Ultra-high-performance concrete (UHPC) is an advanced concrete with superior mechanical strength, ductility and durability properties. However, the influence of steel fiber on its constitutive laws and the specimen geometric dimension effect on its strength had not been paid enough attention. To investigate the effect of steel fibers on the properties of UHPC, specimens with different fiber volume contents and fiber types were tested. Meanwhile, the mechanical properties of UHPC at different ages from 3 days to 28 days were conducted. Moreover, specimens with various geometric dimensions were also prepared to study the effect of specimen geometric dimensions (dog-bone-shaped, prism and cylinder specimens) on the properties of UHPC. The results indicated that elastic modulus, tensile peak stress and the corresponding strain increased as the fiber volume content and curing age increased. Specimens with hooked-end fibers exhibited better tensile performance than those with straight fibers. Furthermore, different geometric dimensions of specimens significantly influenced the tensile properties of UHPC. Based on the experimental results, conversion factors were suggested for the transformation of strength obtained from specimens with different geometric dimensions to reference specimens. In addition, both compressive and tensile constitutive laws were proposed to generate the stress–strain relationship of UHPC.

This study numerically investigated the shear behavior of novel composite shear connectors, which consisted of grouped head studs embedded in high-strength concrete-filled (HSC-filled) shear pockets. The shear pockets were prefabricated and retained open in the precast concrete slab. The finite-element (FE) models were established and verified with the full-scale test results. The validated FE models were further used for parametric studies. In this study, the shear strength of grouped head stud shear connectors almost linearly increased with the stud diameter and infilling concrete strength. However, the stud height had little effect on the shear strength. Increasing the stud spacing and slab thickness could not enhance the shear capacity of composite shear connectors. In addition, the precast method of the shear pocket also had no reduction in the shear strength. Finally, the parametric analysis results were compared with the current design codes. It was observed that those specifications almost had conservative predictions on the shear strength of grouped head studs because the interaction between the concrete crushing and head stud fracture was not considered. A more accurate analytical equation was proposed to predict the head stud shear capacity. The average values of predicted/tested results for all specimens were varied from 0.949 to 1.022, which indicated that the equation could accurately evaluate the shear strength of grouped head studs in high-strength concrete.

A partial-depth, diamond-shaped, ultra-high performance concrete (UHPC) connection with embedded transverse reinforcement between adjacent precast prestressed concrete voided beams (APPCVBs) has been developed by the Federal Highway Administration (FHWA) to overcome the disadvantages of longitudinal cracks within the connections. In this study, the shear behavior of 14 spliced panel specimens with the FHWA developed UHPC connection will be experimentally investigated. One monolithic specimen will be tested as a reference. The test parameters include surface preparation, the compressive strength of the filling concrete, lateral reinforcement details, and the lateral reinforcement diameter. The shear behavior will be evaluated from cracking patterns, failure modes, load–deflection responses, and ultimate load capacity. Formulas will be derived based on the elastic beam theory coupled with the dowel effect of transverse reinforcement. The derived formulas could generally predict the shear strength of the spliced panel specimens with the FHWA developed UHPC connection.

As a novel civil engineering material, Engineered Cementitious Composite (ECC) has attracted more and more attention due to its strain-hardening characteristics, good post-cracking resistance and its unique properties. Bonding between Engineered Cementitious Composite (ECC) and rebar has a great effect on the mechanical behavior of structural members. In this paper, direct pull-out tests were conducted to understand the bond behavior between the ECC and rebar. The test parameters included rebar diameter and type, cover layer thickness, embedment length and fiber volume content. Bond-slip curves, failure and cracking pattern and bond strength were compared and discussed. The test results indicated that the bond strength decreased with the increase of embedded length. Through regression analysis with the test data, the functional relationships between bond strength and cover layer thickness and rebar diameter were fitted well. According to the positive and negative signs of the fitting parameters m and n, the relationship between the bond strength and the cover layer thickness and the rebar diameter could be determined. The bond strength increased obviously with the increase of fiber content. When the fiber volume content was 1, 1.5 and 2%, the bond strength of these specimens were 1.5, 2.5 and 3.1 times that of specimens without polyvinyl alcohol (PVA) fiber.

This paper presents the results of recent research on the interface shear behavior of normal weight and lightweight concrete composite T-beams. In the experimental program 12 beams and necessary...