Masonry Magazine June 1999 Page. 18
As more buildings were built, materials became a little scarcer and thus they began not making these thick walls but started thinning them down. However, there are still examples of this throughout the world. The Monadnock building in Chicago built in 1891 is a 16-story loadbearing brick building with the walls at the lower level 6 feet thick and progressively thinner towards the top.
Many medium rise apartments of 3, 4, 5 stories have brick walls that have walls 24, 21, 17, 13 and 9 inches thick as the walls progress to the top. This is evident if you look at the windows of these medium rise old brick buildings whether it is in Philadelphia, New York, Chicago or Los Angeles.
In 1933 there was a significant earthquake in the city of Long Beach, California. This demonstrated very vividly the lack of shear strength and ductility of unreinforced masonry. Since then reinforcing was required in masonry in seismic areas. This reinforcing added to the lateral strength of in plane and out of plane masonry walls. Vertical strength is excellent whether it was reinforced or not reinforced and thus they could build these tall buildings because of the strength of the brick and masonry used in them. However, lateral strength was deficient and therefore reinforcing had to be introduced.
In 1946 limitations were placed on the h/t ratio for walls.
MINUMUM THICKNESS OF MASONRY WALLS
| Type of Masonry | Maximum Ratio Unsupported Height or Length to Thickness | Nominal Minumum Thickness (inches) |
|-----------------|---------------------------------------------------------|------------------------------------|
| | | |