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Wire arc additive manufacturing (WAAM) is a metal 3D printing technique that allows large-scale elements to be built in a relatively timely and cost-effective manner, well suited to the cost-sensitive construction sector. Despite the potential of this novel technology, the basic properties of WAAM materials remain elusive. This paper presents a comparative study on the microstructure and corrosion behaviour of WAAM steel plates and the conventionally rolled Q345 steel. The WAAM steel exhibited comparable corrosion performance to the conventionally-produced steel within twelve days exposure in 3.5 wt% NaCl solution, including the corrosion current density, and the characteristics of steel/concrete interface, determined through electrochemical impedance spectroscopy (EIS) analysis. Post-corrosion observations revealed that preferential dissolution occurred at (Si, Mn)-rich oxide inclusions, in addition to the general corrosion of surrounding steel matrix. The much higher content of Si and Mn element in the feedstock material WAAM steel resulted in slightly higher susceptibility to localised corrosion, compared to the Q345 rolled steel.

This paper investigated the effects of adopting short alkali-resistant glass fibers on the mechanical properties of fine-grained concrete matrix. In addition, four-point bending tests have been carried out in order to analyze the flexural behaviors of carbon fiber textile reinforced concrete (CTRC) sheets. In this study’s experiments, 19 serial specimens were tested, with consideration given to the short fiber lengths and content, and reinforcing ratio of carbon fiber textiles. It could be found from the test results that the fine concrete matrix had higher mechanical properties with the increases in the lengths and content levels of the fibers. Furthermore, this study’s bending tests of the CTRC revealed that the bending strength and deformability were significantly improved with increases in the fiber content and the reinforcing ratio of carbon textiles. By utilizing short fibers, the cracking load of the CTRC sheets had been improved by 80.35%. The maximum improvement of the ultimate bending load was more than 6 times compared with the specimens without carbon fiber textiles and short fibers. Finally, a trilinear model was proposed to describe the flexural load-displacement curve of the CTRC sheets reinforced by short fibers. It was determined that the predicted data agreed well with the experimental data.

The flexural behavior of rectangular hollow section (RHS) steel beams with initial crack strengthened externally with carbon fiber reinforced polymer (CFRP) plates was studied. Eight specimens were tested under three-point loading to failure. The experimental program included three beams as control specimens and five beams strengthened with CFRP plates with or without prestressing. The load deflection curves were graphed and failure patterns were observed. The yield loads and ultimate loads with or without repairing were compared together with the strain distributions of the CFRP plate. It was concluded that yield loads of cracked beams could be enhanced with repairing. Meanwhile, the ultimate loads were increased to some extent. The effect of repair became significant with the increase of the initial crack depth. The failure patterns of the repaired specimens were similar to those of the control ones. Mechanical clamping at the CFRP plate ends was necessary to avoid premature peeling between the CFRP plate and the steel beam. The stress levels in CFRP plates were relatively low during the tests. The use of prestressing could improve the utilization efficiency of CFRP plates. It could be concluded that the patching repair could be used to restore the load bearing capacity of the deficient steel beams.

The model for chloride transport in concrete was established by considering both effects of diffusion and capillary suction. The model was verified by chloride penetration tests under cyclic wetting and drying conditions. The developed model was used to analyze similarities under different environmental conditions for accelerated tests. The results showed that the influence of external chloride concentration on chloride penetration was smaller with a larger depth. When the ambient relative humidity (RH) decreased, the penetration rate increased when RH was larger than 70%. However, the penetration rate decreased when the RH was smaller than 70%. The results also indicated that when the wetting-to-drying time ratio in a cycle increased, the penetration rate increased first and then decreased after a critical ratio. When the cycle period decreased, the penetration rate first increased and then decreased during a small time period. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation and theoretical analysis on the collapse behavior of a reinforced concrete super-large cooling tower induced by failure of columns. The finite-element model was first validated by a collapse experiment of a 1/100-scaled superlarge cooling tower and was then used to study the collapse process of the prototype tower. A simplified mechanical approach was put forward to analyze the collapse modes of the prototype tower induced by failure of columns with different numbers. The results demonstrated that the collapse process of a cooling tower resulting from failure of columns could be considered as a non-fixed axis rotation problem. The collapse modes were determined by the number of failed columns, which could be further explained by comparing flexural bearing capacities, vertical bearing capacities, and horizontal bearing capacities of the remaining columns and overturning moments, vertical pressures, and horizontal thrusts, respectively. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue behaviour of out-of-plane gusset welded joints strengthened with carbon fibre reinforced polymer (CFRP) laminates. Two notches were introduced at the weld toes adjacent to longitudinal plate ends to simulate the initial damage. Variables including the stress range, single- or double-sided strengthening and modulus of CFRP materials were considered. It was found that both cracks propagated under fatigue loading. All the specimens fractured along one predefined notch when the fatigue crack reached a certain length while the other crack also grew to some extent. Test results showed that the addition of composite materials significantly prolonged the fatigue life of specimens by as much as 1.28 to 8.17 times. Double-sided bond and ultra-high modulus CFRP materials led to a better strengthening efficiency. Thereafter, a series of numerical analyses were performed to study the stress intensity factor (SIF) and crack opening displacement (COD). Local debonding around the crack tip at the adhesive-steel interface was taken into consideration. Finally, the fatigue life of all the specimens was evaluated based on the linear elastic fracture mechanism (LEFM) theory and the predicted results agreed well with the experimental data. [ABSTRACT FROM AUTHOR]