Deflection Issues for Operable Partitions

Operable partitions provide versatility to room layouts. They provide sound separation and aesthetic value. But to a structural engineer, the devil is in the details. These systems must be able to function properly in order to maintain operability and sound retention.

The support of these systems must not only carry the partition weight but also limit the deflection for proper operation. The simplest approach is to place a floor supported system on a slab-on-grade.  But this type of system is rarely specified.

All structures deflect. It is an indication of the elastic properties of the affected member or members. Although easier to accommodate in new structures, adding these systems to existing buildings can be problematic.

Different panel systems possess different deflection requirements. The most common system is the folding partition. Their construction depends on the STC rating (sound transmission class) which affects the deflection limitations. Other systems include accordion doors, movable glass panels, self-supporting panels and portable panels. For this article, we will address the needs of the folding panel partitions.

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Folding Panel Partitions

These panel partitions run along the top track and stack at one or each end of the partition in a closet. The overhead structure above these closets are designed for the accumulated load of the system. The supporting structure over the extended partition is designed for the uniform load of the partition. The weights of these systems usually do not exceed 10 pounds per square foot.

Partition manufacturers require different deflection limitations. A simple statement such as “deflection shall not exceed 1 inch ‘’ does not begin to address what the structural engineer needs to consider. Other questions include:

1. What is the maximum allowable “live load” deflection over a specified width? This specified width may be the width of two panels. The “live load” would be the weight of the panel plus the roof live or snow load.
2. Over the entire length of the partition, what is the maximum “live load” deflection?   This should be greater than the deflection along a portion of the track. For longer partitions of 50 feet or more, this deflection should be expressed as a ratio of length divided by a constant number.

Load and Deflection Requirements

On new construction that utilizes joists or joist girders, the load and deflection requirements should be shown on the construction drawings. You should also consider the maximum allowable depth of the joist for clearance purposes. The joist manufacturer will submit their design during the shop drawing submittal phase.  This is the time to review and coordinate the joist design with the Operable Partition submittal.  On many occasions this results in a conference call with the Strcutural Engineer, Architect and Partition Representative.

On existing construction, it is rare that existing structures will be able to carry the additional load of the partition, let alone meet the deflection requirements. It may be relatively easy to increase the member strength, but to limit the deflection would be quite expensive.

One solution is to install a stand-alone structural member that meets the requirements. The obvious issue here is getting the new members into an existing building. Other structural members duct work, lighting, etc., all will be in the way. Obviously a very expensive alternative. There is a product intended to address this situation, but may also be limited in its applications. http://www.modernfold.com/truss_system.aspx

Refer to ASTM E557-00 (Standard Guide for the Installation of Operable Partitions) for specific instructions.

If possible, early communication between the partition representative, the architect and structural engineer is recommended. Selection of the system after bidding usually leads to expensive modifications.

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Thanks for reading,

David

Written by David Simpson, P.E., SECB, MBA, President, Principal Engineer

David Simpson’s experience includes over 30 years in structural design and project management for industrial, commercial, institutional and nuclear/chemical facilities utilizing steel, concrete, masonry and wood. His accomplishments include design and construction administration of health care facilities, hotels, schools, shopping centers, aircraft hangars, numerous retail facilities and several forensic engineering assignments. He has professional registrations in D.C., Maryland, Ohio, Pennsylvania, South Carolina, Virginia and West Virginia. Simpson graduated from the West Virginia Institute of Technology with a bachelor’s degree in civil engineering and an MBA from West Virginia University.