Tuesday, November 15, 2011

Re: Unreinforced Masonry Wall from 1965

Any chance of pilasters supporting roof beams at 12-ft on-center?  In that case, the h/t would be 12.0 and not 27.0 where h/t ratios for URM walls are no greater than 15.  Aside from that, changing from occupancy category II to III will require upgrade to current code standards.  Unless the walls are long with minimal openings, you would need to look at introducing shotcrete walls or steel braced frames as the LFRS.

On Mon, Nov 14, 2011 at 2:05 PM, Daniel Popp <drp181@yahoo.com> wrote:

We have a renovation project in a low seismic area (SDC B). The 27-foot-tall exterior walls are unreinforced ungrouted (hollow) 8" concrete masonry interwoven with 4" brick face shells (12" nominal thickness). The occupancy is changing from Category 2 to Category 3 (>300 people in one space), so we are obligated to check the existing walls. However, due to the height, I cannot make them work using the "unreinforced masonry" provisions in MSJC Section 2.2.

Does anyone have any idea how the original engineer may have made these walls work in 1965? It strikes me that the code provisions for unreinforced masonry have probably not changed much in 50 years (seismic regions excepted). The owner is very sensitive to budget (who isn't these days?), so I'd like to find a way around an costly retrofit.

Thanks for your input,
Dan Popp, S.E.

David Topete, SE