Masonry columns used only to support light-frame roofs of carports, porches, sheds or similar structures with a maximum area of 450 square feet (41.8 m2) assigned to Seismic Design Category B or C are permitted to be designed and constructed as follows:
1. Concrete masonry materials shall be in accordance with Section 2103.1. Clay or shale masonry units shall be in accordance with Section 2103.2.
3. Columns shall be reinforced with not less than one No. 4 bar centered in each cell of the column.
5. Columns shall not exceed 12 feet (3658 mm) in height.
6. Roofs shall be anchored to the columns. Such anchorage shall be capable of resisting the design loads specified in Chapter 16.
7. Where such columns are required to resist uplift loads, the columns shall be anchored to their footings with two No. 4 bars extending a minimum of 24 inches (610 mm) into the columns and bent horizontally a minimum of 15 inches (381 mm) in opposite directions into the footings. One of these bars is permitted to be the reinforcing bar specified in Item 3 above. The total weight of a column and its footing shall not be less than 1.5 times the design uplift load.
The minimum length of lap splices for reinforcing bars in tension or compression, lld, shall be calculated by Equation 21-2, but shall not be less than 15 inches (381 mm).
(Equation 21-2)
For SI: lld = 1.95d2bfyλ / K√f'm
where:
| db | = | Diameter of reinforcement, inches (mm). |
|---|---|---|
| ƒy | = | Specified yield stress of the reinforcement or the anchor bolt, psi (mPa). |
| ƒ'm | = | Specified compressive strength of masonry at age of 28 days, psi (mPa). |
| lld | = | Minimum lap splice length, inches (mm). |
| K | = | The lesser of the masonry cover, clear spacing between adjacent reinforcement or five times db, inches (mm). |
| γ | = | 1.0 for No. 3 through No. 5 reinforcing bars. 1.4 for No.6 and No.7 reinforcing bars. 1.5 for No.8 through No. 9 reinforcing bars. |
The bar diameter shall not exceed one-eighth of the nominal wall thickness and shall not exceed one-quarter of the least dimension of the cell, course or collar joint in which it is placed.
Reinforcing bars larger than No. 9 in size shall be spliced using mechanical connectors in accordance with ACI 530/ASCE 5/TMS 402, Section 2.1.10.6.3.
Special reinforced masonry shear walls having a shear span ratio, M/Vd, equal to or greater than 1.0 and having an axial load, P greater than 0.05 f'mAn which are subjected to in-plane forces, shall have a maximum reinforcement ratio, rmax, not greater than that computed as follows:
(Equation 21-3)