Question

Could someone give me an example of how to find net uplift wind pressure on a wall or gable roof?

Answer 1

Ans:-

Buildings and their components are to be designed to withstand the code-specified wind loads. Calculating wind loads is important in design of the wind force-resisting system, including structural members, components, and cladding, against shear, sliding, overturning, and uplift actions.

The design wind loads for buildings and other structures shall be determined according to one of the following procedures:

1. Method 1- Simplified procedure for low-rise simple diaphragm buildings with flat, gabled, and hipped roofs.
2. Method 2 – Analytical procedure for regular shaped building and structures.
3. Method 3 – Wind tunnel procedure for geometrically complex buildings and structures.

Method 1 – Simplified Procedure (Based on ASCE code of practice)

The simplified procedure is used for determining and applying wind pressures in the design of simple diaphragm buildings with flat, gabled, and hipped roofs and having a mean roof height not exceeding the least horizontal dimension or 60 feet (18.3 m), whichever is less, and subject to additional limitations.

The steps of the simplified procedure are as following:

1. Determined the basic wind speed, V, in accordance with ASCE 7 Figure 6-1, assuming the wind can come from any direction. ASCE 7 section 6.5.4 includes some provisions for the special wind regions indicated, near mountainous terrain, and near gorges.
2. Determine the importance factor (I) in accordance with ASCE 7 Table 6-1 & Table 1-1.
3. Determine the exposure category in accordance with ASCE 7 Section 6.5.6.
4. Determine the height and exposure adjustment coefficient (λ) from ASCE 7 Figure 6- 2.
5. Determine P_s30, the simplified wind pressure for exposure B, at h=30 ft, for I=1.0, from ASCE 7 Figure 6-2 .

Simplified design wind pressures (P_s) for the main wind force resisting systems of low rise simple diaphragm buildings is determined by the following equation:

P_s = λIP_s30

where,

P_s = the net pressure (sum of internal and external) to be applied to the horizontal and vertical projections of building surfaces. For the horizontal pressures, it is the combination of the windward and leeward net pressures.

Method 2 – Analytical Procedure

Wind loads for buildings and structures that do not satisfy the conditions for using the simplified procedure can be calculated using the analytical procedure provided that it is a regular shaped building or structure, and it does not have response characteristics making it subject to across-wind loading, vortex shedding, instability due to galloping or flutter, or does not have a site location that require special consideration. The steps of analytical procedure, described in ASCE 7 Section 6.5.3 only will be followed.