TY - RPRT
T1 - Material Modelling - Composite Approach
AU - Nielsen, Lauge Fuglsang
PY - 1997
Y1 - 1997
N2 - This report is part of a research project on "Control of Early Age
Cracking" - which, in turn, is part of the major research
programme, "High Performance Concrete - The Contractor's
Technology (HETEK)", coordinated by the Danish Road Directorate,
Copenhagen, Denmark, 1997.A composite-rheological model of
concrete is presented by which consistent predictions of creep,
relaxation, and internal stresses can be made from known concrete
composition, age at loading, and climatic conditions. No other
existing "creep prediction method" offers these possibilities in
one approach.The model is successfully justified comparing
predicted results with experimental data obtained in the
HETEK-project on creep, relaxation, and shrinkage of very young
concretes cured at a temperature of T = 20^o C and a relative
humidity of RH = 100%. The model is also justified comparing
predicted creep, shrinkage, and internal stresses caused by drying
shrinkage with experimental results reported in the literature on
the mechanical behavior of mature concretes. It is then concluded
that the model presented applied in general with respect to age at
loading.From a stress analysis point of view the most important
finding in this report is that cement paste and concrete behave
practically as linear-viscoelastic materials from an age of
approximately 10 hours. This is a significant age extension
relative to earlier studies in the literature where
linear-viscoelastic behavior is only demonstrated from ages of a
few days. Thus, linear-viscoelastic analysis methods are justified
from the age of approximately 10 hours.The rheological properties
of plain cement paste are determined. These properties are the
principal material properties needed in any stress analysis of
concrete. Shrinkage (autogeneous or drying) of mortar and concrete
and associated internal stress states are examples of analysis
made in this report. In this context is discussed that concrete
strength is not an invariable material property. It is a property
the potentials of which is highly and negatively influenced by any
damage caused by stress concentrations such as introduced by
eigenstrain/stress actions like shrinkage, temperature, and
alkali-aggregate reactions.Based on the overall positive results
reported it is suggested that creep functions needed in Finite
Element Analysis (FEM-analysis) of structures can be established
from computer-simulated experiments based on the model presented -
calibrated by only a few real experiments.
AB - This report is part of a research project on "Control of Early Age
Cracking" - which, in turn, is part of the major research
programme, "High Performance Concrete - The Contractor's
Technology (HETEK)", coordinated by the Danish Road Directorate,
Copenhagen, Denmark, 1997.A composite-rheological model of
concrete is presented by which consistent predictions of creep,
relaxation, and internal stresses can be made from known concrete
composition, age at loading, and climatic conditions. No other
existing "creep prediction method" offers these possibilities in
one approach.The model is successfully justified comparing
predicted results with experimental data obtained in the
HETEK-project on creep, relaxation, and shrinkage of very young
concretes cured at a temperature of T = 20^o C and a relative
humidity of RH = 100%. The model is also justified comparing
predicted creep, shrinkage, and internal stresses caused by drying
shrinkage with experimental results reported in the literature on
the mechanical behavior of mature concretes. It is then concluded
that the model presented applied in general with respect to age at
loading.From a stress analysis point of view the most important
finding in this report is that cement paste and concrete behave
practically as linear-viscoelastic materials from an age of
approximately 10 hours. This is a significant age extension
relative to earlier studies in the literature where
linear-viscoelastic behavior is only demonstrated from ages of a
few days. Thus, linear-viscoelastic analysis methods are justified
from the age of approximately 10 hours.The rheological properties
of plain cement paste are determined. These properties are the
principal material properties needed in any stress analysis of
concrete. Shrinkage (autogeneous or drying) of mortar and concrete
and associated internal stress states are examples of analysis
made in this report. In this context is discussed that concrete
strength is not an invariable material property. It is a property
the potentials of which is highly and negatively influenced by any
damage caused by stress concentrations such as introduced by
eigenstrain/stress actions like shrinkage, temperature, and
alkali-aggregate reactions.Based on the overall positive results
reported it is suggested that creep functions needed in Finite
Element Analysis (FEM-analysis) of structures can be established
from computer-simulated experiments based on the model presented -
calibrated by only a few real experiments.
M3 - Report
BT - Material Modelling - Composite Approach
ER -