Lecture 26 Design

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Lecture 26 - Design

• March 26, 2003
• CVEN 444

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Lecture Goals

• Design

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Example - Design
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Example - Design
Preliminary design for the moment and shear
reinforcement. From (ACI 8.3.3) Compute the
values Cm 1/16,1/14, and 1/10 and CV 1.0 and
1.15
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Example - Design
Interior face of exterior support End span
positive Exterior face of first interior
support Exterior face of first interior support
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Example - Design
Determine required flexural reinforcement using
procedure for beams. With 1.5 in. cover, 4
stirrup and 9 or 10 flexural bar, d 19.5 in.
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Example - Design
Compute required steel and b1 0.85 for 4 ksi
concrete
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Example - Design
Use 4 8 bars As 3.16 in2
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Example - Design
The over-design of the beam
The resulting beam layout
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Example - Design
The general design for the flexural steel is
given as
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Example - Design
Determine required shear reinforcement. Find the
Vu at the a distance d from the support.
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Example - Design
The maximum spacing is d/2 19.5 in./2 9.75
in. Use a 4 bar Av 0.4 in2 and spacing 6 in.
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Example - Design
Distance from support where stirrup not required
Use 4 stirrups _at_ 6 in. spacing.
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Example - Design
The bar length for bottom reinforcement
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Example - Design
Shear and moment diagrams are loading condition
cause maximum factored positive moment are shown.
Inflection points 3.5 ft and 22.4 ft
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Example - Design
The moment of the 2 8 bars from the 28 and 29
bars
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Example - Design
The positive moment portion of Mu diagram is
shown, which including the design moment
strengths of fMn for the positive As (2 8 and 2
9) and for 28 separately and necessary
dimensions. For 2 8 and 2 9, fMn 282.3 k-ft
for 2 8 fMn 124.6 k-ft
The location of the point is
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Example - Design
The distance to go beyond either d or 12 db
Controls
The cutoff of the 9 bar is 6.1 ft - 1.6 ft.
4.5 ft and 19.8 ft 1.6 ft 21.5 ft.
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Example - Design
The 2 8 bars extend full span length plus 6 in.
into the supports. The 2 9 bars are cutoff
tentatively at 4.5 ft and 3.5 ft. from exterior
and interior supports.
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Example - Design
Within the development length ld, only 2 8 bars
are being developed in the length 8.45 ft.
Dimension (3) 6.6 ft gt 4 ft Dimension (4) 5.7
ft gt 4 ft
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Example - Design
Check required development length ld for 2 9
bars. Note 2 8 bars are already developed in
length 4 ft from bar end. The clear spacing
between bars
The development length
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Example - Design
For 8 bars, check development requirements at
points of inflection PI
The inflection point Mu 124.6 k-ft/0.9138.4
k-ft and Vu 56.6 k and la greater of 12db or
d 19.5 in.
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Example - Design
With tentative cutoff points located in a zone of
flexural tension, one of the three conditions of
(ACI 12.10.5) must be satisfied. At left cutoff
point (4.5 ft)

The fVn 88.1 k (4 _at_ 6 in. spacing)
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Example - Design
Check the other conditions
The required area is

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Example - Design
For 2 No. 8 bars As 1.58 in2

At the right cutoff point 3.5 ft from support
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Example - Design
Shear and moment diagrams are loading condition
cause maximum factored negative moment are shown.
Inflection points 4.1 ft and 19.0 ft
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Example - Design
The moment of the two 8 bars from the 4 8 bars
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Example - Design
The moment of the two 10 bars from the 4 10 bars
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Example - Design
The negative moment portion of Mu diagram is
shown, which including the design moment
strengths of f Mn for the negative As at each
support(4 8) and for 410 separately and
necessary dimensions. For 48, fMn 252.5 k-ft
for 2 8 fMn 126.3 k-ft and 410, fMn 381.7
k-ft for 2 10 fMn 190.9 k-ft
The location of the point is
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Example - Design
For the 8 bars For the 10 bars
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Example - Design
The required number of bars to be extended. One
third of As provided at support must be extended
beyond the point of inflection a distance equal
to the greater d, 12 db or ln/16.
Controls
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Example - Design
Since the inflection point is located only 4.1 ft
from the support, total length 8 bars will be
relatively short even with the required 1.6 ft
extension beyond the point of inflection. Check
required development length ld for a cut off
location 4.1 ft 1.6 ft 5.75 ft from face
of support.
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Example - Design
With 4 8 bars being developed at same location
(face of support) For a top bar effect a 1.3
For 8 top bars, ld 5.2 ft lt 5.7 ft OK
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Example - Design
Anchorage into exterior column. The 8 bars can
be anchored into the column with a standard end
hook. For a 90o hook with side cover 2.5
in. and end cover 2 in. A modification
factor of 0.7 applies (ACI 12.5.3.2)
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Example - Design
Anchorage into exterior column. Therefore, the
required total embedment length ldh Overall
depth of the column required would be 16 in. The
required ldh for the hook could be reduced by 1
in. (a refinement) if excess reinforcement is
considered
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Example - Design
The area relationship
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Example - Design
The required number of bars to be extended for
the 410 bars. One third of As provided at
support must be extended beyond the point of
inflection a distance equal to the greater d, 12
db or ln/16.
Controls
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Example - Design
For 10 bars

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Example - Design
Since the inflection point is located only 6.0 ft
from the support, total length 10 bars will be
relatively short even with the required 1.6 ft
extension beyond the point of inflection. Check
required development length ld for a cut off
location 6.0 ft 1.6 ft 7.6 ft from face of
support.
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Example - Design
With 4 8 bars being developed at same location
(face of support) For a top bar effect a 1.3
For 10 top bars, ld 6.52 ft lt 7.6 ft OK
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Example - Design
Selected bar lengths for the top and bottom
reinforcement shown
Summary
Note The stirrup spacing should be 4 _at_ 6 in.
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Example - Design
Supplementary Requirements
If the beam were part of a primary lateral load
resisting system, the 28 bottom bars extending
into the support would have to be anchored to
develop the bar yield strength at the face of
supports. At the exterior column, anchorage can
be provided by a standard end hook. (ACI 12.11.2)
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Example - Design
Supplementary Requirements
Minimum width of support (overall column depth)
required for anchorage of the 8 bar with a
standard hook is a function of the basic
development length lhd and appropriate
modification factors.
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Example - Design
Supplementary Requirements
Minimum width of support (overall column depth)
required for anchorage of the 8 bar with a
standard hook is a function of the basic
development length lhd and appropriate
modification factors.
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Example - Design
Supplementary Requirements
At the interior column, 2 8 bars could be
extended ld distance beyond the face of support
into the adjacent span or lap spliced with
extended bars from adjacent span. Consider a
Class A lay splice adequate to satisfy the intent
of ACI 12.11.2
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Homework
Project Part A2 4/7/2003