Joining GFRP tubular profiles into space latticed shell structures

Pultruded glass fibre reinforced polymers (GFRP) profile is a promising structural member for space latticed shell structures because of the advantageous properties such as high strength-to-weight ratio (in pultrusion direction), corrosion resistance and lower maintenance. In particular, when tubular profiles are used, a better resistance against local buckling, global buckling and lateral torsional buckling can be achieved compared with open sections. Despite the advantageous characteristics, the design and fabrication of tubular connections has been identified as a critical issue for the proposed applications due primarily to the geometric constraints of the closed shape, the distinct material properties of FRP, and the threedimensional nature of space latticed shell structures. Until recently, only a limited number of connection systems have been proposed for FRP space latticed shell structures and there is still a need to develop a simple, economic and versatile joining method. This thesis proposed a bolted sleeve joint (BSJ) for assembling GFRP tubular profiles into space latticed shell structures. In the proposed BSJ, the FRP profile and steel connector are telescoped and clamped using mechanical bolts. The end of the steel connector can be incorporated with compatible end fittings for connection to a nodal joint for space latticed shell structure. The proposed BSJ allows the flexibility in adjusting design parameters such as the bolt group configuration, memb9er size and type of fastener, depending on the design requirements. In addition, all connecting elements are commercially available and no advanced techniques are required for the fabrication. The joint performances were investigated at three level, namely joint level, component level and structural level. Stage one Goint level) focused on the joint design and performance under static axial loadings. Four batches of specimens were prepared and tested under static axial tension and compression. Design parameters, including the type of fastener (ordinary bolt or blind bolt), member size, and bolt group layout, were selected and examined. A simple analytical design model was proposed to estimate the joint capacity, showing good agreement with experiment. Design recommendations based on the current investigation were also made for the further improvement of joint performance. Stage two (component level) was an experimental and numerical study on the member capacity of pultruded GFRP square tubular profile with BSJ end conditions. Three batches of specimens assembled with FRP profiles in different lengths and BSJs at both ends were prepared and tested under static axial compression. A detailed 3D FE model considering bolt geometry, contact behaviour, bolt pretension, initial geometric imperfection and FRP failure criterion, was developed and validated with experimental results, showing good agreement. The relationship between effective length factor and member slenderness was derived based on FEA, and then used in conjunction with existing pultruded GFRP box tubular column design equations to predict the member capacity of structural members with BSJ end conditions. The final stage (structural level) investigated the performance of BSJ at a structural level. An experimental investigation was first conducted to obtain the M- () behaviour of BSJ. It was followed by a structural analysis and design of an FRP domed roof with BSJ modelled by spring elements using FEA. The inputs of the joint rotational stiffness and axial stiffness for the springs were determined from the linear portions of the orresponding experimental curves. The ULS and SLS performance of the FRP domed roof were evaluated on a LRFD basis under ASCE-07 design loads. Parametric studies were also performed to identify the effects of joint rotational stiffness, axial stiffness and the materials (steel or pultruded GFRP) used for structural members on the structural performance. Design recommendations were also developed based on the structural analysis and the parametric studies.