Page 504 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.49

In response, another engineering firm conducted a survey of other buildings in the same
city to determine the mortar chloride content. Three mortar specimens were removed from
exterior walls of each of 10 other buildings of various ages, providing a sample of 30 mor-
tar specimens. The sample was sent to the same laboratory that had tested the original seven
mortar specimens.
Seven of the 10 buildings had average estimated mortar chloride contents of 0.2 percent
or more by weight of cement. Sixteen of the 30 mortar specimens had chloride contents of
0.2 percent or more. Based on the lognormal distribution there is better than 50 percent
probability that mortar selected at random from buildings in that city would have a chloride
content of 0.2 percent or more.
Masonry on the 10 buildings has performed adequately for up to half a century with
mortar chloride contents of 0.2 percent or more. The level of chloride in mortar in that case
provided no basis for masonry demolition. A contrary view would require that one-half of
the exterior brick masonry in the city be demolished. 34
In addition, the architect’s design details were found to have contributed to water per-
meance of the exterior walls. Stiff brick masonry veneer was placed over flexible steel
21
studs, which resulted in veneer cracks under coastal winds. Incompatible flashing mate-
rials were juxtaposed, which resulted in their deterioration. Faulty design of flashing and
coping caused leakage of wind-driven rain. Specification for masonry cement mortar
resulted in greater water permeance than would have occurred with portland cement–lime
mortar. 32
It was also alleged that bricklayers did not keep the 1-in (25-mm) airspace between the
masonry and the stud wall clean of mortar droppings, which caused water leaks. The archi-
tect should have known that it is virtually impossible to keep a 1-in (25-mm) airspace clean
of mortar droppings.
As often occurs, the case against the masonry contractor was settled out of court under
a confidentiality agreement, which keeps the settlement conditions secret.

A High-Rise Hotel

In this example, in violation of recommended good practice and the standards of care for
the profession, the architects committed serious design errors and omissions, which the
architects knew or in the exercise of due care should have known would result in cracked
and leaking masonry walls. In violation of law, no provision was made for differential
movement of the masonry and its supporting structure. The architects failed to heed well-
published warnings about failures in the wall system that he chose to use. His design was
improper for base wall flashing and exterior sills. The architect did not require a sufficient
number of vertical expansion joints or weep holes. Flashing was improperly designed, and
other design errors were committed.
Walls were structurally designed to crack, and the cracks admitted wind-driven rain.
The brick masonry veneer/steel stud wall system was introduced and promoted without
adequate research, and the behavior of the system is not generally well understood. Brick
masonry veneer/steel stud construction evolved without either adequate laboratory
research or a sufficient period of field-testing. The current usual design procedure does not
adequately account for the actual behavior of the wall system. The only structural element
holding the masonry on the building is the fine, thin arris of a single thread of an abraded
screw, which is periodically bathed in a salt solution. Corrosion of those screws, due to
water leakage through cracked masonry and due to interstitial condensation, will ultimately
make the wall life-threatening.
A structural analysis was made of exterior walls. Computer printouts of the analysis
were provided. The assumption was made that the masonry wythe was free at the top, as it