Trc

Bending load capacity of reinforced concrete slabs strengthened with textile
reinforced concrete
Frank Schladitz ⇑
, Michael Frenzel 1
, Daniel Ehlig 2
, Manfred Curbach 3
Technische Universität Dresden, Institut für Massivbau, George-Bähr-Straße 1, D-01069 Dresden, Germany
a r t i c l e i n f o
Article history:
Received 24 June 2011
Revised 29 December 2011
Accepted 5 February 2012
Available online 30 March 2012
Keywords:
Strengthening
Reinforcement
Textile concrete
Textile reinforced concrete
TRC
Textile reinforcement
Reinforced concrete
Fine-grained concrete
Carbon
Fibers
Slabs
a b s t r a c t
The use of textile reinforced concrete (TRC) is a very effective method for strengthening reinforced
concrete (RC) constructions. Within the Collaborative Research Centre 528 of the Technische Universität
Dresden (TU Dresden) vast research on TRC was carried out, so as to examine the use of TRC for subse-
quently strengthening the bending load capacity of existing concrete or reinforced concrete components.
As a rule, the experimental research was done at small format reinforced concrete slabs with span widths
of 1.60 m and slab thicknesses of 0.10 m strengthened with TRC. At the same time calculation models
were developed to predict the maximum bending load capacity of the reinforced components amongst
others.
This article describes the experimental and theoretical research reassessing the assignability of the
results gained until now to large scale reinforced concrete slabs with a span width of 6.75 m and slab
thickness of 0.23 m. By using textile high-performance carbon reinforcements based on so-called
heavy-tow-yarns very high strengthening levels can be realized. The results show significant load bearing
capacity increases compared to unreinforced reference slabs. Thus the safe use of bending reinforcements
consisting of TRC could be demonstrated for components with even large span widths and high reinforce-
ment degrees. Simultaneously a distinct decrease of deflection with growing reinforcement degree was
verified at a comparable load level. Calculation results of the presented simplified calculation model
for the estimated bending measurement are consistent with the load carrying capacities determined
experimentally. Using the finite element method (FEM) not only the load bearing capacities but also
the deformations were calculable keenly.
Ó 2012 Elsevier Ltd. All rights reserved.
The application of textile-reinforced concrete (TRC) is a very
effective method for strengthening reinforced concrete (RC) struc-
tures. At the Collaborative Research Centre 528 of the Technische
Universität Dresden (TU Dresden) a vast amount of research has
been carried out on TRC so as to examine the suitability of TRC
strengthening for the subsequent increase of the bending load
capacity of existing concrete or reinforced concrete components.
As a rule, small format reinforced concrete slabs strengthened with
TRC having span widths of 1.60 m and slab thicknesses of 0.10 m
were researched experimentally. Calculation models were devel-
oped to simultaneously predict the maximum bending load capac-
ity of the strengthened components.
This article describes the experimental and theoretical research
for reassessing the assignability of the results obtained until now
on large-scale reinforced concrete slabs with a span width of
6.75 m and a slab thickness of 0.23 m. By using textile
high-performance carbon reinforcements based on so-called
heavy-tow-yarns, very high strengthening levels can be carried
out. The results show significant load-bearing capacity increases
compared to unreinforced reference slabs. Thus, the safe applica-
tion of TRC for strengthening could be demonstrated for compo-
nents with large span-widths and high reinforcement degrees
under bending stress. At the same time, a distinct decrease in the
deflection at a growing reinforcement degree was verified for a
comparable load level. The calculation results of the simplified cal-
culation model for the estimated bending measurement presented
are consistent with the load-carrying capacities determined exper-
imentally. Using the finite element method (FEM), not only the
load-bearing capacities but also the deformations were computed
correctly.
1. Introduction
In respect to a sustainable use of existing building fabrics by
increasing the durability of the structures, the restoration and
0141-0296/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.engstruct.2012.02.029
⇑ Corresponding author. Tel.: +49 351 463 31967; fax: +49 351 463 37289.
E-mail addresses: frank.schladitz@tu-dresden.de (F. Schladitz), m.frenzel@
tu-dresden.de (M. Frenzel), daniel.ehlig@tu-dresden.de (D. Ehlig), manfred.curbach
@tu-dresden.de (M. Curbach).
1
Tel.: +49 351 463 39814; fax: +49 351 463 37289.
2
Tel.: +49 351 463 33776; fax: +49 351 463 37289.
3
Tel.: +49 351 463 37660; fax: +49 351 463 37289.
Engineering Structures 40 (2012) 317–326
Contents lists available at SciVerse ScienceDirect
Engineering Structures
journal homepage: www.elsevier.com/locate/engstruct

the adaptation of existing load-carrying systems to recent de-
mands has become a growing requirement. Therefore, for example,
changes in the use, reconstructions, damage to the existing sup-
porting structure, or altered normative standards may require
the amplification or rather the reestablishment of the load-bearing
capacity of existing concrete elements. In practice, there exist dif-
ferent respective reinforcement methods. The application of TRC
constitutes a new and highly effective method for strengthening
reinforced concrete constructions [1,2]. Besides investigations con-
cerning the TRC reinforcement of RC components for additional
strains with normal force [3], shear force [4], and torsion [5], also
extensive research regarding the flexural strengthening of rein-
forced TRC components was carried out by the Technical Univer-
sity Dresden [6,7].
As a rule, RC slabs with span-widths of 1.6 m, slab depths of
0.6 m, and thicknesses of 0.1 m were tested. Textile fabrics made
of alkali-resistant glass (yarn fineness up to 2400 tex) or carbon
(yarn fineness up to 800 tex) were used as reinforcement. Mean-
while, detailed calculation models for predicting the maximum
bending load capacity were developed. Among others, these mod-
els consider the composite differences between steel and textile
reinforcement, comprehensively. Additionally, simplified measure-
ment procedures not accounting for the composite differences
were generated [6,8].
A calculation model for the determination of the tensile
strength, bending and shear capacity of pure TRC components
can be found in [9,10].
The present article describes the experimental and theoretical
research by TU Dresden and the Torkret Substanzbau AG company
concerning the verification of the assignability of the results ob-
tained so far to large-scale RC slabs as well as the confirmation
of a safe completion of notably higher reinforcement degrees. For
this, the textile reinforcement was made of carbon fabrics with
clearly higher yarn cross sections due to using heavy-tow-yarns. .
2. Experimental research
2.1. Test specimen geometry and materials
For the experimental research, five reinforced slabs measuring
7.00 m/1.00 m/0.23 m (l/w/h) were concreted. One RC slab re-
mained unreinforced for reference. The four strengthened rein-
forced concrete slabs differed in the layer number applied and,
hence, in the thickness of the TRC coating. An overview can be
found in Table 1.
2.1.1. Reinforced concrete body
The reinforced concrete slabs have a lower longitudinal rein-
forcement of 5 bars (d = 12 mm) at intervals of 200 mm and a
transverse reinforcement of 47 units (d = 12 mm) at intervals of
150 mm. Eight pigtail transportation anchors were embedded per
slab. Next to these anchors, additional stirrups (d = 8 mm) were
placed. The concrete cover of the outer longitudinal reinforcement
amounted to 25 mm. The longitudinal section, the plan view, and
the bar schedule of the reinforcement drawing are depicted in
Fig. 1.
Concrete with a maximum grain-size of 16 mm was used. An
average cube compressive strength of 45.5 N/mm2
, an average
splitting tensile strength of 2.9 N/mm2
, and an average Young’s
modulus of 26,150 N/mm2
were detected. The determination of
the concrete compressive strength and the splitting tensile
strength was carried out on cubes (l/w/h = 150 mm/150 mm/
150 mm) and the Young’s modulus at cylinders (Ø/h = 150 mm/
300 mm) according to DIN EN 12390 [11] and DIN 1048 [12].
In compliance with DIN 488 [13], BSt 500 S was used as rein-
forcing steel. The average yield stress amounts of 574 N/mm2
and the average tensile strength of 682 N/mm2
were determined
experimentally according to DIN EN ISO 15630-1 [14].
2.1.2. TRC reinforcement
The TRC reinforcement consists of a textile reinforcement in-
serted into a fine-grained concrete matrix. A polymer-coated fabric
made of carbon rovings (SIGRAFIL C30 T050 EPY) with a fineness of
3300 tex from the SGL Carbon SE company was used as textile rein-
forcement. The heavy-tow-yarns of the fabric were aligned with a
clearance of 10.8 mm in the longitudinal direction and 18 mm in
the lateral direction, see Fig. 2.
Table 1
Tested elements.
Test
specimen
Number of carbon
fabric layers
Slab thickness
(mm)
Thickness
of TRC
layer (mm)
Total
thickness
(mm)
1 None (reference) 230 – 230
2 1 230 6 236
3 2 230 9 239
4 3 230 12 242
5 4 230 15 245
Fig. 1. Formwork and reinforcement drawing.
Fig. 2. Textile fabric.
318 F. Schladitz et al. / Engineering Structures 40 (2012) 317–326

The average tensile strength of the rovings embedded in the
fine-grained concrete was 1200 N/mm2
, and the failure strain came
to 12‰. These values were confirmed by means of eight strain
specimen tests especially carried out for the slab tests according
to JESSE (15). Different reinforcement amounts did not show any
noteworthy impact on the results.
The fine-grained concrete was a convenience blend obtained
from PAGEL Spezial-Beton GmbH & Co. KG (TF10 Pagel-TRC TUDA-
LIT) with a maximum grain-size of 1 mm. The average compressive
strength of the fine-grained concrete could be determined at 89 N/
mm2
and the average bending tensile strength at 5.7 N/mm2
when
testing prisms (160/40/40 mm) according to DIN EN 196 [16].
The TRC reinforcement was arranged in a 6.50 m length med-
ium range. As is characteristic for TRC, the arrangement was car-
ried out with alternating layers of fine-grained concrete and
textile fabric. After applying a 3 mm fine-grained concrete layer
to the pre-wetted surface roughened by sand blasting, the first fab-
ric plane was placed. After that, several 3 mm fine-grained con-
crete and textile layers were applied until the desired number of
layers was reached with a final 3 mm-thick top layer. The strength-
ening work was executed on vertically aligned slabs. Fig. 3 shows
the reinforcement configuration.
2.2. Test set-up
2.2.1. Load application
The test specimen’s load-bearing capacity was verified in a four-
point bending test. In this, bearing strips were aligned at intervals
of 6.75 m. Within the medium range of the slab, the load introduc-
tion was carried out with a single load distributed in two loads at
intervals of 1.5 m by a crossbar. Fig. 4 displays a schematic, and
Fig. 5 shows the load application and the test equipment.
2.2.2. Measurement technique
Besides a load cell for determining the introduced force, vertical
position encoders were arranged at the center of the slab to mea-
sure the deflection. In order to determine the deformation at differ-
ent section heights, photogrammetric measurements (soft- and
hardware by the GOM Gesellschaft für optische Meßtechnik
mbH) were carried out at the longitudinal side of the reference
and the two-layer strengthened slab. For both slabs, a rectangular
field (length: 320 mm, slab height) was sprayed in black and white
within the range of the constant bending moment, see Fig. 6a and
b. The different colors (black and white) form a random pattern for
Fig. 3. Arrangement of the strengthening (bottom und side view).
Fig. 4. Setup of the bending tests.
Fig. 5. Test set-up.
Fig. 6. Vertical position encoders and photogrammetric measuring fields: (a)
reference slab and (b) two-layer strengthened slab.
Fig. 7. Actions.
F. Schladitz et al. / Engineering Structures 40 (2012) 317–326 319

good contrast. Two CCD cameras view the field during the load
application. The deformation of this structure under different load
conditions is recorded by the CCD cameras and evaluated using
digital image processing. The initial image processing defines a
set of unique correlation areas known as macro-image facets, typ-
ically 5–20 pixels across, which are then tracked in each successive
image with sub-pixel accuracy. Using the photogrammetric princi-
ples, the 3D coordinates of the surface of the specimen, which are
related to the facets at each stage of load, can be calculated pre-
cisely, resulting in the 3D contour of the component, the displace-
ment as well as the plane strain tensor.
2.3. Actions
Each slab is initially loaded at its self-weight of approx. 25 kN/
m3
. The self weight gSt may be calculated as a line load and is
1 m Á 0.23 m Á 25 kN/m3
= 5.75 kN/m. The self-weight of the
strengthening layer gV is determined with an Eq. (1) and added
to gSt.
gV ¼ 1:00 m Á ðnumber of layers Á 0:003 m þ 0:003 mÞ Á 25 kN=m3
ð1Þ
Changing loads (P) are applicable when using the testing ma-
chine. A traverse beam distributes the load to two cross beams,
where P/2 acts. P was the applied displacement controlled with a
velocity of 0.05 mm/s. After an initial loading of P = 1 kN, the load
was increased up to P = 10 kN and followed by 2 min of holding
time with constant deflection. Afterwards, the specimen was un-
loaded to P = 1 kN and followed by an augmentation of P to
20 kN. From this loading until the load test end, a holding time
of 2 min with constant deflection was carried out every 10 kN.
Fig. 7 represents these actions.
2.4. Results of the experimental research
Fig. 8 displays the force–deflection-relations referred to the slab
center registered during the slab tests.
To determine the flexural capacity maximum bending moment
was calculated using the following equation:
M ¼
gSt Á l
2
8
þ
gV Á l
2
8
þ
P
2
Á l1 ð2Þ
with gSt is the self-weight line load of the reinforced concrete slab
(see Section 2.3), gV the self-weight line load of the textile reinforce-
ment layers (see Section 2.3), P the machine force, l the span width
of the slab (see Fig. 4) and l1 is the distance between load introduc-
tion and support (see Fig. 4).
By inserting the values gst, l and l1, which amount to the same in
every test specimen, Eq. (2) leads to the following equation:
Fig. 8. Force–deflection relation.
Fig. 9. Calculated moment-deflection relation.
Fig. 10. Exemplary crack patterns (lateral view): (a) reference slab and (b)
strengthened slab.
Fig. 11. Nomenclature and strain distribution.
Table 2
Failure moments and load increase.
Test
specimen
(no.)
Force, P
(kN)
Failure
moment (kN)
Deflection
(mm)
Bearing load
increase to (%)
1 25 66 94 100 (reference)
2 58 110 223 167
3 96 160 229 242
4 119 191 240 289
5 147 228 244 345

M ¼
5:75 Á 6:752
8
þ
gV Á 6:752
8
þ
P
2
Á 2:625 ð3Þ
Values gv and P, which vary with every test specimen, can be
found in Section 2.3 and Fig. 8. Together with the pre-deformations
measured before, they result in moment-deflection relations dis-
played in Fig. 9. The maximum bending moment (failure moment)
and the crack load increases are summarized in Table 2.
Figs. 8 and 9 show that the textile-reinforced test specimens
have a higher flexural capacity than the unstrengthened ones.
Thereby, the bearing load increases with the increasing layer num-
ber of the textile reinforcement.
On the unreinforced test specimen, small load increases lead to
very high deformations at a bending moment of (at least) or ap-
prox. 66 kNm does not fit into the following statement. Beyond this
point, distinct load increases were not to be expected or were not
expected and therefore the test was discontinued at this point.
The failure of the textile-reinforced slabs announced itself by an
audible cracking of the carbon fibers. The test specimens failed in
all cases due to the tensile fracture of the flexural tensile reinforce-
ment of the textile. The tests were stopped after the tensile fracture
of the textile reinforcement. There was no evidence of any other
failure mode (bending pressure failure, shear force failure, steel
failure) at this time.
Apart from an increase in the bearing load, an improvement in
the usability was also achieved. With the growing number of tex-
tile reinforcement layers, the stiffness of the test specimens in-
creased, leading to lower deformations at equal load levels.
Furthermore, the TRC reinforcement led to a finer and smoother
crack pattern see Fig. 10a and b. After the initial crack, the unrein-
forced test specimen showed several large cracks with a clearance
of 200 mm. Much finer cracks with a distance of 10–30 mm oc-
curred on the TRC strengthened test specimens. It could be ob-
served that growing layer numbers resulted in smaller crack
spaces.
3. Theoretical considerations
3.1. Simplified design method
3.1.1. Model introduction
In the following, the rough calculation for determining the
bending load capacity of TRC strengthened RC slabs will be ex-
plained. The calculated load-bearing capacities will subsequently
be verified on the basis of the slab test results. Detailed calculation
methods can be found in [9,11].
For an estimated calculation of the failure moment Mu a rectan-
gular stress distribution within the concrete pressure zone is as-
sumed. Hence, an approximate solution is possible by assuming
the yielding of the concrete steel reinforcement in the ultimate
state of the bearing load capacity. Fig. 11 shows examples of the
nomenclature and the strain relationships in cross section.
With Eqs. (4) and (5) the static effective depths of the steel rein-
forcement ds respectively the textile- strengthened reinforcement
layer dt can be determined.
Static effective depths of the concrete steel reinforcement ds:
ds ¼ h À cnom À
Øs
2
ð4Þ
The static effective depths of the textile strengthened reinforcement
layer dt:
dt ¼ h þ
s Á 0:3 þ 0:3
2
ð5Þ
W is the thickness of the reinforced concrete slab (cm) everything is
okay, Øs the diameter of the steel reinforcement (cm), cnom the nom-
inal size of the concrete cover (cm) and s is the number of textile
reinforcement layers (item).
The expansions of the steel reinforcement es reaching the failure
strain of the textile reinforcement et result from Eq. (6) assuming a
maximum concrete compression strain ec of 3.5‰. From a steel
expansion es of >3.0‰ (fy=E ¼ 574 N=mm62=210000 N=mm2
¼
2:7‰) yielding of the concrete steel is assumed.
es ¼
Àec þ et
dt
Á ds þ ec es > 3‰ ð6Þ
with et is the failure strain of the textile reinforcement (‰) and ec is
the maximum concrete compression strain of the old concrete
(À3.5‰, DIN 1045-1 [17]).
The increase of the compression zone height can be calculated
with the following equation:
x ¼
dt
Àec þ et
Á ðÀecÞ ð7Þ
For the normal concrete used with the assumption of a rectan-
gular stress distribution, the compression zone height x in the con-
crete pressure zone needs to be attenuated by the value k = 0.8
corresponding to DIN 1045-1 [17]
xkorr ¼ k Á x ¼ 0:8 Á x ð8Þ
Table 3
Calculated failure moments.
Test specimen Calculated failure
moment (kNm)
1–Unstrengthened slab 62
2–1 Layer of textile reinforcement 101
3–2 Layers of textile reinforcement 144
Fig. 12. Comparison of calculated and experimentally determined failure moments.
Fig. 13. FE-model of a two layer textile strengthened slab.

The internal lever arms of the inner forces can be calculated
afterwards according to Eqs. (9) and (10).
The internal lever arm for steel reinforcement zs and the textile
reinforcement layer zt:
zs ¼ ds À
xkorr
2
ð9Þ
zt ¼ dt À
xkorr
2
ð10Þ
With the lever arms, given ultimate stresses, and the reinforce-
ment cross sections, the failure moment Mu can be determined
with Eqs. (11)–(13). The tensile forces Fs and Ft for steel and textile
reinforcement are calculable with the following equations:
Fs ¼ fy Á As ð11Þ
Ft ¼ ft Á At ð12Þ
with As is the cross-sectional area of the longitudinal steel reinforce-
ment, At the cross-sectional area of the textile reinforcement, fy the
yield stress of the steel reinforcement and ft is the average tensile
strength of the textile reinforcement.
The failure moment Mu of the strengthened cross section:
Mu ¼ Ms þ Mt ¼ Fs Á zs þ Ft Á zt ð13Þ
To avoid a failure of the concrete pressure zone, the resulting
concrete compressive stress needs to be reassessed afterwards.
When using a constant stress distribution, the permitted concrete
compressive stress fck therefore needs to be attenuated with the
coefﬁcient v = 0.95 (DIN 1045-1 [17]).
The veriﬁcation of the existing concrete compressive stress is
carried out with the following equations:
Fc ¼ Fs þ Ft ¼ As Á fy þ At Á ft ð14Þ
Ac ¼ b Á ðxkorrÞ ð15Þ
rc ¼ Fc=Ac < v Á fcm ð16Þ
with Fc is the existing concrete compressive stress, Ac the cross-
sectional area of the concrete pressure zone, b the width of the con-
sidered slab stripes, rc the existing concrete compressive stress and
fcm is the average concrete compressive stress.
3.1.2. Results
Table 3 displays the calculated failure moments Mu for the ref-
erence and the slabs strengthened with one to four layers of textile
reinforcement.
Fig. 12 contrasts the experimentally determined and calculated
failure moments Mu of Tables 2 and 3. The experimentally deter-
mined load-bearing capacities can be understood well with the cal-
culation approach introduced for the approximated bending
measurement of TRC strengthened reinforced concrete slabs. The
variations amount to less than 10%.
Fig. 14. Uniaxial stress–strain-law. With Ec – elastic modulus for concrete,
fc – uniaxial compressive failure stress, f ef
c – biaxial compressive failure stress,
ft – tension failure stress, rc – compressive stress.
Fig. 15. Biaxial failure function. With Ec – elastic modulus for concrete, fc – uniaxial
compressive failure stress, f ef
c – biaxial compressive failure stress, ft – tension failure
stress, rc – compressive stress.
Fig. 16. Idealized bond-slip laws.
Fig. 17. Idealized r–e-law. With es,y, es,lim, – yield and ultimate steel strain, et,1, et,lim,
– textile and ultimate textile strain, fs,y, fs,u – yield and ultimate steel stress, ft,1, ft,u –
textile and ultimate textile stress, ES – elastic modulus for steel.

3.2. Examinations with the finite element method
3.2.1. Preface
The finite element method (FEM) is a numeric approximation
procedure that is employed e.g. for computations of structures or
their components. They are represented by small finite elements.
The following analysis was carried out with the Atena 2D4
pro-
gram. The slabs to be considered were modeled in a two-dimen-
sional concept room. Due to the symmetrical mounting and
loading, only one-half of the slab was examined and analyzed. The
results were nonetheless effective for the entire component.
Fig. 13 shows the FE-model with the steel and textile reinforcement.
3.2.2. Material model and parameters for old and fine-grained
concrete
Old and fine-grained concrete are modeled as homogeneous
isotropic materials. The implemented material model includes
the following effects of concrete behavior [18]:
non-linear behavior in compression, including hardening and
softening
linear reduction of compressive strength after cracking
linear stress–strain relation in tension
fracture of concrete in tension based on nonlinear fracture
mechanics
biaxial strength failure criterion
tension stiffening effect
The uniaxial stress–strain law and the biaxial failure function
for concrete are schematically displayed in Figs. 14 and 15. Various
parameters are necessary to be able to execute a finite-element
computation. The most important input material and calculation
values are described in Section 2.1.1. A finite concrete element fails
if a combination of principal stresses fulfills the biaxial strength
failure criterion.
3.2.3. Material model and parameters for steel and textile
reinforcement
Both reinforcements are modeled by discrete truss elements
connected to the concrete elements by composite laws. The bond
between the reinforcement and the concrete is defined by a shear-
ing stress-slip-relation (see Fig. 16). A bond slip relation in compli-
ance with model code 90 [19] was applied for the reinforcing steel.
An unconfined concrete can be assumed due to the good bond con-
ditions. The bond slip relation between the concrete and the textile
reinforcement was determined according to [20] in extraction
tests.
Bilinear stress–strain laws are assigned to both steel and textile
reinforcement. Therefore, the elastic bearing behavior until yield
stress occurs and the following plastic hardening behavior until
the tensile strength is reached are being considered for steel.
Fig. 18. Moment-deflection-relation: (a) rt,u/et,lim = 1200 MPa/12.0‰ and (b) rt,u/et,lim = 1200 MPa/11.0‰.
Table 4
Summary of calculated failure moments and maximal deflections.
Textile material parameters rt,u/et,lim = 1200 MPa/12.0‰ rt,u/et,lim = 1200 MPa/11.0‰
Calculated failure moment
(kNm)
Calculated max. deflection
(mm)
Calculated failure moment
(kNm)
Calculated max. deflection
(mm)
Unstrengthened slab 74 315 74 315
1 Layer textile reinforcement 110 210 109 196
2 Layers textile
reinforcement
154 253 154 239
3 Layers textile
reinforcement
194 277 197 264
4 Layers textile
reinforcement
236 286 238 271
4
Atena 2D, Version 4.2.2.0, Cˇervenka Consulting Ltd., Prague, Czech Republic.

The tensile strength of textile reinforcements is determined in
strain specimen tests according to [15]. The tests have shown that
it is acceptable to assume a linear progress of the characteristic
material line after a complete snatch operation of the strain body
and a full extension of the yarns. The yarn undulation and the
accompanying low stiffness of textile reinforcements, unloaded
or loaded only a little, is simulated by a flat rise of the stress–
strain-curve in the first section until reaching stress ft,1. After eval-
uating the strain specimen tests carried out simultaneously to the
component examination, a nearly complete extension of the fila-
ments from a textile stress of ft,1 onward can be expected. The fur-
ther course of the characteristic material line therefore is
characterized by a steeper rise than in its first section. The textile
fails when reaching the textile tensile strength ft,u. The idealized
Fig. 19. Comparison of the calculated and experimental results: (a) ultimate moments and (b) ultimate deflections.
Fig. 20. Reference slab: (a) selection of FE-nodes, (b) photogrammetric measurement, (c) strain ep at compressive zone and (d) es and et at tensile zone reference slab.

stress–strain curves for steel and textile reinforcements are shown
in Fig. 17. The input parameters used in the model are described in
Sections 2.1.1 and 2.1.2.
3.2.4. Calculation results
Fig. 18a displays the moment-deflection-curves in the center of
the slab determined by the FEM-program and compared to the
experimentally measured values. Looking at the two lines of one
slab, e.g. the three-layer strengthened slab, it is obvious that the
two moment-deflection-courses are similar. Furthermore, it is
apparent that a cracked concrete cross-section needs to be as-
sumed from a moment of approx. 40–50 kNm on. The stiffness loss
accompanying this expresses itself in a lower rise of the moment–
deflection-curve. At a deflection of approx. 60–80 mm, a further
decrease of the moment–deflection-rise due to stiffness losses be-
comes evident. This is caused by the onset of the steel reinforce-
ment yielding which leads to a higher stress redistribution from
the steel to the textile reinforcement. That will subsequently be
decisive in the further load increase. Meanwhile, the steel can
hardly absorb more tensile forces due to its plastification [6].
Fig. 18a shows the good correlation of calculated and measured
failure moments. The maximum failure moment difference is ap-
prox. 8 kNm (values see Tables 4 and 2). The deflections show pro-
portionally larger tolerances. For example, when the FE analysis is
applied, the slabs strengthened with two and four layers show up
to 24 and 42 mm higher deflections than actually observed
experimentally.
An improved calculative approximation of the measured mo-
ment-deflection-course can be achieved by increasing the textile
stiffness. For this purpose, a failure strain of 11‰ was assigned
to the textile instead of the average failure strain of 12‰ deter-
mined experimentally. The assigned failure strain is still within
the range of the dispersion of the tensile tests results of the strain
specimens. The corresponding curve progressions are shown in
Fig. 18b. Compared with Fig. 18a it can be noticed that the failure
moment values hardly change whereas the calculated deflections
decrease and further approximate to their measured counterparts.
The summary of the failure moments and deflections is shown in
Table 4 and graphed in Fig. 19a and b. Smaller slab deformations
are obviously detected on stiffer textiles. A notably good accor-
dance between the test and the calculation can be found for the
failure moments (tolerance 8%). As exact deformation calcula-
tions are, in general, to be classified as very difficult, the maximum
deflection tolerance of approx. 11% constitutes a satisfactory result.
The complex load-bearing behavior of TRC slabs can be
simulated well by employing the finite element method. Both
non-linear material laws and non-linear compound relations are
considered in the process. Consequently, the different deforma-
tions and displacements of the component as well as the states
of stress and strain can be analyzed more accurately, allowing for
a better understanding of its load- bearing behavior.
3.2.5. Comparison of FEM-calculation results and the photogrammetric
(GOM) analysis
Fig. 13 shows the finite element model of the two-layer textile-
strengthened slab with a crack pattern under a moment of
154 kNm (acting load P = 90 kN). A 230 mm wide slab section
(see Fig. 6) is focused on, below. In this, the position of the
Fig. 21. Two layer strengthened slab: (a) selection of FE-nodes, (b) photogrammetric measurement, (c) strain ep at compressive zone and (d) strain es and et at tensile zone.

examined section matches the particular photogrammetric mea-
surement, therefore also being within the constant moment
section.
Fig. 20a and b shows the sections of the FE-model‘s longitudinal
side and of the reference slab test, respectively, and Fig. 21a and b
shows those of the slabs that were strengthened double-ply. To be
able to compare both procedures, dot pitch measurements were
conducted, of which one measurement was taken within the com-
pression zone at a distance of 15 mm to the upper slab edge, and
the other measurement was taken at the level of the steel rein-
forcement. In addition, the strengthened slab strain on the textile
reinforcement level was taken in consideration (Fig. 21a and b).
The distances between both points were chosen according to the
observed and calculated crack distances and amounted to
230 mm, 120 mm, and 70 mm. It was assumed that the two differ-
ent reference lengths of 120 mm and 230 mm between the finite
element and the photogrammetric analysis (see Fig. 20a and b)
do not influence the strain determination since the chosen lengths
are more than seven times bigger than the maximal concrete grain
diameter (16 mm) [21]. This way, local strain peaks measurable
with the photogrammetric setup are smeared well for the mean
strain calculations.
The measurement results of the compression zone are shown in
Figs. 20c and 21c, and those of the reinforcement level in Figs. 20d
and 21d. As the force was kept constant for a short period every
10 kN to document crack progressions, the course of the photo-
grammetric measurement in Fig. 21d is serrated.
It can be observed that the characteristic lines of the test show a
course comparable to each particular simulation. Marginal devia-
tions as with the Young’s modulus within the compression zone
(Fig. 20c) as well as the onset of the steel reinforcement yielding
(Fig. 20d) can mainly be attributed to differing material character-
istics as those vary within a distinct range.
Thus, the simulations appear to give a good illustration of the
tests, which particularly matters in respect to the load distribution
at the cross section.
4. Summary
The results introduced in this article concerning the bending
capacity of the large-sized TRC strengthened reinforced concrete
slabs in comparison to unreinforced reference slabs verify the
marked increases in the load-bearing capacity. Here, the safe use
of bending reinforcements made of TRC could be demonstrated
even for components of large span-widths and high degrees of
reinforcement. The load-bearing capacity increases uniformly at
increasing layer numbers. With the four-layer strengthening of
the textile reinforcement, the load-bearing capacity of the rein-
forced concrete slab could be raised to 3.5 times as compared to
its unreinforced counterpart. At equal load levels, a decrease in
the deflections could be observed with increasing layer numbers.
By means of the calculation approach introduced for the esti-
mated bending measurement, the experimentally determined
load-bearing capacities could be reconstructed. A comparison of
experimentally and calculatively determined load-bearing
capacities shows tolerances of less than 10%. These results confirm
those from the small slabs reported in [6,8]. Furthermore, the FEM-
calculation results also indicate good accordance with the experi-
mentally determined values. Consequently, there are now two
methods available for the evaluation of reinforced concrete slabs
strengthened with TRC.
Acknowledgements
The authors would especially like to thank their partners of the
Otto-Mohr-Laboratory, the members of the Collaborative Research
Centre 528, and the German Research Foundation (DFG) for their
sponsorship of the fundamental research concerning TRC within
the special research field ‘‘Textile Reinforcement for Structural
Strengthening and Repair’’. Our gratitude also goes to the Torkret
Substanzbau AG for supporting our practical research.
References
[1] Jesse D, Jesse F. High performance composite textile reinforced concrete –
definitions, properties and applications. In: 3rd International fib congress,
Washington, DC, May 29–June 2 2010; 2010 [paper 157].
[2] Schladitz F, Lorenz E, Jesse F, Curbach M. Strengthening of a barrel-shaped roof
using textile reinforced concrete. In: 33rd Symposium of the international
association for bridge and structural engineering (IABSE), Bangkok, 09.-
11.09.2009. Book of Abstracts and CD-ROM, paper 303_04_01; 2009. ISBN
978-3-85748-121-5.
[3] Ortlepp R, Lorenz A, Curbach M. Column strengthening with TRC: influences of
the column geometry onto the confinement effect. Adv Mater Sci Eng 2009.
http://dx.doi.org/10.1155/2009/493097 [article ID 493097, 5pp.].
[4] Brückner A, Ortlepp R, Curbach M. Textile reinforced concrete for
strengthening in bending and shear. Mater Struct 2006;39(8):741–8. http://
dx.doi.org/10.1617/s11527-005-9027-2.
[5] Schladitz F, Curbach M. Torsion tests on textile-reinforced concrete
strengthened specimens. Mater Struct 2011. http://dx.doi.org/10.1617/
s11527-011-9746-5.
[6] Weiland S. Flexural strengthening of RC-structures by textile reinforced
concrete – interaction between steel and textile reinforcement. Dissertation.
Dresden: Technische Universität Dresden; 2010. urn:nbn:de:bsz:14-qucosa-
37944.
[7] Bösche A. Flexural strengthening of concrete- and reinforced concrete –
structures by textile reinforcement – basics for a calculation model.
Dissertation. Dresden: Technische Universität Dresden; 2007. urn:nbn:de:
swb:14-1197896918623-70942.
[8] Jesse F, Curbach M. Verstärken mit Textilbeton. In: Betonkalender, Ernst und
Sohn Verlag; 2010. p. 457–565.
[9] Hegger J, Voss S. Investigations on the load-bearing behaviour and application
potential of textile reinforced concrete. Eng Struct 2008;30(7):2050–6.
[10] Hegger J, Will N, Bruckermann O, Voss S. Load-bearing behaviour and
simulation of textile reinforced concrete. Mater Struct 2006;39(8):765–76.
[11] DIN EN 12390: testing hardened concrete.
[12] DIN EN 1048: testing concrete.
[13] DIN 488: reinforcing steel.
[14] DIN EN ISO 15630-1: steel for the reinforcement and prestressing of concrete –
test methods.
[15] Jesse F. Load bearing behaviour of filament yarns in a cementitious matrix.
Dissertation. Dresden: Technische Universität Dresden; 2004. urn:nbn:de:
swb:14-1122970324369-39398.
[16] DIN EN 196: methods of testing cement.
[17] DIN 1045-1: concrete, reinforced and prestressed concrete structures.
[18] Cˇervenka V, Jendele L, Cˇervenka J. Atena program documentation: Part 1 –
Theory; 2009. r. 25.
[19] CEB/FIB. CEB/FIP model code 1990. Design Code Comité Euro-International du
Béton, Thomas Telford; 1993.
[20] Lorenz E, Ortlepp R. Berechnungsalgorithmus zur Bestimmung der
Verankerungslänge der textilen Bewehrung in der Feinbetonmatrix. In:
Curbach, M, Jesse F. (Hrsg.). Textile reinforced structures: proceedings of the
4th colloquium on textile reinforced structures (CTRS4) und zur 1.
Anwendertagung, Dresden, 03.-05.06.2009. SFB 528, Technische Universität
Dresden, D–01062 Dresden: Eigenverlag; 2009. p. 491, 502. urn:nbn:de:
bsz:14-ds-1244049857647-62309. ISBN 978-3-86780-122-5.
[21] Müller RK. Der Einfluss der Messlänge auf die Ergebnisse bei
Dehnungsmessungen an Beton – Aus den Arbeiten des Institutes für
Massivbau, TH Darmstadt, Beton Herstellung Verwendung 14; 1964. Heft 5,
Beton-Verlag, Düsseldorf, S. p. 205–8.

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