Latest comparison of design standards for steel structures
Along with the growing industry, it is compulsory for constructions to meet the quality standards to ensure their safety and longevity. For a project, each category will have different evaluation standards. In the article below, BMB Steel will show you an overview of the latest comparisons of design standards for steel structure.
Vietnamese standards for steel structures TCVN 5575:2012 originated from Russia. For Vietnamese standards, all construction procedures must be applied with the method and the SF (safety factor) including:
Accordingly, Vietnam standards for steel structures focus on the stiffness and steel structures must not be deformed excessively.
In terms of calculated intensity, for TCVN, the calculated intensity is calculated by the formula: Standard intensity/ Material safety factor.
In terms of the assumed load, it is calculated with the formula: Standard load * load certainty factor.
According to Vietnam steel design standards, no. 2737:1995 is used as the assumed load for steel structures. The speed of wind load is measured in 3 seconds, in a 20-year period.
The wind pressure coefficient in Vietnam is calculated by wind pressure, not by speed. It is determined by the results of pressure measurement in the wind tunnel model, so it can be applied to cubic objects.
Apart from the design standard in Vietnam, the American steel structure design standard is a method widely applied by contractors. American standard features apply 2 calculation methods:
The relationship of Ft, Fy, Fb: When in tension, the value of allowable stress Ft = 0.6Fy (Fy: yield strength of steel). In compression = Fy x longitudinal flex coefficient. The limit value of bending structure (Fb) value from 0.6-0.67Fy.
Internal force values: M,N,Q caused by standard load, no overload factor. However, the formula for determining internal force has a combination of loads.
Section: The assumed area for US standards is divided into 3 parts: solid section, thin section, and non-solid section. Calculating a solid cross-sectional area will certainly use up the allowable efficiency of the material. For the calculation of the non-solid cross-sectional area, the allowable stress of the material should be reduced. Similar to the thin section, it must be further reduced.
European steel structures standards are calculated with limit standards (bearing capacity and usage limit). The limit stress is calculated using multiple factors to multiply by the yield strength.
Section: Divided into several grades based on thinness (width/thickness). Thicker level 1,2 is charged with higher stress. Level 3.4 is thinner so it is easy to lose the local stability. It is similar to the Vietnamese Standard & American Standard according to LRFD. Thus, the section is divided into 4 types: solid section, non-solid section, plastic section, and thin section.
Load: based on BS 6399, need to consider floor load, wind load and snow load.
Notes of the wind load:
Allowable displacement: calculated as the maximum value due to the used load (live load) regardless of the overload factor. Greater deformation is allowed according to TCVN. For example: ceiling support beam L/360 (according to TCVN L/400); auxiliary beam L/200 (TCVN L/240); and only take the calculated live load, do not take the whole as TCVN.
Safety factor: According to BS 6399, each different load uses a different safety factor: For example: The factor of safety (HSAT) of the dead load is 1.4 (TCVN is 1.2); active load is 1.6 (TCVN is 1.2 or 1.3); wind load is 1.4 (TCVN is 1.2). In addition, the safety factor for the material is taken as 1 since it has been adjusted during the calculation of the material strength. According to TCVN, the safety factor of materials is 1.05 to 1.1 depending on the type of steel. Besides, BS does not have safety factors on building function, working coefficient of structure, while TCVN does.
If the HSATs of BS's are compared with that of TCVN, VN's HSAT is smaller than that of BS. Thus, with the same steel material and bearing the same nominal load, the structure calculated according to TCVN requires less material.
The design load of each country has a certain standard. Here are design load standards in some typical countries:
The design load is determined based on the structure's external factors such as the construction site’s influences, the impacts from the weather, etc. Although each country has its own standards, it is recommended to apply the most fundamental principles to ensure the safety for the construction as well as anticipate errors and dangers to occur.
Current evaluation standards of the steel structure design depend on the steel structure design standards of each country. From them, we are able to use which criteria to apply for evaluation.
In general, in order to evaluate whether a steel structure design is guaranteed or not, it is essential to evaluate the ability, the safety standards, and the load capacity of the structure before and during the design process of steel structures
In terms of using steel structure design standards, the owner should consider these followings:
In the article above, BMB Steel has shared with you the comparisons of the latest steel structure design standards. Hopefully with this information, the owners and contractors can choose the suitable standards for their projects.