PRESENTATION ONT-BEAM DESIGN

BY WSD METHOD

Presented byKhandaker Mehedi HasanStudent ID:10.01.03.158

Department of Civil EngineeringAUST,Dhaka

CE 416 PRE-STRESSED CONCRETE LAB.

Course TeachersLecturer Mr. Galib Muktadir

Assistant prof. Ms. Sabreena Nasrin

Department of Civil EngineeringAhsanullah University of science and Technology

DEFINITION:-A T-Beam is a beam that supports a slab and the slab is built integrally with the beam.

Concrete floor slabs and beams are normally tied together by means of stirrups and bent-up bars if any and then are cast form one mass of concrete. Such a monolithic system will act integrally i.e., it is allowed to assume that part of the slab acts with the beam and they form what is known as a flanged beam, Fig. 1.1

  The part of the slab acting with the beam is called the flange, and it is indicated in Fig. 1.2 by the area Bts. The rest of the section confining the area (t-ts)b is called the stem or web. As Fig. 1.2 indicates.

Fig:1.1 Fig:1.2

Various Possible Geometries of T-Beams

Single Tee

Twin Tee

Box

Square T beam Tapered T beam

Inverted L(Spandrel) Beams

Floor systems with slabs and beams are placed in monolithic pour.Slab acts as a top flange to the beam; T-beams, and Inverted L(Spandrel) Beams.

Analysis of Flanged Section

Positive and Negative Moment Regions in a T-beam

Analysis of Flanged Sections

If the neutral axis falls within the slab depth analyze the beam as a rectangular beam, otherwise as a T-beam.

Analysis of Flanged Sections

Effective Flange Width

Portions near the webs are more highly stressed than areas away from the web.

Analysis of Flanged Sections

eff

f w

actual

4

16

Lb

h bb

From ACI 318, Section 8.10.2

T Beam Flange:

ACI Code Provisions for Estimating beff

weff

wf

42

bb

bh

From ACI 318, Section 8.10

Isolated T-Beams

T-Beam may be singly reinforced or doubly reinforced. When steel is provided only in tensile zone (i.e. below neutral axis) is called singly reinforced t-beam, but when steel is provided in tension zone as well as compression zone is called doubly reinforced t-beam.

Design of T-Beam

The aim of design is:To decide the size (dimensions) of the member and the amount of reinforcement required.

To check whether the adopted section will perform safely and satisfactorily during the life time of the structure.

Allowable Stress – WSD (ASD)

Actual loads used to determine stressAllowable stress reduced by factor of safety

Ultimate Strength – (LRFD)

Loads increased depending on type loadg Factors: DL=1.4 LL=1.7 WL=1.3U=1.4DL+1.7LL

Strength reduced depending on type forcef Factors: flexure=0.9 shear=0.85 column=0.7

Examples:

WSD

Ultimate Strength

Methods of Design

Assumptions:– Plane sections remain plane– Hooke’s Law applies– Concrete tensile strength is neglected– Concrete and steel are totally bonded

Allowable Stress Levels– Concrete = 0.45f’c– Steel = 20 ksi for gr. 40 or gr. 50

= 24 ksi for gr. 60

Transformed Section– Steel is converted to equivalent concrete.

Working Stress Design(WSD) Method

Procedure for Design of Singly Reinforced Beam by Working Stress Method

Given :(i) Span of the beam (l)(ii) Loads on the beam (iii)Materials Grade of Concrete and type of steel. i.e. f'c

& fy

Now, Selecting the suitable diameter of bar calculate the number of bars required

As

Singly reinforced T-beam

Reduced sustained load deflections. Creep of concrete in compression

zone transfer load to compression steel reduced stress in concrete Architectural design & view less sustained load deflection

Reasons for Providing Compression Reinforcement

Effective of compression reinforcement on sustained load deflections

Reasons for Providing Compression Reinforcement

Doubly reinforced T-beam

Layout of doubly reinforced T-beam