1. Name: Farjana Akter
ID:10.01.03.140
Prestressed Concrete Lab
4TH YEAR AND 2ND SEMESTER
SECTION C

2. WELCOME TO
PRESENTATION ON

3. Defines bending moment
A bending moment
is a measure of the
bending effect due to
forces acting on a
beam,
which
is
applied to an element
so that the element
bends.

4. Sign Convention:
Positive: if the external load tends to make the beam sag
Negative: if the external load tends to make the
beam hog (bend upwards)
Stress:
is the internal resisting force per unit area.
σ =F/A

5. Defines Bending Moment stress
Bending moment stresses are
internal stresses caused by bending
moments acting at a given distance
from the neutral axis. It is also
known as flexural stress.

6. Bending Moment stress
Their magnitude is given by the formula:

7. Beams are almost always
designed on the basis of
bending stress.
Distribution of Bending
stress through a beam is
shown in figure:
Bending stresses are tensile
or compressive stresses in
the Beam. A simplysupported beam always has
tensile stresses at the
bottom of the beam and
compressive stresses at the
top of the beam.

8. Depending on the orientation of the beam with
respect to the direction of the forces applied
Bending Moment Stress are of two types:
1. Uni-axial Bending Stress
2. Bi-axial Bending Stress

9. Uni-axial Bending Stress:
If loads are applied in one direction only which produce
stress system is an uni-axial bending stress.
For example: Columns are usually subjected to two
bending moments about two perpendicular axes (X and
Y) as well as an axial force in the vertical Z direction due
to loading.

10. Uni-axial Bending Stress:
With the shown sign convention, bending about X-axis
causes compression in the top part and tension in the
bottom region, whereas bending about Y-axis causes
compression in the left hand part and tension in the right
part. For symmetric sections subjected to uni-axial
bending, the neutral axis is parallel to the moment axis.

11. Bi-axial Bending Stress:
If loads are applied in both x and y-directions, the plate will
have a bi-directional stress distribution. It is also known as
unsymmetrical (skew) bending.

12. Bi-axial Bending Stress:
In biaxial bending (d), the top-left part is subjected to
double compression and the bottom right part is subjected
to double tension. The remaining parts are subjected to
combined compression and tension. This means that the
two moments are not independent but coupled. The
resulting neutral axis is inclined with an angle depending
on the moment values as well as the section properties.

13. According to biaxial bending stress :
for Beam ,
σx = -(Mz y/Iz ) + (Myz/Iy)

14. • There are two method in which biaxial bending
stress are represented by an equivalent uniaxial bending moment stress:
1. Load contour method
2. Reciprocal load method

15.  The analysis of bi-axial bending
stress (manual calculation )for column
is quite impractical.
 A number of computer programs for
biaxial bending are available in
commercially such as PCACOLUMN &
HBCOLUMN

16. OR else Failure
Don’t over stress