Formwork Adhesion (Ha) refers to the resistance encountered between the concrete unit and the mould during the lifting process. This force must be accurately calculated to ensure safe and efficient lifting of precast concrete elements.
Formula Explaination:
Ha: Total formwork adhesion in kilonewtons (kN)
q: Formwork adhesion factor, varying based on the type of mould material:
1 kN/m² for oiled steel moulds
2 kN/m² for varnished timber moulds
3 kN/m² for rough timber moulds
A: Area of contact between the mould and the concrete (m²)
Special Cases:
For certain precast elements, the formwork adhesion can be greater due to the structural complexity. In such cases, an estimated value is derived by multiplying the weight (G) of the precast element by a specific factor:
Ha = 2 × G (for double-T slabs)
Ha = 3 × G (for ribbed elements)
Ha = 4 × G (for coffered elements)
Parameters in Detail:
Contact Area (A): Directly influences the total adhesion force. Larger areas result in higher adhesion forces.
Material Type (q): Different mould materials exhibit different levels of adhesion due to surface texture and treatment.
Thickness (g): Often considered in weight calculations of slabs for accurate load estimations.
Real-Life Applications:
Construction Industry: Ensures safe lifting of large concrete slabs, beams, and precast elements.
Engineering Analysis: Helps in assessing structural stability and lifting equipment capacity.
Project Management: Facilitates accurate estimation of lifting forces, optimizing crane and lifting device usage.
Importance and Safety Considerations:
Preventing accidents by ensuring lifting equipment is not overloaded.
Improving efficiency by minimizing unexpected adhesion forces.
Guiding selection of mould materials for ease of demoulding.
Conclusion:
Accurately calculating formwork adhesion is critical in construction and engineering projects to ensure safety and efficiency. It allows for proper lifting equipment selection, prevents structural damage, and helps in adhering to safety regulations. Understanding how different materials affect adhesion can significantly impact the project timeline and cost.