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IBC 2000 - Structural Design |
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Summary of IBC 2000 - Chapter 16 Structural Design
The International Building Code (IBC) is the model code for a number of states.
The ASCE Standard ASCE 7-98 "Minimum design Loads for Buildings and Other Structures" is the Standard that the IBC 2000 refers to in Chapter 16 "Structural Design" in which loads such as wind, snow, live, and seismic are defined.
In the new codes and standards a major change has been to made as to how wind load is determined as well as to how structural members are designed. Following is a list of some of the changes from the ASCE 7-93, which is similar to BOCA 96 and UBC 97 and to the ASCE 7-98 Standard, which the IBC 2000 is based.
| | ASCE 7-93 | ASCE 7-98 | | LOADS: | | | | Minimum Wind Speed | 70 mph | 85 mph | | Wind Type | fastest mile | 3 second gust | | Basic pressure q x G | 15.5 psf (70 mph) | 13.1 psf (85 mph) | | (Exposure C, 30' elev., Importance = 1.0) | | Wind Maps | - West Coast
- Interior
- East Coast
- Florida | 70-80+ mph
70-90 mph
80-110 mph
90-115 mph | 85+ mph
90 mph
100 to 135 mph
100- 150+ mph | | Cp for Enclosed Buildings, Walls and Gable Roof Buildings, with 20 degree roof slope (G = 0.85) | | Coefficients | - Windward Wall
- Windward roof
- Leeward roof
- Leeward Wall
- Internal pressure/suction | 0.80 pressure
0.75 suction
0.70 suction
0.50 suction
+/- 0.30 | 0.63 pressure
0.81 suction
0.57 suction
0.53 suction
+/- 0.21 | |
DESIGN: |
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| ASD | 1/3 stress increase | no stress increase allowed |
| LRFD | 1.3 x WL | 1.6 x WL | | | | | | | ** This summary of IBC 2000 should only be used as a guideline as most of the information is going to very depending on location of the project. LSA is in no way held responsible for the validity of this information and is not responsible for mistakes made based upon this summary. |
The Ground Snow Load map has been revised and local conditions must be satisfied. Once the Ground snow has been determined and the roof snow calculated, determination of snow load combinations are critical and include:
Drift, Slide, Unbalanced, Partial, Rain on Snow, Ponding.
Section 1608.3.5 Ponding instability - For roofs with a slope less than 1/4" per foot or 1.19 degrees the design calculation shall include verification of the prevention of ponding.
Please note that of critical importance to a lightweight structure is the deflection and the possibility of ponding. A non-linear analysis is typically required to determine ponding for a fabric structure. It is recommended that verification of ponding instability be performed for most if not all fabric structures and the designer is cautioned that the 1/4" per foot listed in Section 1608.3.5 is for typical rigid structures.
Although Seismic Loads are typically of a lesser concern for a lightweight structure than for a normal or heavyweight structure and that wind loads will typically govern design.... seismic forces must be resisted as per the codes.
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