REPORT 108
Concrete pressure on formwork
C.A. CLEAR BSc
T.A. HARRISON PhD BSc CEng MICE MlCT
Thc project leading to this Report was carried out under contract to CIRIA at the
Ccmcrit and Concrete Association where M r Clear is a Research Engineer and
Dr Harrison is Manager of the Civil Engineering Group in the Technical Applications
Directorate.
This Report was prepared with the help and guidance of the Project Steering Group.
In addition to Dr Harrison and Mr Clear, the Group comprised:
R.M. Hand BSc(Eng) CEng MICE
(Chairman)
John Mowlem and Company PLC
C . M. Recves MlCT MlnstSMM
Frodingham Cement Company
Limited
J . M . Dransfield BSc
P. M. Follett BEng CEng MICE
Cement Admixtures Association
Pozzolanic Lytag Limited
M. Grant BSc CEng FICE
Kyle Stewart (Contractors) Limited
P.G.K. Knight BSc(Eng) CEng MICE MIStructE CEGB, Ash Marketing
Rapid Metal Development Limited
P. F. Pallctt BSc CEng MICE MBIM
K. Ward BSc CEng MICE
Sir Robert McAlpine & Sons
Limited
A . R. McAvoy BSc CEng MICE was CIRIA's Research Managcr for thc project.
This project was financially supported by the Cement and Concrete Association,
Civil and Marine Limited, Department of the Environment, Frodingham Cement
Company Limited, and Blue Circle Industries PLC.
L
CIKlA Report 108
Contents
LIST OF ILLUSTRATIONS
4
LIST OF TABLES
4
ABBREVIATIONS USED
5
NOTATlON
5
SUMMARY
6
INTRODUCTION
6
1.
DESIGN METHOD
9
2.
NOTES FOR GUIDANCE
2.1
Cementitious materials and admixtures
2.2
Aggregates
2.3
Mix proportions
2.4
No-fines concrete
2.5
Workability
2.6
Concrete temperature at placing
2.7
Weight density
Vertical form height
2.8
2.9
Shape and plan area of the cast section
2.1 0 Formwork permeability
2.1 1 Formwork stiffness and roughness
2.1 2 Slope of the form
2.1 3 Placing method
2.1 4 Rate of rise
2.1 5 Impact of concrete discharge
2.1 6 Vibration
2.1 7 Underwater concreting
13
13
13
13
13
14
14
14
15
15
16
16
17
17
17
18
18
EXAMPLES
3.1
Bridge abutment
3.2
Partition wall
3.3
Lift sh.aft
3.4
Mass concrete retaining wall
3.5
Bridge column
3.6
‘V’ column
20
21
22
23
25
29
ACKNOWLEDGEMENTS
31
REFERENCES
31
3.
ClRlA Report 108
... .._,
3
...
.I
List of illustrations
Figure 1
Comparison of the ClRlA methods
Figure 2
Cornparison between measured and calculated pressures on
vertical formwork
Figure 3
Design pressure envelope
Figure 4
Example of formwork pressures and deflection measurements
Figure 5
Height value to be used in the formulae
Figure 6
Plan dimensions, showing sections defined as ‘columns’ or
‘walls and bases’
Figure 7
Pressure envelopes on the formwork of a wall with a sloping
face where the fluid head is fully developed
Figure 8
Relationship between rate of rise and pressure
Figure 9
Pressure measurements on an underwater trdmie pour
List of tables
Table 1
Value of coefficients C, and C2
Table 2
Design formwork pressures
4
ClRlA Report 108
Abbreviations used
OPC
LHPBFC
PBFC
PPFAC
RHPC
SRPC
ggbfs
Pfa
ordinary Portland cemeni
low heat Portland-blastfurnace cement
Portland-blastfurnace cement
Portland pulverised-fuel ash cement
rapid-hardening Portland cement
sulphate-resisting Portland cement
ground granulated blastfurnace slag
pu!verised-fuel ash ’
Notation
A
R
c,
c*
D
H
I1
K
pma.
Q
R
T
I\’
ClRlA Report 108
plan area of mass concrete wall, m2
breadth of mass concrete wall, m
coeffcient dependent on the size and shape of formwork, fi
coeffcient dependent on the constituent materials of the concrete,
weight density of concrete, kN/m’ (kg/m’ x 0.00981 )
vertical form height, m
vertical pour height, m
temperature coeffcient taken as
(216
maximum concrete pressure on forniwork, kN/m’
volume supply rate, m’/h
the rate at which the concrcte rises vertically up the form, m/h
concrete temperature at placing, “C
width of mass concrete wall, m
fi
-l2
c
Summary
The Report extends and improves the method used in CIRIA Report I to cover concretes
using admixtures and blends or blended cements. Use of the method is demonstrated in
six examples: bridge atutment, partition wall, lift shaft, mass concrete retaining wall,
bridge column, and V column.
Int roduction
The method given in CERA (now CIRIA) Report
for calculating concrete pressures
on formwork has served the construction industry well since 1965. However, the design
charts were limited to plain ordinary Portland cement concretes, and recent trends are
towards the wider use of admixtures and blends or blended cements.' In addition, the
commercitil need for faster construction has resulted in a general increase in lift heights
and rates of concrete placing. New theories backed up with site data were being
developed'2.3), and it was decided to review the 19G5 design method and to extend it to
cover concretes which contain admixtures and/or blends or blended cements.
CIRIA instigated a further programme of site formwork pressure measurements and
the compilation of a comprehensive data file to contain both the new site measurements
and previously obtained data. This file on formwork pressures contains over 350 sets of
data. Using this data file in conjunction with recent advances in the understanding of the
mechanisms, an improved method of estimating the concrete pressi're on formwork was
formulated.
Many factors affect the formwork pressure, some of which are unknown at the design
stage. There are also other random site effects such as impact on discharge. Because
many of the factors are inter-related, different interpretations of the data are possible,
and there are several safe potential methods for estimating the pressure. The revised
method is based on a model using only factors which should be known or which can be
reasonably estimated at the design stage. The method is sufficiently conservative to
envelop the spread of results for the factors not taken into account.
Figure 1 shows a comparison of measured pressures against calculated pressures
using the calculation methods given in Report 1 and this Report. This illustration only
includes data which are strictly applicable to the Report 1 method (i.e. the concrete
does not contain admixtures, pfa or ggbfs), and where all the data necessary for the
calculation were recorded. Figure I (a) and (b) shows that the new method is as safe as
the previous method. Figure 2 includes the data for concrete containing admixtures, pfa
and ggbfs. Data better handled by hand calculation (because of non-regular section or
other special conditions) were not included in Figures 1 and 2. Hand calculations
showed that a few tall tapering columns gave measured pressures in excess of the
calculated values.
The Steering Group considered all the data, including those not presented in these
illustrations, and concluded that it would be uneconomic to recommend a method which
erivcloped all results irrespective of the exceptional conditions under which some of the
results were recorded. The calculated pressures in Figures 1 and 2 are based on the
recorded placing conditions. In practice, the placing conditions art: estimated. Assuming
that these are normally 'safe' estimates, this has the effect of introducing an additional
factor of safety not shown in Figures I and 2.
A hlend is a ccmenl where ;I Portland cement has bccn combined with a latenl hydraulic binder. usually ggbfs or pfa. a1
the hatching plant.
A hlcnded cenicnt is a c o m b i n n l h of Portland ccmenl with a lalent hydraulic binder (usually ggbfs or pfa). purchased
direcl from a ccment company.
6
ClRlA Report !08
120
0
-
1
c
90
-
O 0f 3
60 -.
00
8 ,
1
0
30
60
90
120
150
I
1
1
180
210
Calculated pressures (kN/mz)
(a) 1965 method
1501
120
0
0
90
0
0
60
0
nn
0
0
0
2
-
0
30
60
90
120
150
180
Calculated pressures (kN/m2)
(b) 7985 method
Figure 1
ClRlA Rcport 108
Comparison of the ClRlA methods
1
21 0
NOTES
1. This illlustration includes the data for Internally-vibrated concrete placed In nominaib vertical formwork
2. Data which contained estimated values of concrete temperature are excluded
3. Data for sloping and irrequial' zbaped formwork are excluded
150
"\
E
120
2
0
v)
I3
U)
ln
90
I
Q
0
U
I3
U)
m
E"
60
0
5
E
.-X
r"
30
0
Calculated pressures (kN/m2)
Figure 2
x
Comparison between measured and calculated pressures on
vertical formwork (all relevant data are included)
ClRlA Rcpori 108
1. Design method
Freshly placed concrete comprises a gradation of particles from coarse aggregate down
to fine cement particles. all of which are suspended to a greater or lesser extent in
water. This is not a stable condition. The loss or displacement of a mere fraction of the
total mix water (by settlement, leakage or hydration) can change the structure of the
fresh concrete from a quasi liquid to a relatively stiff framework of touching particles
with the water contained within the voids. This change in structure is important. While
the aggregates and cement are suspended in water, the concrete exerts a fluid pressure
( D h ) on the formwork, but once a stable particle structure has been created, further
increments of vertical load have an insignificant effect on the lateral pressure. Therefore
the maximum lateral pressure is generally below the fluid head, and it is controlled by
this change of structure (which can take from a few minutes to a few hours).
The following factors affect this change of state (and hence the maximum formwork
pressurc):
Concrete
admixtures
aggregate shape, size, grading and density
cementitious materials
mix proportions
temperature at placing
weight density
workability
Formwork
permeability/watertightness
plan area of the cast section
plan shape of the cast section
roughness of the sheeting material
slope of the form
stiffness of the form
vertical form height
Placing
impact of concrete discharge
in air or underwater
placing method (e.g. in lifts or continuous vertical rate of rise)
vibration
The complex inter-relationships of these factors are not described in this Report. A
rationalised design equation is presented, together with a description of how the variables
should be treated under design conditions.
Using concepts developed at the Cement and Copcrete Association and during
recent research 01the mechanisms creating formwork pressures(*”, the data for OPC
concrete were analysed to quantify the relationships between maximum pressure,
vertical form height, rate of rise, and concrete temperature at placing. Modifications to
these basic relationships were then developed For concrete containing admixtures, ggbfs
or pfa. This analysis led to the following expression for the maximum concrete pressure
on formwork:
~~
*
ClRlA Rcpori 108
~~
The rcrcarch hy Clcar will be puhlirhcd in a Ccmcnl and Concrclc Arscxiatiim H c w r l during 1986
Y
= 11 [
f,,,
where
C I Dt CzK ~ m f i or] Dh kN/m2, whichever is the smaller.
C, coefficient de endent on the size and shape of formwork (see Table I for
values),
C, coefficient dependent on the constituent materials of the concrete (see
Table 1 for values), fi
D weight density of concrete, kN/m'
H vertical form height, m
It
vertical pour height. m
K temperature coeflicient taken as T1616
R the rate at which the concrete rises vertically up the form, m/h
T concrete temperature at placing, "C
d
(
>'
> H , tlie fluid pressure ( D h ) should be taken
When C , f i
as the design pressure.
,&
incorporates the effects of vibration and workability, because these
The term C
factors are largely dcpendent on size, shape and rate of rise. All the effects of the height
of discharge, cement type, admixtures, and concrete temperature at placing are
incorporated in the term:
C2 K
J
m
-
The design chart, Table 2, quantifies these equations for normal U K conditions where
the concrete placing temperature is between 5 and 15°C. Pressure values shown in bold
on the chart are for placing conditions broadly covered by pressure measurements on
site, where the highest recorded pressures were 90 kN/m for walls and 166 kN/m- for
columns. Values not in bold are outside recorded experience. They are in accord with
the general trend, but may be somewhat conservative.
No change is proposed in the design pressure envelope from that given in the
ClRIA Report 1 design method. The envelope (see Figure 3) comprises fluid pressure
to the depth where the maximum pressure obtained from the design equation or chart
occurs and then remains at this value.
Figure 4 is an example of measurements of formwork pressure and deflection taken
on a site. This illustration shows that once a form deflects, it remains in that state until
the tic bolts are released. In theory, a rigid form would experience a reduction in pressure
aftcr the maximum. In practice, forms are not rigid, and some stress remains between
thc form and concrete. For this reason, no reduction in pressure after the maximum is
givcn in the design pressure envelope.
Table 1 Values of coefficients C, and
1
C,
I Value of C,
Concrctc
OPC. RHPC or SRPC without admixtures
OPC. RHPC or SRPC with any admixture, except a retarder*
OPC. RHPC or SRPC with a retarder
LHPBFC. PBFC. PPFAC or blends containing less than 70 % ggbfs
or 40 9h pfa ui!hout admixtures
LHPBFC, PBFC. PPFAC or blends containing less than 70 % ggbfs
or 40 '%pfn with any admixtures, except a retarder*
LHPBFC. PBFC. PPFAC or blends containing less than 70 % ggbfs
or 40 90 pfa with a rctardcr t
Blcnds containing more than 70 96 ggbfs or 40 96 pfa t
I
'
\cc sc.clN,n
0.3
0.3
0.45
0.45
0.45
0.6
0.6
2 I
ClRlA Rcport 108
= I
5
.-
3
W
kW
C l K l A Kcport 108
2
r
Typical envelope of
pressure on formwork
Design pressure
envelope
Height
of
concrete
h (m)
Envelope of pressure if
acted as a fluid
\'\
/concrete
'\\
'\
/
Figure 3
Design pressure
envelope
I
I
'\
I
4
-
\
6
Pressure (kN/mz)
Section: 0.8 x 5 x 6 m long
Concrete: Normal-weight OPC
Concrete temperature at placir-g: 13°C
Slump: 40 mm
Rate of rise: 3.2 m/h
Pressure (kN/m2)
10.00
0
20
40
I
I
Deflection (mm)
60 80 100 120 140
I
I
I
I
0
2.0
4.0
6.0
I
10.30
Calculated vertical
11.00
11.30
0
0
h
5
12.00
F
0
12.30
Porewater pressure on the form
13.00
13.30
14.00
Figure 4
I2
No reinforcement in the vicinity
of the gauge
Deflection
measure on
the back of
the gauge
I
Example of formwork pressures and deflection measurements
ClRlA Report 108
2. Notes for guidance
2.1 CEMENTITIOUS MATERIALS AND ADMIXTURES
Coefficient C2 (see Table 1) takes into account the effects of different cementitious
materials and admixtures. The term 'admixture' in Table I covers the range of products
commercially available in 1985. Within the grouping 'retarder' fall retarders, retarding
water-reducers, and retarding superplasticisers, also any admixlure which is used above
the recommended dosage such that it effectively acts as a retarder.
A major change from existing prac:ke is the recommendation that L iperplasticised
concrete should be included within the gcneral grouping, and that it does not necessarily
require design pressure equal to the fluid head.
2.2 AGGREGATES
While quantifying the design equation, the effects of the aggregate shape and grading
could not be isolated from the other mix parameters, so these factors are not included in
thc design method. With the exception of no-fines concrete (see Section 2.4), the
formula and tables apply !o all graded natural aggregates.
The design equations apply to concrete mixes containing maximum aggregate sizes
up to 40 mm. Pressures with larger maximum sized aggregates iirc likely to be controlled
by the impact on discharge and the heavy vibration required. The design procedures for
light- and heavyweight aggregate concretes are described in Section 2.7.
2.3 MIX PROPORTIONS
The formula and design tables apply to !he whole range of normal mix proportions.
2.4 NO-FINES CONCRETE
Because no-fines omcrete has a particle structure from :,e moment of placing, it results
in a low formwork pressure. Typical design values are of the order of 2 to 2.5 kN/m2,
so that handling stresses are likely to control the design of the form.
2,5 WORKABI LlTY
Slump is not included as a variable in the dcsign chart for the following rsasons:
I . The problems with placing low workability concrete around reinforcr.ment lead to
prolonged vibration and formwork pressures similar to those obtain2d with more
workable concretes.
2. The site data show no consistent direrence in formwork pressure between low.
medium and high slump concretes.
3. Slump is not a good measure of the factors which affect formwork prcssure.
Formwork pressures with flowing concretes are covcred in Section 2.1.
ClRlA Rcport 108
13
2.6 CONCRETE TEMPERATURE AT PIACING
At low rates of concrete placing, hydration effects become a significant factor in determining the maximum formwork pressure. Because these effects depend on the concrete
temperature at placing, the design equation includes a temperature factor
Although this only strictly applies to OPC and RHPC concretes, it is sufficiently
accurate for all types of concrete when used in conjunction with coefficient C2.The K
factor represents 8 d o of stiffening effects, which are dependent on temperature at
placing.
Data for concrete temperatures at placing in excess of 30°C or below 5 ° C are rare,
and it is prudent not to extrapolate the design equation beyond these values. (Out of the
352 sets of data recorded over a number of years, on only 17 occasions were the
temperatures at placing below 8°C.)
2.7 WEIGHT DENSITY
The design chart (Table 2: assumes a weight density of 25 kN/m’. This is a safe value
for normal-weight concretes. The procedure for calculating the maximum formwork
pressure with light- or heavyweight concretes is to use the.appropriate weight density in
the design equation (see Example 2). Thc design charts can be used to obtain the pressure
with light- and heavyweight concrete by taking the chart value and then adjusting pro
ruia by weight density.
2.8 VERTICAL FORM HEIGHT
The vertical form height is important for two reasons:
I . It limits the potcntial maximum pressure which can develop (in general, the maximum
design pressure is not greater than Dh).
2. Height of discharge affects the magnitude of the impact forces.
Both these factors affect the maximum formwork pressure, and they have been incorporated in the design equation as a function of the form height.
Sometimes, the form can be substantially higher than the height of section cast (see
Figure 5). In these cases, the limiting pressure might be the fluid pressure (which is
obtained from the weight density times the actsial pour height). This should be checked
with a separate calculation.
T
Depth of
concrete
h
H
7
5
Figure 5
14
Height value to be used in the formulae
ClRlA Report 108
2.9 SHAPE AND PLAN AREA OF THE CAST SECTION
!n a section of small plan area, vibration can be sufficient to mobilise all the concrete in
il layer and to transmit a relatively high amount of energy to t.he form. This has the
effect of increasing the depth over which vibration is effective, and consequently the
pressure on the form.
In a larger section, all the concrete in a layer is not mobilised at the same time, and
less energy is transmitted into the formwork. The point of concrete discharge and
vibration is normally moved along the section, which allows the concrete a period of
rest before the next layer is placed. The net effect is that in ‘walls’ the maximum
pressures are lower than in ‘columns’. In fundamental terms, a wall is where the concrete
is placed in layers with the point of discharge and vibration moving along the wall, while,
for columns, the point of discharge and vibration is raised vertically. These conditions
can be conservatively defined using the following simple definitions :
wall or base - section where either the width or breadth exceeds 2 m
column - section where boththe width and breadth are 2 m or less.
These definitions are shown diagrammatically in Figure 6.
The few site data recorded for small, single-storcy columns indicated B fluid pressure
distribution. The formula generally predicts fluid head for small columns. This is
reasonable, because small columns can be placed very quickly and vibrated such that
the full fluid head is mobilised. However, an analysis of the forces on column clamps
indicates that they would fail if concrete in columns develops full fluid pressure. It is
therefore widespread practice to design small ply and timber column forms assuming
less than the fluid head. The possible explanation of this anomaly has not been expcrimentally verified.
2.10 FORMWORK PERMEABILITY
Formwork pressure decreases as the formwork permeability increases, if all other
conditions are equal. This reflects the extent to which excess porewater pressure can
dissipate through the formwork. The pressures are substantial!S lower with extremely
permeable form materials such as expanded metal or fabric. In theory, the design
equation should contain a factor for form permeability. Effects such as reduction of
permeability through previous usage and the use of sealers and coatings, throw doubt on
the ‘practicality’ of such a factor. Because the design equation does not includc a factor
for form pcrmeability, the estimated pressures are not applicable to form materials such
as expanded metal, where they effectively act as frce surfaces and prevent the build up
of porewater pressure.
t
3
Figure 6
Plan dimensions,
showing Jections
dofined as ‘columns’
or ‘walls and bases’
ClRlA Report 108
0
Walls and bases
1
2
3
Breadth (m)
15
2.1 1 FORMWORK STIFFNESS AND ROUGHNESS
Study of the data suggests that the use of stiffer forms results in high pressures.
Conversely, independent research work shows that the fonnwork pressure decreases
substantially if a stiff form is moved slightly outwards. In most practical situations, the
stiffness of a form varies from point to point, and it is difficult to quantify. Formwork
stiffness was not, therefore, included in the design equation.
While the concrete is acting as a fluid, the formwork roughness is immaterial, until
a particle structure forms and the concrete starts to develop internal fricc.ion. Compared
with other factors, its influence on the maximum pressure is small, and it has not been
isolated in the design equation.
2.12 SLOPE OF THE FORM
The pressure on sloping forms was not specifically examined in the research, and only a
few experimental results were available. However, the CIRIA method described in this
Report can be used conservatively with non-parallel sided walls with and without a
uniform ratc of rise. If the volume supply rate is varied so that the rate of vertical rise is
constant, the equation or tables can be directly used. The pressure at any level in the
pour is the same on both faces, and the direction of action is perpendicular to the form
(see Figure 7).
The following method is suggested for calculating the pressure envelope with a
constant volume supply rate:
Split the pour into horizontal levels with the vertical distance between each level
I in or less.
2. Calculate the plan area at each level.
I.
Figure 7
Pressure envelopes on the formwork of a wall with sloping face
where the fluid head is fully developed
ClRlA Rcpori 108
I
I
1..
.
.
3. Calculate the instantaneous rate of rise at each level from
uniform volume supply rate (m'/h)
Rlevcl =
plan area at the level considered (m2)
4. Calculate the pressure at each level using the full height of the form, H, with either
the equation or tables;
5 . Produce the design pressure envelope acting at right angles to the form.
This procedure is illustrated in Examples 4, 5 and 6 (pages 23 to 30).
2.13 PLACING METHOD
The difference between placing in lifts and con;iwous vertical placing has been described
in Section 2.9.
The design equations do not apply to conditions where the concrete is being pumped
from below or where pre-placed large aggregate is grouted frqm below. In both these
cases, the formwork pressures are likely to be higher than those given in this Report.
American experience"' suggests that the formwork should be designed to withstand fluid
pressure plus 50% for pump surge.
2.14 RATE OF RISE
The rate at which the concrete rises vertically up the formwork is an important factor,
and it is included in the design equation. In practice;this is never constant, but, the use
of an average rate of rise is normally adequate for vertical formwork. The average rate
of rise might not be applicable when a considerable lift is placed rapidly, followed by a
long delay before the subsequent lift.
As the rate of rise increases, the maximum pressure increases, but the relationship is
not linear. At high rates of rise, changes in the rate of rise have less effect on the maximum pressure than changes at lower rates of rise (see Figure 8).
2.15 IMPACT OF CONCRETE DISCHARGE
The effects of impact on discharge are incorporated into the design equation. Attention
is drawn to the comments in Section 1.8.
Figure 8
Relationship between
rate of rise and pressure
ClRlA Repon 108
Rate of vertical rise
17
..-. . ...
2.16 VIBRATION
The design method assumes normal internal vibration. Deep revibration can substantially
increase the formwork pressure above the calculated value. If this technique is to be
used, the form should be designed to withstand the fluid pressure at the depth of poker
immersion if this is greater than the normal design value.
This design method does not apply to externally-vibrated concrete. The action of
vibrating the form induces stress additional to that created by the concrete pressure.
2.1 7 UNDERWATER CONCRETING
When formwork is designed for use underwater, the buoyant weight density (Density of
concrete - Density of water = 25 - 9.81 3 15 kN/m’) is normally used to calculate
the effective formwork pressure. For fully-submerged sections, the formwork pressure
can be calculated using either
I . the design equation (see page 9) with D = 15 kN/m’
or
2. 0.6 times the value obtained from Table 2 (page 11).
The procedures are based on the assumption that the static water pressure is equal on
both sides of the formwork, and that it does not result in stresses in the formwork. This
is a reasonable basis for design when the water level is not changing, but it can underestimate the pressures where there is a rapid drop in water level during concreting. This
latter situation is analogous to an earth dam subjected to ‘rapid drawdown’. A change in
water level produces an instantaneous change in pressure on the outside of a form, but a
much slower change in the water pressure within the concrete, because that depends
upon the permeability and hydraulic gradient within the concrete. When the water level
is falling rapidly, this effect can result in the horizontal pressure exceeding the vertical
pressure (see Figure 9). On the other hand, a rising water level reduces the formwork
pressure. In these circurnstances, the formwork should be designed to resist the effective
formwork pressure plus a surcharge proportional to the maximum tidal fall.
ClRlA Report 108
_....
,
~
7301
\.
pressure
\
\
\
1400
\
1
Pressure reduction
on the outside of the
form as a result of the fall
in tide level
I
L
Figure 9
Pressure measurements on an underwater tremie pour
ClRlA Report 108
19
3. Examples
The following examples illustrate the procedure for calculating the design pressure
distribution.
3.1 BRIDGE ABUTMENT
Section
Concrete
0.8 x 6 x 5 m high
Abutment details
OPC normal-weight concrete
Concrete temperature at placing 10°C
:.
K
=
(_?”>’
= 1-92
10+ 16
c, = 1.0
H=h=5m
C2 = 0.3
D = 25 kN/m’
K
=
1.92
R
=
5 m/h
Rate of placement 24 m’lh pumped
Ratc of rise
24
- 5 m/h
0.8 x 6
From tables
Pmax
.‘.
H
75 kN/m’
85 kN/m’
= 80 kN/m’
4 m) =
Pmax (at H = 6 m) =
pmax
(at
H = 5 m)
PO kN/m’
< Dh = 125 kN/m’
From formula
P,,,
From tables
80 kN/m’
Pmax =
=
25 ( 1. O d+ 0.3 x 19.2-/,)
=
80 kN/m’
From formula
f,,, = 80 kN/m’
< Dh
Pressure envelope for formwork design
:
5
80 kN/m2
20
ClRlA Report 108
3.2 PARTITION WALL
Section
Concrete
0.2 x 5 x 4 m high
Wall details
OPC lightweight concrete
c, = 1.0
Concrete temperature at placing 15°C
K=
(m6)
36
= 1.35
Rate o f rise 10 m/h
H=h=4m
C, = 0.3
D = 19 kN/m3
K = 1.35
R = 10 m/h
From tables
P, = 70 kN/m*
=
67.1 kN/m2 < 76 kN/m2
From formula
= 65 kN/m2
f'ma,
Pressure envelope for formwork design
P
CIRIA Report 108
65 kN/m2
21
3.3 LIFTSHAFT
Section
0250 mm
-
Plan view (6m high)
Continuous vertical placing and constant vibration unlikely. Therefore treat as a wall
with breadth = 4 x 1.75 m
Equivalent section 0.25 x 7 x 6 m high
Concrete
OPC normal-weight concrete
Concrete temperature at placing 15°C
:. K = (
1 = 1.35
... 15 + 16
36
2
Rate of rise 5 m/h
From tables
P,,,
Shaft details
c , = 1.0
H=h=6m
C, = 0.3
D 25 kN/m’
K = 1.35
R
=
75 kN/m’
= 5 m/h
< Dh = 150 kN/m2
Pressure envelope for formwork design
22
ClRlA Rcpori 108
.._
.i
3.4 MASS CONCRETE RETAINING WALL
Section
I
*
End elevation ( 1 0 m long)
Wall details
c, = 1.0
Concrete
OPC normal-weight concrete with retarder
Concrete temperature a t placing 10°C
.‘. K = (1036
2 = 1.92
)
+ 16
Uniform volume supply rate (Q) One 6 m’ truck every 20 min = 18 m3/h
Rate of rise
H=5m
C2 = 0.45
D = 25 kN/m’
K = 1.92
Q = 18 m’/h
The rate of rise increases as the pour progresses because the
section narrows. Therefore the pressures are calculated for
instantaneous rates of rise at specific levels. The full height of
the formwork is used in the formula, irrespective of the level for
which it is calculated.
R = Uniform volume supply rate (m’/h)
Plan area at level considered (m2/h)
Using formula
Pmax
= D (C,&+
= 25
= 25
CIRIA Rcport 105
C, K,/H-)
C f i + 0.45 x I . 9 2 d m )
(fl+
0.864,/5-)
23
Area, A = Breadth (8)X width ( w )
h (m)
0
T
0.5
1.o
1.5
2 .o
2.5
h
3.0
Calculation o f rate o f rise and pressure
A
R
(m2) (m/h)
-T-pr
12.5
2.00
2.50
50.0
62.5
3.50
4.00
4.50
5.00
87.5
112.5
1.25
10.0
12.5
15.0
17.5
20.0
22.5
25.0
11.5
30.0
32.5
35.0
1.80
1.44
1.20
1.03
0.90
0.80
0.72
0.65
0.60
0.55
0.51
66
65
64
64
63
63
0
12.5
25 .O
37.5
50.0
62.5
65.0
64.0
64.0
63.0
63.0
Pressure envelope for formwork design
Note: Pressurc acts at right angles to face. and the stability of the forms has to be
considered.
24
ClRlA Report IU8
3.5 BRIDGE COLUMN
Section
5r
5n
5m
P!-i
End elevation
2.5 m
Front view
Section cast
Although one plan dimension is greater than 2 m, the section should he
considered a column, because the vibration and vertical placing are
likely to be continuous.
Concrete
OPC normal-weight concrete with air entraining agent
Column details
c, = 1.5
H = 16m
C, = 0.3
= 25 kN/m3
D
ClRlA Report I08
I
i.
25
.
Concrete temperature at placing 1O’C
K = 1.92
Uniform volume supply rate 20 m’/h
Variable. Has to be calculated at specific depths. Pressure calculated
using this rate and the full height of the form.
Rate of rise
Using formula
P = D ( C , a t C2x K
x)-/,
=
25 ( I . 5 f i
=
25 ( 1 . 5 4 + 0.576J16 - 1.5t/B)
t
0.3 x 1 . 9 2 J m )
Calculation of rate of rise and pressure at a uniform volume supply rate of 20 m’/h
h
DIt
(
k
N
(m
1
- /mz)
I
25
2
3
4
5
6
7
8
9
10
II
12
13
14
15
-.- 16
26
50
75
100
125
I50
I75
200
225
250
275
300
325
350
375
400
B
(m)
1.5
1.5
1.5
1.5
1.5
I .7
1.9
2.1
2.3
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Pressure at
h (kN/m2)
P
(kN/m’)
1 .o
1 .o
1 .o
1 .o
1 .o
I .o
1 .o
1 .o
1 .o
I .o
1.2
1.4
I .6
1.8
2.0
2.5
1.5
1 .5
1.5
1.5
1.5
I .7
1.9
2.1
2.3
2.5
3.0
3.5
4.0
4.5
5.O
5.O
13.3
13.3
13.3
13.3
13.3
11.8
10.5
9.5
8.7
8.0
6.7
5.7
5 .o
4.4
4.0
4.0
170
164
I60
I55
147
I40
135
130
127
127
25
50
75
100
125
150
170
164
160
155
a
147
140
135
130
127
127
ClRlA Rcport 108
-
.._,
w
.
.
Pressure envelope for formwork design
Front view
I
i.
ClRlA Report 108
21
Pressure envelope for formwork design
Pressure (kN/mZ)
%I9
I*
I
I
1
1
1
2
1
3
1 - 4
1
5
Z
6
T
7
164E
I
160
155
1
4
,
h
l
9
T10
x 1 1
P 1 2
x 1 3
1-14
Y15
1 1 6
End elevation
28
ClRlA Rcpori 108
,
!
3.6 ‘V’ COLUMN
i
5b
31
2m
--
2m
2m
I
d
F r m t view
4
End elevation
Section
llthough the breadth exceeds 2m, the possibility of continuous
vertical placing and vibration cannot be discounted
Concrete
OPC normal-weight concrete with superplasticiser
Concrete temperature at placing Very cold winter conditions, so taken as 5‘C
K
.‘.
=
[5%)
Column details
c, = 1.5
H=8m
C, = 0.3
D = 25 kN/m2
2
= 2.94
K
=
2.94
Uniform volume supply rate Two 6 m3 trucks per hour = 12 m’/h
Using formula
P = D C C , a + C,
= 25 ( 1 . 5 f l +
= 25 ( IS@
ClKlA Rcport 198
x
K
x
drfl-)
0.3 x 2 . 9 4 d 8 T A )
+0 . 8 8 d t - m )
29
Calculation of rate of rise and pressure at a uniform volume supply rate of 12 m’/h
h
(m)
Dh
(kN/m*)
e
W
(m)
(m)
1
25
50
75
100
125
150
I75
200
2.5
2.5
2.5
2.5
2.5
3.0
2.5
2.0
1
1
2
3
4
5
6
7
8
I
1
I
1
I
1
A
(m’)
(dh)
2.5
2.5
2.5
2.5
2.5
3.O
2.5
2.0
4.8
4.8
4.8
4.8
4.8
4.0
4.8
6.0
R
P
(kN/m’
124
130
138
Pressure at
h (kN/m’)
25
50
75
100
125
124
130
138
Half pressure envelope for formwork design
Pressure (kN/mZ)
I
h (m)
125
I
End elevation
30
CIRIA Report 108
_.... ,
Acknowledgements
P. A. G. Andrews
D. A. Biddlecombe
P. E. Le i3ihan
D. P. Burrage
A. I. L. Byers
R. P. Cannon
J. R. Champion
J . Csllins
A. T. Cornish
J. Dallaway
R. M. Edmeads
P. J. Egan
A. J. Goldsmith
P. S. Goodall
J . Harrington-Lynn
J . E. Harris
J. R. lllingworth
G. S. Kirk
F. Lane
P. R. Luckett
D.Maher
W. E. Murphy
P. L. Owens
K. R. Pook
S. M. Rao
P. L. Rawlinson
B. G . Richardson
P. Rogerson
P. Rowdon
B. M . Sadgrove
M. F. Taylor
C. F. Turner
R. T. Ward
P. F. Watson
R. V. Watsoii
A. S. White
P. Williams
C. J. Wilshere
Taylor Woodrow Construction Limited
GKN Kwikform Limited
Ralfour Beatty Construction Limited
Steveland Products Limitcd
Balfour Rentty Construction Limited
Frodingham Cement Company Limited
Sir Alfred McAlpine & Son 1.imited
Mabey Hire Company Limited
Blue Circle Industries PLC/Cement Manufacturers Federation
Ove Arup & Partners
Cementation Research Limited/Cement Admixtures Association
Fosroc Technology LimitedKement Admixtures Association
Wimpey Construction ( U K ) Limited
Pozament Cement Limited
Department of the Environment
Mabey Hire Company Limited
Wimpey Construction ( U K ) Limited
Blue Circle Industries PLCKement Manufacturers Federation
Sir Robert McAlpine & Sons Limited
Chart Formwork Limited
MB Formwork Limited/National Association of Formwork
Constructors
Cement an i Concrete Association
Consultant
Property Services Agency
Propcrty Services Agency
Stelmo Limited
CIRIA
Taylor Woodrow Constructiop Limited
Cementation Construction Limited
CIRIA
Acrow (Engineers) Limited
Rapid Metal Developments Limited
Tarmac Construction Limited
Stelmo Limited
Cement and Concrete Association
Scaffolding (Grcat Britain) Limited
John Mowlem & Company PLC
John Laing Construction Limited
References
KINNEAR, R.G. ef a / .
The pressure of concrete on formwork
CERA (now CIRIA) Rcport I . April 1965
HARRISON, T.A.
The pressure on vertical formwork when concrete is placed in wide sections
Cement and Concrete Association, Research Report 22, March 1983
HABGOOD, M.G.
Site formwork pressure measurements in wide sections recorded durine the period of
March 1980 to June 198 I
Cement and Concrete Association Departmental Note 2058. 1982
FORD. J . H .
Consolidation of concrete using plastic form liners and plastic coated plywoods
Conference paper, Second International Conferencc on Forming Economical
Concrete Buildings, Chicago, November 1984
ClRlA Kcport 108
i
! . .,
,..
31