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 CASE S3 - Anchorage Failure of Wall Panels, M. Yachnis
Problem:
Movement of precast concrete panels attached to the structural
members.
Symptoms: After a few days of rain, accompanied by freezing temperatures,
joints between the wall precast concrete panels opened up and the panels had
moved outwards from their vertical position.
Collection of Facts: In July of 1975, the Chesapeake Division of the Naval
Facilities Engineering Command (CHESNAVFAC) assisted by Code 04B, NAVFACHQ
performed an engineering investigation of a potentially hazardous situation,
It had been noted that some of the concrete exterior wall panels on Buildings
7 and 8 of the National Naval Medical Center, Bethesda, MD were misaligned and
that the cause of their movement must be determined in order to prevent
further deterioration of their condition.
The study uncovered several factors which contributed to the movement of
the panels. In the original design, there was no adequate provision for the
expansion of individual panels due to temperature change. Contraction and
expansion of the panels caused the mortar joints between the panels to fail,
allowing water to seep in. The expansion of this water upon freezing forced
the panels to move outward to such a degree that some of the panel anchors
failed, leaving the panels offset by as much as 2 inches (Figure 5). In other
places, the l/8 inch wire panel anchors rusted through. In addition, it was
discovered that many of the wire anchors had never been used at all. The
possibility of these panels falling from the building posed a serious threat
to the lives of pedestrians below.
It was estimated that the cost of replacing the existing panels with new
ones was $1.5 million. However, NAVTAC and the Officer in Charge of
Construction, Bethesda, MD, arrived at an alternative solution resulting in
nearly $1 million in savings. The purpose of this case history is to describe
the unique system of chemical anchoring used to repair these buildings, and to
examine the feasibility of using this system for other engineering
applications.
Fig. 5
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