PSI - Issue 64

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

1061

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displacement relationships of the RC- NAC specimens having CFRP strips at different ‘e’, it was found that the load resistance increased significantly for the case of slabs having CFRP strips near the column face, i.e., e = 0. It is due to the magnitude of the shear stresses, which are significantly higher in the column slab interaction region in RC slabs, and the use of CFRP strips close to that region significantly improves the load-carrying capacity. This observation was also found in the case of RC-RAC specimens, in which not only did the use of CFRP strips resulted in the increased load-carrying capacity concerning the RC-RAC specimens without CFRP, but it also overcame the inherent reduced strength associated with the RAC specimens. It was observed that externally bonded CFRP strips increased the stiffness of the slabs, as they exhibited reduced deflections as compared to the slabs without CFRP strips at the same load level for both NAC and RAC specimens. Reduced deflections in the strengthened slabs at same load levels were found to be a function of placement of CFRP strips from the edge of the column. Closer the strips to the column, smaller the deflections in the slabs. The RC- RAC specimens exhibited brittle behavior as compared to the NAC specimens as can be seen in Figure 4. Stiffness mentioned herein, refers to stiff response of the slabs which is reflected by lower deflections at same load levels.

100 120 140 160

100 120 140 160

0 20 40 60 80

0 20 40 60 80

NAC-CFRP-e0 NAC-e=50 NAC e=75 NAC e=100 NAC-NoCFRP

Load (kN)

RAC-CFRP-e0 RAC-CFRP-e=50 RAC-CFRP-e = 75 RAC-CFRP- e=100 RAC-no CFRP

Load (kN)

0

0.5

1

1.5

2

0

0.5

1

1.5

2

Deflection (mm)

Deflection (mm)

(a)

(b)

Figure 4: Load-displacement relationships of (a) NAC and (b) RAC slabs with different placement of CFRP strips from column edge.

The load resistance capacities predicted using FE analysis show an increase in load-carrying capacities in all slabs used with CFRP strips, irrespective of the placement of the strips. A maximum increase (98%) in NAC slabs was observed in the slabs where CFRP strips were provided immediately at the column face (Table 3). This increase in load-carrying capacity is reduced as the CFRP strips are placed at 50 mm, 75 mm, and 100 mm, respectively. A minimum increase (59%) was observed when the CFRP strips were placed 100 mm from the column face.

Table 3: Load exhibited by specimens having different placement of CFRP strips from column edge. CFRP Spacing (mm) Peak Load (kN) NAC % Increase w.r.t. NAC without CFRP RAC % Increase compared toRAC without CFRP

% Increase compared to NAC without CFRP

No CFRP

68.7

-

64.5

-

No increase

0

135.7

98 85 70 59

122.3 110.3 102.6

89 71 59 49

78 61 49 40

50 75

126.89 116.89

100

109.4

96.1

A similar trend can be seen for the case of CFRP-strengthened RAC slabs. A maximum increase (89%) was observed in the slab with CFRP strips adjacent to the edge of the column. This is reduced as the CFRP strips are placed at 50 mm, 75 mm, and 100 mm, respectively. A minimum increase (49%) was observed when the CFRP strips were