Page 393 - Design of Reinforced Masonry Structures

6.44 CHAPTER SIX

FIGURE 6.29 Moments in a wall due to lateral loads and eccentric vertical loads.

6.7 DESIGN OF WALLS FOR GRAVITY AND
TRANSVERSE LOADS

6.7.1 Lateral Support for Walls
Walls may be subjected to both gravity and lateral loads. They must be supported laterally
to restrain against displacement due to lateral loads such as wind and seismic forces. Walls
may span horizontally or vertically. When spanning horizontally, lateral support to masonry
walls may be provided in the form of cross-walls, columns, pilasters, counterforts, or but-
tresses. For walls spanning vertically, lateral support may be provided by floors, roofs,
beams, or girts.

6.7.2 Distribution of Gravity Loads in Walls
Distribution of gravity loads on walls depends on the manner in which the wall supports the
imposed loads. Several cases may be considered:

1. Roofs or floors made from reinforced concrete or prestressed concrete planks may be
supported directly on top of the walls, in which case the axial load on the wall may be
computed in terms of per linear foot of the wall.
2. When wood diaphragms are used, typically the connections are made to a ledger beam

anchored to the walls. Gravity loads from floor or roof joists are transferred to wall
through the anchor bolts. When these joists are closely spaced, the load from all joists
may be distributed to wall on per linear foot basis.
3. In some cases, particularly when spans are large, joists may consist of glued-laminated
or steel beams, which are supported directly on walls over bearing plates (Fig. 6.30). In
such cases, the gravity loads act as concentrated loads. Distribution of such loads in walls
depends on the type of bond pattern (i.e., running bond or other types) used to build the
wall. Loads can only be transmitted through head joints of masonry laid in running bond.
This is so because when running bond is used, the horizontal courses of bricks or blocks
are staggered so that the vertical joints are not continuous. A wall with continuous verti-
cal joints (e.g., stack bond) acts more like a series of adjacent vertical piers, rather than a
cohesive unit. The interlocking bond has a further merit of dispersing loads evenly.