Loading...

Reliability-based Evaluation and Calibration of Load Combinations for the Design of Steel Building Structures of Iran

Mahmoudkalayeh, Soheil | 2018

800 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50767 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Mahsuli, Mojtaba; Ghasemi, Hooman
  7. Abstract:
  8. The objective of this thesis is to evaluate and calibrate design load combinations of steel building structures of Iran based on the reliability theory. The importance of this research stems from recognition that the design load combinations for steel structures in Section 6 of the National Building Code of Iran have been completely adopted from the ASCE/SEI 7-10 standard, whereas the factors that affect these load combinations differ in Iran from those of the United States. Examples are the difference in the construction industry economy, lower quality of here and the differences in probability distributions for the specifications of steel. Hence, the load combinations need to be calibrated based on the domestic information. In this study, the probability distribution of load and resistance parameters are obtained using such information. For this purpose, the probability distribution of the material parameters are calibrated to the data of laboratory experiments. Also, the probability distribution of the geometrical properties of steel profiles are determined through a survey on the fabrication tolerances. Thereafter, seven building archetypes based on the conventional construction in the country are designed in accordance with Sections 6 and 10 of the Iranian National Building Code and Iranian Seismic Standard 2800. Then, 2811 structural members from these seven building archetypes, including beams, columns, and braces were analyzed according to aforementioned load combinations using the first-order reliability method, random field theory, and system reliability in order to determine the safety level of existing structures. The results show that the safety level of existing structures under one of the gravity load combinations and one of the lateral load combinations comprising the earthquake load is not sufficient. Hence, it is necessary to revise the load and resistance factors of these load combinations. For instance, the reliability index for beams in bending in these two load combinations, were 2.9 and 1.46 respectively, which is notably lower than the corresponding target indices of 3.0 and 1.75 from ASCE/SEI 7-10 standard. In the next step, these load combinations are calibrated to achieve the target reliability index by modifying the load and resistance factors. The calibration results show that the resistance factor for bending must be lowered to 0.85 from the original value of 0.9 and, the earthquake load factor in the above-mentioned lateral load combination must be increased to 1.25 from the original value of 1.0. The need for these notable changes shows that the safety level of structures designed in accordance with the current code is lower than the target safety levels in the ASCE/SEI 7-10 standard. This study is a first step towards Indigenization of the National Building Code of Iran
  9. Keywords:
  10. Steel Structures ; Reliability ; Uncertainty ; Limit State ; Load Factor ; Probabilistic Methods ; Code Calibration ; Load and Resistance Factors Design (LRFD)

 Digital Object List

 Bookmark

No TOC