1 Scope
NOTE This specification covers the materials, formwork, reinforcement, placement, embedded items, and curing of cast-in-place reinforced concrete equipment pads located on grade or on an exterior elevated platform. (1.1)
NOTE Equipment pads provide a level, dimensionally controlled, vibration-resistant bearing surface for mechanical and electrical equipment; they isolate the equipment from soil moisture and capillary rise, transfer equipment weight and seismic and wind loads to the subgrade, and provide cast-in-place anchorage for equipment hold-downs and grounding electrodes. (1.2)
NOTE A pad is small in volume relative to the equipment it carries, so the cost of correcting a defective pad is dominated by the cost of removing and reinstalling the equipment that sits on it; anchor bolts in the wrong location, a pad that is out of level, a missing grounding stub, or a pad that has settled each turns into a multi-day setback once the equipment arrives, and the requirements that follow govern the conditions necessary to receive equipment without rework. (1.3)
1.4 Inherited and Supplemental Requirements
NOTE This standard inherits the general requirements of
Cast In Place Concrete for concrete materials, mix design, placement, and quality control.
(1.4.1) NOTE It inherits the requirements of
Concrete Reinforcement for reinforcing steel materials, fabrication, placement tolerances, and cover.
(1.4.2) NOTE It inherits the requirements of
Aggregate Base Course for the base course on which the pad bears and the requirements of
Earthwork for subgrade preparation.
(1.4.3) 1.4.4 Requirements specific to equipment pads — anchorage, embedded grounding, coordination with equipment manufacturer dimensions, finish, and isolation from adjacent flatwork — supplement and do not replace the parent standards.
1.4.5 Where this standard and a parent standard conflict, the more stringent requirement shall govern.
1.5 Design Basis
NOTE This standard does not address the structural design of the pad itself. (1.5.1)
NOTE Pad thickness, reinforcement, and pad dimensions shown on the contract drawings are the design basis. (1.5.2)
1.5.3 The Contractor shall not reduce pad thickness, reduce reinforcement, or alter pad dimensions without written approval from the Engineer of Record.
1.5.4 Default values in this specification represent typical conditions for the 80% case (a 6 in. thick pad reinforced with #4 bars at 12 in. on center each way, top and bottom, with ASTM F1554 Grade 36 cast-in-place anchor bolts) and are not a substitute for project-specific structural design.
2 Referenced Standards
2.1 Materials, fabrication, and installation shall comply with the latest adopted edition of the following standards and codes.
2.2 Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| ACI CODE-318 |
Building Code Requirements for Structural Concrete and Commentary |
| ACI SPEC-301 |
Specifications for Structural Concrete |
| ACI 117 |
Specification for Tolerances for Concrete Construction and Materials |
| ACI 305R |
Guide to Hot Weather Concreting |
| ACI 306R |
Guide to Cold Weather Concreting |
| ACI 308R |
Guide to External Curing of Concrete |
| ACI 347R |
Guide to Formwork for Concrete |
| ASTM C33/C33M |
Standard Specification for Concrete Aggregates |
| ASTM C94/C94M |
Standard Specification for Ready-Mixed Concrete |
| ASTM C150/C150M |
Standard Specification for Portland Cement |
| ASTM C260/C260M |
Standard Specification for Air-Entraining Admixtures for Concrete |
| ASTM C309 |
Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete |
| ASTM C494/C494M |
Standard Specification for Chemical Admixtures for Concrete |
| ASTM A615/A615M |
Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement |
| ASTM A706/A706M |
Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement |
| ASTM F1554 |
Standard Specification for Anchor Bolts, Steel, 36, 55, and 105-ksi Yield Strength |
| ASTM A153/A153M |
Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware |
| ASTM F2329/F2329M |
Standard Specification for Zinc Coating, Hot-Dip, Requirements for Application to Carbon and Alloy Steel Bolts, Screws, Washers, Nuts, and Special Threaded Fasteners |
| ASTM A194/A194M |
Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High-Pressure or High-Temperature Service, or Both |
| ASTM F436 |
Standard Specification for Hardened Steel Washers Inch and Metric Dimensions |
| ASTM E1155 |
Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers |
| IEEE 80 |
Guide for Safety in AC Substation Grounding |
| IEEE C2 (NESC) |
National Electrical Safety Code |
| NFPA 70 |
National Electrical Code (Article 250 — Grounding and Bonding; Article 110.26 — Working Space) |
| IBC |
International Building Code (locally adopted edition) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
| UFGS 03 30 00 |
Cast-in-Place Concrete (Unified Facilities Guide Specification) |
| UFGS 03 30 53 |
Miscellaneous Cast-in-Place Concrete |
3 Submittals
3.1 Action Submittals
3.1.1 The Contractor shall submit the following for the Engineer of Record's review prior to procurement, fabrication of reinforcement, and concrete placement.
3.1.2 No pad shall be placed until the corresponding submittals have been reviewed and returned.
- Concrete mix design for the pad concrete class, prepared in accordance with Cast In Place Concrete, showing cementitious materials, aggregates, admixtures, water content, target water-to-cementitious materials ratio, and the trial batch or field-record documentation establishing the required average strength
- Reinforcing steel shop drawings and bar lists conforming to Concrete Reinforcement, showing bar sizes, grades, lengths, bends, spacing, and concrete cover for each pad type
- Anchor bolt setting drawings, prepared from the equipment manufacturer's certified anchorage pattern for the specific equipment being supported, showing anchor bolt grade, diameter, embedment length, projection above pad, bolt circle or rectangular pattern dimensions, sleeve or template details, and the orientation of the pattern relative to the building grid or compass direction
- Formwork shop drawings or product data for proprietary pad forming systems, including provision for chamfer at exposed edges
- Embedded item layout for each pad type, including conduit stub-ups (size, material, count, orientation), grounding electrode connections (where required), drainage provisions (where required), and any equipment manufacturer-required cooling pits, oil-containment recesses, or cable trenches
- Curing materials and procedure
- For transformer pads: the grounding system layout, including ground rod locations, ground ring conductor (where used), and the connection of the grounding electrode conductor to the pad embed
☐ Concrete mix design (per parent CIP standard)
☐ Reinforcing steel shop drawings
☑ Anchor bolt setting drawings (per equipment manufacturer pattern)
☐ Formwork shop drawings or product data
☐ Embedded item layout (conduits, grounding, drainage)
☐ Curing materials and procedure
☐ Transformer pad grounding layout (where applicable)
3.2 Coordination Submittals
● Equipment manufacturer's certified anchorage drawing for the ordered equipment (required)
○ Catalog footprint or generic family drawing (not acceptable)
3.2.1 The Contractor shall obtain the equipment manufacturer's certified anchorage drawing for the actual ordered equipment — including the actual generator frame, the actual transformer base, the actual chiller unit — and shall not place anchors based on a catalog footprint, a model-family generic, or a "typical" arrangement.
NOTE The anchor bolt setting drawing is the most consequential submittal for an equipment pad and shall not be inferred from a generic equipment cut sheet; differences in frame size, fuel tank configuration, mounting accessory, or shipping split between catalog and ordered equipment routinely move anchor bolt positions by inches, and a pattern poured to the wrong drawing requires demolition and replacement of the pad. (3.2.2)
3.3 Closeout Submittals
3.3.1 The Contractor shall provide the following at substantial completion before pad work is accepted:
- As-built dimensions of each pad: plan dimensions, finished top-of-pad elevation, and the as-set anchor bolt pattern measured between bolt centers
- Field test reports for the pad concrete (compressive strength cylinders) indexed to the corresponding pad
- Documentation of any deviation from the approved anchor bolt pattern or embedded item layout and the Engineer of Record's written disposition
☐ As-built dimensions of each pad (plan, top-of-pad elevation, as-set anchor pattern)
☑ Field test reports for pad concrete (compressive strength cylinders) indexed to pad
☑ Documentation of deviations and Engineer of Record's written disposition
4 Quality Assurance
4.1 Testing Agency
4.1.2 Compressive strength cylinders shall be cast from each pad placement in accordance with Cast In Place Concrete. 4.1.3 A single small pad does not require a full set of cylinders if it is placed from the same truck as a larger element that is tested, but each truck delivered shall be sampled at least once per ACI SPEC-301.
4.2 Special Inspection
● Required — Special Inspector or qualified survey before equipment delivery
○ Required — Contractor self-verification documented in writing
○ Not required — no regulated equipment supported
4.2.1 Special inspection requirements for the pad shall be as set out in the project Statement of Special Inspections and in IBC Chapter 17.
4.2.2 Where the equipment supported is regulated (life-safety generators, fire pumps, designated seismic equipment), pre-installation verification of the anchor pattern, anchor embedment, and pad dimensions shall be performed by the Special Inspector before equipment is set.
4.3 Pre-Pour Conference
4.3.1 For project sites with more than five equipment pads, or for sites with any single pad supporting equipment heavier than 5,000 lb, a pre-pour conference shall be held attended by the Contractor's superintendent, the concrete subcontractor, the equipment installer, the electrical subcontractor (where embedded conduits or grounding are involved), and the Engineer of Record.
4.3.2 The conference shall review the approved anchor bolt setting drawings, the embedded item layout, the relationship of pad finished elevation to surrounding grade and the building floor, the curing duration before equipment may be set, and the procedure for receiving and verifying the equipment manufacturer's anchor template.
5 Environmental and Service Conditions
NOTE Equipment pads located outside the building envelope are exposed to weather and, in cold-climate regions, to freeze-thaw cycling and de-icing chemicals carried in from adjacent driveways and walks. (5.1)
5.2 Exposure Selection
○ F0 — no freezing and thawing exposure
● F1 — freezing and thawing without de-icing chemicals
○ F2 — freezing and thawing with de-icing chemicals
● Exterior, on grade — exposed to weather
○ Exterior, on elevated platform or roof — exposed to weather
○ Interior, in unconditioned space (parking garage, mechanical yard)
○ Interior, in conditioned mechanical or electrical room (use parent CIP standard)
5.2.1 The exposure category selected for the pad concrete shall reflect these conditions and shall not be reduced because the pad is "isolated" or "not part of the structure."
NOTE The most common durability defect in equipment pads is concrete specified without air entrainment in a freeze-thaw region, which spalls progressively at edges and corners until anchor cover is reduced or the bearing surface becomes uneven. (5.2.2)
6 Coordination with Equipment Manufacturer
6.1 Equipment Selection Confirmed Before Pad Construction
6.1.1 No pad shall be formed until the equipment manufacturer and model number have been confirmed, the equipment has been released for fabrication, and the equipment manufacturer's certified anchorage drawing has been received and reviewed.
NOTE Pads built on the assumption that the eventually-ordered equipment will conform to a basis-of-design drawing are at significant risk of dimension error. (6.1.2)
6.2 Anchor Pattern Sources of Error
6.2.1 The following are the most common sources of anchor pattern errors and shall be addressed in the Contractor's pre-pour verification:
- Equipment ordered with a non-standard skid, base, or sub-base (most generators above 60 kW)
- Equipment ordered with manufacturer accessories that change the footprint (sub-base fuel tank, vibration isolators, weatherproof enclosure)
- Equipment with multiple shipping splits that recombine on site (large chillers, oversize switchgear lineups)
- Field-bolted lineups where the as-shipped lineup length differs from the lineup planned during design
- Pad-mounted transformer base footprints, which vary between utility-owned and project-owned units even at the same kVA rating
- Imperial-vs-metric anchor pattern dimensions on equipment from international manufacturers
6.3 Anchor Template
● Steel plate template fabricated from manufacturer's anchorage drawing
○ Plywood template fabricated from manufacturer's anchorage drawing
○ Manufacturer-supplied template (where provided with equipment)
○ Proprietary anchor bolt setting kit
6.3.1 The Contractor shall use a rigid anchor template (steel, plywood, or proprietary template) to position anchor bolts during the pour.
6.3.2 The template shall be fabricated from the certified anchorage drawing, not from a tape-measure layout of bolt positions.
6.3.3 The template shall hold bolts vertical and at correct elevation during placement and consolidation, and shall remain in place until the concrete has set sufficiently to maintain anchor position.
7 Subgrade Preparation
7.1 Base Course Under Pad
4 in. (light equipment, condensing units, small pumps)
6 in. (standard, generators and transformers)
8 in. (heavy equipment, large generators, soft subgrade conditions)
12 in. (per geotechnical report or contract drawings)
Per drawings
7.1.1 The subgrade beneath an equipment pad on grade shall be prepared in accordance with Earthwork and shall receive an aggregate base course in accordance with Aggregate Base Course. 7.1.2 The Contractor shall not place a pad directly on natural undisturbed soil unless the geotechnical report specifically authorizes it for the soil type encountered and the equipment loading anticipated.
7.1.3 The aggregate base course beneath the pad shall be at least as thick as the base course shown on the contract drawings, but in no case less than 4 in. for light equipment (condensing units, small pumps) and 6 in. for heavier equipment (generators, transformers).
7.2 Base Course Moisture
7.2.1 The subgrade and base course shall be moist (not saturated) at the time of pad placement to prevent the base from drawing water from the fresh concrete.
7.2.2 Where dry or hot weather conditions are anticipated, the base shall be lightly sprinkled before placement; standing water shall not be permitted.
● Plywood (structural-grade) with timber framing
○ Steel forms
○ Aluminum forms
○ Proprietary pad forming system
8.1.1 Formwork for equipment pads shall be plywood, steel, aluminum, or proprietary pad forming systems sized to the pad dimensions.
8.1.2 Forms shall be tight enough to prevent loss of cement paste and shall be braced sufficiently to resist the hydrostatic pressure of fresh concrete without bulging beyond the ACI 117 tolerance on plan dimensions.
8.1.3 Earth forms (concrete poured directly against trenched soil walls) are not acceptable for equipment pads.
NOTE Earth forms do not maintain dimension and do not produce the chamfered or formed edges required at exposed corners. (8.1.4)
8.2 Chamfer
3/4 in. chamfer at all exposed edges (standard)
1 in. chamfer (heavy traffic or vehicle-adjacent pads)
Tooled radius edge (where smooth profile is required)
Square edge (only where chamfer would conflict with equipment skirt)
8.2.1 All exposed edges and corners of the pad shall be formed with a 3/4 in. chamfer unless otherwise indicated on the contract drawings.
NOTE Chamfered edges reduce the likelihood of impact spalling, hide minor edge irregularities, and present a finished appearance; sharp 90-degree corners are vulnerable to chipping under foot traffic, equipment carts, snow shovels, and de-icing salt exposure. (8.2.2)
8.3.1 Form release agent shall be applied to all form surfaces before placing reinforcement.
8.3.2 Form release shall be compatible with any subsequent coating or sealer that will be applied to the pad surface.
8.3.3 Diesel fuel and used motor oil shall not be used as form release.
9 Concrete Mix
9.2 The pad concrete is typically a single class used throughout all pads on the project; where pad applications differ significantly (e.g., a light condensing-unit pad and a heavy generator pad), separate mix classes may be specified.
9.3 Mix Properties
3000 psi (light pads, non-freezing exposure)
4000 psi (standard, most equipment pads)
4500 psi (heavy equipment, F2 exposure)
5000 psi (severe exposure or per drawings)
Per drawings
○ 0.55 — F0 exposure, interior or sheltered pads
● 0.50 — F1 freeze-thaw, no de-icing chemicals (standard exterior pad)
○ 0.45 — F2 freeze-thaw with de-icing chemicals
○ Not required (F0 exposure only)
○ Required — 4.5% ± 1.5% (1 in. max aggregate, F1 or F2)
● Required — 6.0% ± 1.5% (3/4 in. max aggregate, F1 or F2 — standard)
○ Required — 7.5% ± 1.5% (3/8 in. max aggregate, F1 or F2)
3/8 in. (thin pads, congested reinforcement)
3/4 in. (standard equipment pads)
1 in. (heavy pads with widely spaced reinforcement)
9.4 Air Entrainment Requirement
9.4.1 Exterior pads in any region that experiences a freezing winter shall be air-entrained without exception.
NOTE Air entrainment is the primary defense against freeze-thaw spalling of edges and corners; specifying f'c alone does not provide freeze-thaw durability, and an unentrained 5000 psi pad spalls just as readily as an unentrained 3000 psi pad. (9.4.2)
10 Reinforcement
NOTE The default reinforcement for an equipment pad is a top and bottom mat of deformed bars in each direction, sized and spaced as shown on the contract drawings. (10.2)
10.3 Where the contract drawings do not specify reinforcement, the default below shall apply.
10.4 Reinforcement Configuration and Cover
○ Single mat — center of pad (light pads, thickness ≤ 4 in.)
● Top and bottom mats — each way (standard, thickness ≥ 6 in.)
○ Top and bottom mats with edge ties (heavy equipment, thickness ≥ 8 in.)
Per drawings
#3 (3/8 in.) — light pads only
#4 (1/2 in.) — standard equipment pads
#5 (5/8 in.) — heavy pads
#6 (3/4 in.) — very heavy generator or transformer pads per drawings
Per drawings
8 in. o.c. each way
10 in. o.c. each way
12 in. o.c. each way (standard)
16 in. o.c. each way (light pads only)
Per drawings
Grade 60 (ASTM A615) — standard
Grade 60 (ASTM A706) — where field welding to embedded anchors is permitted
3 in. (cast against earth — no vapor barrier or topping mud)
2 in. (cast on base course with vapor barrier or topping mud)
1-1/2 in. — bars #5 and smaller (standard)
2 in. — bars #6 and larger
10.5 Reinforcement Support and Placement
10.5.1 Reinforcement shall be supported on plastic-tipped wire chairs, all-plastic chairs, or precast concrete block chairs in accordance with Concrete Reinforcement. 10.5.2 Bare wire chairs shall not be used in exterior or F1/F2 exposure pads because they corrode and stain the pad surface.
10.5.3 Bars shall be tied at intersections sufficiently to maintain position during anchor bolt installation and concrete consolidation.
10.5.4 The reinforcing mat shall be positioned to avoid conflict with anchor bolts and conduit stubs.
10.5.5 Where an anchor bolt or conduit conflicts with a planned bar position, the bar shall be cut and replaced with two bars splayed around the embed, splice length per Concrete Reinforcement; bars shall not simply be omitted at conflicts. 11 Anchor Bolts
11.1 Material and Grade
● ASTM F1554 Grade 36 (standard, general equipment)
○ ASTM F1554 Grade 55 (higher load, weldable variant where indicated)
○ ASTM F1554 Grade 105 (high-load, high-seismic applications)
Per drawings
○ Plain (no coating) — interior or sheltered exposure only
● Hot-dip galvanized (ASTM F2329 / A153) — standard exterior
○ Mechanically galvanized — alternative to hot-dip
○ Stainless steel (ASTM F593) — corrosive environment
1/2 in.
5/8 in.
3/4 in.
7/8 in.
1 in.
1-1/4 in.
1-1/2 in.
Per drawings — equipment manufacturer drawing (deferred by default)
12 × bolt diameter (minimum where not calculated)
Per drawings — equipment manufacturer drawing (deferred by default)
11.1.1 Anchor bolts shall be ASTM F1554 headed or hooked anchor rods, of the grade required by the structural drawings and the equipment manufacturer's anchorage drawing.
NOTE ASTM F1554 Grade 36 is the default for general-purpose equipment anchorage; Grade 55 is used where structural calculations require higher capacity; Grade 105 is used for high-load applications such as large transformer anchorage in high-seismic regions and is rarely required for general equipment pads. (11.1.2)
11.2 Embedment Length
11.2.1 Embedment length shall be the greater of the value shown on the equipment manufacturer's anchorage drawing and the value calculated by the Engineer of Record under ACI 318 Chapter 17 for the design loads.
11.2.2 The Contractor shall not reduce embedment depth to fit a thinner pad without written approval from the Engineer of Record and a revised anchorage calculation.
11.3 Cast-in-Place vs. Post-Installed Anchors
● Cast-in-place during pad pour (standard, required for new pads)
○ Adhesive (epoxy) anchor in existing pad — requires Engineer approval and certified anchor system
○ Mechanical expansion anchor in existing pad — requires Engineer approval
11.3.1 Cast-in-place anchor bolts placed in the wet concrete during the pad pour are the default for new equipment pads.
11.3.2 Where post-installed anchors are used, the anchor product shall be certified under ICC-ES AC308 (adhesive) or AC193 (mechanical), shall be selected by the Engineer of Record for the design loads and exposure, and shall be installed by an installer who has completed the manufacturer's certification training for that anchor system.
NOTE Cast-in-place bolts provide the highest pullout capacity, do not depend on epoxy or expansion mechanisms, and are not subject to seismic anchor reductions that apply to many post-installed anchors; post-installed anchors (mechanical expansion or adhesive) are an acceptable alternative only where the pad already exists, where the anchor pattern is being changed to receive different equipment than originally planned, or where field tolerances cannot be met by cast-in-place installation. (11.3.3)
11.4 Anchor Bolt Projection and Hardware
3 in. (typical, generators and switchgear)
4 in. (typical, transformers with elevated base)
6 in. (elevated mounting or grouted bedding)
Per drawings — equipment manufacturer drawing (deferred by default)
11.4.1 Each anchor bolt shall project above the finished pad surface as required by the equipment manufacturer's drawing to engage the equipment base, threaded into a leveling nut and a top nut over a hardened washer per ASTM F436.
11.4.2 The projection length shall include the equipment base thickness, the grout bed depth (where used), two washers, and the top nut, plus 1/4 in. minimum thread engagement beyond the top nut.
11.4.3 Anchor bolt threads above the pad surface shall be protected from damage and contamination during the curing period and through equipment delivery by capping with plastic thread protectors, by wrapping with tape and plastic, or by greasing and wrapping.
11.4.4 Threads encrusted with concrete or rusted from neglect shall be cleaned and tested before equipment is set.
NOTE Insufficient projection forces field cutting of bolts, which damages threads and is grounds for rejection of the installation. (11.4.5)
12 Embedded Items
12.1 General
12.1.1 All embedded items — conduits, grounding electrode conductors, drains, sleeves — shall be positioned and secured before the pad is poured.
12.1.2 Field cutting or coring of placed pad concrete to add a missed embed shall not be performed without written approval from the Engineer of Record.
NOTE Coring after the fact frequently cuts reinforcement or anchor embedment. (12.1.3)
12.2 Conduit Stubs
Per equipment manufacturer's conduit entry detail
Stop flush with pad surface (cable troughs, switchgear with internal raceways)
Stub up 4 to 6 in. above pad (typical for terminations inside equipment base)
Stub up to coordinate with equipment cable management
Per drawings
12.2.1 Conduit stubs serving the equipment shall enter the pad from below per the contract drawings and shall be terminated above the finished pad surface as required by the equipment manufacturer for that conduit connection.
12.2.3 Conduit shall be capped during concrete placement to prevent debris from entering and shall be supported to resist displacement during pour.
12.2.4 Where conduits are clustered (e.g., multiple feeders entering a generator or a transformer secondary), the cluster spacing shall match the manufacturer's cable trough opening; conduits shall not foul the equipment base.
12.3 Grounding Electrode Connections
NOTE Pad-mounted transformer pads, generator pads, and switchgear pads commonly require a grounding electrode connected at the pad. (12.3.1)
☑ Ground rod(s) driven adjacent to pad with grounding electrode conductor stubbed through pad
☐ Ground ring conductor encircling pad below grade with taps stubbed through pad
☐ Grounding electrode conductor connection to building grounding electrode system
☐ Concrete-encased electrode (Ufer ground) where pad reinforcement is bonded and connected
☐ Not applicable — equipment connected to building grounding system only
12.3.4 Coiling excess conductor inside the pad cavity is acceptable provided the coil does not interfere with cable termination.
12.3.5 For generator pads, the grounding electrode conductor connection shall be coordinated with the generator manufacturer's grounding lug location, with the building grounding electrode system, and with the separately derived system grounding requirements of NFPA 70 Article 250.
12.4 Other Embedded Items
☐ Cable pulling sleeves through the pad to a cable trench below
☐ Drainage opening or sleeve for transformer oil containment
☐ Lifting inserts (cast-in lifting eyes) — for precast-style pads only
☐ Equipment-specific embedded sleeves per manufacturer
☑ None
13 Pad Dimensions and Layout
13.1 Plan Dimensions
- Foot clearance for service personnel walking around the equipment
- NEC 110.26 working space dimensions in front of electrical equipment where the working space is to be on the pad rather than on adjacent paving (typically 36 in. for 0–150 V to ground, more for higher voltages)
- A minimum 3 in. concrete edge beyond the outermost anchor bolt to prevent breakout of the anchor cone
- Manufacturer-required clearance for cable bending radius at conduit stub-ups, control panel doors, and removable covers
Per drawings — pad plan dimensions (deferred by default)
☐ NEC 110.26 working space on the pad (typically 36 in. minimum front, 0–150 V)
☑ NEC 110.26 working space on adjacent paving (pad limited to equipment footprint plus 3 in. edge)
☐ Manufacturer-required service clearance integrated into pad
☐ Cable bending radius envelope at conduit stub-ups
13.1.3 Where the contract drawings show a pad dimensioned with pad plan dimensions, that dimension is the design basis and shall not be reduced. 13.1.4 The Engineer of Record shall confirm whether the NEC 110.26 working space is provided on the pad or on adjacent paving before the pad is dimensioned.
NOTE The choice between providing the NEC working space on the pad versus on adjacent paving is a design decision that affects both pad size and the location of nearby site work such as curbs, fences, and landscaping. (13.1.5)
13.2 Pad Thickness
4 in. (light equipment only — condensing units, small pumps)
6 in. (standard, most equipment pads)
8 in. (medium-heavy equipment, generators ≤ 200 kW, transformers ≤ 750 kVA)
10 in. (large transformers, generators 200–500 kW)
12 in. or more (heavy generators ≥ 500 kW, large transformers, per drawings)
Per drawings
13.2.1 Reducing pad thickness without re-evaluating anchorage is not permitted.
NOTE Pad thickness governs anchor embedment, breakout cone development, and stiffness against equipment-induced vibration. (13.2.2)
13.3 Top-of-Pad Elevation
2 in. (standard, condensing units on paved areas)
4 in. (standard, generator and transformer pads on grade)
6 in. (heavy equipment, areas with high snow accumulation)
Per drawings
13.3.1 The finished top-of-pad elevation shall be set above adjacent grade or adjacent paving such that surface drainage flows away from the pad and that the pad is not submerged under rain or snowmelt.
13.3.2 The pad shall be located by reference to the building grid, property line, or other surveyable control as shown on the contract drawings at pad location plan. 13.3.3 Pad rotation (orientation of the equipment relative to compass direction or building face) shall match the contract drawings and the equipment manufacturer's recommended orientation for cable access, ventilation intake and exhaust, and service access.
NOTE A minimum 4 in. elevation above adjacent grade is typical for transformer and generator pads; a minimum 2 in. is typical for condensing-unit pads on paved areas. (13.3.4)
14 Pour and Consolidation
14.1 Placement Method
● Direct chute from truck
○ Concrete pump
○ Buggy or wheelbarrow (small inaccessible pads)
14.1.1 For most equipment pads, concrete shall be placed by direct chute from a ready-mix truck or by concrete pump.
14.1.2 Free-fall distance shall not exceed 4 ft.
14.1.3 Buggy or wheelbarrow placement is acceptable for small pads not accessible by truck or pump.
14.2.1 Immediately before placing concrete, the Contractor shall verify, in the presence of the Special Inspector (where required) or by self-inspection (where not required), that:
- Anchor bolts are correctly positioned per the template and the manufacturer's anchorage drawing, including pattern dimensions, pattern orientation, and bolt elevation
- All anchor bolts are vertical and at the correct projection
- Conduit stubs are capped, positioned, and braced
- Grounding electrode conductors are positioned and protected
- Reinforcement is in place, supported, tied, and at the correct cover
- The base course is moist and free of standing water
- Forms are tight, braced, and treated with release agent
14.2.2 The pre-pour verification shall be documented in writing.
14.2.3 Concrete shall not be placed until any deficiencies are corrected.
14.3 Consolidation
1 in. (thin pads, congested embeds)
1-1/2 in. (standard equipment pad)
2 in. (heavy pad, sparse embeds)
14.3.1 Concrete shall be consolidated by internal mechanical vibration immediately after placement.
14.3.2 A vibrator head of 1-1/2 to 2 in. diameter is appropriate for most equipment pads; the vibrator shall be inserted at intervals not exceeding 18 in. and shall be held until air bubbles cease rising.
14.3.3 The vibrator shall not be used to move concrete laterally or to drag concrete into corners.
14.3.4 Care shall be taken not to displace anchor bolts during vibration; the anchor template shall be braced sufficiently to resist incidental contact.
15 Finish
15.1 Top Surface
● Steel-troweled smooth — equipment with continuous base, no grout bed
○ Wood-floated — equipment requiring a grout bed for leveling
○ Light broom — pedestrian traffic on or alongside the pad
○ Heavy broom — equipment that may be walked on during service
15.1.1 The top surface of an equipment pad shall be screeded to elevation, floated to consolidate the surface and embed coarse aggregate, and finished to the texture appropriate for the equipment that will be set on it.
15.1.2 A broom finish is required for any surface that a worker may stand on, particularly transformer pads in regions subject to ice.
15.1.3 The top surface shall not be steel-troweled to a glass-smooth finish where equipment will be set on a grout bed.
NOTE Steel troweling is the default for equipment with a continuous, machined base that bears directly on the pad; a wood-floated surface is preferred where the equipment is leveled on a grout bed, because the rougher texture improves grout bond, and over-troweling produces a dense, low-permeability surface to which grout does not bond well. (15.1.4)
15.2 Tolerances on Top Surface
15.2.1 The top surface shall be level within the tolerances given under Tolerances below, and shall be free of high spots, low spots, and trowel ridges that would prevent uniform bearing of the equipment base on the pad or grout bed.
16 Curing and Protection
16.2 Curing Method and Duration
● Curing compound (ASTM C309 Type 1-D or Type 2)
○ Wet burlap covered with polyethylene sheeting
○ Polyethylene sheeting only (interior pads, low evaporation)
○ Insulated curing blanket (cold weather)
3 days — light equipment, no operational loading (condensing units)
7 days — standard, most equipment
14 days — heavy equipment, transformers under load, high-vibration generators
Per field-cured cylinder breaks demonstrating 75% of f'c
16.2.1 Curing compound shall not be applied to areas where a grout bed, sealer, or coating will subsequently be applied unless the curing compound is demonstrated to be compatible or has fully dissipated before the subsequent application.
16.2.2 Where compatibility cannot be confirmed, wet curing shall be used.
16.2.3 The pad shall not be loaded with equipment until concrete has reached at least 75% of f'c, demonstrated by field-cured cylinder breaks taken from the same pour.
NOTE Equipment pads are particularly vulnerable to inadequate curing because their high surface-to-volume ratio causes rapid moisture loss; an uncured pad develops a weak, dusty, permeable surface that subsequently spalls in freeze-thaw exposure. (16.2.4)
NOTE Setting equipment on uncured concrete is among the most common causes of cracking at anchor bolts and edge spalling. (16.2.5)
16.3 Weather Precautions
● Not required — ambient < 90°F, moderate humidity
○ Required — per ACI 305R and [[sync/cast-in-place-concrete]]
● Not required — ambient > 40°F through protection period
○ Required — per ACI 306R and [[sync/cast-in-place-concrete]]
17 Tolerances
17.1 Dimensional tolerances shall comply with ACI 117.
17.2 Tolerance Values
± 1/2 in. on overall plan dimensions
± 1/4 in. on overall plan dimensions (tighter — high-precision equipment)
± 1/8 in. from drawing dimension between adjacent bolts (standard)
± 1/16 in. (high-precision equipment with machined base)
Per drawings — equipment manufacturer drawing
± 1/4 in. on specified projection
± 1/8 in. (where leveling nut adjustment is limited)
± 1/8 in. under 10-ft straightedge (standard equipment pad)
± 1/16 in. under 10-ft straightedge (rotating equipment, generators, pumps)
Per equipment manufacturer's installation tolerance
Within 1 in 40 (1.5 degrees) of vertical
Within 1 in 100 (0.6 degrees) of vertical — high-precision equipment
NOTE Equipment pad tolerances are typically tighter than generic slab tolerances because the pad serves as a bearing and anchorage surface for equipment with specified mounting points. (17.2.1)
17.3 Pattern Tolerance Measurement and Resolution
17.3.1 The pattern tolerance shall be measured against the equipment manufacturer's drawing, not against a tape-measure layout of nominal dimensions.
17.3.2 Where pattern tolerance is exceeded, the Contractor shall not bend, heat, or cut anchor bolts to fit the equipment without written approval from the Engineer of Record; the resolution is either to ream the equipment base or to remove and replace the pad.
18 Joints — Isolation from Adjacent Flatwork
18.1 Isolation Joint Configuration
● Required — full-depth pre-molded joint filler at all interfaces with adjacent slabs or paving
○ Not applicable — pad is freestanding with no adjacent flatwork
● Closed-cell polyethylene foam filler, compressible (standard)
○ Asphalt-impregnated fiber filler
Per drawings
18.1.1 Where an equipment pad is placed adjacent to a sidewalk, driveway, exterior slab, or building floor slab, an isolation joint shall be provided between the pad and the adjacent flatwork.
18.1.2 Isolation joints shall be full-depth pre-molded joint filler in accordance with Cast In Place Concrete. 18.1.3 The joint shall be sealed at the surface with an elastomeric joint sealant where the joint is exposed to traffic, water, or where its open condition would be unsightly.
18.1.4 The sealant shall be compatible with the joint filler and shall be installed in accordance with the sealant manufacturer's instructions.
NOTE The pad and the adjacent slab move differently because of differential loading, thermal cycling, and subgrade differences, and a rigid connection between them produces cracking at the interface. (18.1.5)
18.2 Construction Joints
18.2.1 Construction joints within a single pad shall be avoided.
18.2.2 A pad shall be placed monolithically; cold joints, partial placements, or layered pours are not acceptable in an equipment foundation.
NOTE Cold joints, partial placements, or layered pours produce planes of weakness that are not acceptable in an equipment foundation. (18.2.3)
19 Inspection and Testing
19.1 Pre-Placement Inspection
19.1.1 Pre-placement inspection requirements are stated above under Pour and Consolidation.
19.2 Field Testing of Concrete
19.2.1 Field testing of fresh concrete (slump, air content, temperature) and casting of compressive strength cylinders shall be performed in accordance with Cast In Place Concrete. 19.2.2 For project sites with multiple pads placed from a common pour, a single set of acceptance cylinders may serve multiple pads provided the placements occur on the same day from the same delivered concrete.
19.3 Pre-Set Verification
19.3.1 Before equipment is set on a pad, the Contractor shall verify and document:
- Pad concrete has reached at least 75% of f'c
- Anchor bolt pattern dimensions and projections match the equipment manufacturer's anchorage drawing within the specified tolerance
- Anchor bolt threads are clean, undamaged, and capable of accepting the leveling nut and top nut
- Top-of-pad elevation and levelness are within tolerance
- Embedded conduits and grounding stubs are present, clean, and at the correct locations
- The pad is free of cracks, spalls, exposed reinforcement, or other defects
● Yes — written verification by Contractor with sign-off
○ Yes — Special Inspector observation in addition to Contractor verification
NOTE The pre-set verification protects against the most expensive sequence of failures in equipment installation — equipment delivered to the site, found not to fit, returned to storage at additional cost, the pad demolished and replaced, and the equipment re-delivered — and verification before delivery is inexpensive while the failure mode after delivery is not. (19.3.2)
20 Delivery, Storage, and Handling of Materials
20.1 Storage and Handling
20.1.2 Anchor bolts shall be delivered to the site in clearly identified bundles or boxes with manufacturer's certification (mill test reports for the bolt steel and zinc coating thickness verification for galvanized bolts) and shall be stored on supports above grade in a manner that prevents thread damage and contamination.
20.1.3 Thread protectors shall remain in place from delivery through installation.
20.1.5 Curing compounds, form release, and curing blankets shall be stored in accordance with the manufacturer's recommendations, protected from freezing and from exposure to sunlight where the product is light-sensitive.
21 Repair of Defects
21.1 Defects discovered after form stripping or after pad acceptance shall be evaluated by the Engineer of Record and repaired as directed.
NOTE Common defects in equipment pads and their typical dispositions: (21.2)
| Defect |
Typical Disposition |
| Hairline shrinkage cracks (< 0.005 in.) |
Accept; seal with penetrating sealer if in F2 exposure |
| Surface cracks > 0.005 in. but not through-thickness |
Rout and seal with elastomeric crack sealant |
| Through-thickness cracks |
Engineer evaluation; epoxy injection or replacement |
| Edge or corner spall |
Repair with polymer-modified patching mortar to original profile |
| Honeycombing in formed surface |
Remove loose material, dampen, patch with mortar of same w/cm as parent concrete |
| Anchor bolt out of pattern tolerance |
Engineer evaluation; ream equipment base, relocate bolt, or replace pad |
| Anchor bolt out of plumb |
If within recoverable range, straighten with leveling nut and shim; otherwise replace pad |
| Embedded conduit missing or wrong location |
Core after the fact only with Engineer approval; otherwise modify equipment layout or replace pad |
21.3 Repair Authority
☑ Edge and corner spalls repaired with polymer-modified patch
☐ Surface cracks routed and sealed
☐ Honeycombing patched in formed surfaces
☐ Tie holes patched (where formed)
☐ Anchor pattern deviations evaluated and resolved before equipment delivery
21.3.1 The Contractor shall not perform structural repairs (epoxy injection, replacement, anchor relocation) without written direction from the Engineer of Record.
21.3.2 Cosmetic repairs to non-structural surface defects may proceed in accordance with Cast In Place Concrete. 22 Warranty
22.1 Installation Warranty
1 year from substantial completion (standard)
2 years from substantial completion
22.1.1 The Contractor shall warrant the pad installation against defects in materials and workmanship — including cracks beyond hairline width, surface spalling, anchor displacement, settlement, and frost heave — for the project warranty period from the date of substantial completion.
22.1.2 The warranty shall not apply to damage caused by equipment loads exceeding the design basis, to damage from vehicle impact or other external causes, or to settlement caused by subgrade conditions outside the Contractor's scope.
22.1.3 Material warranties for proprietary anchor systems, post-installed anchors, repair mortars, and joint sealants used in the pad work shall be passed through to the Owner and included in the closeout submittals.