Eurocodes and the structural safety of existing buildings - Considering the publication of the Dutch NEN 8700

Since 1992 there have been a number of proposals to renew calculation methods available to assess the structural safety of existing buildings. But without operational results. Upon publication of the Eurocodes NL decided to renew and to include them in the Dutch building regulations. The question was how. One decided to develop a new Dutch national standard: NEN 8700. That shows how, in conjunction with the 58 Eurocodes, an expert opinion can assessed on the structural safety of an existing building. The Building Decree 2003 will refer to this standard for load actions that have to be taken into account, the response of the structure and the required strength of structure, and will reference to the Eurocodes. The set up of the new standard is explained. A building is classified as an existing building after it has been completed. So the standard applies to all building stock, but the owner primarily must ensure that during the design working lifespan the legally required performance remains satisfied accept accidents. The safety assessment of an existing building differs from that of a new one in ways that are elaborated: - cost in relation to safety; - safety in relation to the reference period; - availability of actual status data versus design data. Unlike the regulations that apply to new buildings the new standard includes: - probability theory; - harmonisation of the Eurocodes with safety of existing building constructions on a arbitrary moment; - acknowledgement of durable safety requirements other than a 1 year period; - exclusion of requirements pertaining to the uncertainties that may arise during the theoretical designlife; - amendment of determination methods for the properties of the structural materials used; and - the ability to review at any time the actual constructed situation. The new standard also establishes the lowest limits of safety levels in the renovation, alteration or enlargement of an existing building. Reliability and load factors are summarized extracted from the underlying TNO report.