Formwork is a mold used to shape concrete until it sets, supported by vertical and horizontal members to carry the weight of fresh concrete. Ensuring safety during the installation, pouring, and removal of formwork is critical because the formwork must withstand significant loads without failure.
Formwork for Columns
One common application of formwork is for columns, where precise shaping and secure support are essential to maintain structural integrity (see Fig 1 for reference). In this article, we will focus on the essential safety measures that must be followed during shuttering works to prevent accidents and ensure quality construction.
Safety Measures for Formwork Installation
Design Considerations
The first step to safe formwork installation is proper design. The formwork must be designed taking into account the span lengths, dead load, the setting temperature of concrete, working loads it will support, and safety factors related to the materials used. Neglecting any of these factors can lead to structural failure or accidents.
Inspection and Material Quality
Before installation, all materials, especially timber and tubular steel components, must be thoroughly inspected.
- Timber formwork should be carefully examined, and any members showing cracks or excessive knots must be discarded to avoid weaknesses.
- Tubular steel centering should be checked for dents, kinks, damaged welds, or signs of wear. Any defective parts must be removed immediately.
- Buckled or broken shuttering members need to be replaced to maintain overall stability.
Structural Stability and Bracing
To prevent collapse during the concrete pour:
- Vertical supports must be well braced or firmly secured so they do not fail if the load shifts or if supports are accidentally struck.
- When combining timber centering and tubular steel, precautions should be taken to prevent unequal settlements.
- After assembling the shuttering skeleton, adjustment screws should be set to their final level and plumb to ensure accurate alignment.
- Frames must be tied together with braces and diagonal supports to form rigid struts capable of carrying the full load.
- Connections should be made with bolts and nuts, avoiding rusted or damaged fasteners that could compromise integrity.
Engineering and Ground Conditions
Proper engineering oversight is crucial:
- The centering layout must be designed and approved by a qualified engineer.
- The soil bearing capacity must be assessed to ensure it can support the formwork and concrete loads.
- Weather conditions must be considered, especially since soil like dry clay can become unstable after rain.
- Props must be set on firm sills on the soil to ensure stability.
- Soil under supports must not be disturbed.
- Adequate drainage should be provided to prevent water buildup from washing, rain, or curing processes, which could weaken soil supporting the formwork.
Inspection Checklist for Centering
Before pouring concrete, a thorough inspection is necessary:
- Verify that footings or sills under all centering posts are sound.
- Ensure all adjustment screws or wedges are tight against the legs of the panels.
- Check that panels are plumb in both horizontal and vertical directions.
- Confirm that all cross braces and locking devices are correctly placed and secure.
- For projections such as chajjas or balconies, ensure props are adequate to transfer the load safely.
Monitoring During Concrete Pouring
The formwork must be continuously monitored throughout concrete pouring:
- Regular inspections should be conducted to identify any signs of failure or movement.
- Tighten wedges or adjust screws as needed to maintain stability.
- Protect the formwork from accidental impact by vehicles or swinging loads on site.
Formwork Removal (Destripping) Safety
Removing formwork requires caution to prevent accidents and damage:
- Destripping should only occur once the concrete has reached sufficient strength, as specified in relevant codes and by the site engineer.
- Only authorized workers should be allowed in the area during removal operations.
- Workers must wear proper personal protective equipment, including helmets, gloves, heavy-soled shoes, and safety belts if working above 2 meters without secure footing.
- When cutting tying wires under tension, care must be taken to prevent backlash that could injure workers.
- Follow the dismantling order prescribed by the site engineer to maintain balance and safety during the removal process.
By adhering to these safety measures, construction teams can ensure the structural integrity of formwork, protect workers, and maintain the quality of the concrete structure. Safety is not just a regulation but a fundamental responsibility on every construction site.