Linear elastic topology optimization and additive manufacturing of planar steel joints : numerical simulation and experimental investigation

Abstract

Welded joints are extensively utilized in the construction of high-rise buildings and grid-shell structural systems, particularly for complex multi-planar steel joints. However, on-site welding of intricate frame systems presents challenges in terms of time consumption and ensuring welding quality, especially for overhead welding. To overcome these hurdles, an innovative solution combines topology optimization (TO) through the Solid Isotropic Material Penalization Method (SIMP) with additive manufacturing (AM) for mass-producing repetitive joints. This approach enhances construction efficiency and ensures high-quality joints by enabling optimized AM joints to be bolted to other members on-site, circumventing on-site welding complications.

This study conducts tensile tests to evaluate the material properties of mild steel, stainless steel, and high-strength steel used in various manufacturing processes. Welded and 3D printed joints employing these materials are investigated to maximize mechanical properties through the potential of AM and TO. A custom non-contact 3D-DIC (Digital Image Correlation) technique based on an open-source tool (MultiDic) is employed to analyze and visualize strain distribution in planar tubular and topologically optimized joints.

The integrated design framework, centered on 3D-printed planar stainless steel tubular joints using the SIMP method, is explored. Optimized joints with varying brace-to-chord width ratios are obtained through computer-aided design software. Independently designed and manufactured joints via 3D printing can be riveted with structural members, simplifying installation and improving construction efficiency by mitigating on-site welding challenges.

Non-contact 2D DIC is employed for intuitive strain distribution analysis in 3D printed and welded planar, tubular joints. Using different printing orientations, the coupon tensile test is proposed to assess the stress-strain relationship. Experimental findings indicate that material additive manufacturing orientation moderately affects yield strength, ultimate strength, and fracture elongation, with minimal impact on Young's modulus.

The optimized joint exhibits distinct failure modes from traditional tubular joints, demonstrating a strong-joint and weak-component mechanism that prevents entire joint failure upon localized damage. Hysteresis loop analysis reveals enhanced energy dissipation in the optimized joint compared to traditional welded joints, thereby bolstering structural seismic performance. This developed framework can be extended to complex spatial joints subjected to multi-planar loads in future applications. Furthermore, this study discusses existing design code limitations and proposes novel strength design methods for additive manufacturing and topology optimization, validated through reliability analysis. The innovative integration of topology optimization and additive manufacturing presents a promising avenue for constructing high-quality, efficient, and reliable joints in high-rise buildings and grid-shell structural systems. (396 words)