Vocabulary

  • Shearwalls: Are cantilevered elements. Plywood provides shear resistance with nails. Edge nailing = 6″ o/c, Field nailing = 12″ o/c.
  • Pin connection
  • Moment connection
  • Overturning moment = Force x height (of shearwall)
  • Overstrength
  • Aspect Ratio: Length:Height of a shearwall- Anything under 2:1 is good, 3.5:1 is the max (unless using a tested product like Simpson strongwall). Between 2:1-3.5:1 can subtract up to 15% shear capacity.
  • FTAO (Force Transfer Around Opening)- must have atleast 2′ of wall inbetween openings (windows only, no doors)
  • Portal Frame (typically used for Garage door walls)
  • Tributary Width: Halfway point between supports- in a truss system this would be halfway between the exterior walls the truss spans. If there is a Ridge beam, this would be the halfway point between the exterior wall and the roof ridge.

General Set up: 

  1. Copy Shearwall schedule from last completed project to new project folder.
  2. Open LFRS diagram views. Look at possible shear lines on existing house- typically continuous exterior walls and continuous interior walls that run the length of the house. Take into consideration the foundation and the roof framing for possible shear line locations.
  3. Update number of shear lines on the LFRS calculator properties. align force arrows to correct lines.
  4. List all Shearwalls in the shearwall schedule and copy forces (Seismic “FE” and Wind “FW”) from the LFRS calculator into the shearwall schedule. Best practices:
    1. Make sure to copy and paste previous entry rows with a spacer on top and bottom for each new shearwall to keep the calculators working correctly.
    2. Each shearwall entry should consist of two rows- a Gridline heading row and a calc row.
    3. List shearwalls in descending order (shearwalls running E-W ((Gridline 1,2,3..)) and then Shearwalls running N-S((Gridline A,B…) starting with existing upper floor
      1. label existing with (Ex) Wall segment name = SW-Gridline|Story|Unique identifier| (EX) if existing
  5. Add shearwalls to LFRS plans with the Typical SW family (Structural component). Align to window openings and wall ends and tag. Note- If on an exterior wall, the shearwall should show the full length of the plywood. When plywood is on the exterior of the building the shearwalls will overlap at corners.
    1. In properties- record name of SW in the “mark” Identity data section and record lengths and update names of shearwalls in each shear line in the Shearwall schedule.
      1. Showing shearwalls between Existing and New LFRS plans: If the shearwall is existing and unchanged during construction, do not add an (EX) on the end in the LFRS plans- but keep both entries in the shearwall schedule for the existing condition (EX) and the new condition. If the shearwall is existing and changed during construction (for example, if a window is added in an existing wall and the shearwall becomes shorter), label with (EX) and mark the shearwall phase demolished as “new construction”. add a new shearwall in it’s place with phase created (New construction) and without the (EX) suffix.
  6. Fill out DL Wall column in shearwall schedule
    1. Wall deadloads found in assembly loads (check if wall is existing or new, exterior or interior
  7. Fill out DL Flr column in shearwall schedule. This is found by finding the tributary width and multiplying by the deadload (either floor load or roof load depending on level).
    1. ex:
  8. Fill out the Uplift column in the shearwall schedule. This is interpolated from the values supplied in the wind parameters multiplied by the tributary width.
    1. ex:
    2. To make this process faster, use a general estimate method (to the right in the example)- decide percentage of area that the edge condition takes up, then average between the two values in the table based on that percentage.
  9.  Parallel Condition: If the joists/trusses run parallel to the shearwall, the dead load will be 0. The roof uplift value will be 50 (this is a conservative estimate)

Analyzing/Designing Shearwalls

At this point scroll over to SW column (AK) and start checking if there are any large forces (vMax) that may require making new shearwall design decisions ex: Vmax was over 800, requiring a SW-8+. This is due to the short length of the wall. This required making a new shearline to re-distribute forces into the interior of the building- in summary:

  • Searched for walls that overlap between levels- once a good candidate was found, we added a new gridline and new shearline to the LFRS.
  • We relabeled all shearwalls accordingly because of new gridline labels on both the LFRS and the shearwall schedule
  • Updated seismic and wind forces on shearwall schedule (forces will be distributed differently on LFRS calculator when it accounts for new shearline

Check the max forces and shearwall capacity columns to confirm that the loads can be handled with SW1-SW4 by selecting the correct SW in the dropdown menu. Don’t forget to select Existing for all (EX) walls.

The next step is designing the appropriate Holddowns for each shearwall. See additional post “Holddowns”