Circular hollow sections (CHS) are hollow structural steel profiles with a circular cross-sectional shape. They provide several beneficial properties as structural members due to their geometry.
The closed circular shape leads to axisymmetric properties allowing uniform stress distribution. CHS have high torsional stiffness and effectively resist torsional loads. This makes them suitable as purlins, rafters and connecting braces subject to twisting forces.
CHS demonstrate equal bending resistance in all axial directions as they lack weak axis limitations of open sections. This enables optimal orientation and reductions in bracing systems. Under axial loading, CHS efficiently resist buckling owing to the rounded form.
When subject to bending, CHS develop a uniform stress distribution with maximum stress at the extreme fibers. Relative to outer diameter, CHS can withstand greater bending moments than rectangular or square hollow sections of similar weight.
The elliptical stress distribution in CHS leads to gradual yielding upon bending rather than sudden failure. This enables ductile performance and energy absorption during seismic loading. CHS columns under eccentric compression also yield progressively prior to buckling.
For structural columns, concrete-filled CHS provide enhanced strength and stability. The concrete infill delays local buckling while the void steel core resists tensile forces. This composite interaction results in higher load capacity within small footprint areas.
Under elevated temperature conditions, CHS demonstrate higher fire resistance than open sections. The hollow core provides insulation and delays heat transfer to the inner steel. This reduces strength loss in building frames or transmission towers exposed to fire hazards.
Varying combinations of diameter, thickness and steel grades allow structural optimization of CHS. High strength steel CHS in thinner sections can achieve weight savings. Design codes like EN 1993-1-1 provide detailed guidance on CHS member capacity checks.
The circular exterior of CHS creates aesthetic architectural forms. It offers smooth surfaces for cladding systems and easy cleaning. Connections to CHS can be made via welding, bolting or proprietary systems for rapid assembly.
Structural analysis of CHS should evaluate member buckling, cross-section classifications, local capacity reduction factors, elastic/plastic stress distribution, deformation limits, axial/flexural/torsional interactions and fatigue checks.
Advanced analysis using finite element methods accurately capture CHS behavior under different loading combinations. Elastic buckling analysis evaluates susceptibility to instability. Non-linear geometric and material analysis simulates progressive yielding and ductility.
In summary, the unique geometry and axisymmetric properties of CHS provide optimal structural performance under axial, flexural, torsional and combined loading. CHS demonstrate uniform stress patterns, high buckling strength, good ductility and capacity enhancement via concrete-filling. Appropriate design and analysis help utilize these benefits across diverse structural applications.
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