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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 $450,000 (24 to 31 dollars per square foot). While we cannot evaluate the usefulness of the building as a school, it is our opinign that the structure could be repaired at much less cost than new construction. This concludes our investigation of Lincoln school. we hope you find our report useful and we will be happy to answer further questions. It has been a pleasure serving you. Please call if you have any questions. Very truly yours, 5'z = X-7s q-- // fit" yw4�44-0� 0,44-44"_7 W. Mahan Principal .,sAl Lesvz'.. f'�� Mahan&De5alvo ._bF`•' �wt. • F'' ,y)_ �$i+ijrfr" 1k".Y' rsa7e•�.' ' . - �rr.t: •H- N.`•7 k `f,�42:L' • :i.. 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 `� �1 Mahan&DeSalvo J -4 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. ��� �t 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