ZLA Major Mech Responses to letter 04 dated 10-4-2016.pdf

Sent: Tuesday, October 04, 2016 4:10 PM

Subject: 80539 Major Mechanical Modernization, Palmdale - Pre-Bid RFIs

Clarification questions regarding the raised floor scope.

1) Can you provide the current elevation of the raised floor in room B119? Reference Drawing A201 and A202: The concrete surface (below raised floor) in Room B119 is 2” lower than the concrete surface (below raised floor) in Room B134. The finish surface of the raised floor is approximately 18” high (with respect to the concrete below) in Room B134, and the finish surface of the raised floor is approximately 20” high in Room B119.

2) Trenches below raised floor appear to be in line with pedestal base locations. Will the trenches, existing or new, impact the installation raised flooring or are they covered and level with the adjacent concrete? The existing trenches are open. Per Sheet Note 19 on Drawing A201, existing steel channels bridging across trenches can be re-used, but Contractor’s seismic design required per specifications shall take this into account.

3) Does the existing equipment to remain sit on stands independent of the raised floor or do they sit on top of the raised floor? If they are not on stands who is responsible for shoring the existing raised floor areas to address seismic loads as required? What are the weights of the equipment in place? In Room B119, AHU-21 through AHU-24 are independently supported. In Room B134, existing electronic equipment is supported by the raised floor as follows: The existing equipment sits on top of the raised floor, and the raised floor and pedestals support the gravity load of the equipment. Existing seismic hold-downs (eye hooks, rods, and turnbuckles) are designed to carry tension from overturning seismic forces. Seismic shear forces are transferred through the raised floor stringer and pedestal system by friction because of the pretension of the hold-downs.

The stringers, floor panels, and pedestals under the equipment shall not be removed per Sheet Note 1 on Drawing A112. Contractor will need to design connection of new floor stringers to existing floor stringers at equipment locations. Please see Note 8 on Drawing A112 requiring the work to be done in phases; this shall also include phasing so that there is enough raised floor system surrounding the equipment for the seismic shear forces or temporary bracing by Contractor. Contractor is responsible for providing supplemental cooling per Sheet Note 8.

4) What is the elevation of the ducting to under the raised floor in relation to the overall raised floor elevation? We are trying to determine if there is adequate room to create a bridge over the duct under the raised floor. Sheet Note 20 on Drawing A201 was meant to note large transfer ducts that are above the raised floor in the locations shown on Drawing M202 on the south side of Room B119 (light lines). Although there are numerous pipes, conduits, cabletrays, cables, etc. under the raised floor, there is no known air ducts except as follows: At the air handling units shown on Drawing M202, shown as AHU-21, AHU-22, AHU-23, and AHU-24, the metal housing of supply air dampers protrudes approximately 7” from the air handling units; the metal housing is under the stringers. Contractor shall reinforce stair stringers as necessary to support the rated loads at this condition.

5) Foam gasket around equipment is typical although perimeter walls and columns typically have a cove base installed covering the small edge gap yet allowing panels to be removed and reinstalled without impacting the seal. Please confirm if this is acceptable. Please note that per specifications, Contractor shall design the raised floor system to meet ASCE 7; this is an essential area. If the design and construction limits the deflection of the raised floor panels so that the gap between the raised floor panels and existing walls is small enough for the cove base to cover, the method stated for the perimeter walls is acceptable. Regarding foam gaskets around equipment, conduit, cabletrays and wiring and other penetrations, the foam gasket material is in the specifications.