KORA_Req._for_Eng._Studies_on_Stouffer_Apts. KU Reference No

Transcription

1 000130

2 1 PURPOSE: Professional Engineering Consultants, P.A. (PEC) was engaged by University of Kansas Design & Construction Management to perform an assessment of Stouffer Place Apartment Building 20 located at 1620 Ellis Drive in Lawrence, Kansas. The purpose of the assessment was to review the structural condition of the existing units at the north end of the building, unit 6 on the first floor and 12 on the second floor. Both units are continuing to experiencing distress in the exterior walls and floor slabs. The structural scope of services includes observation of the existing conditions, reviewing the original construction documents, modification documents made since the original construction, production of a written report documenting the observations and recommendations and an opinion of the probable repair costs. As part of the PEC s project scope, GeoSource Inc. performed a geotechnical investigation. Their report dated January 16, 2013 was sent under separate cover. The evaluation of the property for elements routinely provided by other disciplines, not listed above, is excluded from the report. The following documents were reviewed as part of this assessment: 1956, 1957 and 1961 original building construction plans for various faces of the Stouffer Place Apartments. We also received copies of the roof modifications, stair tower repairs and other site modifications made since the original building construction

3 2 OBSERVATIONS: The initial observations were performed on September 1, The observations of the property were performed by Gary Bond, P.E., Kansas license number Mr. Bond was accompanied onsite by Ms. Laura Gagliano, KU Design & Construction Management, and personnel from KU Department of Housing. The following observations were made during the site visit: The structure is a two-story masonry building with steel bar joists spanning east-west between front and back walls to support concrete slabs at the second floor and roof. The original building was constructed in the late 1950 s and is benched slightly into the hillside on the west. The roof structure has been over-built with wood trusses (above the slab) to improve drainage and provide a gable roof appearance. The exterior grade on the west side is approximately 2 feet above the interior slab elevation. Both the upper and lower apartment units were unoccupied at the time of our visit. LOWER UNIT 20-6 Along the north wall of the lower apartment, we observed an obvious slope in the slab downward from the middle wall to each corner. The slab also sloped downward at each side as you moved closer to the corner. In the west room, we observed approximately 1½ of apparent settlement at the northwest corner and very little settlement at the interior wall, as seen in the pictures below. Original building drawings indicate that the floor slab is not supported at the perimeter walls and is free to float

4 3 As we expected on the other side of the wall in the east room, the slab did not appear to have moved significantly. We did observe a similar dip to the northeast corner of approximately 1. As can be seen in the picture above, where the interior wall intersects the north wall, the corner joint has separated starting about two feet above the floor. On closer inspection at the base of the wall, we observed both new and old separation. The original base molding had been extend approximately 3/8 at some point in time indicating drying shrinkage in the wood or horizontal movement of the wall. The picture at the right shows the opposite side of the wall in the west room and a corresponding gap between the closet trim and wall at the top. The door frame at the bottom of the picture appears to have moved with the north wall and the gap to the door is much wider at the bottom. At first glance, the wall appears to also have rotated slightly. On the following page, the pictures show ceiling cracks that parallel the north wall, indicating that the part of the ceiling has moved with the north wall, separately from the of the ceiling

5 4 UPPER UNIT The upper unit was also unoccupied and appeared to be in the process of being renovated with new paint, a new west window (northernmost) and new unpainted window trim. Large cracks can be seen above and below the window due to movement of the exterior walls

6 5 We also observed that a horizontal gap existed between the second floor and the north wall, which was most noticeable in the west room. It is unclear from the existing drawings how the floor slab would be constructed next to the wall, while the roof slab is show clearly bearing on the wall. It is possible that the slab was built with an expansion joint between the concrete slab and wall, which is how the joist bearing at the front wall is detailed. SOIL INVESTIGATION: As noted in the soils report, at test pit was excavated at the northwest corner of the building and two interior holes were core drilled through the slab. The test pit located the existing footing, which was in general conformance with the original construction documents. We did not find any void below the exterior footing, which appeared to be in contact with the soil

7 6 The two interior core drill locations found a small void below the slab, ranging from ½ to 1½, as noted on the geotechnical boring logs. In the pictures at right, the vapor barrier is seen on the bottom of the slab with gaps to the aggregate drainage fill. While on site, the excavation sub-contractor took laser level measurements of the window sills along the west wall. We found that the majority of the sills were very close to level and in alignment. The exception was the northernmost windows on both levels which were approximately 2 low. In reviewing the cracks in the exterior brick, it appears that the north wall has dropped this amount. The masonry joints have been reworked and grouted over time, with some of the joints being very thick. The cracking starts about 30 feet from the north wall and stair steps up through the second story window, where it was observed on the inside of the room

8 7 The footings supporting the east balcony columns have also settled and damaged the concrete balcony, pulling apart portions of the concrete. As seen in the picture at the right, the balcony should be shored until the support provided by the column can be restored at both north columns. The cracking at the landing is a clear indication of the differential movement occurring in the structure. CONCLUSIONS: Based on the observations and testing performed, it is our professional opinion that the building slab and exterior bearing walls have settled significantly as a result of the extended drought and the large tree adjacent to the north wall as stated in the geotechnical investigation. The lower slab on grade has moved directly with the loss of soil subgrade moisture, while the upper slab has moved with the settlement of the exterior bearing walls. The north wall appears to have settled approximately 2, since the original construction. As the tree has gotten bigger, the roots have continued to take moisture from further under the building slab and foundations. The slab on grade was detailed to float independently from the foundation and thus the movement of the slab is somewhat expected. While not a structural concern, the floor slope and settlement likely detract occupants from renting the space

9 8 From a structural standpoint, we are concerned with the gap between the second floor and the north exterior wall. We believe the north wall is an important element in the lateral stability of the building. We believe that the foundation settlement has allowed the north wall to move away from the building approximately ½. We were not able to observe the bottom of the slab or the joist cross bracing that is shown anchoring into the north wall. We believe that the anchorage may have pulled out of the wall slightly and should be repaired. RECOMMENDATIONS: Based on the observations, PEC recommends that the following items be addressed. 1) Shore the north edge of the balcony and repair concrete beam at the column supports. Estimated repair costs, including temporary shores $ ) Stabilize the north wall to prevent further settlement of the foundation and movement of the wall. There are several approaches that could be considered with varying costs, risks and expected service life. We recommend the first solution below, which would require removal and replacement of the stair to install the underpinning. The second solution was offered for consideration in the soils report movement. a. Underpin the foundation wall with concrete piers extending to rock. Further settlement is eliminated, but future increases in soil moisture could lift the footing and cause damage to the wall. Estimated cost for this scope of work is $47,000. b. Build tree root cut-off wall or cut down tree as described in soils report. Further settlement in this option is unlikely, but not guaranteed. Future increases in soil moisture could lift the footing and cause damage to the wall. Estimated cost for this approach is $ ) Provide a positive connection from the north wall to the second floor and roof slabs to transfer in-plan and out of plane loads. Estimated cost for this approach is $ ) Repairing the slab on grade to provide a level surface could also be accomplished in several ways as noted in the soils report. The approaches listed could return the lower floor to a level condition, similar to the original construction. The slab would still be subject to varying degrees of movement in the future due to changes in soil. Replacing the near surface soils, as recommended, does reduce the potential movement of the slab by improving the stability of the nearer surface subgrade soils. Estimated cost for partial demolition of the floor slab (11-0 x26-8 ), subgrade, rebuilding the interior walls

10 9 is $25,000. Adding 13 feet to the south would include both the lower floor bathrooms for $30,000. The additional slab replacement would extend the soil stabilization past where the exterior brick crack indicates that the settlement has occurred. 5) Repairing the upper slab to a completely level condition is not considered a required structural repair, but could possibly be accomplished by adding thin overlays on the existing concrete slab. Additional measurements would be needed to determine extent of leveling and coordinated with a review of the existing floor structure. 6) At the conclusion of the other repairs, the cracks in the exterior wall should be repaired. We would recommend an allowance of $2000. PEC would appreciate the opportunity to assist in implementing the recommendations in this report. Please do not hesitate to contact us if we can be of further service. DISCLAIMER: This assessment was based on the conditions readily observable at the time of the assessment and any related inspection. Subsequent deterioration of the property may have occurred since the time of any such inspection. There may be unforeseen or hidden damage that was not observed at the time of the observation due to a number of possible issues. No subsurface or other intrusive investigation was made. No survey was performed to determine any dimensions or boundaries. PEC does not have any beneficial interest in the subject property. This report is a qualitative assessment of the property. Construction and/or renovation of the property based on the conclusions or recommendations should not begin until a full set of construction documents are prepared by a licensed professional. The report is written solely for the use of the client listed above and no other party shall have the right to rely on the information contained in the report. This report is not transferable to a third party without written permission of PEC. Reproductions of this report, not bearing the original engineer s signature, are invalid. This Assessment was limited to the items specifically included in the scope of work. Nothing in this report shall be deemed to imply or suggest anything beyond what is specifically stated. The construction cost estimate included within this report is based on preliminary information and should not be considered a final cost of construction