Oregon Caves
Historic Structures Report

Structural Observations

Structural System, Observations

The Chateau's structural system is grounded with a reinforced concrete base spanning the gorge at the bottom two floors. With the exception of a crack in the west end of the north wall of the Boiler Room, this foundation appears to be in good order structurally. The main potential structural problem of the Chateau first appears intermittently on the third floor, where there is some lateral displacement of the exterior wall on the west side. The problem becomes much worse just one level up, especially in the north wing of the structure.

The walls are significantly out of plumb in this area. Each individual door jamb and window opening were measured to determine how far out they were. A four foot level was used against trim at these openings, the rationale being that the door and window trim is nailed directly to the dimensional lumber frame of the structure. The wall surfaces and floors were not used, as local variations could have distorted the actual readings. The plans on the following pages (pages 35-38, omitted from on-line edition) represent the direction and distance of the lateral displacement. All dimensions are the variation from plumb in a four foot span, with the direction indicating which way the top of the piece has moved in relation to the bottom. If the piece was within 1/8" of plumb, the measurement was not recorded.

The fourth floor of the north wing is the worst in the building in terms of displacement. In this area, deviations of up to 1-11/16" were found in a four foot vertical span. The north wall of the wing is the worst, leaning generally out to the north and to the west. The interior finishes have been affected very little by this shift in the building, and with the exception of a few doors that have been shaved or do not operate properly, they are in good shape. The puzzling aspect of this discovery is that there are no readily apparent separation points either inside or outside the structure, indicating that the north wing mass is tending to move as a coherent unit.

However, the amount of lean decreases at the next level up. While there are still deviations of up to 7/8" at the fifth floor level, the walls generally become more plumb at this level. At the sixth floor, the building leans predominantly to the west, but only in two locations toward the west end. The fifth floor leans predominantly to the north, primarily in the eastern end. This seems to indicate that the framing at each floor level is shifting independently, and the wing is not moving as a whole.

The capacity of this end of the structure to withstand various loading conditions should be analyzed by a professional engineer. While the deviation from plumb is not affecting the primary finishes, doors are being altered to retain their operability. Keep in mind that this wing of the building was most seriously affected by the 1964 flood, and the damage could have potentially been caused at that time. Careful recording of the building and its movement in this wing may reveal that the building has settled into this position and is moving no farther. This, again, should be done by a professional structural engineer who can determine the severity of the deviation and propose a remedy, if required. The engineer or consultant should have experience working with historic structures, and a working knowledge of the Secretary of the Interior's Standards for Preservation.

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Last Updated: 22-Sep-2001