Hajime Okamura

SELF-COMPACTING HIGH PERFORMANCE CONCRETE

A self-compacting high-performance concrete has been developed, which is not affected by workmanship during placing and needs no subsequent consolidation. Self-compacting concrete can lead to innovative construction systems, save labour, and eliminate consolidation noise. It has been used in Japan for bridge girders, towers, and piers, and for other structures. It is being used in the manufacture of precast concrete, where it eliminates the need for vibrating machines and their noise. Requirements for self-compactibility vary according to the structure to be built. Self-compacting concrete needs high deformability without separation of materials. To increase its deformability, its water-powder ratio should be increased, or a superplasticiser should be added. Its coarse aggregate content should be limited. As long as a reliable supply of ready-mixed concrete is available, a mix design for general-purpose self-compacting high-performance concrete is available. Self-compacting concrete has minimal bleeding. Its strength is determined by the properties of the binder and the water-cement or water-binder ratio, as for ordinary concrete.

Self-Compactable High-Performance Concrete in Japan

Self-compactable high performance concrete requiring no consolidation in situ has been recently developed in Japan to improve the reliability of concrete and concrete structures. This concrete is a significant material innovation for a new generation of concrete structures. A review of the concrete and the applications are described.

EFFECT OF SUPERPLASTICIZER ON SELF-COMPACTABILITY OF FRESH CONCRETE

The effect of superplasticizer on the balance between flowability and viscosity of mortar in self-compacting concrete was investigated quantitatively. From experimental results, the ratio of funnel speed to flow area of mortar with a fixed amount of superplasticizer was found to be almost constant, independent of the water-powder ratio. A higher amount of superplasticizer resulted in a lower ratio of funnel speed to flow area. The ratio is proposed as an index for the effect of superplasticizer on mortar flowability and viscosity from the viewpoint of achieving self-compactability. This index is convenient for evaluating the amount of superplasticizer for proper flowability and viscosity of mortar using only one set of experimental results. The relationship between superplasticizer amount and its effect was found to differ depending on the type of powder or superplasticizer. The difference can be indicated quantitatively by the proposed index.

Performance Based Design for Self-Compacting Structural High-Strength Concrete

This paper contains an historical review of self-compacting concrete (SCC) and clarifies the original concept. Further, combinations of self-compacting concrete for high strength and durability are discussed in relation to structural concrete design, construction and maintenance, and recent developments of performance-based design codes and manuals for SCC. On the competitiveness in industries, life-cycle cost is estimated for sustainable development of the infrastructure.

FATIGUE BEHAVIOR OF HIGH STRENGTH DEFORMED BARS IN REINFORCED CONCRETE BRIDGES

RESULTS OF BENDING FATIGUE AD OTHER TESTS OF REINFORCED CONCRETE BEAMS USING VARIOUS HIGH-STRENGTH DEFORMED BARS ARE PRESENTED. THE GREATEST FACTOR AFFECTING FATIGUE OF THESE BARS IS THE DEGREE OF SLOPE AT LUG BASES. THE SHAPE OF LUGS WHICH IMPROVE FATIGUE RESISTANCE WITHOUT IMPAIRING BOND IS INDICATED. FURTHER, FATIGUE AND BOND PROPERITES OF VARIOUS DEFORMED BARS, AND CONSEQUENTLY THE LIMITS OF TENSILE STRESS BASED ON FATIGUE OF STEEL, CRACKING OF CONCRETE AND WELDABILITY OF STEEL FOR DESIGN OF REINFORCED CONCRETE BRIDGES ARE DISCUSSED. /RRL/A/

Seismic performance check and size effect FEM analysis of reinforced concrete

Abstract To safeguard against the catastrophic failure of structures designed according to a certain design code, seismic performance check is proposed as the post design check to verify the performance of the designed structure under earthquake. The proposed seismic performance check consists of two stages — a first stage and a second stage detailed check. The first stage employs the apparent dimensions of structures in determining their performance while the second stage uses the numerical tool such as the finite element method. The treatment of size effect in the finite element method is explained based on the simple engineering concept but it is sufficiently versatile and accurate.

STUDY ON THE DESIGN EARTHQUAKE RESISTANCE AND DEGREE OF EARTHQUAKE DAMAGE OF REINFORCED CONCRETE VIADUCTS

Abstract The design earthquake resistance and actual damage caused by the Hyogoken-Nambu earthquake were studied and compared for reinforced concrete rigid-frame viaducts between Sumiyoshi and Nada on the JR Tokaido Line, which sustained the heaviest damage of all railway structures during the Hanshin-awaji earthquake disaster in January 1995 in order to find the design earthquake resistance required to withstand this earthquake. As a result of using the elastic response acceleration converted according to the law of constant energy as an index of earthquake resistance, it was found that structures with an earthquake resistance of 1000–1200 gal suffered column deformation and settlement but did not collapse, and structures with an earthquake resistance of 1200 gal or more experienced only light damage such as cover concrete peeling or less.

Japanese seismic design codes prior to Hyogoken-Nanbu earthquake

Abstract A large number of concrete bridges were damaged by the Hyogoken-Nanbu earthquake. Many of these bridges were found to have crumbled after suffering shear failure. This indicates that the original seismic design of these structures was inappropriate. Bridges that did not suffer shear failure, however, generally survived collapse even if they were severely damaged by bending moment. It has been confirmed that concrete structures do not actually collapse if they have sufficient resistance to shear failure, even if the displacement they experience is far beyond the bending yield displacement. This justifies the latest seismic design methods, in which collapse under the influence of extreme seismic motion is prevented by making the resistance to shear failure adequate enough to ensure the survival of each member. These latest seismic design codes and the changes in the codes are described.

COMPUTER STUDY OF LONG COLUMNS IN FRAMES

AN EXTENSIVE COMPUTER STUDY OF LONG COLUMN ACTION IN FRAMES IS SUMMARAIZED FOR BOTH UNBRACED AND BRACED BUILDING FRAMES. THIS SUMMARY PAPER (1) INDICATES THE WEAKNESS OF THE R-METHOD IN CARING FOR COLUMN BUCKLING IN CERTAIN FRAMES SUBJECT TO SIDESWAY, (2) COMPARES THE ACCURACY OF THE MOMENT MAGNIFIER AND R-METHODS IN THIS AND OTHER SITUATIONS, AND (3) GIVES THE BACKGROUND FOR THE MODIFIED R EQUATIONS MENTIONED AS ALTERNATES IN THE EXPLANATION OF CHANGES OF THE ACI BUILDING CODE. /AUTHOR/

QUANTITATIVE EVALUATION ON THE PARTICLE DISPERSION EFFECT OF A SUPERPLASTICIZER WHEN MIXING TIME IS VARIED

自己充填コンクリート用モルタルの相対フロー面積比と相対漏斗速度比の比を高性能AE減水剤の粒子分散効果の指標として, 練混ぜ時におけるポリカルボン酸系高性能AE減水剤の粒子分散効果を定量的に表した. 練混ぜ水を分割投入して練り混ぜると, 練混ぜ時間の延長によって高性能AE減水剤の粒子分散効果が低下した. この主要因は, セメント粒子の比表面積が水和反応によって練り混ぜるほど増加するためであることを示した. 高性能AE減水剤の吸着量を, 単位セメント重量当たりから単位表面積当たりに置き換えると, 粒子分散効果は単位表面積当たりの吸着量に比例した. 練混ぜ時においても, ポリカルボン酸系高性能AE減水剤の立体障害効果による粒子分散作用を明確に示した.