The Bachelor Enlisted Men Quarters at Henderson Hall consist of a two
level parking garage and a multi-story barracks and dining facility. The
configuration of the total structure is such that the North Building and South
Building enclose a central plaza which is located directly above the garage.
The structural framing of the garage consists of a reinforced concrete
slab, beam and column system. The barracks structural system consists of
precast prestressed concrete hollow core planks supported on bearing concrete
masonry unit walls. Cantilevered beams (out lookers) support the balcony
slabs. These beams were poured integrally with the exterior columns. Precast
concrete panels 5' -9" high and with thickness varying from 4" to 6 l/2"
constitute the handrails which are supported by the outlookers. The handrails
are connected to the outlookers by two steel angles welded to plates which are
anchored to both the handrails and outlookers by steel studs.
An extensive test program was initiated which included:
Concrete cores were taken from the damaged beams and were subjected to
compressive tests. The dimensions of the cores are as follows: Diameter:
3.7 "; Height 7.4"; Area: 1O.75 sq. inches. It was found that the T-day
compressive strength was approximately 4,600 psi which exceeded the design
stress of 4,000 psi. The steel of #3 stirrups was tested with results
exceeding 100,000 psi.
Compressive strength tests were performed on the structural members by
using the rebound (Swiss) hammer. The average compressive strength was
approximately equal to 4,000 psi. Core tests, however, demonstrated
compressive strength greater than 4,000 psi.
The outlookers were measured to be 2 5/8" longer than the construction
drawings required. Even though this increase in length of the outlookers
results in overstressing of the tensile reinforcement, it is not related to
the subject failure.
The exact location of the stirrups in the outlookers was found by using a
reinforcement locator (Magnetometer). Some of the stirrups were not located
in accordance with the construction drawings. However, this condition did not
reduce the loading capacity of the outlookers.
The welds at the connections between the outlookers and the handrails were
visually inspected. Magnetic Particle Inspection (MT) or Dye Penetrant
Inspection (PT) were recommended for some suspect welds.
Computations demonstrated that the tensile reinforcement is slightly
overstressed while the web reinforcement does not meet the applicable ACI
Code. The Code allows a waiver under the condition of performing a strength
evaluation (Load Test).