STRUCTURAL ASSESSMENT REPORT BOLINAS MARINE STATION - BOLINAS, CALIFORNIA

Transcription

1 STRUCTURAL ASSESSMENT REPORT BOLINAS MARINE STATION - BOLINAS, CALIFORNIA College of Marin c/o Swinerton Management & Consulting P.O. Box College Avenue, Building MS-3 Kentfield, California November 3, 2005 Degenkolb Job Number A SUITE 450 Degenkolb Engineers Frank H. Ogawa Plaza Oakland, California phone fax

2 TABLE OF CONTENTS 1.2 Structural Assessment Executive Summary Introduction Building Description Structural and Non-Structural Assessment (Deficiencies) Recommendations Figures Photographs Appendix NOVEMBER 2005 BOLINAS MARINE STATION

3 1.2 STRUCTURAL ASSESSMENT Executive Summary An evaluation of the 5 structures (Laboratory, House, Water Storage Tank, Storage Shed and Dock) at the Bolinas Marine Station was performed by Degenkolb Engineers to identify seismic deficiencies, or weak links, of the structural and non-structural systems at the Life-Safety Performance Level as defined in ASCE 31: Seismic Evaluation of Existing Buildings. The Laboratory and the House are light framed wood construction and were originally constructed in 1914 followed by a remodel in 1964 and the construction of the reinforced concrete water storage tank. The construction of the shed is not formally documented but is of similar construction and vintage to Laboratory and House. The dock was upgraded in 1994 and consists of wood framing supported on multiple timber piers wrapped with polyethylene. Per the Geologic Hazard Assessment performed by Fugro West Inc., the site is located within the State of California Special Studies Zones for the San Andreas Fault and is located within 1080 feet of a splay of this fault. Therefore, the site is potentially subject to very high ground accelerations and potential surface fault rupture. Collapse of the structures is likely in the event that surface rupture occurs within the site. Behind the site is a very steep slope that is potentially unstable. Due to the proximity of the site to the Bolinas Lagoon, there is also the potential for liquefaction. For more detailed information refer to the Fugro West Inc. report entitled Preliminary Focused Geologic Hazard Assessment Marine Biology Laboratory. Our structural evaluation of the Laboratory, House and Storage Shed revealed that the buildings do not meet the Life-Safety Performance Objective. Strengthening of these structures is required to meet this objective. Recommended strengthening measures for the Lab include providing a new plywood roof diaphragm and positive connections between the existing wood posts and girders. Strengthening measures for the House include replacement of the roof and floor sheathing with new plywood, strengthening of the shear walls with new exterior plywood, adding hold downs at the ends of shear walls, and anchoring the brick chimneys to the roof and floors. Strengthening measures for the Storage Shed include replacing the existing sheathing on the north wall with plywood and providing holdowns connecting the walls to the foundation along the north wall. Our evaluation of the Water Storage Tank and the Dock confirmed that these structures meet the Life- Safety Performance Objective. For the Water Storage Tank, we noted that reinforcement of the tank walls is corroding due to water intrusion into the concrete and that the wood roof of the tank is rotting due to prolonged weather exposure. We recommend filling the existing cracks in the walls of the Water Storage Tank and replacing the tank roof to arrest further deterioration. Our site observations also indicated structural damage related to prolonged maintenance of the structures. There is observed water damage of the timber sheathing and framing in the House and water damage is suspected in the Laboratory. We recommend replacement of the damaged structural elements. There are also some life-safety concerns regarding the non-structural components of the building including anchorage of bookcases, containment of hazardous materials, and bracing of mechanical equipment. 1

4 1.2.2 Introduction This report presents the findings of building structural assessments per ASCE 31: Seismic Evaluation of Existing Buildings. Aspects of building performance that are considered include structural, non-structural, and foundation/geologic hazard issues. Lifelines such as water, electrical, gas and waste, etc., beyond the perimeter of the building are not considered. The ASCE 31 evaluation process is 3-tiered with a choice of 2 performance objectives: life-safety and immediate occupancy. The targeted performance objective for the College of Marin is Life-Safety. A Tier 1 evaluation is considered a preliminary phase with the purpose of screening out buildings that are compliant and quickly identifying buildings with potential seismic deficiencies. A Tier 2 evaluation is an analysis of the building that addresses the potential seismic deficiencies identified in Tier 1 screening. A Tier 3 evaluation is a detailed and complete analysis of the building. A Tier 3 evaluation is excluded from this assessment. The scope of work for the building assessments included the following tasks: 1. Reviewing available original construction documents. 2. Making site visits to of each of the buildings. The intent of the site visits was to confirm that the available drawings properly identify the extent of the building, to observe whether significant building modifications have occurred, and to observe the non-structural system bracing and anchorage. 3. Performing the required calculations as required by ASCE Preparing a report summarizing our findings including conceptual level retrofit sketches for seismically deficient buildings that are identified for a Tier 2 level assessment. Supporting documentation including a list of drawings reviewed, ASCE31 checklists, and structural calculations are included in the Appendix Building Description The Bolinas Marine Station is located along the Bolinas Lagoon at 72 Wharf Road in Bolinas, California. The Marine Station consists 5 structures including the Laboratory, the House, the Storage Shed, the Water Storage Tank, and the Dock. A site plan is shown in Figure 1. Per the Geologic Hazard Assessment performed by Fugro West Inc., the site is located within the State of California Special Studies Zones for the San Andreas Fault and is within 1080 feet from the 1906 trace. Therefore, the site is potentially subject to very high ground accelerations and potential surface fault rupture. Laboratory Building name: Bolinas Marine Laboratory Year constructed: Originally 1914, Remodeled 1964 Plan configuration: Rectangular 23 x 39 Number of stories: ASCE 31 Building type: 1 story W2 Wood Frames, Commercial and Industrial 2

5 Structural systems: See Figure 2 Roof Framing: Floor Framing: Foundation System: Lateral System: 1x straight sheathing over 2x6 roof rafters at 16 o.c supported by wood bearing walls 2x6 16 o.c. over wood sleepers Unknown, continuous footing at perimeter and spread footings at interior posts assumed. Diagonal sheathed wood shear walls Non-structural systems bracing/anchorage: Cladding: Ceilings: Lighting: Piping/Ductwork: Building contents: Hazardous materials: Cement asbestos tiles Glued on hard ceiling boards/tiles Ductwork not visible to view. Water distribution line for lab sinks braced in transverse direction only Tall bookcases, could not discern anchorage/bracing. Unknown. Bookcases house many glass containers with unknown chemicals. House Building name: Bolinas Marine House Year constructed: Originally 1914, Remodeled 1964 Plan configuration: Rectangular 23 x 39 Number of stories: ASCE 31 Building type: 1 story W2 Wood Frames, Commercial and Industrial Structural systems: See Figure 3 Roof Framing: 1x straight sheathing over 2x8 roof rafters at 16 o.c supported by wood bearing walls 2 nd Floor Framing: 1x diagonal sheathing over 2x10 16 o.c. over bearing walls Ground Floor Framing: 1x diagonal sheathing over 2x10 16 o.c. over bearing walls or girders supported by wood posts Foundation System: Unknown, continuous footing at perimeter and spread footings at interior posts assumed. Lateral System: 1x diagonal sheathing on wood stud walls 3

6 Non-structural systems bracing/anchorage:. Cladding: Masonry chimneys: Ceilings: Lighting: Piping/Ductwork: Fire sprinklers: Mechanical/Electrical Equipment: Building contents: Hazardous materials: Cement asbestos tiles 2 brick chimneys. No connection to floors or roof visible nor indicated on drawings retrofit details not implemented. Chimneys below the attic level are enclosed in plaster walls. Glued on hard ceiling tiles Surface mounted. Ductwork and piping, if any, not visible to view. Present, heads visible, distribution lines concealed by hard ceiling Wall mounted electric heaters Tall bookcases, not an braced to walls. Unknown, but not likely. Water Storage Tank Building name: Water Storage Tank Year constructed: 1964 Plan configuration: Number of stories: ASCE 31 Building type: Circular, 13 ft. diameter 1 story C2A Concrete Shear Wall Buildings with Flexible Diaphragms Structural systems: See Figure 4. Roof Framing: Foundation System: Lateral System: 2x8 tongue and groove planking spanning to radial 3x8 timber beams supported on 8 circular concrete wall 8 reinforced concrete slab. 8 concrete shear walls Non-structural systems bracing/anchorage: N/A Storage Shed Building name: Storage Shed, See Photo 7 Year constructed: Unknown Plan configuration: Rectangular with approximate dimensions of 11 ft x 23-6 Number of stories: Building type: 1 story Concrete shear wall 4

7 Structural systems: Roof Framing: Foundation System: Lateral System: Gable roof 2x framing with 2x collars ties supported by bearing stud walls Slab on grade, foundation unknown Straight sheathing on roof, diagonal sheathing on walls Non-structural systems bracing/anchorage: Cladding: Ceilings: Lighting: Mechanical/Electrical Equipment: Building contents: Hazardous materials: Cement asbestos tiles Plywood boards mounted to underside of collar ties. Exposed light bulbs. Wall mounted heater. Miscellaneous storage, tools, equipment etc. Unknown, but likely. Store of multiple glass containers with unknown chemicals and metal and plastic containers with flammable liquids. Dock Building name: Dock Year constructed: Original construction date unknown, Structural repairs 1994 Plan configuration: Rectangular 22 x 20 Structural systems: See Figures 5 & 6. Framing: Foundation System: Lateral System: 3x timbers flat over 4x12 pressure treated beams Timber piers wrapped in polyethylene Timber piers Non-structural systems bracing/anchorage:.n/a Structural and Non-Structural Assessment (Deficiencies): Laboratory The straight-sheathed roof diaphragm is not adequate for seismic loads. Water damage is evident at several locations through the ceiling indicating possible deterioration of the wood framing. No positive connection between the timber girders and the columns has been provided which could result in a loss of gravity support during an earthquake. The water pipe suspended from the ceiling has no longitudinal bracing, see Photo 3. House The straight-sheathed roof diaphragm is not adequate for seismic loads. The diagonal sheathed floor diaphragm is not adequate for seismic loads. The diagonal sheathed shear walls are not adequate for seismic loads. The shear walls are not adequately connected through the floor to resist overturning forces. 5

8 Water damage to the roof sheathing and framing is evident at several locations in the attic, see Photo 2. The brick masonry chimney is not reinforced or adequately braced at floor and roof levels for seismic loads, see Photo 1. Some of the bookcases are not braced to the wall and pose falling hazards. Water Storage Tank The concrete tank walls are showing rust stains indicative of corroding rebar. See Photo 4. There is cracking of the tank walls which allows for water intrusion into the concrete and accelerates corrosion of rebar, see Photo 5. The wood roof framing shows signs of deterioration including dry rot and mold, see Photo 6. Storage Shed The narrow shear walls on the north side of the shear are not adequate for seismic loads. The wall mounted heater is not braced for seismic loads. Hazardous and/or flammable materials are improperly stored and could topple over in an earthquake. Dock There are no structural deficiencies for the dock. Site Features The retaining wall at the rear of the house is showing signs of distress and has rotated out of plumb. A propane tank located near the storage tank is not anchored to the concrete pad. Numerous water pipes are interconnected between the buildings, see Photo Recommendations Laboratory Remove the existing straight roof sheathing and replace with new plywood sheathing, see Figure 7. Perform invasive testing to determine the extent of the water damage. Replace framing with signs of dry rot. Provide straps at the girder to column connections, see Figure 8. While bracing of the water pipe is not a life-safety concern, we recommend bracing the pipe in the longitudinal direction to reduce potential damage in an earthquake, see Figure 8. House Remove the existing straight roof sheathing and replace with new plywood sheathing, see Figures 10 & 11. Remove the diagonal straight floor sheathing and replace with new plywood sheathing, see Figures 9 & 11. Replace the existing diagonal sheathing with new plywood at the upper story walls, see Figures 10 & 11. Replace the existing diagonal sheathing with new plywood sheathing and replace the framing receiving edge nailing with 3x members at the lower story walls, see Figures 9 & 11. Provide hold-downs to the foundation and across the 2 nd floor at the ends of all shear walls, see Figures 9, 10 & 11. 6

9 Brace the brick chimney to the roof and floors. If the chimney is no longer operable and not desired by the District, remove the chimney and infill the floor and roof openings. Replace any members with significant water damage. Brace all bookcases. Water Storage Tank Fill any cracks greater than 0.1mm with epoxy. Apply a concrete sealer to the perimeter of the exterior and interior of the tank. This will halt the corrosion of the rebar in the tank walls. In addition, the tank shall be monitored for further cracking or spalling of concrete. If either occurs, we recommend replacement of the tank. Locally remove the existing roof to provide access for inspection of the inside of the tank. Condition of the inside of the tank is unknown. Replace roof framing with significant water damage. Storage Shed Replace the existing diagonal sheathing at the north wall with new plywood. Provide hold-downs at the ends of the shearwall segments on the north elevation. Provide containment of hazardous and/or flammable materials. Provide seismic bracing for the wall-mounted heater. Dock Inspect the dock regularly and perform periodic maintenance. Site Geotechnical engineer to make repair recommendations for the failing retaining walls. Provide anchorage for the propane tank to the existing slab. Though bracing of the water pipes is not a life-safety concern, we recommend the addition of bracing and flexible connections to limit damage that could result from pipe breakage. 7

10 1.2.6 Figures Figure 1 Bolinas Site Plan 8

11 Figure 2 Laboratory Framing Plans and Section 9

12 Figure 3 House Framing Plans & Section 10

13 Figure 4 Water Storage Tank Plans & Sections 11

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16 Figure 7 Laboratory Retrofit Concept - Roof Plan 14

17 Figure 8 Laboratory Retrofit Concept - Ceiling Plan 15

18 Figure 9 House Retrofit Concept - Ground Floor Plan 16

19 Figure 10 House Retrofit Concept - Second Floor Plan 17

20 Figure 11 House Retrofit Concept - Section 18

21 1.2.7 Photographs Photo 1 Bolinas Marine House Brick Chimneys Photo 2 Bolinas Marine House Water Damage at Roof Photo 3 Bolinas Marine Laboratory Plumbing Distribution Line Photo 4 Bolinas Marine Water Storage Tank Elevation (Evidence of Corrosion) Photo 5 Bolinas Marine Water Storage Tank Damage to Tank Wall Photo 6 Bolinas Marine Water Storage Tank Deterioration of Wood Roof 19

22 1.2.7 Photographs (continued) Photo 7 Bolinas Marine Storage Shed West Elevation Photo 8 Bolinas Marine Storage Shed Interior Photo 9 Bolinas Marine Storage Shed Hazardous Materials Photo 10 Bolinas Marine Laboratory Interconnecting Utilities 20