CSA A23.3-04 Changes
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NBCC load & combination factors
c changes from 0.6 to 0.65
Clause 8 – load and combination to appendix
Clause 10 – small changes to slenderness
Clause 11 – major changes
Clause 13 – slab bands
Clause 14 – major re-write
Clause 15 – piles and pile caps added
Clause 21 – major changes
Clause 23 – minor changes
Append D – anchorage is all new
Clause 10 Flexure and Axial Loads
•The old simplified equation for
effective moment of inertia has been
changed.
EI 
0.2 E c I g  E s I st
1 d
EI  0.25 E c I g (1994)
EI 
0.4 E c I g
1 d
(2004)
(1994 & 2004)
Clause 11 Shear and Torsion
• This Clause has major changes.
• The simplified and general method
approach is gone, there is now only one.
• The cases previously covered by the
simplified method are now special cases.
• The general method has been changed and
the tables are gone replaced by equations.
Clause 11 Shear and Torsion
Vc  0.2c f c' bwd
Vc  c  f c' bwdv
Vs 
Vs 
 s Av f y d
dv  0.9d or 0.72h A23.3  04
A23.3  94
s
 s Av f y d v cot 
s
A23.3  94
A23.3  04
Clause 11 Shear and Torsion
11.3.6.2
Values for Special Member Types
Unless permitted otherwise by Clause 11.3.6.3 or Clause 11.3.6.4,
the value of β shall be taken as 0.21 and θ shall be taken as 42° for
any of the following member types
(a)slabs or footings with an overall thickness not greater than 350 mm;
(b)footings in which the distance from the point of zero shear to the
face of the column, pedestal or wall is less than 3 times the
effective shear depth of the footing;
(c)beams with an overall thickness not greater than 250 mm;
(d)concrete joist construction defined by Clause 10.4; and
(e)beams cast integrally with slabs where the depth of the beam below
the slab is not greater than one-half the width of web nor 350 mm.
Vc  c  f c' bw d v  .6  .21 f c' bw  .9d  .1134 f c' bw d
Clause 11 Shear and Torsion
11.3.6.3
Simplified Method
In lieu of more accurate calculations in accordance with
Clause 11.3.6.4, and provided that the specified yield strength
of the longitudinal steel reinforcement does not exceed
400 MPa and the specified concrete strength does not exceed
60 MPa, θ shall be taken as 35° and β shall be determined as
follows
(a)If the section contains at least minimum transverse
reinforcement as required by Equation (11-1) then β shall be
taken as 0.18;
Vc  0.18c
Vs 
f c' bw 0.9d v  0.1053 f c' bw d
 s Av f y d v cot 
s

 s Av f y 0.9d1.43
s

1.29   s Av f y d
s
Clause 11 Shear and Torsion
(b) If the section contains no transverse reinforcement and the specified
nominal maximum size of coarse aggregate is not less than 20 mm
then

230
if d  400 then   0.169 (11  9)
(1000  d v )
(c) Alternatively, the value of b for sections containing no transverse
reinforcement may be determined for all aggregate sizes by
replacing the parameter dv in Equation (11-9) by the equivalent
crack spacing parameter sze where
s ze 
35s z
15  a g
however sze shall not be taken less than 0.85sz. The crack spacing
parameter, sz, shall be taken as dv or as the maximum distance
between layers of distributed longitudinal reinforcement, whichever
is less. Each layer of such reinforcement shall have an area at least
equal to 0.003bwsz, see Fig. 11-2.
Clause 11 Shear and Torsion
11.3.6.4
General Method
The values of β and θ shall be determined from the
following equations
0.40
1300


(1  1500 x ) (1000  s ze )
  29  7000 x
x 
M f / d v  V f  V p  0.5 N f  A p f po
2(E s A s  E p A p )
Clause 13 Two-way Slab Systems
• Major change - added slab bands
• Narrowed the ranges of distribution to
negative and positive steel in the column
strips
Clause 13 Two-way Slab Systems
• Now have four categories:
–
–
–
–
Slabs -0.70 to 0.90 and + 0.55 to 0.65
Drop Panels -0.75 to 0.90 and + 0.55 to 0.65
Slab Bands -0.80 to 0.90 and + 0.80 to 1.0
Slabs on Bands -0.05 to 0.15 within bb and rest uniformly
distributed across entire width (including bb)
– positive moment at all spans where  1  2   1.0
0.50 to 0.60
– positive moment at all spans where  1  2   1.0
0.5  1  2  to 0.6  1  2 
Clause 13 Two-way Slab Systems
• Slab Shear
– size effect for two way (punching) shear 1300 /(1000  d )
– no more principle axis calculations
– One-Way shear on revised perimeter for corner columns,
just d/2 away from column and if column is in from the slab
edge maximum of d beyond
• Edge loads - minimum top steel between columns
• Finite element analysis
– Revised relations to deal with mxy
Clause 14 Walls
• Complete re-write to address the wider range of walls being
designed.
• Three basic categories
– Bearing walls
– Non-bearing walls
– Shear walls
• Covers many general requirements such as:
– lateral support
– concentrated loads
– vertical loads through floors and shear across construction
joints
Clause 14 Walls
•
•
Wall — vertical slab element, which may or may not be
required to carry superimposed in-plane loads, in which the
horizontal length, ℓw, is at least 6 times the thickness, t, and
at least 1/3 of the clear height of the element.
Bearing Wall – a wall that supports
a. Factored in plane vertical loads exceeding 0.1 fc’Ag
b. weak axis moments about a horizontal axis in the plane
of the wall
c. Shear forces necessary to equilibrate the forces in (b)
Clause 14 Walls
•
•
Non-bearing Wall – a wall that supports factored in plane
vertical loads less than or equal to 0.1 fc’Ag and, in some
cases, moments about a horizontal axis in the plane of the
wall and the shear forces necessary to equilibrate those
moments.
Shear wall – a wall or an assembly of interconnected walls
considered to be part of the lateral-load-resisting system for a
building or structure. Shear walls support
a. Vertical loads
b. Moments about horizontal axes perpendicular to the wall
(strong axes bending)
c. Shear forces acting parallel to the plane of the wall
Clause 14 Walls
14.1.8.7
Ties for Distributed Vertical
Compression Reinforcement.
Distributed vertical reinforcement, if stressed in
compression, shall be tied and detailed in
accordance with the provisions for column
reinforcement in Clause 7, except that ties can be
omitted if:
a) the area of vertical steel is less than 0.005Ag,
and
b) the bar size is 20M or smaller.
Clause 15 Foundations
• Extensively revised to add new treatment of
piles and pile caps.
• For example provides reductions for
effective cross section and capacity for
uncased piles.
• Requires design for the range of specified
tolerance with a minimum of ± 50 mm
Clause 21 Seismic design
• A general revision to align with NBCC
changes such as the introduction of Rd and R0
as well as new drift limits.
• Enumeration of code recognized ductile
systems
NBCC Concrete Ductile Systems
SINGLE WALL
Rd = 2.0
Rd = 3.5
COUPLED WALL
Rd = 4.0
Rd = 3.5
MOMENT FRAME
Rd = 2.5
Rd = 4.0
Plastic Hinges to Absorb Energy
Example Unclassified Systems
WALL - COLUMNS
FRAME WALL
OUTRIGGER WALL
BRACED FRAME
Clause 21 Seismic design
• Removal of limit of 55 MPa on f ’c.
• Revised (revised from CPCA Handbook
values) effective stiffness factors for wall
and coupling beams to be used for analysis.
• New relations for transverse reinforcement
for Rd = 4.0 columns including the effect of
axial load level.
Clause 21 Seismic design
21.2.1.2
For the purposes of determining forces in and deflections of the structure,
reduced section properties shall be used. Table 21-1 lists the effective
property to be used as a fraction of the gross section property.
Table 21-1
Element Type
Effective Property
Beam
Ie = 0.4 Ig
Column
Ie = c Ig
Clause 21.6.8.6 Coupling Beam
Ave = 0.15Ag ; Ie = 0.4Ig
Clause 21.6.8.7 Coupling Beam
Ave = 0.45Ag ; Ie =0.25 Ig
Wall
Axe = w Ag ; Ie = wIg
Slab Frame Element
Ie = 0.2 Ig
Clause 21 Seismic design
• Column and wall stiffness reduction factors
Ps
 c  0.5  0.6 '  1.0
f c Ag
Ps
 w  0.6  '  1.0
f c Ag
Column Confinement (Cl. 21.4.4.2)
n Pf Ag f c'
Ash  0.2
shc
n  2 P0 Ach f yh
nl = 4
nl = 8
20
Clause 21 Changes – Ductile Walls
• Clarification of when a wall with openings may be
treated as a solid wall
• Revised requirements for the extent of ductile
detailing over the building height
• Added tying requirements for distributed
reinforcement in ductile walls reflecting changes
to Clause 14.
• Clarified the minimum concentrated reinforcement
requirements for flanged walls
• Explicitly named “buckling prevention” ties
Plastic Buckling + Tension Yield
Clause 21 Seismic design
• Revised relations for wall ductility that
include consideration of the effects of
height to width ratio and design
displacement on ductility demand.
• Relations framed in terms of wall rotational
demand and wall rotational capacity.
• Requirement to check rotational demand
and rotational capacity of coupling beams.
Clause 21 Changes – Ductile Walls
• Introduced a “ductility” limit state for
plastic hinges in walls and coupling beams
• Rotational capacity ≥ Rotational demand
 ic   id
• Added requirement to check rotational demand
and rotational capacity of coupling beams
Rotational Demand (Cl. 21.6.7.2)
f
o
d
 Δf  w

 0.004
Lw
hw
Elastic Displaceme nt  Δ f  w
hw - Lw/2
w 

 hw 

2 

Design Displaceme nt  Δ f Ro Rd
Lw/2
 id 
Δ R R
 f(RdRo -  w
)
id
  s max

 w



Yield Curvature
ic = Lp( u -  y)
Ecu=0.0035
Ultimate Curvature
Ecy=0.002
 ic max
w

2
C
Esy=0.002
  cu  w

 ic  
 0.002   0.025
 2c

w
Plastic Hinge Length 
2
 w   cu  sy   cy 


 ic 

2  c
w 
Es max = 0.05
Rotational Capacity (Cl. 21.6.7.3)
Coupled Walls
21.6.8.2
The inelastic rotational demand on Ductile
Coupled and Partially Coupled Walls shall
be taken as:
 id 
 f Ro R d
hw
 0.004
where Δ f Ro Rd is the total Design
Displacement.
Coupled Walls
Coupling Beams
21.6.8.4
The inelastic rotational demand on coupling beams shall
be taken as:
  f R0 Rd
 id  
 hw
  cg

 u
The inelastic rotational capacity of coupling beams ic
shall be taken as:
(a) 0.04 for coupling beams designed with diagonal
reinforcement in accordance with Clause 21.6.8.7 and
(b) 0.02 for coupling beams designed in accordance
with Clause 21.6.8.6.
Pin Ended Coupling Beam
Pin Ended Example
Pin Ended Case (Cl. 21.6.8.9)
Pin Ended Case (Cl. 21.6.8.9)
21.6.8.9
If the wall at one end of the coupling beam has a
factored resistance less than the nominal coupling
beam resistance, the following requirements shall
be satisfied:
(a) the coupling beam shall satisfy the shear stress
limitations of Clause 21.6.8.5 and the
requirements of Clause 21.6.8.6
(b) the wall shall be designed to the requirements of
Clauses 21.4.4.1 to 21.4.4.3, Clauses 21.4.4.6
and 21.4.5
(c) the joint between the wall and the coupling beam
shall satisfy Clause 21.5.
Torsion on Tubes
Torsion on Tubes
21.6.8.12
Assemblies of Coupled and Partially Coupled Shear Walls
connected together by coupling beams which function as a closed
tube or tubes shall be designed with:
(a)that portion of the overturning moment due to lateral loads resisted
by axial forces in the walls, increased at each level by the ratio of
the sum of the nominal capacities of coupling beams to the sum of
the factored forces in the coupling beams required to resist lateral
loads above the level under consideration
(b)an additional increase in overturning moment resisted by axial
forces in the walls at each level corresponding to the increase in
the sum of the nominal capacities of the coupling beams above the
level under consideration required to resist the accidental torsion.
Forces @ Plastic Hinge Level
Forces @ Plastic Hinge Level
21.6.8.13
In lieu of a more detailed assessment, wall
segments that act as tension flanges in the
flexural mode shall be assumed to have no
shear resistance over the height of the
plastic hinge. For assemblies of wall
carrying torsion as a tube, the shear forces
in the tension flange shall be redistributed.
Clause 21 – Moderate Ductility
• Changes to the requirements for nominally
ductile frame systems reflecting the revised
Rd value
• Moderately ductile frame columns now
have be stronger than the frame beams
• Revised frame column tie requirements
using the new confinement relations
• Trigger added for tilt-up wall systems
Tilt-up Walls
21.7.1.2
Tilt-Up Wall Panels shall be designed to the requirements of
Clause 23 except that the requirements of Clause 21.7.2 shall apply
to wall panels with openings when the maximum inelastic rotational
demand on any part of the panel exceeds 0.02 radians and in no case
shall the inelastic rotational demand exceed 0.04 radians. The
requirements of Clause 21.7.4 shall apply to solid wall panels when
the maximum in plane shear stress exceeds 0.1c f c ' .
Note: Methods for calculating rotational demand on elements of tiltup panels with openings can be found in Explanatory Notes to CSA
Standard A23.3-04 published by Cement Association of Canada.
The seismic performance of tilt-up buildings depends not only on the
performance of the concrete wall panels, but also the performance of
the roof structure and the connection between the wall panels and
the roof. Only the design of the concrete wall panels is within the
scope of this standard.
Clause 21 – Moderate Ductility
• Rotational limit state design approach
introduced for moderately ductile walls
• Simplified method included for cases with
moderate vertical loads or limited lateral
deflections
• Special requirements for squat walls
introduced.
Squat Walls (Cl. 21.7.4)
• Squat Shear Walls, hw/ℓw ≤ 2.0
• Rd = 2.0
• Two possible hinge types
– Flexural yield
– Shear yield
Clause 21 – Squat Walls
Clause 21 Changes – Added Sections
• Requirements for Rd = 1.5 buildings
introduced.
– Frames
– Walls
– 2-way slabs
• New requirements for precast buildings.
– Essentially ACI.
Clause 21 Seismic design
• New section on structural diaphragms.
21.10.3.1
Diaphragm shall be idealized as a system consisting of the
following components arranged to provide a complete
load path for the forces:
(a) chords proportioned to resist diaphragm moments as
tensions and compression forces.
(b) collectors arranged to transfer the forces to, from and
between the vertical Seismic Force Resisting Systems.
(c) either shear panels to transfer forces to, from and
between the chords and collectors or
(d) continuous strut and tie in-plane shear trusses.
Clause 21 Seismic design
• New section on foundations.
– Essentially detailing rules
• Extensive revisions to requirements for
structural elements not part of the Seismic
Force Resisting System.
Clause 21.12 – Gravity Elements
• Introduced rules for the treatment of “nonstructural” concrete elements
• Changes to the displacement limits that trigger
ductile, moderately ductile and conventional
detailing
• Introduction of default requirements for the case
where detailed compatibility calculations are not
performed
• New requirements for slab column connections.
Clause 21.12 – Gravity Elements
Gravity Element Failure
Slab Punching Failure
Gravity Slab/Column (Cl. 21.12.3)
• Slab Column Connections
– Design for gravity two-way shear stresses
– Calculations use EQ load combinations
– RE is reduction in vertical punching shear capacity as a
function of interstorey deflection
 0.005 

RE  
 i 
0.85
 1.0
Punching Test Data
Drift Ratios With and Without Shear Reinforcement
6
Dilger and Cao
Wey and Durrani
Robertson and Durrani
Pan and Mohle (92)
Pan and Mohle (89)
NBCC 2004 Drift Limit
Proposed Equation
Pan and Moehle 40% stress at 1.5% drift
IBC/SEAOC
Dilger & Cao SSR
5
Drift Ratio (%)
4
3
2
1
0
0
0.1
0.2
0.3
0.4
0.5
Vu/V0
0.6
0.7
0.8
0.9
1
Other Clauses
• Clause 22 Plain Concrete
– section added for unreinforced drilled piles
• Clause 23 Tilt-Up Wall Panels
– essentially unchanged, m goes from 0.65 to
0.75
• Appendix D Anchorage
– all new, introduces the method which was in
IBC 2000 and now ACI 318-02 as Appendix D
– based on square 35 angle cone
Appendix D
1.5 hd
1.5 hd
35°
hd
1.5 hd
1.5 hd
Acknowledgements
• Perry Adebar and his graduate students at UBC
• Ron DeVall of RJC
• Vancouver Clause 21Committee
–
–
–
–
–
Patrick Lam
John Markulin
Andy Metten
Rob Simpson
Greg Smith
• National A23.3 Seismic Subcommittee