Guidelines for Detailing of Reinforcement in Concrete Structures

2017 Guidelines for Detailing of Reinforcement in Concrete Structures EC2 & ACI

8.FOUNDATION BEAM (VARIATION 1)

The foundation beam is formed to size by the use of reusable concrete forms. Rebar is laid
in the form and wired together to make a square or rectangular steel cage. This rebar cage
gives concrete the strength it needs to support the structure.

Features of foundation beam.

The support pilings are mechanically connected to the foundation beam by the rebar
cages. This allows the weight of the home to be transferred deep underground. This type of
construction is typically used in areas of steep slopes or extremely wet soils. Regular
foundations have been known to slide downhill on steep slopes during times of heavy
rains. Or in freezing and thawing conditions of winter.

European Code Practice EC2 2

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European Code Practice EC2 2

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9.FOUNDATION BEAM (VARIATION 2)

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10. GRID FOUNDATION (VARIATION 1)1

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11. GRID FOUNDATION (VARIATION 1)2

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WALL FOOTING

European Code Practice EC2

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GRID FOUNDATION (VARIATION 2) 1

European Code Practice EC2

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European Code Practice EC2 2

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GRID FOUNDATION (VARIATION 2) 2

European Code Practice EC2

2

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European Code Practice EC2 2

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FOUNDATION SLAB 1

European Code Practice EC2

2

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ACI CODE REQUIREMENTS FOR MAT FOUNDATION

Mat foundations are commonly used to support heavy loads from multiple columns.
Mats may bear on competent soil, on soil with a low bearing capacity, or be supported on
piles or drilled shaft foundations (caissons). Depending on the total load applied to the mat
and underlying foundation system, the thickness of mat foundations can vary from 1 ft (0.3
m) to more than 20 ft (7 m). The reinforcing system in the mat can be quite substantial, with
heavy reinforcing bar mats in the bottom, top, or both locations within the mat depth.
Improper detailing of the reinforcement can result in constructability issues impacting
other trades, the schedule, and costs. This Detailing Corner describes practices that can be
used to simplify the design, detailing, and placement of mat reinforcement.

Setting the Reinforcement (Minimum requirements)

The mat depth is normally set by shear strength requirements. The amount of
reinforcement As for the top and bottom reinforcing layers is set by meeting ACI 318 Code1
requirements for flexural strength, minimum flexural reinforcement (Sections 10.5.1
through 10.5.4), and shrinkage and temperature reinforcement (Sections 7.12.2.1 through
7.12.2.3). Generally, As will be governed by flexural considerations, either through analysis
or satisfying the minimum requirements. However, as the thickness of the mat increases,
the minimum amount of shrinkage and temperature reinforcement will increase—it could
control for very thick mats. Once this reinforcement quantity is calculated, a suitable bar
size and spacing can be selected. Depending on the layout configuration, the reinforcing
bars can be placed in two layers (one mat) or four layers (two mats) at both the top and
bottom. Per Code Section 7.12.2.2, the bar spacing is limited to five times the slab
thickness or 18 in. (450 mm). Code Section 15.10.4 also sets the maximum spacing of mat
reinforcement at 18 in. Bars that are placed in the interior layers should follow the same
spacing patterns as the main, outer reinforcement so that all bars in different layers are
aligned (Fig. 1). This provides clear passage for concrete placement, which helps to reduce

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voids. It’s considered good practice to select the size of the bars in the interior layers equal
to or smaller than the outer layer reinforcing bars. Some designers prefer to specify bars in
the interior layers with diameters different than the bars in the outer layer of reinforcement
so they can be more easily identified and checked in the field. By a note or a section on the
design drawing, the engineer should specify those bars that will be placed in the outer
layer and the ones in the inner layer. It’s recommended that a clear spacing of at least 3 in.
(75 mm) (more for deeper mats) be provided between the bars to facilitate concrete
placement, as shown in Fig. 1. For Concrete international February 2012 49 deep
foundation mats requiring worker access inside the cage, it’s also good practice to provide
openings in the top reinforcement. This can be accomplished by bundling the bars and
providing additional steel around the resulting opening, as shown in Fig. 2. As noted in ACI
336.2R,2 Section 6.14: “It is essential that the engineer prepare thorough drawings
documenting all phases of the reinforcement placement.... Specification of placement
sequence is very important.

Fig. 1: Typical configuration of reinforcement in a deep mat foundation

Additional bars

Additional flexural reinforcement may be required at heavily loaded or closely spaced
columns or where substructure support conditions change. Any additional top and/or
bottom reinforcement can be in the same layer as the outer, main reinforcement or within
the interior layers. Additional bars should be spaced as a multiple or submultiple of the
spacing for the main reinforcement. For example, if the mat foundation is 6 ft (2 m) thick
and No. 9 (No. 29) bars have been provided at 15 in. (375 mm) on center for the main
reinforcement in each direction for both top and bottom reinforcement, any additional bars
required in any area can be provided at a spacing of 5, 7.5, 15, or 30 in. (125, 190, 375, or
750 mm).

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Other Considerations

Some additional points to consider:

1 - When the column spacing is not laid out on a regular, symmetric grid, consider locating
the bars on an orthogonal grid rather than skewing them with the actual column locations.
Additional reinforcement can then be placed wherever it’s required.

2 - It’s common practice not to use shear reinforcement in a mat. This ensures that the
depth and stiffness is maximized and flexural reinforcement is minimized (ACI 336.2R,
Section 6.1.2, Item 2). However, when shear reinforcement is required, it’s recommended
that the selected vertical bars are larger than the main reinforcement and are placed at
larger spacing—easing identification and inspection. ••It’s preferable to extend column and
wall dowels all the way down to the bottom mat of reinforcement. The dowels should
incorporate a 90-degree hook at the bottom end, so the tail of the hook can be used for
support and elevation control. This also allows the dowels to be tied to both the top and
bottom mats of reinforcement for stability, as the two tie points will properly secure the
dowel bars from displacing (Fig. 3).

3 - If lap splices in the foundation mat reinforcement are to be staggered, they need to be
carefully detailed on the design drawings. Otherwise, the staggered splices for different
layers of reinforcing bars may become quite confusing to place and subsequently inspect.
If it’s possible to avoid staggering splices, this should be the preferred placement for ease
of constructability.

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4 - If the horizontal bars must be anchored at the mat edges, it may be necessary to tilt
hooks so that hook extensions fit within the geometric depth of the footing (this may
require additional horizontal bars in the depth of the footing to hold the hooks at the proper
angle). As an alternative, U-bent bars could be lapped with straight bars in the top and
bottom layers (a hairpin detail—refer to Fig. 6). Depending on the specific reinforcement
layout and spacing, hairpins may be more constructible than individual hooks.

Fig. 6: Designers should consider using U-bars (hairpins) in place of hooked bars for

each bar layer at the edge of a mat foundation

5 - Standees for supporting the top layers of reinforcement should be sturdy and stable
enough to support the weight of the top steel, workers, and equipment. For further
guidance of using standees for supporting heavy reinforcement, see the Detailing Corner
article “Using Standees.”3 In addition, diagonal bracing bars may be required to ensure
stability of the entire reinforcing bar assembly.

6 - The common mill stock length of straight reinforcing bars is 60 ft (18.3 m). However, a
local fabricator may have limitations (such as storage space, crane capacity, and bend
table size), requiring stocked straight lengths less than 60 ft. It is thus advisable to verify
with the local fabricator the maximum available stock length. Because a mat foundation
requires long runs of straight bars, it’s recommended that the maximum straight bar length
be used as much as possible. This minimizes the quantity of potential lap splices. If an
actual bar length shorter than the typical stock length is needed to complete the reinforcing
bar run, this “short bar” should be located at either end of the mat foundation. Alternately,
stock length bars could be provided throughout the mat, with the lap lengths increased
along the run. Although the lap lengths will be greater than Code minimums, material waste
and fabrication costs could be reduced because a long bar will not have to be sheared to a
shorter length. It will also aid in constructability, as a separate bar length bundle will not
have to be inventoried at the construction site.

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MAT FOUNDATION WITH TIE BEAMS

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BOARD PILE (CIDH)

ACI 336.3 R Design & Construction of Drilled Piers

1- Notify the Geotechnical Engineer at least four working days in advance of the
beginning of such work or on resumption of drilling after stoppage. Holes drilled or
cast without continuous observation of the Geotechnical Engineer will be rejected.

2- Drill concentric and vertical pier shafts to diameters and depths indicated. Lengths of
piers are shown on Drawings, based on anticipated subsurface soil conditions.
Adjust length of pier when directed by University's Representative, based on
observations during drilling by Geotechnical Engineer.

3- Place steel liners, if required, immediately after drilling and set firmly in place.
Thoroughly clean loose material from the bottom of piers designated as "end
bearing" on the Drawings.

4- Fill shafts with concrete the same day that they are drilled; do not allow shafts to
stand open overnight. If completion is postponed to the day following the start of
drilling, the Subcontractor shall ream to 6 inches (150 mm) larger in diameter and drill
at least three feet (0.9 m) lower than the depth indicated at no additional cost to the
University.

5- Do not drill holes within 6 pier diameter spacing, of any previously drilled pier until at
least 12 hours have elapsed since casting of previously drilled pier.

6- The installation of drilled piers shall be in accordance with ACI 336.3 and the
requirements listed below. Drilling waste will become the Subcontractor's property
and be disposed of offsite.

7- Maximum Plumpness Variation From Vertical: 1.5 percent of the shaft length. When
the plumpness tolerance is exceeded, the Project Manager shall be notified and an
engineering evaluation performed at the Contractor's expense to determine the
acceptability of the pier.

8- Top Elevation: Maximum plus 1 inch (25mm) to minus 3 inches (75 mm) from
elevation indicated.

9- Location: 4 percent of the shaft diameter or 3 inches (75 mm), whichever is less.
When the location tolerance is exceeded, the Project Manager shall be notified and an
engineering evaluation performed at the Subcontractor's expense to determine the
acceptability of the foundation.

10-A section of [structural steel] [reinforcing cage] with the same [reinforcing]
configuration as the design section shall be available on site for use in an over drilled
pier. The section will be 10 feet (3 m) long [plus the appropriate length to develop the
tension development length of the vertical bars]. If the section is not required, it will
be removed from site by the Subcontractor at the completion of the drilling.]

ACI 336.3 R Design & Construction of Drilled Piers 5

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Eurocode 7

Eurocode 7 (EC7) is based on the limit state design concept and characteristic values, and
the world’s first geotechnical design code to share a common philosophy with the design
methodology for structures. The basic Eurocode design requirements, given in EN 1990,
are that a structure shall be designed and executed in such a way that it will, during its
intended life, with appropriate degrees of reliability and in an economical way sustain all
actions likely to occur during execution and use.

European Code Practice EC7

6

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European Code Practice EC2 2

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PILE CAP

European Code Practice EC2 2

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European Code Practice EC2 2

TWO PILES CAP

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2

European Code Practice EC2

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THREE PILES CAP

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FOUR PILES CAP

European Code Practice EC2 2

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GROUP PILES CAP

1

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European Code Practice EC2 2

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CENTRING BEAM FOR ONE- OR TWO-PILE CAPS

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BORED PILE WITH CAP ACI 336.3 R

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CHAPTER SIX
REINFORCED CONCRETE WALL

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ACI 318 Building Code Requirements for RC Walls

Walls should be designed to resist all loads to which they are subjected,
including eccentric axial loads and lateral forces.

1. Walls shall be designed for eccentric loads and any lateral or

other loads to which they are subjected.

2. Quantity of reinforcement and limits of thickness required by ACI

14.3 and 14.5 shall be permitted to be waived where structural

analysis shows adequate strength and stability.

Minimum reinforcement
— Minimum vertical and horizontal reinforcement

shall be in accordance with ACI 14.3.2 and 14.3.3 unless a greater
amount is required for shear by ACI 11.10.8 and 11.10.9.

— Minimum ratio of vertical reinforcement area
to gross concrete area, ρl, shall be:

a) 0.0012 for deformed bars not larger than No. 5 with fy not less than

60,000 psi; or

b) 0.0015 for other deformed bars; or
c) 0.0012 for welded wire reinforcement not larger than W31 or D31.

— Minimum ratio of horizontal reinforcement
area to gross concrete area, ρt, shall be:

a) 0.0020 for deformed bars not larger than No. 5 with fy not less than

60,000 psi; or

b) 0.0025 for other deformed bars; or
c) 0.0020 for welded wire reinforcement not larger than W31 or D31.

— Walls more than 10 in [250 mm]. thick, except basement walls, shall

have reinforcement for each direction placed in two layers parallel with
faces of wall in accordance with the following:

a) One layer consisting of not less than one-half and not more than two-

thirds of total reinforcement required for each direction shall be placed

not less than 2 in. nor more than one-third the thickness of wall from the
exterior surface;

b) The other layer, consisting of the balance of required reinforcement in

that direction, shall be placed not less than 3/4 in. nor more than one-
third the thickness of wall from the interior surface.

— Vertical and horizontal reinforcement shall

not be spaced farther apart than three times the wall thickness, nor
farther apart than 18 in.

— Vertical reinforcement need not be enclosed by lateral ties if vertical
reinforcement area is not greater than 0.01 times gross concrete area, or
where vertical reinforcement is not required as compression
reinforcement.

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Reinforcement in walls was updated in 2005 to eliminate conflicts
between the notation used for ordinary structural walls and the notation
used for special structural walls . The distributed reinforcement is now
identified as being oriented parallel to either the longitudinal or
transverse axis of the wall. Therefore, for vertical wall segments, the
notation used to describe the horizontal distributed reinforcement ratio
is ρt, and the notation used to describe the vertical distributed
reinforcement ratio is ρl.

Vertical reinforcements for reinforced concrete walls :
(i) Minimum steel percentage : 0.4%. When this reinforcement controls
the design, half of the steel area be on each side;
(ii) Maximum steel percentage : 4%;
(iii) All vertical compression reinforcements should be enclosed by a
link
as shown in Figure below;
(iv) Maximum distance between bars : the lesser of 3 times the wall
thickness and 400 mm as shown in Figure below.

Vertical reinforcements for walls

Horizontal and transverse reinforcements for reinforced concrete walls
(i) If the required vertical reinforcement does not exceed 2%, horizontal
reinforcements be provided as follows and in accordance with Figure
below :
(a) Minimum percentage is 0.25% for = 460 y f MPa and 0.3% for fy = 250
MPa;
(b) bar diameter ≥ 6 mm and 1/4 of vertical bar size;
(c) spacing ≤ 400 mm.
≤ 3h and 400 mm

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Horizontal reinforcements for walls with vertical reinforcement ≤ 2%

(ii) If the required vertical reinforcement > 2%, links be provided as
follows as shown in Figure blow :
(a) to enclose every vertical compression longitudinal bar;
(b) no bar be at a distance further than 200 mm from a restrained bar at
which a link passes round at included angle ≤ 90o;
(c) minimum diameter : the greater of 6 mm and 1/4 of the largest
compression bar;
(d) maximum spacing : twice the wall thickness in both the horizontal
and vertical directions. In addition, maximum spacing not to exceed 16
times the vertical bar diameter in the vertical direction.

Anchorage by links on vertical reinforcements of more than 2%

Plain walls
If provided, minimum reinforcements : 0.25% for = 460 y f MPa and 0.3%
for = 250 y f MPa in both directions generally.

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EC2 CODE

The information given relates specifically to walls which are vertical
loadbearing members. It includes for plain concrete walls as defined in
EC2. Columns, as defined by EC2, with a breadth/thickness ratio of not
greater than four are considered separately.
Walls thinner than 150mm are not recommended. Basement retaining
walls are considered separately in EC2 6.6 code.

Nominal cover to all reinforcement (EC2, Clause 4.4)
Horizontal bars are placed outside the vertical bars and cover is
measured to these.
• Internal use (15mm or bar diameter) + Δcdev (Concrete inside buildings
with low air humidity, XC1) whichever is greater
• External use 35mm + Δcdev (Corrosion induced by carbonation, XC3)
for values of Δcdev

Minimum area of reinforcement (EC2, Clause 9.6.2)

Vertical reinforcement
0.002 Ac (half placed in each face)
Minimum bar diameter to ensure robust cage: 12mm
Horizontal reinforcement (in each face) 25% of the vertical reinforcement
or 0.001 Ac whichever is greater
Preferred minimum bar diameter: ¼ × diameter of vertical bars.

Links
Diameter to be not less than a quarter of the size of the largest
compression bar.

Plain concrete walls
Where reinforcement is required for the purpose of controlling
shrinkage or temperature (also applies to reinforced concrete walls), it
should comply with the following.

Minimum steel area for both vertical and horizontal reinforcement
0.0025Ac.
This reinforcement should consist of small diameter bars closely
spaced and placed (with adequate cover) near the exposed surface. This
reinforcement should be distributed half near each face.

Maximum area of vertical reinforcement (EC2, Clause 9.6.2)
Maximum percentage of gross cross section: 0.04 Ac

Bar spacing (EC2, Clause 9.6.3)
Minimum spacing
75mm (bars 40mm size and greater: 100mm).
Pairs of bars
100mm. When considering the minimum spacing of bars of 32mm size

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or greater, allowance must be made for lapping of bars.
Maximum spacing
Vertical and horizontal bars. The lesser of
• 3 times the wall thickness
• 400mm.

Links
Where the total area of the vertical reinforcement in the two faces
exceeds 0.02 Ac links should be provided (see 6.4.2. The larger
dimension referred to need not be taken larger than 4 times thickness of
wall).
Vertical spacing
The lesser of
• 16 times the size of the vertical bar size or
• twice the wall thickness.
Any vertical compression bar not enclosed by a link should be within
200mm of a restrained bar.
Horizontal spacing
Maximum spacing should not exceed twice the wall thickness.

Anchorage and lapping of bars (EC2, Clauses 8.4 and 8.7)

For high yield steel, 500 Grade Table 6.6 gives typical anchorage and lap
lengths for ‘good’ bond conditions. Lap lengths provided (for nominal

bars, etc.) should not be less than 15 times the bar size or 200mm,

whichever is greater

Notation for layers of reinforcement

Reinforcement is fixed in two layers at right-angles to form a mat,

normally one mat at each wall face:

• abbreviation for near face N

• abbreviation for far face F

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Edge wall connections to slabs
This method for detailing slab to edge walls is described in EC2 section
6.2.2. This is similar to that for beam to edge columns which is
described in 6.3.2. Model detail MS2 shows the reinforcement detail for
such a joint. Where slab starter bars are required and cannot be inserted
through holes left in the wall Model detail MW3 is used.

Half landings
Where starter bars are required for half landings these may be inserted
in the walls. Mechanical shear dowels and couplers may be considered
as alternatives to half joints so avoiding the use of nibs.
Detailing information
Design information for detailing should include:
• Layout and section drawings including details
of slab intersections and holes, and details of the construction system if
known.
• Concrete grade and aggregate size (standard 30/37MPa and 20mm).
• Nominal cover to reinforcement and controlling design consideration,
fire or durability (standard 20mm for internal conditions, 40mm for
external conditions).
• Details of any design reinforcement required including:
– type of reinforcement (standard H)
– bar diameter
– pitch or number
– where it is required
– lap length if other than normal
compression lap.
Otherwise bar size and pitch given in Model Detail MW1 is assumed.
• Details of proprietary reinforcement, insertions and openings, e.g.
conduit, cable ducting, etc., should be given where the placing of
reinforcement is affected. Provide this information at an early stage.

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Horizontal bars are laid outside vertical bars
Nominal cover specified by designer (At least 20 or bar size whichever is
greater). Where there is no specific design requirement the bar size and
pitch given below may be used

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Corner details
For cover, size and pitch of main bars see Model Detail MW1 unless
specified otherwise U-bars to be same size and pitch as horizontal bars.

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Half landing detail

For cover, size and pitch of wall bars see Model Detail MW1.
For details of slab bars see Model Detail MS2, but ‘U’ bars to be Class B
or C steel and of size not greater than 12.
For details of staircases see Model Details MST1 and MST2

Hole details
For cover, size and pitch of main bars see Model Detail MW1.

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CANTILEVER RETAINING WALLS

EC2 makes no reference to this member. It is mentioned in EC7 (26), but
essentially in connection with geotechnical aspects.

Minimum area of reinforcement (EC2, Clause 9.6.2, pr EN 1992-3)

Simple earth retaining walls
Retaining walls which provide means for the water to drain, e.g. weep
holes, and for which minor seeping problems do not create problems.
• Vertical reinforcement

0.002 Ac (half in each face). Minimum bar size 12mm
• Horizontal reinforcement

the greater of 25% of vertical reinforcement or 0.001Ac (in each face)

Water resisting retaining walls or retaining walls which are required to
prevent water seepage, e.g. basements

Restraints can cause cracking to occur in any direction and hence the
minimum steel provided should equal Ac fct / fy in both directions and
the crack widths checked accordingly.

Maximum area of vertical reinforcement (EC2, Clause 9.6.2)

• Maximum percentage of gross cross section: 4%.

Bar spacing (EC2, Clause 9.6.3 and EC2, Part 3 Clause 7.3.3)

• Minimum spacing 75mm (bars 40mm size and greater:100mm)

• Pairs of bars 100mm

When considering the minimum spacing of bars of 32mm size or
greater, allowance must be made for lapping of bars.

• Maximum spacing 200mm

Edge wall connection to slabs

The method for detailing slab to edge walls is described in 6.2. This is
similar to that for beam to edge columns which is described in 6.4.

Mechanical shear dowels and couplers may be considered as
alternatives and are described in 6.2.2.

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Corner details

For most conditions of applied moment Model Detail MW2 is suitable.
However for thin sections with a high applied opening moment a special
detail may be required (see EC2, Annex J, UK National Annex).

Construction joints

Kicker height for walls below ground level should be a minimum of
150mm and cast integral with the foundations.

Full contraction joints should only be used when it is predicted that
shortening along the full length of the wall will be cumulative. Where
necessary they should be detailed at 30m centers.

See Model Detail MRW3B.

Liquid retaining structures should only be provided with movement
joints if effective and economic means cannot otherwise be taken to
minimize cracking.

There are two main options available.

A Design for full restraint. In this case, no movement joints are provided
and the crack widths and spacing's are controlled by the provision of
appropriate reinforcement according to the provisions of EC2, Clause
7.3.

B Design for free movement (see Model Detail MRW3C). Cracking is
controlled by the proximity of joints. A moderate amount of
reinforcement is provided sufficient to transmit any movements to the
adjacent joint. Significant cracking between the joints should not occur.
Where restraint is provided by concrete below the member considered,
a sliding joint may be used to remove or reduce the restraint.

Wall starters

Wall starter bars should always be specified with the base slab
reinforcement and care taken to define them relative to the wall section,
or at least refer to their location on drawing and schedule.

Links in walls

Where the total area of the vertical reinforcement in the two faces
exceeds 0.02 Ac links should be provided.

Detailing information

Design information for detailing should include:

• Layout and section drawings, which include plan dimensions, depths
and levels.

• Dimensions and positions of kickers (standard kicker height below

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ground 150mm, above ground 75mm).
• Concrete grade and aggregate size (standard 30/37MPa and 20mm).
• Cover to reinforcement:
– standard:

50mm to earth face of walls

40mm to external exposed faces of walls

75mm to bottom and side cover to base

25mm to internal faces.
• Detail of design reinforcement required including:
– type of reinforcement (standard H)
– bar diameter
– pitch or number
– position.
• Details of construction joints.
• Details of any services fittings where placing of reinforcement may be
affected, e.g. large openings, puddle flanges.

External cantilever wall

Vertical bars placed on outside for earth faces.
Horizontal bars placed on outside for exposed faces.

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Footing of cantilever wall

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CANTILEVER RETAINING WALLS STEM

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