The R value appears correct. However, per 2213.8.5 the bracing force must
be amplfied by omega (2.2) and from your description, the system probably
has a reliability/redundancy factor of 1.5 if the building area exceeds 6400
square feet. So the bracing gets penalized by an overall factor of 3.3.
From: FSRahbar(--nospam--at)aol.com <FSRahbar(--nospam--at)aol.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Thursday, February 03, 2000 10:34 AM
Subject: "R" Value for Cross Bracing
>I am checking a Metal-Structure building. It is similar to a Butler
>where there are no bearing walls and beams and columns support the entire
>The building is long and narrow, therefore, the seismic loads in the narrow
>direction is somewhat comparable with wind loads. The lateral resisting
>elements in narrow direction are two sets of 3/4" diameter rod cross
>Obviously the rods only work in tension and not compression. The engineer
>the building has used a "R" Value of 5.6 to determine the seismic loads.
>"R" value is taken from Table 16-N, Building Frame System, Item 4, Ordinary
>Braced Frames with Steel.
>My questions are: Is "R" Value of 5.6 correct for this steel rod cross
>bracing? Is the ordinary Brace Frame consist vertical truss and the members
>can take both tension and compression?
>It was my opinion that since the rod cross bracing system is not really
>defined in Table 16-N, the closest system would be item 1-3 with tension
>brace with "R" Value of 2.8.
>I appreciate it someone can try to clear this.
>F. S. Rahbar SE