As the industry develops, construction projects increasingly have to meet quality requirements and comply with certain standards to ensure the safety and durability of the project. In particular, safety factors such as fire resistance and each individual part have separate evaluation standards. Let's learn about design standards with Hai Long Construction production procedure Latest 2024 right in the following article.
1. Steel design standards meet each country's standards
1.1. Vietnam steel design standards
Steel design standard TCVN 5575:2012 comes from Russia. For construction standards in Vietnam, every process needs to comply with design methods and methods, including the following safety factors:
- Load safety factor.
- Safety factor for materials provided for construction process.
- The safety factor is related to the working environment, ensuring labor safety.
Thus, steel design standards in Vietnam focus on stiffness and steel structure, ensuring that they do not deform excessively. As for the calculated strength, according to TCVN, it is calculated using the formula: Standard strength / Material safety factor. As for the calculated load, it will be calculated based on the formula: Standard load * load reliability coefficient.
According to Vietnamese steel structure standards, TCVN 2737:1995 is applied as the calculated load value for steel structures. Wind speed measurement of wind load is performed in about 3 seconds with a 20-year cycle, in which the wind coefficient in Vietnam is calculated according to wind pressure, not velocity. For cubic objects, the aerodynamic coefficient is determined based on the results of measuring the model pressure in the aerodynamic tube.
1.2. American steel design standard AISC 89/ASD
In addition to design standards in Vietnam, the steel structure design method according to American standards is an option used by many contractors today. American standards apply two main calculation methods:
- Method 1: According to allowable stress (ASD) and load factor: Accordingly, the limit stress must not exceed the allowable stress, calculated according to the yield stress formula * (0,6 to 0,67).
- Method 2: According to load factor (LRFD): Load is multiplied by a factor between 1,2 and 1,6; The bearing coefficient is multiplied by a value from 0,75 to 0,9; in which, the limiting stress is the yield limit.
The relationship between Ft, Fy, and Fb is as follows:
- When subjected to tensile force, the allowable stress value Ft = 0,6Fy (with Fy being the yield limit of the steel).
- When subjected to compression, the value is calculated by multiplying Fy with the longitudinal bending coefficient.
- For bending structures, the limit value is denoted Fb and ranges from 0,6 to 0,67Fy.
Internal force values, including M, N, Q, are derived from standard loads without overload factors. However, the formula for determining internal forces is combined with load combinations.
Sections according to American standards are divided into three types: solid sections, thin sections, and non-solid sections. Calculating solid cross-sectional area requires using the entire allowable performance of the material. Meanwhile, for the calculation of non-solid cross-sectional area, the allowable stress of the material needs to be reduced. Similarly, for thin cross-sections, it must also be further reduced.
This standard accepts local warping of the section and allows some parts of the section to be inactive, leading to a decrease in allowable stress. As a result, there are many regulations on the slenderness of beam webs/beam flanges and column webs/column flanges. For example, according to AISC standards, the ratio between the height and thickness of the beam web does not exceed 320, then no reinforcement ribs are required, while according to Vietnamese standards, this coefficient is 100.
1.3. European steel structure design standard Eurocode 3
Steel structure calculations according to European standards are performed based on limit standards, including load-bearing limits and usage limits. The ultimate stress is calculated by multiplying the yield stress by many factors.
Sections are classified into several levels based on slenderness, measured by the width/thickness ratio. Sections of levels 1 and 2, with greater thickness, are calculated with higher stresses. As for sections belonging to levels 3 and 4, they have higher slenderness and are prone to local instability. This viewpoint is similar to Vietnamese design standards and American standards calculated according to LRFD. Based on that, the cross-section is classified into four types: solid, non-solid, flexible and slender.
Loads are calculated in accordance with BS 6399, including determination of floor loads, wind loads and snow loads. In particular, wind load is the pressure from wind speed acting on the structure. When calculating, it should be noted that the aerodynamic coefficient of wind load must consider the negative pressure inside the building with many different values for the aerodynamic coefficient, it is necessary to choose the most dangerous aerodynamic coefficient value to perform. now calculate. For BS 6399, the regulation uses the average wind speed in one hour, with a period of 50 years, while the British standard CP3 also applies the wind speed measured in 3 seconds, with a period of 50 years.
The allowable displacement is calculated as the maximum value due to the service load (live load) without applying an excess load factor. This standard allows larger deformations than TCVN, for example, ceiling support beams L/360 (according to TCVN L/400); secondary beam L/200 (TCVN L/240). In particular, this standard only applies the calculated live load, not including the entire load like TCVN.
The safety factor in BS 6399 is adjusted depending on the different load types. For example, the safety factor (HSAT) for static load is 1,4 (compared to 1,2 in TCVN); for operating load is 1,6 (compared to 1,2 or 1,3 of TCVN); and for wind load is 1,4 (compared to 1,2 of TCVN). Meanwhile, the safety factor for materials in BS 6399 is 1, because it has been adjusted when calculating material strength. According to TCVN, the safety factor of materials ranges from 1,05 to 1,1 depending on the type of steel. Besides, BS does not have safety factors for the function of the building and the working factor of the structure, while TCVN applies and regulates them.
Comparing the total safety coefficients (HSAT) between BS and TCVN, we see that TCVN's HSAT is smaller than BS. Therefore, with the same type of steel material, when subjected to the same nominal load, the structure calculated according to TCVN will consume less material.
2. Design load standards for each country
Design loads for each country are subject to separate standards. Below are some examples of design load standards of some countries:
- Vietnam: TCVN 2737:1995
- USA: UBC 97; MBMA 2002; IBC 2006
- UK: BS 6399: Part 2: 1997 – Load for Building: Part 2 – Code of practice for wind loads; BS 6399: Part 1: 1984 – Design loading for buildings: Part 1 – Code of practice for dead and imposed loads.
- Europe: EN 1991-1-4:2005 A1
- Australia: AS/NZS 1170.1:2002, AS/NZS 1170.2:2011
Design loads depend on external influences on the building, including influences from the construction site and weather impacts. Although each country has its own standards, applying basic principles is still essential to ensure safety and avoid dangerous errors during construction.
3. Note when applying steel structure design standards
When applying design standards for steel structures, investors need to consider the following factors:
- Regarding finances: Carefully consider your budget to suit your abilities.
- Regarding the built environment: Consider whether the environment is sufficient to apply other standards or not.
- It is necessary to carefully study the characteristics of the site and the construction environment. Once chosen to build, synchronizing all elements is important to ensure consistency during the construction process.
- This standard should not be combined with other standards when building because the project will not achieve consistency and ensure safety.
4. Conclusion
Above is information about steel structure design standards and some important notes when applying them. If customers are looking for comprehensive solutions for pre-engineered steel buildings and steel structures, please contact Hai Long Construction via email. info@hailongjsc.vn or phone number 084 6625 888 for advice today.
