Structural Inspection

Transcription

1 General: Background: An inspection and structural analysis have been performed for the purpose of evaluating the buildings structural systems and components. A full set of structural drawings was utilized for our inspection and analysis. The inspection was done on May 12, All observable structural systems were inspected for conformance with the original design drawings and for any signs of distress or other conditions which could compromise the building s structural integrity. Many structural elements were covered with finishes or insulation and thus not accessible for inspection. Physical layout: The L shaped building is configured with two sloped roof classroom wings and a high roof gymnasium at their intersection. The wings have a gable profile with a 1 in 12 slope and a ridge running down the center. The south wing terminates into the south side of the east west wing with roof valleys at their intersection. The gym roof is shed configuration with a 1 in 12 slope to the south. Foundations: Description: Foundations are conventional concrete footings founded on undisturbed native soils or compact fill. Building columns are founded on concrete spread footings that are typically 3 0 square by 12 deep. Highly loaded columns have larger footings. Spread footings at perimeter walls are buried with top of footing at 3 0 below exterior grade. 8 concrete foundation walls are utilized around building perimeter. 1 2 wide by 8 deep concrete strip footings are located below foundation wall at classroom wing end walls, stair alcove foundation walls, interior concrete walls, and perimeter walls of gym. Other foundation walls have no strip footing but instead span between column spread footings which are typically spaced at 14 0 on center. Condition: The foundation is buried and could not be inspected but appeared to be performing adequately. Foundation failure would result in settlements that would be evident in the superstructure and no such distress was observed. The foundation system should have a remaining useful life of years. The building floor is a 5 thick concrete slab on grade reinforced with welded wire fabric. The slabs condition was good with no sign of unusual cracking, settlement, or other deficiencies. Remaining Life Expectancy: The slab should have a remaining useful life of 25 years. Roof Framing: Description: The classroom wings are framed with tongue and groove timber decking spanning between glue laminated wood beams. 4x6 nominal decking is orientated parallel to the roof ridge and typically spans 14 0 between beams. Decking is supported by 7 x22 ¾ deep glue laminated beams. Each beam is supported by two June 2005 Glacier Valley Elementary School Condition Survey Report Page 34 of 178

2 pipe steel columns, one at exterior wall and the other at corridor wall. A reduced depth section of beam cantilevers over the corridor wall to ridge at centerline of building. The reduced beam depth allows maximum clearance for mechanical ductwork running below beam and above the corridor ceiling. The gym high roof is framed with tongue and groove timber decking spanning between glue laminated wood beams. 3x6 nominal size decking is orientated east west and typically spans 9 5 ½ between beams. Decking is supported by 11 x 39 deep glue laminated beams. Each beam is supported by two pipe steel columns, one at each end. Inspections indicated the condition of gym roof framing was good. The only framed floor area is a small mechanical mezzanine at south side of gym. This area is essentially an extension of the classroom wing roof framing. Condition: Inspections indicated the condition of classroom wing roof framing was fair. The majority of roof beams were exposed and showed no signs of excessive checking, splitting or distress. The majority of roof decking was obscured. In classrooms, acoustical ceiling tile was adhered directly to bottom of decking and foil faced insulation attached to bottom of decking prevented inspection above the suspended corridor ceilings. The only decking available for inspection were sections that had been replaced during the latest re roof. Past roof leaks had allowed moisture to penetrate and rot some areas of decking. Pieces of the rotted decking had fallen to the suspended corridor ceiling and were observed during our inspection. It was apparent that some areas of decking had experienced severe rot. The replacement decking was exposed from underside and appeared to be in very good condition. The extent of decking that needed to be replaced and the severity of rot observed in the fragments found on top of corridor ceilings leaves some uncertainty about the condition and long term performance of original decking. We understand a complete inspection was done at the time of last re roof and that all questionable decking was replace at this time. We assume all compromised sections of decking were repaired or replaced during the last re roof. The gymnasium roof beams were exposed to view and easy to inspect. They showed no signs of excessive checking, splitting or distress. Most of the decking was obscured by ceiling tile but a section over mechanical mezzanine was exposed and in good condition. Remaining Life Expectancy: The classroom wing roof framing system should have a remaining useful life of years. The gym roof framing system should have a remaining useful life of years. June 2005 Glacier Valley Elementary School Condition Survey Report Page 35 of 178

3 Structural Analysis Results and Deficiencies A structural analysis has been completed based on information contained in the original construction drawings and confirmed during our on site inspections. The analysis was based on the 2003 International Building Code. The following deficiencies were found. June 2005 Glacier Valley Elementary School Condition Survey Report Page 36 of 178

4 Typical roof decking and glue laminated beam The original building was designed for a roof snow load of 40 psf. The current code roof snow load is a minimum of 50 psf. A check of the decking and framing indicates that the members typically have the reserve capacity to resist the additional 10 psf. The exception is in the inside corner of the building in the roof framing over the toilets and janitor rooms. Both the existing decking and glue laminated beams are overstressed by 30%. The deck spans in this area should be reduced by adding new glue laminated beams centered between each of the existing beams. This will result in an increase in the capacity of the decking and reduce the loads on the existing beams. The existing valley beam should be replaced with a new glue laminated beam to increase the capacity of the framing. New 3 diameter pipe columns and 2 0 square footings at interior wall locations will be needed. $15,000. See architectural deficiency items for additional costs. June 2005 Glacier Valley Elementary School Condition Survey Report Page 37 of 178

5 Snow drifting adjacent to Gym roof Areas subject to snow drifting around the higher gymnasium roof do not have the additional reserve capacity to carry the dead loads prescribed by today s codes. The deck spans in these areas should be reduced by adding new glue laminated beams centered between each of the existing beams. This will result in an increase in the capacity of the decking and reduce the loads on the existing beams. New 3 diameter pipe columns and 2 0 square footings at interior wall locations will be needed. $38,000. See architectural deficiency items for additional costs. June 2005 Glacier Valley Elementary School Condition Survey Report Page 38 of 178

6 Lack of lateral load resisting system No lateral load resisting system is present in longitudinal direction of wings. Exterior walls are plywood sheathed and could act as shearwalls, but continuous strip windows prevent a continuous load path and eliminate the possibility of using the exterior walls as shearwalls. Corridor walls are gypsum sheathed and could provide some nominal lateral load resistance, however the gypsum sheathing stops just above the ceiling and therefore can not be used as a shearwall. Preliminary wind and seismic calculations indicate that ½ plywood should be added to one side of each of the corridor walls. The sheathing could either be continuous the length of the corridor or installed only on the 24 walls between classroom entry alcoves at approximately each fourth classroom with a minimum of two walls on each side of the corridors each wing. For the discontinuous wall remedy, tie struts need to be created to transfer the lateral loads into the shear walls. The tie struts can be created by installing Simpson CMST16 continuous straps on top of the decking. Simpson PHD2 hold down anchors should be provided at each end of each wall segment to resist the over turning loads. The hold June 2005 Glacier Valley Elementary School Condition Survey Report Page 39 of 178

7 downs will require the addition of 2 feet square footings at each location. 5/8 drill in adhesive anchors spaced at 32 on center along each of the shear walls is required. $35,000. See architectural deficiency items for additional costs. (photo not available) Insufficient transverse shear walls Shear walls transverse to the direction of the wings are provided on one side of each on the entry corridors. However, the lateral loads exceed the capacity of these shear walls. Additional plywood sheathing should be added to the existing shear walls. This occurs in nine places. The wall on the opposite side of the entry corridors should also be sheathed with ½ plywood each side. This condition occurs in three locations. These walls all tie directly into the existing glue laminated roof beams. Simpson PHD5 hold downs should be provided at each end of these walls. The hold downs are typically located at the existing interior column footings. $17,000. June 2005 Glacier Valley Elementary School Condition Survey Report Page 40 of 178

8 Insufficient sheathing in roof diaphragm to resist lateral loads Description: The initial construction consists of T&G decking without plywood roof diaphragms. In addition, during the re roof project no sheathing was added at that time. The drawings do not indicate how decking is attached. A check of the capacity of the decking diaphragm nailing based on the typical AITC deck nailing methods was done. The typical nailing pattern does not have adequate capacity based on the current shear wall locations. A new layer of ½ sheathing should be applied over all of the existing 3 and 4 T&G decking. It may be feasible to install plywood on the underside of decking if adequate access will be created by other renewal improvements. For example if ceilings, lights and mechanical ductwork will be replaced, it may provide adequate access such that plywood could be attached to underside of roof deck. Another option would be to wait until the next re roof is necessary and install the plywood at this time. $235,000. See architectural deficiency items for additional costs. June 2005 Glacier Valley Elementary School Condition Survey Report Page 41 of 178