Expert Discusses Design Windloads for Doors and Windows

June 15th, 2012 by DWM Magazine

Design windloads was the topic of the first webinar hosted by the Northeast Window and Door Association (NWDA) yesterday. Joe Reed, director of engineering and product testing at Architectural Testing Inc., discussed the American Society of Civil Engineers (ASCE) 7-05 Minimum Design Loads for Buildings and Other Structures reference code within the ASCE 7 standard and how it is used to establish design windloads for doors and windows installed in buildings. The session also reviewed the ASCE 7-10 standard, a revised and reorganized version of the standard that Reed said likely will be implemented in new building codes.

“The ASCE 7 design standard and its methodologies for determining windloads are primarily pressures for building components and cladding [including] doors, windows, skylights, other cladding systems and curtainwalls,” Reed said.

According to Reed, the ASCE 7 is similar to building codes because of there are a number of versions currently being used.

“Depending on which building code a particular state has, that may reference a different reference code of ASCE 7,” Reed said. “It’s good to know a little about how the versions differ and which ones are relevant to the projects you are working on.”

ASCE 7 has been around for more than 30 years and is a successor to the American National Standards Institute (ANSI) 58.1. Reed said the standard is revised every three years or so.

ASCE 7-05 includes three techniques for establishing design windloads, Reed said. The simplified procedure is used for buildings less than or equal to 60 feet and includes pre-determined design windloads based off measurements. The wind tunnel procedure utilizes actual testing methods with models built to match the actual measurements of the building. But he focused on the analytical procedure, which is a mathematical option to configure the design windload.

“I think [the analytical procedure] is the most common because it’s not really that complicated and it gives you the most precise information,” Reed said.

The basic information required to determine the design win load includes the governing building code, the geographic location, terrain characteristicsand the building’s function and size. Additionally, Reed said the size and location of doors and windows must be noted because of varying pressures throughout the building.

“There are zones on the building where the pressure is different,” Reed said. “Those zones are based on the building’s geometry and are the effects of localized pressure points due to turbulence and other aerodynamic effects.”

Reed said there are seven steps to complete the analytical procedure: the design windspeed, building function, amount of exposure (urban or suburban, etc.), topographic factors, velocity pressure, varying pressure coefficients of the buildingand design wind pressures must be established.

Reed said the entirety of the building envelope has to meet the design requirements as dictated by the code and most product suppliers are aware of this.

“Once the pressures have been established for the building product suppliers make sure either the product manufacturer or the people choosing those products have to make sure they are adequate for the building,” he said. “Normally door and window manufacturers do this by testing in facilities. But you also have to recognize that just because the door or the window has passed the test and has been assigned a specific design pressure, you need to validate the glass itself meets the design pressure requirements and you have to verify the insulation meets the requirements.”

Additionally, Reed discussed the revised ASCE 7-05 code (ASCE 7-10), which he says was developed about one year ago and has made its way into some building codes such as the 2012 International Building Code of Maryland. Among the revisions, he says the new code includes a “revamped wind pressure section to follow methodology of earthquake loads.”

“Overall, we are really just changing the sequence of calculating pressures,” he said.

Written by Erica Terrini, eterrini@glass.com

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