What's New in ASCE 7-10 
by Joe Ebinger

 

ASCE (American Society of Civil Engineers) is the governing body that determines the minimum design loads for buildings and other structures in the United States.  The latest version of the ASCE Standard is ASCE 7-10. This article will discuss the changes in ASCE 7-10 from the previous design standards in ASCE 7-05 for wind and snow design.

ASCE 7-10 wind maps are based on “Ultimate Strength” wind speeds, as opposed to “Allowable Stress” wind speeds used in ASCE 7-05. In the old Allowable Stress Design (ASD) methodology, allowable and actual “Stress” was analyzed, while in the newer Load and Resistance Factor Design (LRFD) methodology, required and actual “Strength” is analyzed.  The main propose of switching over to the (LRFD) design methodology is that it provides a more consistent and uniform Safety Factor under various loading conditions.

Design factors that were hidden in the calculations and applied to a universal wind speed (per geographic location) with (ASD) are now visible as varied wind speeds with the design factors incorporated into the wind speed.  Wind speeds in the ASCE 7-10 wind speed maps are significantly higher than in ASCE 7-05, but because the new wind load factor is 1.0 instead of 1.6, the resulting design pressures and uplifts are comparable and typically slightly lower.

Occupancy Category (Importance) factor in ASCE 7-05 has been replaced by Risk Category in ASCE 7-10. The difference is under ASCE 7-10 wind speed maps are provided for each Risk Category (I, II, III & IV) as opposed to a single map with the Importance factor being incorporated in the velocity pressure design equation. There is a useful website [http://www.atcouncil.org/windspeed/] by The Applied Technology Council that incorporates an interactive Google Map that outputs site specific wind requirements using GPS locations. It also allows the calculated wind design information to be printed or saved as an Adobe Reader “.pdf” file. The website is open to the public and free to use. (Note: Always check with Local Building Department prior to design.)

An “Exposure D” category was added to the Exposure Category definitions in ASCE 7-10. Exposure D applies to sites within 600ft. of the coastline or 20 times the building height, whichever is greater.

In ASCE 7-10 there is a new exception for required unbalanced snow loads for hip and gable roofs. For hip and gable roofs with a slope exceeding 7/12 (30.2 deg.) or a slope less than 0.5/12 (2.38 deg.) unbalanced snow loads are not required to be applied. There is a new thermal factor (Ct) in ASCE 7-10 for “Structures intentionally kept below freezing”: {Ct  = 1.3}.

International Building Code (IBC/IRC 2012) and Florida Building Code (FBC 2010) incorporate the ASCE 7-10 standard. FBC 2010 will go into effect on March 15, 2012, and IBC/IRC 2012 will be adopted throughout the United States as determined by the individual state building departments.

- Employee Spotlight - Joe Ebinger
 
I was born in upstate New York, but have lived most of my life in the Tampa, FL area. I graduated from Mercer University in Macon, GA with a Bachelor of Science in Engineering, with a specialization in Mechanical Engineering. I have been working at Robbins/MiTek for 9 years, and started my first day with the company after coming home from my honeymoon in Vancouver, Canada just the previous day. I have a 1 yr. old daughter who everyday shows me what boundless energy and joy looks like, and a wonderful wife that supports me in everything I do. Outside of work, I am on a constant journey in search of life’s greatest truths. The further down the rabbit hole I go, the more I realize life’s eternal perfection, and I am humbled.
 
One of Joe's many talents is writing Haikus.  See below.
He stands six foot four.

Engineering fills his days.

Crocs adorn his feet.

 
 
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