Are Pre-Engineered Metal Buildings always the most economical solution to satisfy a client's needs?  If you listened to commercials airing on the nations radio stations, you might come to this conclusion.  In reality, pre-engineered metal buildings are the most economical solution only in a limited number of applications.


It is not the structure that makes these systems economical.  A rigid frame is the least economical structural system for most conditions.  The metal skin is where most cost savings are derived in pre-engineered metal buildings.  These systems, while durable, are not very energy efficient and can be quite noisy during wind and rainstorms.  By design, pre-engineered buildings are very flexible and move considerably under gravity and wind loads.  Typically, metal buildings with metal roofing are designed for a live load deflection of L/150.  For a typical 25' purlin span, this would result in a deflection of 2" at mid-span.  The typical wall girt for metal siding is designed to limit horizontal deflection to L/120.  For the same 25' span, this would result in a horizontal deflection of 2" at mid-span.  If interior partitions abutted to the exterior wall, a 2" separation would be required unless the partitions were designed to withstand the wind load transmitted from the girt to the wall.  A similar separation would be required at the steel frames since they are also flexible and have considerable lateral sway under both snow and wind loads.


If your client does not want the look of a metal building, the structure must be stiffened to accommodate other materials.  EIFS type systems usually require a structure to have a horizontal deflection of L/360 or less.  This is about a 7/8" deflection for a 25' span.


If the client prefers a masonry veneer, the horizontal deflection should be limited to L/600 which is about " for a 25' span.

Structural Newsletter

Eeman & Blinn, Inc.

6037 Frantz Rd. Ste. 130

Dublin, Ohio 43017

Phone: 614-791-1575

Fax: 614-791-1768

EemanBlinn@aol.com

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