Masonry Magazine September 1968 Page. 19
NCMA TEK 10
An information series from National Concrete Masonry Association
©1968, National Concrete Masonry Association.
Reinforced Concrete Masonry
An Established Structural System
General
There is a most significant trend towards masonry bearing wall structural systems in Europe, Canada, and the United States. This trend is analogous not only to three- and four-story construction, but more recently to structures up to 16 stories in height. This TEK bulletin serves as an introduction to reinforced concrete masonry technology and describes briefly the appropriate materials and their testing, along with the essential elements of structural design. Mainly highlights are presented here because of its broad scope. The reader should keep in mind that reinforced concrete masonry is similar in many respects to its counterpart reinforced concrete, and yet to those familiar with plain (non-reinforced) masonry, it presents no insurmountable construction problems. Like its counterpart, reinforced concrete masonry seems destined to play an increasingly important role in the construction of high-rise load-bearing structures.
Reinforced concrete masonry is a method of construction in which steel reinforcement is embedded with concrete block and grout so that the masonry, grout and steel act together to resist forces. Solid or hollow concrete block are laid up in mortar so that their alignment forms a continuous series of vertical cavities within the wall framework. In the case of bond beams, horizontal cavities are formed. Steel reinforcing bars are inserted in these cavities, which are then filled with grout to form a bonded composite structural system.
Originally developed in areas subject to earthquakes, reinforced concrete masonry with load-carrying capacity is finding many new applications in multi-storied buildings. Employed where high stresses are encountered, this wall system eliminates the need for thick, massive wall sections and permits a greater span of walls between lateral supports.
A more detailed discussion of the subject will be found in "Design Manual-The Application of Reinforced Concrete Masonry Load-Bearing Walls in Multi-Storied Structures available from NCMA (Publication CM-206, 15)
Grouting
Grout usually is placed only in those wall cavities requiring steel reinforcement. In vertical cavities, the grout is confined by mortaring the masonry cross-webs; in horizontal cavities, it is confined by using masonry units with a solid bottom, or by means of cored bond beam units with metal lath or screen laid in the horizontal bed joint. In some walls all cavities-with and without reinforcement-are grouted to further increase the wall's resistance to loads.
The procedures employed in laying concrete block, placing steel reinforcement, and grouting of cavities will vary with job size, available equipment, and individual preference. The simplest procedure, sometimes referred to as "low-lift" grouting, consists of (1) building the concrete masonry wall to scaffold height, or to a bond-beam course, but not more than four feet; (2) inserting steel in proper cavities; (3) pouring a grout of fluid consistency in those cavities which contain steel; and (4) repeating the operation by laying block to the next height.
FIG. 1-TYPICAL REINFORCED CONCRETE MASONRY CONSTRUCTION USING THE LOW-LIFT GROUTING TECHNIQUE
Place metal lath under bond beam to confine grout.
Steel in Bond Beams is set in place as wall is laid up.
Floor Slab.
Footing.
Vertical steel-Lap 30 bar diameters at splices; hold in position at intervals of 192 diameters.
Place mortar on cross webs adjacent to cells which will be grouted to prevent leakage.
Stop grout 1½” from top.
Place grout in lifts not to exceed four feet; puddle or vibrate in place.
Cells containing steel are filled solidly with grout; vertical cells should provide a continuous cavity, free of mortar droppings, and at least 2 x 3 inches in size.
August, 1968
84
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Concrete Units