Solution Summary: Pre-fabricated Slab Formwork System
Using a pre-fabricated slab formwork system is a prevention through design (PtD) process that addresses worker health and safety risks from collapse, fall from height, heavy manual material handling, and object struck-by exposures associated with constructing traditional formwork. A system generally contains individual pre-fabricated panel forms, or "tables", that inter-connect to form a larger deck formwork for a slab and beam concrete pour. Guardrail components may also be affixed to the system. Once the concrete is cured, these individual tables are generally lowered (stripped) and ready to be relocated and reconnected without dismantling and rebuilding formwork.
Tables can be composed from lightweight material, such as aluminum, for easy relocation. Although some tables are already pre-fabricated based on pre-defined dimensions of a project layout, some systems allow for on-site table customization of their dimensions. For the spaces between tables, infill work will be required such as using filler strips usually made from plywood.
Before concrete is poured into the formwork, the tables are temporarily supported by vertical elements called props or shores which may be made out of wood, aluminum, or steel. Shores help distribute the loads from the form to the ground or the slab below, which may also be the top surface of another floor (on a multi-leveled project).
Once the concrete slab is cured and has gained enough strength determined by a qualified engineer, the tables are stripped and lowered onto a trolley or a form transportation device to be relocated and reused. Because of its light weight, these tables may be maneuvered by two people. For a multi-leveled project, these tables can also be lifted by crane to an upper level and reconnected.
Table VR Pre-assembled Slab Formwork by ULMA Group
Ulma Group slab formwork with shoring. (Photo courtesy of ULMA Construction)
- Automatic locking mechanism for easy prop to Head VR connection
- Beams made from timber or steel and decked with plywood panels
- Formwork erection and handrails are done on ground (except for infill work at heights)
- Prop removal not required when stripping or relocating tables
- Easy infill work as the plywood may rest on beams projecting from tables
- Youtube video on product assembly: https://www.youtube.com/watch?v=TIsihtSOHtI
SKYDECK Panel Slab Formwork by PERI Group
Peri Group slab formwork laid upon beams with teeth. (Photo courtesy of PERI Formwork Systems, Inc.)
- Panels lock in place in the teeth of the beams for easy assembly and change of direction of panels
- All parts are made from aluminum
- Easy to clean due to powder-coated main beams
- Drop-heads on props allow for early striking and table relocation which reduces on-site material requirements
- Youtube on product assembly: https://www.youtube.com/watch?v=kfIAUBmGiy0
During the construction of traditional slab formwork or concrete pouring operations, workers can face the risk of falling off the unprotected sides of the work zone's leading edge. Falls from height typically result in severe injuries or death.
Workers in the nearby area of traditional formwork construction can also be at risk of falling objects such as tools or materials from a level (or levels) above. Being struck-by objects typically result in severe injuries or death. Cuts and punctures can also arise from manual material and tools handling (i.e. using nail guns, saws, etc.).
Lifting heavy materials during the installation of traditional timber formwork can cause injury to muscles, nerves, discs and ligaments of the low back. Repetitive lifting of multiple individual components from a traditional formwork system can lead to low back strain, ligament sprain, a bulging or herniated disc, or other back problems.
The premature removal of inadequate formwork or insufficient shoring (and reshoring on multi-leveled projects) can lead to the collapse of formwork. Workers affected by collapsing formwork typically result in severe injuires or death.
How Risks are Reduced:
In pre-fabricated slab formwork systems, guardrails may be attached to perimeter of the tables before it is placed. Because guardrails are attached and remain fixed from the beginning of the work to the end, the proactive design already establishes active fall safeguards before workers are exposed to the risk.
The reduction or elimination of labor required to construct formwork at heights (because of pre-fabrication and pre-assembly) can eliminate or reduce the need to work with tools and materials at heights thereby reducing the risk of struck-by injuries from falling objects. Associated with that, the risk of cuts and punctures from handling tools and material also decreases. Moreover, the reduction or elimination of carrying tools, coupled with the formwork systems being made from lightweight material, can generally reduce heavy lifting associated with building traditional formwork.
Provided that all manufacturer guidelines and recommendations are followed, the structural integrity of pre-fabricated slab formwork systems are usually safer than traditional formwork systems (generally constructed from timber) reducing the potential of collapse. Pre-fabricated slab formwork systems are pre-engineered and tested by manufacturers to account for all formwork requirements and provide a systematic process of installment reducing potential human error on constructing traditional formwork that may be inadequate or insufficient.
Effects on Productivity:
Using pre-fabricated slab formwork systems can increase productivity of a project. A case study was conducted to compare schedules of using traditional formwork and a modified table formwork system [pre-fabricated slab formwork system] on a high-rise project. The results revealed that "construction schedule was accelerated" when using the modified table formwork system (Kim et al, 2005). Further, using pre-fabricated systems reduce the need for measurement, cutting and assembling wood material on site thereby reducing operation time and the potential for errors and delays (Memarian and Mitropoulos, 2016).
The manufacturer Ulma Construction claims great efficiency using their product TABLE VR due to the requirement of less labor from erection, stripping and material relocation. This system also allows tables to be stripped and relocated without removing the props. The manufacturer Peri Group also claims efficiency using SKYDECK due to its "systematic assembling and only [using] a few slab props" where its "design with drophead allows for early striking and reduces on-site material requirements."
- Although pre-fabrication can reduce several risks, it is also worth to note that other new risks may be introduced. For example, installing pre-fabricated materials may require using cranes which can increase risk of swing struck-by injuries.
- It is important to follow the manufacturer's equipment and operation guidelines when using their products.
- Ensure that guardrails meet any additional structural or load bearing requirements before they are used. For more information, please visit guardrails in Construction Solutions.
- OSHA 1926.703(a) provides safety and health regulations for formwork in construction.
Le, Jean Christophe, MPH - CPWR - The Center for Construction for Research and Training
NIOSH Workplace Solutions
The National Institute of Safety and Health (NIOSH) has published a series of “Workplace Solutions”, which are easy-to-understand recommendations from NIOSH research results. Related to this Construction Solution, please find more information on: Supporting Prevention through Design (PtD) Using Business Value Concepts and Supporting Prevention through Design (PtD) Using Business Value Concepts