Page 490 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.35

Construction Failures
Workmanship. Mistakes in masonry construction include the following:
• Unfilled mortar joints weaken walls and increase water permeance.
• Improper mortar batching usually results in cement deficiency and color variation.
• After cracked or chipped brick is placed in the wall, the manufacturer is no longer responsible.
• The absence of flashing, flashing without end dams, and misplaced or unsealed flashing
contribute to water leakage.
• Bridged expansion joints cause cracks.
• Improper shimming of shelf angles causes cracks (see Fig. 13.21).
• Discontinuity of shelf angles at external corners causes cracks (see Fig. 13.20).
• Strength of reinforced masonry is reduced and corrosion is promoted by voids in grouted
spaces or by substitution of concrete for grout.
• Juxtaposition of stainless steel and mild steel may cause corrosion.
• Misplaced or missing reinforcement weakens masonry.
• Mortar droppings in cavities 2 in (50 mm) and wider can cause walls to leak and can be
avoided. Mortar droppings in cavities less than 2 in (50 mm) wide can be expected.

Construction Tolerances. Masonry construction tolerance problems concern three
issues: structural integrity, aesthetic tastes, and incompatibility of construction tolerances
for masonry supported on structural frames.
It is often difficult but important in establishing fault to determine whether masonry that
is now out of position was misplaced or displaced.
Aesthetic construction tolerances involve vertical alignment of head joints, mortar joint
thickness variation, and out-of-wall plane alignment of masonry units. Figure 13.33 depicts
the aesthetic problem. Statistical data on such tolerances are available, 19 and the MSJC
Building Code Requirements and Specification for Masonry Structures contains prescrip-
tive tolerances. These tolerances should also be referenced in construction documents.
Construction tolerances for structural frames of steel or concrete are much more liberal
than those for masonry. Such difficulties should be recognized during design where they can
be solved much more economically. If not, the contractor should ask for a clarification prior
to construction. Advanced theories of architectural tectonics notwithstanding, two solids
cannot occupy the same space at the same time.
Mason Productivity. Brick may be specified by allowance. That is, the contractor
includes in the bid a specified unit price for purchase of brick, which is subsequently
selected by the architect. The contractor assumes that a local brick of usual characteristics
will be selected. Instead, the architect selects a foreign brick of unusual characteristics,
which causes an unanticipated reduction in mason productivity. The contractor files a
claim. The literature on mason productivity may provide the solution, 12 or productivity
research with specific materials may be indicated.
Temporary Bracing. During a typical month in the United States prior to 1999, falling
walls killed one building construction worker and injured twelve.
Masonry walls under construction that lack the support of floors and roofs sometimes col-
lapse during high-wind events. OSHA requires that employers ensure all masonry walls over
8 ft high are adequately braced to prevent overturning and collapse, but does not provide
requirements for bracing. Since 1999, the Masonry Contractors Association of America has
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published the Standard Practice for Bracing Masonry Walls under Construction with the