Topic: Design

Last updated: April 25, 2019

Fig.16 presents the yield, ultimate and failure loads carrying capacities for the all tested beams. As shown in Fig. 16, the yield load for the top and bottom main reinforcement and the ultimate load for the control beam (CB) were 260, 278 and 347 kN, as previously explained, the sagging tensile reinforcement yielded after the yielding of the hogging main reinforcement and before the maximum load. The yield loads at the hogging and the sagging region were equal to (75% and 80%) of the ultimate load.The yield loads were affected by the region of the strengthening, where unlike the others, the main top reinforcement at the strengthening beams (SSH and SCH) yielded after the mid-span tensile steel yielding, thus, there was a clear variation in the values of the yielding loads, but the yield loads for all strengthening beams were higher than the yield loads of the control beams. The strengthened beam (SCH) had the less sagging yield load between the strengthening beams and it was higher than the sagging yield load of the control beam by about (11.5)%, while the minimum hogging yield load was for the strengthened beam ( SSS) and it increased by about (22.

7)%. Despite the convergence of the failure loads values, but the strengthening by using NSM CFRP bars at the sagging region was higher than the failure load at the control beam by (25%) and it was the best efficiency, even though the least efficient was for the strengthening at the hogging region by using NSM CFRP bars, where the maximum load increased only by (10 %). Serviceability is a basic characteristic of comparison, the serviceability of the tested beams can be determined according to 2 and 3 by using permissible crack width, allowable permitted deflection, and allowable yield strain, Table 6 shows the measurement value of the load at hogging and sagging regions for different levels of flexural crack width (0.1, 0.2, 0.3).

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The flexural crack width ?”w?_cr ” (0.1, 0.2 and 0.3 mm) is the permissible crack width according to 2 and 3. It is clear that strengthening with NSM CFRP bars gave preference for the load at the same crack width at the strengthening region only, but the strengthening by using NSM steel bars had the advantage at both regions, although the service load was fewer at the strengthening region than using NSM CFRP bars.According to 2, the specified service limit is at 0.35 of the yield strain for f_y at least 420 MPa. Therefore the service loads were 151, 178, 151, 161 and 137 kN for beams CB, SSH, SCH, SSS and SCS respectively.

Thus, the strengthening with NSM bars had the advantage at the service loads. The maximum deflection should be compared to the allowable permitted deflections in codes and design guidelines. The allowable deflection permitted by 2 and 3 ranges from L/480 to L/180 depending on the type and function of the structure. The allowable deflection for tested beams according to 2 and 3 should be within the range of 4–11 mm (2,050/480 to 2,050/180) based on the type of structural application. So according to the structural type, the strengthening at the sagging region by NSM steel or CFRP bars was better than other types of strengthening in the case of The allowable deflection equals L/180 and L/480, and the strengthening by using NSM steel bars was better than .

As shown in Table 6.


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