CROSS Safety Report
GRP panels as permanent shuttering
This report is over 2 years old
A reporter highlights problems that were encountered when Glassfibre Reinforced Plastic (GRP) panels were used as permanent formwork on a highway construction project.
Key Learning Outcomes
For the construction team:
Quality assurance and competent supervision along with a well documented inspection regime on site can help to ensure that the structure is built in accordance with the design
Consider introducing a quality control procedure for the inspection of safety critical elements being delivered to ensure they meet the required standards
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Glassfibre Reinforced Plastic (GRP) panels were used, on a highway construction project, for the permanent formwork during the construction of numerous bridge decks. A reporter says that problems were found which included:
The panels were porous. This led to the leaking of fines during a concrete pour and potentially spillage onto the live traffic beneath.
The geometry and makeup of the panels was inconsistent
The assumptions used in the calculations for structural strength did not match the product that was supplied
The panels contained metal sections which had not adhered to the GRP material although this was a requirement of the design
It was found that the supplier used secondary suppliers over which there was poor quality control. The manufacturing process needed to be challenged by the contractor and client on numerous occasions, and as a consequence the production method was radically altered until the final result was of sufficient quality.
GRP panels are widely used to support bridge decks during concrete pours and remain in place thereafter. The performance of the panels must correspond with the design assumptions and quality control in the delivery yard and constant vigilance on site during pours is required.
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Permanent shutters are important structural elements particularly when a slab is cast over an inaccessible area and the consequences of failure would be severe. Shutters should certainly not be porous, and tolerance can be an issue. When panels have a small bearing area a shorter panel may dislodge and fall out during reinforcement fixing and concrete placing.
Risk might be reduced by fixing the panels to the supporting beams. The design of the beams as well as the panels themselves needs to include adequate allowance for the variation in fabrication of panels. GRP panels (and panels made from other materials) can deflect during a pour leading to increased concrete depths and loads resulting in larger than anticipated permanent deflections. There are generic issues here about ensuring adequate control of the requirements for procurement, approvals and inspection.