Stiffness vs Capacity in Shear Lines

In LAVA software, shear lines allow you to adjust the method to distribute the lateral force as Stiffness or Capacity based.  

SDPWS 4.3.3.4.1 requires ‘Shear distribution to individual shear walls in a shear wall line shall provide the same calculated deflection in each shear wall.’ To comply with this requirement, user can define ‘Shear Line’ in LAVA distributing shear force by ‘Stiffness’.

However, SDPWS 4.3.3.4.1 Exceptions 1 also permits shear load to be distributed to individual wall segments proportional to their shear capacities, provided nominal shear capacities are appropriately adjusted. To comply with this requirement, user can define ‘Shear Line’ in LAVA distributing shear force by ‘Capacity’.

Note: The Capacity method checks the aspect ratio (h/b_s) and if it’s greater than 2:1 the capacity is multiplied by 2b_s/h.  

How to Set the Shear Line Distribution

You can set your distribution before you start your project in the Preferences- Settings- Building Layout - Shear Line- Distribution tab.  Or you can adjust the setting on the shear line directly.  

Note: If you change your Preferences after you’ve modeled your Shear lines, it will not adjust the existing Shear lines.  However, any new shear lines drawn will use the new option.  

To adjust the Distribution on a Shear Line, double click on the shear line bubble to open the Shear Line dialog:

Example Stiffness vs Capacity

Here’s an example of how that works if you choose each option.  

One story building, analyzed with flexible diaphragm. Shear Line 1 is located on the right side, consisting of one 4’ panel, one 14’ panel, and one 6’ panel.

Seismic analysis is attached below. Total base shear is 16250 lbs.

For flexible diaphragm analysis, each shear line takes on half of total base shear: 8125 lbs.

Assign Shear Line 1 to distribute shear by ‘Stiffness’:

The total shear (8125 lbs) is distributed to the three panels with the same calculated deflection, 0.15 (or 0.16) inches as shown in screenshot below. The longer panel is Type 11, and absorbs the most load due to its stiffness.

Assign Shear Line 1 to distribute shear by ‘Capacity’:

The total shear (8125 lbs) is distributed to the three panels basing on the shear capacities (high-lighted below). The deflections of the three panels are not uniform, although all within limit by code. The three wall panels are all Type 10.  

Note: SW1 has reduced in capacity due to its aspect ratio greater than 2:1.   LAVA displays the Aspect Ratio in the Shear Wall dialog.