The beam depth required for a span depends on various factors, including the load, material properties, and desired safety margin. One common formula used in structural engineering is the span-to-depth ratio.
In general, the size of the beam for a residential building need to be 9″×12″ (230×300 mm) for a 5m span, 9″×9″ (230×230 mm) for a 3m to 4m span, 10″×14″ (250×350 mm) for a 6m span, 12″×16″ (300×400 mm) for a 7m span, 12″×18″ (300×450 mm) for a 8m span, 12″×20″ (300×500 mm) for a 9m span, 12″×24″ (300×600 mm) for a 10m span.
A widely accepted rule of thumb for the span-to-depth ratio (L/d) is around 20 for simply supported beams. This means the span (L) should be approximately 20 times the depth (d) of the beam.
For example, if you have a 5m span, you might aim for a beam depth of 5m / 20 = 0.25m (250mm). Similarly, for spans of 6m, 7m, 8m, 9m, and 10m, you can calculate the corresponding beam depths using the same formula.
The beam is a flexural structural member of concrete that transfers vertical all the dead load, the live load of the slab to the column. The horizontal load of slab directly transfer to beam. Beam experience bending moment and resist the load applied to it by slab. Maximum quantity of reinforcement provided in middle of tension zone and both end of beam – column joint of compression zone.
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We all know that calculating beam size is essential and indispensable while designing a building. In this post, you will get to know the method of how to calculate the beam depth before designing a beam for 2 to 3 storey building design plans or multi-storey building design plans.
For designing the beam, beam depth should be not only depending on span of beam but it is also depending on height of column for a structure and dead and live load of building acting on it with slenderness ratio.
It is essential to know how to calculate the beam depth size, load calculation and grade of concrete and grade of steel. You can design it with the help of beam design formula and concrete beam design calculator. Just brush the concepts once and start with the given process.
Apart from it, you can easily create a beam design from the concrete beam design formula, available on various sites. Still, as a structural engineer, you must know the beam design formula and their design procedure and have a proper understanding of basic physics principles and engineering statics, as they are significant for designing and sizing beams.
A structural engineer has complete knowledge and is fully equipped to choose the material, size and shape accordingly and check the loads acting on a beam, calculate the forces and stresses on the structure.
How to calculate depth and width of beam?
To calculate the minimum RRC beam size according to IS 456 2000, the ratio between the span and the effective depth of the beam is 7 for a cantilever beam, 20 for a simply supported beam and 26 for a continuous beam. Beam is various type like cantilever beam, simply supported beam and continuous beam.
Standard size of concrete beam should be no less than 9″×9″ (230mm × 230mm), provided with 4pcs of 12mm of Fe500 steel bars and M20 grade of concrete with stirrup T8 @ 6″C/C.
1) Calculation of depth and width of simply supported beam:-
Note as per IS – 13920
A) the width to depth ratio should be more than 0.3 ( width/depth > 0.3).
B) depth of beam shall not be exceeded One by fourth (1/4) of clear span.
Let clear span of beam = 5m = 5000mm
Effective depth = span/basic value
Total depth = effective depth + diameter of bar/2 + clear cover size.
Width of beam = Depth/1.5 ( width of beam should not be less than 200 mm).
Span of simply supported beam = 5000mm
Effective depth of beam d = 5000/20=250mm
Total depth of beam = effective depth + diameter of bar/2 + clear cover size.
Assume clear cover size = 25mm
Diameter of bar =16mm
Total depth D = 250mm +16/2mm +25mm
Total depth D= 283mm, It should be taken as 300mm.
Width of beam = D/1.5, 300/1.5 = 200mm, so width of beam should be not less than 200mm in case of Block wall and 225mm in case of Brick wall. So width of beam taken as 225mm least.
Now check it,
Width/depth =225/300 =0.75 > 0.3, it is safe
Now we can check depth of beam = 1/4×5000= 1250 > 300, yes it is safe.
Depth and width of simply supported beam
Simply supported beam with 5m span, 9″ thick Brick wall, using thumb rule, beam depth should be 300mm and width 225mm, beam size 9″×12″ (230mm ×300mm) using 4pcs of 16mm bar of Fe500 steel bars with minimum M20 grade of concrete and stirrups T8@6″C/C.
2) Calculation of depth and width of Cantilever beam:-
Note as per IS – 13920
A) the width to depth ratio should be more than 0.3 ( width/depth > 0.3).
B) depth of beam shall not be exceeded One by fourth (1/4) of clear span.
Let clear span of cantilever beam = 2m = 2000mm
Effective depth = span/basic value
Total depth = effective depth + diameter of bar/2 + clear cover size.
Width of beam = Depth/1.5 ( width of beam should not be less than 200 mm).
Span of cantilever beam = 2000mm
Effective depth of beam d = 2000/7=285mm
Total depth of beam = effective depth + diameter of bar/2 + clear cover size.
Assume clear cover size = 25mm
Diameter of bar =16mm
Total depth D = 285mm +16/2mm +25mm
Total depth D= 318mm, It should be taken as 325mm.
Width of beam = D/1.5, 325/1.5 = 216mm, so width of beam should be not less than 200mm in case of Block wall and 225mm in case of Brick wall. So width of beam taken as 225mm least.
Now check it,
Width/depth =225/325 =0.69 > 0.3, it is safe
Now we can check depth of beam = 1/4×2000= 500 > 300, yes it is safe.
Depth and width of cantilever beam
Cantilever beam with 2m span, 9″ thick Brick wall, using thumb rule, beam depth should be 330mm and width 225mm, beam size 9″×13″ (230mm ×330mm) using 4pcs of 16mm bar of Fe500 steel with minimum M20 grade of concrete and stirrups T8@6″C/C.
3) Calculation of depth and width of continuous beam:-
Note as per IS – 13920
A) the width to depth ratio should be more than 0.3 ( width/depth > 0.3).
B) depth of beam shall not be exceeded One by fourth (1/4) of clear span.
Let clear span of continuous beam = 5m = 5000mm
Effective depth = span/basic value
Total depth = effective depth + diameter of bar/2 + clear cover size.
Width of beam = Depth/1.5 ( width of beam should not be less than 200 mm).
Span of continuous beam = 5000mm
Effective depth of beam d = 5000/26=192.3mm
Total depth of beam = effective depth + diameter of bar/2 + clear cover size.
Assume clear cover size = 25mm
Diameter of bar =16mm
Total depth D = 192mm +16/2mm +25mm
Total depth D= 225mm, It should be taken as 225mm.
Width of beam = D/1.5, 225/1.5 = 150mm, so width of beam should be not less than 200mm in case of Block wall and 225mm in case of Brick wall. So width of beam taken as 225mm least.
Now check it,
Width/depth =225/225 =1 > 0.3, it is safe
Now we can check depth of beam = 1/4×5000= 1250 > 300, yes it is safe.
Depth and width of continuous beam
Continuous beam with 5m span, 9″ thick Brick wall, using thumb rule, beam depth should be 230mm and width 230mm, beam size 9″×9″ (230mm ×230mm) using 4pcs of 16mm bar of Fe500 steel with minimum M20 grade of concrete and stirrups T8@6″C/C.
Beam depth for 5m, 6m, 7m, 8m, 9m and 10m span & its formula
Beam depth to width ratio:- As per IS – 13920, the ratio between the width and effective depth of the beam should be more than 0.3 ( width/depth > 0.3).
Beam depth to span ratio:- The ratio between the span and the effective depth of the beam is 7 for a cantilever beam, 20 for a simply supported beam and 26 for a continuous beam. This depth to span ratio is used to calculate the minimum RRC beam size according to IS 456 2000.
Beam depth formula:- The beam depth formula for a cantilever beam is L/7 (the effective span to depth ratio of the beam is 7), L/20 for simply supported beam and L/26 for continuous beam.
In general, the depth of the beam for a residential building need to be 12-inches (300 mm) for a 5m span, 9-inches for a 3m to 4m span, 14-inches for a 6m span, 16-inches for a 7m span, 18-inches for a 8m span, 20-inches for a 9m span, and 24-inches for a 10m span.
Beam depth for 3m to 4m span
Typically, for a residential building with an RCC column, the beam depth should be 9-inches (230 mm) thick for spans of 3m to 4m, with a minimum beam size of 9 in. × 9 in. (230 × 230 mm).
According to general Thumb Rule for residential building with rcc column, beam depth for 3m to 4m span should be 9″ (225mm), minimum beam size 9″×9″ (225mm × 225mm) is applicable. Using 2pcs of reinforcement size T12 at top and 2pcs of reinforcement size T12 at bottom of Fe 500 used with M20 grade of concrete with stirrups of T8@6″C/C with clear cover 25mm, as desine structure, height of building and load applied on it.
Beam depth for 5m span
Typically, for a residential building with an RCC column, the beam depth should be 12-inches (300 mm) thick for span of 5m (meters), with a minimum beam size of 9 in. × 12 in. (230 × 300 mm). The depth of the beam is 12- inches and the width is 9- inches.
According to general Thumb Rule for residential building, beam depth for 5m span should be 300mm, minimum beam size for 5m span is 9″×12″ (230mm × 300mm) in which depth of beam is 300mm and width is 225mm, using 2nos of reinforcement size T16 at top and 2nos of reinforcement size T16 at bottom of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm, as desine structure, height of building and load applied on it.
For given span of beam =5m =5000mm, beam depth for simply supported beam is L/20, effective depth should be 5000/20 = 250mm, overall Depth = 250 +12/2+25 = 281mm, it should be taken depth as 300mm, width = 300/1.5= 200mm, but at least width should be 225mm
So beam size for 5m span is 9″×12″ (225mm × 300mm) in which depth of beam is 300mm and width is 225mm, using 2nos of reinforcement size T16 at top and 2nos of reinforcement size T16 at bottom of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Beam depth for 6m span
Typically, for a residential building with an RCC column, the beam depth should be 14-inches (350 mm) thick for span of 6m (meters), with a minimum beam size of 10 in. × 14 in. (250 × 350 mm). The depth of the beam is 14- inches and the width is 10- inches.
According to general Thumb Rule for residential building, beam depth for 6m span should be 350mm, minimum beam size for 6m span is 10″×14″ (250mm × 350mm) in which depth of beam is 350mm and width is 250mm, using 2pcs of reinforcement size T16 at top and 2nos of reinforcement size T16 at bottom of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm,as desine structure, height of building and load applied on it.
For given span of beam =6m =6000mm, beam depth for simply supported beam is L/20, effective depth should be 6000/20 =300 mm, overall Depth = 300 +16/2+25 = 333mm, it should be taken depth as 350mm, width = 350/1.5= 233mm, which is taken as 10″ (250mm), so beam size for 6m span is 10″×14″ (250mm × 350mm) in which depth of beam is 350mm and width is 250mm, using 2nos of reinforcement size T16 at top and 2nos of reinforcement size T16 at bottom of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Beam depth for 7m span
Typically, for a residential building with an RCC column, the beam depth should be 16-inches (400 mm) thick for span of 7m (meters), with a minimum beam size of 12 in. × 16 in. (300 × 400 mm). The depth of the beam is 16- inches and the width is 12- inches.
According to general Thumb Rule for residential building with rcc column, beam depth for 7m span should be 400mm, minimum beam size for 7m span is 12″×16″ (300mm × 400mm) in which depth of beam is 400mm and width is 300mm, using 2pcs of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as Crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm as desine structure, height of building and load applied on it.
For given span of beam =7m =7000mm, beam depth for simply supported beam is L/20, effective depth should be 7000/20 =350 mm, overall Depth = 350 +16/2+25 = 383mm, it should be taken depth as 400mm, width = 400/1.5= 266mm, which is taken as 12″ (300mm)
So beam size for 7m span is 12″×16″ (300mm × 400mm) in which depth of beam is 400mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Beam depth for 8m span
Typically, for a residential building with an RCC column, the beam depth should be 18-inches (450 mm) thick for span of 7m (meters), with a minimum beam size of 12 in. × 18 in. (300 × 450 mm). The depth of the beam is 18- inches and the width is 12- inches.
According to general Thumb Rule for residential building with rcc column, beam depth for 8m span should be 450mm, minimum beam size for 8m span is 12″×18″ (300mm × 450mm) in which depth of beam is 450mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2pcs of reinforcement size T16 at bottom and 2nos of T12 as Crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm as desine structure, height of building and load applied on it.
For given span of beam =8m =7000mm, beam depth for simply supported beam is L/20, effective depth should be 8000/20 =400 mm, overall Depth = 400 +16/2+25 = 433mm, it should be taken depth as 450mm, width = 450/1.5= 300mm, which is taken as 12″ (300mm)
So beam size for 8m span is 12″×18″ (300mm × 450mm) in which depth of beam is 450mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Beam depth for 9m span
Typically, for a residential building with an RCC column, the beam depth should be 20-inches (500 mm) thick for span of 9m (meters), with a minimum beam size of 12 in. × 20 in. (300 × 500 mm). The depth of the beam is 20- inches and the width is 12- inches.
According to general Thumb Rule for residential building with rcc column, beam depth for 9m span should be 500mm, minimum beam size for 9m span is 12″×20″ (300mm × 500mm) in which depth of beam is 500mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as Crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm as desine structure, height of building and load applied on it.
For given span of beam =9m =9000mm, beam depth for simply supported beam is L/20, effective depth should be 9000/20 =450 mm, overall Depth = 450 +16/2+25 = 483mm, it should be taken depth as 500mm, width = 500/1.5=333 mm, which is taken as 12″ (300mm), so beam size for 9m span is 12″×20″ (300mm × 500mm) in which depth of beam is 500mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Beam depth for 10m span
Typically, for a residential building with an RCC column, the beam depth should be 24-inches (600 mm) thick for span of 10m (meters), with a minimum beam size of 12 in. × 24 in. (300 × 600 mm). The depth of the beam is 24- inches and the width is 12- inches.
According to general Thumb Rule for residential building with rcc column, beam depth for 10m span should be 600mm, minimum beam size for 10m span is 12″×24″ (300mm × 600mm) in which depth of beam is 600mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2nos of reinforcement size T16 at bottom and 2nos of T12 as Crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm as desine structure, height of building and load applied on it.
For given span of beam =10m =10000mm, beam depth for simply supported beam is L/20, effective depth should be 10000/20 =500 mm, overall Depth = 500 +16/2+25 = 533mm, it should be taken depth as 600mm, width = 600/1.5= 400mm, which is taken as 12″ (300mm)
So beam size for 10m span is 12″×24″ (300mm × 600mm) in which depth of beam is 600mm and width is 300mm, using 2nos of reinforcement size T16 at top, 2pcs of reinforcement size T16 at bottom and 2nos of T12 as crank bar of Fe 500 used with m20 grade of concrete with stirrups of T10@6″C/C with clear cover 25mm.
Conclusions:-
In general, the depth of the beam for a residential building should be 12-inches (300 mm) for a 5m span, 9-inches for a 3m to 4m span, 14-inches for a 6m span, 16-inches for a 7m span, 18-inches for a 8m span, 20-inches for a 9m span, and 24-inches for a 10m span.