| Applies To | |||
| Product(s): | AutoPIPE, | ||
| Version(s): | ALL | ||
| Area: | Load | ||
| Original Author: | Bentley Technical Support Group |
Problem:
Given ASCE 7-10 ultimate wind speed (say 115 mph instead of the 90 mph which was typical for most of the continental US, OC I & II bldgs) but is this being factored / derated by:
1.0 (for LRFD - “Load Resistance Factored Design”)
or
0.6 (for ASD - “Allowable Stress Design”).
Does AutoPipe give us Service Loads (for consistency between 7-02 and 7-10) or does it give us the Strength (Ultimate) Level Loads ?
Solution:
Short answer, use the higher speeds when using ASCE 7-10, e.g. ultimate wind.
The wind results (pipe forces and support reactions) are based on the methodology provided by ASCE 7 Standard.
From ASCE 7-10 wind loads:
Basic wind speed at 33ft (10m)
ASCE 7-10 defines this as the nominal design 3-second gust wind speed at 33 ft (10 m) above ground for Exposure C category. This depends on the geographical location. ASCE 7-10 provides maps for wind speeds in the USA. The basic wind speed varies from 85 miles/hr in the US West Coast states (California, Oregon and Washington) to 170 miles/hr in Guam. The wind speed can be determined from Figure 26.5 provided in the ASCE 7 code .
Note: 1 mph =1.60934 km/hr and 85 mph = 136.8 km/hr = 38.0 m/s
Most of the ASME Piping codes design are based on ASD. For example, ASME B31.3 states that occasional loads should not be factored and limits the resulting stress to 1.33 times the allowable at temperature (Allowable Stress Design). Where as DNV Offshore provides load effect factors and usage factors to be used in Load and Resistance Factored Design (LRFD) calculations.
Again, AutoPIPE does not derate wind velocities other than that mentioned in code calculation and settings on the Wind dialog. Users would need to input wind speeds (derated or not) according to their specific use case or piping code.
For further details on this subject please see the following AutoPIPE help section:
Help > Contents> Contents Tab> Reference Information> Analysis Considerations> Wind Analysis> ASCE-7-10 Wind Loading Calculations