SOWAtchE-ExistingConditionsRpt.pdf

BUILDING 2451 EXISTING CONDITIONS STUDY –

INNOVA ARCHITECTS – 03 MARCH 2021

INNOVA Architects, Inc. Phone (253) 572-4903 950 Pacific Avenue, Suite 450 – Tacoma, WA 98402 Page 1 of 29

BUILDING 2451 EXISTING CONDITIONS STUDY

THIS SUBMITTAL

Existing Conditions Study – Structural Analysis

CONTRACT

FA4620-18-D-B001 - A-E IDIQ Contract for Multidiscipline Design Services Fairchild Air Force Base, WA

TASK ORDER

FA4620-21-F-0025

PRIME CONTRACTOR

INNOVA Architects Inc.

CONTRACTORS GEOTECHNICAL SUBCONSULTANT

Shannon and Wilson

SUBMITTAL DATE

03 March 2021

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SOW Attachment E - Existing Conditions Report

INNOVA Architects, Inc. Phone (253) 572-4903 950 Pacific Avenue, Suite 450 – Tacoma, WA 98402 Page 2 of 29

Table of Contents

EXECUTIVE SUMMARY

1. INTRODUCTION

2. GENERAL DESCRIPTION OF THE BUILDING

3. DESCRIPTION OF FIELD VISIT

4. APPROACH TO ANALYSIS

5. ROOF FRAMING ANALYSIS

6. WOOD LEDGER

7. COLUMNS

8. CONCRETE BEAM IN CMU WALL

9. SUMMARY OF ANAYLSIS OF FOUNDATIONS

10. GENERAL DESCRIPTION OF LATERAL SYSTEMS OF A BUILDING

11. LATERAL DESIGN CRITERIA

12. WALL OUT OF PLANE

13. WALL TOP CONNECTION OUT OF PLANE FORCE

14. ROOF DIAPHRAGM

15. ROOF CHORD MEMBERS

16. ROOF TO SHEARWALL CONNECTION

17. WOOD SHEARWALL CAPACITY

18. WOOD SHEARWALL ANCHORAGE TO FOUNDATION

19. WOOD SHEARWALL HOLD-DOWNS

20. MASONRY FIRE SEPARATION SHEARWALLS

21. ROOF PARAPETS

22. ROOFING

23. EXTERIOR WALL

24. RECOMMENDATIONS AND CONCLUSIONS

NEXT STEPS

APPENDICES – STRUCTURAL CALCULATIONS AND AS-BUILT STRUCTURAL DRAWINGS

SEPARATE ATTACHMENT – GEOTECHNICAL ENGINEERING REPORT (REPORT IS CURRENTLY IN PROGRESS

AND WILL BE SUBMITTED SEPARATELY WHEN COMPLETED)

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EXECUTIVE SUMMARY

In 2019 INNOVA Architects, Inc. was awarded an IDIQ contract for projects at Fairchild Air Force Base.

On 09 December 2020 INNOVA was awarded a task order under that contract to conduct a study of Building 2451 with specific scope to perform a structural gravity and seismic/wind study and architectural roofing review of the existing structure and if found deficient to propose options to repair the structure to be adequate to support design loads on the structure.

The scope of work also includes to provide geotechnical engineering site analysis to produce a report and analysis of the soil bearing capacity in relation to supporting the foundations of the building. This report is currently in progress and will be submitted separately when completed.

Building 2451 is a wood framed building with reinforced concrete masonry unit (CMU) fire separation walls originally constructed in the 1940s to serve as a storage warehouse. The building is approximately 960’ x 180’ in size. The building is divided into four equal sections or units 240 feet long with 16” thick fire separation walls constructed with reinforced concrete masonry units (CMU). The fire separation wall thins to 12” thick and extends four to five feet above the main roof surface and runs the full width of the building. Each of the four building units have four roof monitors that extend up to five feet above the main roof surface.

The most significant issue we found is the concern for the connection of the roof to the interior CMU fire separation shear walls. It is not currently connected in a manner that meets codes and is therefore one of our higher priority items to be considered for repair.

WOOD LEDGERS

Our analysis reveals that the wood ledger is not adequate to support the full dead load plus snow load plus drifting and that additional bolts are required. The roof purlins bear directly on the ledger and appear to be only connected to the ledger with toe nails; no steel strapping between the purlins and ledger or CMU wall was observed to prevent the purlins from sliding off the ledger due to out of place seismic forces. New steel strapping is required to hold the roof purlins on the ledger.

The lack of an apparent physical connection between the roof diaphragm and the top of the interior CMU walls is a potentially dangerous situation because in an earthquake the roof purlins could pull away and fall off of the ledger, thus causing a collapse of this part of the roof. However, this risk is somewhat reduced by the fact that the wall is braced on both sides by the adjoining roof. So it does not have the same level of risk as an exterior wall would have being braced only on one side. But it is still an item to be considered highly for repair. We don’t classify this as urgent, but if repairs are done to the building, this is an item that should be prioritized in the repair work. The top of this wall should be repaired to properly secure it to the roof with masonry anchors and thru-bolts and strapping it back into the roof structure.

COLUMNS

The bases of the wood columns should be strengthened and further secured to the concrete pedestal bases. It is apparent there have been vehicle impacts to the bottom of the columns and several have

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UNREINFORCED MASONRY WING WALLS AT ENDS OF CMU FIRE SEPARATION SHEARWALLS

We find that the unreinforced masonry wing walls along Grids B and M are not adequate to resist the seismic lateral forces which may occur and may be prone to collapse during a seismic event. The possible lateral failure of the masonry wing walls is a potential hazard; in an earthquake the masonry wall could fall, causing damage to vehicles in the parking areas and loading docks below, or to the stored equipment inside the structure. Occupants in the vicinity and inside the building would be in danger if that were to occur. Although this building has stood for many years, it does not relieve the risk that exists in the event of an earthquake.

ROOFING

The roof is a predominantly a single ply membrane. Sections have roof monitors and are covered with either a batten seam metal, corrugated metal or asphalt.

Primary roof surface slopes to the perimeter to drains via downspouts to the building sewer connection, internal to the building adjacent to columns. Roof slopes at between 2% - 3% to drains, no standing water was observed, and drains were clear of debris. Primary roof was EPDM single ply membrane (1) and was predominantly in good condition with not major issues at seams and flashings. Some minor maintenance issues were noted. Of concern is the EPDM and TPO (2) intersection on the second bay, the dissimilar materials seem to have been seemed and no major issues were observed, however the seaming of these membranes have been known to cause issues.

1 Primary roof EPDM membrane 2 Primary roof TPO membrane

Roof monitors (4) were of a variety of metal roof systems and drain to the primary roof. Roofs appeared to be in acceptable condition and no major issues were observed.

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1. INTRODUCTION

Building 2451 has been evaluated with specific scope to perform a structural gravity and seismic study of the existing structure and if found deficient to propose options to repair the structure to adequately support design loads.

The scope of work also includes conducting a geotechnical engineering site analysis to produce a report and analysis of the soil bearing capacity in relation to supporting the foundations of the building.

Additionally, the integrity of the exterior wall components, fenestration systems, roofing, and roof drainage systems is included in the evaluation.

2. GENERAL DESCRIPTION OF THE BUILDING

Building 2451 is a wood framed building originally constructed in the 1940s to serve as a storage warehouse. The building is approximately 960’ x 180’ in size. The building is divided into four equal sections or units 240 feet long with 16” thick walls constructed with reinforced concrete masonry units (CMU). The fire separation wall thins to 12” wide and extends as a parapet four to five feet above the main roof surface and runs the full width of the building. Each of the four building units have four roof monitors that extend up to five feet above the main roof surface.

The main roof structure consists of wood beams supported by wood columns evenly spaced at 16’ on center with single bays 20’ wide between selected gridlines supported by concrete foundations.

Between the beam lines are 2x10 roof purlins spaced at 24” on center bearing on top of the wood beams for the typical 16’ bays. For the 20’ bays, 2x12 roof purlins spaced at 24” on center span between the wood beams. The roof sheathing consists of wood tongue and groove decking oriented diagonally to the beams. The exterior walls of the high roof consist of wood studs with exterior plank sheathing and bear on concrete beams of the low roof structure. The bottom of the beams at the exterior walls is 13’-4” clear above the concrete floor slab and 15’-2” clear above the concrete floor slab at the center ridge line. At the roof monitors, the bottom of the 2x10 roof purlins is an additional 5’-3” above the surrounding main roof framing.

The roof framing is supported by 6x6 wood columns spaced at 18’ along all numbered interior gridlines The columns bear on a 12” square concrete pedestal raised 11” above the floor slab. The columns are assumed to be attached to the concrete pedestal with a single steel pin.

The exterior walls are framed with 2x6 studs spaced at 24” on center for the entire perimeter of the building. The exterior faces of the wood wall framing are finished and are hidden from view and we were not able to verify the existing framing of the wood walls during our site visit and it is assumed that the studs are continuous from the foundation up to the bottom of the roof framing.

Along the interior gridlines 15, 29 and 43, there is a 16” thick reinforced (assumed) CMU fire separation wall. These interior walls also serve as shearwalls for lateral force resistance. Just below the roof framing, the wall thins to 12” thick and continues as a parapet through the roof framing to an elevation 4’ to 5’ above the roof’s surface. 3x6 wood ledgers bolted to the face of the CMU wall with 5/8” diameter bolts spaced at 24” on center provide support for the roof purlins on both sides of the wall.

The roof purlins bear directly on the ledger and appear to be only connected to the ledger with toe nails;

no steel strapping between the purlins and ledger or wall was observed.

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4. APPROACH TO ANALYSIS - Methodology to Codes

Building codes change over time and are updated routinely about every three years; the state adopts these changes at about that same frequency. Code changes happen for two reasons. First, because over time we learn from experience what did not work as well as we had previously thought. Events such as earthquakes, hurricanes, and tornadoes reveal code inadequacies, leading us to examine existing codes and change them to better model real world building design forces. For these reasons, codes are updated every three years, and sometimes those changes are relatively minor in nature and other times they have significant effects on design.

Second, building codes related to design of wood structures also change over time because the quality and grade of lumber changes over time. In the past, lumber consisted of primarily old-growth timber which resulted in high quality fine grain lumber, superior to the lumber produced now. The allowed design strengths (allowed stresses) of old-growth lumber was high compared to today and the forces we are allowed to use in the design of lumber structures have been reduced over the last 80 years.

Therefore, when analyzed using current codes, which are based on today’s lumber quality, buildings constructed in the past with what might be superior quality lumber are compared to lower current allowed stresses and it may be difficult to prove the older buildings work. Yet the older lumber might be adequate because at the time it was harvested and used for construction it was of high quality and was allowed to have higher, stronger design forces. Currently, when we analyze old lumber buildings, we must consider looking at the older codes which will help us understand the quality of the lumber used at the time of construction.

When analyzing older buildings, we want to consider old codes to understand quality and strengths of the old lumber, but we also want to consider new codes because they have been improved where flaws in design methodology were found and later changed to be more accurate and thus safer for design of occupied buildings.

In this report we take that approach to look at both old and new codes. We compared the design values of the wood beams, purlins and posts from the 2015 NDS Code to those found in the 1986 NDS Code.

When comparing the design values for Douglas-Fir lumber, we found that the values for purlins and studs for a No. I grade in the 2015 NDS Code are equivalent to a Select Structural grade in the 1986 NDS code. We also determined that the values for beams and posts for a No. I grade in the 2015 NDS Code are comparable to a Dense Select Structural grade in the 1986 NDS code. However, since the beams and posts from the 1940s were typically made from older-growth trees with a far denser ring pattern, and the design values for Douglas-Fir lumber are likely higher than those on the 1986 NDS code, it is acceptable in our professional opinion to use the values for Dense Select Structural grade from the 2015 NDS code for beams and posts and Select Structural grade from the 2015 NDS code for purlins and studs.

5. ROOF FRAMING ANALYSIS

INNOVA Architects, Inc. Phone (253) 572-4903 950 Pacific Avenue, Suite 450 – Tacoma, WA 98402 Page 11 of 29 ton capacity and 500-pound capacity and are hung with overhead brackets from the tops of the main wood beams. Our analysis made on the local main roof beams that support the crane reveal that the main roof beams, in our opinion, are adequate to support full dead load of 19 PSF dead load (reduced to deduct weight of roof beam) plus 30 PSF snow load, plus the added crane loads, using the NDS 2015 code with a grade of Dense Select Structural. See Appendix B for the calculations of the roof beams.

Overhead crane in wood shop room. Overhead crane beams hanging from wood beams.

6. WOOD LEDGER

At the three interior CMU fire separation walls, the roof purlins are supported by a 3x6 wood ledger bolted to the face of the CMU wall with 5/8” diameter bolts spaced at 24” on center. The roof purlins bear directly on the ledger and appear to be only connected to the ledger with toe nails; no steel strapping between the purlins and ledger or wall was observed to prevent the purlins from sliding off the ledger due to out of place seismic forces. Our analysis reveals that the ledger is 7% overstressed using the NDS 2015 code for a total roof load of 17 PSF dead load plus 30 PSF snow load. When snow drifting loads are included, our analysis reveals that the ledger is 28% overstressed using the NDS 2015 code for a total roof load of 17 PSF dead load plus 30 PSF snow load plus drifting. This amount of overstress when drifting loads are included is not within an acceptable level and in our professional opinion, the roof ledgers bolted to the CMU walls are not sufficient to support a total roof load of 17 PSF dead load plus 30 PSF snow load plus drifting. This analysis can be found in Appendix D. See photograph below.

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Typical wood ledger and bolts. Note purlin bearing on ledger with no strapping.

The lack of an apparent physical connection between the roof diaphragm and the top of the interior CMU walls is a potentially dangerous situation because in an earthquake the roof purlins could pull away and fall off of the ledger, thus causing a collapse of this part of the roof. Occupants in the vicinity would be in danger if that were to occur. Although this building has stood for many years, it does not relieve the risk that exists in the event of an earthquake. The top of this wall should receive attention to properly secure it to the roof with masonry anchors and thru-bolts and strapping it back into the roof structure.

7. COLUMNS

The columns are 6x6 members measuring 5-1/2” square supporting the roof framing and appear to be in good condition. The majority of the columns observed were braced in both directions at the 11-foot level with 2x6 diagonals attached to the roof framing. All columns bear on a 12” square concrete pedestal raised 11” above the floor slab. The columns are assumed to be attached to the concrete pedestal with a single steel pin. We performed analysis on the columns, including the columns with snow drifting loads and crane loads, and in our opinion, found them to be adequate to support full dead load plus 30 PSF snow load plus drifting or crane loads, provided that the two-way bracing remains in place on all columns. Missing two-way bracing members should be replaced at columns where a bracing member is not present. This analysis can be found in Appendix C.

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Typical column with two-way bracing at top. Typical columns in wood shop room.

At several locations within the building, especially near a dock door that allows for vehicle access inside the building, we observed columns which had been displaced or twisted due to impacts with moving vehicles. A few columns along Grid 56 have been replaced in the past. At the column at Grids J-49, the base of the concrete pedestal had also been damaged by vehicle impact. We recommend that additional steel angle or clips be added between the base of the column and the concrete pedestal to strengthen its connection against vehicle impacts and that the bottom third of the columns be painted with a safety orange or yellow paint to increase visibility.

Bottom of column damaged by vehicle impact. Bottom concrete pedestal at Grids J-49 damaged by vehicle impact.

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8. CONCRETE BEAM IN CMU WALL

At each of the three interior CMU fire separation walls, there are one or two hallway openings spanned by a 17” wide by 21” deep concrete beam. As previously noted, no as-built structural plans of Building 2451 exist so the concrete strength and reinforcing of the beams is unknown.

Our visual observation of the portions of the beams open to view revealed a fairly uniform member with little apparent cracking, warping or displacement at all accessible locations. Measurements were also taken between the bottom of the beams and the floor slab and the dimension was locally consistent throughout the areas of our observation.

Based on the observations we made, our professional opinion is that the existing concrete beams have performed well over time and appear to be adequate to support the loads that exist from the building and which occur seasonally from snow loading on the roof, and therefore will continue to perform well under similar conditions in the future. We performed an analysis of the beam using minimal reinforcing and a concrete strength of 3,000 psi to support this conclusion. See appendix E for calculations.

Typical concrete beam and wood ledger at interior Typical concrete beam bearing at CMU wall.

CMU fire separation shearwalls.

9. SUMMARY OF ANAYLSIS OF FOUNDATIONS

A visual observation of the existing foundations and footings was not possible at the time of our site visit. In addition, no plans are available for review of the original construction of the building, and no geotechnical report is available for review. Therefore, the foundations and footing are of an unknown size and depth. The geotechnical engineer has not yet completed their soil analysis but for the purposes of this report we will assume that that the soil allowable bearing pressure would be 3,000 PSF.

Our visual observation of the portions of the slab open to view revealed a fairly flat slab with little apparent warping or displacement. Measurements were also taken between the top of slab and the bottom of the roof trusses and the dimension was constant throughout the area of our observation.

Based on the observations we made, our professional opinion is that the existing foundation has performed well over time and appears to be adequate to support the loads that exist from the building

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