| Segmental precast concrete bridges have unique advantages in construction speed and environmental protection,and have been vigorously promoted at the government level around the world in recent years.At present,box beams are mostly used in the construction of segmental prefabricated assembled bridges,however the research and application of T-shaped segmental beams are relatively few.This thesis relies on the project of “research on the conversion scheme of sub-section prefabricated T-shaped beam system” of CSCEC Road and Bridge Group Co.,Ltd.In order to study the bending and fatigue performance of T-shaped bridges,six test beams are designed and manufactured for static load and fatigue tests respectively.The static load and fatigue properties of segmental precast concrete T-shaped beams were studied by taking the construction process(integral cast-in-place and segmental precasting)and joint form(large key teeth and double key teeth)as the controlling factors,and the main contents and research conclusions are as follows:(1)Designed and manufactured the test beams and support for this experiment,and obtained the static load failure form,load deflection curve,crack width change law,etc.of segmental prefabricated T-shaped beams through two-point loading test.The results show that the ultimate bearing capacity of the segmental prefabricated assembled T-shaped beam is reduced by 7.9% and 15.1% compared with the overall cast-in-situ beam with the same design,and the bending bearing capacity of the double-key tooth segmental beam is better than that of the large key tooth segmental beam.Before the crack is developed,the mechanical properties such as the stiffness of the segment beam are close to the overall beam,but the stiffness decreases rapidly after cracking.(2)The finite element software was used to establish the overall cast-in-situ and segmental test beam model,and the rationality of the modeling method was verified by load-span mid-deflection curve and beam failure morphology.Based on this batch finite element model,the influence law of the parameters affecting the bending bearing capacity such as prestress,concrete strength,and number of joints was analyzed,and the ratio of the finite element model under different working conditions established in batch to the ultimate bearing capacity of the corresponding overall beam was compared with the reduction coefficient in AASHTO specification of the United States,and it was found that the actual bending bearing capacity reduction coefficient of the precast concrete T-shaped beam was close to the provisions in the specification,but the reduction coefficient under the actual specific working conditions was related to the factors such as segment reinforcement and key tooth type.(3)Apply fatigue load to the test beams manufactured in the same batch as the static load test beams for fatigue testing,and obtained the concrete compressive strain near the joint,the tensile steel bar near the joint,the change law of span deflection and stiffness,fatigue failure form,etc.during the fatigue test.The test results show that the growth of compressive strain of concrete near the joint,tensile strain of tensile reinforcement near the joint,and mid span deflection all follow a three-stage growth pattern.Under the same fatigue load,the fatigue performance of the T-shaped beam processed by the whole cast-in-place process is better than that of the T-shaped beam fabricated by the segmental precast process,and the fatigue performance of the segemental precast assemebled beam with double key teeth is better than that of the segmental precast assembled beam with large key teeth.Based on the results of static loading after different cycles during the fatigue test,the stiffness degradation law of segmental precast concrete beams with different types of kye teeth is obtained.The results show that the stiffness degradation of segmental beams with double key teeth is slower than that of segmental beams with large key teeth. |
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