Masonry Magazine September 1968 Page. 21
EQUIVALENT WALL THICKNESSES
| Wall Construction | 6" | 8" | 12" |
|---|---|---|---|
| | Equiv. Net Solid Thickness | | |
| Solid Grouted Wall | 5.6 | 7.6 | 11.6 |
| 16" o.c. | 4.5 | 5.8 | 8.5 |
| 24" o.c. | 4.1 | 5.2 | 7.5 |
| Vertical Cores Grouted at | 32" o.c. | 3.9 | 4.9 | 7.0 |
| 40° о.с. | 3.8 | 4.7 | 6.7 |
| 48" o.c. | 3.7 | 4.6 | 6.5 |
| No Grout in Wall | 3.4 | 4.0 | 5.5 |
3. REINFORCEMENT:
Steel Reinforcement should conform to Standard Specifications for Billet-Steel Bars for Concrete Reinforcement (ASTM Designation: A 15-) or to Standard Specifications for Rail-Steel Bars for Concrete Reinforcement (ASTM Designation: A 16-).
Deformations of reinforcing bars should conform to Standard Specifications for Minimum Requirements for the Deformation of Deformed Steel Bars for Concrete Reinforcement (ASTM Designation: A 305-).
Wire Reinforcements should conform to Standard Specifications for Cold-Drawn Steel Wire for Concrete Reinforcement (ASTM Designation A 82-).
Structural Design Considerations
In order to provide a sound basis for a specific reinforced concrete masonry structural design, it is first necessary to establish the f'm (ultimate compressive strength) to be used in the design. The designer may do this in two ways-either by the specified unit strength method or by actual testing of sample prisms duplicating the wall configuration.
METHOD 1. Unit Strength Tests
In considering the complete load-bearing wall assemblage, the designer may use an assumed working stress value f'm. In this method, the specified strength of the individual masonry units is reduced by appropriate safety factors-Table I shows assumed compressive strength of masonry (f'm) for the various compressive strengths of the units. Note that the compressive strength of hollow concrete masonry units is based on their net area.
METHOD 2. Prism Tests
A second method, useful in multi-story load-bearing design, is to build prisms from the materials to be used in the structure and take the value
FIG. 5 (a)-AREA OF REINFORCED HOLLOW CONCRETE MASONRY WALL ASSUMED EFFECTIVE IN AXIAL COMPRESSION
Wall 8 inches in thickness
Vertical cores grouted at 32" о.с.
Equivalent net solid thickness, from Table II 4.9 inches
FIG. 5 (b)-T-BEAM SECTION ASSUMED IN FLEXURAL COMPRESSION (MASONRY LAID IN RUNNING BOND)
-b6-
FIG. 5 (c)-AREA ASSUMED EFFECTIVE IN LONGITUDINAL SHEAR
TABLE III
RECOMMENDED ALLOWABLE STRESSES IN REINFORCED CONCRETE MASONRY BASED ON THE BUILDING CODE REQUIREMENTS FOR REINFORCED MASONRY (AMERICAN STANDARD A41.2-1960)
| Type of Stress | Allowable Stresses" | Factor |
|---|---|---|
| Compressive: Axial | fm | 0.20 f'm t |
| Flexural | fm | 0.33 f'm |
| Shear: Beams with no web reinforcement | Vm | 50 psi |
| Beams with web reinforcement | V | 150 psi |
| Bond: Plain bars | u | 80 psi |
| Deformed bars (ASTM A305) | u | 160 psi |
| Bearing | fm | 0.25 f'm |
| Modulus of Elasticity | Em | 1000 f'm |
| Tensile Stress in Longitudinal Reinforcement-Intermediate and Hard Grade Steel Bars | fs = | 20,000 psi |
Allowable stresses may be increased by 3315 per cent where de-signing for wind load in combination with dead and other loads providing the calculated stresses due to dead and other loads alone do not exceed the allowable stresses.
In reinforced bearing walls reinforced with an area of steel not less thas 0.002 times the gross cross-sectional area of the wall, not more thas of which is used in the principal direction and where the principal reisforcement is spaced not more than 48 in. apart. Where the ratio of wall height to thickness exceed's 10, the allowable stress should be reduced proportionally to 0.15 'n for walls having a ration of height to thickness of 25. Where the reinforcement is designed, placed and anchored in position for columns, higher stresses are permitted.
Does not apply to continuous or restrained members which are so constructed as not to provide T-beam or equivalent action