AASHTO GSWLB-1 pdf free download

AASHTO GSWLB-1 pdf free download.GUIDE SPECIFICATIONS FOR WIND LOADS ON BRIDGES DURING CONSTRUCTION.
4.1—EXPOSURE CONDITIONS
4.1.1—General
Wind pressure shall be assumed to be uniformly distributed on the area exposed to the wind. The exposed area shall be the area of the structure components, as seen in elevation taken perpendicular to the wind direction. The wind load shall be the product of the wind pressure and exposed area. The wind shall be assumed horizontal and can come from any horizontal direction. Areas that do not contribute to the extreme force effect under consideration may be neglected in the analysis.
Structures shall be checked at different stages of construction. At each stage, the wind load shall be determined taking into consideration the components erected up to that stage.
For typical bridges, wind loads on the substructure from the superstructure may be determined for the wind in the direction transverse to the bridge in elevation, then adjusted for various angles of attack using the provisions of Article 4.2.3.1.
4.1.2—Wind Speed
The design 3-second gust wind speed, V, used in the determination of construction design wind loads shall be determined as follows:
• For active work zones: 20 mph unless a higher wind speed is specified by the owner.
• For inactive work zones: wind speed shall be taken from Figure 4.1.2-1 and may be modified using the wind speed reduction factor during construction as specified in Article 4.2.1.
• For areas designated as a special wind region in Figure 4.1.2-1: the owner shall approve the 3-second gust wind speed.
The wind speed shall be increased where records, experience, or site-specific wind studies indicate that wind speeds higher than those in Figure 4.1.2-1 are possible at the bridge location, based upon 7 percent probability of exceedance in 50 years.
C4.1.1
For most bridges, the same wind pressure will be used for all components of the structure and the wind load is applied as a uniformly distributed load on the entire exposed area of the structure. However, some situations may warrant using different wind pressures on different components. The most common cases are for long bridges that pass over ground of varying elevations, or when the substructure is unusually tall, which may warrant using different structure heights in determining the wind pressure on different portions of the superstructure or substructure.
At any stage, both the area of the components erected up to this stage and other factors affecting the wind load, such as the number of girders erected, should be considered in determining the wind load.
C4. 1.2
The 20 mph wind speed specified for active work zones assume that erection of the structure will not proceed if the wind speed exceeds this value. Higher wind speeds may affect the ability of the contractor to lift bridge components and make the connections to previously erected components safely.
Figure 4.1.2-1 is taken from the ASCE 7-10 (2010) and is also used by the AASHTO LRFD Bridge Design Specifications.
For buildings and other structures, local building officials typically determine the 3-second gust wind speed to be used in the special wind regions under thcirjurisdiction. Bridge owners will need to develop their own policy for the 3-second gust wind speed to be used in these regions.AASHTO GSWLB-1  pdf download.