Wind Loading of Unreinforced Masonry 1

[DemolitionMan03]

I'm evaluating a 1953 unreinforced masonry wall for bending due to wind load, and I'm having trouble understanding how the ASD Masonry Code (TMS 402-08/ACI 530-08/ASCE 5-08) handles the situation. The wall is non load-bearing structural clay tile, and it appears to be braced only at the top and bottom of the 25-ft height. I calculate a bending stress of 241 psi due to the C&C wind loading.

What do I use for the allowable bending stress: 1/3 * f'm (per Equation 2-17) or the value from Table 2.2.3.2? In my case, the first gives me 333 psi and the second gives me 38 psi. I went forward with the 333 psi and evaluated using the unity equation for flexure and axial compression (self-weight only here), and the wall is barely adequate (0.998). If I use the 38 psi, the wall (that has been standing just fine for 59 years) is 634% stressed.

What am I missing here? Do I not need to worry about the tensile stress (38 psi)? Any code clarifications, resources, masonry-for-dummies explanations, etc. would be appreciated.

BTW, this is my first post on the forum. I've check out the web site occasionally in the past, but recently switched jobs and am finding the site very helpful, so I thought I'd join up. I look forward to hearing what y'all think.

 

[tony1851]

dhengr; can post-tensioning be a viable solution on a wall this slender, and with units of unknown compressive strengh in unknown mortar strength? Draw a vertical cross-section of that wall to scale and it looks scary. I wouldn't even want to go inside that building, let alone start cutting the units top and bottom to thread rods down. How would he evaluate the tension required? Any slight un-allowed for eccentricity and and I wouldn't want to be anywhere near it.