In steel structure design, especially for large-span light industrial buildings (pre-engineered steel buildings), wind loads are often the governing factor determining the size of structural elements and foundation solutions. The promulgation of TCVN 2737:2023 “Loads and Effects,” replacing the 1995 version, created a positive engineering "shock," forcing consulting and construction firms like Hai Long to reshape their calculation procedures to ensure safety in the face of increasingly extreme weather events.
1. The nature of Wind Load in TCVN 2737:2023
The most fundamental change in TCVN 2737:2023 is the method for determining wind pressure. The old standard (1995) used the average wind speed over 3 seconds (3-second gust), but this was converted and interpreted in many different ways, leading to inconsistencies. The new 2023 standard has harmonized with international standards such as ASCE 7 (USA) and Eurocode 1.
TCVN 2737:2023 provides a clear definition of the load recurrence interval. For wind loads used for strength testing (ULS), the recurrence interval can be 430 years or 700 years, corresponding to a low probability of overloading over the lifespan of the structure. This leads to the application of a wind load reliability factor of 2.1 (to convert from a 10-year or 20-year recurrence interval to an ultimate interval), instead of the previous factor of 1.2. This change significantly increases the overturning moment and uplift force at the column base, requiring larger anchor bolts and foundations—a challenge that Hai Long has addressed through optimizing the design of high-strength pile foundations and bolts.
2. Comparison with ASCE 7 and Eurocode 1
- ASCE 7-16: TCVN 2737:2023 is heavily influenced by ASCE 7 in its approach to 3-second wind speeds and pressure coefficients. However, Vietnam's wind map has its own unique characteristics due to its location within a tropical storm zone; therefore, values in coastal areas (such as Quang Ninh and Hai Phong – areas where the Hai Long storm is most active) are often higher than in equivalent areas in the US.
- Eurocode 1 (EN 1991-1-4): Use the 10-minute mean wind speed. For comparison or design conversion, conversion factors must be used. Eurocode is also very detailed in defining terrain and turbulence factors, suitable for structures with complex aerodynamic shapes.
3. Earthquake Loads and Environmental Impacts
Besides wind, TCVN 2737:2023 also refers to TCVN 9386:2012 (accepting Eurocode 8) for seismic design. For industrial plants containing heavy equipment or high-rise racking systems, earthquake loads can become a hazardous factor due to the large mass involved in vibrations.
4. Practical Applications
The application of TCVN 2737:2023 requires steel structure construction units to update their design procedures:
- Software: Use ASCE 7-based automatic wind calculation modules (with Vietnamese parameter adjustments) in software such as Robot Structural Analysis or Tekla Structural Designer to accurately simulate wind pressure distribution, especially at roof edges and wall corners (where the local pressure coefficient is very large).
- Enclosure Design: Roofing and wall cladding sheets must be tested for their ability to withstand higher local suction forces, leading to an increased density of fastening screws or the use of specialized storm clips.
- Frame Optimization: With increasing wind loads, high-strength steel (Q355) frame solutions and tapered sections become more effective in controlling lateral displacement (drift) without significantly increasing structural weight.
TCVN 2737:2023 is a necessary step forward in ensuring the safety of structures in the face of climate change. Although it presents challenges regarding increased design loads, with its solid engineering capabilities, Hai Long Construction transforms this challenge into an opportunity to provide sustainable, safe, and cost-effective structural solutions for its clients, especially FDI investors concerned with the long-term safety of their assets.
