Abstract
The dimensioning of concrete structures for restraint effects caused by
deformation controlled loads has in practice been shown to be difficult.These
loads have therefore often been ignored, even in service state dimensioning,
although their values are greatest just in the service state.This neglect,
sometimes even deliberate, has often led to premature and unexpected cracking
of structures and to other defects arising from cracking.In accordance with
quality concepts in modern construction, the cracking of a reinforced concrete
structure is a quality defect which should be avoided as far as possible or
is to be limited at least to an acceptable level For the purpose of crack
limitation a behaviour model for the structural elementary unit of a one
dimensional structure was formed as follows.The length of the crack spacing
was chosen as the length of the elementary unit, which thus decreases when the
steel stress rises.The initiation density of new cracks is determined by the
density function of the limited normal distribution, which also defines the
crack spacing corresponding to the degree of steel stress.The internal
stresses of the structural elementary unit and the relative deformations, as
well as the slips, are determined by starting from the basic equations of the
interaction between the concrete and reinforcement, which pertain to the so
called sliding bond mechanism.The effect of the socalled non sliding bond
mechanism is combined with the behaviour model by assigning that the bond does
not act over a certain distance on both sides of the crack.This distance was
determined experimentally.The rigidity of the structural elementary unit under
different stress conditions and an approximate appraisal method for rigidity
suitable for manual calculation are also determined by the average strains to
be calculated.The relaxation of restraint effects due to cracking can also be
determined by the proposed method applicable to calculation by a computer.
Using this method the weighted rotations of structural elementary units are
converted into the support rotations, and the corresponding moments are
corrected by the amount which corresponds to the rotation.In order to limit
the cracks caused by restraint effects a closed solution, which is valid in a
limited region and based on the differential equation of sliding bond, is
presented together with a corresponding numerical solution also including
portions of non sliding bond, and which can be used for limiting cracking due
to the restraint effect or brought about by combined load and restraint
effects.For the purpose of dimensioning, diagrams are presented for different
stress types and different concrete strengths, for all bar sizes in use and
the bars having different bond properties and for different reinforcement
levels as well as different variation coefficients of the tensile strength of
concrete.In the experimental section, short term load tests were performed
with two types of statically indeterminate structures which were subjected to
indirect action or direct action or both In the long term tests the statically
indeterminate beams were subjected to the stress of a thermal gradient or a
certain settlement at one support which was forced to take place suddenly and
slowly.The results were compared with the calculated results using a developed
model based on the randomness of crack spacing and on the physical
interaction between the concrete and the reinforcement as established
empirically.No theoretical model for examination of a time effect is
presented.The test results, however, give a suggestive idea of the relaxation
of restraint effects due to temperature and time.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  19 Dec 1986 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513827259 
Publication status  Published  1986 
MoE publication type  G4 Doctoral dissertation (monograph) 
Keywords
 concrete structures
 restraint effects
 temperature
 cracking
 randomness
 dimensioning
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Cite this
Jokela, J. (1986). Dimensioning of strain or deformationcontrolled reinforced concrete beams: Dissertation. VTT Technical Research Centre of Finland.