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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
6979
Non-Linear Analysis of Precast Concrete Segment Joints under High
Compressive Loads
Brian Adjetey Boye1, *Samuel Jonah Abbey2, Adegoke Omotayo Olubanwo3 and Joao Fonte4
1Principal Tunnel Engineer, Jacobs (CH2M Hill)
2Lecturer in Structures/Geotechnics, University of South Wales, UK. (* corresponding author)
3Lecturer in Civil Engineering and Finite Element, Coventry University, Coventry, UK.
4Senior Tunnel Engineer, Jacobs (CH2M Hill)
Abstract
When a precast concrete tunnel lining is loaded, the joints rotate
as the lining deforms leading to varying contact lengths. This
paper presents a numerical study on a precast concrete segment
joint subjected to a high compressive loading, using nonlinear
finite element analysis. The precast concrete segment joint was
idealised as a two -dimensional (2D) prismatic block and
subjected to a 6000kN compressive load. The varying contact
lengths due to deformation of the linings and joint rotation
under loading was represented as varying load widths in the
idealised model. The Mohr Coulomb model was used to
approximate the non-linear behaviour of concrete in tension and
compression with an introduction of tension cut-off to the Mohr
Coulomb model to represent the tensile capacity of concrete based
on mean tensile strength. The transverse tensile bursting stresses
in the idealised block was analysed for different load width
ratios (a/d) and compressive strengths of concrete and
presented as proportions of the uniformly distributed basic
stress on the idealised block. The tensile bursting stress
distributions for varying load widths and characteristics
concrete strengths was developed into design charts for use by
engineers in industries to eliminate the need for extensive finite
element analysis and use of empirical relations. The area under
the bursting stress distribution curve is the total bursting force
and was found to decreases with increase in load width ratio.
Keywords: tensile bursting, precast concrete, tunnel segments,
radial joint, TBM ram, circumferential joint, reinforced
concrete, finite element analysis.
INTRODUCTION
Precast concrete segments are subjected to various load
actions from the time they are cast in the factory, through
various stages of handling, storage and transportation to the
final long-term loads in the ground after installation. One of the
most critical modes of failure is known as bursting. When a
concentrated load acts on one of the joint faces of the segment,
tensile bursting forces develop beneath the applied
concentrated load. These tensile bursting forces are
perpendicular to the applied load. The radial joints are stressed
due to the axial loads in the lining resulting from applied external
ground or hydrostatic loads and should be designed to prevent
failure due to bursting. The circumferential joints are stressed
under the action of the Tunnel Boring Machine (TBM) thrust
rams during construction. Bursting stresses can be estimated
using published design standards and empirical equations and
the accuracy of the various equations are assessed by
comparison with a validated high resolution two-dimensional
(2D) finite element analysis (FEA) model. The key parameters
for bursting design are the total force, peak stress and centroid
of bursting forces. The earliest work in the literature to propose
an equation for the bursting force was by Morsch (1922,1924).
Further theoretical investigations are given in the literature by
Bortsch (1935); Magnel (1949); Sievers (1952); Guyon
(1953,1972); Iyengar (1962); Yettram and Robbins
(1969,1970); Sarles and Itani (1984). Of these the works by
Guyon (1953,1972) and Iyengar (1962) are widely used in the
present-day industry in the design of precast segments. Of these
the works by Guyon [14, 15] and Iyengar [19] are the ones
widely used in the present day industry in the design of precast
segments. The theoretical solutions by Morsch [24, 25] can be
derived using the strut and tie method (STM). The STM involves
representing the flow of forces through the block with a truss
and calculating the forces in the truss with one of the forces
being the bursting force. This conceptual tool has been used for
over a 100 years. For a concentrically loaded block, the STM
solution is as presented in Equation 1.
𝑻𝒃
𝑷= 𝟎.25(𝟏 −
𝒂
𝒅) Eqn. 1
The solution by Iyengar (1962) has been presented in the form
of a chart for use in design. These charts have been reproduced
in Figure 1a and the parameters describing the bursting stresses
have been fitted to equations in Figure 1b. This is also to enable
comparison of the study in this paper to the theoretical
solution.
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
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(a) Stress distribution (b) Summary parameters and fitting equations
Figure 1.0(a-b): Theoretical solution according to Iyengar (Traced from Leonhardt (1964))
More recently, He and Liu (2010); Zhou et al. (2015) used
polynomial equations defining the load transfer paths of force
(isostatic lines of compression (ILC)) to derive equations for the
bursting force and centroid of the force. Their equations for
bursting force included the effects of eccentricity, however, the
peak stress was not included in their study (Table 1). Carlo et
al. (2016) presents a procedure for the design of precast
tunnel segments for mechanical excavated tunnel lining in
fibre reinforced concrete, without any traditional steel
reinforcement. Based on photo-elastic tests carried out by
Sargious (1960), who was working in the same department as
Leonhardt (1960), a formula for the bursting force is given by
equation 2.
𝑻𝒃
𝑷= 𝟎.𝟑(𝟏 −
𝒂
𝒅) Eqn. 2
Leonhardt (1964) proposed this linear relationship (Equation 2)
because the theoretical solution by Iyengar (1962) under-
estimated the bursting force as compared to the experimental
data from Sargious (1960). Leonhardt (1960) also summarised
the previous publication by Iyengar (1962), which was based
on theoretical solutions, in a convenient form (charts) for
reinforcement design. Williams (1982) carried out a series of
tests on the joints of reinforced tunnel segments. The failure
modes were identified. The study concluded that the provision
of transverse steel in the area of maximum tensile stress delays
the onset of cracking and that treating the tunnel-lining segment
as an end-block and designing it to the CP110 design code led
to very conservative results. In the early 1990s, the University
of Texas at Austin carried out dozens of model tests of
anchorage zones (Burdet (1990); Zhou et al (2015), based
upon which the design equations in the AASHTO (2014) and
ACI318 (2014) were developed (Table 1). Moccichino et al.
(2010) carried out flexural and point load tests on fibre
reinforced concrete tunnel segments. These tests assessed the
performance of fibre reinforced concrete as compared to
steel reinforcement concrete and did not include assessment of
the joint bursting capacity. Liao et al. (2015) conducted an
experimental program using small scale specimens with and
without fibre reinforcement. The experimental results were
compared with analytical expressions based on a parabolic
distribution of tensile stress. Burdet (1990) used elastic FE
analysis in his study at the University of Texas in Austin to
propose design equations which were later adopted in the
American Standards. Hengprathanee (2004) carried out linear
and non-linear FE analysis to derive equations for precast
beams (rectangular, "T" and "I" shaped sections)
considering the effects of a support reaction. A convergence
test was carried out to confirm that the mesh size was
appropriate. Load width ratios (a/d) of up to 0.5 and eccentricity
ratios (e/d) of up to 0.4 were used in the study by
Hengprathanee (2004). From the FE results, the bursting force
(Tb) was found to agree with Equation 1 for load width ratios
(a/d) greater than 0.2. However, for a knife edge load (a/d =
0), the bursting force was found to be about (0.42P), which
is much higher than 0.3P according to Leonhardt (1964).
Hengprathanee (2004) proposed a modified equation (xc = 0.5
+ 0.25a/d) for the position of the peak stress. However, the
magnitude of the peak stress was not compared with the FE
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
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results in the study. Gupta and Khapre (2008) used a FE
computer code on the platform of a supercomputer known as
"PARAM 10000" in their study. Gupta and Khapre (2008)
showed that the peak bursting stress increases with eccentricity
but did not include the effects of eccentricity in their proposed
equation. Francis and Mangione (2012) verify the design charts
by Leonhardt (1964) using a numerical analysis for a
concentrically applied load. In their study, the effect of the
contact stress distribution at the joint of a precast tunnel segment
on bursting is highlighted and a procedure for the design of
steel fibre reinforced concrete (SFRC) tunnel segments
involving the use of non-linear numerical analysis is proposed.
The British Standard (BS), BS8110 (1997), gives a table of
values (Tb/P ratios) for estimating the total bursting force (Tb).
The values from this table have been presented as an equation
in this paper for comparison (See Table 1.0). The Eurocode
(2004) provides equations (See Table 1.0) for estimating the
bursting force (Tb). The equations in the Eurocode (2004) take
the effects of the height-to-width (h/d) in account. Therefore,
this paper will proposed a graphical solution for estimation of
bursting force and bursting stress for different load-width ratios
and compressive concrete strength for use in design and
industries.
Table 1.0 Comparison of published equations from literature
Bursting force, Tb Peak Stress, σp Centroid. xc
Guyon (1953, 1972) 1.1 × 0.25(1 −𝑎
𝑑)𝑃 1.1 × 0.47(1 −
𝑎
𝑑)𝑃
ab
-
Leonhardt [20] 0.3(1 −𝑎
𝑑)𝑃
- -
BS8110 (1997) Min of 0.23P and (0.32 − 0.3𝑎
𝑑)𝑃 - -
Eurocode (2004) h/d >= 2, 0.25(1 −𝑎
𝑑)𝑃
h/d < 2, 0.25(1 − 0.7𝑎
ℎ)𝑃
- -
Gupta and Khapre (2008) (0.239 − 0.267𝑎
𝑑+ 0.075𝑣)𝑃
- -
He and Liu (2011) 0.22(1 +2𝑒
𝑑)2(1 −
2𝑒
𝑑−
𝑎
𝑑)∑𝑃 - -
ACI318 (2014) 0.25(1 −𝑎
𝑑)𝑃
- 0.5 (d-2e)
AASHTO (2014) 0.25(1 −𝑎
𝑑)∑𝑃
- 0.5 (d-2e)
Zhou et al (2015) 0.25(1 +
2𝑒
𝑑)2(1 −
2𝑒
𝑑−𝑎
𝑑)∑𝑃
- -
METHODOLOGY
When concentrated forces act on a prismatic precast concrete
member, transverse tensile and compressive stresses are
generated (Leonhardt, 1964; Guyon, 1953,1972; Sarles and
Itani, 1984). The same analogy can be applied to the radial and
circumferential joints of a precast concrete segmental lining.
The contact problem at the radial or circumferential joints of a
precast tunnel lining was idealised as a two -dimensional (2D)
prismatic block as shown in Figure 2a. Where a is the width of
the applied load, d is the depth of the prismatic block, e is the
eccentricity of the applied load, h is the height of the prismatic
block and P is the magnitude of the applied load. When the
tunnel lining is loaded, the joints rotate as the lining deforms
leading to varying contact lengths at the joint, which can be
represented by varying load widths, a, in the idealised model.
The distribution of the tensile stress is non-linear as shown in
Figure 2b. This non-linear curve can be defined by the first
position (x0) of zero tensile stress from the loaded area and the
position (xp) of the peak stress (σp). The area under the bursting
stress distribution is the total bursting force (Tb). The centroid
of the bursting force occurs at a distance, xc from the loaded
area. Values of bursting stress in this study are presented as
proportions of the uniformly distributed basic stress:
𝜎0 =𝑃
𝑏𝑑 Eqn. 3
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
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Figure 2(a-b): Idealisation of precast segment joint
A finite element solver with a nonlinear material model (Mohr-
Coulomb) was used in this study. The use of nonlinear material
model in FEA provides near actual behaviour of materials such as
concrete and cement-soil columns (Abbey et al., 2015, 2016, 2017
and Olubanwo et al., 2017, 2018). The Mohr Coulomb material
model was used to approximate the non-linear behaviour of
concrete in tension and compression. The relationship between
the uniaxial compressive strength (fck) and the equivalent
cohesion (c) in terms of the friction angle was established using
Equation 4 given by according to Prinja and Puri (2005) as:
𝑐 = 𝑓𝑐𝑘1−𝑠𝑖𝑛(𝜑)
2𝑐𝑜𝑠(𝜑) Eqn. 4
The Mohr Coulomb model failure function has been defined in
Equation 5. A tension cut-off was added to the Mohr Coulomb
model to represent the tensile capacity of the concrete based on
the mean tensile strength (fctm) as defined in Eurocode 2, see
Equation 6 and 7. The elastic modulus of concrete was defined as
a function of characteristic compressive strength of concrete (See
Equation 8) based on Table 3.1 of Eurocode 2.
𝐹 =𝜎1+𝜎3
2sin(𝜑) −
𝜎1−𝜎3
2− 𝑐 cos(𝜑) = 0 Eqn. 5
𝑓𝑐𝑡𝑚 = 0.3𝑓𝑐𝑘2
3 if 𝑓𝑐𝑘< 50MPa Eqn. 6
𝑓𝑐𝑡𝑚 = 2.12𝑙𝑛 (1 +𝑓𝑐𝑘+8
10) if 𝑓𝑐𝑘> 50MPa Eqn. 7
𝐸𝑐 = 22000 (𝑓𝑐𝑘+8
10)0.3
Eqn. 8
Table 1: Summary of material properties for different concrete strengths
Cylinder strength,
fck (MPa)
Cohesion, c
(MPa)
Friction
angle,φ (deg)
Tension cut-off,
fctm (MPa)
Elastic Modulus,
Ec (MPa)
Poisson
ratio
30 12.6 10 2.9 32837 0.2
40 16.8 10 3.5 35220 0.2
50 21.0 10 4.1 37278 0.2
60 25.2 10 4.4 39100 0.2
70 29.4 10 4.6 40743 0.2
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
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The dimensions of the model were set up using typical values for
precast concrete tunnel linings (PCTL). A block depth of
300mm was chosen for this study as many segmental linings
are close to 300 mm thick (See Table 1). The block height was
assumed to be equal to the block depth, as the zone of high
tensile stress was not expected to extend more than one block
depth from the loaded face. The block depth was divided into
100 elements in each dimension to give a mesh size of 6 mm x
6 mm (grid dimension of 50 x 50), leading to a model made up
of 7701 nodes and 2500 elements. To ensure second order
accuracy, eight (8) node quadratic plain strain elements were
used. In terms of boundary conditions, the model was fixed
vertically at the bottom, with the leftmost node on the bottom also
fixed horizontally. The FEA model was set up with 9 No
different load widths (a) ranging from 3 0 mm (0.1d) to 270
mm (0.9d) in increments of 30 mm (0.1d). The uniaxial
concrete strength was varied from 30MPa to 70MPa in
increments of 10MPa, which represents the range of strengths
typically used in industry. This lead to a total of 45No different
load combinations analysed in this study. The eccentricity (e)
of the applied load was assumed to be zero. A non-linear
analysis was carried out using the visco-plastic strain method
with the load applied in increments of 2% of the total load (50
load steps). A visco-plastic strain method was adopted for less
computational time and memory requirements. The total load
applied, P was 6000kN greater than the maximum compressive
load of the prismatic block at 70MPa concrete strength as
presented in Table 2 with other model parameters.
RESULTS AND DISCUSSION
Total force is important for determination of the amount of
reinforcement needed to prevent bursting and the position of
the peak stress determines an idealized location of the
reinforcement. Incorrect placement of reinforcement may lead
to bursting failure. The peak stress is essential for the design of
fibre reinforced precast segments, as the value of this parameter
needs to be lower than the tensile strength of the concrete. A
non-linear analysis of the idealised precast concrete segment
joints under high compressive load has considered the effect of
load-width ratio on force and peak stress ratios for different
concrete strengths and compared with previous studies by
(Iyengsr, 1962, Zhou, 2015, Leohardt, 1964 and Eurocode 2)
as presented for different load width ratio (a/d) in Figure 3.
From Figure 3(a-i), the variation of bursting stress (mean
tensile strength) with characteristic compressive strength of
concrete has been established. Figures 3(a-i) show that peak
tensile bursting stress increases as compressive strength of
concrete increases. The effect of increase in concrete strength
on the peak tensile bursting stress diminishes at higher
characteristics compressive strength values of concrete. Figures
3(a-i) also show that increase in load width ratio (a/d) reduces
the amount of concrete at failure. This implies that at higher
load width ratios (a/d) the area under the curve (bursting force)
reduces as shown in Figure 4(a-b).
Table 2: Summary of model geometry and applied loads
Load width, a, (mm) Block depth, d (mm) Load-width ratio (a/d) Force, P(kN) Distributed load (kN/m)
30 300 0.1 6000 200
60 300 0.2 6000 100
90 300 0.3 6000 67
120 300 0.4 6000 50
150 300 0.5 6000 40
180 300 0.6 6000 33
210 300 0.7 6000 29
240 300 0.8 6000 25
270 300 0.9 6000 22
Figure 3(a-b): Variation of bursting stress with distance for different characteristic strengths of concrete.
(a) (b)
a)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
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Figure 3(c-f): Variation of bursting stress with distance for different concrete strength
Figure 3(g and h): Variation of bursting stress with distance for different concrete strength.
(c) (d)
(e) (f)
(g) (h)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
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Figure 3(i): Variation of bursting stress with distance for different concrete strength
The effect of load-width ratio (a/d) on bursting force and peak
stress ratios was investigated on the assumption of zero
eccentricity for the different characteristic strengths of concrete
considered and the FEA results show good agreement with
previous studies. The FEA results presented in Figures 4(a-b)
show that increase in load width ratio causes reduction in force
and peak stress ratios and in good agreement at higher
characteristic concrete strength with theoretical solutions by
Zhou, (2015) compared to the theoretical solutions by
Leonhardt (1964) and Eurocode, 2. From Figure 4a, the results
for the nonlinear material analysis are much lower than that of
Leonhardt at high load concentrations (low load width ratios).
This demonstrates that the Leonhardt solution are conservative
as compared to the nonlinear analysis. Figure 4b shows that the
theoretical solution of peak stress according to Iyengar, 1962
agrees more with the FEA results of the present study at higher
load width ratios however, higher peak stresses were obtained
at lower load width ratios for both solutions due to reduction in
contact area. The nonlinear material analysis can therefore be
used to optimise the design of segmental lining joints and
improve equations in the design codes for practising engineers.
Figure 4(a-b): Variation of peak stress and force ratios with load width ratio for different concrete strength
(i)
(a) (b)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 9 (2018) pp. 6979-6988
© Research India Publications. http://www.ripublication.com
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CONCLUSION
From the non-linear analysis of the idealised precast concrete
segment joints under the applied compressive load, the
following conclusions has been drawn:
The variation of bursting stress (mean tensile strength)
with characteristic compressive strength of concrete
depends on the magnitude of characteristics
compressive strength of concrete.
Peak tensile bursting stress increases as compressive
strength of concrete increases.
The effect of increase in concrete strength on the peak
tensile bursting stress diminishes at higher
characteristics compressive strength values of
concrete.
An increase in load width ratio (a/d) reduces the
amount of concrete at failure leading to reduction in
bursting force.
The plotted charts can be adopted as design charts by engineers
in industry to eliminate the need of conducting extensive finite
element analysis and use of empirical relations in estimation of
bursting stress. The charts are recommended for plain concrete
design and can be developed further for Fibre Reinforced
concrete.
List of abbreviations;
AASHTO American Association of State Highway and
Transportation Officials
ACI - American Concrete Institute
a - width of load area
b - width of prismatic block
BS - British Standard
d - thickness of prismatic block
e - Eccentricity
Ec - Concrete elastic modulus
FE - Finite Element
FEA - Finite Element Analysis
EC - European Code
h - Height of prismatic block
ILC - Isostatic Lines of Compression
𝑷 - Applied force
𝝈𝒑 - Peak stress
𝝈𝟎 - reference stress
STM - Strut and Tie Model
TBM - Tunnel Boring Machine
𝑻𝒃 - Bursting force
xc - Centroid of bursting stress
x0 - distance from load to first position of zero
stress
2D - two-dimensional
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