Concrete light - Three-dimensional filigree trusses constructed of ultra-high performance concrete and CFRP-reinforcement

Under Priority Program 1542 "Concrete light. Future concrete structures using bionic, mathematical and engineering formfinding principles", funded by the Deutsche Forschungsgemeinschaft (DFG), the aim of the subproject "Shape optimized filigree rods made of UHPC and non-corrosive CFRP-reinforcement for variable three-dimensional trusses" is to develop shape-optimized struts and prestressed ties out of innovative materials in accordance with the principle "form follows force". By theoretical and experimental investigations on these two components fundamentals for the realization of modularly constructed slender concrete truss supporting structures shall be created. The article begins with a short overview of the entire subproject and a few relevant material-specific characteristics of ultra-high performance concrete (UHPC) and carbon-fiber-reinforced polymers (CFRP). Subsequently the investigations that have already been carried out on the struts and ties and the essential results are presented. Geometrically linear numerical analysis were used to determine the optimized shapes of the struts in the longitudinal direction when subject to a concentric axial compression load causing failure due to a loss of stability for varying support conditions. Furthermore, short-term compressive tests were carried out to investigate the increase in ultimate load capacity of the concrete members when provided with CFRP confining reinforcement of varying thickness. The findings from both of these studies are presented. With regard to the prestressed ties, the results of pull-out tests for CFRP-bars with varying surface conditions are discussed, and form the basis for assessing the general suitability of the bars for pretensioning. Finally, still ongoing and further investigations planned within the first funding period of the subproject along with further needs for research to realize concrete truss structures are outlined.