International Concrete Abstracts Portal

The influence of alkaline aging on the basalt fiber-reinforced polymer (BFRP) bar reinforced concrete beam has not been thoroughly investigated, and the deterioration level can be further increased in seawater sea sand concrete (SSC) due to increased alkalinity. This study aims to unveil the coupled influence mechanism of accelerated sweater aging and impact loading on the impact resilience of BFRP-SSC beams. The influence of concrete strength, reinforcement ratio, falling weight height, and accelerated aging in seawater on the impact resistance of BFRP-SSC beam is examined. The results indicate that enhancing concrete strength can more obviously increase the peak impact force than enhancing the reinforcement ratio due to the higher strain rate sensitivity. The increased falling weight energy can increase the peak impact force while reducing the residual bearing capacity. The accelerated aging in seawater can reduce the peak impact force and increase the maximum midspan displacement. And the impact failure mode of the BFRP-SSC beam can be changed from concrete crushing to BFRP bar fracture due to the bar degradation. The peak impact force of beam specimens soaked in seawater at room temperature and 55°C conditions is reduced by 13.8% and 15.5%, while the maximum midspan displacements are increased by 32.2% and 47.1%, respectively. This study can serve as a solid base for the impact design of FRP bar reinforced seawater sea-sand and concrete beams.

Additive construction augments the laborious construction of structural concrete; however, its implementation remains mostly limited to building envelopes. Culvert construction benefits from alternative methods due to the high demand for transportation infrastructure. In this study, extrusion-based 3-D concrete printing (3DCP) is developed for the first time for culvert construction. Large-scale unreinforced concrete pipes were printed, and the early-stage (e.g., buildability), mechanical, and durability properties of two commercially available 3DCP materials were determined. Additionally, the specimens were tested structurally and exceeded the expected structural performance (by about an average of 32%) under the three-edge bearing test. However, the desired durability was not met due to the porosity of the specimens. The mix design with microfibers exhibited marginally higher compressive and tensile strength, but did not meet durability criteria similar to non-fiber material. Results indicated the 3DCP feasibility for pipe culvert construction and mapped further direction for widespread implementation and addressing concrete pipe durability issues.

This paper presents the implications of variable bond for the behavior of concrete beams with glass fiber-reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded reinforcing bars, which are intended to represent sequential bond damage. Conforming to published literature, three shear-span-to-depth ratios are taken into account: arch action, beam action, and a transition from arch to beam action. When sufficient bond is provided for the element-level testing, the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the shear-span-to-depth ratio from 1.5 to 3.7, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams by up to 40.2% and the slippage of the partially bonded reinforcing bar dominates their flexural stiffness. Compared with the case of the beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of reinforcing bar stress is dependent on the shear-span-to-depth ratios, and, in terms of using the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of reinforcing bar stresses with bond damage when subjected to arch and beam actions.

This paper presents the torsional behavior of hollow reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) U-wraps. Test parameters involve variable wall thickness in the section and the width and spacing of the externally bonded CFRP sheets. An experimental program is conducted with 27 beams (three unstrengthened and 24 strengthened) to examine their capacities, shear flows, and force distributions when incorporating a ratio of 0.27 to 0.46 between the areas of the hollow and gross cross sections. The stiffness and capacity of the test beams are dominated by the wall thickness, and the effectiveness of CFRP strengthening becomes pronounced as the void of the beams decreases. The presence of CFRP redistributes internal shear forces in the cross section, which is facilitated by narrowing the spacing of the U-wraps. The effective zone of CFRP retrofit is positioned near the outer boundary of the strengthened section. Regarding crack control, multiple discrete U-wraps with narrow spacings outperform wide U-wraps with enlarged spacings. While the location of a shear-flow path is dependent upon the wall thickness, the width of the U-wraps controls the effective shear-flow area of the beams. The size of the void is related to the stress levels of internal reinforcing components, including yield characteristics. Transverse stirrups are the principal load-bearing element for the unstrengthened beams; however, the reliance of the stirrups is reduced for the strengthened beams because the U-wraps take over portions of the torsional resistance. Through a machine learning approach combined with stochastic simulations, design recommendations are proposed.

Recent tests showed that anchorage failure could be the primary mechanism that limits the strength and deformation capacity of column-footing connections. An experimental program consisting of the reversed cyclic load testing of 16 approximately full-scale column-footing subassemblages was thus conducted to investigate the effect of various reinforcement details on connection strength, drift capacity, and failure mode. The main parameters evaluated were type of anchorage for the column longitudinal bars (either hooks or heads), extension of column transverse reinforcement into the footing, and longitudinal and transverse reinforcement ratios in the footing. Test results indicate that even when column longitudinal reinforcement extends into the joint with a development length in accordance with ACI 318-19, a cone-shaped concrete breakout failure may occur, limiting connection strength and deformation capacity. The use of transverse reinforcement in the connection over a region extending up to one footing effective depth away from each column face proved effective in preventing a concrete breakout failure. However, for the specimens with column headed bars, extensive concrete crushing adjacent to the bearing side of the heads and spalling beyond the back side of the heads led to significant bar slip and “pinching” in the load versus drift hysteresis loops at drift ratios greater than 3%. The use of U-shaped bars in the joint between the column and the footing or slab, as recommended in ACI 352R-02, led to improved behavior in terms of strength and deformation capacity, although it did not prevent the propagation of a cone-shaped failure surface outside the joint region. Based on the test results, the basic concrete breakout strength, Nb, corresponding to a 50% fractile, in combination with a cracking factor ψc,N = 1.25, is recommended when using Section 17.6.2. of ACI 318-19 for calculation of concrete breakout strength in connections similar to those tested in this investigation.