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Design of Weir
and Conditions for Stability & Maximum Stress
By: Haseeb Jamal
In any hydropower projects the diversion
structures occupies the key position.
Among these diverging structures weir is
the most commonly used structure, because of its simple design and operation.
Different types of weir can be used as
diverging structures some of them are given below:
o Sharp crested weir
o Broad crested weir
o Ogee weir
o Tyrolean weir
o Weir with lateral
intake etc
Lets consider a general case of weir
design.
Forces
on Weir
The forces acting on a weir built on a
impervious foundation may be static or dynamic. The static forces include:
o Normal water
pressure on the upstream face of the weir.
o Normal water
pressure on the downstream face of the weir.
o The weight of the
water supported by the crest and the weight of the weir.
Dynamic
forces
The dynamic forces acting on weir includes:
o Erosive or the
scouring forces on the downstream side of the weir produced either by high
velocity or by the impact of water pouring over the weir.
o The force of impact
of floating matter against the crest on the upstream side of the weir.
Conditions
for Stability of Weirs
There are some conditions that are required
to be satisfied for the stability of the weir. These includes:
o There must be no
tension in the masonry or in the contact plane between weir and the foundation.
o There must be no
overturning.
o There must be no
tendency to slide on the joint with the foundation or any horizontal plane
above the base.
o The maximum toe and
heel pressures in foundations should not exceed the prescribed safe limits.
Failure by crushing is not considered here, as it generally does not occur,
being a low structure.
Condition
of Maximum Stress on Weir
In the case of a dam the condition for
maximum stress is when the water level above the base is maximum. i. e. when
the head is maximum.
But in case of a weir design, when the
discharge increases the near water level also builds up and the difference
between them will become less and less.
So, the weir is subjected to maximum head
when the water level on the upstream side is maximum and no water passes over
the crest.
Let us know in the comments what you think about the concepts in this article!
Haseeb Jamal
I
am a Civil Engineer, graduated from University of Engineering and Technology,
Peshawar, Pakistan in 2010. I also have a PG-Diploma in Disaster Management and
MS in Urban Infrastructure Engineering (In Progress). My expertise include
civil related softwares like AutoCAD, SAP2000, MS Project, Primavera, MS Office
and GIS. My technical skills include project management, monitoring and
evaluation, structural assessment, disaster risk management, Quantity survey,
land survey, material testing, site management and technical writing. I am
trained in writing project progress reports as well as proposals and concept
papers. I have also received advanced training on surveying, proposal writing,
Monitoring and Evaluation of projects as well as organizations.
I
have worked as Project Engineer at National Research and Development
Foundation, Peshawar and CENCON Associates. I also worked with Spectra
Engineering Solutions as Senior Civil Engineer in monitoring of World Bank and
UNDP funded projects all over Khyber Pakhtunkhwa and FATA. Currently, I am
working as Deputy Manager Development at NayaTel, Peshawar.
https://www.aboutcivil.org/weir-design-stability.html
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