403A Formwork 2 — Questions and Answers
Question 1: What is the main structural concern when designing formwork for a concrete slab?
- Wind load on the form edges
- Supporting the dead load of wet concrete and live loads during construction (Correct answer)
- Preventing the concrete from drying too quickly
- Matching the thermal expansion of the reinforcing steel
Correct answer: Supporting the dead load of wet concrete and live loads during construction
Slab formwork must support the substantial dead load of wet concrete (approximately 24 kN/m³) plus construction live loads including workers, equipment, and material storage. Shoring and reshoring must be engineered accordingly.
Question 2: What are walers (wales) in wall formwork systems?
- Vertical supports that hold form panels together
- Horizontal members that stiffen the form panels and distribute the pressure from ties (Correct answer)
- Diagonal braces that prevent the forms from tipping
- Bottom plates that anchor the forms to the footing
Correct answer: Horizontal members that stiffen the form panels and distribute the pressure from ties
Walers are horizontal members (typically doubled 2×4s or steel channels) attached to the outside face of form panels. They stiffen the forms, distribute lateral concrete pressure, and provide attachment points for form ties and bracing.
Question 3: What is the purpose of chamfer strips in formwork?
- To create a bevelled edge on exposed concrete corners (Correct answer)
- To seal joints between form panels
- To hold reinforcing steel in position
- To create drip edges on overhead concrete
Correct answer: To create a bevelled edge on exposed concrete corners
Chamfer strips are triangular pieces of wood or plastic placed in the inside corners of formwork. They create a bevelled (angled) edge on the finished concrete, preventing sharp 90-degree corners that are prone to chipping and damage.
Question 4: In cold weather concreting in Canada, what is the minimum concrete temperature at placement recommended by CSA A23.1?
- 5°C
- 10°C (Correct answer)
- 15°C
- 20°C
Correct answer: 10°C
CSA A23.1 recommends a minimum concrete temperature of 10°C at the time of placement during cold weather conditions. Insulated forms, heated enclosures, or concrete blankets may be needed to maintain adequate curing temperatures.
Question 5: What is the purpose of reshoring (backshoring) in multi-storey concrete construction?
- To add temporary walls for wind bracing
- To re-support previously stripped floors that haven't reached full design strength (Correct answer)
- To add vibration dampening during construction
- To protect curing concrete from rain
Correct answer: To re-support previously stripped floors that haven't reached full design strength
Reshoring involves reinstalling temporary vertical supports under concrete floors that have been stripped of their original formwork but haven't yet achieved full design strength. This distributes construction loads from upper floors to lower levels.
Question 6: What material is most commonly used for residential foundation formwork in Canada?
- Steel panel systems
- Plywood and dimensional lumber (Correct answer)
- Aluminium forms
- Fibreglass forms
Correct answer: Plywood and dimensional lumber
Plywood (typically 19 mm or 3/4 inch form-grade) combined with dimensional lumber for studs, walers, and bracing is the most common formwork system for residential foundations in Canada due to its low cost and availability.
403A Formwork 2
What is the main structural concern when designing formwork for a concrete slab?