What are the calculation methods for the bearing capacity of steel supports
The calculation of the bearing capacity of steel supports needs to be combined with material characteristics, stress forms, and structural specifications to ensure that they do not experience strength failure, stability failure, or excessive deformation during construction. The main calculation methods are as follows:
1、 Strength calculation
Based on the material strength limit, verify whether the stress of the steel support under load is lower than the allowable value. The core formula is:
σ=N/A≤[f]
σ is the calculated cross-sectional stress (N/mm ²), N is the axial force (tension or compression, kN), and A is the net cross-sectional area (mm ²);
[f] Design values for compressive/tensile strength of steel (e.g. 215N/mm ² for Q235 steel and 310N/mm ² for Q355 steel, according to the "Design Standard for Steel Structures" GB 50017).
Note: Bending members (such as crossbars) require superposition of bending stress, calculated according to σ=M/W ≤ [f] (M is the bending moment, W is the section resistance moment).
2、 Stability calculation
For the compressed steel support (such as vertical pole and slant support), the overall stability shall be considered, and the formula is:
N/(φ·A)≤[f]
φ is the stability coefficient, which is related to the slenderness ratio λ (λ=L0/i, L0 is the calculated length, i is the section turning radius) and the type of steel. It is obtained through a standard lookup table (for example, when the λ of the hinged pole at both ends is large, the value of φ decreases and the bearing capacity decreases);
The calculation length L0 needs to be adjusted according to the support constraint conditions (such as when the two ends of the crossbar are rigidly connected to the upright, L0 is taken as 0.5~0.7 times the actual length).
3、 Node connection strength calculation
Verify the bearing capacity of connectors (bolts, fasteners, pins) to prevent nodes from being damaged before the members:
Bolt connection: Calculated based on the number of shear planes, N ≤ n · [Fv] (where n is the number of shear planes and [Fv] is the design value of the shear bearing capacity of a single bolt);
Fastener connection: According to the "Safety Technical Specification for Steel Pipe Scaffolding with Fasteners in Construction" JGJ 130, the design value of the anti sliding bearing capacity of right angle fasteners is 8kN, and that of rotary fasteners is 8kN;
Pin shaft connection: Verify the shear and hole wall pressure on the pin shaft, with τ=N/(A τ) ≤ [τ] (where τ is the shear stress and [τ] is the allowable shear stress of the pin shaft).
4、 Deformation verification
To control the deflection of steel supports under load and avoid affecting structural stability, the formula is:
v≤[v]
V is the deflection (mm), and the bending member is calculated according to v=5qL ⁴/(384EI) (q is the uniformly distributed load, E is the elastic modulus of steel 206GPa, and I is the moment of inertia of the section);
The allowable deflection [v] is usually taken as L/250 (L is the length of the component), and the precision support is taken as L/300.
When calculating, it is necessary to combine specific engineering specifications (such as scaffolding reference JGJ 130, foundation pit support reference JGJ 120), and prioritize using software modeling (such as PKPM, MIDAS) to assist in analysis to ensure the accuracy of the results.
