Guide to Upgrading Seismic Safety in Steel Portal Frames

Imagine a sudden earthquake violently shaking buildings—what becomes your primary concern? Undoubtedly, it's structural safety. For portal frame structures constructed with cold-formed thin-walled steel, their seismic performance directly impacts life and property safety. But how earthquake-resistant are these structures, and how can their performance be improved?

This article examines the seismic behavior of cold-formed steel portal frames, highlighting their advantages and challenges while providing practical structural safety enhancement solutions.

Cold-formed thin-walled steel, as the name suggests, refers to steel sections shaped through cold-forming processes. Compared to traditional hot-rolled steel, cold-formed thin-walled steel offers these distinct advantages:

• Lightweight design: The thin walls result in lighter structures, reducing inertial forces during earthquakes and decreasing structural loads.
• High-strength material: Typically manufactured from high-strength steel, these sections exhibit superior yield and tensile strength for greater load capacity.
• Design flexibility: Cold-forming allows diverse cross-sectional shapes that can be optimized for specific requirements, improving material efficiency.
• Construction efficiency: Components are easily connected and installed, shortening project timelines and reducing costs.

These benefits have made cold-formed steel portal frames widely adopted in industrial facilities, warehouses, and commercial buildings.

While cold-formed steel portal frames offer numerous benefits, their seismic performance presents specific challenges:

The thin walls of cold-formed sections make them prone to local buckling and overall instability, affecting load-bearing capacity and seismic resistance. Key improvement measures include:

• Additional bracing: Strategic bracing prevents member buckling and enhances structural stiffness.
• Section optimization: Selecting appropriate cross-sections improves bending and torsional resistance.
• High-strength materials: Using steel with higher yield and tensile strengths increases load capacity.

Joints critically influence overall structural performance. Common connection methods include bolting, welding, and self-drilling screws. Ensuring reliability requires:

• Appropriate connection selection: Choosing suitable methods with thorough reliability analysis and testing.
• Joint optimization: Enhancing geometric configurations to improve load-bearing and deformation resistance.
• Construction quality control: Strict adherence to design specifications during installation.

This refers to a structure's energy dissipation under cyclic loading. Cold-formed steel frames typically exhibit poorer hysteretic performance, necessitating improvement strategies like:

• Ductile connections: Designing joints that undergo plastic deformation to dissipate energy.
• Dampers: Installing damping devices to increase energy absorption capacity.

To improve earthquake resistance, multiple approaches can be implemented:

• Implementing multi-span systems and additional bracing to increase stiffness
• Conducting detailed finite element analysis for accurate seismic assessment
• Accounting for multiple hazard scenarios in design calculations

• Selecting higher-grade steel materials
• Applying corrosion protection treatments
• Implementing strict material quality control

• Using high-strength bolts
• Optimizing welding techniques
• Designing joints for greater ductility

• Strict adherence to design specifications
• Enhanced quality inspection protocols
• Proper corrosion and fire protection measures

• Base isolation systems
• Energy dissipation devices
• Structural health monitoring systems

An industrial facility with cold-formed steel portal frame sustained earthquake damage. Retrofit measures included:

• Adding cross-bracing between columns and roof
• Strengthening critical connections
• Replacing severely damaged members

Post-retrofit evaluations confirmed significant seismic performance improvements meeting current code requirements.

Cold-formed steel portal frames represent an efficient structural solution with broad application potential. Continued advancements in connection technologies, energy dissipation methods, and monitoring systems will further enhance their seismic resilience, ensuring safer built environments.