Experimental Research On Shear Behavior Of High-strength Reinforced Concrete Beams With UHPC Permanent Formwork

High-strength reinforced concrete structures are currently developing rapidly.High-strength reinforced concrete beams have the same complex formwork engineering problems as ordinary reinforced concrete beams,and high-strength reinforced concrete beams have larger crack widths than the ordinary concrete beams under the same strip.Ultra-high performance-concrete（UHPC）possess ultra-high tensile strength and compressive strength,but its promotion is limited due to its high price.The application of UHPC as permanent formwork in beams can better solve the complexity of the formwork engineering,improve the mechanical performance and durability of the structure,and reduce the cost of UHPC.At present,there is still a lack of shear research on composite beams at home and abroad,and there is no shear test study on UHPC permanent formwork high-strength reinforced concrete beam.Therefore,it is of great application value to carry out shear test research on UHPC permanent formwork high-strength reinforced concrete beams（hereinafter referred to as composite beams）.The main contents of this paper are as follows:（1）Different conditions such as shear span ratio,formwork type and presence or absence of formwork were designed to observe the experimental phenomena of crack development and ultimate failure mode of composite beam.The results showed that the main crack of high-strength reinforced concrete beams with a shear span ratio of 2 was mainly formed by multiple cracks,and the main cracks of composite beams under the same shear span ratio was generally a development of bending shear crack.With the increase of shear span ratio from 2 to 2.5and 3,the development speed of cracks to the loading point of the bearing gradually increases,and the brittleness of the beam became larger when it failed.（2）The test data such as load deflection,concrete strain,and crack width was analyzed to check the influence of various factors on development of cracks.The results showed that the main cracks of high-strength reinforced concrete beams with shear span ratio of 2 were mainly formed by the penetration of multiple cracks,while the main cracks of composite beams under the same shear span ratio generally included bending shear cracks.Under the same shear span ratio,the U-shaped formwork composite beam had a relatively small crack width than the bottom formwork composite beam,and there was no concrete crushing mark in the shear compression zone at failure.With the increase of shear span ratio from 2 to 2.5 and 3,the development speed of cracks to the bearing loading point gradually increases,and the brittleness of beams increases at failure point.（3）The influencing factors of shear resistance of composite beam were analyzed,and its applicability was analyzed based on the current multiple specification forms.The calculation method of separating high-strength reinforced concrete beams from UHPC permanent formwork was proposed,and this method was applicable for analysis.The Abaqus finite element software were used to numerically simulate the shear resistance of composite beams.The results showed that the average ratios of formulas of the GB50010-2010 standard,ACI318-08 standard and Zsutty statistical analysis applied to the shear design of composite beams were 2.47,4.55 and 1.91,respectively.The coefficient of variation was 0.14,0.23 and 0.11,respectively.The formula recommended by the French code,Xu Haibin method and plastic upper bound theory were used to calculate the UHPC permanent template,and the average value of the sum of the shear capacity of the UHPC permanent template and the ordinary concrete beam was 1.41 and the coefficient of variation was 0.14 compared with the experimental value.The method of calculating the UHPC permanent formwork and the high-strength reinforced concrete beam separately could be used for reference in the design of composite beams.The simulated overall situation was basically consistent with the actual situation,and the simulated load-displacement curve was larger than the test load-displacement curve,and the failure cloud image can better reflect the crack situation.Parameter expansion analysis shows that the shear strength increases with the increase of concrete strength,while the side formwork has a great influence on the shear strength of composite beams.