AMCM 2011 Presentation for "Numerical analysis of early-age thermal and moisture effects in RC wall"

Numerical analysis of early-age

thermal and moisture e�ects in RC wall

DSc. Eng. Barbara KLEMCZAKMSc. Eng. Agnieszka KNOPPIK�WRÓBEL

Silesian University of TechnologyFaculty of Civil Engineering

Cracow, 14 June 2011

IntroductionNumerical model

Analysis of RC wallConclusions

Introduction

concrete curing

cement hydration process

dissipation of heat and migration of moisture

temperature and moisture gradients

stresses

self-induced, restraint stresses in structure

Barbara Klemczak, Agnieszka Knoppik Early-age thermal�moisture e�ects in RC wall



Introduction

thermal�moisture in�uences

massive structures

foundations

gravity dams

medium-thick restrained structures

RC walls of tanks, abutments, castagainst old foundation




Thermal and moisture analysisThermal�shrinkage strainsStress analysisImplementation

General assumptions

1 phenomenological modeldecoupling of thermal�moisture and mechanical �elds

full coupling of thermal�moisture �elds

2 stress state determined under the assumption thatthermal�moisture strains have distort character

3 viscoelasto�viscoplastic material model of concrete





Thermal and moisture analysis

Coupled thermal�moisture equations

T = div(αTT gradT + αTW gradc) +1cbρ

qv

c = div(αWW gradc + αWT gradT )− Kqv

Initial conditions

T (xi , t = 0) = Tp(xi , 0)

c(xi , t = 0) = cp(xi , 0)

Boundary conditions

nT (αTT gradT + αTW gradc) + q = 0

nT (αWW gradc + αWT gradT ) + η = 0





Thermal�shrinkage strains

Imposed thermal�shrinkage strains εn:

volumetric strains

dεn =[dεnx dεny dεnz 0 0 0

]calculated based on predetermined temperature and humidity

dεnx = dεny = dεnz = αT dT + αW dW





Stress analysis

viscoelastic area

σ = Dve(ε− εn − εc)

viscoelasto�viscoplastic area

σ = Dve (ε− εn − εc − εvp)

Figure 1: Failure surface

possibility of crack occurrence

sl =τoct

τ foct

Figure 2: E�ort level





Implementation

A set of programs:

TEMWIL

thermal�moisture �elds

MAFEM

stress analysis




General caseParametric study

Input data

concrete class C25/30, steel class RB400cement type CEM I 32.5R, 450 kg/m3,temp.: ambient Tz = 25◦C, initial of concrete Tp = 25◦C,wooden formwork of 1.8 mm plywood, no insulation, noprotection of top surface; removed in 3 days (72h).

Figure 3: Geometry and �nite element mesh of analysed wall





Thermal and moisture analysis

Figure 4: Temperature distribution in the wall [◦C] after 16 hours

Figure 5: Moisture distribution in the wall (x100) after 16 hours





Stress analysis

1.2

1.8

2.4

stre

ss [

MPa

]

-1.2

-0.6

0

0.6

0 2 4 6 8 10 12 14 16 18 20

stre

ss [

MPa

]

time [days]

Figure 6: Stress σx in time for cracked (surface) element





Stress analysis

(a) at expansion (16 hours) (c) at contraction (4.5 days)

Figure 7: Stress distribution





Parametric study of thermal�moisture cracking

(a)XZ=0m (b)YZ=3.5m

(c)XZ=0.35m (d)YZ=10m

Figure 8: Cracking pattern�basic case

Analysed parameters:

1 Tp and Tz

2 time of formworkremoval





In�uence of placing and adjoining concrete temp. di�.

(a) XZ=0m (b) YZ=3.5m

(c) XZ=0.35m (d) YZ=10m

Figure 9: Cracking�Tp = Tz = 15◦C

(a) XZ=0m (b) YZ=3.5m

(c) XZ=0.35m (d) YZ=10m

Figure 10: Cracking�Tp = 15◦C , Tz = 25◦C





In�uence of time of formwork removal

(a) XZ=0m (b) YZ=3.5m

(c) XZ=0.35m (d) YZ=10m

Figure 11: Cracking�removal after 7 days

(a) XZ=0m (b) YZ=3.5m

(c) XZ=0.35m (d) YZ=10m

Figure 12: Cracking�removal after 25 days




Conclusions

Importance

need to ensure desired service life and function of the structure

on-going examination of early-age cracking problem

Numerical model

qualitatively and quantitatively proper results

conformation with present knowledge and experience

Contribution

multi-parameter numerical model of thermal�moisture e�ects inearly-age concrete and its implementation


AMCM 2011Cracow, 14 June 2011

AMCM 2011 Presentation for "Numerical analysis of early-age thermal and moisture effects in RC wall"

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Transcript of AMCM 2011 Presentation for "Numerical analysis of early-age thermal and moisture effects in RC wall"