TCVN 2737:2023: Loads and Actions

The modern foundation for safe and efficient structural design in Vietnam.

TCVN 2737:2023 is Vietnam’s national standard specifying the values of loads and actions used in the design of construction projects. This standard replaces TCVN 2737:1995, marking a significant step towards harmonization with advanced international design standards, particularly the European Eurocodes system. The standard aims to ensure safety, sustainability, and economic optimization for civil, industrial, transportation, and technical infrastructure projects.

2023

Year Issued

Replaces 1995

Previous Version

Eurocodes

Approaching Standard

Highlights and New Updates

Explore the core changes that enhance design quality and safety.

Wind and Seismic Load Zoning Maps

Updated wind pressure and design ground acceleration zoning maps based on the latest observational data, detailed down to the district level, enhancing load determination accuracy.

Harmonization with Eurocodes

Adopts the design philosophy and methodology of Eurocodes, especially EN 1990 (Basis of structural design) and EN 1991 (Actions on structures), synchronizing with international practice.

Accidental Actions

Adds and details provisions for accidental actions such as impact, fire, explosion, and human actions, suitable for complex modern building types.

Load Combinations

Introduces new load combination factors, clearly distinguishing between ultimate limit state (STR) and serviceability limit state (SLS), optimizing the design.

Crane Loads

Provides more detailed and clearer guidance for determining dynamic loads from cranes, including horizontal braking forces and skewing forces, suitable for industrial building design.

Structural Reliability

Emphasizes the concept of reliability and Consequence Classes, allowing safety levels to be adjusted according to the importance and risk of the structure.

Comparison with International Standards (Eurocode 1)

TCVN 2737:2023 has made significant steps towards Eurocode, but specific differences remain. Interact with the chart to compare key aspects.

Overview Wind Loads Seismic Loads

Classification of Loads and Actions

Understanding how the standard classifies load types is key to applying it correctly in design.

Permanent Actions (G)

These are loads that exist throughout the structure’s service life and change little in value. They form the basis of all structural calculations.

• Self-weight of the structure: Concrete, steel, masonry, and other constituent materials.
• Weight of finishes: Plaster, floor coverings, suspended ceilings.
• Earth pressure, static water pressure: Acting on basement walls, foundations.
• Prestressing forces: In prestressed concrete structures.

Variable Actions (Q)

These are loads that can vary in magnitude and location during the structure’s use. They are divided into long-term and short-term.

• Imposed loads (Live loads): People, furniture, equipment on floors and roofs.
• Wind loads: Pressure and suction forces from wind on the building envelope.
• Snow loads: In regions with snow (less common in Vietnam).
• Crane loads: Dynamic and static loads from crane operations.
• Loads due to temperature changes: Causing material expansion and contraction.

Accidental Actions (A)

These are loads with high intensity but low probability of occurrence, which can cause severe consequences for the structure.

• Seismic actions (Earthquake loads): Inertia forces generated by ground motion.
• Fire actions: Reduction in material strength due to high temperatures.
• Explosion actions: Pressure from internal or external explosions.
• Impact loads: From vehicle collisions or other objects hitting the structure.

Application and Benefits

Master the application process and understand the benefits that TCVN 2737:2023 brings to Vietnam’s construction industry.

Application Process in Design

1. Classify Structure

2. Determine Loads

3. Combine Loads

4. Analyze Structure

Step 1: Determine the building class and structural type to select appropriate factors.

Step 2: Calculate all permanent, variable, and accidental actions that may affect the structure based on Annexes and zoning maps.

Step 3: Create the most unfavorable load combinations for the ultimate limit state (ULS) and serviceability limit state (SLS).

Step 4: Use the internal forces from the load combinations to design and verify the structural members.

Key Benefits

• ✓

  Enhanced Safety and Reliability

  With more accurate input data and modern calculation methods, the standard helps design structures with better resistance to adverse effects.

• ✓

  Techno-Economic Optimization

  More rational load classification and combinations help avoid material waste, leading to economical design solutions that still ensure safety.

• ✓

  International Integration

  Compatibility with Eurocodes facilitates Vietnamese engineers working on international projects and attracts foreign investment and technology.

Comprehensive Technical Analysis of TCVN 2737:2023 – Loads and Actions: Updates, International Comparison, and Practical Application

Part I: Foundational Principles and Scope of TCVN 2737:2023

1.1. Introduction: The Urgent Need for Modernization

TCVN 2737:2023, issued under Decision No. 1341/QD-BKHCN dated June 29, 2023, officially replaces TCVN 2737:1995, a standard that had served Vietnam’s construction industry for nearly three decades. Compiled by the Institute for Building Science and Technology (IBST), the new standard aims to address the limitations of its predecessor while responding to the country’s rapid economic development and deep international integration.

This replacement was an inevitable step. The 1995 standard, though foundational, had become obsolete. Key shortcomings included the lack of provisions for modern load types (e.g., heavy vehicle garages, helicopter pads, fire trucks), outdated wind load data and calculation methods, and inconsistent reliability factors. These inadequacies necessitated a comprehensive update to ensure structural safety and economic efficiency in the modern context.

The core philosophy of the new standard represents a major shift, moving from a traditional approach to a modern, science-based method harmonized with leading international code suites like Europe’s Eurocodes and the USA’s ASCE 7. This transition aims not only to enhance design accuracy and ensure safety but also to facilitate collaboration on international projects. Adopting a “common language” in structural design lowers technical barriers for international investment and cooperation. Therefore, revising the standard is not merely a technical update but also a tool of economic and industrial policy, intended to modernize the entire construction industry ecosystem—from university education and engineering practice to software application and international bidding—thereby enhancing the competitiveness of Vietnam’s engineering sector.

1.2. Scope of Application and Key Definitions

This standard specifies requirements for loads, actions, and their combinations used in the structural calculation of buildings and structures across various sectors, including civil, industrial, technical infrastructure, and transportation. The standard is applied in conjunction with TCVN 9379 (Basis of structural design and foundations) and references other specialized standards like TCVN 9386 for seismic actions.

The standard is based on the limit state design philosophy, classified into two main groups:

• Group 1 (Ultimate Limit States – ULS): Related to the failure or collapse of the structure (e.g., strength, stability).
• Group 2 (Serviceability Limit States – SLS): Related to normal use conditions and durability (e.g., deflection, vibration, cracking).

Understanding the terms defined in the standard is crucial for correct application:

• Characteristic (basic) value of a load: The principal representative value of a load specified in the standard.
• Design value of a load: The value used in calculations, determined by multiplying the characteristic value by the corresponding reliability factor.
• Load reliability factor (γ_f): Accounts for the possibility of unfavorable deviations of loads from their characteristic values under normal operating conditions.
• Building importance factor (γ_n): Adjusts the load level based on the consequences (social, economic, environmental) if the structure fails or is damaged.
• Load combination factor (ψ): Accounts for the reduced probability of the simultaneous occurrence of the maximum design values of several variable actions.

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Part II: In-depth Analysis of Load Provisions and Major Updates

2.1. Dead Loads and Live Loads

The principle of calculating dead loads from the self-weight of structural and non-structural components remains largely unchanged, but the standard emphasizes the importance of using accurate data for material densities.

For live loads, TCVN 2737:2023 introduces significant improvements and expansions to reflect the usage functions of modern buildings:

• Addition of New Load Cases: The standard addresses critical omissions of the 1995 version by including specific provisions for heavy vehicle garages, fire truck access routes, and helicopter landing pads.
• Distinction between Long-term and Short-term Loads: The new standard provides a clearer methodology for determining the long-term component of live loads, a crucial factor affecting time-dependent effects like creep and long-term deflection. This is a significant improvement over the combined values in the 1995 version’s tables.
• Live Load Reduction Factors: The standard introduces provisions for live load reduction, allowing for more economical design of compression members like columns and foundations in multi-story buildings, a common practice in international codes.

2.2. Wind Loads: A Comprehensive Methodological Shift

The most significant and revolutionary update in TCVN 2737:2023 is the complete overhaul of the wind load calculation method. The standard discards the old approach, which separated static and dynamic components based on a simple height threshold (H < 40 m). Instead, it adopts the Gust Effect Factor (G_f) method, a more sophisticated methodology conceptually similar to the American ASCE 7 standard. This method integrates both static and dynamic (resonant) wind effects into a single, more accurate procedure applicable even to low-rise buildings.

The characteristic value of wind pressure is now determined by the formula:

W_k = W_(3s,10) × k(z_e) × c × G_f

Where:

• W_(3s,10) – Basic Wind Pressure: This is the wind pressure corresponding to a 3-second gust wind speed with a 10-year return period. This is a key change from the 20-year return period in TCVN 2737:1995. The wind pressure zoning map has also been simplified to 5 main zones, eliminating sub-zones like I-A, II-A.
• k(z_e) – Exposure and Topography Factor: This factor is no longer a simple linear function of height. Its calculation is now more complex, depending on the building’s aspect ratio (H/B) and terrain category, with formulas referenced from ASCE 7-16.
• c – Aerodynamic Coefficient: This coefficient is determined based on the building’s geometric ratios (e.g., H/D) and is looked up from tables in Annex F, which were compiled based on EN 1991-1-4 and SP 20.13330.2016. This provides more detailed values for windward (pressure) and leeward/side (suction) surfaces.
• G_f – Gust Effect Factor: This is the core innovation. This factor accounts for the structure’s dynamic response to wind turbulence. For “rigid” structures (with a fundamental natural period T₁ ≤ 1 s), G_f can be taken as a constant (e.g., 0.85). However, for “flexible” structures (T₁ > 1 s), this factor must be calculated based on the structure’s dynamic characteristics and the wind turbulence intensity.

Reliability Factor γ_f = 2.1: A Crucial Safety Enhancement

The design wind load for the ultimate limit state (ULS) is determined by multiplying W_k by the reliability factor γ_f. For wind load, this factor is set at a seemingly high value of 2.1.

This factor is not an arbitrary safety margin. It performs a specific probabilistic function: converting the wind pressure from a service-level event (10-year return period) to a safety-level, ultimate event with a much lower probability of occurrence, corresponding to a return period of approximately 430 years. This resolves a major conceptual flaw in the old standard, which often confused building lifespan with wind return periods.

This approach reflects a sophisticated risk-based design philosophy. The old standard used a single basic wind pressure (20-year return period) with a modest reliability factor (1.2), conflating serviceability requirements (preventing excessive deflection under frequent winds) and ultimate strength requirements (preventing collapse during rare storms). The new standard clearly separates these two design objectives. It starts with a lower-level, more frequent wind event (W_(3s,10)) to calculate the characteristic load W_k. Studies show this results in a lower characteristic load value compared to the old standard, making it easier to satisfy serviceability limit state criteria like displacement. This is an economic optimization, avoiding over-design for everyday conditions. Then, the standard applies a very large reliability factor (γ_f = 2.1) to determine the design load for ULS. This factor mathematically transforms the load to represent a much rarer and more severe storm (approx. 430-year return period). Analyses confirm that the design wind load for ULS under the new standard is 1.5 to 2.3 times higher than under the old standard. This is a significant enhancement in safety. Thus, TCVN 2737:2023 implements an advanced design philosophy, enabling engineers to design structures that are both economically efficient under normal operating conditions and significantly more resilient against extreme weather events.

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Part III: Comparative Analysis with International Standards

3.1. TCVN 2737:2023 vs. TCVN 2737:1995: Summarizing the Evolution

To highlight the scale of the update, the direct comparison table below points out the main changes, providing a quick reference for practicing engineers transitioning to the new standard.

Table 1: Summary Comparison between TCVN 2737:2023 and TCVN 2737:1995

Item	TCVN 2737:1995	TCVN 2737:2023	Reason / Significance
Wind Calculation Method	Separated Static/Dynamic components	Gust Effect Factor (Gf) Method	Integrates static and dynamic effects, more accurate, aligns with international standards.
Basic Wind Return Period	20 years	10 years	Lower characteristic load, favorable for checking serviceability limit states (deflection, drift).
ULS Design Return Period	Implied ~50-100 years	Explicit ~430 years	Safety level is quantified and significantly enhanced.
Wind Reliability Factor (γf)	1.2 (for 50-year life)	2.1	No longer a general safety factor, but a probabilistic conversion factor from 10 years to ~430 years.
Trigger for Dynamic Analysis	When H > 40 m	All buildings (via Gf)	Correctly recognizes that even low-rise buildings have dynamic responses.
Special Live Loads	Limited scope	Expanded (garages, helipads, fire trucks)	Meets the practical needs of modern buildings.
International References	Mainly SNiP (Soviet)	Combination of ASCE 7 / EN 1991	Modernization and integration with global design practices.

3.2. Comparison with Eurocode 1 (EN 1991-1-4)

TCVN 2737:2023 heavily references EN 1991-1-4, especially for the detailed aerodynamic coefficients (c) in Annex F. Both standards follow a component-based approach to determine wind pressures.

However, there are fundamental differences in the methods for determining peak velocity pressure and dynamic response. Comparative studies suggest that, for the same site conditions, characteristic wind loads calculated according to Eurocode can differ significantly (often higher) from TCVN 2737:2023. Furthermore, the design return periods for ULS in Eurocode are often much longer (e.g., >4000 years for certain risk categories), indicating a different level of safety calibration.

An important note for engineers is that mechanically applying the ‘c’ coefficient tables from Eurocode is insufficient. TCVN 2737:2023 reportedly omitted some important notes and context (e.g., regarding slender structures with h/d > 5), which could lead to misapplication if the original EN 1991-1-4 is not consulted for complex cases.

3.3. Comparison with ASCE 7 (Minimum Design Loads for Buildings and Other Structures)

The clearest international parallel for TCVN 2737:2023 is with the ASCE 7 standard, particularly ASCE 7-16. The Gust Effect Factor (G_f) method, including the calculation formulas, is directly inherited from this standard. The importance factors (γ_n) also show similarities.

Regarding load combination philosophy, ASCE 7 uses the LRFD (Load and Resistance Factor Design) method with specific calibrated load factors for different combinations (e.g., 1.2D + 1.6W, 0.9D + 1.6W). Although TCVN 2737:2023 also uses a partial factor method, the combination factor values and the calibration basis may differ.

Despite the similar methodology, the safety calibration differs. ASCE 7-22 specifies ULS design wind loads for return periods of 700 years (ordinary buildings) and 1700 years (important buildings). These periods are significantly longer than the ~430-year return period of TCVN 2737:2023, indicating that ASCE 7 is calibrated for a higher safety level or different regional hazards.

Table 2: Comparison of Wind Load Design Philosophies (TCVN 2737:2023 vs. EN 1991 vs. ASCE 7)

Parameter	TCVN 2737:2023	EN 1991-1-4	ASCE 7-22
Core Methodology	Gust Effect Factor (Gf)	Peak Velocity Pressure	Gust Effect Factor (Gf)
Velocity Averaging Time	3-second gust	10-minute mean	3-second gust
SLS Return Period	10 years	Not directly applicable	Not directly applicable
ULS Return Period	~430 years	Variable, e.g., 700-3000 years	700-1700 years
Source of Aerodynamic Data	Combination EN/SP	EN 1991-1-4	Wind Tunnel Data
Handling Dynamic Response	Gust Effect Factor (Gf)	Dynamic Factor (cd cs)	Gust Effect Factor (Gf)
Design Moment (Example)	Intermediate	Lowest	Highest

The analysis shows that TCVN 2737:2023 is not a direct copy of any single international standard but a selectively “hybrid” product. It adopts the G_f method from ASCE 7, aerodynamic coefficients from EN 1991, and the use of importance factors from Russian standards. This pragmatic approach allows for rapid modernization by leveraging recognized international research. However, it also creates a potential risk. Standards like ASCE 7 and EN 1991 are internally consistent systems where all factors (γ_f, G_f, c, etc.) are calibrated to work together to achieve a target reliability level. By mixing components from different systems, there is a risk of “incompatibility” or unintended consequences, as noted by experts. Therefore, the “hybrid” nature of TCVN 2737:2023 is both its greatest strength (rapid modernization) and its greatest challenge. This places a higher demand on practicing engineers, requiring them not just to mechanically apply the standard’s text but also to understand the fundamental principles of the source standards (ASCE 7, EN 1991) to handle ambiguities and ensure safe designs.

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Part IV: Application and Practical Implementation for Engineers

4.1. Step-by-Step Wind Load Calculation Example

Below is an illustrative example of the steps to calculate wind loads for a typical high-rise building according to TCVN 2737:2023, based on data from a sample problem.

• Building: 17 stories, 70 m high.
• Location: Ho Chi Minh City (Zone II).
• Terrain: Category B.
• Plan Dimensions: 30 × 50 m.

Step 1: Determine Basic Parameters

• Height H = 70 m, Dimensions B × L = 30 × 50 m, Wind Zone II, Terrain Category B.

Step 2: Determine Basic Wind Pressure W_(3s,10)

• Look up the wind pressure zoning map in the standard for Zone II to get the W_(3s,10) value.

Step 3: Calculate the Factor k(z_e)

• Determine the equivalent height z_e at each floor level, depending on the H/B ratio.
• Apply the formula in the standard to calculate k(z_e) for each height z_e. Note that this distribution is no longer linear.

Step 4: Determine Aerodynamic Coefficient c

• Calculate the H/D ratio (e.g., in the X-direction, D=50 m, H/D = 70/50 = 1.4).
• Look up Annex F to find the coefficient c for the windward (pressure) and leeward (suction) faces.

Step 5: Calculate Gust Effect Factor G_f

• Assume the building’s fundamental natural period T₁ > 1 s (flexible structure).
• Calculate G_f based on the formula depending on turbulence intensity I(z_s) and the structure’s dynamic characteristics. If T₁ ≤ 1 s, G_f = 0.85 may be used.

Step 6: Synthesize Characteristic Wind Load W_k

• At each floor level, multiply the calculated factors: W_k = W_(3s,10) × k(z_e) × c × G_f.

Step 7: Calculate Design Wind Load W_tt

• Apply the reliability factor γ_f = 2.1 to obtain the design load for the ULS limit state. Example, in the X-direction: W_ttX = 2.1 × W_kX.

4.2. Integration with Structural Analysis Software (ETABS)

Implementing the new standard in software like ETABS requires a careful workflow:

• Define Wind Load Patterns: Define wind load patterns that accurately reflect the non-linear pressure profile according to the k(z_e) factor.
• Assign Loads: Apply the calculated load values to the structural model. Pay special attention to torsional effects, which are not detailed in TCVN 2737:2023 and may require reference to other standards to determine accidental eccentricity.
• Define Load Combinations: Set up load combinations for both ULS and SLS according to the new standard’s requirements.
• Support Tools: Specialized software and Excel spreadsheets have now been developed to automate this calculation process and integrate with ETABS, helping design offices transition more smoothly.

4.3. Impact on Design and Economic Effects

The application of TCVN 2737:2023 has direct impacts on design outcomes and construction costs:

• Structural Members: The significantly higher design wind load for ULS (1.5 to 2.3 times increase) will often require larger structural members (columns, beams) and a stiffer bracing system to meet strength and stability requirements.
• Foundations: Analyses of numerous building designs indicate that the increased overturning moment due to the new wind loads can lead to a substantial increase in foundation requirements, such as more piles or larger pile caps.
• Reinforcement: Larger moments and shear forces will demand higher reinforcement ratios in concrete members.
• Serviceability Limit State: Conversely, the lower characteristic load value W_k makes it easier to satisfy serviceability criteria like lateral drift, which was often a challenging constraint for steel structures under the old standard.

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Part V: Conclusion and Strategic Recommendations

5.1. Summary of Benefits and Improvements

TCVN 2737:2023 represents a major leap forward for the Vietnamese construction industry, bringing clear benefits:

• Enhanced Safety: Applying a probabilistic approach with a ULS return period of ~430 years for wind loads significantly increases the resilience of structures against extreme weather events, a crucial factor in the context of climate change.8
• Rational Economy: The two-level approach (SLS/ULS) allows for more economical designs, avoiding over-conservatism for everyday service conditions while still ensuring safety for rare events.
• International Harmonization: The standard helps modernize engineering practice in Vietnam, facilitating collaboration with international partners, adopting global technologies, and ensuring a consistent level of quality and safety.
• Improved Accuracy: The new methodologies, especially for wind loads, have a stronger scientific basis and more accurately describe how loads act on structures.

5.2. Recommendations for the Engineering Community

To maximize the benefits and mitigate risks when applying the new standard, the engineering community should take specific actions:

• Continuous Professional Development: Design firms and individual engineers need to invest in training programs to master not only the new provisions but also the theoretical background of the source standards (ASCE 7, EN 1991). This is not a standard that can be applied mechanically.
• Update Software and Tools: Design offices need to ensure that their software and in-house calculation tools are updated to accurately reflect the provisions of the new standard.2
• Need for Official Guidance: Due to its “hybrid” nature and potential ambiguities (e.g., missing notes, torsional effects), there is an urgent need for IBST and the Ministry of Construction to issue detailed explanatory documents and design guides (similar to ASCE 7’s “Commentary”) to ensure consistent interpretation and application throughout the industry.
• Future Revisions: The standard should be considered a living document. Future revisions should focus on resolving inconsistencies, integrating more local Vietnamese climate research and data, and continuing the path of harmonization with the next generation of international standards.