Study On Calculation Method Of Shear Capacity Of Recycled Concrete Beam Based On Modified Compression Field Theory

The emergence of recycled concrete solves two major problems in the current construction industry.On the one hand,it solves the problem of unmanageable large amounts of construction waste in China;on the other hand,it also provides sand and gravel aggregates that meet the requirements for engineering construction.And recycled concrete is a sustainable and environmental friendly building material that can turn waste into wealth.In this paper,recycled concrete beams as the research object,and its shear capacity is the main entry point to study the calculation method of the shear capacity of recycled concrete beams.The test method of controlling the influencing factors is used to study the shear of recycled concrete beam.A series of tests are carried out by designing different recycled aggregate replacement rate and shear span ratio,that’s in order to study and analyze the failure model,rebar strain curve and crack width of the recycled concrete beam performance characteristics and so on.Test results show that,6 test beams were damaged by shear pressure and 1 test beam was damaged by cable-tension.When the shear-span ratio does not change,with the increase of the recycled aggregate replacement rate,the stirrup strain and the maximum width of the crack increase significantly.The shear capacity of recycled concrete beams are lower than ordinary concrete beams.The calculation value is quite different from the test result,and the calculation value is obtained by using the calculation method in the design specification of concrete beams.The calculation method of shear capacity of concrete structures cannot be simply applied to recycled concrete structures.According to the shear capacity characteristics of recycled concrete beams,the shear model of recycled concrete beams with stirrup was established.The model adopts a modified pressure field theory that fully considers the factors of aggregate interlock capacity,and proposed that the shear capacity of recycled concrete beams mainly consists of the aggregate interlock capacity and the stirrup effect.According to the linear change of the crack width of the recycled concrete beam along the crack surface,considering the influence of the stirrups on the crack width,an approximate calculation formula of the crack width of the recycled concrete beam based on the modified pressure field theory was proposed.Due to the external old mortar and damage of internal raw aggregate,the performance of recycled coarse aggregate will be weaker than natural aggregate.The calculation method for the equivalent coefficient of particle size of recycled aggregates was established,which used the concept of the average ratio of recycled aggregate modulus to natural aggregate modulus.Based on the approximate calculation formula of the crack width and the equivalent coefficient of the particle size of the recycled aggregate,the calculation formula of the bite force of the recycled aggregate was derived.Finally,the calculation formula of the shear capacity of the recycled concrete beam was obtained.The theoretical calculation results were compared with the test results of 6 recycled concrete beams by self-made,the results show that the theoretical value is good agreement with the test value.Using 87 groups of domestic and foreign experimental data verified the effectiveness of the proposed method.And a new method was provided for designers to predict the ultimate shear capacity of recycled aggregate concrete beams.