For cast-in-situ beams supporting slab (monolithic casting), a beam considered as a flanged section than a rectangular one, and this is because the slab part just right adjacent to the beam bends in flexure together with the beam integrally.

As a result of deformation variation [quantitatively] between rectangular and flanged beams, many international codes recommend the use of a T or inverted L section beam for modeling [analysis] and design as a result of flexural stiffness variation. For the use of a flanged section both on a model for analysis and design for dimensioning first, the effective width needs to be computed.

*Flanged section, effective beam width according to EN 1992: Clause 5.3.2.1*

Effective flange width,* b_{eff}* ,for a T and inverted L beams defined as ;

*b _{eff } = ∑ b_{eff,i }+ b_{w} ≤ b *

*and*

*b*_{eff,i }= 0.2 b_{i }+ 0.1 l_{o}≤ 0.2 l_{o}** b_{eff,i }≤ b_{i}**

Typical flanged section:

**sample example**

The effective flange width for a beam marked below, and **b/h = 25 cm / 50 cm . **

*Solution:*

Location of the beam: *Exterior beam*

There is no transverse beam to the left (L – beam, l_{2} = 0 ), whereas a transverse beam to the right is, l_{1} = 6.00 m. b_{1} is the distance between the support face (column) and the mid-span of the transverse beam.

i.e. l_{o} = 0.85 * 6.00 m = *5.10 m **and* b_{1} = (l_{1} -b_{w}) / 2 = (6.00m – 0.25 m) /2 = *2.875m*

*b _{eff,1} = 0.2 b_{1} + 0.1 l_{o } < 0.2 l_{o} *

*b _{eff,1} = 0.2 * ( 2.875m ) + 0.1 * ( 5.10 m) _{ } < 0.2 * ( 5.10 m)*

*b _{eff,1} = 1.085 m < 1.02 m*

*b _{eff} = b_{eff,1} + b_{w} = 1.02 m + 0.25 m*

**∴** *b _{eff} = 1.27 m = 1270 mm*

**Note:** *the consideration of a flanged section beam on a finite element model would be a necessity for a moment-resisting ductile frame while analyzing of a seismic load.*

**Try:** For the same beam cross-section above [b/h], put your answer on the comment section below for the effective flange width of the marked beam.

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