Project Links
Ahwahnee Comprehensive Rehabilitation Plan Implementation: Seismic Improvements
Yosemite National Park » Ahwahnee Comprehensive Rehabilitation Plan Implementation: Seismic Improvements » Document List
JUSTIFICATION: The Ahwahnee seismic upgrades is an action being implemented as part of the Ahwahnee . The majority of the seismic construction will be completed concurrently with the kitchen floor project.
SCOPE:
This project will provide structural seismic retrofits to comply with current seismic safety standards for existing federal buildings. Yosemite National Park is located within the influence zone of several seismic fault systems. The soils underneath the hotel exhibit characteristics that have potential for liquefaction during a seismic event. Based on recent engineering investigations, the hotel does not comply with Federal Emergency Management Agency (FEMA) ICSSC RP-6 criteria for life safety and collapse prevention during 500-year and 2,500-year seismic events. The scope of seismic strengthening work documented in the 2011 CRP is as follows:
- Brace Dining Room in N/S Direction
- Brace Dining Room in E/W Direction
- Interconnect Dining Room Stone Columns
- Reinforce Hotel Stone Chimneys
- Brace Two-Story Tall Gypsum Block Walls
- Replace Deteriorated Floor Slab at Kitchen
- Brace Entry Walkway and Porte Cochere
- Exterior Granite Veneer Anchorage
- Anchoring of Major Equipment
- Reinforce Cottage Chimneys
- Snow Load Strengthening of Dining Room Roof
- Expand Snowmelt and Retention at Dining Room Roof
- Rehabilitate Historic Doors and Windows at Dining Room
- Partial—Replace Glazing to Meet Seismic Requirements
- Rehabilitate Historic Doors and Windows at Ground Floor
- Partial—Replace Glazing to Meet Seismic Requirements at Solarium
- Rehabilitate concrete patio terrace
- Replace non-historic windows in main hotel guest rooms
The park has identified one item during the current design process that was considered but dismissed during the 2011 plan but is now being recommended by the design team. Another item was determined that it needed an expansion of the scope to achieve optimal results. These actions would not result in additional impacts to the building than analyzed in the 2011 CRP and all work would be concealed and not visible from the significant spaces in the building. The justification for this work is included in enclosure 2 and is summarized as follows:
South Wing (Solarium) Shear Walls - The 2011 CRP alternatives considered and dismissed construction of shear walls at the building core and the South Wing . The CRP assumed that the floors were a rigid diaphragm, which is not the case. In response, the current design reintroduces construction of concrete shear walls at the South Wing (between the Lounge and Mural Room and the Lounge and the Winter Club Room), but not at the building core. This would not add thickness to the wall and would provide necessary strengthening. The existing walls are plain plaster over gypsum block walls with a void behind most of this wall except adjacent to the fireplaces in the two small rooms. This is a relatively easy wall to strengthen and no irreplaceable historic fabric is destroyed.
Great Lounge Bracing on East and West Walls - The 2011 CRP selected action included bracing on the north and south ends of the Great Lounge. During the design effort, it was discovered that additional bracing is needed to achieve the required strengthening. This work involves minimal removal of plaster finish in horizontal strips between the glazed sections of the wall in order to install steel strap. Structural steel would be completely concealed by finished work.
SCOPE:
This project will provide structural seismic retrofits to comply with current seismic safety standards for existing federal buildings. Yosemite National Park is located within the influence zone of several seismic fault systems. The soils underneath the hotel exhibit characteristics that have potential for liquefaction during a seismic event. Based on recent engineering investigations, the hotel does not comply with Federal Emergency Management Agency (FEMA) ICSSC RP-6 criteria for life safety and collapse prevention during 500-year and 2,500-year seismic events. The scope of seismic strengthening work documented in the 2011 CRP is as follows:
- Brace Dining Room in N/S Direction
- Brace Dining Room in E/W Direction
- Interconnect Dining Room Stone Columns
- Reinforce Hotel Stone Chimneys
- Brace Two-Story Tall Gypsum Block Walls
- Replace Deteriorated Floor Slab at Kitchen
- Brace Entry Walkway and Porte Cochere
- Exterior Granite Veneer Anchorage
- Anchoring of Major Equipment
- Reinforce Cottage Chimneys
- Snow Load Strengthening of Dining Room Roof
- Expand Snowmelt and Retention at Dining Room Roof
- Rehabilitate Historic Doors and Windows at Dining Room
- Partial—Replace Glazing to Meet Seismic Requirements
- Rehabilitate Historic Doors and Windows at Ground Floor
- Partial—Replace Glazing to Meet Seismic Requirements at Solarium
- Rehabilitate concrete patio terrace
- Replace non-historic windows in main hotel guest rooms
The park has identified one item during the current design process that was considered but dismissed during the 2011 plan but is now being recommended by the design team. Another item was determined that it needed an expansion of the scope to achieve optimal results. These actions would not result in additional impacts to the building than analyzed in the 2011 CRP and all work would be concealed and not visible from the significant spaces in the building. The justification for this work is included in enclosure 2 and is summarized as follows:
South Wing (Solarium) Shear Walls - The 2011 CRP alternatives considered and dismissed construction of shear walls at the building core and the South Wing . The CRP assumed that the floors were a rigid diaphragm, which is not the case. In response, the current design reintroduces construction of concrete shear walls at the South Wing (between the Lounge and Mural Room and the Lounge and the Winter Club Room), but not at the building core. This would not add thickness to the wall and would provide necessary strengthening. The existing walls are plain plaster over gypsum block walls with a void behind most of this wall except adjacent to the fireplaces in the two small rooms. This is a relatively easy wall to strengthen and no irreplaceable historic fabric is destroyed.
Great Lounge Bracing on East and West Walls - The 2011 CRP selected action included bracing on the north and south ends of the Great Lounge. During the design effort, it was discovered that additional bracing is needed to achieve the required strengthening. This work involves minimal removal of plaster finish in horizontal strips between the glazed sections of the wall in order to install steel strap. Structural steel would be completely concealed by finished work.