Formwork construction plays a pivotal role in the overall cost of concrete structures, often accounting for up to 60% of the total project expenses. As such, reducing the cost of formwork construction is critical for achieving overall project cost efficiency. This can be greatly influenced by decisions made during the design phase. By adopting innovative materials, accessories, and prefabricated formwork components, designers can meet project goals while minimizing expenses.
To support cost-effective formwork practices, the Concrete Reinforcing Steel Institute (CRSI) has outlined several recommendations. These strategies, ranging from design choices to material standardization, provide practical approaches to optimizing formwork construction.
Recommendations for Cost Reduction
1. Simplify the Framing Scheme
Using a single framing scheme throughout the project improves labor efficiency and reduces costs associated with mobilization and material handling. Workers become more proficient when the design remains consistent, minimizing errors and streamlining construction. While a second framing scheme might occasionally be justified for large-scale projects, the general rule is to maintain uniformity wherever possible.
2. Standardize Beam and Joist Design
Uniformity in the depth of beams and joists can lead to significant cost savings. Although this approach may increase the volume of steel and concrete used, the reduction in formwork expenses typically outweighs these additional costs. For heavily loaded beams, designers can adjust the width—making it four or five times the depth—without deviating from the standard depth.
Furthermore, using consistent beam outlines, regardless of differences in load or span, simplifies formwork preparation. Variations in reinforcement ratios can accommodate the required load, further optimizing costs without compromising structural integrity.
3. Optimize Column Design
Uniform column spacing is another key recommendation to achieve consistency across columns, joists, and beams. This not only simplifies formwork construction but also reduces costs.
Increasing form reuse is another cost-saving measure. Standardizing column sizes horizontally within a single storey and vertically across multiple levels allows for repeated use of the same forms. Adjustments to reinforcement and concrete strength can accommodate varying loads, ensuring that structural requirements are met without requiring custom forms.
4. Maintain Consistent Floor-to-Floor Heights
Consistency in floor-to-floor height reduces complexity in column forming. In cases where changes in height are necessary, it is preferable to make these adjustments in upper storeys. This approach simplifies column formwork adjustments, as cutting is easier and less expensive than extending column forms.
5. Use Drop Panels and Steel Shear Heads
Replacing tapered columns with small drop panels is a cost-effective alternative for flat plate systems. Steel shear heads can further simplify formwork by eliminating the need for capitals and drop panels, provided the slab thickness meets the minimum requirement of 200 cm. To reduce material waste, the height of drop panels should align with standard lumber dimensions.
6. Standardize Form Sizes
Employing standard form sizes for one-way joists and two-way domes minimizes the need for special fabrication. This reduces both material costs and production time, as standard forms are easier to source and handle during construction.
7. Maximize the Use of Minimum-Sized Members
Forming members such as slabs, walls, and columns with minimum thicknesses—consistent with fire ratings and structural requirements—can optimize material use. These members can serve multiple functions, such as supporting loads, resisting lateral forces, or acting as partitions or exterior walls. This multi-functionality reduces the need for additional components, further cutting costs.
8. Consider Flat Plate Systems
For spans up to 7.6 meters, flat plate systems are often the most economical choice. This forming system is not only cost-effective but also the shallowest and fastest to construct. Its simplicity and efficiency make it ideal for projects where reducing time and material usage is a priority.
9. Allow Reasonable Tolerances
Tight construction tolerances increase labor demands and associated costs. By permitting reasonable tolerances in areas where strict precision is unnecessary, projects can avoid excessive labor hours and associated expenses. However, in locations requiring high precision, such as connections or alignment-critical areas, stricter tolerances should still be enforced.
10. Establish Clear Form Removal Guidelines
Specifying when forms can be stripped is another crucial factor in optimizing costs. For walls and columns, time limits can be established, while strength requirements should guide form removal for beams and slabs. Additionally, reshoring should be considered to prevent excessive deflection until the design strength is achieved. This approach protects structural integrity while ensuring efficient use of resources.
Conclusion
Cost-effective formwork construction begins with thoughtful design decisions. By standardizing components, maintaining consistency, and optimizing material usage, designers can significantly reduce project expenses. Recommendations from the Concrete Reinforcing Steel Institute highlight practical strategies for achieving these goals, from employing a single framing scheme to utilizing flat plate systems. By adhering to these guidelines, project teams can streamline construction processes, improve labor efficiency, and ultimately achieve substantial cost savings.