Performance Evaluation Of Lattice Columns Using Pultruded Fiber-Reinforced Polymer (FRP) Structural Profiles

Lattice steel structures have been widely used in a variety of civil infrastructure applications and are one of the most important structural forms, due to their structural efficiency (i.e., low weight-to-strength ratio), ease of fabrication and rapid erection. Corrosion of steel has presented a long-standing problem under the interactive and cumulative effects of severe climatic and aggressive geomorphic conditions. Pultruded fiber-reinforced polymer (FRP) profiles have gained wide applications in civil infrastructure and have emerged as one of the most promising and affordable solutions to this issue because of their favorable combination of high strength and stiffhess-to-weight ratios; lightness; excellent corrosion resistance; unmatched design and manufacturing flexibility; ease of handling, transportation, and installation. Therefore, pultruded FRP shapes are the ideal material to construct the lattice structures. Currently, the lower rate of development of all-FRP structures is due to two main reasons. One is the difficulty in FRP connections because of the orthotropic nature and the low elastic modulus of FRP profiles compared with steel. The other is no consensual design codes for all-FRP structures. Therefore, there is a great need to develop the better FRP joints and investigate the consensual design methods for all-FRP structures.In this paper, three types of pultruded FRP profiles (i.e., glass fiber/polyester resin, glass fiber/vinylester resin and basalt fiber/vinylester resin) were tested to evaluate their material properties (i.e., tensile, compressive, flexural and shear properties) and failure modes. Finally, pultruded BFRP shapes (basalt fiber/vinylester resin) was adopted as the main material to construct the all-FRP lattice column according to the comparisons and analysis of the test results.In the investigation of connections, eight new typologies of FRP joints were proposed and tested to examine their fundamental performance. Subsequently, connection tests about the single-leg bolted connection and the Steel-FRP joint that replicated the connections between the chord and tie elements in all-FRP lattice column and the laced column repaired with pultruded FRP angles, respectively, were performed on the basis of the above-mentioned research. And some useful suggestions were provided about the connections in all-FRP lattice column and the laced column retrofitted with pultruded FRP shapes.The closed-form equations for global buckling, local buckling and the interaction between local and global buckling modes of pultruded FRP shapes that were loaded axially were compared with the corresponding test results of many researchers to assess the accuracy of corresponding equations. Finally, some useful suggestions were provided about the use of these equations. Meanwhile, the revised equation based on the Euler equation considering the shear deformation was proposed and the FRP column curves and the equation using the stable coefficient ((p) to take the initial geometric imperfections into account were also proposed. Full-scale structural tests were performed to assess the effectiveness of pultruded FRP profiles for rehabilitating lattice steel columns. And the effect of joint slippage in laced structures was also investigated through the numerical simulation and joint test. Finally, a simple and efficient finite element (FE) model for the accurate prediction of structural response of lattice steel structures incorporating the influence of joint slip was proposed and validated.In the investigation of FRP structures, an all-FRP laced column was first tested under axial loading. The data for the ultimate strength load-displace response and strains of typical members were recorded and compared with the corresponding parameters of steel laced column with identical conditions. Subsequently, the second all-FRP laced column was tested under lateral loading, and the axial compressive ratio of the laced column was 0.2. Similarly, the test results were compared with the corresponding parameters of steel laced column with identical conditions to evaluate the static behavior of all-FRP laced column. Finally, the third all-FRP lattice column was tested under cyclic loading to determine the seismic behavior.Based on the research in steel structures, closed-form equations from different codes and researchers were used to predict the performance of all-FRP laced column. And the predict results were compared with the results from numerical simulation to assess the accuracy of these closed-form equations. Finally, a preliminary design method for all-FRP structures was proposed.