Masonry Magazine April 2002 Page. 14
TMS/continued from page 12
Special Reinforced Shear Walls - Special reinforced shear walls are designed essentially the same as intermediate reinforced shear walls with the additional requirement that the maximum spacing of the vertical prescriptive reinforcement shall not exceed 48 in. (1219 mm), one-third the length of the shear wall, or one-third the height of the shear wall. Also, the minimum cross-sectional area of the vertical reinforcement shall be one-third of the required horizontal reinforcement. Special reinforced shear walls may be used in any SDC (A, B, C, D, E, or F).
Table 2 Allowable Flexural Tension, psi (kPa) Perpendicular to Bed Joints for Fully Grouted Hollow Unit Masonry
| | Mortar Types | |
| --- | --- | --- |
| | Portland cement/lime or Mortar cement | Masonry cement or air entrained portland cement/lime |
| | M or S | N | M or S | N |
| | 65 psi (previously 68 psi) | 63 psi (previously 58 psi) | 61 psi (previously 41 psi) | 58 psi (previously 29 psi) |
Allowable Flexural Tension Modifications
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Recent research supported revisions to the allowable flexural tension values for grouted unreinforced masonry elements when subjected to flexural tension perpendicular to the bed joints as show in Table 2.
Empirical Design Modifications
The threshold limit of wind speed for empirical design was changed to be compatible with the new provisions of ASCE 7. That is, previous provisions of the MSJC prohibited empirical design of masonry in regions where the design wind pressure exceeded 25 psf (1197 MPa). The revised limitation is changed to a wind speed limit of 110 miles per hour (145 km/h) three second gust. Shear wall spacing requirements for empirically designed building were clarified so that the maximum length-to-width ratios for diaphragm panels must follow the values in Table 3.
Table 3 Diaphragm length-to-width ratios for Empirically Designed Masonry
| Floor or roof diaphragm Construction | Maximum length- to-width ratio of Diaphragm panel |
| --- | --- |
| Cast-in-place concrete | 5:1 |
| Precast concrete | 4:1 |
| Metal deck with concrete fill | 3:1 |
| Metal deck with no fill | 2:1 |
| Wood | 2:1 |
Support of Veneer by Wood Construction
Although not applicable to all forms of masonry construction, masonry veneer having an installed weight of less than 40 psf (195 kg/m2)and a height not exceeding 12 ft (3.7 m) is now permitted to be supported on wood members. This form of construction, often realized as a cost-effective solution in wood-framed residential structures, was previously not permitted due to perceived concerns over fire safety and cracking resulting from excessive de- (more on page 16)
14 MASONRY APRIL, 2002