Portal steel structure optimization design method and steps
August 02 03:23:40, 2025
The light gantry steel structure offers several advantages, including low cost, lightweight design, ease of installation, and a short construction period. As a result, it has gained significant popularity in recent years and is widely used in industrial plants. However, during actual engineering design, the variable cross-section dimensions of the steel members—especially for gantry structures—require multiple trial calculations to determine. Unfortunately, many designers lack sufficient experience, which leads to inefficient design processes. Poorly chosen cross-sections can cause uneven stress distribution across the structure, resulting in suboptimal economic performance and reduced structural safety. In some cases, certain members may even experience excessive stress, exceeding the material’s design strength. Even with plastic deformation allowing for some stress redistribution, potential safety risks may still remain in the overall structure.
The main optimization goal when designing a gantry steel structure is to minimize both the amount of steel used and the overall cost while ensuring structural safety. This objective can be simplified by focusing on selecting economical and reasonable cross-sectional dimensions. The aim is to achieve the smallest possible cross-sectional area while still meeting the requirements for strength, stiffness, and stability.
The optimization method used for gantry steel structures is similar to that of grid steel structures. It typically involves the asymptotic full-stress method, where the cross-sectional dimensions of each member are iteratively adjusted through repeated calculations until they reach or approach a full-stress state. Once all members no longer require modification, the total steel usage is minimized, achieving the lowest cost. This process ensures that each section is optimized to maximize bending resistance while minimizing material use, based on the external loads applied.
The step-by-step optimization analysis for gantry steel structures includes the following steps: First, determine the initial cross-sectional dimensions of the structural members, often based on software recommendations or designer judgment. Next, perform a finite element analysis of the variable-section members under various loading conditions, including load combinations, strength checks, and stability assessments. Then, using the full-stress optimization method, re-evaluate and adjust the cross-sectional dimensions of each member based on actual load effects and constraints. These second and third steps are repeated iteratively until the selected cross-section sizes stabilize. Finally, check the deformation of beams and columns to ensure compliance with relevant specifications. If deformation limits are not met, further optimization is performed using proportional parameters, and the process is repeated until all components meet the required standards. Full-stress optimization often requires multiple cycles, typically converging within 10 iterations, though stiffness-related optimizations may only need 1–3 cycles to meet deformation requirements.
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