How to calculate the bearing capacity of steel formwork for rental manufacturers of construction steel formwork?

1、 Load combination calculation
Basic load type
Permanent load: self weight of formwork (theoretical weight of Q235 steel formwork 6mm thick 47.1kg/m ² 11), self weight of newly poured concrete (24kN/m ³ 10)
Variable load: Construction load ≥ 2.5kPa, vibration load 4kPa, wind load 0.5kN/m2 (included when span>20m)
Working condition combination formula
Bearing capacity calculation: 1.2 x permanent load+1.4 x variable load
Stiffness verification: only consider the standard value of permanent load
Example: When pouring the floor slab, the total load design value is 1.2 × (0.5+24h)+1.4 × (2.5+4) (h is the thickness of the concrete)
2、 Material strength calculation
Selection of cross-sectional parameters
Template thickness: 6-8mm for conventional engineering, increased to 10-12mm for large-span engineering
Section modulus: I-beam main rib W=401.4cm ³ (taking 16 # I-beam as an example)
Strength verification formula
Bending strength: σ=M/W ≤ f
(M=QL ²/8, Q is uniformly distributed load, L is span, f=210MPa corresponds to Q235 steel)
Shear strength: τ=VS/(Ib) ≤ fv
(V is the shear force, S is the static moment, I is the moment of inertia, and b is the thickness of the web plate)
3、 Supporting system verification
Calculation formula for checking project control standards
The slenderness ratio of the pole stability is λ ≤ 150 N/(φ A) ≤ f (where φ is the stability coefficient)
Fastener anti slip single fastener ≥ 8kN, double fastener ≥ 12kN R ≤ Rc (R is horizontal force, Rc is anti slip force)
Foundation bearing capacity ≥ 150kPa P=N/A ≤ fg (A is the area of the cushion plate)
4、 Deformation control requirements
Stiffness index
Template deflection ≤ L/400, support system settlement ≤ 3mm/10m
Example: For a beam template with a span of 4m, the maximum allowable deflection is 4000/400=10mm
Pre compression test
Load 120% of the design load for 24 hours, with a deformation of ≤ 3mm/m
Real time monitoring using displacement sensors, immediate warning for exceeding 2mm limit value
5、 Adjustment of safety factor
Type of working condition, partial coefficient, dynamic coefficient
Bearing capacity verification 1.2 1.4
Stiffness verification 1.0-
Pre stressing tension 1.05-
6、 Typical calculation results
Taking Q235 steel formwork with a span of 4m and a thickness of 6mm as an example:
Uniformly distributed load design value q=28kN/m (including safety factor)
Section modulus W=401.4cm ³
Maximum bending moment M=28 × 4 ²/8=56kN · m
Bending stress σ=56 × 10 ⁶/(401.4 × 10 ³)=139.5MPa ＜ 210MPa (satisfied)
acceptance criteria
Standard basis for allowable deviation of testing items
Bearing capacity compliance rate ≥ 95% GB50204-2025
Connection node strength torque compliance rate 100% JGJ162-2024
Stability of support system, verticality of upright pole ≤ 2 ‰ JGJ74-2025