Emergency escape and rescue openings require a clear 36-inch-wide path to a public way. 1%. 78. Once you input these values, you will have your grid length dimensions, it’s that easy. Figure 2 shows the minimum bar extensions given in ACI 318-14, Building Code Requirements for Structural Concrete and Commentary, Figure 8. Anchor bolts are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the wood sill plate. That is about a #4 bar at 10 inches on center. For slabs 200 mm thick or greater the bar size and spacing should be limited to control the crack width and reference should be made to section 7. For residential slab on grade applications, the minimum spacing of grade 60 #3 or #4 rebar is typically 4 inches on center. Stocked in half inch increments between 6. In slabs with an average thickness of less than 6 inches, the spacing should be. 33_2_0. H3: #8 Rebar (8 rebar size). This will provide adequate reinforcement for most applications. Fiber and welded wire are only used for shrinks cracks, non structure cracks, cosmetic cracks. Finally, take a look at the calculation results: grid length = 5. Concrete Slab Rebar Spacing Guideline By Terry Smith. aggregate, you'd need 1. In inches the diameter of a #5 rebar is 5/8″ and that of a #4 rebar is 1/2″. For a slab this thin you would use wire mesh instead. 65*6) = 1. If your two slabs have different spacing for their rebar mats, measure and mark so your dowels fall in the middle of the spacing of the second slab. First, find the area of the slab. The splices should have at least 2 ft overlap into the new pour. For very thick slabs, such as those 8 inches or more in thickness, half-inch rebar or larger is used. It create a bending of the slab. You don’t need an 8mm Rebar on your 4” thick slab. With our rebar calculator, you can eliminate. No, you do not need rebar for a 4-inch slab of concrete on grade. Include 1/3 to 1/2 the sq footage of the shop in exterior concrete - a large apron in front of the door for outside work on vehicles and generous walkways along the sides. 1% reinforcement in a 4-inch thick slab is #3 bars in both directions at 24-inches. 6 for the recommended CJ spacing for unreinforced concrete slabs-on-ground as follows: Note that CJ spacing in a 4-inch slab should be between 8 feet and 13 feet. Additional joints should be considered if the topping slab thickness mandates a closer spacing than the base slab to limit uncontrolled cracking. Rebar Spacing. of Engineers (Army TM 5-809-12) that you can download for free from thier website. However, if the concrete slab is meant to be the footing of a small structure, #4 rebar with a diameter of 1/2-inch should be used. 4 inch Joist Spacing SLAB MESH THICKNESS SIZE 3 in. 440 2 2. To get the rebar in the bottom 1/3rd of the slab, a 1" chair would been perfect for a 4" slab, a 2" would be good for a 6" Slab, and a 3" for something crazy thick like 8"+. 2 mm in diameter. For beams, these distances are 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, respectively. To find the exact size of the slab by slab Rebar calculator. No, you do not need rebar for a 4-inch slab of concrete on grade. Leave a few inches of space between the mesh and the edges of the forms to prevent rust. The #3 rebar has a weight per length of 0. For example: A #5 [#16] bar is approximately 5/8 inch [16 millimeters] in diameter: a #9 [#29] bar is approximately 9/8 inches [29. This illustrates a common problem for the concre t e s u b c o n t ra c t o r : How do you place a l e v el slab of uniform thickness ove r steel beams that can va r y in eleva-MINIMUM VERTICAL REINFORCEMENT AND SPACING (INCHES) b, c: Soil classes and lateral soil load d (psf per foot below grade) GW, GP, SW and SP soils 30: GM, GC, SM, SM-SC and ML soils 45: SC, ML-CL and inorganic CL soils 60: 6 feet 8 inches: 4 feet (or less) #4 at 48 #4 at 48 #4 at 48: 5 feet #4 at 48 #4 at 48 #4 at 48: 6 feet 8 inches #4 at. 2 cm) long, one half each way". Add 5%-10% additional material for some waste or spills. A 4-inch-thick slab cast on the ground and in permanent contact with it will float and rebar is not required. If the slab is expected to bear heavier loads, such as from heavy vehicles, then larger diameter rebar or closer spacing may be required. Most concrete slabs last 30–40 years and can last up to 100 years if properly installed and sealed. Use a metal-cutting blade or disc in a reciprocating saw, circular saw or grinder to cut the rebar. For flatwork, such as slabs-on-grade and driveways, a minimum thickness of four inches is required, but increasing the thickness to five inches can add nearly 50 percent to the load-bearing capacity. ) In metric the bar size is approximately its diameter in millimeters: a 25 bar is 25. According to this method, you will need two rebars for a footing width of 16 inches, four rebars for a footing width of 24 inches, and so on. slabs, walls, and joists - #14 and #18 bars - ½ inch; Slabs, walls, and joists - #11 bars and smaller - ¾ inch ; Beams and columns - 1½ inches ; 2. For a 6 in. Wood sole plates at all exterior walls on monolithic slabs, wood sole plates of braced wall panels at building interiors on monolithic slabs and all wood sill plates shall be anchored to the foundation with minimum 1 / 2-inch-diameter (12. Say your forklift has a contact area of 1 square foot. 2-1/4 inch rebar high chair is. For example, #8 rebar = 8/8 inches (or 1 inch) in diameter. Slabs, walls/dividers, and joists – 11 bars and littler – ¾ inch. Generally speaking, a. Fa b r ic may also be supported at the center of the slab, or it may be installed in two flat layers with the top layer (nega-t i v e steel) extending on either sideInterlocking PVC spacers to provide 1-1/2" spacing between ducts and 3" cover of concrete for the outer ducts, spaced 5 feet on centers will be used. The spacing of the rebar is also determined by the weight and size of the slab. Thick slabs Thick slabs are concrete slabs with an overall thickness of 4-6" or greater and can be either grade level (slab on grade) or below grade (i. Use a groover to cut grooves about 25% into the depth of the concrete. Spacing of bar supports depends upon the size of the reinforcing bar being supported. When spacing the rebar, it is important to ensure it is evenly distributed and in accordance with the local building codes. e. The architect's instructions on the plan are: “New conc slab with #3 transverse bars at 12” O. Raise the form sides 1/2-inch to create a slab that is a full 4 inches thick. Then use a “gauge board”—a 1×4 with blocks screwed to it—to position the other side. Rebar is used t o help improve concrete’s resistance to loads andThe maximum diameter of bar used in slab should not exceed 1/8 of the total thickness of slab. 376 lbs/ft or 0. 5. The 6mm rebar should be arranged in a grid pattern, spacing out the rebar at 6 to 12 inches. Designed for #4 and #5 rebar,. 5 bars or littler – 1½ inches. The reason is because the lower part of the slab (from the center of the thickness down) is in tension when the load is on the top of the slab. For a patio you can use a grid spacing of 24 inches. View More. For example, a 4 inch slab of 3000 psi concrete, 4 feet by 8 feet, with reinforcing mesh will hold up to 34,800 lbs. 5 rebar, then measure and mark for your dowels at a 18. The maximum diameter of bar used in slab should not exceed 1/8 of the total thickness of slab. A 4-inch-thick slab cast on the ground and in permanent contact with it will float and rebar is not required . Provide Construction Joints (ie, transverse joint) @ 40'-0" intervals if you have a long driveway. 72 percent. When a=4. Calculate the rebar size, spacing, and number: Use the structure’s specifications to determine the rebar size needed for the concrete. 0. Main bar is also called tension. 9_sqrt (0. For a 400 square foot slab, the man hours required to finish a two-car concrete garage slab is about 13 hours. For flat slabs like driveways and patios, spacing is roughly 18″ to 24″. spacings: #4 bar = 18. What size rebar do I need for a 4 inch slab? You will need a #3 rebar for a 4-inch slab. For example, if both slabs have rebar mats that are spaced at 18 inches and use No. Placing more rebar/less spacing than required leads to higher crack width formation in slab because the higher weight of rebar would lead to higher deflection. The details of slab reinforcement are given below. Thickness of concrete slab depends on loads and size of the slab. For a 400 square foot slab, the man hours required to finish a two-car concrete garage slab is about 13 hours. Every concrete slab should have a minimum. Furthermore, if the concrete. PROWORX 3-in x 60-in x 3-in Steel Slab Bolster. New concrete slabs must conform to the above. Construction joints also have this spacing for strip placement of the concrete. So if you have, say a 3/4" max. And a cross-sectional area of 0. Rebar of ten forms a st eel skeleton-like framew ork within footings, walls, slabs, columns, roofs, bridges, driveways, highways, and other concr ete. Rebar Spacing; D2-8F: 4. 8 wire transversely). Content intended for mature audiences. 6. Great for use when pouring concrete slabs. If the slab is more than 24 inches thick, #5 (#5/8 inch diameter) rebar may be required. 64 mm) between longitudinal rebar 2 and 3, which is the same as the rebar. 87 d Spacing of bar = Design of Continuous Slab Suppose a slab is supported at the ends and also at intermediate points on beams, the maximum sagging and hogging moments to which the slab is subjected to due to uniformly distributed load, can be computed as follows: Let = intensity of dead load per square metre. 60 per square foot for materials and labor. The concrete contractors said that these rebar chairs were a great idea, but the execution and labeling of the product was very poorly thought out. Slab footing Rebar may be easily determined with the help of the footing Rebar calculator. No, you do not need rebar for a 4 – inch slab of concrete on grade. Another beam might have a 11⁄ 2-or 2-inch camber. The appropriate rebar spacing for most of the slabbing is 12-inches. PROWORX 3-in x 60-in x 3-in Steel Slab Bolster. Anchor bolts are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the wood sill plate. To calculate Total Area of a multi sided slab, first divide the shape into rectangles or squares. Plan out your control joint spacing 24-36 times. 34 and $7. 4 x Modulus of Rupture fs = allowable working stress of the reinforcement (psi) T =range of temperature the slab is expected to be subjected to (F o)Stretch a string between two screws installed at the edge of both ends of the form boards. H1: #4 Rebar (4 rebar size) Diameter: 1/2 inch; Weight per Foot: 0. The thickness of rebar should be no more than 1/8 that of the slab, so a 4” slab shouldn’t have steel greater than #4 or 1/2″ bar. 1. Here:The size of rebar needed for a 4-inch slab depends on several factors, such as the type of material used for the slab, the type of project, and the size and weight of the load it will be required to carry. Common size of rebar used for 4 inch slab, it may vary from size. 72 percent. Average: Rebar in Concrete Slab Estimator. Guidance for joint spacing to minimize out-of-joint. spacings: #4 bar = 27. For a 4-inch RCC (Reinforced Concrete) slab, using #3 (3/8-inch diameter) or #4 (1/2-inch diameter) rebar is typical. For a 4" slab on grade house, what would you say about #3 vs #4 rebar, and the spacing? I was going to do #4 at 12" - Answered by a verified Structural Engineer. For example, if a 6-inch-thick slab is used with #3 rebar at 18 inches on center, the percentage of steel for a 12-inch width would be: (0. Most reinforcing bars bearing a Metric diameter mark Now, divide each measurement by the 14-inch spacing. (This convention begins to break down for bar diameters above #8. Beams and columns: 1½ inches. transverse wire spacing with smooth No. 6, Figure R404. (iii) three-fourths the minimum specified clear spacing between individual reinforcing bars or wires. Proper and even spacing is also important. ) (12 in. No. The spacing will depend upon the wire size and the wire spacing. 5 inch line of your patio slab to keep the dowels in the upper portion of the slab. Concrete Thickness. You can multiply the bar size by 1/8 to get the nominal diameter in inches. The diameter of bar generally used in slabs are: 6 mm, 8 mm, 10 mm, 12mm and 16mm. A 4-inch-thick slab cast on the ground and in permanent contact with it will float and rebar is not required. 15 percent of total cross-sectional area. 561 kg/m. stress. A few rules of thumb for control joints: Space them 2 to 3 times in feet the thickness of the slab in inches (4" slab = 8' to 12' max); Joints should create nearly square sections; joints should be struck or sawn to a depth of 1/4 the slab thickness; Sawn joints need to be cut before shrinkage cracks occur, no more than 12 hours. If the slab is 4 inches or less than it should not be reinforced. Tractor. I used no. If shear reinforcement is required for in-plane strength, s shall not exceed the smallest of 3h, 18 inches, l w /3. That's 144 square inches. Step-4: Rebar Calculation Process Of The Slab Panel-A 4. Concrete can be mixed in a wheelbarrow, mortar pan, or mixer. inches thick and about 4 x 4 inches square. Maximum spacing of main bar is restricted to 3 times effective depth or 300 mm whichever is. Likewise, the top reinforcing mat is to be tied to the bottom reinforcing mat on a 4 foot grid in floors of concrete slab bridges. How big is a sheet of concrete mesh? Standard sheet sizes range from 4m (length) x 2m (width) 8m2 up to 6m (length) x 2. Maximum spacing of main bar is restricted to 3 times effective depth or 300 mm whichever is less. However, it is better if 10mm or 12mm diarebar can be used with spacing of 100-125mm (4-5’’) between rebar. 4" is plenty, be sure the base is good - compacted, free draining, etc use a relatively tight mix, ie low water to cement ration, slump in the 3 to 3. To calculate Total Area of a multi sided slab, first divide the shape into rectangles or squares. With our rebar calculator, you can eliminate. 2)(12 in. First, you need to consider the size of the rebar and the spacing between them. 35 to $6. The sill plate is 2-inch (51 mm) or 3-inch (76 mm) nominal. Second, most designs require’spacing rebar’ of two inches. See STRIPS. The evaluation of rebar spacing results shows that the maximum standard deviation for rebar spacing is 0. Prices for your concrete slab will vary. A concrete slab costs between $4. 2(1) shall be air entrained as specified in Table R402. 59 per square foot. Number 4 rebars spaced 12 inches on center (center-to-center distance) on both the top and bottom faces and in each way as well, i. 19 rebars for the slab. Contractors sometimes use the “1/8 Rule,” meaning the size of the rebar is 1/8 the thickness of the slab. MATERIALS The materials used to construct the dowel bar shall meet the following requirements: 4. For very thick slabs, such as those 8 inches or more in thickness, half-inch rebar or larger is used. Horizontal-need 2 rebars each run with 3 or 4 runs of rebar 2 feet apart and rebar size 1/2 inch or 5/8 inch. Another beam might have a 11⁄ 2-or 2-inch camber. For a 4-inch RCC (Reinforced Concrete) slab, using #3 (3/8-inch diameter) or #4 (1/2-inch diameter) rebar is typical. A 2-inch cover is usually provided for these. Build forms. 375 inches, which is equivalent to 9. However, many engineers and contractors use a rule of thumb of keeping the rebar spacing to 2 – 3 times the. 7. Anchorage shall be in accordance with Section R403. 34 and $7. 5. The compacted aggregate base is first, followed by a 6 mil polyethylene vapor barrier, then insulation, then rebar or wire mesh, or both. If you are in a climate subjecting the floor to freezing, get air added to the concrete. For a flat slab, such as a driveway, consider placing the rebar in an 18 inch grid spacing, keeping the edge rebar at the same distance from each side. 4 inch of p r otection. 1. The grade shall be as specified by the. 5. 16 inches for a number three bar. The installation of the rebar is critical for the success of the overall project. In that case, a 4-inch slab of higher strength concrete could typically support upwards of 15,000 PSF. 43/30 = 0. However, generally, a 6mm rebar is suitable for a 4 inch slab. Use a metal-cutting blade or disc in a reciprocating saw, circular saw or grinder to cut the rebar. Hercules 3 in. The Rebar and Concrete in a Slab calculator computes the total length and weight of rebar and the volume of concrete needed for a slab. Position and placement of RebarsMin reinforcement is 0. This thicker rebar will improve the durability of a 4-inch slab and therefore its lifetime. 4 wire mesh, I would like to use rebar in place of the wire mesh as in my experience wire mesh usually ends up in the bottom of the slab, I also do not think a 4″ slab is enough for a shop that will have 80,000lb trucks in it. Fig 4: Rebar Tying details. Expansion grooves should be cut into the wet concrete to provide additional crack resistance. CRSI’s Reinforcement Anchorage and Splices includes tables of required lap splice lengths based on these variables. For a 6" thick slab with GR60 bar per the ACI318 I get the following max. If your concrete will be stamped, ask about the best ways to avoid interrupting the pattern. MATERIALS The materials used to construct the dowel bar shall meet the following requirements: 4. A good compacted base below the concrete is equally important. A 4 – inch -thick slab cast on the ground and in permanent contact with it will float and rebar is not required. a weak concrete has a compression. This gives the following information: You need the given quantity, 18, rebar, size 5 (5/8 inch diameter), with 9 bars laying in each direction, the top rows perpendicular to the bottom ones. For commercial loaded slabs I go 3000 psi minimum, and usually 4000 psi. 33 inches. #4 is 4/8”, or 1/2”. Running Bar Points (Length - Left to Right): Running Bar Points (Width - Top to Bottom): Calculate Rebar Quantity and Mesh From Total Slab Area and Perimeter. The main reinforcement of the slab panel “A” is marked as (1). This translates to roughly 5/8 inch rebar and must be spaced equally along the slab to create a proper grid. Provide adequate joint spacing:. Calculates approximate Rebar Length from total slab area and perimeter. (UBC), may require the use of rebar in 4-inch concrete slabs. rebar strength is in tension, so by adding rebar to BOTTOM of foundation, it counter acts the load of compression. Common size of rebar used for 4 inch slab, it may vary from size. For example, a 4 inch slab of 3000 psi concrete, 4 feet by 8 feet, with reinforcing mesh will hold up to 34,800 lbs. To form consistent, parallel sides for a curved sidewalk, build one side first. Concrete slabs-on-ground shall contain micro- or macro-synthetic fiber reinforcement. 8 mm) ±1/2 inch (±12. So if you have, say a 3/4" max. Retaining Walls: The most commonly used rebars in retaining walls are #3, #4 and #5. That way you can use the forms themselves as a guide for the final base height. Our plastic rebar support “High Chairs” range in size from 3” to 14” in height. 5% reinforcing steel in the top 2 inches of the slab in both directions can allow you to eliminate joints. Step-4: Rebar Calculation Process Of The Slab Panel-A 4. For slabs of septic tanks, you usually use #3 and #4 bars. In conjunction with the bar callouts in Figure 1, minimum extensions for the top and bottom reinforcing bars in the column and middle strips must be provided. The plastic chairs are designed for the rebar rods to snap easily into. 74 sq feet 5000/2. How to lay a concrete slab. Build the Form. Table 1-Minimum Shrinkage and Temperature Reinforcement steel for non-SES floors or SES floors with a secondary liner. In general, it will be necessary to provide supports for reinforcing steel in deck slabs and overhangs, railings, bent diaphragms, intermediate diaphragms, bent caps, approach slabs and culvert slabs. 75-in 500-Pack Polypropylene Rebar Chair. The rated separation for two-family dwellings is 1 hour whether or not a lot line exists between units. Tables are for 2500 psi concrete and Grade 60,000 psi rebar 4. to 8 in. 12. Slabs, walls, and joists –. Suppose the foreman accidentally uses #3 bars instead of #4 at a 5 inch center-to-center spacing. But as the depth grows, so does the need for reinforcing the structure. Generally speaking, a 4-inch slab of normal weight concrete (145-165 pounds per cubic foot) with a 28-day compressive strength of at least. the calculator will give you the default spacing values (for rebar – rebar it’s 40cm, and for edge – grid it’s 8cm). What size rebar for 4 inch slab. For slabs and pads, the distance between rebar is normally 4-6 inches apart. We placed the rebar, which is 1 1/8 inches in diameter, in a one-foot grid with two levels. The tensile strength of concrete is typically taken as 10 to 15% of the compressive strength, so only about 400 or 500 psi. Space the joints no more than 2-3 times (in feet) of the slab’s thickness (in inches). 87 (round up to 13) Add one rebar to your result: 13 + 1 = 14. 1 (a) (5) of ACI 318-19, nominal maximum size of coarse aggregate shall not exceed the least of (i), (ii), and (iii): (i) one-fifth the narrowest dimension between sides of forms. 73 per square foot for concrete installation. If you have expansive soil or a significant frost depth, #4 rebar at no more than 12 inches on center is a good choice. The tolerances on rebar position, as defined by ACI 117, “Tolerances for Concrete Construction and Materials,” are shown in the table. o Minimum 6 inch thick continuous concrete footings not less than 18 inches wide and reinforced with two continuous #4 rebar rods. PROWORX 3-in x 60-in x 3-in Steel Slab Bolster. 1. Vertical placement tolerance for reinforcement in slabs-on-ground is ± 3/4 inch from the specified location. This doesn't really eliminate cracks, but results in very. 4/1. For one layer of 6x6 W1. Generally, it is recommended to have at least the. That way you can use the forms themselves as a guide for the final base height. 25" 3,000 PSI / 28 Day Aging #6 Rebar: 12 in: D2-10 Models: 4. 65 and the thickness of the slab is 6 inches, M = 0. Talk to your local building inspector or hot tub retailer for more specific guidance on slab thickness for your situation. longitudinal and transverse. (see below for more information on contraction joints)Second, most designs require’spacing rebar’ of two inches. In some cases, concrete needs reinforcement with steel mesh. (Video) Rebar Spacing, Made Easy (DesignBuildDoug). Fill in the price and single rebar length that you will buy at your supplier: rebar price = €2/m single rebar length = 6 m. Running Bar Points (Length - Left to Right): Running Bar Points (Width - Top to Bottom): Calculate Rebar Quantity and Mesh From Total Slab Area and Perimeter. Do you need rebar for 6 inch slab? Rebar is recommended for. If you have a 5 inch slab and multiply it by 24 to 32 you will find that your joints should be placed every 120 to 180 inches or 10 to 15 feet; Or another way to figure this out is to times it by 2 or 3 in feet. The important part is the use of support to achieve proper placement within the slab. 78. If the floor is designed as a reinforced-concrete slab requiring rebar in the tension zone, the designer should specify the correct rebar position. 1: Calculate The Main bars. 75-in 500-Pack Polypropylene Rebar Chair. Generally, one stick of rebar per 8 inches of footing width will suffice. 16 wire longitudinally and smooth No. and type of reinforcement bars are crucial to the success of any project. 2. x 6 -W2. 6. Do you need rebar for 4 inch slab? No, you do not need rebar for a 4 – inch slab of concrete on grade. Allow concrete to cure. in thickness, columns, walls, and parapets. Build forms. Having more bar would only increase the strength of the slab, as long as. As per the present market rates, the average cost of concrete for a 400-square foot slab, the typical size for a two-car garage, ranges between $583 and $637 or between $1. Tying should include bars near the ends of the bridge and bars near the curbs. 525 mm. To find the exact size of the slab by slab Rebar calculator. For example, a size 4 rebar will have a diameter of 4/8” or ½ inches. But if you feel that the slab is in a sensitive position and extra protection is needed, you can add rebar to it. 2-inch chairs at the sup-p o r ts for a 31⁄ 2-inch slab; 2-inch chairs for a 4-inch slab; 21⁄ 2- i n c h chairs for a 41⁄ 2-inch slab and 3-inch chairs for a 5-inch slab. Before beginning a concrete project, consult a professional engineer to determine the code requirements and what size and spacing of rebar will best meet. Does a 4-inch slab need rebar? By: Olin Wade (Remodel or Move Stuff) Watch This Video To Learn More About Using or Not Using Rebar For Concrete Driveway Watch on It. 34 inch (8. The reinforcing steel sagged during placement between the support chairs, causing the 3/4-inch spacing to be infringed upon. Regardless of beam spacing, the top mat must be tied to the forms or the bottom reinforcing mat at 4 foot spacing. Type and spacing of the control and construction joints. a car weight about 5000lb. ( rS) Rebar Size (2,3,4,5,6,7,8,9,10,11,12,14,16,18,20) Use Size "0" for. 7 mm) anchor bolts spaced not greater than 6 feet (1829 mm) on center or approved anchors or anchor straps. 4. Additionally, any slab poured over 4 inches should also be bonded with mesh fabric to the 2 preceding layers of clear of construction joint material to ensure the slab is adequately supported. You can't get that in a four inch slab. Rebar in patios, basement floors, footings and driveways may vary from size 3 to 6. 23 inches For a 4" thick slab with GR60 bars I get the following max. To reinforce a 4” concrete slab or driveway with steel rebar, determine the grid spacing and rebar size – #3 or #4 in a 12” to 18” grid. Reinforced slabs – where welded wire mesh or rebar is used to reinforce the slab. The appropriate rebar size depends on the project, with #3 and #4 being common choices. ( D) Depth of slab. 5x the maximum aggregate size. For example, 4 inches patio slab will need rebar. To truly reinforce concrete, the percentage has to. 3 Joints in Unbonded Topping Slab. The ribs aren’t included in the measurement and the diameter is expressed in eighths of an inch. On average are required, for 10 square meter with 12cm thick slab, 19 strips of 3/8” rods (9ml each one), are 171 ml. Some, even, go so far as to recommend NO reinforcing, allowing the deck to actually arch across the span to the supporting girders. Benefits of Using Rebar in a 4-Inch Slab. Main bar is also called as shortest span bar usually used at bottom of slab having spacing 4 inch between the two bar. For most residential slabs, such as patio slabs and sidewalks, #4 rebar (1/2-inch diameter) spaced 12 inches apart is recommended. View More. Prices for your concrete slab will vary significantly depending on many factors, including the slab’s thickness, concrete type, and size. Main reinforcement which is based on the maximum bending moment shall not be less than 0.