PSI - Issue 64

Shamsoon Fareed et al. / Procedia Structural Integrity 64 (2024) 1057–1064 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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at 100 mm from the column face. The results of strengthened RAC slabs were also compared with those of NAC slabs without CFRP, and it was observed that all the slabs exhibited higher loads as compared to the NAC slab without CFRP, showing that the use of CFRP with RAC can help overcome the inherent weakness of RAC. . The identical FE model was used to investigate the influence of slab thickness on the behavior of two-way RC slabs, with varying thicknesses of 75 mm, 100 mm, and 125 mm. It is pertinent to mention here that in this parametric investigation, ‘ e ’ was kept constant at 100 mm, as used in the experimental investigation. The load-displacement relationships for NAC and RAC slabs having thicknesses of 75, 100, and 125 mm are shown in Figure 5. It was observed that in the case of RC-NAC specimens, an increase in the thickness of the slab resulted in increased load-carrying capacity, stiffer response and significantly reduced deflection. It was also observed that the overall behavior of the slabs was completely different from each other, both in the elastic range and the plastic range. It is because the initial response of the two-way slabs is governed by the local stiffness, which is a function of slab thickness and strength. This resulted in initial responses not similar to the responses observed for the case of slabs with the same thicknesses. RC-RAC slabs also demonstrated behavior similar to the one observed in RC-NAC slabs. Use of CFRP strips does not influenced the overall behavior of NAC and RAC specimens.

100 150 200 250 300

RAC- CFRP- s75 RAC- CFRP- s100 RAC- CFRP- s125

NAC- CFRP- s75 NAC- CFRP- s100 NAC- CFRP- s125

100 150 200 250 300

Load (kN)

Load (kN)

0 50

0 50

0

0.5

1

1.5

2

0

0.5

1

1.5

2

Deflection (mm)

Deflection (mm)

(a)

(b)

Figure 5: Load-displacement relationship for specimens having different thicknesses and prepared with (a) NAC and (b) RAC.

Table 4 presents the maximum load-carrying capacities predicted using FE analysis carried out for varying thicknesses of NAC and RAC slabs. As expected, the load-carrying capacities of both NAC and RAC slabs increased when the thickness of the slabs was increased, as the punching capacity of concrete is proportional to the thickness of the slabs. An increase of 105% was observed in RAC slabs of 100 mm as compared to 95% in their NAC counterparts, whereas, an increase of 167% was noted in RAC slabs of 125 mm as compared to NAC slabs of similar thickness. This again highlights the effectiveness of the use of CFRP along with RAC. The role of CFRP strips in providing resistance to punching shear stresses is more pronounced in the case of RAC than NAC.

Table 4: Load exhibited by specimens having different thicknesses. Thickness (mm) NAC

Peak Load (kN)

% Increase with respect to 75mm

% Increase with respect to 75mm

RAC 96.1 197.0 256.2

75

109.4 213.6 235.7

-

-

100 125

95

105 167

115

The load-displacement relationships for the comparison of RC-NAC slabs, with and without CFRP strips, are shown in Figure . It was found that for the case of slabs without CFRP strips, the load-carrying capacity of the slabs increases with the increase in the concrete compressive strength. Increased load-carrying capacities were observed at almost the same deflections for all RC slabs indicating increased stiffness with an increase in compressive strength. When comparing the behavior of RC slabs strengthened with CFRP strips with slabs without CFRP strips, load carrying capacity as well as deflection increased almost twice for each concrete compressive strength.. The overall enhancement in the behavior of RC slabs with CFRP strips can be attributed to the high stiffness of the CFRP strips.