Abstract
This study was carried out in order to study the flexural behavior of fiber-reinforced ultra-high-performance concrete (UHPC) containing hybrid microsteel straight fibers and natural fine aggregates under four-point flexural loading. The experimental results revealed that the fiber pullout mechanism had a progressive pullout (collapse) mode. A highly flexural crack developed when the fiber pulling mechanism was explicitly triggered, leading to the failure of most beams. The maximum load in beams reinforced by 1.2, 1.6, and 2.0% exceeded that in beams without longitudinal reinforcement by 56, 73, and 94%, respectively. Further, bar reinforcements at 125, 115, 95, 85, and 75 mm depths led to increases of 56, 55, 73, 96, and 94% in beam load capacity, respectively. In addition, bar reinforcement at 115, 95, 85, and 75 mm depths reduced the beams’ ductility by 40, 23, 35, and 39% compared to those with 125 mm depth. All studied UHPC beams had an uncracked phase that extended to a curvature of about 7.5 × 10−6 rad, which occurred at about 10 kNm. The use of the design of experiments was exploited in this investigation to develop a prediction model for the ultimate moment capacity of UHPC beams. This prediction model took into account the sectional and material properties of UHPC beams. To carry out this analysis, a database of 25 beams, developed by other investigators, as well as the present authors, was utilized. With a mean prediction-to-test ratio of 0.92, this prediction model had a reasonable performance capacity. In turn, this model was used to generate isoresponsive surface contours that could be used for UHPC beam design.
Highlights
The drawbacks of conventional concrete have been largely overcome through the development of steel-fiber-reinforced high-performance concrete ( known as ultra-high-performance concrete (UHPC)
It can be concluded that the ductility of the UHPC beam decreased as its effective depth decreased
The maximum observed curvatures were observed for the beams with bar-effective depths of 125 and 115 mm. These findings suggested that increasing the bar-effective depth of the UHPC beam would likely enhance its curvature capacity
Summary
Concrete is one of the principal materials used in construction. Normal concrete, has some demerits (i.e., its poor ductility and tensile strength) that make it unsuited for use in advanced infrastructure [1]. The use of a low water-to-binder percentage and high content of fine-constituent materials has resulted in the higher durability to UHPC, allowing this concrete to tolerate harsh environmental conditions [22] Due to these unique properties, UHPC has been effectively employed in infrastructure (e.g., pedestrian [23,24] and road [25,26] bridges), buildings (e.g., [27,28,29]), and the retrofitting of pre-existing structures [30,31]. Few practical methods are available to calculate the moment capacity of bar-reinforced UHPC beams incorporating hybrid fibers, a few models are recommended by some engineering institutes to estimate the loading strength of UHPC beams containing steel fibrous systems [37,38,39]. To broaden the applicability of UHPC, additional research aiming at more accurate methods for calculating the moment capacity of reinforced UHPC beams is required
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