What size beam do I need for a 21 foot span, beam size for 21 foot span, rcc beam size for 21 feet span, steel beam size for 21 feet span, wood beam size for a 21 foot span, lvl beam size for 21 feet span.

The size of the beam needed to span 21 feet depends on various factors including the load it needs to support, the type of wood or material used, and the local building codes. For a rough estimate, you could consider using a 10″×20″ RCC beam, 10-12″ GLULAM or LVL (laminated veneer lumber), a triple 2×14 wood beam or a double 2×16 wood beam for 2-3 storey residential building applications.

Beam is generally made of reinforced concrete providing with reinforcement Steel. or made of timber, wooden structure or Laminated veneer lumber (LVL) or Glulam is one of the most widely used engineered wood products for constructional applications.

It is load bearing structure and flexural member of concrete that vertically transfer all the incoming dead load, live load and self load of rcc slab to the column via column beam joint through development length of structure element.

Size of beam generally depending on span between two support and all the load acting on it. Beam is structural member subjected to flexural stresses and shear forces. The size of the beam (width and depth of beam) are governed by the different type of shear forces and stresses.

When the beam is subjected to loading the bending moment is developed and the moment carrying capacity of the beam depends mainly on the depth of the beam.

How the size of beam could be decided?, in case of RCC beams an appropriate width of the beam is assumed on the basis of experience, the magnitude of maximum bending moment and in some cases on the basis of the width of the wall present below the beam. This width of the should be sufficient to provide rebars with sufficient side cover and spacing between the bars. After assuming the width the effective depth of the beam is calculated based on the bending moment and then the overall depth of the beam is determined by adding effective cover to the effective depth calculated.

Beam is different types like cantilever beam, continuous beam, simply supported beam, fixed beam, overhanging beam, lintel beam, primary beam and secondary beam. A cantilever beam is a rigid structural element that extends horizontally,one end is free and is supported at only one end. Simply supported beam is supported at two end and continuous beam is supported by more than two support end.

Beam is provided with the top bar which experience compression and bottom bar which experiences tension. Mainly tension bar encounter the bending moment and stirrup of which are provided to incounter the shear forces.

We can always take the standard size of the rcc concrete beam size at least 230mm x 230mm (9” x 9”) in which width and depth of beam is 230mm (9″). The depth of the beam increases or decreases according to their span and applied load on the beam. Now there is remarkable question “what size beam do i need for a 21 foot span?”.

**There is various method to deciding beam size its width and depth of beam. 1) IS 456:2000, 2) Thumb rule method**

**1) According to IS 456:2000** for designing of minimum size of RCC column for 2- 3 storey building its recommendation is:- a) for cantilever beam span to effective depth ratio is 7 (span/effective depth=7), b) for simply supported beam span to effective depth ratio is 20 (span/effective depth=20) and c) for continuous beam span to effective depth ratio is 26 ((span/effective depth=26).

**2) Thumb rule method:**

You can also calculate the size and depth of the beam according to thumb rule method mention below:- 1 foot (span of the beam) = 1Inch (depth of beam), If the span of the beam is 21 feet, then the depth of the beam will be 2 inches, beam depth taken as 22″ and beam width 21/2= 11″, taking as 12″.

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**What size beam do i need for a 21 foot span**

**RCC beam size for 21 feet span**:- for 21 foot span, size of reinforced beam for 2-3 storey residential building, using thumb rule, is about 10″×20″ in which beam width is 10″ and beam depth is 20″, providing with minimum of 4 nos of 12mm bar at top, 4nos of 16mm bar at bottom and 2 nos 16mm as crank bar of Fe500 with Stirrups T8@6″C/C and M20 grade of concrete ratio (1:1.5:3) with clear cover 25mm.

**Steel beam or rsj size for 21 feet span**

as per general thumb rule, for 21 feet span size of steel beam or universal beam or w beam or I beam or UB’s or hot rolled section or Rolled steel joist (RSJ) should be ISMB 350 or UB 350×140 or W14 used for residential building or projects or construction in which depth of section of beam is 350mm (14″) and width of flange or width of beam is 140mm (5.5″). This is ideal, standard and most suitable size of steel beam or RSJ beam used for 21 feet span under normal load condition.

**Wood beam size for a 21 foot span**

as per general thumb rule, for a 21 foot span, size of wood beam or lumber joist should be 2×14 which placed at 16″ apart from centre used for residential building or projects or construction in which depth of section of beam is 350mm (14″) and width of beam is 50 mm or 2″. In general terms, joist or beam which spaced 16 inches apart on Centre can span 1.5 times in feet their depth in inches.

**LVL beam size for a 21 foot span**

as per general thumb rule, for a 21 foot span, size of LVL beam or GLULAM should be 10 to 12 inches deep and 3 inches wide, thus you need something like a 10-12″ GLULAM or LVL to span upto 21 feet and can use simple 2×14 dimensional lumber at 16″ apart from centre as floor joists used for residential building or projects.

**Conclusion**:-

For 21 foot span, size of reinforced beam for 2-3 storey residential building, using thumb rule is 10″×20″ or 10-12″ GLULAM or LVL, 2×14 dimensional lumber/wood beam at 16″ apart from centre as floor joists, ISMB 350 or UB 350×140 or W14 can span upto 21 feet that used in residential building.