NEXCEL PI Prof. Liu Tianqiao gave a presentation on CICE2023
Time: 2023/08/09 Publisher： oiginal Views：
From July 24 to 26, the 11th International Conference on FRP composites in Civil Engineering (CICE2023) was held in Rio De Janeiro-Brazil. Tianqiao Liu, Professor of Beijing University of Technology, member of CICE2023 Organizing Committee, as well as Principal Investigator of NEXCEL 2022TDA Project, was invited to attend the conference and gave a presentation entitled Non-Linear Behaviors of Pultruded GFRP Composites.
In civil engineering, construction materials and/or structural components are often required to exhibit certain ductile failure characteristics so as to ensure an anti-collapse capacity under extreme loading conditions. However, the poor ductile behavior is often deemed a well-known weakness of pultruded GFRP profiles which typically show linear-elastic behavior with sudden-brittle failure. In this regard, enabling a non-linear behavior (also referred to as pseudo-ductile behavior) for pultruded GFRP profiles could potentially promote their applications. Present authors conducted a literature review and selected compression and shear loading conditions to investigate the pseudo-ductile characteristics of pultruded GFRP profiles.
First, present authors conducted axial-compression tests on GFRP short columns. The GFRP columns (i.e., box-sections) were fabricated through pultrusion and pullwinding techniques (see Figure below), and five different types of specimens were produced. Column heights were 50mm and 400 mm. Test results revealed that the dominant failure mode of all column specimens was progressive compressive failure. Notably, a substantial amount of pseudo-ductile behavior after peak load was observed for all specimens, which is different from the behaviors observed in previous studies.
Second, present authors carried out bolt hole bearing tests on bolted connections of pultruded GFRP profiles (see Figure below). Similarly, five types of specimens were fabricated through pultrusion and pullwinding techniques. In this test, plate-shaped standard specimens were fabricated following ASTM D5961, meanwhile box-shaped non-standard specimens were fabricated to protect the circumferential integrity of the winding fibers of pullwound profiles. All specimens failed in the manner of shear-out. Furthermore, all specimens exhibited evident pseudo-ductile behavior after reaching their peak loads. Moreover, box-shaped non-standard specimens generally displayed higher peak loads as compared to the plate-shaped standard specimens, and the pseudo-ductile behavior of non-standard specimens was more prominent. Remarkably, under the circumferential restraint of winding fibers, the shear strength of a pullwound specimen was observed to be higher than its pultruded counterpart.
In conclusion, experimental results of this work have successfully demonstrated that pultruded GFRP profiles can exhibit a certain level of pseudo-ductile failure characteristics when subjected to compression and shear loading conditions. This phenomenon is attributed to the progressive failure of GFRP composites. In United States, some states have prescribed that steel structures shall be designed only within their linear-elastic region when considering normal loading conditions, and the ductile capacity shall be used only for extreme loading conditions. Following the design principles of steel structures, it might be feasible to enable a certain degree of ductile capacity for pultruded GFRP profiles such that those special requirements for extreme loading conditions can be satisfied. Undoubtedly, this will further expand the possible applications of pultruded GFRP composites. In addition, some novel manufacturing techniques (e.g., pullbraiding, pullwinding and curved-pultrusion) can help to realize nonlinear fiber architectures and nonlinear geometric properties, thus enhancing the designability of pseudo-ductile capacity of pultruded GFRP profiles.
More details：https://doi.org/10.5281/zenodo.8070765