T beams and terms used in T beams : Breadth of Web (bw),Thickness of the Flange (Df),Overall Depth of the Beam (D),Effective Width of the Flange (bf),Effective width of the compression flange of the flanged beam in Reinforced cement concrete
T beams and terms used in T beams in Reinforced cement concrete
T BEAMS
In RCC construction, slabs and beams are cast monolithic-ally. In such construction, a portion of the slab act integrally with the beam and bends along with the beam under the loads. This phenomenon is seen in the beams supported slab system as shown in Fig. 2.11.
The portion of the slab which acts integrally with the beam to resist loads is called as Flange of the T-beam or L-beam. The portion of the beam below the flange is called as Web or Rib of the beam. The intermediate beams supporting the slab are called as T-beams and the end beams are called as L-beams.
The flange of the beam (part of the slab) contributes in resisting compression by adding more area of concrete in compression zone. This results in increasing moment of resistance of the beam section. However, if the flange is located in tension zone, the concrete are of the flange is to be neglected (cracked) and beam is treated as a rectangular beam.
TERMS USED IN T BEAMS (Fig. 2.12)
Breadth of Web (bw)
Breadth of web is the width of the beam supporting the slab. It should be sufficient enough to accommodate the tensile reinforcement properly. The ratio of width of web to the depth of web is kept as \[\frac {1}{3} to \frac {2}{3}\].
Thickness of the Flange (Df)
The thickness of flange of the T-beam is equal to the thickness or depth of the slab forming the flange of the beam.
Overall Depth of the Beam (D)
Overall depth of a flange (Df) and depth of the web (dw). It is generally assumed as \[\frac{1}{12} to \frac{1}{15}\]
For continuous beams, the overall depth is assumed as follows :
\[For light loads : \frac{1}{15} to \frac{1}{20} of span\]
\[For medium loads : \frac{1}{12} to \frac{1}{15} of span\]
\[For heavy loads : \frac{1}{10} to \frac{1}{12} of span.\]
Effective Width of the Flange (bf)
It is that portion of slab which acts integrally with the beam and extends on either side of the beam forming the compression zone. The effective width of flange mainly depends upon the span of beams, thickness of slab and the breadth of the web. It also depends upon the type of loads and support conditions.
The effective width of flange should not be greater than the breadth of web plus half the sum of clear distances to the adjacent beams on either side as shown in Fig. 2.13.
Effective width of the compression flange of the flanged beam
The effective width of the compression flange of the flanged beam can be calculated as follows (Cl. 23.1.2 of Code IS 456).
(a) For T-Beams :
\[b_{f}=\frac{l_{0}}{6}+b_{w}+6D_{f}\]
(b) For L-Beams :
\[b_{f}=\frac{l_{0}}{12}+b_{w}+3D_{f}\]
(c) For Isolated Beams :
The effective flange width shall be obtained as below but in no case greater than the actual width.
(i) T-Beam. \[b_{f}=\frac{l_{0}}{\left ( \frac{l_{o}}{b}+4 \right )}+b_{w}\]
(ii) L-Beam, \[b_{f}=\frac{0.5l_{0}}{\frac{l_{o}}{b}+4}+b_{w}\]
where bf = Effective width of flange
bw = Breadth of web
Df = Thickness of flange
b = Actual width of flange
l0 = Distance between the points of zero moments (for continuous beams, l0 is taken as 0.7 times the effective span)