Fiber reinforced uhpc and its effect on load carrying capacity of composite tube members according to current design codes

The main objective of using reinforced ultra-high performance concrete (UHPC) by different type and volume of fibers with concrete filled steel tube (CFST) structure is to minimize the size of the structural steel tube and to improve the mechanical, fracture, and shrinkage properties of concrete core. This provides high strength and performance for the composite elements. Accordingly, this thesis consists of two parts: First describes the experimental behavior of UHPC reinforced with various fiber types and concentrations. While the second part presents the research results of the structural behavior of axially loaded steel tube column filled with ultra-high performance fiber reinforced concrete (UHPFRC). For this, 19 UHPC mixtures containing micro-steel, hooked-steel, and micro glass fibers up to 2% volume fractions were produced. All designed mixtures were tested for the mechanical, fracture and physical performance. On the other hand, three outer diameters to wall thickness D/t ratios (30, 60, and 90) corresponded by 300, 450, and 600 MPa of yield strength (fy) of the steel tube were used to calculate the axial load capacity (Nu) of circular CFSTs infilled with mentioned UHPFRCs via design equations given by Eurocode 4 (EC4), American Concrete Institute (ACI), American Institute of Steel Construction (AISC), Architectural Institute of Japan (AIJ), and Chinese (DL/T) codes. The results of code comparison revealed that AIJ and DL/T were so near to EC4 followed by AISC then ACI.