The Technical File | Groundforce

Groundforce Shorco | Technical File Issue 3.0 Download these files at: A) Principles of Temporary Works Design Design engineers will be familiar with both “Permissible Stress” and “Limit State” design concepts. At the time of writing, it remains current practice within the UK temporary works community, to continue to adopt permissible stress concepts for small scale temporary works. With the adoption of Eurocodes and the consequential eventual replacement of the traditional design methodology, loads or actions on support systems will be need to be calculated and presented in terms of limit state design values. Obviously, when designing around proprietary equipment these design loads will need to be equated to limit state resistance values for the equipment being considered. It is vitally important therefore in the transition period between permissible and limit state philosophy to fully understand the various design terms to ensure that load factors are applied correctly, thus ensuring that equipment is correctly specified to operate safely within its capacity. B) The Concept of Safety Evidence of safety was traditionally recognised by quoting values for load capacity (or resistance) for shoring equipment in terms of (safe) working load capacity. That is, the ultimate values for resistance parameters (calculated by recognised standards) are reduced by a lumped (safety) factor, typically between 1.5 and 2.0 to generate working values and subsequently quoting these in standard load charts. These charts are then used to equate with actual or unfactored working values of load for the member being designed. It is more difficult to specify the equivalent level of “safety” as such with a limit state approach as partial factors are applied to both the loads (or actions) and resistances as depicted on the diagram below. Technical Services i.ii Where: 1: Mean Load. 2: Characteristic Load. 3:: Limit State Design Load. 4: Limit State Design Resistance. 5: Characteristic Resistance. 6: Mean Strength. γ F : Partial Factor for Load. γ M : Partial Factor for Resistance. To gain an approximate comparison between allowable and limit state designs, the safety margin can be approximately recognised by the product of γ F multiplied by γ M.