Experimental Study On Shear Behavior Of Reinforced Autoclaved Aerated Concrete Slab

In recent years,prefabricated and energy-saving buildings have gained national attention.While autoclaved aerated concrete slabs(ALC)are prefabricated in the factory and suitable for assembly.It is widely used in the roofs,walls and floors of industrial and civil buildings,and is favored by modern prefabricated buildings and green buildings.However,the disadvantages of ALC board are easy to absorb water,loose material,low elastic modulus and small section stiffness.In the process of practical engineering use and structure test,shear failure often occurs,which makes it difficult to meet the basic requirements of "strong shear and weak bending".Therefore,it is limited to become the development direction of ALC plate as the main stressed member of the structure.At present,in order to further promote the application of aerated concrete in building roof,a new structural form,ALC composite slab,is proposed.At present,there are many researches on the bending performance of ALC plates in China,but there are few researches on the shear performance of ALC plates and ALC composite plates.This paper takes ALC plate and ALC composite plate as the research object,and systematically studies the shear properties of the two based on tests and finite element analysis.The main work is as follows:(1)Through literature retrieval,the results of shear failure in ALC plate mechanical performance tests published from 1980 to 2017 were collected,and the ultimate bearing capacity of ALC plate tests of each unit were statistically analyzed,as well as the types of reinforcement,measured longitudinal reinforcement strength and reinforcement ratio,providing reference for the test design.(2)Through the shear test of 18 ALC plates and 12 ALC composite plates,the failure pattern,load-deflection curve,stress distribution of longitudinal bars and aerated concrete,and ultimate bearing capacity of the specimens were obtained,and the influences of reinforcement ratio of longitudinal bars,reinforcement grade and shear span ratio on the mechanical properties of the specimens were clarified.(3)The following conclusions are obtained through the experiment: 1)The stiffened ALC plate is easy to form strong bending and weak shear members.Shear span ratio(λ)less than 2,baroclinic failure occurs;Shear-span ratio(λ)at 2～3,shear-pressure failure;Shear span ratio(λ)at 5,cable-pull failure occurs;the ALC plate with single reinforced section is prone to shear failure if the shear span ratio is greater than 5.2)If the oblique crack is close to the anchorage bar or through the anchorage section,it may weaken the anchorage force and reduce the shear strength of the plate.3)The main characteristics of ALC composite plates subjected to shear failure are the small crack spacing and the large number of cracks.The pouring concrete composite layer effectively reduces the crack spacing and improves the shear resistance of the inclined section of ALC composite plates.(4)the test results were compared with the relevant specifications at home and abroad,and the finite element model of ALC composite plate was established.The analysis showed that: 1)As for the calculation method of shear capacity of ALC plate without abdominal rib with high longitudinal reinforcement,the calculation results obtained in the technical regulations of China are relatively deviated,and the calculation results obtained in the European specifications are relatively safe.The calculation formula of RILEM materials association is reasonable.2)According to the existing experimental results,the new formula has good applicability for ALC plates with high and low longitudinal reinforcement,which can be used as a reference for the shear design of ALC plates in the future.3)The calculation formula reflects the following two characteristics of ALC composite plates: considering the influence of the composite parameters on the anti-shear performance after the composite plate is folded,the influence of increasing coefficient and changing section size of reaction force on the shear capacity of ALC composite plates is put forward.According to the difference between the strength of aerated concrete of ALC slab and that of laminated concrete,the concept of reduced concrete strength is put forward.The calculated value according to the fitting formula is very close to the experimental value.