This paper presents a brief overview of the tensile test methods for concrete and cementitious composites. Comparisons of uniaxial tension test results for a round robin test conducted as part of a project of the Japan Concrete Institute Technical Committee (JCI-TC) for Ductile Fiber-Reinforced Cementitious Composites (DFRCC) are introduced. Four types of tensile test methods for four types of DFRCC were used in this round robin test. The results differ according to the testing method and compacting direction of DFRCC. The relationships between the tensile test results and tensile characteristics calculated from bending test results are discussed. The possibility of establishing a standard test method for the evaluation of the tensile characteristics of DFRCC has been discussed by the Japan Concrete Institute Standard Committee. This discussion was based on the report of the JCI-TC and the results of the round robin test. Items that were discussed in further detail were (a) difficulties of uniaxial tension test as a standard test method, (b) treatment of DFRCC that does not have a strain hardening branch in tension, (c) adaptability of strain-based evaluation for cracked materials, and (d) relationship between uniaxial tensile characteristics and bending characteristics. The Standard Committee proposed the standard test method using the 4-point bending test to obtain bending moment-curvature curves. An evaluation method for the tensile strength and ultimate strain of DFRCC was added as an appendix of non-mandatory information. This method is considered to be one of the evaluation methods for the tensile characteristics of DFRCC.
High Performance Fiber Reinforced Cement Composites (HPFRCC) show multiple cracking and strain-hardening behaviors in tension. Current applications in Japan include bridge decks, building dampers, retaining wall, irrigation channels and so forth. While the novel properties of HPFRCC are well known, the required performance and its criteria have not been clarified. For example, in addition to tensile load bearing capacity, protection against penetration of substance through fine cracks is also important. Clarification of the required performance and its criteria for HPFRCC is important to evaluate the design concepts of each application. This paper introduces recent applications using HPFRCC in Japan, focusing on required performance.
It is essential to introduce performance-based design systems and develop new technologies for meeting the social requirements of building structures. This paper begins by discussing the need for damage mitigation for building structures under performance-based design. Based on this concept, the application of a High Performance Fiber Reinforced Cementitious composite (HPFRCC) device is introduced. This device is a HPFRCC short column reinforced with steel bars that has very high strength, stiffness and ductility compared with conventional RC columns with the same configuration and bar arrangement. An analytical study on the seismic response of a soft first story building with and without such HPFRCC devices was performed as a case study to investigate the feasibility of the proposed technique for damage mitigation against large earthquakes. The results indicate that HPFRCC devices can reduce the drift angle of the soft first story from 2% to 0.5% in the case of seismic input with maximum velocity normalized at 50 cm/s. Since a drift angle of 0.5% means an elastic response of the structure, HPFRCC devices are confirmed to have significant potential as a new structural technology for damage mitigation.
High-performance fiber reinforced cement composites (HPFRCC) are highly ductile and characterized by pseudo strain hardening in tension. High-level in structural performance through the application of HPFRCC is expected. However, many uncertainties remain regarding the influence of the tensile characteristic of HPFRCC on the shear resistance mechanism of structural elements utilizing HPFRCC. Though FEM analysis is an effective engineering tool to analyze the relationship between the material characteristics and the structural performance of elements, a robust constitutive model is indispensable for obtaining accurate results. This paper proposes constitutive models based on basic test results. The proprieties of the model are confirmed based on a comparison between the analytical simulation and the structural test results for shear failure behavior. The analytical results using the proposed model match reasonably well the experimental results of HPFRCC structural elements.
Engineered Cementitious Composites (ECCs) have recently demonstrated their high performance with pseudo strain hardening (PSH) behavior in civil engineering structures and buildings. These materials incorporate low cost fibers such as Polyvinyl Alcohol fibers, which often rupture in composites. Such fiber rupture type ECCs tend to have inferior and unsaturated PSH behavior compared with those incorporating properly designed pull out type fiber. The present study focuses on presenting practical design criteria to achieve saturated PSH behavior in fiber rupture type ECCs. These criteria are proposed based on two performance indices, which are measures of energy exchange during steady state flat crack propagation and stress level to initiate micro-cracks. The latter performance index necessitates a new cracking strength prediction theory, which is proposed in the current study. Finally the cracking strength theory is justified using tensile test data, and the criteria are proposed based on the data in terms of these two indices.
Reactive Powder Concrete (RPC) reinforced with short steel fibers is characterized by ultra-high strength and high fracture toughness. Because of its excellent properties, RPC may be suitable as an advanced material for reinforced concrete structures subjected to impact loading. Thus, the objective of this study was to find out the effects of strain rates on tensile behaviors of RPC specimens subjected to rapid loading. The influence of the loading rates on failure modes, tensile stress-elongation curves and tensile stress-crack opening curves was investigated. Furthermore, based on the test results, a rate-dependent bridging law expressing the relation between tensile stress and crack opening was proposed.
The aim of this study was to develop an analytical model based on a fiber model technique for representing the behavior of a reinforced Reactive Powder Concrete (RPC) beam subjected to rapid flexural loads. In the analytical model, first, the moment-curvature relationship of the section of the RPC beam was calculated, considering the fact that the constituent materials, i.e., RPC and reinforcing steel, exhibit strain rate effects on mechanical properties. Then, the load-midspan deflection relationship was obtained through the moment-curvature relationship. The analytical model was applied to the experimental results for verification. The analytical results were in good agreement with the experimental results. Subsequently, analytical investigations were performed to find out the influence of variables, such as loading rates, compressive strengths, the amount of reinforcing steel and the volume fraction of steel fibers, on the behaviors of RPC beams.
The aim of this study was to experimentally examine the impact response of a RPC (Reactive Powder Concrete) beam and develop an analytical model to represent its impact response. Thus, a drop hammer impact test was performed to investigate the influence of drop height of the hammer on the impact response of the RPC beam. Subsequently, a static flexural loading test was conducted to find out the residual load carrying capacity of the RPC beam after impact loading. In the impact analysis, the two degrees of freedom mass-spring-damper system model was used. The analytical results were in good agreement with the experimental results when high damping for the local response at the contact point was assumed.
An experimental investigation was carried out to generate the complete stress-strain curves of steel fibre reinforced high strength concrete under axial compression. The experimental program consisted of testing 100 x 200 mm concrete cylinders. The experimental variables of the study were concrete strength levels (58.03 MPa and 76.80 MPa), volume fractions (0.5% to 2.0%) and aspect ratios (20 and 40) of flat crimped steel fibres. The effect of the mixed aspect ratio of fibres on the stress-strain behavior of steel fibre high strength concrete was also studied by blending short and long fibres. The effects of these variables on the stress-strain curves are presented and discussed. The results indicate that high strength concrete can be made to behave in a ductile manner by the addition of suitable fibres. It is concluded that short fibres are more effective in controlling early cracking, thereby enhancing the strength of the composite, whereas long fibres are more effective in providing post peak toughness. Concrete strength seemed to have an adverse effect on the deformability of fibre reinforced high strength concrete. Based on the test data obtained, a simple model is proposed to generate the complete stress-strain relationship for steel fibre reinforced high strength concrete. The proposed model has been found to give a good representation of the actual stress-strain response.
Experimental results from tests on seven 650 mm deep large-scale reactive powder concrete (RPC) I-section girders failing in shear are reported herein. The girders were cast using 150 170 MPa steel fiber RPC and were designed to assess the capacity to carry shear stresses in thin webbed prestressed beams without shear reinforcement. The tests showed that the quantity and types of fibers in the concrete mix did not significantly affect the initial shear cracking load but increasing the volume of fibers increased the failure load. A design model is developed to calculate the strength of the RPC beams tested in this study. The model is based on crack sliding and uses plasticity theory combined with observations from the variable engagement model for mode I failure of fiber reinforced concrete. The results of the model are compared with test data and show a good correlation.
The pullout test is a conventional test method for calibrating interfacial shear bond characteristics of Fiber Reinforced Polymer (FRP)-concrete interfaces. However, due to the small bending stiffness of FRP sheets/strips and the highly non-linear interface fracturing mechanism, a well-recognized analytical approach to the accurate interpretation of the pullout test results remains to be achieved despite extensive studies particularly when the aim is to calibrate a local bond stress-slip model, which is necessary for developing bond strength and anchorage length models avoiding the use of empirical formulations. This paper introduces a newly developed non-linear bond stress-slip model for analyzing full-range strain distributions in FRP and shear bond stress distributions in the interface bond layer during pullout tests, along with a new anchorage length model and bond strength model that were developed accordingly. Compared with other existing bond models, the bond model described here has two advantages besides its simplicity: (1) it incorporates the most important interface parameter, the so-called interfacial fracture energy, in all analytical processes and links it successfully with all other important bond parameters; (2) it is a general and unified approach that allows for the first time consideration of the effects of the adhesive bond layer in non-linear analysis of FRP-concrete interfaces. Further, a unified bond stress versus slip expression is formulated to show the differences in local bond stress-slip relationships at the loaded and free ends in pullout tests, so that the effects of the bond length used in a pullout test on the calibration of the interfacial bond stress-slip model can be clarified. The reliability of all proposed models is verified through a comprehensive comparison of the experimental and analytical results.
A time-dependent structural analysis method under multi actions in consideration of drying shrinkage due to moisture transfer and rebar corrosion due to chloride ions penetration as well as external load actions was developed. The Rigid-Body-Spring Networks (RBSN) model and the truss networks model were used for structural analysis and mass transfer analysis, respectively. In addition, mass transfer through bulk concrete and mass transfer through cracks by setting truss networks on the boundaries of Voronoi particles, was also considered. The developed method was confirmed to simulate well the deterioration process due to mass transfer for initial cracking behavior and ultimate behavior of concrete structures.
Path-dependent fatigue constitutive models for concrete tension, compression and rough crack shear are proposed and directly integrated with respect to time and deformational paths actualized in structural concrete. This approach is experimentally verified to be consistent with the fatigue life of materials and structural members under high repetition of forces. The mechanistic background of the extended truss model for fatigue design is also investigated. The coupling of fatigue loads with initial defects is simulated and its applicability is discussed as a versatile tool of performance assessment.
A damage index for seismic performance of RC members is proposed on the basis of 3D multi-axial fiber analysis. The elasto-plastic and fracturing model for concrete compression is applied for estimation of the fracture parameter, which is defined as the reduced elastic stiffness for each micro-cell component of member cross sections. The averaged fracture parameter over the cross section is treated as the index of cross-sectional damage for the remaining axial force-carrying mechanism. This index provides an approximation of damage related to seismic performance level II (reparable after seismic actions) not only for one-directional but also multi-axial flexure. This method is also effective for RC members confined by lateral ties.
Transient nonlinear analysis is proposed as a way of predicting the long-term deformation of cracked reinforced concrete and a mechanistic creep constitutive model for post-cracking tension-stiffness is presented. The effect of drying shrinkage is integrated into the predictive scheme using the thermo-hydro physics of porous media, and a simple equivalent method of analysis is discussed for the practical performance assessment of structural concrete. Careful verification of the model is carried out with respect to the creep deflection of RC beams and slabs subjected to multi-axial flexure. Three-dimensional fiber and plate & shell elements are used for the space discretization of the analysis domain.