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Florida Building Code: 150% Overturning

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This topic came up a few weeks ago in relation to a requirement of the Florida Building Code in the High Velocity Hurricane Zone. I thought some of you might find this informal opinion published by the Florida Building Commission helpful.

Date: Thu Apr 24 2003

Report #: 2354

Code: Building

Section: 1620.2

Question:

Is it the intent of Section 1620.2 to apply 150 % of overturning wind load to the load combination of 0.6 D

+ W of Section 1609.4.1?

Answer:

No. For the High Velocity Hurricane Zones, Section 1611.1.7 states that any conflicts between this code

and ASCE 7 the more stringent requirement shall apply. Section 2.4 of ASCE 7 requires dead load to be

reduced 40% when resisting wind loads (Basic load combination 5. 0.6D + W), yielding overturning

stability of 167% of wind load. This load combination would apply to overturning, as well as uplift and

sliding. Therefore, the ASCE 7 load combination would take precedent and accomplishes the desired

excess overturning capacity.

Commentary:

The requirements in 1620 are similar to what was in the 1997 Standard Building Code and ASCE 7-95.

The 1997 SBC and ASCE 7-95 both limited the overturning moment due to wind load to 2/3 of the dead

load stabilizing moment, which results in overturning stability of 150% of the wind load overturning

moment. The ASCE 7 Wind Load Committee and the SBCCI Wind Load Committee relocated this

requirement to the load combinations section for clarity of applicability.

 

Christopher A. Banbury, PE
Vice President
Nicholson Engineering Associates, Inc.
PO Box 12230, Brooksville, FL 34603
7468 Horse Lake RD, Brooksville, FL 34601
(352) 799-0170 (o)         (352) 754-9167 (f)
www.nicholson-engineering.com