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Good morning!. New words. Beam 梁 Tension 拉伸 Compression 压 Shear 剪 Torsion 扭转 Bending 弯曲 - PowerPoint PPT PresentationTRANSCRIPT
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New wordsBeam 梁Tension 拉伸Compression 压Shear 剪Torsion 扭转Bending 弯曲Concave side 凹面Convex side 凸面
Exersize •measure the tendency of one part of a beam to be slided with respect to the other part•-------(shear force)•the tendency for one part to be rotated with respect to the other part•-------(bending moment)
Review:In last week, we have learned columns made of :
timber steel concrete
New member –beam
Question: in considering the beam
what are we concerned with?
Answer: the effects of the forces
Five forms of deformation
TensionCompression
ShearBendingTorsion
Internal forcesFor example: the internal forces that result
from bending deformations are compressive on the concave side and tensile on the convex side
•SF&BM measure the tendency of one part of a beam to be slided with respect to the other part (SF effect),and the tendency for one part to be rotated with respect to the other part(BM effect)•The question we need resolve is to calculate the SF&BM
Shear Force
CalculationThe SF at any section A in a straight beam is the algebraic sum of all vertical forces lefts of that point
SFA=∑VLA
Eg1: 3KN 5KN A B C D 2M 2M 1M 8KN
STEPS•Cut the beam at point B ,so we will get part of the shear force of the beam
8KN 3KN
A B
If we cut the beam at point C ,what will happen to the
SF?
TRYING… What about point D?
TRYING…
SFD•If we plot the value of the SF at all point along the axis of a beam, we’ll obtain the Shear Force Diagram
8KN 5KN
Principle for solving the SFD
• Calculate the shear forces at the following significant positions:– At the start and end of the beam– At every support– At every point load– At the start and end of every
distributed load
Conclusion:•We find that at a point load
the SF changes instantaneously and the SF diagram shows a step.
Eg2:
A B C D 2M 2M 1M
Steps:•First calculate the reaction
at support A.
•Then cut the beam at point D
•Finally plot the SFD 15
A B C D 2M 2M 1M
Conclusion:•When there is an UDL,we
see the SF change by equal intervals ,and the SFD will have a constant slope.
Have a Try 4KN 6KN 3KN
A B ① ② ③
Bending Moment
BML=∑ALL
•The BM at any section A in a straight beam is the algebraic sum of areas of the SFD left of that point
Eg3
A B C D 2M 2M 1M 8KN 5KN
A B C D
NOTE•Locate the positions of zero
SF, as these will also be positions of maximum BM.
The result is:
0
16KN
26KN
HAVE A TRY 4KN 6KN 3KN
A B ① ② ③
CONSIDER•All we learned today is the simply supported beam, then what about continuous beam?
•Let’s talk about it on next lesson!
Homework:Exersize1
a/b/c/f
Bye byeSee you next
class