STRUCTURAL DESIGN CRITERIA

6.3.1 Structural design criteria are presented for Electrical, Control, Standby Generator Buildings along with buried facilities such as wet wells. Each is discussed below.

6.3.2 Electrical, Control, Standby Generator Buildings: These buildings are typically non-occupied support buildings consisting of either cast-in-place concrete, tilt-up concrete, or fully grouted masonry bearing walls with steel or timber framed roof framing systems.

The intent of these buildings is to protect the electrical-mechanical equipment from the elements. Specific guidelines are as follows:

a. The exterior of these buildings can consist of either exposed masonry or concrete or a stucco type of finish system. The roofing material ranges from built-up roofing, to composite shingles, to concrete tiles, to standing seam metal roofing. All roofing materials and the installation of these materials should conform to the requirements specified in the National Roofing Contractors Association (NRCA) Roofing and Waterproofing Manual.

b. These buildings should be fully enclosed, sealed, and weather stripped to prevent rain water from entering the interior. The construction of the building exterior walls should achieve a minimum insulation rating of R-19. The building ceiling should have a minimum R-30 insulation rating. A vapor capillary break should be placed below the building slab on grade to prevent weeping of subgrade water into the building.

c. If access to the roof is required for removal or maintenance of equipment, fall protection anchors must be located where personnel can attach anchors before stepping on the roof. In the areas of the roof access hatch, the roof surfaces should provide traction and adequate footing for safety.

d. The doors for these buildings will typically consist of exterior rated steel doors conforming to the requirements specified in Steel Door Institute (SDI) 100

requirements. Any fire doors required should conform to NFPA 80 requirements. The associated door hardware should be at a minimum commercial rated hardware. Door pulls, cover plates, and striker plates should be stainless steel. Locks should allow personnel to open and secure the door from the inside. Locks with interchangeable type cylinders should be provided and should be dead bolt type. Hardware for fire doors should be UL listed. Any glass or glazing associated with these buildings including windows should conform to the following standards:

(1) Flat Glass Marketing Association (FGMA) Glazing Manual and Sealant Manual (2) Sealed Insulating Glass Manufacturers Association (SIGMA), TM-3000 Vertical

Glazing Guidelines and TB-3001 Sloped Glazing Guidelines

e. All glass and glazing should be fabricated and installed for normal thermal

movements and wind loading. Normal thermal movement is defined as that resulting from an ambient temperature range of 120°F and from a consequent temperature range within the glass and glass framing members of 180°F.

f. Interior concrete floor surfaces should be protected with a sealer-hardener coating.

Nonskid-type floor coatings should be provided around pumps and equipment where maintenance will be performed. Floors should be sloped to floor drains or sumps at a slope of not less than 1/8-inch per foot (1%), or greater where warranted.

g. Floor gratings in all areas except the pump station wet well should be aluminum.

Floor grating in the pump station wet well should be fiberglass reinforced plastic.

Floor drains or gratings should be located to minimize drainage across the floor.

Floor drains should be provided in every room except the generator and control room.

h. The Engine-Generator Room should be equipped with monorails with trolley hoists for routine maintenance functions. Doors should be sized for generator removal.

Removal of generators and engines should be accomplished by portable equipment provided by others. Provisions should be included for access hatches, lifting hooks, hoisting systems, roll-up doors and other means to provide maintenance.

i. An intermediate platform should be provided for access to vertical wastewater pump drives greater than 100 hp in size.

j. Lifting eyes attached to the ceiling should be provided directly above the valves and equipment items weighing more than 100 lbs that are not accessible by bridge cranes or monorails. The Consultant should ensure adequate horizontal and vertical

clearance between the overhead crane hoists and other installed equipment to allow lifting and moving motors and pump equipment to the station doors via the monorail.

k. Structural design of the building should conform to the following design codes.

(1) 2001 California Building Code (CBC)

(2) American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete

(3) American Institute of Steel Construction, Manual of Steel Construction

(4) Concrete Masonry Association of California and Nevada, Design of Reinforced Masonry Structures

(5) National Forest Products, National Design Specification For Wood Construction

(6) The Aluminum Association, Aluminum Design Manual

l. Loading of these buildings for structural design purposes should conform to Section 16, Structural Design Requirements of the CBC and include as a minimum the following:

(1) Dead Load: Self Weight of Structural Elements

Mechanical Equipment and Piping Loading Electrical Equipment and Conduit Loading Fire Sprinkler Loading as Appropriate

(2) Live Loads: Minimum Roof Live Loading of 20 pounds per square foot (psf) Other Live Loads as Appropriate

(3) Lateral Loads: Seismic Loading – Zone 4

Wind Loading – Basic Wind Speed 90 mph

(4) Deflection of grating and cover plate should be limited to ¼ inch for 100 psf live load or 1/240 of clear span, whichever is smaller. Weight of grating or plate segments should be limited to 80 pounds maximum, unless otherwise noted.

m. Each equipment item should be mounted on a reinforced concrete equipment base in accordance with applicable codes and the manufacturer’s recommendation. Edges on concrete pump bases should be chamfered with a minimum one-inch chamfer.

Anchor bolts should be stainless steel, 300 series minimum. Wedge type or chemical type anchor bolts are not allowed for rotating equipment.

6.3.3 Underground Structures: Design criteria includes the following:

a. The wet well should be constructed of shrinkage-control concrete mix with low specific conductivity suitable for wastewater storage structures. Wet well walls and ceiling should be protected with PVC sheet liner embedded in reinforced concrete.

Wet well exterior walls should be epoxy coated. Dry well should be constructed of reinforced concrete.

b. Buried structures should be designed to resist flotation without wall friction resisting the outside surfaces when the wet well is empty. Groundwater should be assumed to be at the surface. A factor of safety (against buoyancy) of 1.10 for 100-year flood condition should be used for design purposes. For normal conditions, the factor of safety should be 1.50.

c. Access doors to the wet well should be provided. All internal areas of the wet well should be visible from the access doors. Hatches should be installed with either safety webbing across the hatch opening or removable handrails that can be placed in

chocks around the opening, according to the District’s M&O preference. A stairway for access into an underground pump station dry well should be installed in lieu of a ladder.

d. Areas around any confined space entry should be designed to be suitable for use with the District’s retrieval equipment. Permanent access ladders and manhole steps should not be installed in wet wells.

e. Waterproofing should be provided on the exterior buried walls of non-hydraulic structures and water stops should be installed at all concrete construction joints. Seals