thesis_lwc.pdf

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European Union Brite EuRam III

LWA concrete under fatigue loading.

A literature survey and a number

of conducted fatigue tests.

EuroLightCon

Economic Design and Construction with

Light Weight Aggregate Concrete

Document BE96-3942/R41, June 2000

Project funded by the European Union

under the Industrial & Materials Technologies Programme (Brite-EuRam III)


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The European Union Brite EuRam III




EuroLightCon




Contract BRPR-CT97-0381, Project BE96-3942


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Although the project consortium does its best to ensure that any information given is accurate, no liability or responsibil-

ity of any kind (including liability for negligence) is accepted in this respect by the project consortium, the authors/editors

and those who contributed to the report.

Acknowledgements

This report, concerning Task 5.1.4.3, is written by Wim Bennenk. The report is based on a study performed by Sonjavan Lier and Adriaan de Vlieg, as junior researchers at the Eindhoven University of Technology, department Structural

Design. The study is coached by the author, assisted by Aleks Milenkovic and Math Pluis on behalf of Spanbeton. The

tests are performed in the Van Musschenbroek Laboratory at the EUT, managed by Sip Overdijk. Adriaan de Vlieg and

Martien Ceelen conducted the tests. This report is a mutual effort of EUT and Spanbeton.

Information

Jan P.G. Mijnsbergen, CUR, PO Box 420, NL-2800 AK Gouda, the Netherlands

Tel: +31 182 540620, Email: [email protected]

Information on the EuroLightCon-project and its partners: http://www.sintef.no/bygg/sement/elcon

ISBN 90 376 03 48 3


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The European Union Brite EuRam III




EuroLightCon




Contract BRPR-CT97-0381, Project BE96-3942

Selmer ASA, NO

SINTEF, the Foundation for Scientific and Industrial Research at the

Norwegian Institute of Technology, NO

NTNU, University of Technology and Science, NOExClay International, NO

Beton Son B.V., NL

B.V. VASIM, NL

CUR, Centre for Civil Engineering Research and Codes, NL

Smals B.V., NL

Delft University of Technology, NL

IceConsult, Lnuhnnun hf., IS

The Icelandic Building Research Institute, IS

Taywood Engineering Limited, GB

Lias-Franken Leichtbaustoffe GmbH & Co KG, DE

Dragados y Construcciones S.A., ESEindhoven University of Technology, NL

Spanbeton B.V., NL


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LWA Concrete under fatigue loading

A literature survey and a number of conducted fatigue tests

BE96-3942 EuroLightCon 5

Table of Contents

PREFACE 7

SUMMARY 11

SYMBOLS 13

1 INTRODUCTION 15

2 A CONCRETE FATIGUE MODEL 17

2.1 Uniaxial tensile behaviour [9] 17

2.2 A deformation-controlled uniaxial tensile test [9] 18

2.3 S-N curves and Whler diagrams [9] 19

2.4 The cyclic creep curve 19

2.5 E-modulus 20

3 LOADING 22

3.1 Constant amplitude 22

3.2 Variable amplitude 23

3.3 Presentation of results 24

4 THE MINER RULE 25

4.1 General 25

4.2 Concrete under compression 25

4.3 Concrete under tension 26

4.4 Conclusion 26

5 PARAMETERS INFLUENCING FATIGUE OF CONCRETE 27

5.1 Concrete characteristics 27

5.2 External factors 28

5.3 Climate aspects 29

6 S-N CURVES 30

7 TESTS WITH DIFFERENT LOADING TYPES 35

7.1 Compressive tests 35

7.2 Tensile tests 36

7.3 Tensile-compression tests 36

8 CALCULATION PROCEDURE 37


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6 BE96-3942 EuroLightCon

9 PERFORMED TESTS IN DELFT AND GENT 38

10 TESTS AT EUT 40

10.1 Required arrangements capacity 40

10.2 Test arrangement 41

10.3 Performed compression test 43

10.3.1 Applied loading scheme 43

10.3.2 Measuring procedure 43

10.3.3 Measuring results 44

10.4 Performed tension-compression test 49

10.4.1 Applied loading scheme 49

10.4.2 Measuring procedure 49

10.4.3 Measuring results 49

10.4.3.1 Compression/tension test LWA-TC1 5110.4.3.2 Compression/tension test LWA-TC2 53

10.4.4 Analyses and conclusions 54

11 REFERENCES 55

12 NOMENCLATURE 56


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PREFACEThe lower density and higher insulating capacity are the most obvious characteristics of Light-

Weight Aggregate Concrete (LWAC) by which it distinguishes itself from ordinary Normal

Density Concrete (NDC). However, these are by no means the only characteristics, which jus-

tify the increasing attention for this (construction) material. If that were the case most of the de-

sign, production and execution rules would apply for LWAC as for normal weight concrete,

without any amendments.

LightWeight Aggregate (LWA) and LightWeight Aggregate Concrete are not new materials.

LWAC has been known since the early days of the Roman Empire: both the Colosseum and the

Pantheon were partly constructed with materials that can be characterised as lightweight aggre-gate concrete (aggregates of crushed lava, crushed brick and pumice). In the United States, over

100 World War II ships were built in LWAC, ranging in capacity from 3000 to 140000 tons and

their successful performance led, at that time, to an extended use of structural LWAC in build-

ings and bridges.

It is the objective of the EuroLightCon-project to develop a reliable and cost effective design

and construction methodology for structural concrete with LWA. The project addresses LWA

manufactured from geological sources (clay, pumice etc.) as well as from waste/secondary ma-

terials (fly-ash etc.). The methodology shall enable the European concrete and construction in-

dustry to enhance its capabilities in terms of cost-effective and environmentally friendly con-

struction, combining the building of lightweight structures with the utilisation of secondary ag-gregate sources.

The major research tasks are:

Lightweight aggregates: The identification and evaluation of new and unexploited sources spe-

cifically addressing the environmental issue by utilising alternative materials from waste. Fur-

ther the development of more generally applicable classification and quality assurance systems

for aggregates and aggregate production.

Lightweight aggregate concrete production: The development of a mix design methodology to

account for all relevant materials and concrete production and in-use properties. This will in-

clude assessment of test methods and quality assurance for production.

Lightweight aggregate concrete propert ies:The establishing of basic materials relations, the

influence of materials characteristics on mechanical properties and durability.

Lightweight aggregate concrete structur es: The development of design criteria and -rules with

special emphasis on high performance structures. The identification of new areas for applica-

tion.

The project is being carried out in five technical tasks and a task for co-ordination/management

and dissemination and exploitation. The objectives of all technical tasks are summarised below.

Starting point of the project, the project baseline, are the results of international research work

combined with the experience of the partners in the project whilst using LWAC. This subject is

dealt with in the first task.


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R24 Prefabricated bridges, June 2000

R25 Chemical stability, wear resistance and freeze-thaw resistance of lightweight aggregate

concrete, June 2000

R26 Recycling lightweight aggregate concrete, June 2000

R27 Mechanical properties of LWAC compared with both NWC and HSC, June 2000R28 Prestressed beams loaded with shear force and/or torsional moment, June 2000

R29 A prestressed steel-LWAconcrete bridge system under fatigue loading

R30 Creep properties of LWAC, June 2000

R31 Long-term effects in LWAC: Strength under sustained loading; Shrinkage of High

Strength LWAC, June 2000

R32 Tensile strength as design parameter, June 2000

R33 Structural and economical comparison of bridges made of inverted T-beams with top-

ping, June 2000

R34 Fatigue of normal weight concrete and lightweight concrete, June 2000

R35 Composite models for short- and long-term strength and deformation properties of

LWAC, June 2000R36 High strength LWAC in construction elements, June 2000

R37 Comparison of bridges made of NWC and LWAC. Part 1: Steel concrete composite

bridges, June 2000

R38 Comparing high strength LWAC and HSC with the aid of a computer model, June 2000

R39 Proposal for a Recommendation on design rules for high strength LWAC, June 2000

R40 Comparison of bridges made of NWC and LWAC. Part 2: Bridges made of box beams

post-tensioned in transversal direction, June 2000

R41 LWA concrete under fatigue loading. A literature survey and a number of conducted

fatigue tests, June 2000

R42 The shear capacity of prestressed beams, June 2000

R43 A prestressed steel-LWA concrete bridge system under fatigue loading, June 2000


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SUMMARYThis report of sub-task 5.1.4.3 concerns the fatigue strength of concrete in general and LWAC

in particular. From the literature survey, the important issues for testing the fatigue strength of

concrete are described in chapter 2. There are references with the research performed by Hor-

dijk at Delft University of Technology for his PhD thesis. The existing methods to estimate the

fatigue lifetime of dynamically loaded structures, such as the Miner Rule of Palmgren-Miner

hypothesis, are discussed in chapter 4. The types of loading are discussed in chapter 3. The in-

fluence of the type of loading as well as the magnitude of the loading and the frequency are dis-

cussed in chapter 5. In this chapter also attention is paid to the influence of the type of concrete

and external factors, such as temperature and humidity. The presentation of data is discussed in

chapter 6, while tests with different loading characteristics are presented in chapter 7. Some ofthe tests performed at the Delft University of Technology Eindhoven, tension fatigue tests, as

well as at the University of Gent, bending fatigue tests are reviewed in chapter 9.

This literature survey is complementary to the study of Spanbeton concerning the fatigue

strength and the study and research performed by Betonson and the EUT for the prestressed

steel-concrete composite bridge, where a typical and essential detail is tested on its fatigue

strength.

Additional to the literature survey, some tests are performed at the Van Musschenbroek Labora-

tory at the EUT. The loading is related to a design study of a bridge, composed with prestressed

precast inverted T-beams and an in situ cast concrete deck-slab, conducted by Spanbeton in sub-task 5.1.4.2. The study resulted in two representative loading cycles for the deck-structure; one

loading with a variation in the compressive upper and lower stresses and another one with the

combination of tensile- and compressive stresses.

Test specimen have been produced of LWA concrete, grade C55. The ultimate capacity of

forces versus frequency for the test arrangements is determined.

- The fatigue strength under sinusoidal compressive stresses between 16.5 and 33 MPa at a

frequency of 5-10 Hz was satisfying. The test specimen resisted ten million of loading cy-

cles.

- For the tensile-compression test, the feasible tension capacity of LWAC had to be learned

in some preliminary tests. The final tests showed that 10 million cycles were feasible.

Keywords:LWAC C55, literature survey, LWAC bridge-decks, stress variation, frequency, compression

fatigue test, tension-compression fatigue test.


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SYMBOLSLatin upper case symbols E modulus of elasticity

Es secant modulus

F force

Ms miner sum

N normal force

Ni number of cycles

R stress ratioR radius

S stress levelS displacement

Latin lower case symbolsd difference in.

lmeas length between measure points

fc design value compression strenght of concrete

fcm mean tensile strength concrete

fcf uniaxial design tensile strength for concrete under fatigue loading

fc;rep representative value of compression strength concrete

fc,;ep;f representative uniaxial tensile strength for fatigue

fc(t)m mean tensile strength concrete after t days

fcm mean compression strength concrete

fck characteristic value of tensile strength concrete

fckf characteristic cube strength for fatigue

fckt characteristic cube strenght for fatigue after t days

ft design value tensile strength of concrete

i cycle number

n number of cycles

t time

Greek lower case symbols displacement strain

seco

secondary creep increase per cycle

m material factor stressmin minimal compression stressmax maximal compression stressmin minimal tensile stressmax maximal tensile stress

frequency


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1 INTRODUCTIONIn the EuroLightCon project- Economic Design and Construction with LightWeight AggregateConcrete - the structural applications of LWAC are centralised in research task 5. One part of

that research concerns the fatigue behaviour of concrete. Although in some building structures

the live load is of a cyclic nature, fatigue is usually an important issue in civil structures, such as

bridges, viaducts, platforms, due to traffic loads, sea waves, wind etc.

The general study in task 5.1.4.3 concerns the fatigue behaviour of concrete in the deck struc-

tures of concrete bridges, composite bridges as well as for box-beam applications, all with

prestressed precast units.

The study concerns a literature survey and a number of fatigue tests. Spanbeton has studied the

fatigue loading in bridge decks in sub-task 5.1.4.2. Based on design calculations Spanbeton se-

lected two representative stress combinations acting in a bridge deck. These stress combinations

are the bases for a number of fatigue tests on LWAC. The tests are performed in the Van Muss-

chenbroek Laboratory of the Eindhoven University of Technology, faculty of Architecture, de-

partment Structural Design.

Fatigue of concrete is also a subject in the study of Spanbeton, report of sub-task 5.1.4.2 and the

study of EUT together with Betonson, report of sub-task 5.1.4.1, concerning the fatigue resis-

tance of a recently developed prestressed steel- LWA concrete bridge system. In the three men-

tioned reports the subject is fatigue-related. For the EUT, it means, a new research project inthis field of design, and at the same time a challenge to confront junior researchers with this im-

portant subject.

In general, the fatigue loading of concrete can be seen as a process of internal changes of the

structure of the hardened concrete, mostly called damage that results in a crack propagation

and finally in failure when a number of loading cycles is exceeded. By the presence of micro-

cracks in concrete, the fatigue mechanism is explainable, but in essence not completely known.

As said, previously, concrete structures are usually statically loaded. Bridges are dynamically

loaded, caused by traffic loads and wind loads.

Research learns that some hundreds of loading cycles at a high stress level will not lead to fa-

tigue failure. In general, variations in the normal live loads on floors and stairs will not cause

fatigue effects. The check on fatigue resistance is necessary for structures sensitive for vibra-

tions, such as slender chimneys, poles, and structures with a very variable live load, traffic

loads, such as for bridges and roads.

It is very usual to multiply a static load with an impact factor > 1, to transform the dynamic load

into an increased static load, which covers the dynamic effects. That is called a quasi-static

load. Fatigue of concrete structures is only important for specific applications, as previously

mentioned. Besides that, the number of failures, due to fatigue, is very small, which means that

the design method is covering the loading history correctly. The design and calculation methods


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are based on long-term experiences and practise, so it is impossible to calibrate these methods

on the existing reliable concrete structures, because the safety factor can not be determined in a

non-destructive way.

The attention is mostly paid to the fatigue of the material. The fatigue strength of concrete is inprinciple lower than the strength under short-term static loading. A load that varies in time as

well as in magnitude substantially can lead to a material failure.

The fatigue strength is a long-term issue and has to be reviewed for the structures designed life-

time. Fatigue is an Ultimate Limit State failure mode. Cracking, deflection and the loss of stiff-

ness are aspects of the Serviceability Limit State.

Fatigue effects can occur in the concrete, in the reinforcement as well as in the bond between

concrete and reinforcement.

The fatigue strength is depending on the following aspects:

- The maximum stress,

- The minimal stress,

- The frequency of the loading cycles,

- The nature of the load, sinusoidal or stochastically,

- The grade of the concrete,

- The rate of hydration,

- The rate of hydration and test conditions- under water or above water.


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Figure 2 The fictitious model and the Dugdal-Barenblatt model [9]

The size of the zone and the stress transfer length depends on the crack-width. This briefly de-

scribed model is also to link to the model of Dugdale-Barenblatt concerning the yielding of

steel, where a plastic zone with crack-closing stresses is assumed ahead of a crack tip, see Fig-

ure 2b. In this model the crack-closing stresses are equal to the yield stress of steel.

2.2 A deformation-controlled uniaxial tensile test [9]When a test specimen is strained in uniaxial tension, it will respond elastically in the first stage.

The load-deformation is linear up to the peak, see line I. The tensile stresses are -on macro-

level- uniformly distributed over the cross-section. So, in fact, the stress-strain curve for the

concrete can replace the load-strain curve of the test specimen. At peak load, micro-cracks indi-

cate the zone where the continuos macro-crack will develop, the so-called softening or process

zone. In fact, the crack will develop in the weakest zone. See also Figure 3.

Figure 3 Load-deformation relations under tensile loading [9]


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The transferable load decreases when the deformation of the process zone increases. Outside the

zone the loading decreases. Stronger cross-sections follow curve line II. The model predicts and

describes the results of research adequately.

2.3 S-N curves and Whler diagrams [9]As far as cyclic loading or fatigue loading is concerned, a distinction is generally made betweenlow cycle high amplitude fatigue and high cycle low amplitude fatigue. The former involves

few load cycles of high stress at a lower rate of loading (earthquakes, storms, etc.), while the

latter is characterised by a great number of cycles at low stress at a higher rate of loading (traffic

loading, wind and wave loading, etc.) The main characteristic of fatigue behaviour of concrete

is the number of load cycles, N, that can be performed before failure occurs. N increases when

the upper load level decreases. When the relative maximum load or stress is plotted against log

N, a linear relationship is the result, as shown in Figure 4a. In the next diagram 4b is shown that

the fatigue strength is also depending on the lower stress. A decreasing lower stress level results

in a decreasing number of cycles to failure. Stress reversals have more detrimental effect on ten-

sile fatigue than repeated tensile stresses.

Figure 4 Whler diagram [9].

2.4 The cyclic creep curveIf the deformation is recorded during a fatigue test on plain concrete and plotted against the

number of cycles performed, the curve, known the cyclic creep curve, will be obtained. One can

distinguish three parts in the curve:

1 The deformation increase per cycle decreases by a higher number of performed cycles.

2 The increase of the deformation is constant

3 Just before failure occurs, the deformation increases rapidly.


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Therefor it is possible to conclude the number of cycles within the lifetime from the measured

stress variation. The ultimate strain can be used as a criterion for fatigue failure:

= = =d

dnN

d

dn

dt

dtN

No*

In which = the frequency.

So the formula can be written as:

log log log log = + o

N

For a constant value of the addition log e + log N is almost constant in value. The number ofcycles to conduct before failure occurs is also depending on the frequency. A lower frequency

leads to a smaller number of cycles up to failure, as shown in Figure 7.

Figure 7 The relationship between the cyclic creep rate and log N. [9].


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3 LOADINGFatigue loads do not always have a sinusoidal character but are, in the contrary, mostly irregular

or stochastically distributed in the time. Due to the fact, that the irregularity of the load at the

same time means unpredictability, one needs statistics to characterise the load. To describe a

random process, the process is split into - n sinusoidal sub-processes that vary in duration.

3.1 Constant amplitudeIn research projects, the constant amplitude test is often applied. The test specimen is loaded

with a force, varying sinusoidal in time between a maximum and a minimum value, see Figure

8. The frequency is constant.

Figure 8 Constant amplitude

The objective of the test is to learn the number of loading cycles - N i- before the test specimen

fails. The number of cycles - Ni - is also depending on the upper and lower stress, maxandmin. This is shown in a 3-D diagram. By using a fixed value for min i, the Whler diagram isobtained, see Figure 9.

Figure 9 The 3-D presentation and the Whler diagram as a cross-section.


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Within the constant-amplitude tests one can distinguish:

Compressive compressive cycles: Both maxand minare compressive stresses. The rate ofmaxand minand the static compressive stress is called

S maxand S min.Tension- tension cycles: Both maxand minare tensile stresses. The rate of both

maxand min and the static tensile stress is called S maxand S min.

Compressive tension cycles: min is a compressive stress. maxis a tensile stress. S maxis the rate between the compressive stress min and thestatic compressive stress and S minis the rate between the

tensile stress maxand the static tensile stress.

The Miner rules are based on tests with constant amplitudes.

3.2 Variable amplitudeLoad blocks with constant amplitude can vary in magnitude; the numbers of cycles as well as

the upper and lower stress are parameters to simulate the aimed load. Such a load is also called a

program-load, see Figure 10.

Figure 10 A program load

It also possible to change the duration of a block, which means irregularities in the blocks inter-

faces, called a variable amplitude load, as shown in Figure 11. In this example the frequency

does not change.

Figure 11 Variable amplitude load.


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3.3 Presentation of resultsTest results can be presented in different ways. In a test with constant amplitude, the number of

loading cycles until failure is depending on maxand min. The results can be presented in a 3-Ddiagram. On one axis the value of maxand the other one the value of min.is presented. The

third axis represents logN i. In Figure 12 tests results for plain concrete under uniaxial compres-sive stress are shown. To easy the user, a 2-D presentation is made, in which for instance

min iis constant or a constant stress ration R is chosen, as in a Whler diagram.In the case the stress variations are constant, one gets a Goodman diagram, not very practical in

use.

Figure 12 Goodman diagrams.


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4 THE MINER RULE

4.1 GeneralMost of the tests on fatigue behaviour of concrete are performed with a constant amplitude load.

In reality the load is not that regular of nature. By applying the Miner rule, it is also possible the

estimate the fatigue lifetime for other loading histories.

The Miner rule can simply be written as:

=

=c

i NiMs

1

1

In which c is the number of cycles during the intended lifetime.

The number of loading cycles - N i- is derived from constant amplitude tests. Via this value the

stress level of each separate cycle is taken into account. In this value one can express the influ-

ence of the concrete grade, the hydration rate, the test conditions and the loading frequency.

The interpretation of the Miner rule is as follows:

Each separate cycle causes a - hypothetical contribution to the damage in the concrete with a

value 1/Ni. According the presented rule one can add all separate contributions in a random se-

quence. As soon as the sum is equal to 1, fatigue failure will occur. Up till now there exist no

physical explanation for the damage 1/Ni. It was not yet possible to connect the damage with a

number of present cracks in the concrete.

4.2 Concrete under compressionIn 1977 StuPOC launched a research project concerning the applicability of the Miner Rule for

concrete under compression. A probabilistic approach was chosen, in which some material as-

pects such as compressive stress, shrinkage and creep are considered. The fatigue life of con-

crete and so the Mshas a stochastic character.

The formula is then as follows:

=

=c

i NimedMs

1 )(1

It was learned in the project that on a log-scale med(M) = 0.47, substantially lower than 1. By

multiplying the stresses with a factor 0.97 the Miner hypothesis predicted the result rather accu-

rately.


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4.3 Concrete under tensionAt Delft University of Technology the applicability of the Miner hypothesis for concrete under

tension has been investigated. Program loads with blocks were used to study the influences of

the sequence of the loading. The magnitude of max varied in the tests, sometimes high stressesand sometimes lows. In general the Miner sum Ms was beyond 1. When for Ms the cyclic creepis taken into account the value of Ms is close to 1.

4.4 ConclusionQuite a number of arguments can be mentioned against the Miner rule of Palmgren-Miner hy-

pothesis. All these arguments are based on the lack of a physical damage model; nevertheless

the Miner rule is frequently applied in the daily practise. The rule is simple and research did not

proof that the rule is not applicable or not reliable enough. Hordijk [9] states: The hypothesis

does not accurately reflect to concretes. One reason for this, for instance, is that the sequence

effects are not taken into account. Nevertheless, it is applied in the daily design practice, first ofall because it is simple, secondly, because no better method is available and, thirdly, because the

description of concrete behaviour under random loading is adequate enough for most cases.

His research project is based on the application of fracture mechanics, another approach.

In the research project [3] the sequence of loading cycles is studied. The value of max variedper block. However, no conclusions could be drawn.


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5 PARAMETERS INFLUENCING FATIGUE OF CONCRETEQuite a number of parameters are influencing the fatigue lifetime of concrete. These parameters

can be divided into three groups:

- Concrete composition and concrete properties

- External factors, such as loading sequence

- Climate factors, temperature and humidity.

5.1 Concrete characteristics

In general, it is expected that the concrete grade is not influencing the fatigue strength as long asthe applied stresses are respecting that concrete grade and as long as normal strength concrete,

NWC, is concerned. For high strength concrete, HSC, a more brittle material, decreases in fa-

tigue strength is expected and for lower-ones an increase. Research at TNO-IBBC in 1997

learned that the fatigue strength decreases when the concrete is more brittle.

A general conclusion is that the fatigue lifetime is longer for high strength concrete than for

normal strength concrete, as long as the maximum relative stress is high enough. For instance:

0.7 < (max / fcm) < 0.9. However, the influence of the higher concrete strength is not sufficientlyclear. Considering that the application of HSC leads to more slender structures while the fatigue

strength of concrete is becoming more dominant, due to the increase of the dynamic load in

comparison with the dead load.

The dominant parameters in the mix composition, such as the water cement ratio, the applied kg

cement and the percentage air do not influence the fatigue strength, when expressed in general

terms in relation to the static strength.

When concrete is conditioned under water the decrease of the fatigue strength increases with a

higher water cement ratio in comparison with test specimen not conditioned under water.

The presence of silica fume in the concrete did not show significant differences in test results.

However, LWA concrete composed with silica fume, can be loaded to a higher stress level in

fatigue. The most likely explanation is as follows:

In NWC the cracks appear normally in the transfer zone of 5 10 m between paste and aggre-gate, a zone with unsound hydration products. In LWAC the quality of the transfer zone is

higher. The stiffness of LWA grains and the paste are more in balance for LWAC. Stress peaks

are smeared, so less cracking can be expected for LWAC with silica fume as filler.

As for high strength concrete the reduction of the total mass is also important in comparison

with the dynamic load. The reduction is a consequence of the lower mass per m and not spe-

cifically a result of a more slender structure, as for HSC may be expected. The fatigue behaviour

of LWAC is not extensively researched. Cornelissen [8] concludes from his research that the

fatigue behaviour of LWAC is depending on the type of LWA.


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5.2 External factorsThe fatigue strength is depending on the relative stress value S max= max/ fc(t)m. When S maxin-creases the number of loading cycles until failure occurs decreases. The difference between the

bottom stress minand the upper stress max determines the amplitude and is influencing the fa-

tigue behaviour. In S-N curves the values for minare referred to log N and S max. With an in-crease of the amplitude the number of cycles until failure decreases as can be seen in Figure 13.

Figure 13 S-N curves

In fatigue test with S minas relative compressive stress the fatigue strength under tension shows

a decrease of the fatigue strength, in comparison with the tests in which S maxis a relative ten-

sion stress, Cornelisse [8]. So in those cases the stress passes the zero axis, the fatigue strength

decreases. Probably the explanation is found in the interaction between cracks, due to tension

and due to compression, but also the repeating stresses in and around the crack tips may causethat decreasing effect.

The number of loading cycles, until failure, decreases with a decreasing frequency of the load.

The upper limit of the strength is higher than the long-term strength of the concrete. The reduc-

tion factor of the fatigue strength is smaller than the reduction factor for the frequency. The life-

time of a test specimen - expressed in time increases with a decrease of the frequency of the

load cycle. In the CUR-report 163 one can read:

It is shown in general that a decrease of the frequency with a factor 100 leads to a decrease of

the number of loading cycles, until failure, with a factor 100. That means: the effective fatiguelifetime is a factor 100 longer, see Figure 14.

With a decreasing secondary creep velocity, sec.

, the lifetime increases. In Figure 14 the peak

deformations are plotted against the time. [2]. At a lower frequency sec.

decreases, which means

a longer time until failure, so a longer lifetime.


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6 S-N CURVESThe S-values represent the quotient of the real acting stress and the uniaxial compressive con-

crete strength, the bending tensile strength and the uniaxial tensile strength. Working with S maxand S minthe positive values are always used. For tensile -compressive test maxis a tensile stressand mina compressive stress. S minis always related to the compressive cube strength.To compare the results of a number of tests for a fixed value for S minthe following graphs are

presented:

Table 1. The overview of the tests to present in the following graphs.

Abbreviation Loading type Circumstances7

BT Bending-tension-tension DryBTD Bending-tension-compression Dry

CT Centrally tension-tension Dry-wet

CTd Centrally tension-tension Dry

CTn Centrally tension-tension Wet

CTl Centrally tension-tension Dry

CTDa Centrally tension-

compression

Dry-wet

CTDb Centrally tension-

compression

Dry-wet

CTDI

4

Centrally tension-compression

Dry

Ha5

Bending-tension-tension Dry

Hb6

Bending-tension-tension Dry

1. LWA concrete

2. 0.025 < S min< 0.700

3. S minvalue of 0.1, 0.2 and 0.3

4. LWA concrete, S min= 0.2

5. HSC without micro silica fume

6. HSC with micro silica fume

7. Dry specimens, Wet specimens 2 weeks under water level, 2weeks in open air

Wet specimenswere sealed.


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Figure 15 S-N curves for the test series with S min= 0

Figure 16 S-N curves for the test series with S min= 0.1

1

1 2 3 4 5 760

0.7

0.6

0.5

0.4

0.3

0.8

0.9

LogN

Smax BT

'BTD'

CTCTd

CTn'CTDa''CTDb'

HaHb

Smin = 0.0

1

1 2 3 4 5 760

0.7

0.6

0.5

0.4

0.3

0.8

0.9

LogN

Smax

BT'BTD'CT

CTdCTn'CTDa'

'CTDb'H aH b

Smin = 0.1


34/58


35/58




Figure 19 S-N curves for the test series with S min= 0.4

The S-N curves, based on the tests performed at Delft University of Technology and the Gent

University of Technology, are as follows:

Dry test specimensTension-tension:

Centrally loading and bending of NWC

LogN = 12.78 11.82 x S max+ 17.57 x S min 18.40 S maxx S min.

Centrally loading of LWAC

LogN = 15.35 15.38 x S max.

Bending of HSC

LogN = 12.36 10.24 x S max+ 1.88 x S min.

1

1 2 3 4 5 760

0.7

0.6

0.5

0.4

0.3

0.8

0.9

LogN

Smax

Smin = 0.4

BTCTCTdCTn'CTDa'HaHb


36/58




Tension-compression:

Bending of NWC (tensile failure)

LogN = 9.19 6.86 x S max.

Centrally loading of LWAC (tensile failure)

LogN = 7.36 6.58 x S max.

Centrally loading of NWC (compressive failure)

LogN = 10.44 8.00 x S min.

Wet specimensTension-tension:

Centrally loading of NWC

LogN = 12.50 11.94 x S max.

Dry and wet specimensTension-compression:

Centrally loading of NWC

LogN = 8.71 7.46 x S max. (0.025 < S min< 0.700)

LogN = 9.09 7.37 x S max 2.51 x S min (S min,0.1, 0.2 and 0.3)


37/58




7 TESTS WITH DIFFERENT LOADING TYPESThe research on the fatigue resistance of concrete concerns tests with the following loading

schemes:

- varying compressive stresses,

- varying tensile stresses or

- a combination of both.

7.1 Compressive testsIn this part the behaviour under variable compressive stresses is discussed.

A test specimen is installed in the arrangements and loaded centrally with a static compressiveforce until failure. Repeating this procedure for several similar test specimens, same composi-

tion, same hardening conditions, same age etc, it is possible to calculate f cm, the mean value of

the compressive stresses at failure. This is necessary to calculate the relative stresses S maxand S

min, the ratio between the acting stresses and fcm.

The loading velocity in the test shall never exceed the velocity of the loading cycles in the struc-

ture. The fatigue strength is overestimated when the loading velocity id too high.

To obtain a continuous stress distribution, at variable amplitude stresses, reference stresses are

used to describe the variation in the values of the amplitudes. One can choose a minimal stress,

a maximal stress or an average stress as a base for reference. See Figure 20.

Figure 20 Variable amplitude stress, referred to a maximal stress (a) or a minimal stress (b)

In fatigue compressive tests performed with constant amplitudes, it is shown that the number of

loading cycles Ni, until failure is not only depending on the minimal stress or the maximum one,

but also depending on:

- The concrete quality

- The rate of hydration

- The hardening and test conditions

- The change in loading frequency


38/58




The Miner Rule does not give any information concerning the development of strength and

stiffness during the lifetime. Therefor static tests are performed to measure the strength and the

stiffness. Fatigue test results show that particularly under compressive-tension loading the stiff-

ness may decrease with 40 to 80%.

7.2 Tensile testsTo load a specimen with a tension force, the test specimen is fixed to the arrangements. Steel

plates are glued at the topside as well as at the bottom side, to fix the specimen by screws to the

test arrangements. The steel plates have to be glued plan-parallel to the axes of the test speci-

men, to avoid any eccentricity during testing. The uniaxial stress of the concrete fcmis obtained

form a number of uniaxial tensile tests. The relative stresses S maxas well as S minare referred to

fcm.

7.3 Tensile-compression testsThe uniaxial tensile capacity of concrete is approximately 15 to 20 times lower than the com-

pression capacity. The tests are performed in the same way as for the tensile tests, described in

the previous part. Regarding the fact that S min is a compressive force, the average compressive

strength fcmhas to be determined by tests.


39/58




8 CALCULATION PROCEDUREThe characteristic concrete compressive cube strength fckfthat has to be taken into account for

fatigue, can be derived from fckt. The ages as well as the hardening conditions of the concrete

then have to be reviewed.

The relationship for fatigue is as follows:

2/302

)30'(' mmN

ff cktckf

= In which,

fckf = the characteristic cube strength to take in account for fatigue.fckt= the characteristic cube strength after t days of hardening.

For concrete grades C30: fckf = fckt

The material factor for concrete is: m= 1.2

The design strength is equal to:

ckfckfmfrepccfffff '71.02.1/85.0'''

.. ===

The representative value for the tensile strength in fatigue tests can be derived from:

30'8.0 .... frepcfrepc ff += In which:

fc.rep.f= representative uniaxial tensile stress for fatigue in N/mm.

However, the material factor is now: m= 1.4

The design value for the uniaxial tensile stress for dynamic loading is:

52'57.04.1)30'8.0(' ...... frepcfrepcmfrepccf ffff +=+== In which:

fcf= design uniaxial design strength for concrete under fatigue loading

With the correct formula for LogN a Whler diagram can be designed.

Ni= the number of loading cycles until fatigue failure

R = stress ratio in a cycle R = min i/ max i.


40/58


41/58




Figure 22 Test arrangement at DUT.

Prestressed beams 150 x 280 x 2300 mm have been applied to perform fatigue bending tests in

the Magnel Laboratory in Gent. The beam was loaded in the middle of the span. Due to the

prestressing, compressive stresses are acting in the fibres at the bottom side of the beam before

the bending test starts. The frequency of the cycle was 8 Hz; the amplitude was constant.


42/58




10 TESTS AT EUT

10.1 Required arrangements capacitySpanbeton investigated the fatigue behaviour of concrete bridge decks. The results are presented

in the report of sub-task 5.1.4.2. The design results are input for the tests to perform at the van

Musschenbroek Laboratory of EUT. Some other aspects are considered before starting the test

series.

For bridges the average frequency is 0.05 Hz, according CUR-report 93-13, page 28.

For railroad bridges the frequency of the loading cycle is 0.06 Hz for train transporting ore.

For transport of goods the frequency is 0.15 Hz and for passenger trains 1.0 Hz.

The time needed to perform a test with 10 x 106cycles at 5 Hz is approximately 25 days. For 10

Hz approximately 12 days.

The pre-design of the test specimen dimensions and the arrangement capacity have to be deter-

mined firstly.

Two types of test will be performed for LWAC:

- Uniaxial compression test

- Uniaxial compression tension test.

The concrete grade is C55.

The amplitude for uniaxial compression testsis between 0.3 x fckand 0.6 x fck. For a cylinder

with a diameter of 70 mm, so a plain surface of 3848,5 mm, the required force is:

F min= -0.3 x 55 x 3848.5 = - 63500 N

F max = -0.6 x 55 x 3848.5 = -127000 N

F average= = - 95000 N

The amplitude for uniaxial compressive-tension testsis between 0.424 x fc.rep. and 0.10 x fck.

For a cylinder with a diameter of 70 mm, the required forces are:

F min= + 0.424 x 3.5 x 3848.5 = + 5710 N

F max= - 0.100 x 55 x 3848.5 = - 21170 N

F average = = - 7730 N

Due to the test arrangements capacity the final dimensions of the test specimens are:

- 100 x 100 x 500 mm for the reference test regarding the E-modulus

- 100 x 100 x 500 mm, with a constriction in the middle of the height, the reduced cross-

section is 70 x 100 mm. The length of the constriction is basically 110 mm. See Fig-

ure 23.


43/58




The constriction of the prism is required for the tensilecompression test, but at the same time

also attractive regarding the feasible frequency at the required compressive stresses, which is

explained in the next part. The concrete mix composition for LWAC is presented in Table 2.

Table 2. Concrete mix compositions for LWAC C55.Component Percentage

Cement Geseke CEM 52,5R

OFT3 0,7 %

ON2 0,5%

Limestone 6,7 %

Lytag 6-12 mm 38%

Lytag 0,5-6 mm 26%

Lytag 0-2 mm 10%

Sand 0-2 mm 26%

W/C-ratio 0,40

Figure 23 Test specimen.

10.2 Test arrangementThe arrangements for the fatigue tests have not been used for a long period of time in the labora-

tory, so checks regarding functionality, capacity in relation with frequency and required adjust-

ments were necessary. The arrangement is shown in figure 24.

Figure 24 Arrangement for fatigue tests.

The feasible frequency range is firstly measured under compression. The cross-section of the

test prism is 100 x 100 mm. It is loaded between 30% and 60% of the characteristic compres-

sive cube strength. The stress variation is a sinus curve. The possible combinations of maximum

forces and the possible frequencies are shown in Table 3.

70

100 100

115

80

110

80

115


44/58




Table 3 Feasible maximum forces and frequencies.

Static force

[kN]

Amplitude of force

[kN]

Frequency

[Hz]

288 45 5

266 66 5252 82 8

248 88 10

246 86 12-14

It is obvious that it is feasible to obtain high frequencies especially with lower forces, due to

required displacement of the jacket to build up and release the force. In fact, the time needed for

the oil-flow in the jacket. The maximum capacity in compression is 340 kN.

For the tensile-compression test, the objective is to load the prism with a cross-section of 100 x

100 mm between 42% of the bending tensile strength and at 10% of the characteristic cube

strength. For concrete C55:

F max= -0.10 x 55 x 100 x100 = - 55000 N > 55 kN.

F min= +0.42 x 3.5 x 100 x100 = +14700 N > 15 kN.

Already in the start of the test, problems were arising with the specimen as well as with the fix-

ing of the specimen in the arrangement.

- In the first attempt the glued joint between arrangement and test specimen failed at a

static tensile force of +6 kN. (foto right)

- In the second attempt the same failure happened at a static force of +10 kN.

- In the third attempt the joint performed well at 15 kN, but now the concrete failed after3 cycles. (foto left)

Figure 25 Failure of concrete (left) and failure of glue joint (right) during test of arrangement.

The conclusion had to be that the specimen was loaded to a too high level, but the arrangement

is capable to perform the aimed tests as such. So the tension force had to be adjusted.


45/58




10.3 Performed compression test

10.3.1 Applied loading schemeThe base of the test is loading the specimen between 30 and 60 % of the characteristic strength.

For a specimen with a surface area of 70*100 mm and a characteristic strenght of 55 N/mm,

this means a maximum compression force of 0,6*55*70*100=231 kN and a minimum compres-

sion force of 0,3*55*70*100=115,5 kN. In testing this gives a loading of a static force of 172

kN with an amplitude of 57,8 kN.

10.3.2 Measuring procedureThe measuring procedure is followed up and recorded. The procedure is followed up at the start

of the test and during the execution of the test. More in detail:

The test specimen is positioned and glued.

The normal force is introduced until the static load is achieved.

The dynamical compression force is introduced - sinus curve at a frequency of 0.1 Hz.

A number of cycles are measured with a high speed, two detailed measurements per second.

The frequency is increased in steps until 11 Hz.

For a number of steps a check on the span is made, to adjust the loading curve.

The measuring speed is then decreased to two measurements per minute.

The test is running.

After 1 million cycles the frequency of the dynamic compression force is decreased to 0.1 Hz.

The measuring speed is 2 measurements per second.

A detailed measurement takes place during 1 minute.

All measured data are recorded and stored in the computer.

A new measurement is starting with a slow cycle at 0.1 Hz.

The frequency is then increased; the test is running or is progressing.

The test stops at 10 million cycles or earlier when the test specimen fails.

The data can be presented in graphically.

The objective of the detailed measuring during the test is to check all-important issues at that

very moment. The detailed measuring is possible at the frequency of 0.1 Hz; 20 measurements

per cycle with a measuring speed of 2 per second. At a frequency of 10 Hz it is only possible to

measure trends.

After a detailed measurement it is possible to draw a graph with on one axis the strain and onthe other the force. From this graph you can get the E-modulus of the specimen. This is a good

indicator for testing the specimen on fatigue.

The strain is measured with strain-measurers, glued on the specimen at both sides of the test

area. Figure 26 shows a strain-measurer glued on the specimen.


46/58




Figure 26. Strain-measurer on the specimen

10.3.3 Measuring resultsIn total there have been conducted two tests for the fatigue capacity under compression forces.

The first specimen was tested with 10 million cycles, the second with 2,5 million cycles. The

results of both tests are given in graphs of detailed measurements for determining the E-

modulus.

10.3.3.1 Compression test LWA-C1In table 4 the values of the forces and the displacements are given during the test.

Table 4 Forces and displacements during test LWA-C1.

# cycles F- F+ S- S+

0 230,7 115,9 -2,53 -1,99

911000 231,2 115,6 -2,61 -2,05

1740600 231,1 115,7 -2,53 -1,97

2462250 231,6 115,2 -2,46 -1,90

6974173 232,0 115,0 -2,32 -1,75

7679237 232,1 114,6 -2,31 -1,74

8284413 232,1 114,7 -2,41 -1,82

9361178 232,3 114,7 -2,38 -1,78

10167992 231,9 115,0 -2,40 -1,79

F = forces in specimen [kN];

S = vertical position of the specimen [mm].

The graphs of detailed measurements during the test are shown in Figure 27 In the left graph the

strain is measured during a period of time, and in the right graph the E-modulus is determined.


47/58




0,001

0,0011

0,0012

0,00130,0014

0,0015

0,0016

0,0017

580 590 600 610 620 630

Signal Nr [ 0.5 sec / sign 0.1 Hz ]

Strain[m/m

]

strain 1 strain 2

y = 23892x - 4,9173

15

20

25

30

35

0,001 0,0011 0,0012 0,0013 0,0014 0,0015 0,0016 0,0017

strain [ m/m ]

SigmaN/mm2

Strain 1 Strain 2 Linear (Strain 1)

y = 24230x - 9,8763

0

10

20

30

40

0,001 0,0012 0,0014 0,0016 0,0018 0,002

strain [ m/m ]

Sigma

N/mm2


0,0010,00110,00120,00130,0014

0,00150,00160,00170,00180,00190,002

170 190 210 230 250 270 290


Strai

n[m/m]

Strain 1 Strain 2

y = 24284x - 10,142

10

1520

25

30

35

40

0,001 0,0012 0,0014 0,0016 0,0018 0,002 0,0022

Strain [ m/m ]

SigmaN/mm2


0,0010,00110,00120,00130,0014

0,00150,00160,00170,00180,00190,002

0,0021

170 190 210 230 250 270 290Signal Nr [ 0.5 sec / sign 0.1 Hz ]

Strain[m/m]

Strain 1 Strain 2

-0,001-0,0008

-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

80 100 120 140 160 180 200 220Signal Nr [ 0.5 sec / sign 0.1 Hz ]

Strain[m/m]

Strain 1 Strain 2

y = 23911x + 34,319

10

15

20

25

30

35

40

-0,001 -0,0008 -0,0006 -0,0004 -0,0002 0 0,0002 0,0004

Strain [ m/m ]

S

igmaN/mm2



48/58




y = 24372x + 33,509

10

15

20

25

30

35

40

-0,0008 -0,0006 -0,0004 -0,0002 0 0,0002 0,0004

Strain [ m/m ]

SigmaN/mm2


-0,0008

-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

120 140 160 180 200 220 240


Strain[

m/m]

Strain 1 Strain 2

y = 24428x + 28,766

10

15

20

25

30

35

40

-0,0006 -0,0004 -0,0002 0 0,0002 0,0004 0,0006

strain [ m/m ]

Sigma

N/mm2


-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

0,0006

320 340 360 380 400Signal Nr [ 0.5 sec / sign 0.1 Hz ]

Strain

[m/m]

Strain 1 Strain 2

-0,0002

00,0002

0,0004

0,0006

0,0008

0,001

0 20 40 60 80 100 120


Strain[m/m]

Strain 1 Strain 2

y = 23948x + 16,033

10

1520

25

30

35

40

-0,0002 0 0,0002 0,0004 0,0006 0,0008 0,001

Strain [ m/m ]

Sig

maN/mm2


-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

0,0006

250 300 350 400 450 500 550


S

train[m/m]

Strain 1 Strain 2

y = 23660x + 25,825

10

15

20

25

30

35

40

-0,0006 -0,0004 -0,0002 0 0,0002 0,0004 0,0006

Strain [ m/m ]

SigmaN/mm2



49/58




Figure 27 Graphs of detailed measurement and E-modulus of LWA-C1.

In table 5 the values of the E-modules obtained from the graphs are ranged.

Table5 Values of E-modules during test LWA-C1

# cycles E-modulus

2000000 23892

2500000 24230

3500000 24284

3500000 23911

6800000 24372

7600000 24428

7600000 23948

7600000 23660

8200000 23835

9200000 23993

10100000 23971

-0,0008

-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

100 120 140 160 180 200 220 240 260 280 300


Strain[m/m]

Strain 1 Strain 2

y = 23835x + 29,94

10

1520

25

30

35

40

-0,0008 -0,0006 -0,0004 -0,0002 0 0,0002 0,0004

Strain [ m/m ]

Sigm

aN/mm2


-0,0008-0,0006

-0,0004

-0,0002

0

0,0002

0,0004

320 360 400 440 480 520 560


Strain[m/m]

Strain 1 Strain 2

y = 23993x + 31,365

10

15

20

25

30

35

40

-0,0008 -0,0006 -0,0004 -0,0002 0 0,0002 0,0004

Strain [ m/m ]

SigmaN/mm2


y = 23971x + 19,645

10

15

20

25

30

35

40

-0,0004 -0,0002 0 0,0002 0,0004 0,0006 0,0008

Strain [ m/m ]

SigmaN/mm2


-0,0004

-0,0002

0

0,0002

0,0004

0,0006

0,0008

100 120 140 160 180 200 220 240 260


Strain[m/m]

Strain 1 Strain 2


50/58




Remark:some values (#cycles) are given twice: this means the test has been stopped for a pe-

riod of time. The measurements took place right before stopping and right after proceeding the

test. Three times 7600000: ditto, one times extra because of breaking of the cable.

The specimen did not fail before the 10 million loading cycles were achieved.

10.3.3.1 Compression test LWA-C2In Table 6 the values of the forces and the displacements are given during the test.

Table 6 Forces and displacement during test LWA-C2


0 231,6 114,9 -1,38 -1,99

789000 231,6 114,8 -1,29 -1,89

790000 231,6 114,9 -1,29 -1,88

2446233 231,7 115,1 -1,22 -1,82



The graphs of detailed measurements during the test are shown in Figure 28, similar to LWA-

C1.

Figure 28 Graphs of detailed measurement and E-modulus of LWA-C2.

y = 21952x + 20,901

0

5

10

15

2025

30

35

-0,0004 -0,0002 0 0,0002 0,0004 0,0006 0,0008

Strain [m/m]

SigmaN/mm

2


-0,0004

-0,0002

0

0,0002

0,0004

0,0006

0,0008

1 9 1 7 25 33 41 49 57 65 73 81 89 97

Signal Nr [0,5sec/sign 0,1Hz]

Strain[m/m

]

Strain 1 Strain 2

-0,0002

0

0,0002

0,0004

0,0006

0,0008

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99

Signal Nr [0,5sec/sign 0,1 Hz]

Strain

[m/m]

Strain 1 Strain 2

y = 21751x + 18,707

0

510

15

20

2530

35

-0,0002 0 0,0002 0,0004 0,0006 0,0008

Strain [m/m]

Sigm

aN/mm2



51/58




In table 7 the values of the E-modules are ranged.

Table 7 Values of E-modules during test LWA-C2# cycles E-modulus

790.000 21952

2.440.000 21751

The specimen did not fail before the 10 million loading cycles were achieved.

10.4 Performed tension-compression test

10.4.1 Applied loading scheme

The base of the test is loading the specimen between 42% of the flexural strenght and 10 % ofthe characteristic strength. For a specimen with a surface area of 68*98 mm, a characteristic

compression strenght of 55 N/mm and a flexural strenght of 3,8 N/mm, this means a maximum

maximum compression force of 0,1*55*68*98=21,99kN and maximum tensile force of

0,45*3,8*68*98=10,99 kN. In testing this means a static force of 5 kN and an amplitude of 15

kN.

10.4.2 Measuring procedureThe measuring procedure and the measurements are equal to those in the compression test.

10.4.3 Measuring resultsThere have been conducted several tests for the fatigue capacity under compression/tension

forces. During the execution it appeared that there had to be made an adjustment in the forces,

because of early failure of the specimen.

The first specimen collapsed during the positioning-procedure, at a tensile force of 2 kN. See

figure 29.

Figure 29 Failure of the specimen at tensile force of +2 kN


52/58




It was necessary to take a new specimen. The stresses were adjusted, taking into account the

mass of LWA-concrete. The maximum tensile stress was determined on

0,42*1,9*(2000/2400)=0,66 N/mm. The maximum compressive stress did not change.

The new combination of stresses give the following combination of required forces on thespecimen with an area of 68*98 mm: a static value of 8,7 kN with an amplitude of 13,1 kN.

The second specimen cracks before the first cycle, just outside the test-area. See figure 30.

Figure 30 Glued crack just outside the test-area.

The crack was glued and the specimen is tested under the adjusted load of Fmax=-21,9 kN and

Fmin=+4,6 kN at a frequency of 10 Hz.

After 1,1 million cycles one strain-measurer indicates a crack. It appeared to be a crack in themiddle of the test area. At the same time the glued area on the bottom joint was loose: Figure

31.

Figure 31 the glue joint let loose


53/58




Figure 32 Crack through strain measurer (detail).

The specimen failed and had to be replaced.

The only available specimen was the one used in the compression test. After positioning the

specimen the next combination of forces was generated: Fmax=-23,1 kN and Fmin=+4,5 kN at a

frequency of 10,5 Hz.

After 1250 cycles the glued surface at the bottom let loose. The specimen was positioned again

with forces: Fmax=-22,5 kN and Fmin=+4,5 kN at a frequency of 11 Hz.

Finaly the test was running during 10 million cycles.

10.4.3.1. Compression/tension test LWA-TC1In Table 8 the values of the forces and the displacements are given during the test.

Table 8 Forces and displacements during the test LWA-TC1


0 22,5 -4,5 -4,06 -3,86

4500000 22,3 -4,5 -4,13 -3,91

5500000 22,3 -4,5 -4,11 -3,90

6400000 22,5 -4,5 -4,13 -3,90

10200000 22,5 -4,4 -4,11 -3,88



The graphs of detailed measurements are shown in Figure 33 Similar to the compression test the

left graph shows the train measured during a period of time, and right graph the determination

of the E-modulus.


54/58




Figure 33 Graphs of detailed measurements and E-modulus of LWA-TC1

-0,0004

-0,0003

-0,0002-0,0001

0

0,0001

0,0002

1850 1860 1870 1880 1890 1900 1910 1920Signal Nr [ 0.5 sec / sign 0.1 Hz ]

Strain[m/m]

Strain 1 Strain 2

y = 19611x - 1,3459

y = 16067x - 0,1364

-6

-5

-4

-3

-2

-1

0

1

-0,0004 -0,0003 -0,0002 -0,0001 0 0,0001 0,0002

Strain [ m/m ]

SigmaN

/mm2

Strain 1 Strain 2Linear (Strain 1) Linear (Strain 2)

-0,0001

0

0,0001

0,0002

0,0003

0,0004

2220 2240 2260 2280 2300


Strain

[m/m]

Strain 1 Strain 2

y = 19710x - 0,6448

y = 16255x + 0,1286

-2

0

2

4

6

-5E-05 0 0,00005 0,0001 0,00015 0,0002 0,00025 0,0003 0,00035

Strain [ m/m ]

Sigm

aN/mm2


y = 15857x + 0,1519

-2

0

2

4

6

-0,0015 -0,001 -0,0005 0 0,0005

Strain [ m/m ]

SigmaN/mm2


-0,0015

-0,001

-0,0005

0

0,0005

6380 6400 6420 6440 6460 6480


Stra

in[m/m]

Strain 1 Strain 2

-0,0003

-0,0002

-0,0001

0

0,0001

0,0002

0,0003

6950 6960 6970 6980 6990 7000 7010


Strai

n[m/m]

Strain 1 Strain 2

y = 19611x - 2,2228

y = 16318x - 0,0719

-6

-4

-2

0

2

-0,0003 -0,0002 -0,0001 0 0,0001 0,0002 0,0003

Strain [ m/m ]

SigmaN/mm2



55/58




The measurements of the E-modules are ranged in Table 9.

Table 9 Trend E-modulus during test LWA-TC1

# cycles Eleft Eright Eaverage

4500000 19611 16318 179655500000 19611 16067 17839

6400000 19710 16255 17983

10200000 - 15857 -

Between 6,4 and 10,2 million cycles the value of the left strain-measurer shows a constant

value. It indicates the strain-measurer let loose. This is the reason the last value of the E-

modulus on the left side is not calculated.

The second test in compression/tension is conducted on a specimen of a new series. The base of

the second test is 2,0 million cycles.

10.4.3.2 Compression/tension test LWA-TC2In Table 10 the values of the forces and the displacements are shown during the test.

Table 10 Forces and displacements during the test LWA-TC2


0 22,1 -4,6 -4,05 -3,85

3.200.000 22,7 -4,3 -4,07 -3,85



The graphs of detailed measurements are shown in Figure 34.

Figure 34 Graphs of detailed measurements and E-modulus of LWA-TC2

The result is given in table 11

Table 11 Trend E-modulus during test LWA-TC2

# cycles Eleft Eright Eaverage3.200.000 22682 22681 22682

-0,00015

-0,0001

-0,00005

0

0,00005

0,0001

1 21 41 61 81 101Signal Nr [0,5 sec / sign 0.1 Hz ]

Strain[m/m]

Strain 1 Strain 2

y = 22682x + 2,3302

y = 22681x + 2,4815

-1

0

1

2

3

4

5

-0,00015 -0,0001 -0,00005 0 0,00005 0,0001Strain [m/m]

SigmaN/mm2

Strain 1 Strain 2L inear (St ra in 2) L inear (St ra in 1)


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10.4.4 Analyses and conclusionsIn order to analyse the results of the tests, the specimens are submitted to a static test. This gives

information about the E-modulus of the concrete. The static tests have been conducted with a

reference-prism and with some of the test specimens. In the test the compression force is in-

creased and the E-modulus is determined between 30 and 95% of the maximum force.

The results of the obtained E-modules are given in Table 12.

Table 12 E-modules of static tests

Specimen Eleft Eright EaverageReference-prism 21592 22739 22166

Compression #1 24340 24771 24556

Tension/compr.#1 25597 25193 25395

Tension/compr. #2 25664 25089 25377

The results show the E-modulus in a static compressive situation is about 24000 N/mm.

In comparison with the results of the fatigue tests it appeared the specimen in the compression

tests had a similar E-modulus during the whole test. The value of the E-modulus in the first

compression/tension test is low compared with the static value. Still, the specimen did succeed

the fatigue test. The second compression/tension test shows normal values of the E-modulus.

It can be concluded that both tests did succeed in the fatigue test. The compression test gave no

problems. The reduction of the E-modulus is negligible.

The compression/tension tests gave some problems at starting a test. The biggest problems wererising when the specimen got under a tensile force. A few times the glue-joint did fail and some-

times the specimen itself failed under a static tension. The problems with the glue-joint were

caused by the smooth surface of the glue-area. Under a little tension the outside skin of the area

let loose. Often the second time went well, because of the better grip of the glue. The early fail-

ure of the specimen under a tensile force can be explained through the inhomogene structure of

the concrete. Despite the start-problems the test succeeded while it was running.

In total there are conducted four successful fatigue tests on LWA-concrete specimens. Two

tests, one compression and one compression/tension test, reached 10 million cycles, while the

other two reached about 3 million cycles.

The value of the E-modulus is a good indicator for decreasing resistance against fatigue. In all

tests the reduction was small. The results of the tests show the LWA-concrete has sufficient fa-

tigue resistance under the given stresses.


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11 REFERENCES[1] Siemes Vermoeiing van beton deel 1: drukspanningen; IRO-MaTS/CUR VB rapport

112, Gouda, december 1983.

[2] Cornelissen & Jakobs Vermoeiing van beton deel 2: trek-en trekdrukspanningen;

IRO-MaTs/CUR VB rapport 116, Gouda, oktober 1984.

[3] Cornelissen & Jakobs: Vermoeiing van beton deel 3: trek- en trekdrukspanningen

(2); IRO-MaTS/CUR VB rapport 137, Gouda, december 1988.

[4] Siemes: Vermoeiing van beton deel 4: drukspanningen (2); IRO-MaTS/CUR VB

rapport 163, Gouda, april 1993.

[5] Siemes: Vermoeiing van beton, rekenprocedure en achtergronden;IRO-MaTS rap-

port 93-13, Gouda, december 1993.[6] Cornelissen: constant amplitude tests on plain concrete in uniaxial tension and tens i-

on-compression rapport 5-84-1, januari 1984.

[7] Cornelissen & Timmers: Fatigue of plain concrete in uniaxial tension and alternating

tension-compressionrapport 5-81-7, oktober 1985.

[8] Cornelissen: State of the art report on fatigue of plain concreterapport 5-86-3, okto-

ber 1986.

[9] Hordijk:Local approach to fatigue of concrete, Oud-beijerland, 1991.

[10] Hordijk:Tensile and tensile fatigue behaviour of concrete; experiments, modelling

and analyses, Heron rapport vol. 37, 1988, no.3.

[11] Siemes: Fatigue evaluation of concrete structures Preliminary studies, procedures and

examples, Heron rapport vol. 33, 1988, no.3.[12] Petkovic:Properties of concrete related to fatigue damage with emphasis on high

strength concrete,Trondheim, december 1995.


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12 NOMENCLATURELWA Lightweight aggregate

LWAC Lightweight aggregate concrete

NDA Normal density aggregate

NDC Normal density concrete

HSC High strength concrete

w/b water binder ratio

w/c water cement ratio

CEB Comit Euro-international du Bton

CEN Comit Europen de NormalisationCTR Cost Time Resources (form)

EN European Standard

FIB Fderation Internationale du Bton

FIP Fderation Internationale de la Prcontrainte

MG Management Group

TC Technical Committee (CEN)

TG Task Group

TLG Task Leaders Group

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