To address the dual bottlenecks of high energy consumption in traditional remanufacturing through remelting and performance degradation in direct reuse, this study proposes a short-process remanufacturing method based on laser remelting technology, establishing a circular pathway of “dismantling-remelting-certification-reuse. ” As a regenerative repair technique, laser remelting offers advantages such as superior mechanical properties of the remelted layer, elimination of surface defects, and optimization of the microstructure. Although this technology has proven effective at the material level, systematic research at the member scale remains insufficient. In this study, the mechanical and microstructural properties of the remelted layer were characterized through uniaxial tensile tests and metallographic analysis. Defect measurements and axial compression tests were conducted on laser-remelted recycled H-section steel stub columns fabricated using four different scanning strategies to evaluate the improvement in axial compressive performance and the effectiveness of the repair. A finite element model was developed using Abaqus to validate the experimental results and reveal the mechanisms underlying the improvement in mechanical performance. The results indicate that the centrally symmetric scanning strategy using a single robotic arm (with a power of 1.5 kW and a scanning speed of 1.2 m/min) increases the yield strength and ultimate bearing capacity of the members by more than 27% and 38%, respectively. Metallographic analysis shows that laser remelting transforms coarse surface grains into fine dendrites, forming a high-strength remelted layer, with the component transitioning into a “remelted layer-substrate-remelted layer” composite structure. Finite element simulations further elucidate the synergistic load-bearing mechanism of this composite structure under axial compression. This study fills the research gap regarding the performance of laser-remelted recycled steel structures at the member scale, providing a theoretical foundation for practical engineering applications.

In order to study the mechanical property of reworked coupons of locally corroded steel plate repaired with laser cladding technology, this paper studied the effect law of forms of corrosion, treatment of corrosion interface, corrosion depth, and scanning path of laser cladding on the mechanical property of reworked coupons through uniaxial tensile test. And it obtained the force-displacement curve and mechanical property reduction factors of the locally corroded steel plate and its reworked coupons repaired by laser cladding. The results show that the modulus of elasticity, yield strength and ultimate strength of locally corroded steel plate coupons repaired by laser cladding technology are roughly equivalent to those of intact coupons, and its ultimate elongation can be recovered to more than 70% of that of intact coupons. Soft treatment of cladding layer side-substrate interface or increasing the overlap region can move fracture location from the cladding layer side-substrate interface to the substrate and further enhance the mechanical properties of the repaired coupons. Laser cladding technology can repair steel plates of different depth of corrosion and the mechanical performance of the repaired coupons is not sensitive to the scanning path.

As a crucial method for connecting steel structures, welding plays a vital role in ensuring structural integrity, and the fatigue performance of welded joints directly affects the overall safety of steel structures. To enhance the fatigue performance of welded joints in steel structures, this study proposed the use of laser remelting treatment on the welded joints. For this purpose, this study conducted high cycle fatigue tests on the as-welded joints and laser remelting treated welded joints of Q355 steel plate butt welding. The stress levels for high-cycle fatigue tests were determined through tensile tests on as-welded joints. Fatigue fracture surface analysis was conducted using scanning electron microscopy (SEM). Based on the experimental results, stress-life (S-N) fatigue curves were fitted for both the as-welded joints and the laser-remelted welded joints, and the results were compared with standard fatigue design curves specified in relevant codes. The experimental results show that laser remelting treatment can change the location of fatigue fracture in welded joints, prevent failure at the weld toe and thereby significantly improve the fatigue life of welded joints, with an average increase of 244% to 499%. The fatigue fracture analysis show that there were mainly ratchet crack sources and a few subsurface crack sources in the as-welded joints, and there are mainly corner crack sources and edge crack sources in the laser remelted joints; the fatigue performance design curves provided by the American Steel Structure Code ANSI/AISC360-22, European Code EN 1993-1-9:2005, and Recommended Method for Offshore Steel Structure Design DNV-RP-C203 can be applied to the fatigue performance of as-welded joints, while these curves tend to be conservative for laserremelted welded joints.

This paper carried out axial compression tests on nine circular steel tube confined steel reinforced (CSTCSR) concrete short columns, one circular steel tube confined (CSTC) concrete short column and one circular steel tube column filled with steel-reinforced concrete. The main purpose of this research is to study the influences of yield strength of steel tube and shape steel, diameter-thickness ratio of steel tube, concrete strength, inner surface treatment method of high-strength steel tube and restraint mode on the failure mode, strain response, axial compression bearing capacity and ductility of CSTCSR concrete short column. The results show that the failure mode of high-strength circular steel tube confined high-strength steel reinforced (HCSTCHSR) concrete short column is overall shear failure, and there is no obvious local buckling on the surface of high-strength steel tube, and the development of oblique cracks of concrete is effectively restricted by the embedded high-strength shape steel. For CSTCSR concrete short column, the axial compression bearing capacity ratio and ductility coefficient of this column with high-strength steel tube and high-strength shape steel are increased from 1.37 to 1.49 and from 2.22 to 3.25, respectively, compared with those of CSTCSR concrete short column using ordinary-strength steel tube and ordinary-strength shape steel. It is concluded that the HCSTCHSR concrete short column has more excellent axial bearing capacity and ductility, and high-strength steel using in such column can be fully utilized. On the basis of “technical standard for steel tube confined concrete structures” (JGJ/T471—2019) and the results of parametric analysis in this study, a modified formula for axial bearing capacity of HCSTCHSR concrete short column was proposed by using the existing confined concrete’s constitutive model to provide scientific basis and data support for practical engineering application.

Concrete-filled steel tube (CFST), as a kind of structure with broad development prospect, has good bearing capacity and plastic deformation ability. As a common form, rectangular concrete-filled steel tube column is widely used in engineering practice. Based on the two problems of inconsistent constraints on long and short sides and insufficient constraints on core concrete existing in practical application of rectangular concrete-filled steel tube, this study explored a new type of rectangular concrete-filled steel tube member, namely rectangular concrete-filled steel tube column reinforced by built-in profiled stirrup. Therefore, this study carried out the axial compression tests on 11 rectangular concrete-filled steel tube columns reinforced by built-in profiled stirrup, 2 rectangular concrete-filled steel tube columns with built-in racetrack stirrup, and 2 ordinary rectangular concrete-filled steel tube columns. It analyzed the influences of the coupling distance, steel tube thickness, concrete strength grade, stirrup spacing, stirrup diameter, built-in steel quantity on the axial compression bearing capacity and ductility of rectangular concrete-filled steel tube columns reinforced by built-in profiled stirrup. The findings reveal that reducing the thickness of the rectangular steel tube and embedding the resulting steel into the core concrete as profiled stirrup can effectively improve the axial compressive bearing capacity and ductility of the specimen, while maintaining the total amount of steel used. Additionally, the axial compression behavior of rectangular concrete-filled steel tube columns reinforced by built-in profiled stirrup can be divided into four stages: elastic stage, elastoplastic stage, plastic strengthening stage, and descending stage. Compared to ordinary rectangular concrete-filled steel tube columns, those reinforced by built-in profiled stirrup exhibit a more complete plastic strengthening stage. Based on the experimental results and parametric analysis, this study derived a calculation formula for the axial bearing capacity of rectangular concrete-filled steel tube columns reinforced by built-in profiled stirrup using an existing confined concrete constitutive model. This study can provide scientific basis and data reference for practical engineering applications.