Limit State Design to Eurocode – methodology, design procedure and application
Spangsbjerg Kirkevej 103, 6700 Esbjerg, Denmark
The design of a structure must ensure that under the worst loadings the structure is safe, and during normal working conditions the deformation of the members does not detract from the appearance, durability or performance of the structure. Despite the difficulty in assessing the precise loading and variations in the strength of the concrete and steel, these requirements have to be met. Three basic methods using factors of safety have been developed; (1) The permissible stress method in which ultimate strengths of the materials are divided by a factor of safety; (2) The load factor method in which the working loads are multiplied by a factor of safety, and (3) The limit state method which multiplies the working loads by partial factors of safety and also divides the materials' ultimate strengths by further partial factors of safety. The Eurocode provides a unified approach to structural and geotechnical design, with partial factors allowing uncertainty to be accounted for at source that often resulting in serious inconsistencies. The Eurocode can be used in conjunction with numerical analysis procedures for a broad range of situations. Various design methods and operational techniques, which take these uncertainties into account, have been developed and used. At present, the most advanced operational method of structural design accepts the partial factor format usually applied in conjunction with the concept of limit states. The lack of available theoretical tools and knowledge is obvious in the case of gross errors, which are often the decisive causes of structural failures.