Presentation on T-Beam Design: Singly and Doubly by USD method

1. Ahsanullah University of Science
& Technology
Pre-stressed Concrete Lab
CE-416
Course Teacher:
Mr. Galib Muktadir & Sabreena N.Mouri
Department of Civil Engineering

2. WELCOME TO MY PRESENTATION

3. Presentation on:

4. Definition of T-Beam:
 When slabs are monolithically casted with
beams in a positive moment zone, part of the
slab act as a part of the beam and resist the
longitudinal compression. The resulting
section is T beam.

5. Definition of T-Beam:
 The top of the t-shaped cross section serves
as a flange or compression member in
resisting compressive stresses.
 The web of the beam below the compression
flange serves to resist shear stress and to
provide greater separation for the coupled
forces of bending

6. Fig:T-Beam

7. Ultimate Strength Design(USD)
Method:
 Based on the ultimate strength of the
structure assuming a failure condition either
due to concrete crushing or by yielding of
steel. Addition strength of steel due to strain
hardening is not encountered in the analysis
or design.
 Actual working loads are multiplied by load
factor(>1) to obtain the ultimate design load.
 ACI (American Concrete Institute)code
emphasizes this method.

8. Positive bending moment for
T-Beam:
 In the analysis and design of floor and roof
systems, it is common practice to assume
that the monolithically placed slab and
supporting beam interact as a unit in resisting
the positive bending moment.

9. Negative bending moment for
T-Beam:
 It should be noted that when the T-Beam is
subjected to negative moment, the slab at
the top of the stem (web) will be in tension
while the bottom of the stem is in
compression. This usually occurs at interior
support of continuous beam.

10. Effective flange width:
 The effective slab width is a concept used
in flexural analysis of concrete T-beams
and concrete-steel composite beams to
simplify the computation of flange
bending stresses. In order to determine
the ultimate moment capacity of
composite beams, the ultimate stress in
the effective flange width is needed.

11. Effective flange width of T-Beam:

12. Effective flange width of T-Beam:

14. Strength Analysis:

16. For equilibrium we have,
Case I:

17. Case II:

18. And Nominal moment capacity will be,
Mn = Asf fy (d-hf/2)+ (As - Asf) fy (d – a/2)

19. Trial:
In USD method,
For trial,first assume ‘a’ is
within the range.
-if a≤ hf , analyze as rectangular
beam.
-If a>hf , analyze as T Beam

20. Design Procedure of T-Beam:
1.Compute the design moment (Mu).
2.Assume the effective depth.
3.Decide the effective flange width
(b) based on ACI criteria.
4.Compute the practical moment
strength (φMn) assuming the total
effective flange is supporting the
compression.

21. Design Procedure of T-Beam:
5.If the practical moment strength (φMn) is
bigger than the design moment (Mu), the
beam will be calculated as a rectangular Tbeam with the effective flange width b. If
the practical moment strength (φMn) is
smaller than the design moment (Mu), the
beam will behave as a true T-shape beam.

22. Design Procedure of T-Beam:
6.Find the approximate lever arm distance
for the internal couple.
7.Compute the approximate required steel
area.
8.Design the reinforcement.
9.Check the beam width.
10.Compute the actual effective depth and
analyze the beam.

23. Singly Reinforced Beam:
 A singly reinforced beam is one in which
the concrete element is only reinforced near
the tensile face and the reinforcement,
called tension steel, is designed to resist the
tension.

24. Doubly Reinforced Beam:
 A doubly reinforced beam is one in which
besides the tensile reinforcement the concrete
element is also reinforced near the compressive
face to help the concrete resist compression. The
latter reinforcement is called compression steel.
When the compression zone of a concrete is
inadequate to resist the compressive moment
(positive moment), extra reinforcement has to
be provided if the architect limits the dimensions
of the section.

28. Advantages:
 Can be placed in almost all weather conditions
 Are manually placed, thus not requiring any




special equipment
Do not require hardcore back fill beneath beams
Provide an immediate dry working platform
The ideal option where site access is limited
T-Beams are most often used for sunrooms,
extensions and small projects.

29. Disadvantages:
 The T-beam has a big disadvantage
compared to an I-beam because it has no
bottom flange with which to deal with
tensile forces. One way to make a T-beam
more efficient structurally is to use an
inverted T-beam with a floor slab or bridge
deck joining the tops of the beams. Done
properly, the slab acts as the compression
flange.

30. THANK YOU
. . .