Pultruded glass fiber reinforced polymer (GFRP) composites are extensively applied in the field of ultra-high voltage power transmission due to their excellent electrical and mechanical properties, and the design considering its performance degradation characteristics under fatigue loading is the key to the application. This study carried out static load tests and fatigue tests under different conditions with the pultruded unidirectional GFRP. A fatigue life prediction model was established based on a piecewise linear constant life diagram determined by S-N curves. According to the stiffness degradation law under different stress ratios, a modified damage accumulation model based on the improved trigonometric function was presented to describe the nonlinear stiffness degradation process under both tension-tension and tension-compression fatigue loads. The correlation model between residual strength and residual stiffness was established to predict the strength degradation precisely. The results show that the stiffness degradation processes of GFRP under tension-tension and tension-compression fatigue loads are significantly different. The model proposed in the paper can accurately predict the residual strength under the two conditions. Under compression-compression fatigue load, there are two different patterns for the stiffness degradation processes, and the residual strength test shows that the strength within the first 70% fatigue life does not exhibit a significant degradation.The prediction model for the residual strength and residual stiffness of GFRP under different fatigue loading provides a guide for the durability design of GFRP.

Corrosion of cable-strut structures during long-term service life will cause cross-sectional area loss of steel members, which will lead to redistribution of internal force and affect safety performance of the structure. This paper established three failure modes including member strength failure mode, cable relaxation failure mode and node deformation failure mode based on the reliability theory and structural limit state, and further obtained reliability limit control inequalities under critical states of different failure modes. Through mechanical derivation, it derived the formula for the members’ internal force variation as well as nodal displacement variation of cable-strut structure due to variation of cross-sectional area. Based on the formula, the influence coefficient matrix in the reliability limit control inequality can be calculated. By introducing the corrosion model of steel and combining it with nonlinear programming, it proposed the method to determine the members’ area-loss limit of cable-strut structure. The numerical example of a Levy cable dome was carried out and the calculated area-loss limits were compared with the current limit in specification. The result shows that the calculated area-loss limit of most members in the cable-strut structure under the strength failure mode and deformation failure mode is higher than the durability specification limit, but the area-loss limit under the relaxation failure model is smaller than the durability limit. If the structure is designed and maintained according to this limit value, the cable relaxation failure may occur. The safety specification limit is strict for steel cable members, but it is the same as durability specification limit for steel bar members. Therefore, the area-loss limit under three failure modes and specification limits should be considered comprehensively and the final limit should be controlled according to the most stringent results.

To study the whole-process structural performance of new spread slab beam bridges, this paper investigated the damage development and failure mechanisms from construction to in-service stages with beam clear spacing, beam number and prestressing steel arrangement as key parameters. The nonlinear numerical analyses were preformed on the bridge system with using ABAQUS software. Research outcome indicates that the beam failure and mixed beam-slab failure are two main failure patterns for this new bridge system. When the beam clear spacing is small, the deformation of all beams is consistent, and the ultimate strength is relatively higher, which is prone to the failure of beams. On the contrary, when the beam clear spacing is large, the transverse load transfer capacity is relatively weaker and the deformation-lag effect exists among different slab beams, resulting in the mixed beam-slab failure. For spread slab beam bridge cases with similar bridge width and span length, a relatively larger beam spacing value is unfavorable for the transverse load sharing, and the ultimate strength of the entire bridge system may be significantly reduced by 40%~50%. The bearing capacity of bridge cases with less beam numbers can be improved by increasing the prestressing steel amount, and the ultimate strength of a single slab beam may be increased by 10%~30%. However, the camber issue at the precasting stage should be handled with caution in the design. Compared with the integral casting concrete beam bridge, this composite beam bridge system is different in the displacement and stress responses obtained from the whole-process analysis, but their difference in the ultimate strength is small. In general, the new spread slab beam bridge system shows good strength and deformation capability, and the characteristics of light weight, low profile and easy construction, owning a good application prospect in China.

In order to investigate the optimization design method of medium and large span continuous steel girder steel fiber reinforced concrete (SFRC) composite bridge deck, the study used SFRC to replace C50 concrete pavement in the original design, and established SFRC composite bridge deck steel box girder segment model by Abaqus for parameter analysis. And the influence characteristics of SFRC plate thickness, steel roof thickness and reinforcement ratio on the bending stiffness and steel structure stress of the main beam were investigated. The study is based on the cracking characteristics of SFRC obtained by the combination of SFRC composite plate partial tension test and numerical simulation and the existing continuous steel girder structural characteristics. On this basis, the main girder elastic bending stiffness and key cross-section stress were taken as the constraints, and the upper structural self-weight and material cost were taken as the optimization objectives to optimize the mid-span 50 m and 80 m continuous steel girders. Finally, based on the variable optimization results, Midas was used to establish a bar model considering SFRC cracking in the negative moment region to verify the reasonableness of the optimization results. The results show that the finite element analysis method of plastic damage introduced in the paper is reliable, and the relationship between the SFRC crack width and the tensile damage factor can characterize the SFRC cracking state. The 80~120 mm thick SFRC layer on the continuous steel girder increases the elastic bending stiffness of the main girder by 17%~24% after participating in the force; the bending stiffness of the main girder decreases by 13%~20% when the width of the SFRC crack reaches 0.20 mm; the stress of the steel roof plate decreases by 7%~12%, and the negative bending capacity of the main girder does not change significantly. Increasing the thickness of top plate and reinforcement ratio can effectively improve the stress of steel roof. Through the optimization analysis of SFRC layer thickness, reinforcement ratio, steel roof and roof stiffener size, compared with the original design, the optimized steel consumption of 50 m and 80 m continuous steel girders with SFRC deck panels is reduced by 13% and 6% respectively, the weight of the superstructure is reduced by 12% and 6% respectively, and the cost of the material is reduced by 14% and 9% respectively. The optimized design process and optimization results can be used for the design of the continuous steel girder in SFRC deck panels. The optimized design process and optimization results can provide reference for the popularization and application of SFRC composite bridge deck in continuous steel girder.

Most double steel plate-concrete composite shear walls use bolted or welded ribs to make the steel plate and concrete work together. However, this connection method may lead to low integrality and plastic deformation efficiency, as well as complex fabrication. Welded multi-cavity double steel plate-concrete composite shear walls are able to avoid these problems effectively. In order to investigate the seismic performance of welded multi-cavity double steel plate-concrete composite shear wall, a three-dimension solid-shell model of composite shear wall is established by using the constrained concrete true triaxial plasticity-damage constitutive model and the steel elastoplastic hybrid strengthening-ductile damage constitutive model. The hysteresis curve, skeleton curve, stiffness degradation curve, elastic stiffness, bearing capacity, cumulative energy dissipation, equivalent damping viscosity coefficient and ductility coefficient obtained by the model are in good agreement with the existing quasi-static test results. The analysis results show that: (1) the axial compression ratio has little effect on the elastic stiffness and bearing capacity of the composite shear wall model, while the stiffness and bearing capacity of the composite shear wall model decrease linearly with the increase of shear span ratio; (2) the axial compression ratio has little effect on the total plastic energy dissipation of the composite shear wall model, while the shear span ratio has a greater effect, and the total plastic energy dissipation of the shear wall decreases with the increase of shear span ratio; and (3) both the axial compression ratio and the shear span ratio do not change the energy dissipation allocation mechanism of each component of the shear wall model, which means that the energy dissipation of the composite shear wall model is mainly due to the outer steel plate and the inner partition.

In order to enhance the bearing capacity and durability of thin-walled stainless steel structures, a kind of seawater sea sand concrete-filled CFRP-stainless steel sandwich tube structure, that is, in which the inner and outer walls of stainless steel tube were pasted with CFRP (Carbon Fiber-Reinforced Polymer) composite constrained seawater sea sand concrete, was designed. Then, monotonic static axial compression tests were carried out on 18 short column specimens, with the number of pasting layers and pasting methods of CFRP as the variation parameters. The failure process and morphology of the specimens were observed, the load-displacement curves and material strain distribution data were obtained, and the variation law of the axial compression mechanical properties of the specimens was analyzed. The results show that: (1) the internal and external CFRP can effectively improve the bearing capacity and deformation capacity of the structure; (2) the failure modes of the specimens without CFRP and the specimens with internal CFRP are both shear damage, but the shear damage will change to waist drum damage with the increase of the number of external CFRP layers; (3) with the same pasting methods, the bearing capacity, deformation capacity and energy dissipation capacity of the specimens increase non-linearly with the increase of the number of CFRP layers; and (4) with the same pasting layers, the mechanical properties of the specimens with internal CFRP are better than those with external CFRP, and the ultimate bearing capacity of the specimen with one or two internal CFRP layer respectively increases by 5.6% or 6.7%, as compared with that of the specimen with external CFRP, and the energy dissipation capacity of the specimen with one internal CFRP layer is equivalent to that of the specimen with two external CFRP layers. Moreover, the strain analysis results show that CFRP and stainless steel have good cooperative performance before the specimen is damaged. Finally, based on the limit equilibrium method and by considering the strain hardening effect of stainless steel, a formula for calculating the ultimate axial compressive bearing capacity was proposed and 73 sample data were collected for verification, finding that the calculated values accord well with the test ones.