Building formwork, also known as shuttering, is a critical temporary structure in construction projects, particularly in Kenya where rapid urban development demands efficient and safe practices. For Quantity Surveyors, understanding the construction and dismantling of formwork is essential for accurate cost estimation, resource planning, and contract management. This chapter focuses on the structural elements of building formwork, highlighting their roles, types, and considerations that influence both design and dismantling phases within the Kenyan construction context.

2.1 Structural elements

Formwork structural elements provide the necessary support and shape to concrete until it gains sufficient strength. These elements must be carefully selected, assembled, and dismantled to ensure safety, cost-effectiveness, and quality of the finished structure. Quantity Surveyors need to comprehend these components to prepare precise bills of quantities and anticipate potential risks and delays in the project schedule.

2.1.1 Types of Structural Elements in Formwork

The structural elements of formwork are categorized based on their function and position within the system. Each type contributes uniquely to the stability and shape of the concrete element being cast.

Primary Structural Elements

Primary elements directly support the weight of the fresh concrete and live loads during construction. These include:

• Form Panels: These are the surfaces against which concrete is poured, typically made of plywood, steel, or plastic. Their quality affects the finish of concrete and influences reusability.
• Beams and Girders: Horizontal members that support form panels, transferring loads to the supporting framework.
• Posts and Props: Vertical supports that carry loads from beams to the ground, adjustable to accommodate different floor heights.
• Strongbacks: Vertical stiffeners fixed to form panels to prevent bulging under concrete pressure.
• Walings: Horizontal members that tie the form panels and strongbacks together, distributing loads evenly.

Secondary Structural Elements

Secondary elements assist in maintaining the integrity of the formwork but do not carry primary loads. These include:

• Bracing: Diagonal supports that stabilize the entire formwork structure against lateral forces such as wind or accidental impacts.
• Ties and Anchors: Devices that hold opposing form panels together, resisting the lateral pressure from fresh concrete.
• Sheathing: The surface layer that directly contacts the concrete; it can be made from timber, steel, or plastic-coated materials for ease of stripping.

Material Considerations

Formwork elements vary in material selection, impacting durability, cost, and handling:

• Timber: Common in Kenyan sites due to availability and ease of modification but less durable and prone to warping.
• Steel: Offers strength and reusability, suitable for repetitive casting in commercial projects.
• Plastic and Composite Materials: Increasingly used for specialized formwork systems where smooth finishes and rapid dismantling are required.

2.1.2 Functions and Load-Bearing Roles of Structural Elements

Each structural element in formwork plays a specific role in safely supporting and shaping the concrete until it cures. Understanding these roles helps Quantity Surveyors anticipate resource allocation and project timelines.

Load Transmission

• Form Panels hold the concrete in shape, resisting the direct pressure exerted by the wet mix.
• Beams and Girders transfer loads from form panels to vertical supports, ensuring stability.
• Posts and Props carry the cumulative load down to the foundation or ground, preventing collapse.

Stability and Safety

• Bracing prevents lateral movement, which could cause formwork failure and safety hazards on site.
• Ties and Anchors maintain the correct spacing between panels, avoiding bulging or misalignment.
• Strongbacks and Walings reinforce form panels against deformation, ensuring dimensional accuracy of the concrete element.

Adaptability and Adjustability

• Adjustable Props allow fine-tuning of formwork heights, accommodating variations in floor levels or design changes during construction.
• Modular Components facilitate quick assembly and dismantling, essential for tight project schedules common in Kenyan urban developments.

2.1.3 Selection Criteria for Structural Elements in Kenyan Construction Projects

Choosing appropriate structural elements for formwork depends on several factors related to project requirements, site conditions, and economic considerations.

Project Scale and Complexity

• Large commercial projects in Nairobi often require steel or engineered modular formwork systems for speed and reusability.
• Smaller residential buildings may rely on timber formwork due to lower initial costs and local availability.

Concrete Specifications

• The type of concrete mix and pour height influence the strength requirements of formwork elements to resist pressure.
• High-strength concrete or rapid-setting mixes necessitate stronger, more rigid formwork materials.

Site Environment and Accessibility

• Sites with limited access or uneven terrain, such as some county government projects in rural areas, may require lightweight and easily transportable elements.
• Weather conditions, including heavy rains during Kenya’s long rains season, demand moisture-resistant materials to prevent degradation.

Cost and Availability

• Timber remains the most economical and readily available material in many Kenyan regions.
• However, the total cost of formwork includes not only material purchase but also labor for assembly, dismantling, and potential wastage.

Durability and Reusability

• Projects aiming for sustainability and cost reduction over multiple pours benefit from steel or plastic formwork that can be reused multiple times.
• Timber formwork, while cheaper upfront, may incur higher replacement costs due to wear and damage.

2.1.4 Implications of Structural Elements on Quantity Surveying Tasks

The choice and management of formwork structural elements significantly impact the Quantity Surveyor’s scope of work, including cost estimation, procurement, and project control.

Accurate Bill of Quantities Preparation

• Understanding the specifications and quantities of form panels, props, ties, and bracing helps in preparing detailed bills, reducing the risk of underestimation.
• For example, a SACCO building project in Kisumu required detailed measurement of adjustable props to ensure budget accuracy.

Cost Control and Value Engineering

• Knowledge of material lifespans and reusability informs decisions on whether to invest in steel or timber formwork.
• Quantity Surveyors can advise clients on long-term savings versus immediate costs, balancing project budgets effectively.

Scheduling and Resource Planning

• The assembly and dismantling time of various structural elements affect the critical path in project schedules.
• For instance, hospital expansion projects in Mombasa utilized modular steel formwork to expedite construction within tight timelines.

Risk Management and Compliance

• Proper specification of formwork components ensures compliance with safety standards, reducing the risk of accidents and associated liabilities.
• Quantity Surveyors play a role in verifying that contractors include adequate provisions for formwork safety in their tenders.

Chapter Summary

This chapter explored the key structural elements involved in building temporary works, emphasizing their role in supporting concrete during construction. Various types of formworks were discussed, highlighting their specific applications and suitability for different construction tasks. The chapter examined the materials used in formwork, focusing on their properties and advantages to ensure durability and safety. Accurate formwork measurements and dimensions were presented as critical factors for achieving the desired shape and stability of concrete structures. Timber properties were analyzed in detail, considering strength, workability, and resistance to environmental factors. The processes of formwork construction and installation were described step-by-step to ensure efficient and secure assembly. Finally, the chapter covered the proper techniques for dismantling formwork to prevent damage to the concrete and allow for safe reuse of materials.