Reliability assessment of wind load combinations based on Iranian National Building Code

Abstract

The new generation of design codes is established by reliability-based calibration methods. The overall aims of these methods are to achieve consistent levels of safety or structural reliability under different type of uncertainties. According to these methods, the acceptable reliability level of structures is obtained based on statistical descriptions of loads and resistance and also consideration of different types of uncertainties such as the physical uncertainty, the statistical uncertainty and the model uncertainty. In the last decades, based on reliability-based calibration approaches, load and resistance factor design (LRFD) method has been developed for steel buildings design. In this method desired level of safety is obtained by a set of partial load and resistance factor. The design load combinations for steel structures in Iranian National Building Code (INBC), Part 6, are generally based on other codes such as ASCE/SEI 7-10 standard and National Building Code of Canada (for wind load factors), while the effect of Iranian statistical data for load and resistance has not been considered. In comparison to other loads, such as gravity loads, wind load has a high degree of uncertainty and also it is completely site dependent. Therefore it is important to estimate a suitable statistical model for wind load and also investigate the reliability level of structures subjected to wind load combinations. This paper is a parametric study to assessment the reliability level of wind load combinations for steel beams based on INBC. For this purpose, wind load statistical data are provided for whole of Iran by the climatology data of wind speeds. Based on the FOSM method explicit formulation for reliability index of beams is calculated. The reliability indices for a range of practical load ratios are obtained and compared to the target reliability index. The results indicated that reliability level of wind load combinations in INBC is lower than target reliability index. One of the main reasons for the low level of reliability index for wind load combinations is related to underestimation of reference speed. The results show that by considering the reference speeds based on statistical data, reliability index approaches to target reliability index.

Keywords

• reliability analysis
• iranian national building code
• load combinations
• wind load
• statistical parameters