| High-Strength concrete has been widely used in civil engineering structures,but its shortcomings such as its heavy weight and poor crack resistance restrict the spanning ability and durability of bridge structures.The research on lightweight of high-performance concrete is currently an important research focus.This research group has prepared a Lightweight Ultra-High Performance Concrete(LUHPC),whose basic mechanical properties are:compressive strength greater than 110MPa,splitting strength greater than 12MPa,elastic modulus greater than 3.8×10~4MPa,The apparent density is less than 2100kg/m~3.As a new material,LUHPC has not been analyzed for its flexural performance,so it is very necessary to study the flexural performance of LUHPC beams.This article is based on Hubei Province’s major project on technological innovation,“Development of lightweight ultra-high-performance concrete and its application in prefabricated bridge engineering(2018AAA001)”,designed and produced reinforcement ratios of 0.3%,2.3%,4.2%,6.8%,8.7%,16 LUHPC beams with HRB400 and HRB500 reinforcement,and 7 high-strength concrete beams with the same reinforcement ratio were made as a comparison,and their flexural performance tests were carried out to study the failure form and load-deflection curve of LUHPC beams and the laws of influences of the reinforcement ratio and steel bar strength on the ultimate bearing capacity,cracking bending moment and ductility.According to the measured strain distribution law of mid-span concrete under the limit state,a correction formula for flexural bearing capacity is proposed,which simplifies the stress figure of the compression zone to a triangle and considers the contribution of the concrete tensile stress in the tension zone.This work provides a certain theoretical and experimental basis for the engineering application of LUHPC new materials.The main work completed is as follows:(1)When the reinforcement strength is HRB400 and the reinforcement ratio is 2.3%,4.2%,6.8%,the ultimate bearing capacity of the LUHPC beams is increased by26.9%～35.7%.When the reinforcement ratio of the LUHPC beam is 0.3%,less reinforcement failure occurs,and when 8.7% super reinforcement failure occurs.When the suitable reinforcement beam is damaged,the crack distribution is thin and dense.Under the same reinforcement ratio,the cracking moment and ultimate bearing capacity of LUHPC beams are higher than that of high-strength concrete beams,and their ductility is significantly better than that of high-strength concrete beams.(2)When the reinforcement strength is HRB500,the reinforcement ratio is 2.3%,4.2%,6.8%,and the ultimate bearing capacity is increased by 12.5%～30.1%.Under the same reinforcement ratio,the ultimate bearing capacity of LUHPC beams is increased by 10.5%～28.5%compared with HRB400 steel bars,but the cracking bending moment does not change much.(3)Simplify the stress figure in the compression zone into a triangle and simplify the stress figure in the tension zone into a rectangle,in which the reduction coefficient k of the tensile strength is 0.65.The calculated values are in good agreement with an average error of 4%.The calculation model proposed in this paper has good accuracy.(4)According to the test,the steel fiber influence coefficient calculated for the crack width and the material influence coefficient for calculating the cracking bending moment of the LUHPC beam is obtained.Provide a basis for the calculation of crack width and cracking bending moment. |
