These are the technical specifications used by the Architects, Engineers, Permitting Personnel and Builders for construction of Monolithic Domes.
Performance Specification for Monolithic Dome Construction: Section 13160 Pre-Engineered Concrete Dome
PART 1 – GENERAL
Drawings and general provisions of the Contract, including General Conditions and Division 1 Specification sections, apply to work specified in this section.
Description of Work: Extent of pre-engineered dome is shown on the Drawings. All domes shall be constructed to meet the Requirements of construction as described in the latest edition of the International Building Code.
Type: Is a free-span reinforced concrete dome including ring beam foundation.
Design: The concrete dome shall be designed in accordance with the latest edition of the International Building Code and design guidelines of the Monolithic Dome Institute. The dome shall be designed for the following loads:
- Live Load 40 P.S.F. (unless otherwise noted)
- Collateral Load 10 P.S.F. (unless otherwise noted)
- Wind Load 120 M.P.H.
- Seismic Category D
- Soil Bearing per local conditions
The loading combinations and unbalanced loadings considered shall conform to the requirements of the International Building Code.
Tolerances: Tolerances will normally be within + or – 3% of the radius of curvature except at foundation which will be + or – 1/2 % of building radius.
Permits: The Owner shall be responsible for obtaining all required building permits, as well as obtaining inspections and approvals of all state and local regulatory agencies having jurisdiction.
The dome shall be manufactured by a Monolithic Dome Builder having at least 5 years experience constructing Monolithic Domes of this size and scope.
The Contractor shall provide a written warranty in accordance with the manufacturer’s standard coverage. From the date of final acceptance any defects in materials and/or workmanship shall be promptly repaired or replaced at no cost to the owner for the following minimum periods:
- All building components – one year.
- Structural integrity of the dome – 5 years. This warranty is limited to structural failure only from normal use – not acts of God or abuse.
PART 2 – MATERIALS AND METHODS:
RING BEAM FOUNDATION:
Transit mixing per ASTM C 94. Ring wall and footing thickness determined by structural design for height selected, superimposed loads, and allowable bearing pressure, but not less than 8". The foundation will meet the following minimum standards:
- Minimum 28 day compressive strength – 3000 psi
- Portland Cement: Shall conform to ASTM C 150, Type I or II with a minimum mix design requirement of 5.0 sacks per CY.; or
- Maximum course aggregate size = 1"
- Air Entrainment – 5% (+1.5%)
- The reinforcing steel shall be ASTM A 615 grade 60.
- No calcium chloride shall be added to the concrete.
- Slump = 2" minimum 4" maximum at point of discharge.
This Section covers the mixing, placing, finishing and curing of shotcrete. Shotcrete shall be composed of Portland Cement, sand, 3/8" minus aggregate and water as specified or approved. The required proportions shall be assembled, well mixed, placed, finished and cured as hereinafter specified. It shall be uniformly dense and sound.
Shotcrete: Shotcrete is a mixed mortar of cement, sand, 3/8" minus aggregate, and water projected at high velocity onto a surface. The force of the jet impacting on the surface compacts the material. A relatively dry mixture is used so that the material supports itself minimizing sagging or sloughing, even when used for vertical and overhead applications. The cement, sand, aggregate, and water are mixed by suitable means, and then pumped through a hose by a specially designed mortar pump. The high velocity impact is developed pneumatically by injecting compressed air at the nozzle.
Rebound: Rebound is defined as aggregate mixed with some cement which ricochets off the surface.
- Portland Cement shall meet the requirements of Type I, II, III, IV or V as specified by Portland Cement Association. Type used to be as required by job usually I or II.
- Water: Water cement ratio should be held between .41 and .48 with .45 as target. Slump tests can be taken (Slump test on shotcrete mixes are not reliable but only indicators.) Depending on aggregate, slump may vary form 2" to 7".
- Ad mixtures: Admixtures may be used, provided they do not impair the density of the shotcrete or are corrosive to steel and concrete. All admixtures must be approved by the Engineer prior to their use.
- Fine aggregate shall meet the requirements set as previously specified in this section and shall meet the following gradation requirement:
Sand: well graded sand may be used for shotcrete applications. Sand shall generally consist of the following gradation:
|Sieve Size —||% Passing by Weight|
The fineness modulus shall fall between 2.70 and 3.00
Aggregate: A 3/8" minus aggregate should make up 10% to 30% of the mix design. Aggregate may be left out of final finish coat for smoother surface.
- General: The mix shall under no circumstance be leaner than 752 lbs. of Portland Cement to each cubic yard of concrete, (100 lbs. of cement may be substituted with 100 lbs. of fly ash.)
- Shotcrete Strength: Shotcrete strengths of 28 days shall be no less than 4000 psi.
Testing of Shotcrete Samples:
- Windsor Test Probe: The dome concrete shall be tested on a periodic basis with a Windsor Test Probe. Tests should occur at 7, 14, and 28 days as directed by the Owner’s representative. The dome contractor shall conduct the test with its equipment, and test shall be observed by the Owner’s representative.
- Special Inspections: Special inspections of the shotcrete shall be conducted as required by I.B.C. Sec. 306(a).
- Alternative Testing: Alternative Testing may be requested by the Owner. Cubes may be sawed, or cores having a minimum diameter of 2 inches and a L/D of 1 or greater may be drilled from test specimens prepared specially for testing purposes or from the structure under construction. Results must be corrected to L/D=2 as described in ASTM C 42.
- Shotcrete test specimens shall be shot on a plywood form in one continuous operation to the required height of the block. The size of the blocks shall be such that 9 test cubes or cylinders can be made from each block.
- One shotcrete test specimen shall be made during each day’s operation. Four cubes or cylinders shall be cut or cored from each shotcrete block seven days after its application. Two cubes or cylinders shall be tested for the seven-day strength. The other two shall be tested at 28 days.
- The remainder of the shotcrete blocks shall be cured and stored until after the 28 day test has been made and until the Engineer has informed the Contractor in writing that no additional tests are required. All shotcrete specimens shall be properly numbered and dated, and a record shall be made by the Contractor as to the relative location of the work for which these samples were prepared. All cubes or cylinders shall be dense and free from sand pockets.
- The cost of cutting, coring and testing cubes by a recognized testing laboratory shall be borne by the Owner.
- Batching equipment shall be capable of proportioning the cement and aggregate to the degree of accuracy required by these Specifications.
- Mixing equipment shall be capable of thoroughly mixing the aggregate, sand and cement in sufficient quality to maintain placing continuity, shall be self-cleaning and capable of discharging all mixed material without any carry-over from one batch to another. The equipment shall be inspected and cleaned at least once a day, more often if necessary, to prevent accumulations of batched material.
Placing and Finishing:
- General: Shotcrete shall be applied in a steady, uninterrupted flow.
- Position of Pneumatic Nozzles: The nozzle shall, as much as possible, be held at an approximate right angle to the surface and shall be kept at the proper distance from the surface dictated by good practice standards for the type of application, type of nozzle and air pressures employed. However, when encasing reinforcing steel, the procedure of the shooting at right angles may be modified in order to better direct the material around the bars. Whenever shooting of shotcrete on, around, through, and behind reinforcing steel is required, the nozzleman shall apply the material at the wettest possible consistency and at least wet enough that minimal shotcrete buildup will take place on reinforcing steel when shooting through this layer of steel.
- Shotcreting More Than One Layer: Sufficient time shall be allowed for each layer of shotcrete to set up so it may take the next layer without sagging. To insure proper filling of corners and recesses the initial coats shall be applied as wet as possible but shall still be dry enough that minimal sagging will occur.
- Wall Construction: Every precaution shall be taken to remove rebound from the bottom areas and corners of the wall as fast as it develops. The material shall be applied sufficiently wet so that a proper flow of shotcrete into the corners may be expected.
Curing of Shotcrete:
Interior shall be kept closed to prevent water vapor loss. During hot dry weather the building may be kept closed longer; up to 30 days as needed until concrete reaches 4000 psi.
- Meet or exceed ACI building code requirements for temperature and shrinkage steel.
- Deformed Bars: ASTM A615, A616, or A617 grade 60 (60,000 psi yield strength).
- Maximum spacing between the bars shall not exceed 18" or five times the shell thickness.
- Annular or ring reinforcement shall have a maximum allowable stress of 24,000 psi. Accurately place reinforcing as show on final approved drawings.
In order to reduce the thermal gradient in concrete, polyurethane foam shall be installed over the outside surface of the concrete dome meeting the following requirements:
- Thickness: as required by engineering plans
- Density: Minimum 1.9 or 2 lbs./cubic foot
- K factor: .12
- Permeability: 3.0 perms
- Compressive strength:30 psi, 90% closed cells
- Flamespread: less than 75,
- Smoke development: Less than 450.
- The surface shall be properly primed before application of the polyurethane.
SINGLE PLY FABRIC ROOF MEMBRANE:
Shall be PVC impregnated into a polyester scrim as manufactured by Seaman Corporation, or approved equal.
- Tongue tear: 270/250 psi minimum
- Grab tensile: 1000/950 psi minimum
- Strip tensile: 550/500 psi minimum
- Flame Retardant: CFM Title 19 or NFPA 701
- The fabric shall be 28 oz per square yard minimum weight.
All materials shall be installed and completed in a workmanlike manner. The owner reserves the right to direct, in writing to the Trade Contractor, the removal and replacement shall be at the Trade Contractor’s expense.