Existing Masonry Wall

[anwelton]

I am trying to design some awning covers for our office building as we are renovating. I am having issues in determining the existing properties of our masonry wall (the building was build back in the 1950's). Is there a way to determine strength properties without doing testing? If so, can you please guide me to a manual that will help me?

Thanks!

 

[concretemasonry]

Just assume the minimum ASTM standards for materials (ASTM C90 for CMUs). The standards have not changed materially for 70 or 80 years. Current units are 30% to 60% over the current "ancient" standards. Even 50 years ago, strength would have been beyond the minimal standards. Now, block are not made to the low current low ASTM standards because manufacturing and curing materials just make a unit far superior to the current minimum standards. The material costs (cement and admixtures) are not big factors since process is automated.

Depending on your location, try to apply the old local requirements to your situation and loads if there was a real design standard then. It may have just been an empirical standard at that time.

The major factor is the current condition of the masonry wall. For compressive wall strength, the mortar strength is of little consequence and cannot be verified, since ASTM suggests using the lowest strength mortar possible.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

You should not use 1950's era loads. Those should be based on the current codes.

The issue for an awning cover would be the load from the awnings based on wind loads and possibly snow loads depending on where you are located.

The awning, if cantilevered off the wall, would induce bending in the wall of some amount - the issue is what the wall is currently required to support (roof load, lateral wind loads, self weight, etc.) and to what extent will the awning add to that bending in the wall.

The other issue would be to determine how, or if the wall is reinforced or grouted as this would have an effect on wall capacity as well as the type of attachment you would have to use.

No easy way to do that (without original design plans) except to perhaps drill into the wall at each 8" cell to determine the extent of grouting and possibly rebar. Once you find a grouted cell that is accessible, break into a face shell and chip in to reveal the rebar location and size. Then do the necessary structural calculations.

The calcs and local demo might not be necessary depending on the relative magnitude of the awning loads with respect to the overall design loads on the wall....a good structural engineer can help if you hire them.