The flexural behavioral properties of ultra high performance concrete (UHPC) low-profile T-beams reinforced with a combination of steel fibers and steel reinforcing bars were investigated in this paper. Five large scale T-beams were tested and analyzed regarding their deflection, ductility, strain, curvature, load capacity and crack development. The experimental variables include the reinforcement ratio, the slenderness (length to diameter ratio) of the fiber reinforcements, and the fiber type. The experiments showed that all specimens exhibit flexural failure with the yielding of steel bars and excessive expansion of flexural crack, and the compression zone in the reinforced UHPC low-profile T-beam is not crushed because of the ultra high compressive strength and area of UHPC. In addition, it was concluded that using hooked-end fibers can effectively increase the specimen’s durability-based cracking load in comparison to straight fibers of same slenderness, whereas the reinforcement ratio and the slenderness of the fibers have little influence on this. Increasing the reinforcement ratio and using hooked-end instead of straight fibers increase the load capacity and bending stiffness of the specimen, as well as reduces the crack width at comparable applied load. A model was established to compute the ultimate capacity of UHPC low-profile T-beams and the prediction agrees well with the experimental results in the present and published investigations.

The flexural cracking behavior of ultrahigh performance concrete (UHPC) beams was experimentally studied in this paper. Eight UHPC beams were tested and analyzed regarding their crack pattern, crack spacing and loadcrack width curves. The test variables included reinforcement ratio, reinforcement diameter and UHPC cover thickness. The results indicated that crack width of UHPC increased linearly with the increase of applied load until the yielding of steel rebars. When the applied load was beyond the yielding load, one or two flexural cracks developed into localized cracks, followed by a rapid increase in crack width. Besides, increasing the ratio of steel rebars and appropriately decreasing the thickness of UHPC cover were beneficial to decrease mean crack spacing and maximum crack width, whereas reinforcement diameter had little influence on these characteristics. Predictions of crack width by existing FRC/UHPC codes were evaluated and compared with the experimental results. The comparisons indicated that predicted values by NF-P18-710, MC 2010, CNR-DT 204, and RILEM TC-162-TDF models showed a good accuracy with experimental ones. The highest deviation for mean crack spacing and maximum crack width were less than 18 and 8%, respectively. However, CECS 38 model gave the largest deviation about 60 and 25% for prediction of mean crack spacing and maximum crack width, respectively. Among them, NF-P18-710 model exhibited the best accuracy with average ratio and SD of 1.01 and 0.17, respectively. K E Y W O R D S crack spacing, crack width, flexural cracking behavior, UHPC cover thickness, ultrahigh performance concrete (UHPC) beams 1 | INTRODUCTION Ultrahigh performance concrete (UHPC), as an advanced cement-based composite material, has been developed in many countries. 1-6 Many investigations in terms of material properties have been conducted in recent years. 7,8 Compared with normal concrete, UHPC exhibits much

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Connections in the assembled precast elements become essential locations for creating structural continuity. However, the construction challenges of conventional steel sleeve connections, such as rebar embedment length, rebar congestion, and formed grout defects (i.e., voids), are still a concern area for researchers and engineers. In this study, a proposed ultrahigh performance concrete (UHPC) grouted sleeve connection was presented for assembled precast elements, which might reduce defects, enhance durability, and accelerate structure construction. The tensile test of grouted sleeve connection with different grouting materials, rebar diameters, and anchoring lengths was conducted to determine an optimal anchoring length used in the flexural design.The precast specimens with the UHPC grouted sleeve connection were tested under flexural load. Also, strain changes in concrete, sleeve, and rebar were reported in tensile and flexural tests. The tensile test results showed two types of failure modes, the rebar rupture and bond failure between rebar and grouting. The recommended rebar anchoring length in the flexural design was six times the rebar diameter. The flexural test results showed that the precast specimen with or without the shear key has a similar failure mode as compared to the cast-in-place specimen, while their average cracking load, yield load, and ultimate load were 27.9%, 11.0%, and 7.4%, respectively, which is less than those of the cast-in-place specimen. Also, the flexural cracking resistance was the highest in the sleeve segment, followed by the joint region and the rebar segment. This study provides a reference for the design of the UHPC grouted sleeve connection for assembled precast elements.