In 1986, the LRFD Code was proposed by AISC to replace the ASD Code. However, the LRFD Code seems to have a big problem on the so-call FACTOR. Actually, the original definitions are from ASCE 7, but both of ASCE 7 and AISC have become the relative organizations. In Taiwan, every engineer knows the building weight is about 1.0tf/m^2/floor, and the live load in the Technical Rulers for Architectures is 300kgf/m^2/floor. Therefore, according to the calculations of LRFD Code, the factor of safety shall be 1.292 for the common design case.
In mechanical engineering, the minimum factor of safety is 1.5, and this value means that you don't consider any extra analysis, fatigue analysis, for example. In the AISC ANSI 360-10/2012 manual, the fundamental assumption for the dead load and live load is 1:3, so that the factor of safety is 1.5 which is the same as the mechanical design. If the dead load is larger, the factor of safety shall be lower. However, compared with the live load, every building is very heavy. Hence, the factor of safety is lower than what engineers think, and it has become a unreasonable value.
In Taiwan, most engineers take the ASD Code to design the steel structures, and the LRFD Code is just taken by the younger engineers. Besides, the ASD Code is always is always chosen by the designers of steel bridges. Before the FACTOR problem is solved, I think the ASD Code is the better choice for steel designers. Actually, I have studied more than 40 structural reliability books, and I think this problem seems to be a big assumption fault.
Reference
In mechanical engineering, the minimum factor of safety is 1.5, and this value means that you don't consider any extra analysis, fatigue analysis, for example. In the AISC ANSI 360-10/2012 manual, the fundamental assumption for the dead load and live load is 1:3, so that the factor of safety is 1.5 which is the same as the mechanical design. If the dead load is larger, the factor of safety shall be lower. However, compared with the live load, every building is very heavy. Hence, the factor of safety is lower than what engineers think, and it has become a unreasonable value.
In Taiwan, most engineers take the ASD Code to design the steel structures, and the LRFD Code is just taken by the younger engineers. Besides, the ASD Code is always is always chosen by the designers of steel bridges. Before the FACTOR problem is solved, I think the ASD Code is the better choice for steel designers. Actually, I have studied more than 40 structural reliability books, and I think this problem seems to be a big assumption fault.
Reference
- AISC（2012）AISC ANSI 360-10, American Institute of Steel Construction
- 內政部營建署（2011）建築技術規則，內政部營建署。
