The new composite application of seawater sea sand concrete (SSC) and fibre-reinforced polymer (FRP) bars had broad development prospects. In this paper, the load levels and stirrup spacing were the main research parameters. The fatigue behaviour of carbon fibre-reinforced polymer (CFRP) bar-reinforced SSC beams was studied by four-point bending tests, and the development laws of fatigue crack width and fatigue deflection were deeply discussed. Results revealed that excessive stirrup spacing might change static failure modes of CFRP bar-reinforced SSC beams, resulting in a reduction in mechanical behaviour. This paper preliminarily suggested that the maximum stirrup spacing should be 200 mm. The fatigue failure mode of CFRP bar-reinforced SSC beams in this paper was mainly shear fatigue failure. The fatigue crack width and fatigue deflection increased with the cycle number. When the cycle number reached 80% of fatigue life, the fatigue crack width increased by about 100%. When the beam specimens were close to fatigue failure, the increase in fatigue deflection ranged from 166.5% to 188.9%. Load levels had a significant impact on fatigue life, and a fatigue limit of 0.5 was proposed as a threshold. In addition, the larger the stirrup spacing, the greater the growth rate of fatigue crack width and fatigue deflection. Therefore, based on the calculation equation for the maximum crack width in the code, the influence of stirrup spacing, load levels and n/N was further considered in this paper. Considering the influence of stirrup spacing and load levels, a calculation equation for fatigue deflection was proposed. Finally, the fatigue design concept was improved, and the fatigue life was further subdivided into the fatigue life on bearing capacity and normal service.

Many existing structures require retrofitting and reinforcement due to aging and damage. The stability of the retrofitted structure is key to the retrofitting scheme, while construction safety during the retrofitting process is another crucial consideration. This study proposed an evaluation method for assessing the stability and construction process of steel structure retrofitting projects based on an ANSYS finite element analysis. By establishing a nonlinear finite element model of a retrofitted gymnasium roof truss structure, the overall stability of the system was systematically verified. The dynamic simulation of demolition and retrofitting procedures was conducted using the birth-and-death element technique, and a comprehensive safety assessment framework covering the entire construction process was developed. The case analysis demonstrated that this method can simulate the redistribution of internal forces during component demolition and identify potential risks. The effectiveness of the retrofitting strategy was evaluated by comparing the nonlinear stability coefficients of the structure before and after retrofitting, indicating improved performance within the scope of the finite element model. The research results demonstrated the feasibility of incorporating modeling, simulation, and assessment in retrofitting projects and provided a reference for similar retrofitting projects.

The FRP–concrete–steel double-skin tubular column (DSTC) is a novel composite column designed to meet the structural demands for high strength, exceptional durability, and lightweight characteristics. To investigate the axial compression performance of DSTCs, this study conducted axial compression tests on 16 circular DSTCs and three circular fully filled columns (FCSCs). This research focused on analyzing the effects of steel tube wall thickness, void ratio, rubber content, steel fiber content, and GFRP tube wall thickness on stub columns’ failure modes, load–displacement curves, load–strain curves, and stress–strain relationships of concrete. The results demonstrated that GFRP tube wall thickness is the most critical parameter influencing the bearing capacity and deformation capacity of the column. The ultimate bearing capacity of all specimens ranged from 1606.9 to 3447.9 kN; the peak displacement of the specimens ranged from 7.49 to 17.77 mm. Increased void ratios decrease bearing capacity but enhance ductility, whereas steel tube wall thickness and steel fiber content have relatively minor effects. Based on the experimental results, models for the ultimate bearing capacity, ultimate strain, and stress–strain relationship of short columns were proposed, taking into account rubber content. The average predicted-to-experimental capacities ratio is 0.97 and the predicted load–displacement curves match well with the experimental curves, indicating the very high accuracy of the proposed models.