Finite Element Study On Mechanical Properties Of AAC Masonry Infilled Steel Frame Structures With Circular-arc Openings

Autoclaved Lightweight Aerated Concrete(AAC)masonry infill wall embedded in steel frame is a common method of infill wall.Nevertheless,the infill wall will bear the force together with the steel frame,the infill wall is easy to be damaged and cracked when the story drift reaches a certain degree.Based on the principle that setting openings at the corners of the infill wall can weaken the tension(compression)band,a series of specimens of infill wall with circular-arc openings at the corners embedded in steel frame were established by using ABAQUS software,one bare steel frame,one AAC masonry infilled steel frame without any measures,and several AAC masonry infilled steel frame with circular-arc openings of different sizes.The influence of circular-arc openings at the corners of the infill wall on the load-bearing capacity,ductility,stiffness degradation,strength degradation and energy dissipation capacity of steel frames was studied by numerical simulation analysis under low cyclic load,and the optimal range of the size of the circular-arc openings was determined.Moreover,the numerical simulation analysis of AAC masonry infilled steel frame with circular-arc openings under the unidirectional horizontal load was carried out,and the influence of three variables,namely,the size of circular-arc openings,the friction coefficient between infill wall and steel frame,rise-to-span ratio,on the mechanical performance of AAC masonry infilled steel frame with circular-arc openings was studied.The influence of different variables on the mechanical degree of AAC masonry infill wall was analyzed,and the range of different variables was determined.It provided a theoretical reference for practical engineering.(1)In order to study the influence of circular-arc openings at the corners of the infill wall on the hysteretic behavior of steel frames,39 specimens were designed,including one bare steel frame,one AAC masonry infilled steel frame without any measures,and 37 AAC masonry infilled steel frame with circular-arc openings of different sizes.The numerical simulation analysis of 39 specimens under low cyclic load was carried out.It is found out that the circular-arc openings at the corners of the infill wall can weaken the contribution of AAC masonry infill wall to the load-bearing capacity of steel frame,are effective in delaying the failure of the infill wall,in reducing the additional stiffness of the infill wall for the steel frame structures,and in delaying the stiffness degradation rate of AAC masonry infill wall embedded in steel frame;the circular-arc openings can also change the failure mode of the AAC masonry infill wall.According to the results of finite element analysis,it is suggested that the radius(l)of circular-arc openings should be(1/7 ～ 1/10)times of the height of AAC masonry infill wall.(2)In order to study the influence of three variables,namely,the size of circular-arc openings,the friction coefficient between infill wall and steel frame,rise-to-span ratio,on the mechanical performance of AAC masonry infilled steel frame with circular-arc openings,three series of 42 specimens were designed and analyzed by finite element numerical simulation under unidirectional horizontal load.The results show that the existence of AAC masonry infill wall enhances the load-bearing capacity of steel frame,while the circular-arc openings at the corners of the infill wall weaken the participation of AAC masonry infill wall in the load-bearing capacity of steel frame,and the weakening strength gradually increases with the increase of the size of circular-arc openings.It is found that the load-bearing capacity,initial stiffness and plastic deformation performance of AAC masonry infilled steel frame with circular-arc openings are greatly affected by the size of circular-arc openings,the friction coefficient between infill wall and steel frame,rise-to-span ratio.With the increase of the size of circular-arc openings,the decrease of friction coefficient and rise-to-span ratio,the load-bearing capacity and initial stiffness of AAC masonry infilled wall steel frame structure with circular-arc openings decrease.The larger the friction coefficient is,the greater the stiffness effect of the infill wall on the steel frame is,and the greater the force transferred to the infill wall is,so the infill wall enters the elastic-plastic stage earlier and fails in advance.The friction coefficient should be between 0.3 and 0.4.Moreover,when the rise-to-span ratio is too small,the failure speed of the infill wall is accelerated,and the brittle failure is prone to occur.In practical engineering,the design with too small rise-to-span ratio should be avoided as far as possible.