5 research outputs found
Modeling of viscoelastic properties of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) under low to high tensile stresses
The purpose of this paper is to explore the UHPFRC time-dependent behavior under sustained tensile loading at very early age (3 days) and to highlight its sensitivity to the level of loading by laboratory testing and numerical analysis. Uniaxial creep and relaxation tests were performed at 3 days age at various stress levels by means of a Temperature-Stress Testing set-up (TSTM). Under low tensile stresses, the material exhibits a linear viscoelastic behavior. Under high tensile stresses the creep response becomes non-linear. A numerical algorithm was used to convert the creep results into relaxations and compare them with measured relaxations. A generalized Maxwell chain model was applied to predict the UHPFRC tensile relaxations at a low load level
TENSILE CREEP OF UHPFRC UNDER LOW AND HIGH STRESSES
The purpose of this paper is to investigate experimentally the UHPFRC time-dependent behavior under sustained tensile loading and to determine the effect of the stress level on the creep response. Uniaxial tensile creep tests were performed at various stress levels by means of an optimized testing set-up. An Acoustic Emissions equipment was used in parallel to correlate the creep deformations with damage. From 29 % to 85 % stress level, the material exhibited a linear viscoelastic behavior. The UHPFRC response under higher stress levels close to strain hardening remains an open question
Time-Dependent Response of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) under Low to High Tensile Stresses
Ultra High Performance Fibre Reinforced Concretes (UHPFRC) are characterised by high mechanical performance, extremely low permeability and tensile strain hardening. For structural applications, in composite structures they are very well adapted for reinforcement and protection of existing concrete members. Cast in-situ, they undergo under restraint development of tensile eigenstresses at early age, which can lead in some specific cases of applications to localised macrocracking of a new layer and loss of protective function. On the other hand their tensile viscoelastic potential helps mitigate these stresses. The objective of this study was to investigate the tensile viscoelastic properties of UHPFRC at early ages and long-term in creep and relaxation tests. A large experimental campaign with tensile creep and relaxation tests was performed, with load levels ranging from 30 to 90% of the tensile strength, including creep and relaxation tests during the strain hardening phase, at two different loading ages of 3 and 7 days. Three main testing setups were used: TSTM (Temperature Stress Testing Machine), creep rigs and closed-loop servo-hydraulic testing machine with additional Acoustic Emission detection. The influence of early age evolution in mechanical response and underlying mechanisms governing this response were discussed. Linear viscoelastic models were used to analyse and to highlight on the basis of the experimental results the non-linear behavior depending on solicitation level and loading sequence. The non-linear threshold for viscoelastic response was estimated for the material loaded at 3 and 7 days. The early age mechanical response at 3 days was proportional to the load level in the instantaneous part for three stress levels tested 30, 60 and 90% of the tensile strength, and showed non-linear creep from 60% on. It was observed that for a very low stress level of 13% the creep deformation was decreasing. Relaxation tests with compensation of simultaneously monitored shrinkage deformation were performed, and showed a viscoelastic potential similar to the one observed for creep for the low load level of 30%. Incremental creep and relaxation tests were successfully performed for 3 days age specimens. For higher stress levels, the viscoelastic response from creep tests was more pronounced than in relaxation tests, which was highlighted by analysis with linear viscoelastic models. The creep response at 7 days showed that the threshold for non-linear viscoelasticity is close to 9 MPa (81% of the tensile strength) load level. The Acoustic Emission non-destructive testing method was used to get insight on the physical mechanisms involved in viscoelastic deformations. A strong correlation between AE number of events and the deformation was found, also the amplitude and energy of AE events was found to be of the same order during the instantaneous and delayed deformations. UHPFRC loaded at 7 days age in incremental test showed linear behavior until very high stress level corresponding to the hardening domain. The non-linear and tertiary creep was obtained during the last loading step, for 12 and 11 MPa respectively, which occurred in the hardening domain. The Acoustic Emission monitoring confirmed very close correlation between non-linear creep and AE cumulative number of events induced by microcracking. In order to precisely detect non-linear phenomena in incremental test, analysis with linear viscoelastic models was performed. Comparison between creep and relaxation test results showed that non-linear viscoelastic phenomena were more actively involved in creep tests. The outcomes of this research, bridging the material science and structural engineering, provide useful data to foster applications in new and existing structures, making the best use of the tensile viscoelastic potential of UHPFRC
Estructura del mercado laboral mexicano: División y movilidad entre los sectores formal e informal
Modeling of viscoelastic properties of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) under low to high tensile stresses, Symposium on Concrete Modelling
Abstract The purpose of this paper is to explore the UHPFRC time-dependent behavior under sustained tensile loading at very early age (3 days) and to highlight its sensitivity to the level of loading by laboratory testing and numerical analysis. Uniaxial creep and relaxation tests were performed at 3 days age at various stress levels by means of a Temperature-Stress Testing set-up (TSTM). Under low tensile stresses, the material exhibits a linear viscoelastic behavior. Under high tensile stresses the creep response becomes non-linear. A numerical algorithm was used to convert the creep results into relaxations and compare them with measured relaxations. A generalized Maxwell chain model was applied to predict the UHPFRC tensile relaxations at a low load level