| With the further development of constructions,the concrete structures with high durability are needed and required for the constructions subjected to severe environments.The steel bars or strands replaced by fiber reinforced polymer(FRP)in concrete are the positive and effective way to improve the durability.In this study,the pullout-winding equipment was used to manufacture different kinds of FRP bars,then the production technique,mechanical properties and bond properties with concrete of FRP bars were investigated.Based on the study of FRP tendon anchorage technique,the anchoring and prestress applying method of RC one-way slab externally prestressed with FRP tendons was proposed.Finally,the flexural property and calculation method of RC one-way slab externally prestressed with FRP tendons were investigated.The main contents in this thesis are presented as follows:(1)Using the pullout-winding equipment,the different types of Glass Fiber Reinforced Polymer(GFRP)bars were prepared while the Steel and Glass Fiber Reinforced Polymer(SGFRP)bars were developed by mixing glass fibers and steel wires.The effects of rib form,bar diameter and volume fraction of steel wire on the FRP bar mechanical properties were investigated.The effects of volume fraction of steel wire and rib form on the shearing property and torsional property were analyzed,respectively.The improvements of the FRP bar pullout-winding equipment and technology were suggested on the existing problems.(2)The bond test of 42 pull-out specimens was conducted to investigate the effects of rib form,volume fraction of the steel wire,concrete cover thickness and concrete strength on the failure model,bond stress-slip curve and bond strength of FRP bar embedded in concrete.The surrounding concrete of FRP bar was assumed as cracking elastic material with residual strength.The calculation models of maximum bond stress,bond strength and basic anchorage length of ribbed FRP bar in concrete were proposed.The bond stress-slip curves of pull-out specimens under splitting and pull-out failures were proposed according to the previous stress-slip curve model.(3)The working mechanism and failure modes of wedge anchorage for FRP tendons were analyzed.The critical conditions of pre-tightening force and self-lock were determined according to the working mechanism.The radical stress distribution of interface between FRP tendon and wedge was proposed.Meanwhile,the calculation model and simplified method of carrying capacity for FRP tendon wedge anchorage were presented.Two new kinds of simple FRP tendon bond-type anchorages with internal thread or plug were designed to improve the bond strength between steel sleeve and filled medium.The carrying capacity and the peak bond stress between FRP tendon and filled medium of FRP tendon bond-type anchorage can be improved.Also,the length of anchorage can be reduced.(4)Based on the study of FRP tendon anchorage,the anchoring and prestress applying method of RC one-way slab externally prestressed with FRP tendons was presented.With varying prestress and ratios of external prestressing FRP tendons,five RC slabs externally prestressed with GFRP tendons and one control for comparison were tested to analyze the flexural property.The test results show that the one-way slabs performed a slight decrease in ductility,when they were strengthened by GFRP tendons.However,the flexural capacity,stiffness and crack development were significantly improved.With the increase of prestress and ratio of external prestressing FRP tendons,the cracking moment and ultimate moment were improved by 24%~121% and 38.6%~103%,respectively.(5)Due to the crack propagation,the ultimate bearing capacity state of RC one-way slabs externally prestressed with GFRP tendons was reached,which showed a different failure mode from RC beams.According to the failure mode,the calculation model of effective stress in the external FRP tendon,the prediction method of cracking moment and ultimate moment for RC one-way slab externally prestressed with FRP tendons were proposed based on the bond reduction coefficient and plastic hinge length.Moreover,by following the current calculation model,the calculation method of short-term stiffness for RC one-way slab externally prestressed with FRP tendons was suggested. |
