Steel Moment Frames

By Nate Rogers, E.I.T. | April 13, 2020

Building structure needs to be designed not only to hold up gravity loads but also to handle lateral loads from wind and earthquakes.

In most typical residential situations, shear walls are constructed to provide a lateral structural system. To do this, structural sheathing (such as plywood) is applied to the full height of the shear wall (usually exterior but could be interior if needed). This method is relatively inexpensive and is what is naturally installed regardless of lateral load designs.

One caveat of constructing shear walls is that they require full floor-to-ceiling sections of walls and not interrupted by window or door openings.  The length of the shear wall also affects how much lateral load the building can withstand. With these limitations, there are examples where typical shear walls cannot be used, such as the following:

  • An exterior wall with many tightly-spaced windows
  • Large garage door openings
  • A wall with floor-to-ceiling glass windows

So, how do they build it? Creating a moment frames is a common solution. Moment frames are designed to resist lateral loads by using special beam-to-column connections designed by a structural engineer. This connection is almost impossible to create in wood and the structure’s material usually ends up being steel.

Steel moment frames can enable homeowners to add huge beautiful windows, which would be otherwise impossible. Moment frames create design flexibility because they do not require diagonal braces and take up less space than the typical shear wall.

For a single moment frame, a designer only needs to make room for two posts and a single beam rather than a long, uninterrupted section of wall. Of course, moment frames come with a higher price tag than shear wall bracing because of their material strength and design flexibility. For the best and most cost-effective solution, it is critical to involve a structural engineer early in the design. Team Engineering has experience designing all types of lateral force resisting structures including residential and commercial shear walls and moment frames.

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