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

When the building structure is subjected to accidental extreme loads,initial failure of component occurred,which may lead to serious disproportionate collapse of the whole structure.When the vertical load-bearing member in the structure is seriously damaged or failed,it is often assumed that the "catenary action" composed of the joint and beam is to take on the vertical load,thus forming a new force transmission path.The vertical loads are transformed to the side beams,which resist the vertical load by the axial force of the beam.In view of this,the progressive collapse resistance of the structure is greatly dependent on the performance of the joint in the structure system.The closed section has many advantages,such as higher strength-to-weight ratio,higher flexural modulus and so on,which made it widely used.However,the connection of closed section members is a key problem,as the traditional bolt is not applicable for closed section connections.The blind-bolted connections ware focused in the field of building structures because it can be installed by single side,which is convenient for construction and it also has good mechanical properties.Among different connections,there are various measures to improve the tying force of the beam-column connections.For the closed section components connected by blind-bolts,the concrete can be considered to fix the blind-bolts and help improve the valid tying of the bolts with bended end.The progressive collapse behavior of blind-bolted angle connections with concrete filled steel tubular columns is 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 with concrete filled steel tubular columns are conducted,with emphasis on the influence of different parameters,such as angle thickness,the presence of web angles and bolt anchorage.The failure modes,load–deformation relationships and strain development are obtained.(2)Based on the experimental results,the load transfer mechanisms during the entire loading process as well as the load resistance mechanism of connections are examined.Meanwhile,the anti-collapse performance of the joints is analyzed,and the factors that affect the performance of joints to resist progressive collapse are analyzed.The test results show that angle thickness,presence of web angles and welded reinforcement have certain influences on the load capacity and rotation capacity of the joints.Among them,the bearing capacity of joint with web angles is significantly improved,and the force mechanism is greatly improved when compared to others joints.(3)Detailed three dimensional finite element(FE)models are constructed by means of ABAQUS,and the reasonable boundary conditions and material properties are set to obtain the load-displacement curves,development of section forces.By comparing to the test results,the FE models are verified.The stress distribution of the model can explain the development of internal forces and resistance mechanism of the blind-bolted connections.(4)Based on the experimental and numerical results,collapse mechanism and mechanical behavior of blind-bolted angle connections with concrete filled square tubular columns and H-beams are further discussed.The advice on improving method and further study on the behavior of blind-bolted connections are summarized.