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2022

Wood Shear Walls + Mechanical Openings

Wood shear walls can be sensitive to openings, and mechanical openings can often move around during design. It is critical that the final locations of mechanical openings are coordinated with the structural engineer.

Wall Types

As window systems and insulation have become more energy efficient, architects have increased the percentage of openings in exterior walls without sacrificing the thermal performance of the building. Because of this, it’s essential to understand what types of walls are permitted for a given wall configuration.

Wood shear walls with openings are permitted to be designed in a number of ways, with each method having its pros and cons. All wall types are limited to a maximum height to width ratio, otherwise known as the aspect ratio. The following information is based on a wall sheathed with wood panels rated for lateral resistance with blocking at panel edges.

Example

With a 10ft wall height, for a typical shear wall, the pier needs to be 2’-10” wide min, or 5ft wide to avoid a reduction in capacity. Using the force transfer around opening method (strapping above and below a window), smaller wall piers can be used since the height considered is just window height. Note that even with the force transfer around the opening method, wall piers must be at least 2ft wide.

Structural + Geotechnical

Additional borings per building can save your project money; however, the number of borings per building has been trending down over the last several years. Consider one boring per 10,000 SF to 20,000 SF of building footprint (two borings minimum). Ask your Structural Engineer to consult with the Geotechnical Engineer to help identify the best number and location of borings on your projects.

Structural + Geotechnical

In areas with medium to large seismic activity, soft soil at a building site can trigger a code requirement for "Foundation ties" or grade beams tying individual column footings together. These ties can be expensive. Sometimes soil borings are inadequate to accurately determine how soils will behave during an earthquake. Geotechnical engineers can conduct a geophysics analysis that can obtain a more accurate picture of seismic performance. Oftentimes, a geophysics analysis can eliminate the need for grade beams. Next time your project has an E or F site classification, ask your Geotechnical engineer if a geophysics assessment would result in a stiffer site class & save your project money.

Structural + Geotechnical

An important aspect of a geotechnical report is estimating the different amounts of foundation settlement that would occur between various parts of the building. This is called differential settlement. If not properly accounted for in the design, larger amounts of differential settlement can cause damage to finishes, glazing, exposed concrete or masonry & in some cases structural instability. To help reduce problems on your projects, make sure the geotechnical report gives an estimated differential settlement & includes the reference distance. One inch of settlement over one foot is much different than one inch over one hundred feet. Talk to your structural engineer about the report, they should be able to compare the report values to those allowed by code in Table 12.3-3 of ASCE 7-16.

New Loads on Open Web Steel Joists

A tag on the steel joists can be helpful in determining the joist loading capacity. If the joist tag is not available, the structural engineer can measure the joist with a tape measure and calipers to get a good sense of the joist’s capacity. The engineer can check if the horizontal chords or the diagonal web members need to be strengthened for the new load. One way to strengthen joists is to weld a round bar to the bottom chord and/or additional angles at the webs.  See pictures below.

Existing Building Remodel

During a remodel of an existing building, a few things could lead to the floor or roof needing to be strengthened:

  • Additional load needs to be supported
  • New loading criteria as a result in a change of occupancy
  • An existing support for the members was moved or removed

One way to accomplish this is for a structural engineer to design a new member to share the load with the existing one by "Sistering" the two together as shown in the pictures above. Your engineer should know to also check the supports of this reinforced beam - a stronger connection at the ends may be necessary.

Floor Vibrations

Maximizing floor deck span is a way to reduce floor vibration while also reducing the number of floor framing beams. This can reduce costs in the floor system while getting the floor performance desired by building users. Talk to your structural engineer about how to optimize your floor system considering these factors.

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