In a relatively active seismic zone, are heavy timber concentrically braced frames allowed? If so, what values (such as ‘R’) should be applied?

We didn’t find any discussion in any of the codes we’ve referenced. Nothing either allowed or disallowed. The prevalence of surviving historical structures suggest these may be viable.


The 2003 International Building Code (IBC) does not define seismic design coefficients for timber braced frames or three hinged arches. The only U.S. code source for this type of information is the 1997 Uniform Building Code (UBC). 1997 UBC Table 16-9 provides design coefficients for building frames and bearing wall systems. For braced frames in bearing wall systems (where frames are carrying gravity load as well as lateral load) reduced R factors are assigned. For heavy timber braced frames in 1997 UBC, R = 2.8 is assigned. For drift, Eq. 30-17 is applicable with the value of 0.7R being analogous to IBC’s Cd factor.