This paper describes the seismic behavior of new reinforced concrete (RC) building structures using ultra-high-strength fiber-reinforced concrete (UFC) with 200 MPa strength. A series of tests of columns and frames in UFC buildings subjected to seismic forces were conducted to obtain basic data of their behavior and to provide guides for design and construction. The test results are summarized as follows. 1) UFC, which is basically a brittle material, could be well confined with high-strength lateral reinforcements. 2) Stable behavior of columns could be obtained even under very high axial compression when they were well confined with high-strength lateral reinforcements. 3) Steel-fibers in UFC significantly enhanced the shear resistance of columns and frames. Analytical investigations indicated that the shear behavior of a column and a frame can be well evaluated by considering the contribution of steel fibers to the tensile resistance of UFC.
This paper aims to show the importance of autogenous shrinkage for the serviceability performance of reinforced high-strength concrete (HSC) flexural beams, and also the effectiveness of low-shrinkage HSCs (LS-HSC) made by using expansive additive and/or shrinkage-reducing chemical agent and/or Belite-rich low-heat Portland cement for improving the flexural serviceability performance of beam. From the design equation point of view, this paper also proposes a new concept for evaluating flexural crack width and deformation of RC beams taking into consideration the early age deformation of concrete before loading. The experimental results show that autogenous shrinkage of HSC significantly affects increases in crack width and deformation of RC beams, while LS-HSCs markedly improves their serviceability performance. The present concept, which takes into account strain change in tension reinforcement and curvature change in the cracked section before and after loading, is effective in explaining the effects of shrinkage and expansion of concrete before loading on maximum crack width and flexural deformation of RC beams. JSCE (Japan Society of Civil Engineers) code equations for predicting maximum crack width and flexural deformation into which the present concept is incorporated improve the prediction accuracy compared with conventional equations and show fairly good agreement with experimental results.
Tank leaching tests were carried out to investigate the behavior of leaching trace elements from monolith samples. This study consists of two series, and the trace element used was hexavalent chromium. In Series I, the influence of the leachant/surface area of the specimen (L/S ratio) on the leaching amount was investigated. The leaching amount was found to increase with the amount of worked water. This shows that any L/S ratio can be selected in the tank leaching test. In Series II, the influence of the curing conditions of concrete on the leaching amount was investigated. In the case of concrete cured under sealed conditions, hexavalent chromium hardly leached. On the other hand, in the case of concrete dried in the room, the amount of leaching of hexavalent chromium became large. Carbonation was found to cause the decomposition of cement hydrates and the release of fixed hexavalent chromium. The leaching of hexavalent chromium from using concrete was evaluated from these results. When water works continuously against concrete, the leaching of hexavalent chromium hardly affects the environment for water. When rainwater flows on the drying surface of concrete, the amount of leaching at the first rainfall was comparatively large, but deceased with subsequent rainfall.
To enhance the lateral strength, stiffness, and ductility of reinforced concrete bare frames, which are vulnerable to large seismic excitation, a simple, convenient, economic, and effective retrofit concept of cast-in-site partial or full, thick hybrid wall using additional concrete sandwiched by steel plates and high-strength steel bar prestressing is proposed in this paper. The frames were retrofitted by casting additional wing-walls adjacent to columns (referred to as opening-type wing-walls) and additional panel-walls into bare frames (referred to as non-opening-type panel-walls). The frames thus retrofitted were experimentally investigated under simultaneous cyclic lateral forces and a constant vertical load. It was verified that the proposed retrofit technique for bare frames is effective in terms of increasing lateral strength, stiffness, and ductility. For the analytic assessment of the proposed retrofit technique, design guidelines to calculate flexural strength, shear strength, and lateral force resistance capacity are suggested.
The non-embedded column bases of steel reinforced concrete buildings were severely damaged by the 1995 Hyougoken Nanbu Earthquake. Many anchor bolts and longitudinal reinforcing bars were fractured, mainly due to the lack of consideration of the tensile force caused by the overturning moment during earthquakes. This report examines the strength and deformation capacity of non-embedded column bases. The strength of a column base can be estimated from the summation of the strengths of the components unless the bond between the concrete and reinforcing bars has deteriorated. A high tensile force reduces the ductility of the column base. A formula is proposed for predicting the deformation capacity of column bases using the parameter “effective tensile force ratio” considering bond strength as well as tensile strength.
As emerging advanced construction materials, strain hardening cementitious composites (SHCCs) have seen increasing field applications recently to take advantage of its unique tensile strain hardening behavior, yet existing uniaxial tensile tests are relatively complicated and sometime difficult to implement, particularly for quality control purpose in field applications. This paper presents a new simple inverse method for quality control of tensile strain capacity by conducting beam bending test. It is shown through a theoretical model that the beam deflection from a flexural test can be linearly related to tensile strain capacity. A master curve relating this easily measured structural element property to material tensile strain capacity is constructed from parametric studies of a wide range of material tensile and compressive properties. This proposed method (UM method) has been validated with uniaxial tensile test results with reasonable agreement. In addition, this proposed method is also compared with the Japan Concrete Institute (JCI) method. Comparable accuracy is found, yet the present method is characterized with much simpler experiment setup requirement and data interpretation procedure. Therefore, it is expected that this proposed method can greatly simplify the quality control of SHCCs both in execution and interpretation phases, contributing to the wider acceptance of this type of new material in field applications.
The nonlinear behavior of fractured quasi-brittle materials is conventionally modeled with a fictitious crack model, which relates stresses on the crack surfaces to the corresponding crack widths. Its definition for fiber reinforced concrete is only possible by introducing a cohesive model for the matrix, and by modeling the pullout of randomly oriented fibers. To this aim, a new cohesive interface model, able to predict effectively the pullout response of inclined fiber, is presented in this paper. Based on the nonlinear behavior of steel fibers and cementitious matrixes, the proposed approach also takes into account the bond-slip relationship between the materials. By means of an iterative procedure, numerical results similar to experimental data can be obtained. In particular, maximum pullout forces at given inclination angles, as well as the complete pullout load vs. displacement diagrams, can be correctly predicted. Moreover, according to test results, the proposed approach shows, from the first pullout stage, the dependence of the response both on crushing of cementitious matrix and on yield strength of steel fibers.
Specimens cured in several simple adiabatic containers were examined to estimate in-place strength in structures of 150 MPa concrete. It is shown that containers holding two rows of five specimens produce good results. These containers were used for control testing of actual building operations. Specimens cured in the adiabatic containers resulted in 91-day strength value comparable to those of cores taken from mock-up columns.
Numerous skyscrapers are being built using reinforced concrete construction in Dubai, UAE. Because the use of high-strength concrete is advantageous for skyscrapers from a number of aspects, concrete with a 100 N/mm2 compressive strength was produced using materials locally available, and its properties while fresh and after hardening were investigated. Its placing performance in a mock-up column and in-situ strength development were also examined to investigate its applicability to actual construction. As a result, it was confirmed that the properties of fresh concrete are retained with little change over the required period, and that hardened concrete presents good mechanical and durability properties. Mock-up testing also revealed that the placeability of the concrete was sufficiently good, and the compressive strength and elastic modulus of cores drilled from the mock-up were found to be satisfactory for concrete of compressive strength of 100 N/mm2.
This paper presents the design of an 80-story reinforced concrete (RC) high-rise building using 200 MPa ultra-high-strength concrete. Static nonlinear push over analyses, Level-1 and Level-2 nonlinear earthquake response analyses and nonlinear wind response analyses were carried out. Based on the three-dimensional static nonlinear analyses of the building subjected to design earthquake loading in two principal directions, the obtained maximum axial load ratio for the first story columns of 200 MPa compressive strength concrete were 0.53 and 0.48, respectively, at the ultimate limit state, which meets the design criterion based on the allowable compressive stress of concrete. The maximum story drift angle obtained under the synthetic wave motion at the construction site was smaller than the design limiting value of 1/100. While yield hinges developed only in some of the short beams, no yield hinge in columns was observed. The maximum ductility of 1.28 obtained in the beams is lower than the design limiting value of 4.0. The maximum story shear force for the level-2 wind load was almost half that of the level-2 earthquake load when using the lumped-mass model. The analyses confirmed that the use of 200 MPa concrete enables structural designers to provide the member sections with adequate sizes comparable to that of ordinary high-rise RC buildings. The analytical results showed that the performance of the building satisfies the design criteria for serviceability limits, design limits and ultimate limits.
Cyclic loading tests were carried out on ultra-high strength RC columns under high axial load conditions. Effective concrete strength of 200 MPa with high-strength steel fibers (SF) was used. The investigated parameters were: 1) volumetric ratio of steel fiber, 2) lateral reinforcement ratio, and 3) axial loading type. The main characteristics of the tested columns (maximum strength, deformation capacity and equivalent viscous damping factor) are presented and the influence of various parameters is discussed. The test results revealed the advantage of using SF in terms of strength and damage control. The maximum strength of the tested columns using SF, assessed using a number of different formulas, proved to be on the safe side. On the other hand, in the case of columns in which SF was not used, the estimated maximum strength was found to be larger than the tested value, except when using NZS3101 equation. This difference is probably due to early spalling off of the cover concrete.
The tests concerning use of concrete with recycled aggregates (RAC) presented in different countries were focused on material properties. Very few serial tests were done on structural reinforced-concrete members with RAC to be compared with similar members with natural aggregate concrete (NAC). Such tests are necessary because it is difficult to predict the influence of differences in particular properties on the overall behaviour of reinforced concrete members made of various mixtures of recycled aggregate concrete. The aim of the tests presented in the paper was to determine differences in behaviour of simple reinforced concrete members made of RAC, with different contribution of recycled aggregates, in comparison with members made of concrete with natural aggregate (NAC) only. The results of replacing by recycled aggregate the coarse and fine aggregate or the coarse aggregate only were particularly taken into consideration. 16 series of beams and 5 series of columns have been selected for tests. The comparison of results showed similar bearing capacity of members in the series, and significantly greater deformations of concrete in members with recycled aggregate concrete. Differences in load-bearing capacity could be neglected in practice, but the differences in deformability should be considered carefully at beam deflection assessment, as well as at columns shortening analysis.
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