PSI - Issue 60

Swathy S et al. / Procedia Structural Integrity 60 (2024) 591–603 Swathy S et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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strengthen four slabs using four different configurations. Stiffness and deformation capacity were improved in the slabs. Sohaib et al [9] examined the using polypropylene fibre in concrete to achieve maximum strength of concrete by using optimum weight of polypropylene fibres. The addition of small amount of polypropylene improved the mechanical properties of concrete. Nadia Nassif et al [10] studied the punching shear strength behaviour of flat slabs reinforced with the addition of 1% and 0.5% of macro synthetic fibres to the slab. As a result, there is an increase of about 30% to 70% of the shear strength and 40% to 80% of the energy absorbance respectively. All these studies elucidated the failure for flab slab and their influences on the load carrying capacity, ductility, deformation capacity and stability of structure. The properties of polypropylene fiber reinforced concrete that enhance the shear performance and increases the ductility. Following all the above studies, this study focuses at investigating strengthening technique of two-way flat slab using BFRP fan as a new method of strengthening against line loading. Consequently, this study aims to examine the two strengthening technique using BFRP fan and Basalt laminates to increase the load carrying capacity and the enhance the ductility over addition of optimum percentage of polypropylene fiber reinforced into the slab, to increase the strength of existing slab and thus focus the possibility of enhancement of the punching shear strength and flexural strength at the same time. Strengthening with basalt fiber string is cost effective when compared to its high strength, corrosion resistance, multifunctional use which provides the designer flexibility to improve the bearing capacity without affecting the size of the structural concrete component. A sample is designed for the critical section and the reduction of dimension is done using Cauchy similitude. 2. Experimental study Three typical specimens were tested to investigate the efficacy of applying BFRP fan and laminates. The configurations of all the specimens were formed to be square slabs with dimensions of 1000 x 1000 x 135mm and reinforced with bottom square mesh of 12 ϕ 12 and square mesh of 12 ϕ 10 at the top, to achieve sufficient flexural strength. Only the slab is tested. Fig 2 shows concrete dimension and the reinforcement details of specimen. The concrete mix for casting was designed to develop a strength of cube of about (f cu ) of 35 N/mm 2 for all samples. Two sets of three cube of dimension 150mm x 150 mm were casted in which one set is reinforced with polypropylene fibre of optimum percentage of 0.3% and the cube strength is determined by curing and testing it after 28 days. Fig 3 shows the polypropylene fibre. A control specimen SP1-CS was cast and prepared to measure the load carrying potentiality of the reinforced slab without any strengthening of BFRP string and laminates. The rest of the specimen are strengthened using BFRP fan and laminates. Cross sectional area of BFRP string drilled over the slab is 22 mm 2 and the specimen SP2-SBF was strengthened using 16 BFRP fans which are double stranded. The slab SP3-SBL strengthened using basalt strip on both the faces of the slab. Table 2 illustrates the details of test performed of all the mentioned conditions. Investigation is performed on flat slab with two strengthening technique. One of the techniques was that, the flat slab is strengthened by inserting BFRP string through drilled slots and grooves are made in the shape of fan to impregnate the string on on top and bottom surface of the slab. The other technique is strengthening using basalt laminate in which basalt strip is placed as a radial pattern on both top and bottom surface of the slab. The actual slab considered is a flat slab of 3000mm x 3000mm 155 thick designed for live load of 4 KN/m 2 resting on a column of 300 mm x 300 mm. Fig 1 shows Critical section for punching shear failure at d/2 distance from the face of the column for two-way shear. After calculating the nominal and designed shear, it was found that the designed shear stress of the slab is greater than the nominal shear strength and thus the critical section at a distance of d/2 satisfies for the designed slab.