B08_Attach 3 Report 3_Assessment of Structural Stone at Steel Visitor Center.pdf

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November 21, 2019

Mr. David W. Ziemer Phone: 907-360-1204 Senior Associate Email: dziemer@rimarchitects.com RIM Architects 645 G Street, Suite 400 Anchorage, Alaska 99501

RE: Assessment of the Structural Stone at Steel Visitor Center at Crater Lake National Park in Crater Lake, Oregon

Dear Mr. Ziemer, On September 30, 2019 Jensen Hughes (JH) performed nondestructive testing (NDT) services at the Steel Visitor Center at Crater Lake National Park, Munson Valley District, Oregon. JH performed NDT of the exterior stone walls using ground penetrating radar (GPR) between multiple sets of windows from grade to the building’s roof. RIM Architects require information on the construction of the stone walls from NDT to develop methods for seismic upgrades, and the construction of the exterior stone walls was unknown. This report presents our findings from the non-destructive testing performed on the exterior stone wall of the Steel Visitor Center using GPR.

SITE BACKGROUND

The structure is a two-story wood-framed building with a crawlspace and partial basement. The exterior walls of the building are constructed of stone masonry predominantly finished on the exterior with large natural stones and wood trim. (Photograph 1)

As documented in the Historic Structure Report, the building was constructed in 1932 as a Ranger

Dormitory for Crater Lake National Park staff. Additional construction took place from 1933-1935 to address deficiencies in the original construction and to complete landscaping around the building. The building was rehabilitated in 1985-86 to serve as a visitor contact station.

Assessment of the Structural Stone at Steel Visitor Center at Crater Lake National Park in Crater Lake, Oregon PAGE 2 OF 8

JENSEN HUGHES

Photograph 1 – East (front) elevation

SCOPE OF WORK

As shown on architectural drawings provided by RIM Architects, the existing stone walls are load bearing and constructed with concrete, mortar and stones. The walls are wider at the base and narrower at the top and have an average thickness of approximately 18 inches. The purpose of the NDT investigation was to establish the thickness of the stones comprising the exterior walls.

Individual stones were assessed at three (3) locations identified by RIM Architects on the west side of the Visitor Center using GPR. Individual stones at Location A, Location B, and Location

C were assessed using GPR as-buit stone wall thickness conditions. (Photograph 2)

Steel Visitor Center at Crater Lake National Park in Crater Lake, Oregon PAGE 3 OF 8

Photograph 2 – West (rear) elevation annotated

Proper use of GPR technology for material thickness measurement requires condition-specific calibration to enhance accuracy and reliability. Therefore, JH collected calibrated the GPR instrumnent using hand-measurable sections of the stone wall’s cross-section along window openings. Although the measured stones exhibited varying densities, the calibration factor used consistent among the different stones observed. However, due to natural inclusions and other unique features contained in the stones, not all stones were measurable through GPR.

The mortar beds surrounding the natural stones, and the presence of materials and/or voids behind the outermost observed stone layer were not assessed through GPR. Therefore, the GPR data presented in this report is limited to the material thickness of the outermost observed stones.

Our scope of work did not include assessment of the quality of the wall construction.

INVESTIGATION FINDINGS

Location A

Photograph 3 below presents the minimum and maximum stone thickness values determined according to GPR for each outermost observed stone for Location A. The total average thickness of the individually measured stones for Location A is 10.5 inches. The stones observed at or near grade level appear to be more rounded and natural in shape, compared to the stones at the top of the wall, which showed evidence of being mechanically shaped and squared. Stones annotated with “N/A” (not applicable) visually appeared porous in nature and/or contained cracks and natural cleavages (discontinuities) within the stone. The porosity and natural discontinuities of these stones resulted in weak and unreliable GPR signals.

Location C Location B Location A

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Photograph 3 – Location A, Minimum and Maximum Thickness Values (inches)

Visual observation of the exposed stone at the window jambs along the north and south window openings of location A indicate the exterior stone wall is composed of multiple stone wythes or courses of stones as depicted in Photographs 4 and 5. Locations depicted in Photographs 4 and

5 were subsequently used for general GPR calibration.

Photograph 4

Photograph 5

Photograph 4 Photograph 5

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JENSEN HUGHES

Location B

Photograph 6 below presents the minimum and maximum stone thickness values determined according to GPR for each outermost observed stone for Location B. The total average thickness of the individually measured stones for Location B is 11.5 inches. A stone and mortar infill at a vent location was observed within Location B.

Photograph 6 - Location B, Minimum and Maximum Thickness Values (inches)

Location C

Photograph 7 below presents the minimum and maximum stone thickness values determined according to GPR for each outermost observed stone for Location C. The total average thickness of the individually measured stones for Location C is 14 inches. The stone and mortar infill at the door, window and stairwell location was observed within Location C.

Infill Vent

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Photograph 7 - Location C, Minimum and Maximum Thickness Values (inches)

Exposed stones at the north window jambs and along the base of the wall indicate the exterior stone wall is composed of stones of varying thickness and varying wythes or courses of stone across the height of the wall as shown in Photographs 8 and 9. These locations were subsequently used for general GPR calibration.

Photograph 8

Photograph 9

Historic Images

A literature review of the nearby structures that were constructed in the same architectural style and era as the Steel Visitor’s Center (originally the Ranger’s Dormitory or Club House) was done to further support and confirm the NDT findings. As manager of the field construction in the

Infill

Photograph 8

Photograph 9

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JENSEN HUGHES

Munson Valley District in 1932, Sager oversaw the design and construction effort of the

Superintendent’s Residence, Naturalist's Residence and the Ranger Dormitory. The building process for these structures was described in Tweed, Soullier, and Law's study "National Park

Service Rustic Architecture, 1916-1942,":

"...First, a wooden formwork outlining the interior surface of the outside walls was erected atop a concrete and stone foundation. This form was sufficiently sturdy to support the frame of the second floor roof gable. While the second floor was being constructed, work went forward on the masonry walls. One by one, massive boulders weighing hundreds of pounds each were lifted into place, leaving a space of a few inches between the back of the stone and the wooden formwork. This space was filled with concrete. After the masonry had been completed, the interior form was removed, leaving behind a smooth interior concrete wall finish with nailing strips embedded within it. When the interior formwork was removed the weight of the second story and roof was transferred to the masonry walls.1

The construction process outlined indicates that the exterior walls are load-bearing in that the composite stone and concrete walls support the roof and upper floors. The placement of the rough stones facing towards the wood formwork2 further created a cavity for the concrete backfill, which has a varying degrees of thickness through the full height of the wall. The description of concrete backfill and stone-laying technique is supported by visual observations from the field as well as detailing from architectural drawings supplied by RIM Architects. Historic photos of the

Superintendent’s Residence Building in Munson Valley District provide an example of the construction process employed for this building. (Figures 1 and 2)

Figure 1 – Construction of the

Superintendents Residence, 1932 (Source:

Crater Lake Institute)

Figure 2 - Construction of the

Superintendents Residence, 1932

(Source: Crater Lake Institute)

CONCLUSIONS

1 William C. Tweed, Laura Soullier, Henry G. Law, "National Park Service Rustic Architecture, 1916- 1942," National Park Service, Western Regional Office, Division of Cultural Resource Management, February 1977, 66-68.

2 "Specifications for a Superintendent's Residence and a Naturalist's Residence at Crater Lake National Park," July 6, 1932, Central Classified Files, 1907-49, RG 79, NA, pp. 1-2, 4

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JENSEN HUGHES

The GPR investigation showed that the walls were built of single and multiple courses, or layers of natural stones of varying thickness. Based on visual observations, literature and historic photo review, and the information collected through NDT, the stone walls were constructed employing a variety of stone thicknesses along the full height of the exterior walls. The walls were constructed using either a single or multiple courses of stone and mortar with a concrete backfill.

We appreciate the opportunity to assist RIM Architects on this project. Should you have any questions or require additional information, please do not hesitate to call.

Sincerely, Stephen Stacey, PE (Illinois) Marjorie Lynch

Civil Engineer Senior Engineer

SStacey@JensenHughes.com mlynch@jensenhughes.com mailto:SStacey@JensenHughes.com