Lecture 23 Shear Design

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Lecture 23 Shear Design

• March 19, 2003
• CVEN 444

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Lecture Goals

• Shear
• Shear Design
• Project

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Example Design of Stirrups to Resist Shear
From flexural design
fc 4000 psi fy 60 ksi wsdl
1.2 k/ft wll 1.8 k/ft fys 40 ksi wb
0.5 k/ft
will use either a 3 or 4 stirrup
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Example Design of Stirrups to Resist Shear
Consider the pattern loading on the beam and
determine the envelope of absolute maximum shear
along the beam for a symmetric beam with
uniformly distributed loads, a straight line
drawn between the maximum at the end and midspan
is adequate.
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Example Design of Stirrups to Resist Shear
The maximum shear is where,
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Example Design of Stirrups to Resist Shear
The maximum shear is Note
Multiply by 1.15 for end moments _at_ face of 1st
internal support when using ACI shear coefficient
1.15 Vumax (section 8.3)
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Example Design of Stirrups to Resist Shear
The wall is an interior section so the
coefficient is 1.0. For shear the reduction
factor, f, is 0.75.
How do you get maximum shear the center?
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Example Design of Stirrups to Resist Shear
There is no pattern load for dead loads Vdl 0
_at_ center
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Example Design of Stirrups to Resist Shear
There is a pattern load for live loads at the
center of the beam
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Example Design of Stirrups to Resist Shear
Compute the Vu max at the center
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Example Design of Stirrups to Resist Shear
The shear envelope can be constructed using the
values of two maximum at the two location end and
the center.
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Example Design of Stirrups to Resist Shear
Calculate the equation of the line to bound the
shear force and
The slope of the shear forces.
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Example Design of Stirrups to Resist Shear
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Example Design of Stirrups to Resist Shear
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Example Design of Stirrups to Resist Shear
114.8 k gt 0.5Vc Need shear reinforcement
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Example Design of Stirrups to Resist Shear
The area, Av, is twice the area of the bars Ab
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Example Design of Stirrups to Resist Shear
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Example Design of Stirrups to Resist Shear
The maximum spacing is 13.1 in.
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Example Design of Stirrups to Resist Shear
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Example Design of Stirrups to Resist Shear
Reinforcements can be used for shear
reinforcement. The beam does not need to be
redesigned.
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Example Design of Stirrups to Resist Shear
Strength requirement is given as
Instead of solving for s, we can plot the Vc
Vs, where
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Example Design of Stirrups to Resist Shear
Using this technique (ACI 11.3.1), various Av and
spacing s can be used. The maximum V is
determined at the distance,d from the wall.
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Example Design of Stirrups to Resist Shear
The shear force are
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Example Design of Stirrups to Resist Shear
This is one possibly form to check
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Example Design of Stirrups to Resist Shear
There always going to be a shear reinforcement
close to the support. Use the minimum spacing, 4
in., so that the first stirrup has 4 in. Spacing
can be computed as
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Example Design of Stirrups to Resist Shear
If we are using 8 4 stirrups _at_ 7 in. spacing, 7
in. is less than 7.92 in. So,
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Example Design of Stirrups to Resist Shear
Compute the location of the point and
find Compute Vn
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Example Design of Stirrups to Resist Shear
Compute the next spacing
Use s 9 in., which is find for 4 bar. Trying
to fit the reinforcement inside the beam.
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Example Design of Stirrups to Resist Shear
If we are using 6 4 stirrups _at_ 9 in. spacing, 9
in. is less than 11.3 in. So,
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Example Design of Stirrups to Resist Shear
Compute the location of the point and
find Compute Vn
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Example Design of Stirrups to Resist Shear
Use a 3 bar for
Use s 12 in., because the smax is 13.1 in.
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Example Design of Stirrups to Resist Shear
If we are using 8 3 stirrups _at_ 12 in. spacing,
12 in. is less than 13.1 in. So,
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Example Design of Stirrups to Resist Shear
Compute the location of the point and find This
is at the middle of the beam. Under Vc/2 no
stirrups are need other than the minimum.
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Example Design of Stirrups to Resist Shear
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Example Design of Stirrups to Resist Shear
There is a mistake for the problem! What is the
error?
The spacing of the 3 bar is 12 in. and the max
spacing between bars is 11.7 in., so go back and
redesign. Easy way would be to use 4 instead of
3 bars.
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Example Design of Stirrups to Resist Shear
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Class Project
The structural floor plan of a three-story
(ground floor, two suspended floors, and a roof)
office building is shown on the next page. The
roof covers the hole used for the elevator shaft
and stairwells. The new building will be located
in Houston, Texas. The floor systems consist of
one-way pan joists slabs supported in one
direction by beams located on column lines A
through F. In addition, beams are located on
column lines 1 and 4 as part of the lateral force
resisting system.
0.75L
0.75L
0.75L
0.75L
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Class Project
The design loads for the floor (in addition to
the self-weight) include a superimposed dead load
(SDL) of 20 psf to account for moveable
partitions, ceiling panels, etc. and a
superimposed live load (LL) to be determined from
ASCE 7-95. In addition, a 0.5 kip/ft. wall load
is applied around the building perimeter. The
design loads for the roof (in addition to the
self-weight) include a superimposed dead load
(SDL) of 10 psf.
0.75L
0.75L
0.75L
0.75L
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Class Project
Overview of Required Design

• Design the continuous beams of the first floor on
  column lines D and E of the second suspended
  floor assuming that they support the one-way pan
  joist floor system (3 parts).
• Design the slab of the second suspended floor as
  a one-way pan joist system supported in one
  direction on column lines A through F (3 parts).
• Design and detail the columns for all three
  stories for the location where column lines E and
  2 intersect (1 part).
• Design the roof system as a two-way slab without
  beams (1 part).
• Design the footing for the column on column lines
  E and 2 (1 part).

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Class Project
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Class Project
The Joist detail for section 1-1
The beam detail for section 2-2
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Class Project
Team Performance It is expected that all
assignments related to the project will be done
in teams. Each assignment must contain
computations that are initialed by the
calculators (or originators) and initialed by the
checker(s). Members of the team will rotate
between calculation and checking tasks. It is
recommended that two persons calculate for each
assignment (i.e., In a four-person team, two
persons should provide calculation services on
odd numbered assignments and checking services on
even number assignments. In a three-person team,
each person should rotate so that they are
checking every third assignment.) Those not
performing calculations are responsible for
checking them and must be afforded ample time to
thoroughly check the calculations. If revisions
are necessary, those performing the calculations
must make the corrections. Each sheet must be
initialed by the originator and checker. A cover
sheet with the signature of each team member must
be included with each assignment. Assignments
that are not signed or initialed by all team
members will not be accepted.
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Class Project
Peer Evaluation Peer evaluation is a common
practice in the engineering community. Critical
evaluation is a necessary component of improving
the engineering profession. It is generally
believed that honors and awards granted by peers
are the highest possible honors. After all, it
is our peers who know best what is required to do
an adequate, good, or outstanding job. Your
individual project grade will depend on an
evaluation by your peers at the end of the
semester. The evaluation form will have a format
similar to the one provided on the back of this
sheet. Evaluation forms will also be collected
during the middle of the semester for an
unofficial assessment of group performance.
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Class Project