| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 96 === In this research, the fatigue behavior and damage of lightweight concrete (LWAC) beams subjected to cyclically dynamic loading was investigated and compared with that of corresponding normal weight concrete (NWC) beams. Traditional hydraulic press machine (MTS) was adopted with identical loading amplitudes on the basis of force control. Dynamic loading tests were implemented with 4 levels of loading magnitude (Pmean/Py=0.64、0.56、0.48 and 0.40). For each level, the loading amplitude (Pamp=(Pmax− Pmin) /2) was set to be constant values (Pamp=8 kN). Loading frequency is 2Hz. Further, if the specimen subjected to two million cycles of dynamic loading without entire failure, the static loading tests were performed to access the residual strength of beam.
The experiment results showed that the relation between stiffness degeneration (kN/k0) and loading levels (Pmean/Py=0.64、0.56、0.48 and 0.40) of NWC beams is not obvious, but the relation of both in LWAC beams is obvious. For the higher loading level(Pmean/Py=0.64、0.56), the stiffness degeneration extent of LWAC beams is higher than that of NWC beams. However, for the lower loading level (Pmean/Py=0.48、0.40), the stiffness degeneration extent of LWAC beams definitely is less. For the higher loading level, the displacement amplitude ratio (△N,amp/△0 ) of LWAC beams were higher than that of NWC beams. In contrast, for the lower loading level, LWAC beams were lower. Besides, less residual deformation (△Rd) could be observed in the LWAC beams for the same loading level. The magnitude of mean loading has a conspicuousness effect on fatigue damage for NWC and LWAC beams. Fatigue damage of beams gradually increases with an increase of the loading level. For the higher loading level, the fatigue damage of LWAC beams is higher than that of NWC beams. Besides, for the lower loading level, the fatigue damage of LWAC beams obviously is much less than NWC beams.
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