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Ultra‐high performance concrete (UHPC) offers superior tensile properties in comparison to normal and high‐strength concrete. This is known to largely depend on the fibers included in the UHPC mixtures. Among the available types of fiber, steel fibers have been commonly used in the current practice. However, given the price and availability issues associated with steel fibers, there has been growing interest in benefiting from synthetic fibers in UHPC. This was the motivation for the current study to investigate the potential of five synthetic fibers by evaluating how the tensile properties of the UHPC mixtures made with a hybrid of steel and synthetic fibers are influenced under direct tension. The synthetic fibers of choice consisted of nylon, polypropylene, polyvinyl alcohol, alkali‐resistant glass, and carbon fibers. By using a dog bone test setup, the main tensile properties of the developed mixtures (i.e., direct tensile strength, elastic modulus, and stress–strain relationship) were systematically determined. The results extracted from direct tension tests were then further processed in conjunction with digital image correlation analyses to investigate the formation and propagation of cracks, as well as the post‐cracking response. The original findings reported from this study are expected to pave the way to broaden the fiber types that can be considered for the structural applications of UHPC, especially where high tensile stresses/strains are anticipated. [ABSTRACT FROM AUTHOR]

Summary: Concrete‐filled steel tubes (CFSTs) have received growing attention, owing to their rapid construction, reduced labor requirement, and reasonable material cost. While in service, the CFSTs can be subjected to unexpected impact loads, originating from vehicle and vessel collision, as well as water‐ and wind‐borne debris impact. Such extreme loading events often cause a partial or complete failure of conventional CFSTs, risking the safety and performance of the entire structural systems that rely on them. To address this issue, the current study explores how two advanced composite materials, including ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) and carbon fiber‐reinforced polymer (CFRP), can be utilized to provide superior mechanical properties and minimize the vulnerability of CFSTs to impact loads. The composite materials under consideration are appropriate for both new and existing structures, in which normal‐strength concrete can be replaced with UHPFRC, while CFRP sheets can further strengthen the CFSTs. For obtaining in‐depth insights, a computational framework validated with the experimental tests was developed in the current study. Using a set of representative impact scenarios, various response measures, such as internal forces and deflections, as well as the energy absorbed by the CFSTs, were recorded during impact simulations. The investigations were then further extended to capture the influence of the main design parameters related to concrete, CFRP, and steel tube. From the conducted investigations, an energy absorption index was introduced, as a measure to evaluate the performance of CFSTs under impact loads. [ABSTRACT FROM AUTHOR]