Masonry Magazine June 1999 Page. 24
8" Concrete Masonry Units.
f'm=1500 psi Vertical Load Eccentricity=7.31: Lateral Load=23.4 psf
f'm=1500 psi fy=60000 psi Special Inspection Req'd; Phi=8
b=12"; t=7.625" d=3.812"; Solid Grouted
Min. As=.0007 sq. in./ft.
Min. As=.0640 sq. in./ft.
Max. As=.0053 sq. in./ft.
Max. As=.2424 sq. in./ft.
Deflection Control=.007 H"
Wt of Wall=78 psf
Seismic Zone IV
W Wind=20.3 psf
Parapet Height=2'-6"
Thin Wall Masonry Construction
Read As = 0.19 sq.in./ft
Steel/Spacing for vertical steel
Use #8 @ 48" o.c.
Or use #6 @ 24" o.c.
Minimum Horizontal Steel
Use #5 @ 48" o.c.
By the use of design aids it is very easy to determine the amount of steel required. This would conform to the requirements of the building code and can be checked by either computer calculations or longhand calculations.
Therefore the technique of design is no hindrance to the use of this method of design and construction.
The construction of tall slender walls is the same as construction of ordinary walls. Footings are poured, reinforcement is placed and masonry lay up started. Prior to this, all materials must be checked to make sure they conform to both the plans and specifications and the building code and ASTM specification requirements.
The walls may be partially grouted which means grouting at the location of vertical steel only or solid grouted depending upon the code and fire rating requirements structure.
As the masonry walls are built, either with hollow clay units or concrete block masonry, they can be either grouted as they are built as in the low lift method of construction in which the walls would be built 5 or 6 feet high and then grouted and continued in this process until it is topped out, or the walls can be constructed by high lift grouting in which the walls are built to their full height, reinforcing put in in its sproper position and the walls grouted to its final height. Either method of low lift grouting or high lift grouting is an acceptable method.
The construction techniques are the same for building slender walls or regular, normal masonry walls. There is no hardship to the con tractor to build either one. In fact with the use of continual inspection, he has the advantage of being able to do grouting as he wants to with out waiting for the inspection, and he is able to move ahead and make sure that all systems are go.
Why aren't tall slender walls used more often? They are as needed when the requirements show that you need walls that are higher than normal, this technique is an immediate advantage. As the engineering profession uses the technique of design for which design aids are read- ily available from many sources they will be using this method to save materials, to provide faster construction and more economical walls.
I urge the mason contractors to become familiar with the idea of thinner walls, why build 10-inch walls when 8-inch walls will do the job. Why build 8-inch walls when 6-inch walls will do the job. This will result in more masonry buildings being built and are economical buildings. It may be suggested to the structural engineer about in- vestigating the possibilities of tall slender walls.
REFERENCES
1. Test Report on Slender Wals, Structural Engineers Association of Southern California and American Concrete Institute Southern California Chapter Task Committee on Slender Was, 1983
2. Masonry Wals Stand TALL. Under Seismic Testing, published 1990 by the Masonry Institute of America
3. 1985 Uniform Building Code Sec. 2411, published by the International Conference of Building Officials
4. 1997 Masonry Codes and Specifications, edited by John Chrysler, PE. and Thomas Escobar Assoc. AlA published by the MLA
5. Tal Slender Wals Estimating Curves 2nd Ed. by James E. Amhein, S. and Donald E. Lee SE. published 1994 by the Masonry Institute of America
6. Multi-Story Slender Masonry Walls, Analysis Design Construction by Lawrence G. Seina, SE and Jefferson W. Asher S.E. published 1986 by the Higgins Brick Company Redondo Beach, CA
7. Informational Guide to Grouting Masonry by James E. Amein, SE.published 1990 by the Masonry Institute of America, Los Angeles, CA
8. Reinforced Concrete Masonry Construction Inspector's Handbook, 3rd Ed. By James E Amhein, S. E and John Chrysler, PE, published 1996 by the Masonry Institute of America, Los Angeles CA
9. Application and Construction of Slender Walls by James E. Anstein, SE-Masonry Construction Magazine, Dec. 1998