Changes in determining wind load according to QCVN 02-2009/BXD compared to TCVN 2737-1995

Posted date 04/03/2016

2.767 view

Posted date 04/03/2016

2.767 view

Changing natural conditions will directly impact construction works. In order for construction works to exist and serve our lives, as construction engineers, we need to calculate so that the works are capable of withstanding those impacts.

MSc. Nguyen Dinh Khoa

As society develops, construction works are constantly developing. In addition, natural factors also change due to human impact on the surrounding environment.
In the past, in Vietnam, the weather in the North was divided into four distinct seasons, while in the South, there was a rainy season and a dry season. Due to climate change, the weather today no longer follows that rule. There have been heat waves in the fall, or strong storms in the winter.
Changing natural conditions will directly impact construction works. In order for construction works to exist and serve our lives, as construction engineers, we need to calculate so that the works are capable of withstanding those impacts.
Since 1995, TCVN 2737-1995 standard has been born to support designers in determining loads and impacts on structures. In 2009, to supplement changes due to the environment, Construction Standard QCVN 02-2009/BXD was born. However, up to now, QCVN 02-2009/BXD has not been widely used because most of our engineers are still familiar with TCVN 2737-1995 standard or because they have not updated new information and regulations. This invisibly makes the designed structures not suitable for natural conditions and not in accordance with legal regulations.
This article only mentions the changes in determining wind load according to QCVN 02-2009/BXD compared to TCVN 2737-1995 .
1. Construction life
Previously, there were not many solid constructions in our country, with a lifespan of about 50 years. Section 6.17 of TCVN 2737-1995 reflected the construction reality in Vietnam when considering the maximum lifespan of a construction is 50 years. Currently, many high-rise buildings have been built, with a lifespan of over 100 years. Table 4.3 and Table 4.4 of QCVN 02-2009/BXD have supplemented the missing part of TCVN 2737-1995 when considering the lifespan of a construction up to 100 years. This is also consistent with the situation of climate change.
2. Wind load reliability factor
- According to section 6.3 of TCVN 2737-1995, the wind load reliability coefficient is taken as γ=1.2. In addition, in table 12 on wind load adjustment coefficient, it is stipulated that:

Assumed useful life (years)	5	10	20	30	40	50
Wind load adjustment factor (η)	0.61	0.72	0.83	0.91	0.96	1.00

Thus, the calculated value of wind load is obtained with γ and η (η: wind load adjustment coefficient), with the data in Table 12 we can only determine the wind load for buildings with a lifespan of 50 years. Currently, there are many buildings with a lifespan of over 100 years, with complex climate changes, research is needed to determine the wind load for buildings with a lifespan of over 100 years.
- QCVN 02-2009/BXD does not specify the reliability factor of wind load, only mentions the wind pressure conversion factor. Table 4.3 specifies the wind pressure conversion factor from the 20-year return period to other return periods.

Repeat cycle (years)	5	10	20	30	40	50	100
Cycle conversion factor	0.74	0.87	1.00	1.10	1.16	1.20	1.37

- If we equate the recurrence interval with the assumed usage time of the two tables above, we will see that γ*η corresponds to the Conversion Factor of table 4.3 QCVN 02-2009/BXD. Then we can determine the wind load for structures with a lifespan of over 100 years.
- In the calculation according to TCVN 2737-1995, the reliability coefficient γ=1.2 and the calculated load of the wind load is multiplied by the wind load adjustment coefficient η. Thus, to have consistency between TCVN 2737-1995 and QCVN 02-2009/BXD, we take the reliability coefficient as γ=1.2 and the wind load adjustment coefficient is determined by taking the Cycle Conversion Coefficient divided by γ. Then we get the result as in the following table:

Assumed Life Time or Recurrence Period (years)	5	10	20	30	40	50	100
Cycle conversion factor	0.74	0.87	1.00	1.10	1.16	1.20	1.37
Reliability coefficient (γ)	1.20	1.20	1.20	1.20	1.20	1.20	1.20
Wind load adjustment factor (η)	0.61	0.72	0.83	0.91	0.96	1.00	1.14

We can completely use the above table in combination with TCVN 2737-1995 to determine the wind load acting on the structure.
3. Wind pressure zoning
Since 1995, the administrative zoning of our country has changed a lot, and climate change has also affected the wind pressure zoning. The wind pressure zoning is determined according to table 4.1 of QCVN 02-2009/BXD, which has updated those changes. For example, in table E1 TCVN 2737-1995, the name of Hai Hung province is still there, while in table 4.1 QCVN 02-2009/BXD, it has been changed to Hai Duong and Hung Yen provinces. Therefore, in the calculation, we should use table 4.1 of QCVN 02-2009/BXD instead of table E1 of TCVN 2737-1995.

References

1 – TCVN 2737-1995 Loads and impacts – Design standards;

2 - QCVN 02-2009/BXD National technical regulation on natural condition data used in construction.

Changes in determining wind load according to QCVN 02-2009/BXD compared to TCVN 2737-1995

Register for admission consultation 2025