Q8: What
are the primary building codes covering masonry construction?
A:
"Building Code Requirements for Masonry (ACI 530.1-92/ASCE 6-92/TMS 402-92)" by
the American Concrete Institute, American Society of Civil Engineers and The Masonry
Society; and the Uniform Building Code. The ACI-ASCE-TMS masonry code is
referenced in the BOCA National Building Code and Standard Building Code.
Q9: Who
publishes specifications and design guides for masonry construction?
A:
ACI, ASCE and TMS have issued "Specifications for Masonry Structures (ACI
530.1-92/ASCE 6-92/TMS 602-92)", which is an integral part of the building code cited
in the Answer to Question 8. Two comprehensive design publications were recently issued: Masonry
Designers' Guide by TMS and ACI; and Concrete Masonry Design Tables by the National
Concrete Masonry Association (NCMA). The Brick Institute of America (BIA), the Masonry
Institute of America (MIA), NCMA, and the Portland Cement Association (PCA) publish a
variety of technical information. Some of their publications are listed in the References.
Q10: Do masonry walls
require reinforcing steel?
A:
The building code governing the location where the structure is to be built usually will
have minimum requirements for "reinforcement". For non-seismic, non-load bearing
conditions the usual minimum is horizontal ladder or truss type joint reinforcement spaced
24 in. vertically, and a horizontal bond beam with 144 rebar at each floor level. Vertical
rebar may be required depending on the clear story height of the wall.
Q11: What is a "fully reinforced" masonry wall?
A:
A fully reinforced wall is one designed to resist both dead and live vertical loads (load
bearing wall) plus lateral loads due to either wind or seismic forces. The codes then
require rebar in both directions. For instance in Seismic Zones 3 and 4, the minimum
horizontal and vertical reinforcement is #4 rebar spaced 48 in. on center, 144 at the base
and top of wall, 144 at all floor levels, and 1-#4 jamb, sill, and head bars at openings.
Lateral load requirements will usually govern the amount of rebar required, normally much
more than the code minimums.
Q12: Is rebar the only reinforcing steel used in masonry?
A:
No, steel wire manufactured in a ladder or truss configuration, or expanded metal lath, is
placed in the 3/8-in. horizontal mortar joint, whereas rebar is within fully grouted cells
or fully grouted bond beam units. Special truss or ladder configurations, wire ties, or
metal straps are also used to hold a multi-wythe wall together.
Q13: How is masonry reinforcing (rebar) furnished to the jobsite?
A:
In a similar manner as the rebar for cast-in place concrete, that is, by means of a supply
contract between the fabricator and either the general contractor or the masonry
subcontractor. The contract should be specific with regard to the requirements for
detailing, that is, it should spell out whether open or closed end block is specified,
whether high- lift or low-lift grouting techniques will be used, and whether or not
complete placing drawings are to be furnished.
Q14: How are masonry walls detailed?
A:
Detailing procedures vary from region to region, but in general, masonry walls are
detailed in a similar manner as concrete walls (refer to Question 13). Figure 11
illustrates a placing drawing for a masonry wall in a seismic zone using open end block
and high-lift grouting techniques. Figure 12 illustrates a placing drawing for a masonry
wall constructed with closed end block and low-lift grouting procedure. However, it must
be noted that some masonry contractors purchase the rebar in stock lengths, preferring to
cut and place the rebar as the mason lays up the CMU.
Q15: What is meant by
"low-lift" and "high lift" grouting?
A:
These terms are decreasing in use as both designers and contractors realize the practical
and economical feasibility of building masonry walls in floor height (or higher)
increments. Generally, "low-lift" procedures limited the height of laid-up CMU
to 4 feet, but it is hard to envision how a cavity of that height can be cleaned without a
clean-out opening. "High-lift" grouting requires a cleanout opening of
sufficient size to remove mortar drippings and other debris at the bottom of all cavities
to be grouted. Fluid consistency grout is placed in all cavities with reinforcing bars and
any other cells required to be grouted, and then consolidated with a vibrator. Generally,
grout is placed in successive 4-foot lifts to allow better consolidation procedures.
