This paper discusses the solutions for topology optimization of spatially discrete structures. The optimization objects are the structural weight and the maximum displacement. The optimization variables include structural node coordinates, and the improved MOEA (Multi-objective Evolutionary Algorithm) method is used to optimize the structure. The innovation of this study is that it breaks through the shortage of constant node position in the optimization thought of traditionally discrete structure in the “Ground Structure Approach” and uses the coordinate of the node as the optimization variable for the optimization calculation. The result is not a single one but a set of optimal solutions through the evolution (i.e., Pareto optimal solutions); on this basis, the most suitable solution can be found according to the boundary conditions or other related requirements. Using the C# language to compile the calculation program, ANSYS finite element software is used to analyze the structure, and the Pareto front surface was automatically drawn to determine the optimal layout form of the discrete structure. The analysis results show that the improved MOEA method can provide an effective method to solve such optimization problems.

Four prestressed high-strength concrete pile- (PHC pile-) pile cap connections under low-cycle loading were tested to study the test phenomena, failure modes, hysteretic performance, ductility, and bearing capacity. The PHC piles were reinforced with steel fiber and deformed bars and CFRP. The tests results showed that the connections were damaged by bending. The concrete of the caps were squeezed to be crushed. The concrete of connection was crushed and formed a hinge joint that resulted in the connection rotating unrestricted, and the rotation capacity of connection increased. The PHC pile reinforced with steel fiber and deformed bars can improve the displacement ductility of the connections. The finite element software ABAQUS was used to simulate the nonlinear behavior of pile-cap connections. The prediction agreed relatively well with the experimental results. The stress and strain of specimens were studied. The connections should be designed with enough rotating capacity and make sure the cap will not be damaged by squeezing or prying due to the rotation of pile end.

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In this paper, in order to further study the mechanical behavior of T-shaped stiffened concrete-filled steel tubular (CFST) columns, numerical programs of eccentrically compressive T-shaped stiffened CFST columns were developed to calculate moment M-ϕ curvature curves of cross section and column. The calculated curves with the numerical programs agree well with the experimental results. A parametric analysis was carried out to calculate M-N correlation curves of cross section and column to investigate influence of concrete strength fck, steel yielding strength fy, steel tube thickness t, slenderness ratio λ, and loading angle θ. On the basis of parametric analysis, simplified resistance models of T-shaped CFST section and column were proposed and verified by the numerical analysis results. The simplified resistance models are reliable to predict the mechanical behavior for engineering application.

As an ideal layout scheme for launch vehicle, bearing co-bulkhead tank can improve the slenderness ratio of launch vehicle, reduce structure weight and increase structure efficiency. In this paper, a novel cryogenic tank co-bulkhead was fabricated by vacuum assisted resin transfer molding (VARTM) process. Consisting of LD10 alloy and polymethacrylimide (PMI) foam-sandwich, the new cryogenic tank co-bulkhead was designed with variable-thickness, hemi-ellipsoid structure, thermal insulation and bearing function. Fundamental temperature distribution, thermal stress and low-temperature load sensitivity of the foam-sandwich co-bulkhead were also assessed by finite element analysis and environment tests in simulated service environment. The results showed that the analog values highly agreed with the test results, and thermal insulation and bearing function of the foam-sandwich co-bulkhead could satisfy the design requirement, which proved the reliability of bonding quality and feasibility of the bonding technique.