Biaxial flexural response of Strain-Hardening UHPFRC circular slab elements

The biaxial flexural response of strain-hardening UHPFRC circular slab element is investigated experimentally and analytically using the ring-on-ring test. The Digital Image Correlation (DIC) technology is applied to capture the 3D full-field of strain and deflection of the tensile surface through the whole loading process. Based on DIC analysis, a quasi-elastic limit is determined additionally to characterize the flexural response of UHPFRC under biaxial stress condition. The random and uniform distribution of matrix discontinuities in UHPFRC in the quasi-elastic domain, as well as multiple fictitious crack formation in hardening domain, is highlighted. In addition, ring-on-ring test and Four-Point Bending Test (4PBT) results are compared with special emphasis on flexural strength and characteristics of matrix discontinuity development. The results show higher ultimate flexural strength and energy absorption capacity at ultimate limit from the ring-on-ring test, and almost same flexural strength at the quasi-elastic limit for both tests. Finally, a simplified inverse analysis is proposed for the ring-on-ring test based on the elastic slab bending and yield line theories. The calculation results indicate a 19% lower tensile elastic limit stress of the UHPFRC, while an almost equivalent value of tensile strength is obtained from the ringon-ring test, compared with the 4PBT results. (C) 2020 Elsevier Ltd. All rights reserved.

Assessment of the constitutive properties from small ball punch test: experiment and modeling

Raul Alejandro Bonadé, Emiliano Campitelli, Philippe Spätig

An assessment of the true stress-true strain relationship has been done by means of tensile and small ball punch tests on austenitic and tempered martensitic steel at room temperature. A finite element model was developed and validated to calculate the force-deflection curve obtained from the ball punch experiment. The effects of the specimen thickness and material properties on the overall shape of the ball punch test curve are discussed. The constitutive behavior assigned to the specimen for the calculations was determined from the tensile test but we showed that assumptions have to be done to extend it to large strains as those arising during the punch tests. Using an inverse methodology, it was possible to show that a linear strain- hardening stage takes place at large strains. The potential for evaluating the evolution of the strain-hardening capacity after irradiation is outlined. (C) 2004 Elsevier B.V. All rights reserved.

2004

Static and Fatigue Biaxial Flexural Behavior of Strain-Hardening UHPFRC Thin Slab Elements

Xiujiang Shen

Cast-in-place thin layers of Ultra-High Performance Fiber Reinforced Cementitious Composites (UHPFRC) on the specific zones of existing reinforced concrete (RC) bridge decks has been demonstrated to be a technically efficient and economic rehabilitation and strengthening method. In these applications, the thin UHPFRC layer, serving as tensile reinforcement, increases the bending and shear resistance of UHPFRC-RC composite members through its in-plane tensile resistance and deformability. Bridge deck slabs are the most fatigue loaded structural elements in bridges, and the actual stress state caused by wheel loading is nearly equi-biaxial and far from uniaxial. Bridge decks are expected to be subjected to a high number of fatigue stress cycles, which may exceed several hundred million. Accordingly, this thesis is devoted to study experimentally and analytically the static and fatigue biaxial flexural response of strain-hardening UHPFRC thin slab elements. For a given UHPFRC mix, there are no intrinsic tensile properties. The representative behavior, especially the strain-hardening response, is dependent on the fiber distribution. The present thesis introduces firstly the uniformity factor for considering the local fiber distribution within an UHPFRC element. Accompanied with the fiber orientation factor and efficiency factor, the influence of uniformity on the strain-hardening response of UHPFRC under uniaxial tension is investigated quantitatively by means of experimental campaign and mechanical analysis. The direct tensile test (DTT) was carried out on dumbbell specimens, extracted from a UHPFRC slab element, to characterize the tensile behavior of UHPFRC. Before tensile testing, actual fiber distribution of each specimen was measured by the non-destructive test (NDT) method using a magnetic probe. Finally, the most likely ÎŒ_2 values are determined for UHPFRC layers with different thickness. In a next step, the biaxial flexural response of UHPFRC thin slab elements using ring-on-ring test method is investigated experimentally and analytically. Based on the testing results, a quasi-elastic limit is introduced to characterize the flexural response of UHPFRC under biaxial stress condition. In addition, an in-depth comparison between ring-on-ring test and 4-Point-Bending-Test (4PBT) results, with special emphasis on flexural strength and matrix discontinuity development, is conducted. An original analytical inverse analysis method for determining the biaxial tensile properties of UHPFRC from ring-on-ring test is developed based on yield line and elastic slab bending theories. The inverse analysis results are validated against the experimental evidence, particularly based on DIC analysis. It is concluded that the elastic limit is 18% lower, and almost equivalent tensile strength of UHPFRC subjected to biaxial stresses under biaxial stress condition, compared with those under uniaxial condition. And a relatively small biaxial hardening strain is highlighted. Finally, four series of flexural fatigue tests under constant amplitude fatigue cycles up to Very High Cycle Fatigue (20 million cycles) are conducted using circular slab elements. The fatigue stress level S is ranging from 0.50 to 0.68, targeting the fatigue endurance limit of UHPFRC material and fatigue strength under biaxial stress condition. The fatigue damage evolution is analyzed in terms of central deflection as well as development of fictitious crack propagation and opening.

EPFL2020

Static and Fatigue Biaxial Flexural Behavior of Strain-Hardening UHPFRC Thin Slab Elements

Xiujiang Shen

EPFL2020