Author(s)

M. Holický

Abstract

The collapse of a number of lightweight roofs during the winter period of 2005/2006 initiated an international discussion concerning the reliability of roofs exposed to permanent snow load. In some countries, all available measurements of snow loads have been newly evaluated and relevant standards have been promptly revised. Newly developed maps of snow loads are based on the principles of the European standards specifying the characteristic value of snow load on the ground as the 98 fractile of annual extremes (50 year return period). This paper provides a critical analysis of presently accepted design procedures taking into account available data of snow load. In the reliability analysis permanent load is described by normal distribution, snow load by Gumbel distribution and resistance by lognormal distribution. It appears that the partial factor design method provided in the present European standards may not guarantee an adequate reliability level of lightweight roofs. An alternative procedure for the safety design of roofs exposed to self weight and snow load only is therefore proposed. Keywords: lightweight roofs, snow load, safety, design. 1 Introduction The reliability of lightweight roofs has become an important topic of structural design, particularly after the winter period 2005/2006 when a number of roofs in Europe collapsed. In some countries, available measurements of snow loads have been newly evaluated and relevant standards have been promptly revised. Newly developed maps of snow loads take into account the principles of valid European standards [1–3] specifying the characteristic value of snow load on the ground as the 98 fractile of annual extremes. The design value of snow load is then determined using the partial factor 1,5.

Keywords

lightweight roofs, snow load, safety, design.