for civil engineers in estimating RC flat slab punching shear strength.

The Two-way hollow slab system (biaxial voided slab) is an innovative slab system, being adopted all over the world as an alternate for the conventional solid slab. It reduces the self-weight up to 50% in comparison with solid slabs without significant change in its structural performance. The voided slab consists of void formers in shapes like spherical, donut, and cuboid. Experimental and analytical investigations were carried out to study the behaviour of biaxial voided slab under one-way flexure. Voided slab specimens were prepared and tested with two different shapes of voids namely sphere and cuboid, which were manufactured using recycled polypropylene. Comparison of experimental and analytical studies showed that the ultimate load-carrying capacity of voided slabs was higher or similar to that of solid slab. An analytical study was carried out using the yield line analysis in conjunction with Indian Standards. It was found that the capacity of voided slab can be estimated by yield line analysis. The flexural stiffness of voided specimen is approximately 50% lesser in comparison with solid slab of identical dimensions and reinforcement at yield stage. The reduction in flexural stiffness is mainly due to the presence of void former and the maximum void ratio at a section defines the flexural stiffness of the voided slab. Nevertheless, the deflection is under serviceable limit for both the specimens for 75% of ultimate load. Ultimately, it is found that the behaviour of voided slabs under one-way flexure can be predicted by provisions of Indian Standards with necessary correction for loss of cross-section caused by voids.

The flat slab is gaining popularity among architects. The flat plate slab provides a way for architect to achieve completely flat ceiling with no beam protrusion. There is also improvement in the construction speed and cost savings from using this system which requires only simple formwork. But when load acting on the slab is large or clear span between columns is more so it is required to increase the slab thickness; hence the self –weight of slab is increased due to increased volume of slab and also more amount of steel is required to resist this increased weight of slab. Voided slabs eliminate concrete where it isn’t needed and the subsequent weight reduction due to this eliminated concrete makes longer span possible. In this study the design process for flat plate slab is compared with voided slab lightened with U-Boot Beton through a design comparison of total slab area 40m by 40m having panels of 10m by 10m and also the deformation of both type of slabs is analysed by using ETABS software.

Effect of using Engineered Cementitious Composites (ECC) on failure behavior of flat slab-column connections

Influence of stirrup detailing on punching shear strength of flat slabs

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Experimental and theoretical investigations of UHPC-NC composite slabs subjected to punching shear-flexural failure

Voided slab systems were developed using segmented void formers such as spherical or oval plastic balls for two-way slab applications. This type of slab is expected to behave like a general two-way reinforced concrete slab because it has segmented voids, rather than the continuous voids of hollow core slabs. However, the structural behaviors of two-way voided slabs with segmented voids have not been clearly verified. Therefore, this paper analyzes the possibility of applying a donut-type two-way voided slab, which was investigated with a 12-point two-way bending test focused on global behaviors, including its load bearing capacity, flexural stiffness, ductility, deflection, and load distribution. In addition, the design method of a donut-type two-way voided slab was reviewed through the yield line method. The test results showed that one donut-type two-way voided slab acted like a conventional two-way reinforced concrete slab with the load distributed evenly between the different directions; however, another donut-type two-way voided slab with different characteristics showed uneven load distribution with different crack patterns. In addition, the yield line method could predict the load bearing capacities of the donut-type voided slabs with approximately 95% accuracy.

Present study involves the experimental analysis of spherically voided biaxial slabs. The intention was to eliminate the unused concrete in massive slab constructions. Three voided slab specimens (2900 mm × 2900 mm × 100 mm) were cast. The voids were created by introducing spherical-shaped high-density poly propylene void formers in between the compression and tension layers of the slab. The parameter varied was the spacing of the void formers, which were kept as 20, 30 and 50 mm. The corresponding reduction in volume of concrete for the above-mentioned spacing was 22.7, 18.4 and 12.21%, respectively. The slabs were subjected to area loading instead of regular five-point loading. Analytical calculation for the ultimate load carrying capacity was carried out similar to biaxial solid slab. Comparison of load deflection behaviour showed that void spacing between 20 and 30 mm may be provided to satisfy both strength and serviceability criteria. The percentage reduction in volume of concrete was found to be directly proportional to percentage reduction in cost of construction.

A punching shear mechanical model for reinforced concrete flat slabs with and without shear reinforcement

Punching shear strength of flat slabs with different punching reinforcement configurations

To predict the punching shear strength of recycled aggregate concrete (RAC) thin flat slabs, a model was constructed based on their failure mechanism under punching shear. For accurate predictions, a novel size effect factor was suggested for thin slabs. The proposed model was validated by comparing its predictions with RAC thin flat slabs’ experimental results. Additionally, a natural aggregate concrete (NAC) thin flat slab database was utilized to further evaluate the proposed model’s applicability. The model’s accuracy and reliability were rigorously assessed by comparing it with existing design equations. The comparison results demonstrated that the proposed model consistently aligned best with experimental results across all test parameters. It also outperformed the existing design equations, as evidenced by statistical parameters: a mean of 1.05, the lowest coefficient of variation (COV) of 0.148, the highest R2 at 0.90, and disparity rate reaching 100% in the range of 0 to 0.2. Moreover, the proposed model demonstrated a good fit for NAC thin flat slabs, with a mean value of 1.01 and a COV of 0.201. To provide insight into the design of RAC flat slabs, the influences of recycled aggregate (RA) content and key design parameters on punching shear strength were thoroughly analyzed.

Steel fibers in reinforced concrete increase the performance of slab-column connection once they increase ductility and energy absorption capacity of the concrete. The use of fibers in flat slabs may increase strength and change the mode of failure. The objective of this work is to present an experimental evaluation of punching shear strength of reinforced concrete flat slab with steel fibers and punching shear reinforcement. Eight square slabs, size 1800 mm by 1800 mm by 130mm, were loaded until failure by punching shear around the column. The models were divided in two groups, depending on the type of the concrete used (with or without steel fibers). The steel fiber volume used in the slabs of second group was of 0.9%. Each group was composed of four slabs: one without shear reinforcement and three with shear reinforcement (studs) distributed radially around the column. The use of steel fibers increased the ultimate strength of all flat slabs. In one of the slabs, the association of steel fibers with shear reinforcement changed the failure surface from outside to inside the punching shear reinforcement region.

This paper offerings a wide-ranging study to investigate the punching shear behavior of reinforced concrete flat slab with openings. The study involved of eighteen specimens tested under static load and divided into two series; the first group included flat slabs with openings while the second series were slabs with openings with varied compressive strength. The used variables were the opening location and number in addition to the compressive strength of slabs (40,50, 60, and 70 MPa). The results showed that the slabs behaves linearly until it reaches about average value 23.5% of their ultimate strength for solid slab and by (23%) for the slabs with opening. The openings presence affected the load carrying capacity which decreased the average cracking load by (31%) and ultimate load by (28%) when compared with the solid slab. Regarding the opening location, placing the opening near the central column led to decrease in the cracking and ultimate load of the flat slab with maximum decrement in the ultimate load was by (60.2%) when compared with the solid slab. increase of the compressive strength enhanced punching shear strength of the slabs with opening. The ductility and energy absorption of flat slabs were decreased with the existence of the opening and enhanced when the compressive strength increased.

The increasing use of FRP composites to strengthen and repair the structural bearing components, also low weight, high flexibility, ease of transportation, high speed, ease of cutting in desired sizes, ease of performance and possibility of external strengthening are the major reasons for using the FRP laminates in repairing concrete structures compared to other methods. One usage of FRP laminates is strengthening the reinforced concrete slabs. Present article studied the impact of type and number of composite layers in flexural strengthening of the reinforced concrete voided slabs with FRP laminates. The voided slabs are used to reduce concreting volume, costs and also decreasing weight of the structure. Some of these buildings and bridges have been severely damaged due to natural disasters including earthquake, wind or fatigue of materials and alkaline and acidic corrosive agents. Therefore, repair and strengthening the bearing surfaces of above structures is vital and economical. Present research has investigated the parametric study of the impact of type and thickness of FRP fibers on flexural behaviour of strengthened voided slabs using different FRP systems (CFRP-GFRP). For this purpose, the voided concrete ceiling is modelled in ANSYS software, then it is compared to the available laboratory model for verification of the problem. After the verification, by changing the parameters of type and thickness of RFP fibers in the modelled voided slab, ultimate strength of the slab has been studied. These studies have showed that the slabs retrofitted with GFRP fibers have a better ductility compared to the slabs retrofitted with CFRP fibers, but ultimate strength of the slabs retrofitted with CFRP is significantly more than the slabs strengthened with GFRP fibers. It was also found that by increase in the number of laminated composite layers in retrofitted voided slabs, ultimate capacity of the voided slabs is increased.