structural assessment
TRANSCRIPT
-
8/9/2019 Structural Assessment
1/28
1
STRUCTURAL ASSESSMENT
REPORTfor
Existing Structure at Cooley Landing
2100 Bay Road, East Palo Alto, California
-
8/9/2019 Structural Assessment
2/28
2
Executive Summary
Structech Engineering Inc. performed an evaluation of the existing boat shop structures at the
Cooley Landing site in East Palo Alto. The existing structure is composed of two (2) sections, a
one story, building (North Section) relocated to this site in 1963, and a two story addition to the
south end of the older one-story section constructed at the site in 1965 (South Section).
The purpose of this assessment is to evaluate the feasibility of restoring the existing structures
for safe public access in serving the East Palo Alto Community.
The evaluation task included assessment of the existing structural members, such as roof,
bearing walls, foundations, and interior slab on grade for both gravity loads as well as lateralloads (wind and seismic).
Our firm has concluded the following:
Structural framing of the roof, floor, and bearing walls, with some strengthening andenhancement may be able sustain the minimum gravity and lateral loads as prescribed by
the California Building Code (CBC).
The existing foundation may be adequate for the anticipated light commercial serviceloads. The North Section (one-story) however, does not appear to be anchored to its
foundation properly.
Interior building slab shows signs of age and cracks have developed in several places.We do not believe that the slab in underlain by any type of moisture barrier.
The exterior siding has been exposed to the elements for too long without properprotection. Siding has decayed in several areas, and on the west elevation is in contact
with adjacent grade.
The boat launch structural steel has been exposed to the elements without properprotection. The rust is more pronounced at the steel posts where it is within the water
level. We believe with proper care and some repairs this structure can be reused for light
service loads.
-
8/9/2019 Structural Assessment
3/28
3
Table of Content Page
Description of Structure 4
Structural Assessment and Recommendations
1. Roof Framing System 52. Wall Framing System 63. Second Floor, Exterior Rear Balcony, and Access Stairs 74. Foundations 85. Boat Launch 96. Site Drainage Adjacent to the building 97. Conclusions 10Appendix I Cooley Landing Photos 11
Appendix II Cooley Landing Schematics 27
-
8/9/2019 Structural Assessment
4/28
4
Description of Structure (Photos 1-10)
The structure is composed of two sections and was used as a repair facility (See Photo 1):
North SectionThis section is the original one story building; relocated to this site. The building has12-6 wall plate height and a gable roof with slope of 4:12. The roof is supported on wood trusses
placed at 6-0 on centers and intermediate 2x6 roof rafters between trusses at 2 feet on centers. It is
stated that the North section was moved to Cooley Landing about 1963 in 3 sections (See Photos 2-5).
This section of the structure was used as boat repair area.
The building foot print dimensions are 32 feet wide by about 69 feet long, connected to the 2-story
South Section addition. This section has little or no seismic or wind load resisting features at the current
state.
South SectionThis section is a two story addition to the North Section. The section has two levels,
with balloon framed walls. Each level is approximately 9-0 high. The roof is gabled with a 4:12 slope.
The roof framing seems to be composed of 2x6 rafters. The second floor is framed with 2x12 at 16" on
centers. This section was constructed about 1965. (See photos 5 - 10). The structure appears to be
unfinished with exposed plywood as siding. The interior walls have no wall sheathing or insulation.
This portion has a second floor deck facing the San Francisco Bay.
The building approximate foot print dimensions are 32 feet wide by 35 feet long and is connected to the
south face of the North Section.
-
8/9/2019 Structural Assessment
5/28
5
Structural Assessment and Recommendations
1. Roof Framing System (Photos 11-16)The roof framing system over the one story North Section is composed of tar paper and gravel
roofing over 1x 6 horizontal wood slat which are placed perpendicular to the main load carrying
roof trusses, spaced at 6-0 on centers, and intermediate 2x6 roof rafters, spaced at 2' on centers.
Based on the age of the structure and the excessive exposure of tar paper and gravel roofing, we
believe the nailed connections between roof slats and the roof framing members are inadequate
to resist any uplift generated by wind load on the roof . The system also lacks the required roof
diaphragm features needed to resist lateral loads.
The roof rafters and the top chord of the trusses are supported by intermediate purlins, spaced at
8 feet from side walls running along the longitudinal direction of the building (See Photos 11-
13). The roof trusses are constructed from 2x6 wood chords and web members with 1 to 3
machine bolts connections depending on the location. The bottom cord of the trusses are
attached to 1x6 cross braces with a single machine bolt (See Photos 1416), and at some
locations the bottom chord cross bracing has been cut to accommodated electrical and other
equipment clearances.
The two story South Section roof system is constructed with 2 x6 rafters at 2-0 on centers with
plywood roof sheathing. We believe that the roof plywood in this section has also deteriorated
and will require replacement before a new roofing is installed.
Recommendation 1 : It is recommended that a comprehensive analysis of the building roof system for
gravity and lateral loads to be performed per American Society of Civil Engineers (ASCE) publication
7-05 and the 2007 California Building Code (CBC). Any repairs to the roof should include the creation
of a diaphragm system such as plywood sheathing and proper nailing to the framing members below.
The framing, which includes roof rafters and roof trusses, should be evaluated for anticipated loads and
reinforced accordingly to meet the minimum code requirements. While major roof repairs are
anticipated, we advise that the roof for both North and South Sections be protected temporarily in order
to minimize further weather damage to the framing members.
-
8/9/2019 Structural Assessment
6/28
6
2. Wall Framing System (Photos 1-10 & 17-21)The general construction of the exterior load bearing walls in the older North Section is 2x6
studs at 24" on centers. At approximate wall height of 12'-6", we believe that the stud size is
adequate for this section. The South Section exterior walls are composed of 2x4 studs, balloon
framed at 16" on centers. Based on the length and slenderness of these studs some modification
may be necessary in these walls in order to account for the excessive stud heights. In all cases, a
thorough examination of all wall framing for exposure and termite damage is in order prior to
any modification or reinforcement.
Crane runway on the North Section of the building is supported by wood corbels attached to 6x6
wood posts. The connections of the wood corbel to the wood post are via a machine bolt and a
partial bearing within a notch on the post (See Photos 17-18). If the future use of the building
would require full usage of the crane, a detailed analysis of the crane support system would be
required per ASCE 7-05 and the 2007 CBC. If the future use of the building would require the
carne to operate in an entirely unloaded mode, the system of railing and supports should be
evaluated by calculations and careful visual examination of its condition to assure ultimate
safety for the building occupants and visitors.
As it can be observed from Photos 1-9 and 18 through 21, the existing exterior walls have
number of window and door openings. The North Section's exterior siding is believed to be of
milled redwood (all three elevations). There are visible damages to the siding in some areas
resulting from exposure, rotting, and breakage. Even with adequate repairs and partial
replacement, the existing wood siding is inadequate to resist any lateral loads induced by wind
or earthquake. If it is desired to keep and refurbish the existing wood siding, the damaged areas
may be replaced with similar dimensional wood siding, milled to existing specifications to
preserve the originality. In such case, the retrofit of the exterior load bearing walls will have to
be accomplished by applying structural sheathing to the inside face of the wall framing to
provide adequate lateral load carrying capacities. Alternatively, the existing siding can be
removed and replaced with similar dimensional and architectural siding after application of
plywood and building paper to the exterior side.
-
8/9/2019 Structural Assessment
7/28
7
The South section is entirely sheathed with unprotected plywood panels. This section has large
openings on two sides. The remaining solid walls would need to be retrofitted to act as lateral
load resisting elements with proper plywood sheathing and anchorage. The existing plywood
siding is damaged and is not usable for any purpose.
Recommendation 2: It is recommended that a comprehensive structural analysis of the combined
building sections to be performed for gravity and lateral loads (seismic and wind) per ASCE 7-05 and
the 2007 California Building Code (CBC), to determine the required lateral load resisting systems. This
effort should include the usage of as many existing structural members as possible, but adding the proper
devices, anchorage, and connections that will bring the entire building up to current building code
standards.
3. Second Floor and Balcony in South Section (Photos 22-26)We were not able to access the second floor at the time of our site visits because of failing
exterior stairs and the fact that all openings to this area were boarded up. We did note that the
floor framing is 2x12 joists spaced at 16" on centers supported by two (2) interior bearing walls
located at about 14 feet and 24 feet of exterior west wall (See Photos 22-25). The floor joist
members are believed to be adequate for the anticipated gravity loads, however, the floor
decking and the nailing to the floor joists will have to be examined and verified for the building
use and lateral load diaphragm demand/capacity per ASCE 7 -05 and the 2007 CBC.
This assessment is within the parameters of Recommendation 2 in the previous section.
There is a cantilever wood balcony at the rear (facing the Bay) of the South Section. Because
of the excessive exposure to elements, we believe that this area is currently unsafe for any
type of usage. A telling sign of this condition is the fact that the exterior stairway leading
to the balcony has completely failed for the similar reasons. If the balcony is to be used in
the future, we recommend removal of the existing damaged joists and installation of new
floor joists overlapped with joists inside the building. As an alternative, the balcony can
be supported on the building wall at one end, and support beam and posts at the outer
end. Both of these alternatives require structural calculations to ensure adequate capacity
per ASCE 7-05 and 2007 CBC for commercial use application.
-
8/9/2019 Structural Assessment
8/28
8
4. Foundations (Photos 27-29)Based on our preliminary investigations and exposing a small portion of the exterior footings for
both building sections, we have determined that the existing foundation is generally composed
of an exterior grade beam and monolithically poured in place slab on grade floor. The existing
exterior grade beam appears to be in good condition (no major structural cracks observed), and
in compliance with the requirements for the area, as outlined in theReport File Number
770771/007 by Kleinfelder, dated May 23, 2007. The depth of the exterior grade beams for
both building sections were approximately18 inches. The width of these grade beams were
estimated to be between 12 to 15 inches. These footings seem sufficient in size for light
commercial type use of the building. Our staff did not perform exploration or testing for
concrete reinforcing steel within the footings. This inexpensive and non-destructive testing
should be done within the frame work of a major structural design and analysis as to ensure that
the foundation can sustain the induced gravity and lateral loads to the fullest extent possible. It is
important to mention that the use of fully loaded operational crane or generally using the
buildings for industrial operation would require a more robust foundation system capable of
resistance against crane or equipment induced vibrations.
The interior slab on grade has developed cracks and slight heaves in various locations. This slab
seems to be of poor quality, without a moisture barrier, and unknown reinforcement. The latter,
combined with the fact that the building site was previously used as a disposal area suggests that
some of the cracking may be attributed to swelling of sub grade below, or uneven loading
caused by crane usage and heavy boat loads. There is also a possibility that methane gas
produced by decaying disposed material may exist throughout the site, including below the
building slab. While it is possible to repair the existing slab and seal it with an epoxy coating
capable of preventing methane leakage inside the building, it is much more cost effective in the
long run to remove the existing slab in its entirety and replace it with a new reinforced slab.
Providing a stable and compacted sub grade and proper vapor barrier below the new slab will
better accommodate future uses of this building.
Recommendation 3: It is recommended that a non-destructive testing be done to determine the
existence of horizontal steel reinforcement near the top and bottom of the exterior grade beams. This is
-
8/9/2019 Structural Assessment
9/28
9
critical because the uplift and downward forces produced in seismic and wind loading conditions cannot
be fully resisted without reinforcement in the footings.
Based on our observations, we found no anchor bolts connecting the North Section walls to the exterior
grade beams. As a part ofRecommendation 2, the required wall anchorage to the foundation can be
calculated based on ASCE 7-05 and the 2007 California Building Code (CBC). We recommend using
Simpson "Titen" or epoxy anchors in the existing concrete.
5. Boat LaunchThis is an existing structure composed of two rows of 12" diameter steel posts and series of
pipes, wide flanges, and channel steel members as main support. The system supports a
movable open steel platform previously used to lower the boats into the water. Our visual and
preliminary inspection has revealed that excessive rust has developed on most of the structural
steel because of contact with salt water and lack of maintenance. This is more notable in places
where standing water can occur, and on the steel posts where it meets the Bay's water level. In
our opinion this structure is no longer reliable to carry heavy boat loads in the current state. The
structure can however be modified and possibly retrofitted for a walking or fishing platform.
The latter requires design modification and fortification to mitigate the effects of rust in several
places as well as removal of excess weight not necessary for the lighter usage.
6. Site Drainage Adjacent to the building (Photos 1-10)Based on the field geotechnical investigation report by Klienfelder (Report File Number
770771/007 by Kleinfelder, dated May 23, 2007), an approximately a two (2) inch thick
pavement section has previously been placed at the north and west elevations of the North
Section. This paving is at or in some locations above the top of the grade beam or the interior
slab. Thus, some untreated structural members and wood siding are in direct contact with the
adjacent grade, resulting in decaying and deterioration of the wood members.
The soil strata under the pavement and surrounding the building perimeter are composed of
fill to depths of about 18 feet. The fill consist of about 5 to 10 feet of soft to very stiff lean
clay underlain by very loose to medium dense clayey sand to about 18 feet below ground
-
8/9/2019 Structural Assessment
10/28
10
surface. The above soft to very stiff clay is very susceptible to seasonal moisture
changes; therefore, a positive drainage away from the building would be required to
avoid excessive foundation movement and cracking.
Recommendation 4: It is recommended that the paving be removed and lightly excavated to an
elevation of minimum 6 inches below the top of the slab and grade beam to avoid direct contact of
wood members with adjacent grade. If another pavement slab is planned, It should be placed no less
than two(2) inches below the top of the building interior slab elevation. Furthermore, the areas
adjacent to the entire building should be sloped away (minimum 2%) for positive drainage from the
perimeter foundation. This is critical in avoiding a cycle of moisture recharging and drying of the
underlying perimeter soil.
7. ConclusionsThe scope of this report has been to concentrate on the structural assessment and integrity of the
existing building. The contents and recommendations provided in this report are based on
multiple site visits, observations, and exploratory excavations adjacent to the exterior
foundations of the North Section and South Section. We are optimistic that a majority of the
framing members can be used as originally intended, but additional modern load resisting
features are required to ensure the structural reliability the building and safety of the future
occupants. Through a comprehensive structural analysis of the existing structure and based on
the current building code requirements, a feasible, value engineered solution for remedial work
can be presented to perform retrofit of the existing buildings to conform to the governing
California building codes for life safety and safe occupancy. The analyses will include an
assessment of each structural components for performing and demonstrating safe behavior under
the imposed and superimposed limit loads and load combinations as required by the governing
codes. Upon completing the required analysis, a final set of plans and construction documents
can be developed and submitted to the Chief Building Official at the City of East Palo Alto for
his review and approval. It has been our experience that all retrofit projects will benefit from
close cooperation of engineers and contractors during the construction. Our firm believes that
such team work will increase efficiency and optimizes the work, thereby reducing engineering
-
8/9/2019 Structural Assessment
11/28
11
Appendix I
Cooley Landing Photos
-
8/9/2019 Structural Assessment
12/28
12
Photo 1 - Cooley Landing (North Section & South Section)
Photo 2 - Cooley Landing North Section North Elevation
-
8/9/2019 Structural Assessment
13/28
13
Photo 3 - Cooley Landing North Section West Elevation
Photo 4 - Cooley Landing North Section & South Section East Elevation
-
8/9/2019 Structural Assessment
14/28
14
Photo 5 - Cooley Landing North Section East Elevation
Photo 6 - Cooley Landing South Section West Elevation
-
8/9/2019 Structural Assessment
15/28
15
Photo 7- Cooley Landing South Section South Elevation
Photo 8 - Cooley Landing South Section South Elevation
-
8/9/2019 Structural Assessment
16/28
16
Photo 9 - Cooley Landing South Section West Elevation
Photo 10 - Cooley Landing South Section East Elevation
-
8/9/2019 Structural Assessment
17/28
17
Photo 11 - Cooley Landing North Section Roof Framing
Photo 12 - Cooley Landing North Section Roof Framing
-
8/9/2019 Structural Assessment
18/28
18
Photo 13 - Cooley Landing North Section Framing Trusses and Rafters
Photo 14 - Cooley Landing North Section Roof Framing Trusses Cross Tension Members
-
8/9/2019 Structural Assessment
19/28
19
Photo 15 - Cooley Landing North Section Roof Framing Trusses and Cross Tension Members
Photo 16 - Cooley Landing North Section Roof Framing Trusses Chord and Web Members Connections
-
8/9/2019 Structural Assessment
20/28
20
Photo 17 -Inside view, Cooley Landing Exterior Wall and Corbel
Photo 18 - Cooley Landing Exterior Wall and Crane Runway Support
-
8/9/2019 Structural Assessment
21/28
21
Photo 19 - Cooley Landing Exterior Wall at North Section, Wall Opening
Photo 20- Cooley Landing Exterior Wall at 2-Story South Section Opening
-
8/9/2019 Structural Assessment
22/28
22
v
Photo 21- Cooley Landing Exterior Wall at 2-Story South Section South Wall Opening
Photo 22- Cooley landing 2-Story South Section 2ndfloor Joists
-
8/9/2019 Structural Assessment
23/28
23
Photo 23- Cooley landing 2-Story South Section 2ndfloor Joists & Blocking
Photo 24- Cooley landing 2-Story South Section 2ndfloor Joists @Bearing Wall Support
-
8/9/2019 Structural Assessment
24/28
24
Photo 25- Cooley landing 2-Story South Section 2ndfloor Joists @ Bearing Wall
Photo 26- Cooley Landing 2-Story South Section Balcony and Stair Access
-
8/9/2019 Structural Assessment
25/28
25
Photo 27 - Cooley Landing North Section Exterior Grade Beam Foundation
Photo 28 - Cooley Landing North Section Exterior Grade Beam Foundation
-
8/9/2019 Structural Assessment
26/28
26
Photo 29 - Cooley Landing South Section Exterior Grade Beam Foundation
-
8/9/2019 Structural Assessment
27/28
27
Appendix II
Cooley Landing
Schematic
Plans and Elevations
-
8/9/2019 Structural Assessment
28/28