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    Anchored blind bolted connections within concrete filled square steel hollow section columns
    Agheshlui, Hossein ( 2014)
    Concrete filled steel hollow sections are suitable choices for columns of low to medium rise commercial buildings. Despite the merits of these sections, connecting a steel I-beam to a hollow section column using conventional bolts is not easily possible due to lack of access to the inside of the hollow section. To overcome this limitation, blind bolts that can be installed from one side are used. However, connections using blind bolts are limited in the achievable level of moment-carrying capacity and stiffness due to the inherent flexibility of the face of the tubes, especially in the case of square hollow section (SHS) columns. The aim of this research was to develop strong and stiff connections to concrete-filled square hollow section (CFSHS) columns. To achieve this aim, a new type of blind bolt, the AJAX anchored blind bolt, was developed at the University of Melbourne in collaboration with AJAX Fasteners. In this type of blind bolt, a headed stud extension was added to the AJAX Oneside blind bolt and was anchored within the infill concrete. This resulted in an improved stiffness and strength when the bolts were subjected to tensile forces. Double T-stub anchored blind bolted connections were proposed to connect I-beams to concrete filled SHS columns. To study the behaviour of the proposed connections, two tiers of experimental programs and a numerical (FE) study were conducted in this research. The first tier of the experimental program focused on the investigation of the tensile behaviour of anchored blind bolts that make a defining contribution to the overall flexural behaviour of the proposed connections. The individual and group behaviour of anchored blind bolts were studied by conducting three series of pull-out tests. In these tests, the influence of the important parameters on the tensile behaviour of anchored blind bolts was investigated. These parameters included the steel tube section size, the bolt diameter, the embedment depth, and the group behaviour of AJAX anchored blind bolts. After conducting the tensile tests, finite element modelling was undertaken to simulate the tensile behaviour of anchored blind bolts. The models were calibrated against the experimental data. The FE modelling was conducted to provide a more comprehensive understanding of the tensile behaviour of anchored blind bolts when used in concrete filled square hollow sections. Furthermore, it was used to perform a comprehensive parametric study. Based on the thorough knowledge obtained from the FE simulations and the parametric studies, a theoretical model was developed to estimate the tensile behaviour of AJAX anchored blind bolts. In the second tier of the experimental program, the behaviour of the anchored blind bolted connections within typical structural frames was investigated. A moment resisting frame with a composite floor system of a medium-rise commercial building located in a low-to-medium seismicity region was designed using anchored blind bolted connections. A sub-assemblage of this frame was selected to be fabricated and tested under gravity load and cyclic loads replicating earthquake loads. The results of the sub-assemblage test showed that anchored blind bolted connections can be successfully used as semi-rigid moment-resisting connections within structural frames. In summary, it was found that the concrete infill has a significant influence on the stiffness and strength of the anchored blind bolts. It was shown that AJAX anchored blind bolts can reach the ultimate tensile capacity of the equivalent standard structural bolts if identified requirements are met. Simple theoretical equations were proposed to estimate the stiffness of anchored blind bolts. The proposed anchored blind bolted connections were implemented in the frame model of a medium-rise commercial building and an acceptable lateral resistance was achieved for the frame. A design procedure was also proposed for the design of composite (with floor slab) anchored blind bolted connections of universal beams to concrete filled SHS steel columns.