BFMBFM Project No. 04123.09

BFMBFM Project No. 04123.09

April 18, 2005

DRAFT COPY ONLY

Eric Zabilka, AIA

Omni Architects

212 North Upper Street

Lexington, KY 40507

RE: Northern Kentucky University

Old Science Building

Joist Floor Slab Investigation

BFM Project No. 04123.09

Dear Eric,

As requested we have inspected the supported mechanical room floor structures of the Old Science Building. Our report is as follows.

PURPOSE:

The purpose of this study was to investigate the existing conditions of the concrete pan joist floor system concentrating in the mechanical rooms of the Old Science Building. Using the construction documents, the governing code of the time and data collected during site visits BFM was to determine the condition of the joist floor system and provide opinions and recommendations.

INTRODUCTION:

The building was originally designed by Fisk Rinehart & Hall McAllister Stockwell as Architect and Senler, Campbell & Associates as Structural Engineers. The building was constructed from 1972 to 1974 and has been in service now for 31 years.

The client expressed interest in installing new mechanical units in the building as part of this renovation project. BFM was told that the new HVAC units would weigh approximately 13,000 pounds and the new fan would weigh approximately 3000 pounds, which should be less than or equal to the existing units. After a preliminary analysis of the existing floor construction for the proposed new mechanical systems the floor joist capacity was found to be inadequate to carry the new mechanical equipment. During the review meeting to discuss our preliminary findings for the renovation project, we were requested to investigate if there could be a problem with the floor joist load capacity under existing conditions.

Mike McReynolds and FaLena Perry with BFM’s office visited the site on April 8, 2005. During the site visit they experienced severe vibrations of the joist floor system in the mechanical rooms. This vibration has been an ongoing complaint of the building users for many years. The vibration was thought by the university to be caused by inadequate equipment vibration isolators and out of balance mechanical unit fans. During this site visit, field measurements were made to determine the existing floor deflection. In addition, photographs of the floor slabs in each of the mechanical rooms were taken to show existing cracking in the existing floor slabs.

OBSERVATIONS:

Observations were limited to the mechanical rooms on the second, third, fourth and fifth floors of the building. In each mechanical room, cracks in the slab were recorded and photographed. Floor slab deflection was determined using a simple laser level by Titan.

Floor deflection was determined in each mechanical room. Deflection in Room 200 was measured to be 1.0 inches, Room 300 had a floor deflection of 1.6 inches, Room 400 had a deflection of 1.1 inches, and Room 500 the deflection was measured to be 0.7 inches.

Observations of each room found many similarities which included: cracking along and adjacent to both existing interior stud walls and running the length of the room, multiple slab penetrations, concrete pads varying in thickness from 3 ½ inches to 5 inches, on which the mechanical unit sits, and a construction joint in each mechanical room (except Room 300). The construction joint is located roughly 16 feet 10 ¾ inches from the north wall and is under the mechanical unit, and can be seen in Photograph #1.

Along both walls, parallel to the pan joist ribs, offset some distance from the walls, were continuous cracks in the floor. Most of those cracks ran the entire length of the room and connected the floor penetrations, located along both sides of the room as seen in Photograph #2. These cracks were measured to be 1/16th of an inch wide at their largest point.

Spring type vibration isolators were observed to be on all of the HVAC units in each mechanical room investigated and on the fans hung from the floor above in each Mechanical Room. See Photographs #’s 12 and 13.

In Room 200 continuous cracks along both long walls were recorded, as shown in Photograph #3. Photograph #4 shows the ceiling slab of Room 200 and the crack running between slab penetrations. This same crack was observed in the floor slab of Room 300 above, leading us to believe the crack fully penetrates the thickness of the slab. This was not limited to only one area as it was seen on top and bottom of other floors as well. Other cracks in the second floor slab were noted further in from the stud walls. These cracks extended to the mechanical unit pads and we believe are running the length of the room. All of these cracks are occurring off center of where the joist ribs were located below. An example of this can be seen in Photograph #5. This photograph is taken of the underside of the third floor slab under the mechanical unit. There was also one additional crack observed in the underside of the third floor slab. This crack was closer to the middle of the room and was also running adjacent to the concrete pad located above.

Room 300 had similar cracks running the length of the room on either side of the room. Photograph #6 shows one of the cracks running along the north side of the room, connecting the floor penetrations. Photograph #7 shows the crack running along the south side of the room’s floor slab. There are four cracks in the floor slab of this room running adjacent to the joists below. One other crack of importance ran across the pan joist ribs and was connecting three parallel cracks orthogonally. This crack is located 4’-11 inches off of the western wall and only 3’-3 inches from the adjacent column.

Cracks extending the length of Room 400 were recorded and shown in Photograph #8. In Room 400, cracks were noticed in the underside of the slab above and were located beside the 2nd and 3rd joist ribs from the north wall. These same cracks were observed in the floor of Room 500; therefore the cracks extend through the slab in these locations as documented by Photograph #9.

Also documented by Photograph #9 is moisture and rusting indicating a possible problem with moisture control. Another example of this can be seen in Photograph #10. This photograph shows the ceiling of Room 200. All along this crack are white calcium or sodium deposits.

Room 500’s floor slab has four continuous cracks running next to the joist below. This was the greatest number of cracks found that run next to the joists, not including cracks adjacent to walls. These cracks were 3 feet apart coinciding with the joist spacing of 3 feet center to center. Photograph #11 shows one of these cracks from the room below.

CONCLUSIONS:

The governing building code at the time of design could have been American Concrete Institute 318, either the 1963 or the 1971 edition. The 1963 ACI building code limits the total load deflection to L/360 for the floor system. The 1971 ACI building code limits the total deflection to L/480 minus the deflection of the structure before addition of non-structural elements. The L/360 calculation limits the maximum deflection to less than 1.3 inches. The deflections were measured with only dead load and equipment loads applied at the time. If the design live loads were applied the measured deflections would have been greater by some amount.

As previously stated deflections were as follows: 1 inch in Room 200, 1.6 inches in Room 300, and 1.1 inches in Room 400 and 0.7 inches in Room 500. Room 500 has a smaller deflection in our opinion due to a cantilevered condition in the floor slab system that reduces deflection in the span in the mechanical room under investigation. In Room 300 the deflection was measured by BFM to be 1.6 inches exceeding the L/360 limitation in its present state without any live load applied. If the floors in the mechanical rooms were to receive their design live loads, we believe that both Room 200 and Room 400 would have measured deflections at or exceeding the limit of 1.3 inches set in the ACI code.

The 1963 ACI code states that beams must have a minimum depth in inches of L/23; this edition of the code does not specifically recognize ribbed one-way slabs. The 1971 ACI code states that beams or ribbed one-way slabs should not be less than L/18.5 inches in depth. For the 39-foot span examined per this report, the minimum depth of the ribbed one-way slab should have been 20.3 inches per the 1963 ACI code or 25.3 inches per the 1971 ACI code. The floor system in Old Science is a 3-inch slab with 16 inches deep joists for a total depth of 19 inches. This shallow depth could explain the excessive deflection and could also contribute to excessive vibration.

The 1963 and 1971 ACI codes limit the distance between lateral supports (distribution ribs) of a beam/pan joist rib to 50 times the least width of the compression flange or face. Therefore at least one distribution rib (lateral support) should have been included in the joist floor system. The Concrete Steel Reinforcing Institute, publications of 1960 and 1971 recommends two distribution ribs for this length of span. Neither the ACI code requirement nor the CRSI recommendations have been met in the existing construction of the Old Science Building.

Distribution ribs are included in pan joist floor slab systems to transfer loads to multiple joists. The lack of distribution ribs will allow each joist to act singularly if cracks occur. There are cracks running parallel to the joists therefore many of the ribs are acting as single load carrying elements instead of a continuous floor system with multiple ribs as intended.

Noticeably extreme vibrations were observed in each mechanical room. Vibration can be damaging to a building and it is our opinion that the vibrations present in this structure are enlarging the already present cracks, making the situation worse. It must be noted that vibration is a serviceability issue and was not measured by BFM nor is directly regulated by the ACI.

RECOMMENDATIONS:

It is the opinion of BFM that the floor construction in the second, third, fourth and fifth floor mechanical rooms are structurally inadequate to carry the existing mechanical units and required code live loads. In addition because of the excessive deflection and vibration the floor slabs are tearing themselves apart and because of this there original floor load capacities have been reduced. In our opinion continued use of the mechanical equipment will continue to deteriorate the floor slab systems structural load carrying capacity, however, based upon the lack of past data we cannot predict at what point the floor system will be unable to support it’s own weight and the weight of the existing mechanical equipment. We recommend immediate repair work to each mechanical room’s floor slab to bring them up to required load carrying capacity and to prevent further deterioration from occurring.

Temporarily shoring of the mechanical room floor structure does not appear to be practical because the amount of ductwork, piping and the units themselves prevents installation of beams and posts at the appropriate support areas. In addition, the shoring would be required to extend to the basement floor slab where temporary foundations would be required. Due to past problems with the existing slab heaving we think this may create new problems with the slab on grade. As a temporary measure the mechanical room floor loading should be kept at a minimum by eliminating any stored materials or unused equipment and repair work done to the slab as soon as possible.

We recommend strengthening the existing floor slab system in the mechanical rooms. This work may not be possible to accomplish without removing the existing HVAC equipment, ductwork and plumbing lines. Removing the existing mechanical equipment will require limiting the use of the building during the repairs.

In our opinion there are two possible options that BFM considers as viable options for repairing the existing mechanical room floors. One option is to relocate the mechanical units and repair the floors, allowing them to support classroom or office loads only. This could be done with limited demolition to the floor slabs. This option would require relocating the HVAC to either an independent frame above the roof as previously designed or to a slab on grade location either in the building or outside.

Option two assumes that the existing rooms will continue to remain as mechanical rooms, if so, then these floor slabs will need to be extensively reinforced which will require significant demolition of the existing slab and construction of a new intermediate support frame to minimize the loss of head room. Structural reinforcing of the floor slab system will also be required on all floors, in the adjacent column bays next to the mechanical rooms. Additionally access to these adjacent rooms will be required on both sides of the mechanical room, to support the existing dead load, throughout demolition and construction of the new mechanical room floors. This work would not be able to be accomplished without first removing the existing HVAC equipment, ductwork and plumbing lines.

We appreciate the opportunity to provide you with our investigation and report. If you should have any questions concerning our observations, opinions and recommendations, please contact either Ethan Buell or Mike McReynolds.

Sincerely,

Buell•Fryer•McReynolds, Inc.

Ethan A. Buell, P.E.Michael L. McReynolds

PresidentProject Manager

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