Short-term behav ior
Flexural capacity and load-deflection response-The
unstrengthened control beam showed a cracking load of
9.2 kN (2.1 kip), followed by yielding and ultimate loads of
38.0 and 39.5 kN (8.5 and 8.9 kip), respectively, as given in Table 1.The beam strengthened with one strip ofNSM CFRP (Beam S0-1) exhibited improved behavior in comparison to the control beam , including 23.9%, 32.4%, and 70.9% for cracking, yielding, and ultimate loads, respectively. Such enhanced performance is attributed to the additional tensile resistance provided by the CFRP strip that lowered the neutral axis depth of the beam (that is, 1.2% and 6.4% for uncracked and cracked states, respectively, according to sectional analysis), thereby increasing its compression zone; however, the CFRP caused rather brittle behavior of the strengthened beams, as shown in Fig. 5(a). The beam strengthened with two strips of CFRP (S0-2) demonstrated slightly enhanced flexural capacity relative to the one with one strip (S0-1), including increases in cracking, yielding, and ultimate loads by 8.8%, 6.2%, and 3.9%, respectively. It should be noted that the insignificant increase in the ultimate capacity of Beam S0-2 was due to its distinct failure mode compared to that of Beam S0-1 (to be discussed). Figure 5(a) shows the load-deflection behavior of the short-term beams at midspan. All three beams revealed similar responses until cracking took place, whereas the strengthened beams demonstrated higher stiffness than the unstrengthened control within a service load range. This implies that the strengthened beams better resisted crack propagation when the flexural load was applied . As discussed previously, the two-strip beam exhib ited marginally improved flexural b havior in comparison to the one-strip counterpart-in particular, beyond yielding of the beam due to an enhanced stress sharing mechanism (that is, the applied tensile stresses were shared by the steel reinforcement and the NSM CFRP). To further examine the efficacy of the NSM CFRP from a serviceability perspective , the effective moment of inertia of each beam, 1., was calcu lated using Eq. (1) and shown in Fig. 5(b).
ระยะสั้น behav iorความจุ flexural และโหลด deflection ที่ตอบสนองแสดงการโหลด cracking ของคานควบคุม unstrengthened9.2 โหลดช็อปปิ้ง (2.1 กีบ), ไปมาแล้ว โดยผลผลิต และช่วงสุดท้ายของ38.0 and 39.5 kN (8.5 and 8.9 kip), respectively, as given in Table 1.The beam strengthened with one strip ofNSM CFRP (Beam S0-1) exhibited improved behavior in comparison to the control beam , including 23.9%, 32.4%, and 70.9% for cracking, yielding, and ultimate loads, respectively. Such enhanced performance is attributed to the additional tensile resistance provided by the CFRP strip that lowered the neutral axis depth of the beam (that is, 1.2% and 6.4% for uncracked and cracked states, respectively, according to sectional analysis), thereby increasing its compression zone; however, the CFRP caused rather brittle behavior of the strengthened beams, as shown in Fig. 5(a). The beam strengthened with two strips of CFRP (S0-2) demonstrated slightly enhanced flexural capacity relative to the one with one strip (S0-1), including increases in cracking, yielding, and ultimate loads by 8.8%, 6.2%, and 3.9%, respectively. It should be noted that the insignificant increase in the ultimate capacity of Beam S0-2 was due to its distinct failure mode compared to that of Beam S0-1 (to be discussed). Figure 5(a) shows the load-deflection behavior of the short-term beams at midspan. All three beams revealed similar responses until cracking took place, whereas the strengthened beams demonstrated higher stiffness than the unstrengthened control within a service load range. This implies that the strengthened beams better resisted crack propagation when the flexural load was applied . As discussed previously, the two-strip beam exhib ited marginally improved flexural b havior in comparison to the one-strip counterpart-in particular, beyond yielding of the beam due to an enhanced stress sharing mechanism (that is, the applied tensile stresses were shared by the steel reinforcement and the NSM CFRP). To further examine the efficacy of the NSM CFRP from a serviceability perspective , the effective moment of inertia of each beam, 1., was calcu lated using Eq. (1) and shown in Fig. 5(b).
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