Page 452 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.3

Construction cost Expansion joints
Construction quality control Fire resistance
Construction technique Maintenance
Control joints Radiation shielding
Corrosion Restoration
Cracked, warped, or chipped units Staining
Deflection Strength during construction or in service
Demolition Volume change
Dimensional tolerance Water, heat, or sound transfer or absorption
Durability Workmanship

Masonry falls off a building facade somewhere in the United States about every three
weeks. In the decade, or so, prior to 1999 at least 49 such masonry failures killed 30 people
and injured over 80 in the United States. The failures occurred under normal loading condi-
tions, not during construction, and the buildings were not subject to earthquake, hurricane,
tornado, fire, blast, collision, or demolition.
It has been the author’s experience with hundreds of masonry failures that the primary
cause of failure was design error or omission in about 50 percent of cases, construction
error or omission in about 25 percent of cases, and inadequate materials in about 15 percent
of cases. The owner’s failure to mitigate damage by proper maintenance was the primary
cause in about 10 percent of cases.
Although masonry has the richest history and tradition of all building trades, modern
masonry construction is subject to a myriad of problems due to relatively recent changes in
the way masonry is used in structures. The use of masonry as a veneer attached to other dis-
similar materials has introduced detailing problems that continue to reveal themselves
through failures as buildings constructed in the past several decades age. 11
Only an experienced engineer who is supported by a wide array of other experts and lab-
oratory facilities should investigate masonry failures. Site visits are required to define the
problem, collect data, and conduct tests. Document discovery, interviews with persons
involved with the failure, literature searches, and perhaps chemical and physical research
can provide information to supplement that obtained by site visits. Reports to the client can
be used as a basis for solving an anticipated problem or settling a claim. When that is not
possible, arbitration, mediation, or litigation often results, which may involve depositions,
court testimony, and preparation of exhibits by expert.

STRUCTURAL ENGINEERING PROPERTIES

Incorrect assumptions about wall weight can result in a multiplicity of design errors involv-
ing structure, acoustics, and heating, ventilating, and air conditioning (HVAC) systems. An
increase in wall weight can provide increased resistance to fire, sound transmission, and roof
uplift as well as reduced air conditioning costs and can contribute to passive solar heating
and cooling. The compressive strength of masonry is affected by the strength and size of
masonry units, mortar strength, mortar joint thickness, workmanship, moisture content, and
exposure to freezing. Compressive strength and modulus of elasticity of masonry constructed
since the mid-twentieth century are typically much greater than the building code–assumed
values. Shear strength increases with compressive stress. As long as mortar remains plastic,
an increase in the water-cement ratio increases the bond strength of mortar to masonry units.