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Re: Min. masonry reinf

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Years ago, I, too, was curious about the basis for the code's minimum 
reinforcing requirement for masonry, so I wrote the Masonry Institute of 
America.  In a letter dated October 20, 1971, the MIA Director of 
Engineering, James E. Amrhein, wrote:

      "...[T]he requirement for minimum amount of reinforcing steel in 
masonry walls is a result of the requirement of minimum amount of reinforcing 
steel in concrete walls.  The concept was that if minimum steel is required 
in concrete walls to take care of shrinkage, temperature stresses etc. 
something should also be provided in masonry walls.

      Because masonry is a prefabricated product, either brick or concrete 
block, much of the shrinkage has already taken place prior to construction, 
therefore, it was considered that only one half the amount of steel would be 
required in a masonry wall as in a concrete wall.

      ...."

So much for the requirement being from a rational, albeit logical, basis.

[My Opinion]  As far as minimum masonry reinforcing in flexural members, it 
should be not less than what would be required for 1.5 times the cracking 
moment of unreinforced masonry.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Bill Sherman wrote:

. > Donn Wooldridge wrote: 
. >  
. > >More grouting, more reinforcing !!  The minimum steel percentage is 
. > based on equivalent solid thickness which increases with the grouting!! < 
. >  
. > What is your basis for using "equivalent solid thickness" as the basis 
. > for minimum reinforcing steel?  UBC minimums are based on a percentage of 
. > "gross cross-sectional area".  Since the definition for "net area" (at 
. > the front of the Masonry Chapter of UBC) refers to "gross cross-sectional 
. > area minus the area of ungrouted cells ...", I would interpret gross 
. > cross-sectional area to be the total area within the perimeter of the 
. > unit regardless of grouting.   
. > 
. > 
. >