HomeMy WebLinkAbout1988_Structural Investigation of Lincoln School_ 1�
Mahan&DeSatva
CONSULTWG ENGINEERS
1411 FCuithAverm Bldg..
Seattle. WashlVon 98101
(206) 624-8150
(206) 624.44N
August 31, 1988
Mr. John Pope, Superintendent
Port Angeles School District
216 East 4th
Port Angeles, Washington 9'83,62
I
^CH^Of_ DISTRICT No. 121
Port Angeles, WA 98362
Subject: Structural Investigation of Lincoln School
Dear Mr. Pope,
We have completed our investigation of the structural condition of
Lincoln School. Attached is our report which summarizes our
findings.
The investigation consisted of two parts. First, an inspection of
the building was conducted during a site visit on August 3rd. The
purpose of the inspection was to determine the condition of the
structure and the locations. and extent of deterioration. The
second part of our investigation consisted of an analysis of the
structure to determine its capacity to sustain code -prescribed
forces, both gravity and seismic.
Regarding physical condition, we found the structural elements to
be in fair to good condition through except for the floors of the
East Addition and all floors and roofs of the Library/Service Wing.
Deterioration (decay) due to moisture exposure is so extensive in
these two areas at that their total replacement will be necessary.
In general, the vertical loading capacity (gravity loads) of the
structure is adequate at .-or near code -prescribed levels of stress.
However, the structure'does not perform as well (on paper) when
subjected to seismic forces. The main reason for this apparent
deficiency is that the structural elements - roof, floors and walls
- are not properly connected to provide a continuous load path for
these lateral forces from roof to foundation. Our report
recommends several modifications to correct this deficiency.
Several systems withih'the building are excluded from our
investigation since their evaluation is not within our expertise.
August 31, 1988
Mr. John Pope
.Port Angeles School
Re: Lincoln. School
Page Two
µ
District
Some of these excluded systems are power, heating, plumbing,
lighting, hardware, interior finishes, doors, windows, trim, and
furnishings. Basically, our investigation is intended to cover
structural systems only.
To summarize, our investigation has found the Lincoln School to be,
except for the two areas -of extensive deterioration noted above, a
basically sound structure in need of much maintenance work and
several structural alterations to provide a -'viable lateral force -
resisting system for seismic safety. We estimate the cost of
maintenance repairs, of the structure only, and the cost of
alterations for seismic safety could range from $350,000 to
$450,000 (24 to 31 dollars per square foot). While we cannot
evaluate the usefulness of the building as a school, it is our
opinign that the structure could be repaired at much less cost than
new construction.
This concludes our investigation of Lincoln school. we hope you
find our report useful and we will be happy to answer further
questions. It has been a pleasure serving you. Please call if you
have any questions.
Very truly yours, 5'z = X-7s q-- // fit" yw4�44-0�
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W. Mahan
Principal
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REPORT OF INSPECTION; ANALYSIS, AND RECOMMENDATIONS
FOR REPAIR OF LINCOLN SCHOOL AND ADDITIONS
for
Port Angeles School District
Port Angeles, Washington
August 31, 1988
`��'' irahan&DeSa[vo
Main Buildinq
Construction:
This two story structure is constructed of exterior
unreinforced masonry walls 9" & 13" in thickness and
interior reinforced concrete walls, beams and columns. The
roof is a system of timber trusses and rafters. The second
floor is a reinforced concrete joist system. The first
floor is an unreinforced concrete slab on grade with
reinforced structural slabs covering duct trenches.
Inspection:
The site investigation revealed the overall condition of the
structure to be fair to good. The roof framing is dry and
in good condition though there are a few areas of staining
of the roof sheathing. The roofing and flashing are in fair
condition. A few of the asphalt shingles are missing and the
flashing requires recaulking. The second floor is in good
condition with no apparent sagging or deflection. The
concrete stair slabs appear to be sound though they require
cosmetic repair. At the first floor the concrete slab on
grade is level and appears to be in good condition. The
timber subfloor over the concrete slab is in poor condition
in some areas and will require patching and/or replacement.
The foundation shows no evidence of settlement or cracking.
The masonry walls are sound though the mortar will require
tuckpointing. There has been minor water damage to the
interior finishes in this portion of the structure. This
will require some patching and/or replacement.
Analysis of Structure:
A review of the existing drawings, Sheet 1 to 12, prepared
by Harold H. Ginnold, architect, was conducted to determine
the structures load carrying capacity for both vertical 'and
lateral loading conditions. The roof framing members act
together as a system. Though the stress levels of
individual members are above allowable levels when subjected
to code -prescribed vertical loads, the system acting
together shows no evidence of distress after some 75 years*
of use. It is, in our opinion, reasonable to assume that,
as long as no new loading (i.e., heavier roofing materials)
or modifications are imposed on the system, it will continue
to function safely. The second floor system of concrete
joists, beams, columns and walls is adequate for the
vertical loading, assuming that the allowable compressive
stress of the concrete is 2000 lbs. per square inch psi and
the reinforcing steel is of the size and spacing shown on
the drawings. The drawings do not specify shear reinforcing
for any of the concrete joists or beams. The shear stress
iri these members, when currently prescribed load factors are
applied to vertical loads, range from 70 to 130 psi, stress
`=�1 ' Mahan&aeSatvo
Page Two
levels which today would require shear reinforcement. The
soil bearing pressure on the foundation due to vertical
loads averages approximately 3000 lbs per square foot and
may be as high as 4000 lbs. per square foot in isolated
areas. Since we see no evidence of foundation displacement
we assume these values are acceptable.
Repairs Required for Seismic Safety:
The lateral loads for this portion of the building were
calculated based on current code requirements for
earthquakes. The Uniform Building Code (UBC) gives existing
straight roof sheathing with roofing an allowable diaphragm
shear value of 100 pound per lineal foot (plf). The
existing roof diaphragm is within these limits if new
collector members approximately 15 feet in length are added
at four locations. These collectors will be connected to
the existing masonry wall at each end of the 2nd floor
balconies. The UBC allows no diaphragm shear values for
plaster lath ceilings. Since the diaphragm shear at the
ceiling of the second story can be as high as 215 plf, a new
diaphragm will be required at this level. In addition to
the new roof collectors and ceiling diaphragm the exterior
masonry walls must be connected to the roof and ceiling
diaphragms with bolts running through the existing wall.
These through -bolts are grouted in place, with a steel
bearing plate on the outside of the structure. The new
anchors will transfer the diaphragm forces into the walls
and will prevent the walls from falling away from the
building in an earthquake. The interior concrete walls must
also be mechanically attached to the ceiling diaphragm to
transfer lateral loads and stabilize the top of the wall
against forces acting perpendicular to the wall. In
conjunction with anchoring the diaphragms to walls, chord
members are required to resist a 770 lbs perimeter force at
the roof and a 1250 lbs force at the ceiling of 'the second
story. Lastly, this structure has roof parapets which range
in height from 18 to 48 inches. The portions of these
parapets which are taller than their thickness will require
bracing. This bracing may be required all along the
parapets or just at the highest ends, depending on their
actual height to thickness ratio.
The second floor shear walls, of both masonry and concrete,
have a maximum shear stress level of 6.1 psi, except for the
masonry walls at each end of the second floor balconies.
These four walls have a shear stress level of 16.0 lbs per
square inch and may require strengthening for both shear and
overturning forces. The parapets at the second floor
balconies will require bracing.
=�\\\ Mahan&DeSalvo
Page three
The second floor consists of a concrete joist and slab
system. At shear walls perpendicular to the direction of
the joist span, the floor appears to be positively connected
to the shear walls. Chord members are provided by concrete
beams and walls. The maximum diaphragm force at these
locations is 568 plf at concrete walls and 62 plf at masonry
walls. At shear walls parallel to the direction of the
Joist span the floor may not be positively connected to all
shear walls. At concrete walls it is likely there is
Positive connection but at masonry walls new connectors will
probably be required. These connectors will be similar to
the through -bolts described for new roof and ceiling to wall
connections. The maximum diaphragm force at these locations
is 748 plf at concrete walls and 367 plf at masonry walls.
New chord members may also be required at masonry walls and
can be added in conjunction with the new through wall
anchors.
The first floor shear walls are both unreinforced masonry
and reinforced concrete. The maximum shear stress in the
masonry walls is 13.5 lbs per square inch. The maximum
shear stress in the concrete walls is 16.5 lbs per square
inch. For walls in this condition these values are
acceptable and new shear walls are not required.
�' Mahan&DeSatvo
West Addition
Construction:
The one story west addition is constructed of exterior
unreinforced masonry walls 9" & 13" in thickness. Interior
bearing walls are 2x6 studs @ 16" o.c., with wood roof
framing. The floor slab and foundations are unreinforced
concrete.
Inspection:
The site investigation revealed the overall condition of the
existing construction to be good. The roof framing is dry
and in good condition. For comments and observations on the
roofing & flashing zefer to the discussion of the east
addition. The foundation shows no evidence of settlement or
cracking. The masonry walls are sound though the mortar
will require tuckpointing. Deterioration of mortar is more
pronounced at exterior downspouts. The concrete floor slab
is level and appears to be in good condition. The existing
wood floor furring will need patching and/or replacement due
to minor water damage at a few locations. This damage has
also affected some of the interior finishes requiring
patching and/or replacement of plaster finishes.
Analysis of Structure:
A review of the existing drawings, Sheets 1 thru 4, prepared
by Harold H. Ginnold, Architect and of our on -site
observations was conducted to determine the load carrying
capacity of the structure, both for lateral and vertical
loading conditions. The structural components of this
building addition were found to be adequate for vertical
loads, assuming allowable stresses of 1500 psi in bending
for wood members, 18,000 psi for steel members, and a soil
bearing pressure of approximately 2250 lbs per square foot.
These values are within acceptable limits for construction
of this time period.
Repairs Required for Seismic Safety:
The lateral loads for this addition were analyzed with
regard to the effects of a major earthquake. The roof
diaphragm maximum shear force is 185 plf, while the existing
roof sheathing has an allowable value of only 100 plf. This
indicates that a new layer of plywood will be required.on
the roof to transfer the diaphragm forces into the walls.
In addition, mechanical attachment of the roof sheathing to
walls will be required. This is usually accomplished with
new bolts running through the existing wall, grouted in
place, with a steel bearing plate on the outside of the
structure. These new anchors will also prevent the walls
from falling away from the roof in an earthquake. This
portion of the building has cantilevered parapets of
Mahan&DeSalvo
Page two
unreinforced brick which extend above the roof 16 to 30
inches. These parapets must be braced to prevent them from
falling off during an earthquake. Lastly with regard to the
roof, chord members will be required to resist a 2200 lb.
force. These members can be added in conjunction with the
new through -wall anchors. The masonry walls for this area
have a maximum shear stress of 7.7 lbs per square inch when
analyzed for earthquake forces. These walls are in good
condition, therefore this stress level is acceptable and new
shear walls will not be required.
Mahan&QeSaivo
East Addition
'Construction•.
The one story east addition is constructed in much the same
manner as the west addition. The differences consist of a
timber floor system with joists supported by beams and
posts. A lattice -work truss supports the roof framing at
the building center line. The truss is not visible so its
construction has not been verified. However, we are
assuming that the construction is as shown on the existing
drawings.
Inspection:
The site investigation revealed the overall condition of- the
existing construction to be good to poor. The foundation
and walls show evidence of settlement. It is our opinion
that the settlement took place shortly *after or during
construction and that patching of existing cracks in the
masonry will be sufficient. Beyond the cracking due to
settlement, the masonry walls are sound except for the brick
arch over the east exit. Mortar is missing from several
brick joints requiring some repair and rebuilding. As with
the west addition the masonry will need to be tuckpointed.
General Repairs Reaui� red:
The east addition has sustained a large amount of water
damage. This water is coming from the roof in the area of
the roof drains and scuppers. These drains and scuppers are
clogged allowing water to back up on the roof and leak down
into the building. This leakage has caused heavy damage to
the interior ceiling finishes but the timber roof members
appear to be sound. The timber floor system has been
heavily damaged due to decay and will require total
replacement. This replacement will include the interior
concrete foundation pads. New crawl space vents will need
to be cut into the existing masonry to prevent this
condition from recurring. The water damage has also
affected much of the interior finish, requiring patching
and/or replacement.
The roof of the east addition was inspected during our site
visit. The roofing is in fair condition as is the parapet
cap flashing. The parapet skirt flashing and the flashing
at the reglet at the main building intersection are in poor
condition. They will likely require replacement. Re-
attachment and caulking of roof flashing will be necessary
at many locations. These observations also apply to the
west addition.
The vertical load carrying capacity is similar to the west
addition. If the lattice work truss was used, its
connection to the wall should be examined. It should be
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Mahan&DeSalvo
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Page Two .:
noted.that all other vertical load'carrying systems have
-been-shown to be adequate and we believe it is probable that
the truss connection is also appropriate. The maximum soil
bearing pressure for the east addition is slightly higher
than for the west addition. It is approximately 2750 lbs
per square foot.
Repairs Required for Seismic Safety:
This portion of the building will also require strengthening
to resist lateral forces. The comments made for the west
addition apply to this east addition as well.
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t Mahan& DeSalvo
Library Addition & Existinq Service Buildin
Construction:
This two story addition was constructed above and, adjacent
to the one story service building using timber roof and
floor framing, a few exterior stud walls on the second floor
and unreinforced masonry walls.
Inspection & General Repairs:
The site investigation showed the condition of this portion
of the structure to be fair to very poor. There is a large
hole in the second story roof and the openings in the low
roofs for skylites have not been sealed. These areas have
allowed a large amount of water to damage the structure.
This damage is so severe that the timber framing throughout
this area will require replacement. The replacement of this
framing will allow the roof and floor diaphragms to be
rebuilt for the lateral earthquake forces required by the
code. The installation of through -wall anchors will also be
required to transfer the lateral forces from the new
diaphragms into the existing walls. The condition of the
existing masonry walls is good except for the south wall of
the fan room. This wall has a large crack and wall
displacement has occurred over the existing door. It may be
necessary to rebuild a portion of this wall. The structural
slab and the concrete beam appear to be in good condition
and are structurally adequate. However, since this
concrete beam directly supports the cracked masonry wall,
further investigation of the beam and its foundation support
will be required in the future. Lastly the existing covered
shelter at the west side of service building appears to be
in good condition and will require only minor repairs. The
covered shelter on the east side has been damaged by fire
and will likely require total replacement.
Repairs Required for Seismic Safety:
The lateral loads for this portion of the structure were
calculated for a major earthquake. As discussed above the
replacement of the roof and floor framing will include
provisions for the lateral earthquake forces. The existing
unreinforced masonry walls serve as shear walls. Our
analysis has shown some of these walls to be highly
stressed, as much as 22.5 lbs per. square inch. This is due
in part to the forces from the cantilevered masonry stack.
Removal of the stack will help but it is still likely that a
few of the shorter masonry walls will require strengthening
for both shear and overturning forces. If the masonry stack
is not removed it must be strengthened. Finally all
parapets which are more than 12" tall will require bracing.
Mahan&DeSatvo