Menokin: Structural Stabilization and Assessment · grouting, shoring of the basement window lintel with concrete block, and the placement of crack monitors at various locations (Photo

Menokin, Richmond County, Virginia February 17, 2004 Robert Silman Associates, PLLC Structural Narrative

Menokin:

Structural Stabilization and Assessment

Richmond County, Virginia

Prepared for:

John Milner Associates, Inc. 5250 Cherokee Avenue

Suite 300 Alexandria, VA 22312

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Structural Narrative The ruins of Menokin present building fabric dating back to circa 1769. The majority of the house structure is currently collapsed, with much of the material apparently lying largely within the footprint of the original structure. A protective enclosure was constructed approximately two years ago, which spans over the ruins and provides protection from direct rain and snow from above; the sides remain open and result in some continued exposure to the environment, particularly around the perimeter. Included amongst the structure that remains standing are the two main chimney stacks, the southwest and northeast corner walls, and some wood framing of the roof, second and first floors at the northeast corner. The objective of this evaluation is to provide structural recommendations for stabilization and safety during the removal of debris and historic fabric. The following narrative is based upon on-site observations from visit on September 26, 2003. Visual observations were made from the ground, the existing access platforms, and from a lift. SOUTHEAST QUADRANT Existing Conditions Masonry Walls The south and east foundation walls are currently buried beneath a pile of stone masonry from the collapsed walls of the floors above; thus, these walls could not be observed at this time. The north end of this quadrant is defined by the brick masonry mass of the east chimney and dividing wall. The west side of this quadrant is defined by a brick basement wall with an opening into the central north-south hall. The opening is spanned on the west side of the wall by a wood lintel which exhibits significant deflection, but appears intact (Photo 1); the east side of this wall appears to have previously had a similar wood lintel, however this element is now missing and significant portions of masonry are rotating toward the debris of the southeast corner (Photo 2). Debris is currently leaning against this wall. Though the weight of collapsed debris may have been part of the reason for the east lintel failure, this same debris may in part be supporting this portion of masonry. Problematic to debris removal in the southeast corner is the remaining portion of the first floor brick masonry wall dividing the living room and the bedroom (room names as indicated in the 1940 HABS drawings). This wall presents a large vertical crack, significant brick deterioration or disassembly at the first floor level, and large displacements

Photo 1: Deflected Lintel west of SE Quadrant

Photo 2: Masonry opening west of SE Quadrant – North End Bearing

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both in and out of the plane of the wall. Though this wall is not supporting any loads above, it does represent a significant weight that is in an unstable condition (Photos 3 & 4). Fireplace and Chimney Masonry The east chimney stack presents a Flemish Bond brick above the roof level, transitioning to English Bond below the roof within the interior. The masonry structures appear relatively intact and stable, however there are localized areas of masonry deterioration or minor instability. One such area is where there are missing or deteriorated wood nailers (wood members built into the masonry, replacing the interior wythe of brick and serving as a nailable surface on the masonry wall), however, the frequency of header courses minimize the negative effects of these conditions in the overall structural behavior. The difference in color of the exterior brick, relative to the interior, may be a reflection of the long term environmental exposure, however, the quality of the once interior brick below the roof line should be considered with regard to the future exposure (exterior brick is often of a higher quality to assure greater resistance, so the lesser quality interior brick may be more susceptible to deterioration). Fireplace openings are typically created by segmental arches with a narrow iron lintel supporting one wythe of infill brick below. No major rusting of the iron elements was observed, however some long term protection should be implemented so as to avoid rusting and deterioration of the surrounding masonry, particularly at the lintel bearings. The east chimney includes an offset above the attic floor level; the corbelled brick appears to be somewhat compromised and the effects of this eccentric offset need to be evaluated in the overall stability of the masonry structure (Photos 5 & 6). Structural Guidelines for Debris and Fabric Removal This is the first area of proposed material removal. Of the four quadrants, this is most readily accessible from the ground, which should allow for workers and archeologists to walk in and perform some removals by hand, or as otherwise devised by the contractor and consulting team. With regard to safety and structural stability, there are three primary areas of concern with the performance of this work: the west

Photo 3: First Floor Wall Cracking and Displacment

Photo 4: First Floor Wall Deterioration and Disassembly

Photo 5: East Chimney – Upper South Face

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basement wall below the living room (as indicated in the 1940 HABS drawings), the remaining portion of the first floor brick masonry wall dividing the living room and bedroom, and the east chimney, as listed below: • We recommend shoring the lintel and spanning masonry

of the west basement wall prior to removal of the debris in the southeast quadrant (See Photos 1 & 2). Simple timber posts supporting a new wood lintel should suffice to support this load. Some localized debris removal will be required to clear a space down to the floor level below the wall opening to create a sound bearing condition for the temporary shoring. Temporary Shoring Sketch SE-01 indicates the design implemented during the first phase of work.

• The first floor brick masonry wall which divides the living room and bed room will require temporary shoring, both in and out of the plane of the wall, prior to commencement of debris removal. Diagonal bracing elements which connect to the existing wood platform frame can serve to sandwich the existing wall in place and provide stability to potential lateral movements. Temporary Shoring Sketch SE-02 indicates the design implemented during the first phase of work.

• The east chimney was analyzed for temporary stability within the existing configuration. Our analysis found there to be sufficient masonry to resist the required lateral loads, given the level of bracing and projected minimal impact of the Phase One work at the southeast quadrant. Further consideration would need to be given with respect to the projected work in the northeast quadrant.

Photo 6: East Chimney – Base of South Face

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Temporary Shoring Sketch SE-01

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Temporary Shoring Sketch SE-02

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SOUTHWEST QUADRANT Existing Conditions Masonry Walls The remaining exterior masonry walls at the southwest corner are in poor condition, with substantial cracking and areas of bulging or displaced masonry. The rubble stone foundation wall presents substantially deteriorated mortar joints. There is evidence of previous efforts to stabilize and monitor the condition of these walls, including mortar replacement or grouting, shoring of the basement window lintel with concrete block, and the placement of crack monitors at various locations (Photo 7). Minimal ties exist between the walls and the temporary wood platform within (Photo 8). There are significant amounts of debris on the interior face of these walls, which are likely exerting outward forces on the walls. The west wall exhibits lateral displacement at its base, likely due to the debris pressures. The roughly cut vertical profile of free north edge of the west wall also presents some corbelled masonry that does not have substantial masonry weight to serve as a counterbalance. The south wall also presents outward bulging of its base, particularly below the first floor window. The basement area of this quadrant contains a brick masonry barrel vault that apparently served as the wine cellar (Photo 9). Viewed from a limited access area from the corridor to the east, the barrel vault appears to have maintained its structural form; however, closer evaluation will be required once the debris is removed and access to the wine cellar is gained. The 1940 HABS drawings indicate that there is a small space between the south wall of the wine cellar and the south exterior wall. This area is likely filled with debris and is a potential area where water and rotting material will collect and cause accelerated deterioration to the surrounding structure. Fireplace and Chimney Masonry The west chimney stack, similar to the east, presents a

Photo 7: Southwest Corner

Photo 8: South Wall

Photo 9: Basement Vault

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Flemish Bond brick above the roof level, transitioning to English Bond below the roof within the interior. The masonry structures appear relatively intact and stable, however there are localized areas of masonry deterioration or minor instability. One such area is where there are missing or deteriorated wood nailers (wood members built into the masonry, replacing the interior wythe of brick and serving as a nailable surface on the masonry wall), however, the frequency of header courses minimize the negative effects of these conditions in the overall structural behavior. The difference in color of the exterior brick, relative to the interior, may be a reflection of the long term environmental exposure, however, the quality of the once interior brick below the roof line should be considered with regard to the future exposure (exterior brick is often of a higher quality to assure greater resistance, so the lesser quality interior brick may be more susceptible to deterioration – Photo 10). Fireplace openings are typically created by segmental arches with a narrow iron lintel supporting one wythe of infill brick below. No major rusting of the iron elements was observed, however some long term protection should be implemented so as to avoid rusting and deterioration of the surrounding masonry, particularly at the lintel bearings. The west chimney does not present the same offset as the east, but does have some apparent stability issues relating to brick deterioration or disassembly at the first floor level on the south side (Photo 11). That portions of the current access platform are being supported on this south side presents a potentially unstable condition, wherein the platform support may be compromised, or, the platform may in fact now be serving to brace the mass of the chimney (Photo 12). Structural Guidelines for Debris and Fabric Removal • Bracing of south and west walls. Temporary Shoring

Sketch SW-1 indicates a typical approach to implementing lateral bracing. Two lines of continuous beam bracing run horizontally along the top and approximate midheight of walls, spanning between the frames. (4) new frames total. Assume (4) additional 6x6 posts to “sandwich” walls. Top of frames must extend over wall and connect to second floor of existing observation platform. See also Temporary Shoring Sketches SW-2 and SW-3.

Photo 10: West Chimney –South Face Brick Deterioration

Photo 11: West Chimney – Base of South Face

Photo 12: West Chimney – Platform Support on South Face

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• Shoring within windows to support existing lintels on south wall.

• Placement of short 6x6 post shores at base of west chimney onto soundly bearing sill plates. Provide for lateral tie-back of new post shores to assure stability.

• (2) new 4x4 posts at SW and NW corners of west chimney to support perimeter bracing and diagonal struts tying into the second floor level of the observation platform.

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Temporary Shoring Sketch SW-01

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Temporary Shoring Plan SW-02

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Temporary Shoring Plan SW-03

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NORTHWEST QUADRANT Existing Conditions Existing structure is largely collapsed. Some stones of the existing north and west foundation walls are apparently being partially retained by the mass of the debris. Structural Guidelines for Debris and Fabric Removal • Remove debris in concert with removal of loose or

unstable stones of the north foundation wall. • Maintain or re-establish as required the support conditions

for the existing observation platform. • Introduce west chimney bracing as part of work described

for Southwest Quadrant. • Debris removal will facilitate access to the Northeast

Quadrant from the basement level. NORTHEAST QUADRANT Existing Conditions This quadrant retains the largest percentage of original wood framing that is still in its original configuration. Though there is significant amounts of shoring already in place, we do recommend implementing some additional shoring or bracing to assure a greater level of security and stability during the removal of materials. The exterior masonry of the northeast corner appears relatively stable, with some isolated areas of apparent instability at the disassembled wall edges and at the basement and second floor window openings. Structural Guidelines for Debris and Fabric Removal • Provide lateral bracing between existing posts which

support the northeast hip beam and the main rafter girder along the north face of the east chimney (Temporary Shoring Plans NE-1).

• Provide (2) 4x4 posts to support new (2) 2x6 roof beam serving to support existing roof rafter west of the hip beam. New posts bear on existing wood shoring beams. Provide diagonal bracing to stabilize tops of new posts

Photo 13: Northwest Quadrant

Photo 14: Northeast Roof Framing w/ Temporary support of hip and

rafter girder.

Photo 15: Unsupported Studs

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(Temporary Shoring Plans NE-1). • Secure suspended studs at west wall of Northeast

Quadrant. Provide additional hanging straps to each stud and provide support at base of studs with new spanning “sill-type” member or tying to an existing member.

• Shore existing lintels within basement window and second floor window on North Façade.

• Provide 4x4 post shores for corbelling stones at north side of east entrance. Bear one post on existing masonry wall and one post on existing wood platform. Tie posts together with 2x4 members top and bottom with galvanized gage metal straps as “X”-bracing (Temporary Shoring NE-2).

• Introduce posts and diagonal bracing of chimney from Southeast Quadrant (see Temporary Shoring NE-2 and SW-3).

• New “X”-bracing along east side of central platform corridor, linking top and bottom levels between existing posts (see Temporary Shoring NE-2 and SW-3).

Photo 16: East Elevation at Northeast Quadrant

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Temporary Shoring Plans NE-1

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Temporary Shoring Elevation NE-2

Documents

Menokin: Structural Stabilization and Assessment · grouting, shoring of the basement window lintel with concrete block, and the placement of crack monitors at various locations (Photo