Existing Masonry Shear Wall SDC D

[bgsmith]

I have a project that is a remodel of an existing one-story masonry building with wood rafter roof framing. The building is located in seismic design category D region. The existing masonry walls have horizontal reinforcing consisting of ladder joint reinforcing only and vertical rebar spacing of #4 at 48" o.c. Per ASCE 7-05 a masonry shear wall in this area would need to be a special reinforced masonry shear wall. If the existing wall is modified (new openings cut in, added fire sprinkler weight) can you use this wall as part of the seismic force resisting system since it does not meet the requirements of a special reinforced masonry shear wall? Would you have to construct a separate seismic resisting system along this wall?

Thanks for any input or past similar projects.

bgsmith

 

[jdgengineer]

In my opinion it depends on the modifications that are done. Per Section 3404.4 of the 2009 IBC you are allowed to increase the demand to capacity ratio by up to 10% by either reducing the capacity of the element or by adding additional load. Therefore, as long as the alterations do not increase the DCR by more than 10% you are ok to use the existing masonry wall.

If you increase the DCR by more than 10% than per Section 3404.4 you are required to show the element meets requirements of current building code requirements. It's my opinion that this element would then need to be designed as a Special Reinforced Masonry wall or to have a supplementary lateral system installed.

 

[bgsmith]

jdgengineer:

What you laid out is the same way I was reading the code. In my case we will be decreasing the capacity of the existing shear walls by more than 10% by cutting in new windows and doors and/or adding load to the walls by a new sprinkler system and mechanical units.

If it is an existing masonry wall there is no way to design it as a special reinforced masonry shear wall if the existing reinforcing spacing does not meet the ACI code is there?

This seems like it would be a common remodel (existing masonry exterior walls with new owner wanting more openings) but wanted to see how everyone was handling it.

 

[haynewp]

You have to go by that IBC section, even though I don't like it. I had almost the exact situation recently and I was looking at putting in a steel system adjacent to an existing concrete wall where a large opening was being cut.