Determination of characteristic compressive strengths in existing structures - Assessment based on a small number of samples

摘要

Construction in existing buildings has gained increasing significance in the construction industry in recent years. When the structural framework of existing buildings is modified, or if extreme conditions come to bear, such cases must always be assessed on the basis of current building regulations. New computer-aided analysis must accordingly be carried out, for which reliable basic data are essential. The characteristic properties of the construction materials currently being used in the building play a key role here. Assessment of in-situ compressive concrete strength in structures is regulated in DIN EN 13791:2008, in which a distinction is made between direct and indirect procedures. Determination of characteristic in-situ compressive strength based on the results of direct investigation methods - i.e., investigations of the concrete core. This extent will be limited for reasons of economy and for prevention of damage to the building. Two methods are available: method A (more than 14 test values) and method B (3 to 14 test values). As an alternative to evaluation according to DIN EN 13791:2008, DIN EN 1990:2010 offers a statistical procedure: the so-called Bayesian method for determining the characteristic properties of a the property of a construction material. Both normal distribution (ND) and logarithmic normal distribution (LND) can be applied here.