Lecture 24 Shear Design

1
Lecture 24 - Shear Design

• October 25, 2002
• CVEN 444

2
Lecture Goals

• Project
• One-way slab design

3
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
4
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
5
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).

6
Class Project
Follow detailed instructions on separate
assignment sheets!!!
7
Class Project
8
Class Project
The Joist detail for section 1-1
The beam detail for section 2-2
9
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.
10
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.
11
Class Project
12
Discontinuities at Bar Cutoff
ACI 12.10.5
Prohibits flexural bar cutoffs in zone of
flexural tension, unless 1 of the following is
satisfied.
(1) (2)
Extra stirrups are provided at the cutoff points.
(See Sec. 12.10.5.2 for details)
13
Discontinuities at Bar Cutoff
Prohibits flexural bar cutoffs in zone of
flexural tension, unless 1 of the following is
satisfied.
ACI 12.10.5
For No 11 bars smaller Increase shear
strength is required when bars are cutoff in a
tension zone.
(3)
14
Joist Design
Flat Slab reinforcement is calculated for bending
or minimum reinforcement for shrinkage and
temperature.
(1)
(ACI Sec 7.12.2 )
15
Joist Design
Shear Design of Joist Ribs (Joist - Section 8.11)
(2)
16
Joist Design
17
Joist Design
18
One-Way Slab Design
Design of one slabs is like design of parallel
12 beams.
Thickness of One-Way Slabs
Minimum thickness for solid one-way slabs not
supporting or attached or attached to partitions,
etc. Likely to be damaged by large deflections
ACI Table 9.5(a)
19
One-Way Slab Design
Thickness of One-Way Slabs
The table calculates the minimum thickness t
( l span length in inches) (normal weight
concrete fy 60 ksi see code for
modification factors)
20
One-Way Slab Design
Thickness of One-Way Slabs Table A-14 tmin,
when damage to non-structural components may occur
21
One-Way Slab Design
Thickness of One-Way Slabs
Fire Rating
This is equal to the number of hours for
unexposed surface to rise a set amount usually
250 o F
3.5 in. 1 hour 5.0 in.
2 hours 6.25 in. 3 hours
22
Cover for Slab Reinforcement
ACI Sec. 7.71 (min. cover for corrosion
protection)
( 1.) Concrete exposed to earth or weather.
5 and smaller 1.5 in. 6 and larger 2.0
in.
( 2.) Concrete not exposed to earth or weather.
11 and smaller 0.75 in.
Min. covers for fire ratings should also be
considered.
23
One-Way Slab Design
Reinforcement
Typical Reinforcement in a one-way slab
24
One-Way Slab Design
Cutoffs
If requirements for use of ACI Moment
Coefficients
Figure A-5 one-way slab
25
One-Way Slab Design
Need to confirm thickness is adequate for one-way
shear. Difficult to place shear reinforcement in
a slab. Minimum area of shear reinforcement
required in slabs if
26
One-Way Slab Design
Need to confirm thickness is adequate for one-way
shear. Difficult to place shear reinforcement in
a slab.
Minimum area of shear reinforcement required in
slabs if
ACI Sec. 11.5.51
Usual use
ACI Eqn. 11-3
27
One-Way Slab Example
The cross section of a continuous one-way solid
slab in a building is shown. The slabs are
supported by beams that span 24 ft. Between
simple supports. The dead load on the slabs is
that due to self-weight plus 60 psf The live
load is 120 psf. Design the continuous slab and
draw a detailed section. Given fc 3 ksi, fy
40 ksi.
28
One-Way Slab Example
Determine the thickness of the slab.
Minimum thickness of interior bay
29
One-Way Slab Example
Use h 6 in.
Dead weight
30
One-Way Slab Example
Determine the load on the floor
For slab design r is seldom gt 0.01. Use c/d 0.2
31
One-Way Slab Example
Find the coefficient of the moment diagram
The maximum moment is
32
One-Way Slab Example
Find d for the design
If b 12 in. then d 3.46 in., which for c/d
0.2 so d 5 in., the slab is OK.
33
One-Way Slab Example
Find the coefficient of the shear
The maximum shear is
34
One-Way Slab Example
Check the shear capacity of the slab
Use h 6 in., d 5 in. and wu 0.354 k/ft
35
One-Way Slab Example
Minimum about of steel is (use ACI 7.12 )
Moment capacity of the beam
36
One-Way Slab Example
Compute the moments
Moment capacity of the beam
37
One-Way Slab Example
Compute the moments
38
One-Way Slab Example
Check the assumption
Assumption will work!
39
One-Way Slab Example
Use 4 bar Ab 0.2 in2 The maximum spacing ACI
7.6.4
The spacing on the first location
40
One-Way Slab Example
Select 15 in. for the spacing to calculate the
provided area.
41
One-Way Slab Example
Actual spacing.
42
One-Way Slab Example
Summary
43
Homework
Project Part A1 Due 11/4/2002 Part
A2 11/8/2002 Individual
Homework 6.1 6.6 11/1/2002