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["Nels Roselund, SE" <njineer(--nospam--at)att.net>]

Dennis,

 

Some thoughts on your 1920's Firehouse retrofit and adaptive reuse:

 

When making an addition to an old masonry building, rather than separating the new from the old with a seismic joint, I generally make the new walls of masonry or concrete [walls that would have rigidities in the same range as the old walls] and design them into the building's lateral load resistance system so that the design lateral loads to the old walls are reduced, or at least not increased.  The new walls would be designed to resist lateral loads determined by wall relative rigidities, with stresses based on the modern building code.  This requires drag struts between new and old construction, and results in a well interconnected and tied-together structure.  Would this work for your project?

 

Even if the f'c value is 600 psi, 1/2 x sq-rt f'c is a sizeable value.  For a building with walls that probably have few openings [except at the front], I expect that in-plane shear will not control the design.

 

Can the very-low-strength concrete tests be related to visible local conditions, such as cracks or deteriorated concrete?  If so, repair of the local damage conditions would make it reasonable to ignore those tests.  Concrete deterioration is often related to conditions near grade, and often related to moisture -- even in my Death Valley project, structures with 75 + years of weather exposure show moisture damage -- it rains hard occasionally, and water not conducted quickly away from the building will penetrate and do its dirty work.  Wall anchors are high in the wall are not likely to be in deteriorated concrete -- I expect that you will find that adhesive anchors will have ample strength.  I agree, however with Michael's recommendation for testing of anchors.  The Evaluation Service Reports generally provide for use in concrete of 2000 psi minimum strength.  Let me know if you'd like a referral to adhesive anchor suppliers who has been very accommodating with testing assistance for anchors in unconventional materials on my projects.

 

I have no concrete building demolition notes.  However, my General Notes assign full responsibility for jobsite safety and existing-building protection to the contractor, including compliance with applicable construction safety rules, means, methods, sequence of work, safety equipment, worker safety training, and emergency procedures.

 

Thanks, Dennis for the personal note sent by separate email -- I'll be back in touch with you.

 

Nels

 

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net