A novel column consisting of steel, concrete and fiber-reinforced polymer (FRP) is presented and assessed through experimental study. The sectional form of steel–concrete–FRP–concrete (SCFC) columns has a square steel tube as the outer layer and a circular filament-wound FRP tube as the inner layer, and concrete is filled between these two layers and within the FRP tube. Thus the column can be regarded as a concrete-filled square steel tube (CFST) with a FRP-confined concrete core (FCCC). In comparison to existing composite column sections, several advantages are achieved such as ease of connection to beams, the stronger confinement of core concrete, ductile response, and residual load capacity. 18 SCFC stub columns are tested with different concrete strengths, FRP tube thickness and steel tube thickness in comparison to four traditional composite columns. The distinctive behaviors of SCFC columns, including significant post-yield stiffness, ductile failure, and stable residual bearing capacity are found. Test results show that the strengths of concrete, FRP, and steel are effectively utilized at different stages, including the initial linear stage, the secondary linear stage (hardening stage), and the post-peak stage. The influences of key design parameters on the mechanical characteristics of initial compressive stiffness, peak strain, residual load-bearing capacity, and ductility are also clarified.
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Shear walls are commonly used as structural elements to resist earthquake. The seismic performance of shear wall can be guaranteed under small earthquakes, but problems exist when it is subjected to large earthquakes. To improve the ductility and energy dissipation capacity of shear walls in large earthquakes, shear failure must be avoided and the performance of plastic hinge region must be improved. The adaptive-slit shear walls (ASSW) is proposed in this paper The mechanical characteristics of ASSW satisfy the requirements of structures under different seismic level. Therefore the damage process of ASSW can be controlled and the ductile shear failure can be realized, which obviously improve the seismic performance of shear wall structures.
为进一步提高煤炭资源的回收率，减少矿井储量积压，挖掘生产能力，延长矿井寿命，积极完善、推广“三下”采煤技术体系已成为矿井挖潜增产的重要技术途径。通过对建筑物下、铁路下、水体下采煤技术体系的介绍，阐述了“三下”开采的重要性及其发展前景。
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目的：探讨塑性跟骨钛板治疗Sanders Ⅲ、Ⅳ型跟骨骨折的疗效。材料与方法：自2001年2月至2008年6月，对18例23足Sanders Ⅲ、Ⅳ型跟骨骨折，采用塑性跟骨钛板加自体髂骨植骨进行复位内固定治疗。结果：本组病例随访6～36个月，平均随访时间18．5个月。按Maryland足部评分标准评价，优8足，良11足，中3足，差2足，优良率78．2％。结论：本方法治疗SandersⅢ、Ⅳ型跟骨骨折复位满意，固定牢靠，术中自体髂骨植骨，术后早期关节功能锻炼，疗效肯定，是一种目前治疗Sanders Ⅲ、Ⅳ型跟骨骨折的较好方法。
Combining Al (namely, aluminum alloy) and CFRP (carbon-fiber-reinforced polymer) jackets to form structural members can yield many advantages and a bilinear behavior, which can enhance their advantages and mitigate any disadvantages. CFRP–Al hybrid tubes, which are used as axial load members in spatial structures, are investigated in this study by using compression experiments and a theoretical analysis. Formulas that describe the compressive bearing capacity with and without local buckling before yielding are proposed for stub hybrid tubes. In addition, their compressive behaviors are simulated by using the finite element method (FEM). A good agreement in the test results is achieved. The effect of the number of pairs of CFRP layers, the diameter-thickness ratio (DT ratio) and width-thickness ratio (WT ratio), and the fiber direction are described based on finite element analysis (FEA). Finally, a design approach for compressive CFRP–Al hybrid stub tubes is proposed.
This study presents a new fiber reinforced polymer tube/filling strengthening method (i.e., FRP tube/filling strengthening) that creates a new composite compression member with a novel mechanical behavior, “bilinear behavior.” Previous experimental and theoretical studies have been conducted based on the ultimate state of the section. To thoroughly study the stiffness and entire loading process of this novel member, finite element analysis (FEA) models are built in this paper. First, the model development process considers the initial defections and interface properties, and these models are verified by the experimental results. Two models of typical load-axial displacement curves describe the experimental results: a Bilinear model and a Trilinear model. Second, finite element modeling (FEM) is used to conduct a parametrical analysis that considers 7 parameters, and the results identify the mechanism of the strengthened member. Specifically, the Bilinear model corresponds to an unreinforced or relatively weakly reinforced specimen, and the Trilinear model corresponds to a relatively strongly reinforced specimen. If the exterior restraint system is weak, then the core steel buckles and subsequently yields; this behavior is described by the Bilinear model. If the exterior restraint system is strong (e.g., the length or the bending stiffness of the exterior restraint system is great), then the specimen can continue to bear a higher force after steel yielding until elastic-plastic buckling occurs; this behavior is described by the Trilinear model. Third, the FEA results and previous experimental and theoretical studies are used to obtain the stiffness and load-axial displacement curves, which are helpful for the design process. In general, relatively accurate FEA models are built in this paper that are capable of describing the mechanical behaviors of the novel member.
This work focused on restrained torsion performance and calculation methods of pultruded GFRP I-section profiles. Material shear properties were tested by V-notched tests, showing significant material nonlinearity. Restrained torsion tests were conducted for six I-section profiles. Three I-section failure modes were found: local buckling failure caused by restrained normal stress at the end, shear failure of the flange-web junction at the midspan and compression failure at the end. Subsequently, finite element analysis was conducted. UMAT based on Puck model was utilized to consider the nonlinearity of shear properties, and simulations and experiments agreed well. Shear property nonlinearity had little influence on the I-section restrained torsion behavior. Vlasov theory was extended to orthotropic materials. The formula of local buckling caused by restrained normal stress was developed based on energy theory. Furthermore, calculation methods to predict restrained torsion failure were proposed and compared; the proposed methods were the most effective.
The elastic buckling load of an axially compressed piecewise member was derived under various ideal boundary conditions based on the differential element method; then, the result was simplified for a symmetrical member. The theoretical results were found to be consistent with existing formulas for the elastic buckling load of uniform members. Then, the elasto-plastic buckling of an axially compressed piecewise member composed of steel and elastic materials was investigated and found to be quite different from that of a pure steel member, and a theoretical analysis approach was developed. In elasto-plastic buckling analysis, the load-bearing capacity of the steel section in the ultimate state is determined considering initial imperfections and steel hardening. Furthermore, the symmetric method for obtaining the load-bearing capacity of this member was obtained based on the ultimate state of the critical section, which is simple and reparative for design. The theoretical results of the elasto-plastic buckling analysis were consistent with experimental results, therein obtaining an average error of 4%.
