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A novel steel-UHPFRC composite deck system, consisting of upper thin reinforced UHPFRC slab, hot rolled sections as longitudinal ribs, and steel strips as transversal reinforcement, is proposed originally in this paper. Considered as more economic and sustainable structure, the new composite deck is a promising alternative to traditional orthotropic steel deck (OSD) in long-span bridge. In this context, due to the relatively thin UHPFRC layer, the punching behavior of new composite deck becomes one of the dominant issues, which determines the spacing of steel trips. Hence, this paper presents the results of punching tests on 12 new composite deck slabs with various spacing of steel strips. All slabs failed in punching-flexure mode with a clearly delimited punching cone and significant flexural cracks on tensile surface. Moreover, the presence of steel strips can increase the punching shear resistance and flatten the inclination of critical shear cracks.

A lightweight steel-UHPFRC composite beam structure, consisting of a half rolled section with in- built steel dowels as connectors and a T-shaped UHPFRC component, is proposed originally in this paper. The excellent properties of steel and UHPFRC materials can be exploited fully and properly, and the presence of in-built steel dowel is expected to allow effective force transmission between steel and UHPFRC components, benefiting from its higher shear resistance and ductility. Two composite beams with various heights of UHPC web are tested by 4PBT method, aiming at validating this concept and investigating the flexural behavior under sagging moment. And a high resolution Digital Image Correlation (DIC) system is applied during testing, in addition to conventional measuring techniques. Moreover, the sectional analysis method considering the tensile properties of UHPFRC is applied to predict the flexural.

The article “An analytical inverse analysis to determine equi-biaxial tensile properties of strain-hardening UHPFRC from ringon-ring test”, written by Xiujiang Shen, Eugen Bruhwiler, Emmanuel Denarie and Wanghu Peng was originally published electronically on the publisher’s.

The equi-biaxial tensile properties of strain-hardening UHPFRC are determined and investigated based on an original analytical inverse analysis of results from ring-on-ring tests. First, the analytical inverse analysis method is developed based on the elastic slab bending and yield line theories. Using this method, a new objective criterion for the determination of the elastic limit stress of strain-hardening UHPFRC is provided, and a point-by-point inverse analysis is used to obtain the strain value at the end of hardening. This method reduces uncertainties regarding assumptions and avoids any iterative procedures. The inverse analysis results are put into perspective with experimental evidence, particularly based on DIC measurements. Moreover, the uniaxial tensile properties are also derived from the inverse analysis of 4PBT results and compared with the equi-biaxial tensile properties from the proposed inverse analysis. The inverse analysis results show a 18% lower elastic limit stress, and almost equivalent tensile strength of UHPFRC subjected to equi-biaxial stresses, compared with the corresponding values from uniaxial stress. Moreover, a relatively small equi-biaxial strain at the end of hardening is highlighted.

This paper investigates experimentally the equi-biaxial flexural fatigue behavior of thin circular slab specimens made of Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRC), using ring-on-ring test method. The circular slab-like specimens represent an external tensile reinforcement layer for reinforced concrete (RC) slabs or a new thin slab element for the application, e.g. in bridge construction. Four series of flexural fatigue tests under constant amplitude fatigue cycles up to Very High Cycle Fatigue (20 million cycles) are conducted with varying stress levels S ranging from 0.47 to 0.76, targeting at the endurance limit of UHPFRC material and fatigue damage propagation under equi-biaxial stress condition. By means of digital image correlation (DIC) system, the tensile surface of each slab is monitored continually during testing, and the fatigue damage evolution is studied in terms of central deflection propagation. Based on the fatigue test results, a fatigue endurance limit is determined to be S=0.50, and four stages of fatigue damage evolution are characterized for the UHPFRC slabs with fatigue failure.

Orthotropic steel bridges were found to experience early fatigue failures of several welded connections in the steel deck plate. The welding process inevitably produces welding residual stresses and deformations that should be evaluated and considered to better understand the fatigue life of steel bridges. Aiming to study the residual stress distribution of hybrid steel u-rib stiffened plates, the blind hole method was applied. Various parameters, including the plate widths, the ratio of the u-rib thickness to the motherboard thickness, and the steel strength of the combination of the u-rib with the motherboard, were considered, and nine specimens were subjected to experimental tests. The results indicate that strain release factors have great impact on the calculated residual stress: as the value of strain release factor increases, the calculated residual stress in absolute term increases accordingly. However, due to experimental errors, as the ratio of the motherboard to the u-rib thickness varies from 1:2 to 1:2.5 and the u-rib spacing increases from 120 mm to 160 mm, the residual stress value and the distribution change are not obvious; when different steel strengths were used in the specimens, as the material yield strength of the motherboard (u-rib) increases, the residual tensile stress peaks of the motherboard (u-rib) increase, while the residual tensile stress distribution of the u-rib (motherboard) remains essentially the same. Based on the comparison between the cutting method and the blind hole method, the values from residual stress test points appear to be similar; from the perspective of measuring points' distribution and the directions of the tested residual stress, the cutting method cannot test the weld location, and the residual stress at the measuring point can only be obtained along the cutting direction because the blind hole method can test the weld location residual stress, and the residual stress of the measuring point can be obtained in any direction.

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.

Representative and accurate characterization of the tensile behavior of strain hardening Ultra High Performance Fiber Reinforced Cementitious Composite (UHPFRC) remain a challenge. Currently, the uniaxial methods, like direct tensile test (DTT) and 4-point bending test (4PBT), are commonly applied, although the biaxial tensile condition has been widely recognized in the UHPFRC applications, e.g. thin UHPFRC layers as external reinforcement for RC slabs. In this paper, results from ring-on-ring testing of circular slab-like specimens are presented to determine the equi-biaxial tensile response by means of inverse analysis using 3D finite element method (FEM). In addition, DTT, using structural specimens cut from large square plates, and 4PBT, using standard specimens cast in mould individually, were carried out. The tensile response from 4PBT was derived through inverse analysis using 2D FEM. Finally, the corresponding results from the three different testing methods under either uniaxial or biaxial stress condition were analyzed and compared in terms of tensile characteristic parameters, tensile material law, fracture process, and energy absorption capacity. While the three testing methods did not show significant difference in tensile strength, significantly higher strain hard-ening deformation was identified in the case of biaxial stress conditions.

The biaxial flexural fatigue behavior of thin slab elements made of strain-hardening Ultra High Performance Fiber Reinforced Cementitious Composite (UHPFRC) is investigated experimentally by means of the ring-on-ring test method. Fourteen flexural fatigue tests under constant amplitude fatigue cycles up to the Very High Cycle Fatigue domain (20 million cycles) are conducted with varying maximum fatigue stress level S ranging from 0.50 to 0.68. Digital Image Correlation (DIC) technology is applied to capture the 3D full-field strain contours on the tensile surface through the entire fatigue test. Test results presented in the S-N diagram reveal a fatigue endurance limit under biaxial flexural fatigue at S = 0.54. Fatigue tests exhibiting failure show four distinct phases of damage evolution, while only the first two phases are observed in the case of run-out tests. DIC analysis reveal formation and propagation of multiple fine fictitious cracks that dominate the stable fatigue propagation phase with slow rate, representing the longest part of fatigue life of the UHPFRC specimen. Finally, the secant modulus of deflection and fictitious crack opening with respect to fatigue cycles is found to characterize quantitatively fatigue damage evolution.

on-uniform fiber distribution can significantly reduce the extension of multiple-cracking and favor crack local-izations in Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) members under tension with important implication on the sought durability. This work aims at fostering the coupling between a novel Non-Destructive Technique, namely Magnetic Inductance Method (MIM), and Finite Element Method (FEM) to predict the effect of nonuniform fiber distribution on the micro-cracking response of UHPFRC samples under tensile loading.First, uniaxial tensile tests on 5 dumbbell samples of UHPFRC with 3.8% of steel fibers showed that tensile ductility is much affected by the degree of uniformity of the fiber distribution. Thus, FEM analysis was performed with the Concrete Damaged Plasticity model (CDP) in Abaqus software, where the UHPFRC tensile law was scaled by a field variable based on the fiber orientation factor and the fiber efficiency factor (li0 and li1) measured by Magnetic Inductance Method (MIM). The field variable scales the UHPFRC tensile law between an upper and a lower bound of the tensile law estimated by a fiber pull-out model and a cohesive law for concrete matrix, respectively. The accuracy of the proposed MIM-FEM method was verified against the experimental results by considering the load-displacement curve, the asymmetric displacement, the crack pattern, the fracture energy, and the evolution of the microcrack opening. Based on the presented results, the proposed MIM-FEM method can map and quantitatively analyze the effect of non-uniform fiber distribution for UHPFRC members under tension, thus providing potential application value for infrastructures, pre-casting and architectural applications more broadly.