CE-416

Course Teacher:Mr. Galib Muktadir & Sabreena N.Mouri

Department of Civil Engineering

Ahsanullah University of Science & Technology

Pre-stressed Concrete Lab

WELCOME TO MY PRESENTATION

Prepared by: Sadia Mannan Mitu ID:10.01.03.102

Presentation on:

T-Beam DesignSingly & Doubly:USD

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.

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

Fig:T-Beam

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.

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.

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.

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.

Effective flange width of T-Beam:

Effective flange width of T-Beam:

Strength Analysis:

For equilibrium we have,

Case I:

Case II:

And Nominal moment capacity will be,

Mn = Asf fy (d-hf/2)+ (As - Asf) fy (d – a/2)

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

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.

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 T-beam 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.

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.

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.

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.

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.

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.

THANK YOU . . .