MONOLITHIC DOME CONSTRUCTION

A Seminar report submitted to Bangalore University in partial fulfillment of the requirements for the award of first semester

MASTER OF ENGINEERING CIVILMajor: Structural EngineeringByNaveen R.I SemesterUNDER THE GUIDANCE OFDr. SADATH ALI KHAN ZAI

FACULTY OF ENGINEERING CIVILUNIVERSITY VISVESVARAYA COLLEGE ENGINERINGBANGALORE UNIVERSITY, JNANABHARATHIBANGALORE - 560056

DECEMBER 2010

BANGALORE UNIVERSITYFACULTY OF ENGINEERING CIVILJNANABHARATHIBANGALORE -560056

CERTIFICATEThis is to certify that the Seminar work entitled Monolithic Dome Construction submitted by Naveen R in partial fulfillment of the requirements for the award of the degree of Master of Engineering in Civil Major: Structural Engineering during the year 2010-2011 is a bonafide research work carried out by him.

Dr. Sadath Ali Khan Zai Dr. V.Deveraj Guide and Assistant Professor Professor and Chairman Faculty of Engineering Civil Faculty of Engineering Civil Bangalore University, Bangalore University, Bangalore 560056 Bangalore-560056

SynopsisMany memorable structures throughout history, have been built using the thin shell hemispherical shape of the dome. These timetested monuments surpass many in beauty and longevity. Continuing in the tradition of these magnificent edifices, Dome Technology engages the latest engineering and architectural technologies to produce aesthetic, functional, and economical schools, gymnasiums, water parks, community centers, and industrial facilities. At a fraction of the cost of a conventional structure, each building benefits from unobstructed views, seating efficiency, great acoustics, and space utilization. Modern insulated concrete dome construction combines several materials to create a strong, efficient, weatherproof structure. Compared to other types of structures for the same application. The Dome is rested upon Ring Beam. Continuous reinforcing bars are embedded in the ring beam foundation. These rebar dowels securely connect the dome to its footing. The ring beam creates a solid base on which to construct the dome. The dome structure then itself is raised upon this beam laying the Airform and reinforcement mesh and then covering it up with shotcrete. This seminar attempts to provide a glimpse on the current trend in the construction of Monolithic Dome

CONTENTSTable of ContentsINTRODUCTION1 23456

1. Introduction Today, in this modern world, there are different types of structure they may be either a steel structure or concrete structure or the combination of both steel and concrete or structure made up of other material. Of these structures the Monolithic concrete dome is the latest and of great demand of structure constructed. In 1976 Mr. David B South and his brother Barry and Kandy South developed an effective method to develop Monolithic domes and in 1979 first monolithic dome was constructed in Shelley Idaho. Right now there are number of monolithic building in the world. There is an institute (chairman. David B.South) in the Italy, which are, doing research work on various aspect of the domes they also provide design of the monolithic domes. The largest monolithic dome in the world is the home of Faith Chapel Christian Center in Birmingham, AL. It seizes the record at tall, and in diameter. Inside is a floor area of in two levels. Domes have been popular in the construction of buildings since ancient times. This particular design has the important characteristic of withstanding adverse climatic conditions such as earthquakes, tornadoes, floods, hurricanes, or even tropical storms. Earlier domes were used only in religious buildings, however its usage has now been seen in constructing residence buildings as well. Houses with dome construction are usually found in regions which experience heavy winds and extreme climatic conditions. The trend is speedily catching up in constructing residential buildings and public structures such as schools and colleges. A Monolithic Dome is a super-insulated, steel-reinforced concrete structure that can be designed for virtually any use: office or business complex, school, church, synagogue or temple; gymnasium or sports arena: theatre or amphitheatre, airplane hangar, factory, bulk storage facility, house or apartment complex, military installations etc. The monolithic word is made up of two words Monolithic= mono+lithic Mono means single Lithic is derived from a Greek word Lithos which means A large single upright block of stones. Domes are of roof shaped like the top half of ball.

1.1 History of Monolithic Domes

Throughout history, the dome has been the architectural form of choice wherever efficiency and strength are required of a structure. From the simple igloo that shelters the Arctic hunter through the ravages of a blinding storm, to the aweinspiring magnificence of the Sistine Chapel, the dome has been used in every culture, on every continent, as one of man's most versatile constructions. Today, modern construction techniques and materials reinforce the dome's position as the most classically versatile of all structures. The insulated concrete dome is the ideal solution wherever strength combined with low construction costs are called for. Compared to other types of structures, the domes enclose more volume with the greatest floor area, and the least amount of surface area and perimeter. Superbly energyefficient, firesafe, and with an inherent strength that enables it to withstand whatever nature throws at it, hurricanes, earthquakes, even tornadoes. It's no wonder that the modern concrete dome is experiencing a surge of popularity throughout the world.1.2 Necessity of Monolithic Concrete domeThe buildings such as houses, schools, churches, storage facilities, industrial and commercial buildings and stadiums for athletic events such as football, hockey, basketball and baseball, usually have some basic requirements such as the following:1. Economy Structure should be economical to build and maintain.2. Safety Buildings should resist elements such as fire, wind, seismic, vandalism and deterioration.3. Aesthetics and Comfort Requirements for a storage facility or a horse barn would be much different than for a house or church.1. EconomyConcrete is the most common building material used throughout the world, followed by wood, steel and a number of miscellaneous materials. It has proven to be available and economical in many locations. However, it takes a lot of energy to produce Portland Cement used to produce concrete. So, if we use concrete, we should use a type of building that requires a minimum amount of material, that in turn, requires the minimum amount of energy for producing the material to build the building. If we build concrete thin shell buildings, such as domes, a much smaller volume of building materials will be utilized. This will result in a very efficient use of building materials and hence reduce energy use and pollution. Maintenance and upkeep of a concrete building is generally much less than that of a more conventional wood frame building. A dome, will always use less material to cover the same space utilized by a square conventional building. Less material means less cost, or higher quality materials for the same cost, or both. Monolithic Domes provide great strength.2. SafetyBuildings should be capable of providing safety from the elements without excessive costs. Heat and air conditioning costs twice as much as energy used by most concrete dome homes. If a fire attacked the outside of a Monolithic Dome, it might melt the foam, but the concrete would still be there.Most reinforced concrete Monolithic Domes are easily designed to withstand earthquakes and powerful winds. It becomes easier and more economical to build a safe, reinforced concrete house that provides safety by utilizing a Monolithic Dome building than any other type of structure. Concrete dome buildings succeed in providing safety better than most other buildings.3. Comfort and AestheticsComfort is the homey, intimate term which implies the imparting of cheer, hope and strength as well as the lessening of pain. It is very comfortable, meaning the temperature is very consistent and the fuel consumption is economical. Buildings are built as permitted by local building codes for the welfare and safety of the public, and we should remember that building codes are not designed to prevent damage to buildings. That is unrealistic given the magnitude of possible earthquakes and winds. Rather, the aim is for buildings to resist catastrophic damage and thus prevent deaths and serious injuries. 1.1 Advantages of monolithic domes Domes are energy efficientIn Monolithic Domes, the walls are a composite of a roofing membrane, foam insulation, and steel-reinforced concrete. With the concrete inside and the insulation outside, the concrete is protected from the outside elements. Concrete, which conducts and holds heat easily, absorbs the differences in the interior temperature over the day. During the night, the concrete radiates energy back into the interior. This flywheel action dramatically reduces the temperature variations between the day and night.

Durability

The dome, when finished, is earthquake, tornado and hurricane resistance. Recently, a number of monolithic domes constructed using MDI (Monolithic Dome Institute) techniques have survived major disasters. Climate controlThe monolithic dome, for a number of reasons, is very energy efficient. The spherical sections of the dome offer minimal surface area for the volume they contain, so there is less surface for heat transfer with the outside air. The one piece construction of the monolithic dome also eliminates many of the seams through which air can leak, though this is mitigated to some degree in residential domes by the addition of multiple doors and windows. By placing the insulating foam on the outside of the concrete shell, the concrete acts as a heat sink inside the building, reducing interior temperature fluctuations far more than the traditional home's insulation inside of a brick or stone veneer.2. Monolithic dome construction

Fig 1. Typical Monolithic Dome

Current construction methods

A reinforced concrete foundation, or "ring beam", is constructed, defining the shape of the base of the structure. The fabric form, or air form, is attached to the foundation and inflated with an air blower. The air form contains an airlock to allow workers to enter the form while it is inflated. A layer of polyurethane foam is sprayed on the interior of the form. (Its purpose is to give rigidity to the air form, secure the rebar in place, provide support for spraying in the concrete mixture, and insulate the final structure.) Rebar is attached to the outside layer of foam, using clips that are attached to the foam. Concrete is sprayed over the rebar frame. After the concrete has set, the blower is turned off. The exposed surface of the air form may be left as is, or a surface treatment such as paint, tile, etc., may be applied. 2.1 The FoundationBuilding the monolithic dome with the placement of a circular concrete foundation topped by a reinforced - concretes slab. This slab not only serves as the floor of the building, it also holds down the inflated form to help prevent the dome from shifting due to internal loads or an earth quake. The amount and size of reinforcing steel vary, depending on building size and usage, but all the slabs require rebar in two directions and dowels that tie into the shell from the foundation.

Fig 2. Ring Beam FootingRing Beam Footing: Continuous reinforcing bars are embedded in the ring beam foundation. These rebar dowels securely connect the dome to its footing. The ring beam creates a solid base to construct the dome on. Rebar is bent over so that the Airform can be slid over the rebar and attached to the footing. Vertical rebar is placed on the interior of the hoop rebar and wired immediately to the hoop rebar, except as the rebar approaches the footing. As the rebar cage approaches the footing, the vertical rebar out of the footing should be directly in the center of the dome shell for a short distance above the footing. This short distance varies by size of the dome, but generally 10% of the height is an effective distance. Here the vertical rebar acts to prevent moment connection problems between the dome and the footing. It is important that hoop bars be securely tied to each other at the lap. Much strength is added to the structure by hoop bars.

2.2 Monolithic Airform and its errection.Fig 1.3 Monolithic airformsMonolithic construction process demands an Airform. The Monolithic Airform is a balloonlike, inflatable structure that determines the shape and size of a dome. Its made of PVC-coated nylon or polyester fabric, available in several weights and colors. The Airform is a highly engineered fabric structure that should be handled with great care. The rebar is bent over the footing to avoid tearing the Airform during inflation. Therefore, the Airform should be placed at the location of the Airlock before proceeding to unroll it. The errection process is detailed as below:a) Laying it OutThe Airform should be laid out over the foundation. The Airform will be attached on one side, then its opposite. Then the quarter points, and their opposites and continued evenly all the way around. The Airlock is then attached to the appropriate opening.Once the Airform is in place, bolted down, and inspected, it can be inflated. b) Attaching the AirformAirforms can be attached a number of ways. The most common is a thin metal strap that is screwed on the outside with concrete screw anchors as shown below

Fig 1.3a Attaching airform c) Attaching Inflator FansAfter the Airform is attached, inflator fans are attached to the domes via air tubes that are welded in place.

Fig 1.3b Inflator fans d) Attaching AirlockOnce the air is turned on, the air lock is attached. The air lock serves as the entry point to the dome during the construction process. The airlock has two doors, so that while entering the dome, pressure will not be lost.

Fig 1.3c Attaching Airlock e) Dome inflationDual fans are used, and often dual power sources, to decrease the chance of power loss. Keeping the air pressure in a dome is the most important factor during dome construction. Inflator fans are started and the Airform is inflated. Air pressure must be regulated. As the building inflates, the easiest way to adjust the pressure is by opening the airlock doors. When the Airform first becomes tight, the inside air pressure should be held at a minimum. Airform should then be checked for weak spots, holes, etc. Airform tie-down should then be completely checked. Whenever possible, let the Airform stand at least 12 hours before continuing construction. This gives it time to stretch.2.3 REGULATING AIR PRESSURERegulating the air pressure is a very important part of the construction of the dome. It takes very little pressure to inflate the Airform to its proper shape. Be sure to close the air flow if drying occurs in the concrete phase of construction. As air pressure is increased on a bare Airform, the chance of Airform breakage is also increased. In addition, if there is any over-inflation after the initial concrete is applied, the Airform can stretch and crack the concrete. If pressure is increased while hanging rebar, rebar hangers may be pulled out of the foam.Uplift must be consideredUplift is approximately 5 pounds per square foot of floor area per inch of water column. Footing must be heavy enough to hold this weight down. This is another reason the floor and the footing are often combined on smaller structures.2.4 POLYURETHANE FOAM APPLICATION The airform surface must be dry before applying polyurethane foam. Any moisture on the surface before spraying will cause blistering. Also the foam will not adhere to a wet surface. Give the Airform time to dry. Heat can be applied to the inside to eliminate moisture if needed. The following are the steps involved in Foam ApplicationStep 1: PRIMETreating the Airform with Monoform Primer is an absolute must! Monoform creates a better bond between the Airform and the foam; it acts as a glue for the foam. It can be applied with an airless paint gun over the entire interior Airform surface. It can also be rolled on. A thin layer is all that is needed (300-400 sq. ft. per gallon). The primer should be allowed to dry completely before applying foam.

Step 2: Choosing a Foam and ApplicationFoam comes in several set times and is available for cold or warm weather. The speed of foam used depends on the season and climate. Accurate ratio foam will rise perpendicular to the surface being sprayed against. If the foam slides, it is not setting fast enough. Use the fastest setting foam available for the season and climate. The foam machine needs to be adjusted to spray one part Chemical A and one part Chemical B (1:1 ratio). Off-ratio foam will result in too much of one chemical on the Airform. Seal bottom of the interior surface of the Airform with foam. Do not cover rebar in the keyway or spray foam in the keyway.Spray the first layer, working up from the bottom. Spray foam evenly to 1/2-inch thickness on entire interior Airform surface. The foam will dry to the touch in three to four seconds, but cross linking literally takes hours. The foam will have lots of stretch and pull for a considerable amount of time. After the gun is running well, and after the first pass, start at the top and work down, especially on hot days. Heat generated by the foam rises, making a hotter work environment. Step 3: Test ThicknessSpray another 1/2- to 3/4-inch layer of foam, making the total thickness, at this point, an inch and a quarter. Test the thickness of the foam by gently probing with an ice pick. Too much probing may make holes in the foam which can cause blistering. A lot of probing also increases the risk for puncturing the Airform.

Step 4: Rebar HangersRebar hanger placement requires extensive details; Rebar hangers are 2-inch square thin steel base plates with a wire welded perpendicular in the center and barbs protruding the opposite side from the wire. These barbs are pressed into the initial 1.5 inches of foam before the additional layers of foam are applied. Rebar hangers are part of the Airform package.

2.5 Rebar Placement in a Monolithic Dome

Fig 1.5 Hoop rebar attachment to rebar hangers 2.5.1 Necessity of RebarIts important to understand why we use rebar (reinforcing steel bar) in concrete. It is used to absorb tension forces in concrete, since concrete has very poor strength as a tension material. But the major rebar in a beam is the bottom where it will hold more. If the rebar were placed in the top, it would not hold much. Rebar also helps move the temperature around in the concrete, mitigating the stresses created by uneven temperatures and shrinkage in the concrete. In places where this is the primary purpose for the rebar, its referred to as temperature steel. Rebar also helps measure the thickness of the shotcrete as it is applied.In a Monolithic Dome, rebar is placed to counteract the tension forces within the concrete. Pressure can be or is applied to the dome from many sources: snow, wind, gravity, berming, burying, walking on the dome, hanging lights, sound systems, towers, falling airplane engines, attached structures, etc.2.5.2 Types of Rebars used in the Construction of Monolithic Domesa) Hoop RebarRebar that actually does the most good to hold the dome up is hoop rebar that goes around the dome. Hoop rebar performs somewhat like the hoops on a barrel. Hence, they should be located as far toward the outside as is practical. As pressure is applied to the Monolithic Dome, the dome will try to dimple immediately under the pressure. Adjacent to that area, the dome will try to buckle outward, but will be prevented from doing so by the hoop bars. Therefore, hoop bars should always be on the outside surface next to the urethane foam. Just as hoops on a wooden barrel do no good on the inside of the barrel, hoops on a concrete dome need to be to the outside. If they are on the inside, they can be more easily ripped out of the concrete when unbalanced pressures are applied to the dome.Obviously, rebar needs concrete surrounding it to glue it together. So hoop rebar should be about 5/8" to 1" from the outer surface of the concrete (bottom of the urethane). For a Monolithic Dome, hoop rebar is placed first.b) Vertical RebarThe vertical layer of rebar is laid against the hoops. For Monolithic Domes requiring thicker shells, rebar should still be placed to the outside. 2.5.3 CodesMost Monolithic Domes built as homes require a minimum thickness of 2.5" of concrete. Codes require rebar be placed not further apart than 5 times the thickness of the concrete. Hence, most of the rebar in smaller domes up to 100 in diameter is placed at a minimum of 12" on center.Lower portions of Monolithic Domes are generally thicker, so rebar can often be placed further apart. Concrete, as it fills in around the rebar, becomes the glue that holds the rebar together and transfers tension from the concrete to the rebar.Code calls for rebar to have 5/8" of cover on the outside surface if the outside surface is protected from the weather (i.e. painted, covered with urethane foam or a tarp, otherwise protected from the elements). When a thickness of 2.5" of concrete is specified, the outside hoop rebar should be 5/8" in from the outside surface of the concrete.2.6 Rebar Hanger Placement and Final Foam ApplicationAttach one rebar hanger at the top center of the dome. To secure the center top hanger, a thin layer of foam is sprayed over the hanger. If rebar hangers are not covered with enough foam, they will not be secure enough to hold the rebar. The top center hanger is now used as a marking guide. To mark placement of other hangers, tie a non-stretching string or wire to the top center hanger. Attach a marker/chalk to opposite end of the string. Begin marking for hangers at the domes base as noted below and work upward.After the rebar hangers are placed, secure the hangers by completing the foam spraying job with 1/2 to 3/4 inch of foam at a perpendicular angle to prevent excess foam buildup on the hangers. When foaming is complete, begin tying the rebar.2.7 ShotcreteShotcrete 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.2.8 Basic Steps for Applying Shotcrete to a Monolithic DomeLayer One The shotcrete is started at the bottom of the dome. First, a thick, tapered layer of shotcrete should be applied around the entire circumference of the dome, at the base, up to about one foot high. This ensures the concrete on the footing is good concrete and not rebound shotcrete. A 1/2" to 1" layer is then sprayed on the surface from ground level up to about 6 high. From 6 high on up to the top third of the dome, a 1/2" layer is applied. The top third of the dome is covered with 1/4" to 1/2" of shotcrete.Layer TwoSecond layer is usually applied on the second day. Up to a 1" layer is applied from ground level to approximately 8. From 8 to the top, a 1/2" layer is then applied.Layer ThreeThe third layer is an exact duplicate of the second layer, except that dome will support more weight and the layers can go on thicker and higher.The concrete around the base of the dome will be strong enough to support additional concrete if it is needed for extra thickness.Layer FourLayer four is a repeat of the third. The base should be worked for smoothness. Particular attention should be given to the depth gauges. Final LayerThe final layer should be relatively thin (about 1/4" to 1/2") to permit a smooth finish. Before spraying this last layer, depth is checked. If adequate thickness is not reached by this time, it is necessary to spray additional layers as needed.The finishing layer of concrete should be sprayed from the top down. It seems easier to make a nice finish if the final concrete layer starts at the top.3. Problems with monolithic domes:There are three main issues with monolithic domes:1. Polyurethane foam, vinyl and concrete are not the most sustainable materials to build with. Polyurethane foam is petroleum based, can't be recycled easily and produces toxic smoke when it's burnt. The vinyl airform again is petroleum based and there are some questions over the lifespan of the airform. At least the concrete is pretty permanent, even if it has a large initial co2 footprint.2. If the vinyl membrane is damaged in any way water can seep into the insulation beneath which will end up like a huge soggy sponge. Fire, vandalism even falling tree limbs are a worry for the monolithic dome owner. Air-forms can be repaired or covered in aluminium to protect them but it does increase the cost considerably.3. Monolithic domes are virtually hermetically sealed, this makes them great for storing materials that need a constant humidity, but when it comes human habitation; washing, cooking and bathing all produce water vapour which has to be removed from the building by dehumidifiers or forced air ventilation, as there isn't enough natural ventilation in this type of dome structure. The only way to get air movement through a dome structure is to have a hole covered with a cowl top dead centre of the dome. 3.1 DisadvantagesWhile the monolithic dome has numerous demonstrated engineering advantages, there are also some disadvantages, both engineering and social.3.1a Engineering The techniques used in monolithic dome construction are very different from normal construction methods, so only specially trained construction crews are suited for building a dome using the modern techniques. The curved surfaces inherent to monolithic dome construction often result in oddly shaped rooms when divided up, which can result in wasted space in narrow corners. There are issues of wasted floor space due to wall curvature and problems fitting furniture. This effect can be minimized by constructing the dome on a stem wall, or by using an airform of such shape as to allow for straight, vertical walls at ground level. The monolithic dome's lack of seams may make it too well sealed; dehumidifiers are required in all but the driest climates.3.1b SocialSocial disadvantages of monolithic domes are to a large degree shared by geodesic domes, due to the similar shape and unorthodox construction. These disadvantages are: The radically different appearance of the domes also decreases the appeal for their use as private residencesthe standard circular base doesn't fit well on small lots found in many areas, and the strange appearance and design may run afoul of neighborhood building covenants. Depending on the situation, a large variety of variations available from the standard circular shape can avoid some of these problems. Building permits may be difficult to obtain if local officials are not familiar with the monolithic dome. Resale of a monolithic dome home may be difficult because of its unconventional appearance.4. Design example of Monolithic DomeThe 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 conditionsThe 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.5. MATERIALS AND METHODS:5.1 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.5.2 SHOTCRETE: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.5.2.1 Materials:1. 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.2. 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".3. 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.4. Fine aggregate shall meet the requirements set as previously specified in this section and shall meet the following gradation requirement:5.2.2 Sand: well graded sand may be used for shotcrete applications. Sand shall generally consist of the following gradation:Sieve Size % Passing by Weight

No.4 100 %

No.8 90 %

No.16 85 %

No.30 60 %

No.50 30 %

No.100 10 %

The fineness modulus shall fall between 2.70 and 3.005.3.3 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.5.3.4 Proportioning:1. 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.)2. Shotcrete Strength: Shotcrete strengths of 28 days shall be no less than 4000 psi.5.3.5 Testing of Shotcrete Samples:1. 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 Owners representative. The dome contractor shall conduct the test with its equipment, and test shall be observed by the Owners representative.2. Special Inspections: Special inspections of the shotcrete shall be conducted as required by I.B.C. Sec. 306(a).3. 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 42.4. 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.5. One shotcrete test specimen shall be made during each days 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.6. 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.7. The cost of cutting, coring and testing cubes by a recognized testing laboratory shall be borne by the Owner.5.4 Shotcrete Equipment:1. Batching equipment shall be capable of proportioning the cement and aggregate to the degree of accuracy required by these Specifications.2. 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.5.5 Placing and Finishing:1. General: Shotcrete shall be applied in a steady, uninterrupted flow.2. 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.3. 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.4. 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.5.6 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.5.7 SHELL REINFORCEMENT:Reinforced design:1. Meet or exceed ACI building code requirements for temperature and shrinkage steel.2. Deformed Bars: ASTM A615, A616, or A617 grade 60 (60,000 psi yield strength).3. Maximum spacing between the bars shall not exceed 18" or five times the shell thickness.4. Annular or ring reinforcement shall have a maximum allowable stress of 24,000 psi. Accurately place reinforcing as show on final approved drawings.INSULATION: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:1. Thickness: as required by engineering plans2. Density: Minimum 1.9 or 2 lbs./cubic foot3. K factor: .124. Permeability: 3.0 perms5. Compressive strength:30 psi, 90% closed cells6. Flamespread: less than 75,7. Smoke development: Less than 450.8. 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 Ferarri, 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.6. Conclusion 1. SustainabilityMonolithic Domes have real strength. They can withstand the force of a tornado, hurricane or earthquake. Their lifespan is measured in centuries. Hence they do not need to be replaced.2. Energy EfficiencyThe Monolithic Dome is energy efficient. It will usually save fifty percent on heating and cooling costs compared to a comparable conventional building.3. Green MaterialsOwing much to their design, Monolithic Domes require the smallest surface area and employ the fewest materials to enclose space. A dome, will always use less material (generally 50% to 75% less) to cover the same space utilized by a square conventional building. Less material means less cost, or higher quality materials for the same cost, or both.

9. REFERENCES

a) www.monolithic.comb) The Dome Builder Handbook by John Prenis.c) Urethane Foam by David B. South and David Vaughan.d) Large Thin concrete Domes Using Air Supported Forms and Cable Nets A Thesis by Robert J Hash.