HomeMy WebLinkAbout012 STRUCTURAL CONDITIONS ASSESSMENT
August 23, 2021
HomeBase Partners
20 North Tracy Avenue
Bozeman, MT 59715
Re: Structural Conditions Assessment – Original Bozeman Deaconess Hospital
15 West Lamme Street, Bozeman, MT
At your request, we performed a general structural conditions assessment and summary report for
the original Bozeman Deaconess Hospital in August of 2020 regarding the structural stability and
code-required stabilization efforts prior to any occupancy of the building. In general, we assessed
the building for life-safety based on the 2018 International Building Code and 2018 International
Existing Building Code (IEBC), which are both adopted by the State of Montana and the City of
Bozeman. In this limited assessment, we based our findings on the structural condition of the
building as well as the seismic, wind and snow loads for the City of Bozeman.
At this time, we understand that the building will remain unoccupied until such time as it can be
demolished to make way for a new building project. We are providing this letter to summarize our
conclusions from the previous report for your convenience.
The recommended repairs in our original report are intended to increase life-safety of the structure
and, in our professional opinion, are critical to re-occupying the building in any fashion. While the
IEBC has allowances in place to recognize that existing buildings have served their purpose for the
current use and occupancy, we feel that the heavy nature of the building and the deterioration of
the upper-level concrete makes it susceptible to failure or severe damage in a design seismic event.
The recommended upgrades are critical to ensure life-safety no matter the future use of the building, and it should not be occupied without these repairs.
Gravity Structural System
The gravity structural system of the building consists of reinforced concrete roof and floor slabs
supported by reinforced concrete beams and columns, and an assumed reinforced concrete
foundation. Exterior walls consist of hollow-clay tile with an exterior brick veneer with no visible
connection to the gravity structural elements.
At the 3rd and 4th floors where the structure was exposed at the interior, we observed significant
defects throughout where concrete had not consolidated at the time of construction or had been
damaged during the life of the building around critical areas in the beams, columns, and slabs, leaving
the rebar exposed. These conditions require significant repair, patching, or new steel reinforcements
to ensure that the integrity of the gravity system be maintained and structural failure does not occur.
Typically, this includes concrete testing and repair systems coupled with significant steel framing
throughout to reinforce or replace concrete members. We were unable to observe the structure at
the 1st and 2nd floors due to finishes, but it was assumed that similar conditions exist at those levels.
At the exterior of the building, we observed water damage at the brick parapets at the roof level
and at the reinforced concrete entry. Damage included missing mortar and loose bricks at the
parapet and exposed rebar with spalling concrete at the front entry feature. Left in their current
state, these elements will be subject to additional freeze-thaw cycles and deterioration with
continued weather exposure. These parapets should be repaired and braced to the building. Lateral Structural System
As discussed in our report, there is no code-recognized lateral force resisting system for this building
that meets current day seismic design according to the 2018 IBC, and Bozeman’s seismic zone D is
considered a high seismic zone. In a design-level earthquake, the current lack of an adequate seismic
force resisting system and the heavy nature of the concrete roof and floors could cause major damage
or failure to the building. The primarily concrete and masonry building is heavy and inflexible, and
results in higher seismic loads with more sudden failures. The wall-to-roof and floor connections are currently not adequate to resist out-of-plane seismic loading, and the risk of the walls separating from
the roof or floors in a seismic event could lead to severe damage.
The brick parapets at the roof level and reinforced concrete entry are also weakened due to water
and freeze-thaw exposure and could easily fall away from the building in a seismic event.
Mountain View Care Center
The Mountain View Care Center (MVCC) is scheduled to be demolished in the coming months. The MVCC was an addition to the original hospital building and originally served as the extended care
facility. When constructed, it appears the new addition was built directly adjacent to the existing
building with its own structure, creating a double wall at the interface. Openings in the original
building exterior wall were created to tie the spaces together and presumably mechanical, electrical,
and plumbing services pass between the buildings. While we have not been able to observe this
condition, we assume these buildings also bear on separate foundation systems given the timing of
their construction. While demolition of MVCC occurs, care must be taken not to undermine or damage the original Bozeman Deaconess building. The existing openings must also be infilled and be weather tight to prevent exposure of the original building to the exterior elements.
Summary
Building on the summary in our original report, an occupancy based, or modification-driven full IBC
upgrade may not be required depending on the scope. However, structural damage and deficiencies
in both the gravity and lateral systems were observed throughout the building and must be
addressed in conjunction with the Building Official and Owner. There are numerous areas that
should be deemed “Dangerous Conditions” by the building official per the IEBC section 1205.2
should any occupancy or use be considered and would be required to be remedied.
Sincerely,
DCI Engineers
Matthew Hubbard, PE, Principal
Enclosure: Original Bozeman Deaconess Hospital – Structural Conditions Assessment
August 26, 2020 Andy Holloran HomeBase Partners 20 North Tracy Avenue Bozeman, MT 59715 Re: Structural Conditions Assessment – Original Bozeman Deaconess Hospital 15 West Lamme Street, Bozeman, MT Dear Andy: At your request, we have performed a general structural conditions assessment for the original Bozeman Deaconess Hospital, located at 15 West Lamme Street in Bozeman, Montana. The purpose of this report is to identify the general structural systems and evaluate the basic life-safety of the building in order to aid the HomeBase in decisions regarding the building’s future use. Our assessment is based on the 2018 International Existing Building Code (IEBC) and the 2018 International Building Code (IBC). The enclosed report details our observations and recommendations. If you have any questions regarding the enclosed report, or if we can be of further assistance, please contact Jami Lorenz at (406) 207-7392. Sincerely, DCI Engineers
Jami Lorenz, PE Principal
Enclosure: Original Bozeman Deaconess Hospital – Structural Conditions Assessment
Original Bozeman Deaconess Hospital – Structural Conditions Assessment
We visited the original Bozeman Deaconess Hospital, located at 15 West Lamme Street on June 17, 2020 and again on August 18, 2020 with the design team. The intent of our visit was to assess the life safety of the building and the required retrofits necessary to repurpose the building for a residential or office use, whether it could adapted for a vertical addition, as well as possible incorporation with an adjacent new office building.
This report both identifies the main structural framing systems of the building and addresses required and recommended structural upgrades for potential future uses. This report is intended to be a high-level, qualitative assessment and does not include specific analysis based on site-specific conditions. This report concerns only the structural components and elements that are an integral part of the
structural load resisting system for the building. Our assessment is based on the 2018 International Existing Building Code (IEBC) and the 2018 International Building Code (IBC).
Figure 1: Bozeman Deaconess Hospital building viewed from Lamme St. Method of Investigation The investigation was based solely on visual observation and limited to structural elements that were exposed to view. No destructive testing was performed during the site visit. At the time of this report, there were also no original building construction documents available to supplement our observations. Our commentary and recommendations are based both on our findings on-site and on our understanding of similar construction methods in Bozeman and during the early 1900s.
PART 1: Building Description and Observed Structural System
The original building was constructed in 1920 with two additions on the east and west sides, added at later times. This report addresses only the original Bozeman Deaconess building and does not address the later additions. The original hospital is a 4-story, ‘L’ shaped building, with wings extending to the north and west of the main entrance. Each level has an approximately 5,500-sf footprint (Appendix A). The roof framing system was seen to be a concrete slab, measured at one location as approximately
6” thick. The roof is supported by interior columns with capitals (Figure 2) as well as by concrete
beams and columns at the exterior walls. While there are some beams running between columns in the interior space, they are randomly located and appear to be secondary structural elements supported primarily by the columns. We observed exposed steel reinforcement in multiple locations (Figure 3).
Due to finishes on the first and second floor, we were only able to observe the primary structure on
the third and fourth floors. Based on our observations, we assume the second, third and fourth floors
are all of similar construction. Each floor is a concrete slab; we were unable to determine the slab thickness or any information about the location and frequency of any slab reinforcement. These floors are supported by a similar column and capitol construction, with concrete beams and columns at the perimeter of the slab. The interior walls at the lower levels are primarily infill walls, assumed to be
wood or steel stud framing. These walls are not bearing elements and have been removed on the
third and fourth levels. The exterior walls appear to be constructed of 4” hollow clay tile infill with a 4” brick masonry veneer (Figure 4). These walls are assumed to be unreinforced as this was the typical construction method for this time period. The foundation walls are cast-in-place concrete extending from grade level to the slab-on-grade located approximately 3’-0” below grade. These are assumed to extend further and likely sit on a strip footing, but we were unable to verify either of these conditions at the time of our visit and without excavation to expose the foundation. As the concrete columns stack on each level and are the primary structural members, the columns are assumed to sit on large concrete spread footings. Due to interior floor slabs and finishes, were unable to verify any concrete footing sizes. Gravity Framing System As noted above, the primary gravity framing system for this structure is cast-in-place concrete slabs supported by concrete columns. Based on the column locations and the sporadic placement of the concrete beams it is likely that the slab acts in two-way bending between columns. The dropped
concrete beams were likely added to support localized structural elements. Additional investigation into the as-built conditions or access to original construction documents would be required to provide a more in-depth assessment or analysis of the existing gravity framing system. Lateral Framing System Typical of buildings constructed at this time, there is no explicit lateral system in this building. Overall, the concrete columns, floor slabs and exterior walls have provided some amount of lateral support for the life of the building. However, the building has never experienced a design-level seismic event per current building codes. The exterior walls constructed of unreinforced brick and hollow clay tile are likely the primary lateral system.
Observed Conditions The building did not appear to have experienced any major structural distress or failures over the life of the building, and the structural elements of the building framing and foundation were observed to
generally be in adequate overall condition. However, on the third and fourth floor it was observed that the structural concrete columns and slabs had significant issues with consolidation around the rebar at the time of construction and/or have deteriorated over time (Figures 3 and 5). These conditions would require significant repair and patching prior to any future occupancy at all locations where they occur. Since the structural elements were not visible on the 1st and 2nd floors, we are assuming for this report that similar issues with consolidation and/or deterioration exist on those levels as well and would require structural retrofit prior to occupancy. The exterior clay tile infill walls were observed to be in marginal condition as well and have missing blocks or broken face shells in many locations (Figure 4). As outlined below, the structural retrofit recommendations require that new attachments to these walls be installed directly to new wood or metal stud wall framing to support the walls for out-of-plane seismic loads, which requires the removal of existing plaster finishes that can damage the face shells of the tiles. The current condition and relative fragile state of these tiles could make this retrofit difficult to install in the field.
Part 2: Proposed Modifications The proposed change in occupancy and potential alteration of this building will be governed by the 2018 International Building Code (IBC) and International Existing Building Code (IEBC). In general, the IEBC allows for minor changes and alterations to structures without upgrading the gravity or
lateral systems to current-day code standards. These allowances are in place to recognize that the building has served its purpose for a similar use and occupancy and performed well in the past. However, there are some very specific triggers in the IEBC that require a building to be brought up to current-day IBC standards. These triggers can include additions, change of use or occupancy, or alterations of the space. The upgrades required by the IEBC are intended to increase life-safety and reduce structural and architectural damage to the building in the event of a design-level earthquake. This can include upgrades for gravity loads (dead, live, and snow) and/or lateral loads (wind and seismic). The following section describes the structural code implications of various proposed modifications. Change of Occupancy The previous occupancy as well as the original design occupancy were both for Hospital/Medical use. The proposed future use is Residential or Office as outlined in the IBC/IEBC. This change in occupancy does not increase live loads on the main floors of the building, and as such, does not trigger occupancy-based structural gravity or lateral upgrades per the IEBC. However, with a renovation project, validation of the existing structure for the code-required live loads for residential or office use would be required. There may be necessary upgrades with the more in-depth analysis should we determine the structure is inadequate for this loading during the design phase. Additionally, utilizing the roof for a roof-top deck or any vertical addition to the top of the building would require full lateral and gravity upgrades to the entire building.
Re-roofing & New RTUs Roof areas affected by the addition or replacement of new rooftop equipment are required to be upgraded to support the new dead, live, and snow loads, including any snow drift. This requirement is typically triggered by equipment weighing more than 300 pounds. While we are uncertain of the
specific details, our understanding is that a new residential or office building would require new mechanical equipment exceeding the 300-lb weight limit. As such, significant structural upgrades would likely be necessary including potentially re-roofing the building to accommodate those new units. Reconfiguration of Space We understand this project to be a 100% reconfiguration of the space but that it likely would not significantly affecting the existing structural elements. If the main existing structural elements are modified (concrete columns removed, large openings introduced in the floor slabs, or new openings added to the exterior walls) these code implications will need to be-revisited. The removal of any of the primary structural elements would trigger a full 2018 IBC lateral upgrade to the building since there is no code-approved lateral system for the building. If these structural modifications can be avoided, this level of alteration does not require a full IBC-level lateral upgrade. However, as discussed below we highly recommend installing a new lateral resisting system to ensure life-safety for the occupants of the building. The structural items that are required to be updated based on IEBC code requirements are the following, based on the site location’s Seismic Design Category (D) and the extent of non-structural alterations:
• Connections added to anchor the unreinforced masonry walls to the roof.
• Any existing unreinforced masonry parapets should be investigated and analyzed. Bracing will need to be added if they are found to be deficient in their ability to resist seismic forces.
• The exterior brick and hollow clay tile walls must be braced at the floor and roof levels to resist out-of-plane forces (ie: to support their own self weight lateral load in an earthquake). Recommendations 1) Brace Exterior Walls and Parapets for Out-of-Plane Seismic Loads: Unreinforced masonry construction and hollow clay tile are no longer allowed as construction types in seismically active areas such as Bozeman. In a seismic event, they may not support their own weight for out-of-plane seismic forces and can thus pose significant threats to life-safety. Assuming there are to be new furred walls installed on the interior side of all perimeter walls, the tile and brick can be tied and braced to the new wood or steel stud framing members with anchors similar to Helifix anchors (Figure 6). For estimating purposes, these can be assumed to be installed @ 3’-0” on center in each direction. New angles with epoxy anchors would also be installed at the perimeter to anchor the walls to the floors and slab. See Appendix A for additional information.
2) New Lateral System: Since there is no clear lateral system in this building, and because the renovation lends itself to the introduction of new wall elements, we highly recommend introducing a new lateral system to this building. This would greatly improve the building’s life safety performance in any future seismic events. If changes to the use on the roof, such as a roof-top deck, or any additions are made to the building, this upgrade would be required.
Since the floors and roof are concrete, this could easily be done with the addition of selective CMU walls in discreet locations throughout the building. Some potential locations for CMU shear wall additions could be an 8” CMU core around the elevator, with additional 8” CMU wall elements located at the building perimeter. The new shear walls would require the addition of
supporting foundation elements, most likely a concrete grade beam with helical piers. See Appendix A for additional information. 3) Concrete Structural Repairs: Based on our observations, deterioration and consolidation issues are assumed to exist at floor slabs, beams and columns that will require structural repair. Appendix A outlines the requirements for these repairs and assumes approximately 5% of the floor area on each floor would require some level of these repairs. In addition, with further analysis there may be connections between columns, beams and slabs that require retrofit in some areas of the building to transfer loads properly between these elements. Summary The Bozeman Deaconess Hospital can be reconfigured into an office or residential space with the structural retrofits outlined above and in Appendix A. The change in occupancy from hospital to residential or office does not trigger occupancy based structural upgrades per the 2018 IEBC. If the main gravity and lateral elements are not significantly modified or removed (concrete columns removed, large openings added to any floor or roof diaphragms or openings significantly modified in
the exterior walls) then the space can avoid a modification driven full IBC lateral upgrade. Appendix A outlines the following structural upgrades to be installed prior to future occupancy of the building. Required - Exterior Wall and Parapet Bracing, Concrete Repairs: Based on our understanding of the extents of the renovation, the IEBC does require bracing of the unreinforced masonry and hollow clay tile walls (all exterior walls), which can be achieved through connections to the existing roof and floor structure and new interior metal or wood stud furring walls. Repairs to all damaged or deteriorated concrete structural elements will also be required prior to occupancy. Recommended- New Lateral System: Finally, the installation of a code-approved lateral system is highly recommended to improve life-safety for the building occupants with the introduction of a new CMU shear wall system as shown in Appendix A. Any modification to the occupancy of the roof or any new additions to the building would also trigger the required installation of this system. Overall, the building requires significant upgrades to ensure it can function adequately and provide life-safety to the occupants following a renovation or adaptive reuse. A thorough cost-benefit analysis is highly recommended as to what can be reasonably salvaged while still providing a functional and safe building from all aspects in conjunction with the structural integrity.
Figure 2: Concrete roof, columns and capitals
Figure 3: Evidence of concrete slab reinforcement
Figure 4: Typical hollow clay tile at exterior walls
Figure 5: Unconsolidated Concrete @ Structural Beams
Figure 6: Sample detail showing Helifix DryFix anchors intalled through wood framing tosupport brick veneer beyond.
(N) 2x Wood or Metal Stud Wall
(E) CONCRETE SLABWITH NEW ANGLEATTACHMENT TOBRICK WALL, L4X4X1/4WITH 5/8" DIA. X 4"EMBED EPOXYANCHOR @ 4'-0" O.C.
New Lateral System
1) 8" CMU Walls Fully Grouted and Reinforced #5 @ 16" o.c., Ea. Way (15'
length typical), all floors.
2) Foundation will be reinforced 2'-0" wide x 4" deep reinforced concrete gradebeam for length of wall with (2) helical piers x 20' deep each end.
APPLENDIX A: PRELIMINARY STRUCTURAL
RECOMMENDATIONS
(For Estimating Purposes Only)
Concrete RepairsAssume 5% of square footage on each floor will require the following:
1) Removed loose or damaged concrete around exposed rebar at columns, beams and slabs.2) Wire brush all rust/deteriorated areas of exposed rebar.
3) Install Bonding Agent over all exposed areas (Euclid brand "Dural Prep AC" or equivalent)4) Install Repair Material (Euclid brand "Eucocrete" or equivalent).
Exterior Wall Bracing
All exterior walls, all floors will require the following:
1) Removed existing wall finishes to expose the hollow clay tile infill wall. 2) Install new 6" metal stud wall adjacent to tile.3) Install helifix anchors into exterior brick wall through tile and attach to metal
studs.
Parapet Bracing
1) Removed roofing to expose parapet at perimeter of building.
2) Repoint existing brick where deteriorated (assume 50% surface area).
2) Install new parapet bracing, wood framing with sheathing, attached to brick.3) Reinstall roofing over bracing and tie in with existing roof.
New Lateral System
1) 8" CMU Walls Fully Grouted and
Reinforced #5 @ 16" o.c., Ea. Way (15' length typical), all floors.
2) Foundation will be reinforced 2'-0"
wide x 4" deep reinforced concrete
grade beam for length of wall with (2)helical piers x 20' deep each end.
3) Cast-in-place reinforced concrete
"drag strut" beam @ re-entrant corner
required, 2 places, each floor