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Falsework economy

A new industry guide on concrete flat slab formwork and falsework will result in safer, faster and more cost effective construction says Colin Cleverly.

The Guide for flat slab formwork and falsework is based on work undertaken as part of the world's most ambitious concrete research programme, the European Concrete Building Project at BRE Cardington. It examines the operations relating to formwork, falsework and in particular, backpropping, and emphasises how it is within the process, not with the hardware, that the opportunities for increased performance and cost savings exist.

Much of the advice given in the guide is aimed at identifying areas of the process where changes would bring benefits. With temporary works accounting for some 30% of the total cost of a concrete frame, the cost savings can be considerable.

The research carried out at Cardington was led by CONSTRUCT, the Concrete Structures Group, together with the Universities of Birmingham and Leeds and the Building Research Establishment. After identifying optimum formwork systems for concrete frame construction, the team undertook detailed comparative site studies during construction of a seven-storey insitu building - the first of four concrete frame buildings to be built as part of the European Concrete Building Project.

The generic types of proprietary formwork and falsework used included a prop and timber system for floors one and two, an aluminium flying table system for floors three and four and a skeletal steel system with aluminium beams on floors five and six. The roof used an aluminium frame system as falsework for two types of permanent precast concrete formwork.

Each system was monitored during use and the new guide incorporates the findings of the on-site research. An important finding of the Cardington research was that there are distinct advantages in considering wholesale temporary enclosures to the building under construction, although these can impose unnecessary limitations to the concept of temporary works.

A major finding of the research was that whatever the formwork system used, the greatest potential for increased safety and economies lies at the conceptual and design stage.

The safe and effective use of manpower is influenced by competence and supervision, and by the quality and adequacy of the designs prepared both for the temporary works and for the permanent structure.

Encouraging permanent works designers to make the kind of decisions that optimise the temporary works has direct safety, performance and economic advantages which in turn result in more efficient and cost effective construction. This is in full accordance with the objectives of the recent Egan report.

Although not intended to impose restrictions on permanent works designers, the guide highlights their responsibilities insofar as they affect the safety of constructors given the significant influence that temporary works have on the final structure and its buildability.

The constructor also has a significant role to play. A major recommendation is the promotion of the responsibilities taken by the constructor when managing the temporary works. The importance of the temporary works co- ordinator in managing assembly, construction, striking, backpropping and all the technical aspects of the temporary works cannot be overlooked. Ideally, this appointment should be made at a very early stage of the design process so as to be in a position to provide technical guidance to other members of the project team.

The guide emphasises the importance of the permanent works designer and the temporary works co-ordinator having a thorough understanding of the backpropping and striking requirements for flat slab construction. This is especially important since it is likely that recent slab buildings with low values of live to dead load have been stressed during construction to above their service load. To provide assistance the guide provides flowcharts and details of the range of options for safe control and loading of flat slabs during construction.

The guide follows the main chronological stages of the construction process: pre-contract; pre-construction planning; construction; striking the slabs and backpropping. For each stage the role and responsibilities of the client, permanent works designer and temporary works co-ordinator are outlined.

Although not intended to be used as a design manual, the guide will be complementary to the Concrete Society's Formwork - a guide to good practice and to the current BS5975 Code of Practice for Falsework.

Colin Cleverley is executive secretary of CONSTRUCT - the Concrete Structures Group.

For further information and copies of the Guide for flat slab formwork and falsework contact CONSTRUCT, tel: 01344 725744.

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