Response Of Blind-bolted Angle Connections With Steel Tubular Column Against Progressive Collapse

When the building structure is subjected to accidental extreme loads,it usually happens with the disproportionate collapse of the initial damage part.When the vertical load-bearing member in the structure is seriously damaged or failed,it is often assumed that the "suspension action" composed of the joint and beam is to take on the vertical load,thus forming a new force transmission path.In view of this,the progressive collapse resistance of the structure is greatly dependent on the performance of the joint in the structure system.In current steel structures,open section beams and columns are dominant in design and construction,but they are being gradually replaced by the closed section member,as Hollow structural sections exhibit inherent architectural and structural advantages over other structural steel counterparts,such as higher strength-to-weight ratio,higher flexural modulus and so on.However,the connection of closed section members is a key problem,as the traditional bolt is not applicable for closed section connections.Meanwhile,welding has the disadvantages such as heavy workload and difficult construction,and welded joints is generally a type of fully-rigid connection,which is not conducive to seismic resistance.Nevertheless,a special bolt system named blind bolt has provided the development of a new bolted connection alternative.The blind bolt only need unilateral operation which improves the efficiency of construction.Additionally,blind bolt shows excellent mechanical performance.Therefore,it has been widely concerned by scholars and engineers at home and abroad.The progressive collapse behaviour of blind-bolted angle connections and combined channel/angle connections are studied in this paper by experimental and numerical investigation.The main work can be summarized as follows:(1)The Pseudo-static progressive collapse experiments on four blind-bolted angle connections and four combined channel/angle connections are conducted,with emphasis on the influence of different parameters,such as angle thickness,the presence of web angles,installation position of bolts.The failure modes,load-deformation relationships and strain development are obtained.(2)Based on the experimental results,the load transfer mechanism during the entire loading process as well as the load resistance mechanism of connections are examined.Meanwhile,the anti-collapse performance of two types of joints is analyzed,and the factors that affect the performance of joints to resist progressive collapse are analyzed.The test results show that the distance of bolts on column to flanges of the beam,angle thickness and presence of web angles have certain influences on the load capacity and rotation capacity of the joints.Among them,the bearing capacity of joint for web angle is improved,and the force mechanism is greatly improved compared to others joints.(3)Detailed three dimensional finite element models are constructed by means of ABAQUS,and the results are validated against the available experimental results.Furthermore,the loading process of connections are discovered and discussed by the verified finite element models.(4)Based on the experimental and numerical results,collapse mechanism and mechanical behavior of blind-bolted angle connections combined channel/angle connections are further discussed.Compared with the performance of combined channel/angle connections,the merits and deficiency for the behavior of blind-bolted connection joints are summarized.