INDICATIV P8596
REINFORCED CONCRETE
STRUCTURAL WALLS
A). CALCULUS OF THE
TRUCTURAL WALLS SECTIONS
1. Plastic zones
There are considered plastic
zones of the structural walls the following situations:

for the coupling beams, the whole span;

for the structural walls (isolated or coupled), the zone having the
length l_{p} measured from their base:
l_{p} = 0.4h + 0.05H
In
the case of multistory buildings, this dimension is upward averaged to a whole
number of stories, if the limit of the plastic zone exceeds the height of a
level with more than 0.2H_{level}. If not, it is downward averaged to a
whole number of stories.
The
zone from the base of the wall limited in this way is called Zone A.
The rest of the wall, less loaded and with reduced design demands compared with
zone A, is called Zone B.
2. The dimensioning values of the sectional efforts.
2.1. The dimensioning values
M of the bending moments
The
values are determined with relations from the figure:
a) In over structure (above
the infrastructure or foundation):
M = k_{M}wM_{s}£wM_{s,o}
b) In infrastructure:
M = 1,5wM_{s}
_{}
where:
M_{s} = bending moment from the design seismic
loading; at the basement level has the value M_{s, o};
w = .. between the overturning moments;
M_{o, cap} = computed at the basement level
of the structure, associated to the strength capacity of the structural wall, cantilevered or
coupled, and the value of the overturning moment;
M_{o} = from the design seismic loading (see
the figure):
_{}
M_{i,cap} = the
capable moment at the base of cantilever wall i;
N_{i} = the axial effort at the base of the
cantilever wall i, produced by the horizontal forces, in the case of the
plastification of the coupling beams extremities;
L_{i} = the distance from the axis of the
cantilever wall i to the reference point with respect to whom the moments are
computed;
k_{M} = correction coefficient of
the walls bending efforts.
2.2. The dimensioning values
Q of the shear forces
In the case of the
structures for which the seismic forces are taken over in totality by the
structural walls, the value of Q is determined with the relation:
1,5Q_{s} £ Q = k_{Q }w Q_{s} £ 4 k_{Q} Q_{s}
where:
Q_{s} = the shear force from the design
seismic loading;
k_{Q} = correction coefficient of
the shear forces:
1,2
£ k_{Q} = 1 + 0,03n £ 1,5
n = the number of stories
2.3. The value of the design
shear force for the coupling beams
It is determined with:
_{}
where:
= the
absolute values of the capable moments in the sections at the extremities of
the coupling beams, from both senses of action of the moments, established on
the base of the design strength R_{a}
of the reinforcement; for the value of M_{cap}^{sup}, the
reinforcement contribution in the active
zone of the floor will be taken into consideration;
l_{r} = l_{o} = the
span of the coupling beam.
2.4. The
dimensioning axial forces from the coupling walls
The
dimensioning axial forces from the
coupling beams are estabished on the base of the wall equilibrium in the
situation of plastified coupling beams, but without the 25% increased value of
the bending strength capacity ,considered in the above relation.
3. The computation of the
longitudinal and transversal reinforcement of the structural walls
3.1. The
computation of the longitudinal reinforcement
The
computation of eccentrical compression (tension) of the structural walls is
made according to the prescriptions from the STAS 10107/090 code.
3.2. The
computation of the structural walls for the shear force
The
computation for the shear force is made in inclined sections and horizontal
sections at the casting level.
a) The
computation in inclined sections
In the case
of the structural walls with the ratio between the elevation height and the
section height H/h > 1, the dimensioning of horizontal reinforcement A_{a
o} for the shear force in inclined sections is based on relation:
Q £ Q_{b} + 0,8
A_{ao} R_{a}
where:
A_{a o} = the sum of the
horizontal reinforcement sections intersected by a 45^{o} inclined
crack, including the belt beams reinforcement and the continuous reinforcement
from the active zone of the floor (include three floor heights on both sides of
wall), if the crack crosses the floor;
Q_{b} = the shear
force taken over by the concrete, with
the values:

Q_{b} = 0,3bhs_{o} £ 0,6bhR_{t} for the zone A of the wall;

Q_{b} = bh(0,7R_{t} + 0,25s_{o}) for the zone B of the wall.
σ_{ο} = the
average compression stress in wall section. When σ_{ο}_{ }is tension,
is taken with minus sign in zone B and zero in zone A.
b) The
computation in horizontal sections at casting levels.
The
dimensioning is made according to the prescriptions from the STAS 10107/090
code.
4. The computation of the
reinforcement from the coupling beams
The
computation of the longitudinal reinforcement is made according to the
prescriptions from the STAS 10107/0 90 code.
4.1.
Coupling beams reinforced with horizontal bars in stirrups
The
transversal reinforcing is determined from condition that these ones have to
take over the whole design shear force, according to relation:
_{}
where:
A_{ae} = the necessary area
of the section of one stirrup;
a_{e} = the distance
between the stirrups;
n_{e} = the number of the
stirrup legs.
4.2.
Coupling beams reinforced with inclined bars
The area A_{ai} of the
inclined reinforcement on each diagonal is determined with the relation:
_{}
where α = the inclination angle of
reinforcement.
B) CONSTRUCTIVE REQUIREMENTS
1. The wall reinforcing. General provisions
1.1. The reinforcement
overlapping
a) It is recommended that
the vertical reinforcement to be realized without hooks.
b) For the reinforcement
with independent bars, in the potential plastic zone (zone A), the minimum
overlapping lengths are given in the table.
Reinforcement

Minimum overlapping
lengths for bars from:

OB 37

PC 52, PC 60

Horizontal bars, including
those from the belt beams and the vertical bars from the web
reinforcement.


Without hooks: 70d

50d

With hooks: 50d

Structural vertical bars with Aa situated at
the extremities

In the same section it is overlapped 50% or less
than the total reinforcement area.

Bars with d ≤ 20 mm

Without hooks: 70d

50d

With hooks: 50d

Minimum 600 mm

Bars with d > 20 mm are
over lapped by welding

In the same section it is overlapped more than 50%
of the total reinforcement area.

Bars with d ≤ 16 mm

Without hooks: 70d

60d

With hooks: 50d

Bars with d > 16 mm are
over lapped by welding

For
the zone B the minimum overlapping lengths are with 10d less than those from
the table. Also, in the zone B it is not necessary the overlapping by welding
of the reinforcement with d ³ 16(20) mm.
1.2. The reinforcement
anchorage
a) Horizontal bars from the
belt beams and the horizontal independent bars from the field reinforcement at
intersections in T or L shapes.
Bars with.:
l_{a} = 40d (OB 37, PC 52, PC60)
Bars without: l_{a} = 40d (PC 52, PC60)
l_{a}
= 60d (OB
37)
b) Horizontal bars from the
coupling beams. According STAS 10107/090
c) Vertical bars from walls
anchored in foundations. According to STAS 10107/090
d) Vertical boarding bars of
the openings which are anchored in a wall at an inferior level. l_{a}
will be determined such that to contain a corresponding number of vertical bars
from the current reinforcement of the inferior wall, but minimum 2.00 m.
The mesh, which form the continuous
reinforcement of the walls, will be connected with hooks in order to insure
their position during the concreting.
Usually, there will be at least:

4 hooks/m^{2} for bars with d < 8 mm;

6 hooks/m^{2} for bars with d > 8 mm.
2. Field reinforcement of the structural walls
2.1. The strength
reinforcement
It
is stipulated in the following cases:

in zone A

in zone B, when Q > Q_{b};

in short walls (H/h < 1)
In zone A, regardless the type of wall, the minimum reinforcement percentages are
those from the table.
Outside the wall A, the
minimum reinforcement values for zone F will be adopted.
The calculus seismic zone

Minimum reinforcement
percentage for

Horizontal bars

Vertical Bars

OB37

PC52, PC60

OB37

PC52, PC60

A,B,C,D,E

0.30%

0.25%

0.25%

0.20%

F

0.25%

0.20%

0.20%

0.15%

The minimum diameter:

6 mm for horizontal reinforcement

8 mm for vertical reinforcement
The maximum distance:

350 mm on horizontal direction

250 mm on vertical direction
2.2. The constructive
reinforcement
It is realized from two nets
Φ5 at 200 mm, from STNB, one at each part of the wall, or with other
steel reinforcement having equivalent diameters.
For the wall core around the stairs, on the
whole length, and for the last level in all cases, horizontal reinforcement
will be added having the following minimum percentage:

0.25% for OB 37

0.20 for PC 52 or PC 60
3. Local reinforcement of the vertical elements
3.1. The reinforcement of
the zones from the structural walls extremities
In the zones from the
structural walls extremities, on the surfaces indicated in the figure1, for
lamellar sections, in the figure 2, for sections having boundary elements, and
in figure 3 for coupled walls sections, the reinforcement is realized with
cages of the same type as those used for columns.
The
minimum vertical reinforcement percentage of this zones
reported to their area are showed in the table:
The calculus
seismic zone

Minimum reinforcement
percentage

OB 37

PC 52

zone A

zone B

zone A

zone B

A, B, C, D, E

0.6%

0.5%

0.5%

0.4%

F

0.4%

0.4%

The local reinforcement will
have to obey, from the point of view of distribution and the minimum number of
bars, the details from the figure:
The
concentrated reinforcement together with the vertical reinforcement situated in
the web and the flange of the walls, including that in the intermediary
intersections, have to insure the wall section a superior bending strength
capacity compared to the cracking moment M_{f} of the section,
determined with:
M_{f} = Nr_{s}
+ 0.5 c_{pl} W_{f} R_{t}
where:
r_{s} = distance from the center
of gravity of the section to limit of the central core, situated on the same
part with the eccentrically force N;
W_{f} = the cracking resistance modulus of
the section, computed considering the tension zone completely plastificated;
c_{pl} = coefficient which takes
into consideration the partial plastification of the tensioned zone of the
section; see table 15, STAS 10107/090.
Stirrups
Minimum diameter: Φ6 mm
and d/4 (d = the minimum diameter of the vertical bars of the A_{a} reinforcement).
Maximum distances:
zone A:

125 mm, but no more than 10d, for design seismic zones A  E;

150 mm in design seismic zone F;
zone B:  200 mm, but no more than 15d.
The
stirrups of the cage will be made such that their area have
at least the same strength capacity as the horizontal reinforcement from the
adjacent fields. In the case when this reinforcement is interrupted in the
cage, it is properly overlapped with the cage stirrups.
3.2. The confining
reinforcement in the compressed zones
If the height of the
compressed zone of the sections, when the strength capacity is reached, is
higher than the limit value (x > x_{lim}), a special confining
reinforcement in the compressed zone will be realized on a length of at least
x/2.
The confining reinforcement
quantity A_{a}_{ o}, in each direction
is computed with relation:
_{}
where:
a_{e} = axial distance between
sets of confining stirrups;
c = dimension of the central core between the
confining stirrups, measured perpendicular to the stirrups braces;
Also,
in the A_{a}_{ o} reinforcement can be
considered the horizontal reinforcement of the web, if this one is bent after
the vertical bars and properly anchored.
In
the zones where the longitudinal reinforcement percentage takes over the value
2/R_{a} (N/mm^{2}), supplementary measures will be taken such
that to avoid buckling of the bars situated in the potential plastic zone. The
confining reinforcement A_{a}_{ o} can
have this role. In these zones it is recommended that the transversal
connection by stirrups and hooks of the vertical bars with diameter d > 16
mm to be done with a maximum distance of 6d.
3.3. The reinforcement of
structural walls intersections
The
interior intersections are reinforced with cages with 2 crossed stirrups, which
make the connection with the horizontal reinforcement of the walls.
The maximum distance between the stirrups: 200 mm.
The
minimum vertical reinforcement of the intersection zones: 4 Φ12 ¸ 8 Φ10.
3.4. The reinforcement
around the openings
Around
openings with small dimensions reported to the wall dimensions, and which do
not influence significantly the general ensemble behavior, a constructive reinforcement
will be realized on each side with at least two bars Φ10 mm and having the section
equivalent to the reinforcement interrupted by the opening.
3.5. The reinforcement of
the walls and floors intersections
A belt reinforcement having
at least four bars will be made along the width of the wall.
Minimum
diameter of the bars: 10 mm.
4. The reinforcement of the coupling beams
4.1. The reinforcement with
longitudinal bars and vertical stirrups
a) The longitudinal bars
resulted from the bending moment dimensioning, placed at the superior and
inferior part of the section
Minimum diameter of bars: Φ10
mm.
Recommended
steel types: PC 52, PC 60.
b) Intermediary longitudinal
bars placed on lateral sides
Minimum diameter of bars: Φ8 mm.
Minimum reinforcement
percentage reported to the bh_{r} section:

0.20% for seismic zones A  E;

0.12% for seismic zone F
c) Vertical stirrups
Minimum diameter of bars: Φ6 mm.
Minimum transversal
reinforcement percentage: 0.20%
Maximum distance between
stirrups: a_{e} £ 8d; a_{e} £ 150 mm (d = longitudinal reinforcement bars
diameter placed at superior and inferior part of section).
4.2. The reinforcement with
crossed inclined bars
Anchorage length of the inclined
bars: > 60d;
Distance between stirrups:
> 6d (d= diameter of the inclined bars);
Minimum diameter of the
stirrups: d/4;
Minimum horizontal
reinforcement percentage: 0.2%;
Minimum transversal
reinforcement percentage (with stirrups): 0.15%.