Vol. 5, No. 1, Division E (Materials, Concrete Structures and Pavements), Journal of JSCE (in English)
Vol. 73, No. 1, Division E2 (Materials and Concrete Structures), Journal of JSCE (in Japanese)
Vol. 72, No. 4, Division E2 (Materials and Concrete Structures), Journal of JSCE (in Japanese)
Vol. 72, No. 3, Division E2 (Materials and Concrete Structures), Journal of JSCE (in Japanese)

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SHEAR BEHAVIOR OF REINFORCED CONCRETE AND PRESTRESSED CONCRETE TAPERED BEAMS WITHOUT STIRRUPS

Chenwei HOU, Takuro NAKAMURA, Takayuki IWANAGA, Junichiro NIWA
Vol. 5 (2017) No. 1 p. 170-189 (in English)

Abstract:
This study aims to clarify the shear resistance mechanism of reinforced concrete and prestressed concrete tapered beams without stirrups. Three series of seven beams with different parameters (a/d ratios and prestress levels) were tested. The results showed that there is no effect of the taper on the short beam due to the arch action. The slender RC tapered beam had the higher shear capacity, while the RC tapered beam in large a/d ratio (a/d equals to 5.0) had the smaller shear capacity. When the prestressing force was introduced, the tapered beam again had the larger shear capacity. In addition, nonlinear FEM analyses were conducted to complement the experiments and verify the results, which showed a good agreement including load-deflection curves, load capacities, and crack patterns. A new evaluation method for the shear capacity of tapered beams without stirrups was finally proposed, by determining the location of the critical section through the nonlinear FEM analyses.

STUDY ON BEARING CAPACITY OF AIRPORT PAVEMENT DAMAGED DUE TO THE 2011 TOHOKU REGION PACIFIC COAST EARTHQUAKE

Yukitomo TSUBOKAWA, Naoya KAWAMURA, Junichi MIZUKAMI, Ryota MAEKAWA
Vol. 5 (2017) No. 1 p. 58-67 (in English)

Abstract:
The 2011 Tohoku Region Pacific Coast Earthquake struck off Tohoku and Kanto regions of Japan on 11 March 2011. We conducted investigations of structural and surface damage to pavement in the runway, taxiway and apron at Sendai Airport for the purpose of re-opening the airport for commercial flights. Many cracks were confirmed in the asphalt pavement in the runway and taxiway. However, it was clarified that these cracks except the one in the taxiway were not fatal structural damage that would hinder the provisional use of the airport. Large settlement was confirmed in a part of the asphalt pavement in the taxiway and concrete pavement in the apron due to liquefaction. It was confirmed that these settlement areas needed to be reconstructed for the re-opening of the airport. Furthermore, the effect of the void underneath the cement concrete slab on FWD deflection was clarified.

SHEAR REINFORCEMENT EFFECT FOR RC BEAMS BY POST SHEAR REINFORCING METHODS WITH PLATE AND HEAD ANCHORED SHEAR REINFORCING BARS

Yuji KUMAGAI, Takuro NAKAMURA, Jun SAKAMOTO, Hitoshi TAKEDA, Junichiro NIWA
Vol. 73 (2017) No. 1 p. 118-132 (in Japanese)

Abstract:
This study aims to clarify the shear reinforcement effect for RC beams by post shear reinforcing methods with plate and head anchored shear reinforcing bars (PHB). Three specific test series with total of seven RC slender beams were carried out under the four point bending test to investigate the influence of spacing, diameter and embedded length of PHB without the normal construction methods. All specimens had a rectangular cross section with a/d ratio of 3.2. The results showed that the shear capacity of RC beams was affected by the spacing of PHB, whether they are crossed by shear cracks or not. However the effect was smaller than that by using effective coefficient βaw. This effect was reduced by enhancing the spacing of PHB, however the reduction ratio can be improved with a larger shear reinforcement ratio. Furthermore, the shear reinforcement effect can be promoted by shorter embedment length. Finally, this paper proposed the equations to predict the shear capacity of RC beams with PHB by considering the spacing and the number of PHB. The shear capacity calculated from the proposed equation showed a reasonable accuracy to estimate the experimental shear capacity.

STUDY ON DURABILITY OF CLINKER-FREE CONCRETE WITH A BINDER COMBINING DEHYDRATED SLUDGE POWDER WITH OTHER INDUSTRIAL BY-PRODUCTS ADMIXTURE

Ken OHKAWA, Shinichi AOKI, Tetsushi KANDA, Haruki MOMOSE, Tetsurou KASAI
Vol. 73 (2017) No. 1 p. 107-117 (in Japanese)

Abstract:
Increasing demand on the reduction of CO2 emission in the construction industry has required development of new concrete without ordinary Portland cement. Such concrete, e.g., geopolymer, has draw-back in terms of carbonation resistance when applied to reinforced concrete structures. To account for this improvement, the authors focused on clinker-free concrete involving dehydrated sludge powder (DSP) produced from waste ready-mixed concrete, which is returned from construction site to concrete manufacturer without used for construction work. In this study, durability of proposed clinker-free concrete with a binder combining DSP with other industrial by-products was studied in terms of carbonation resistance and cracking resistance. As a result, it was confirmed that, at an appropriate water-binder ranges and using DSP with less than about 8,000 cm2/g of specific surface area by 60-80% of binder, the proposed concrete showed equivalent or higher carbonation resistance than that of normal concrete, and when applied to PCa members, showed sufficient cracking resistance under restraint rebars, while free shrinkage strain was 100 to 200 μ larger than that of normal concrete.

EXPERIMENTAL STUDY ON THE EFFECTS OF MORTAR SURFACE DEFECTS ON THE CHLORIDE ION PERMEABILITY

Katsuya MITA, Yoshitaka KATO
Vol. 73 (2017) No. 1 p. 93-106 (in Japanese)

Abstract:
Surface defects of reinforced concrete structures are often evaluated only by appearance, so the effect surface defects have on the mass transfer resistance of the surface layer of concrete has not been fully explored. In this study, sand streaks and surface bubbles were intentionally caused by varying specimen shape for mortar as a basic study, and their effects on chloride permeability were studied experimentally. As a result, bleeding water could be related to the generation of sand streaks and surface bubbles, and, when sand streaks and surface bubbles occurred, chloride ion penetration was found to be deeper than in the reference specimen. On the other hand, even when sand streaks and surface bubbles did not occur, depending on the specimen shape, in some cases there were locations where bleeding water tended to accumulate. Due to the accumulation of bleeding water, the surface quality of the mortar was reduced, and there was a possibility that the chloride ion permeability increases.

EVALUATION OF MICRO STRUCTURE OF THE HARDENED CEMENT PASTE FROM THE VIEW POINT OF PORE CONNECTIVITY

Toshiyuki SUDO, Tatsuhiko SAEKI, Tsuyoshi SAITO
Vol. 73 (2017) No. 1 p. 82-92 (in Japanese)

Abstract:
The purpose of this research is to quantify the amount and the diameters of connective pore structure and to study the effects on the mass transfer properties. Specifically, the diameters of “ink-bottled pore structure” were specified with a combination of the data from a mercury intrusion porosimeter and water vapor adsorption. As a result, ink-bottled pore diameters in hardened cement paste were 10nm-20nm. Also, the amounts of ink-bottled pore structures were decreased by the use of admixtures, and the mass transfers were inhibited. It was estimated that these results were related to the nano/meso-C-S-H structures.

AN INVESTIGATION ON SHEAR RESISTANT MECHANISM OF RC BEAM BASED ON BEAM ACTION AND ARCH ACTION

Takuya IWAMOTO, Hikaru NAKAMURA, Li FU, Yoshihito YAMAMOTO, Taito MIURA
Vol. 73 (2017) No. 1 p. 70-81 (in Japanese)

Abstract:
Shear resistant mechanism was evaluated by using the detailed stress distribution obtained from analysis of RC beam failed in shear. First, the validity of the local stress distributions of concrete and stirrups obtained from 3-D RBSM was confirmed by comparing the test results of RC beams failed in shear. Next, the applicability of decoupling shear resistant mechanism of beam and arch actions using the stress distributions obtained from analysis was presented. In addition, it was clarified that based on the analytical results, shear resistant mechanism at shear strength of the analyzed RC beams was composed by arch mechanism and truss mechanism in beam action independent on web reinforcement ratio. As a result, the necessity for redesigning the shear strength equation based on the shear resistant mechanism was proposed.

EFFECTS OF DRYING SHRINKAGE OF CONCRETE ON SHEAR BEHAVIOR OF REINFORCED CONCRETE BEAMS WITHOUT SHEAR REINFORCEMENT

Hikotsugu HYODO, Ryoichi SATO, Kenji KAWAI, Ken-ichiro NAKARAI
Vol. 73 (2017) No. 1 p. 50-69 (in Japanese)

Abstract:
In order to investigate the effects of drying shrinkage of concrete on shear strength of reinforced concrete (RC) beam without shear reinforcement, the loading test of the RC beams was carried out. Major factors were water-to-binder ratio of 50% and 35%, effective depth of 250,500 and 1000mm as well as the amount of concrete shrinkage. Test results showed that the drying shrinkage of concrete decreased the shear strength of RC beams as well as enhanced significantly the size effect on shear strength of RC beams. Heightening of concrete strength also enhanced the size effect on shear strength of RC beams. Based on the results, a mechanism of the combined effects of drying shrinkage, effective depth and concrete strength on the shear strength of RC beams was proposed. Furthermore, the conventional equation which incorporated an equivalent tension reinforcement ratio considering shrinkage effects showed fairly good agreement with the experimentally obtained shear strength including its size effect.

EVALUATION OF AIR-VOID SYSTEMS IN CONCRETE BY POINT PROCESS STATISTICS AND ESTIMATION OF THE CONVENTIONAL SPACING FACTOR

Takuma MUROTANI, Hidefumi KOTO, Shin-ichi IGARASHI
Vol. 73 (2017) No. 1 p. 36-49 (in Japanese)

Abstract:
Distribution of air voids in concrete was regarded as 2D spatial point processes. Characteristics of their distribution were evaluated by several spatial statistics functions. Furthermore, a characteristic distance between air voids was defined in the nearest neighbor distance function. Correspondence between the characteristic distance and the conventional spacing factor was investigated. Clustered distribution of air voids due to the presence of aggregate particles were properly estimated by the spatial statistics functions. However, as far as the cement paste matrix was concerned, it was possible to assume that air voids were distributed randomly except a range of short distances. Thus, spatial structure of air-void systems, in particular the characteristic distance between air voids could be simply simulated as a random point process. Furthermore, the characteristic distance of real air-void distribution was almost the same as the conventional spacing factor. Compared to the conventional spacing factor that is obtained by following the ASTM C457 procedure, the characteristic distance is quite easy to obtain. Furthermore, taking account of the fact that the characteristic distances measured for real distribution in concretes are plotted within the 95% confidence interval of binominal random point process, air-void systems in concrete can be assumed as 2D Poisson point process. Thus, a simple equation to obtain the spacing factor from a point process was proposed. The spacing factor was correctly estimated by the equation. Therefore, the characteristic distance of air voids defined in this study can be used as a new distance parameter between air voids, alternatively it may be used as a parameter to estimate the traditional spacing factor.

EVALUATION FOR ASR DETERIORATIONS BASED ON ANALYSES OF STIRRUP DAMAGE AND INTERNAL CRACKING OF CONCRETE

Nobuo UEHARA, Kenji KOSA, Hirotaka MASUDA, Yuji UEZONO
Vol. 73 (2017) No. 1 p. 1-15 (in Japanese)

Abstract:
For investigating correlations among external and internal cracking of concrete as well as the stirrup damage caused by ASR deterioration, several specimens arranged by main reinforcement and stirrup are exposed under outdoor environment. The detailed observation and evaluation are performed for specimens with severe deterioration degree. As a result, it is noted that cracking in external concrete is perpendicular to surface and stagnate at the depth of stirrup; while, the internal cracking has the trend to generate with various direction and short length due to the constraint from stirrup. Further, it is considered that the stirrup confinement is effective when suffering deterioration without stirrup rupture; however, under the circumstance where stirrup rupture occurs, external cracking has the possibility to extend through the deeper position around the rupture location of stirrup, accompanied by acutely increasing width and differences in level on the surface.

EVALUATION OF THE SHEAR CAPACITY FOR STEEL REINFORCED CONCRETE SHORT BEAMS UNDER FIXED BOTH ENDS

Yuki NAKATA, Ken WATANABE, Toshiya TADOKORO, Masaru OKAMOTO, Manabu IKEDA, Yukihiro TANIMURA
Vol. 72 (2016) No. 4 p. 440-455 (in Japanese)

Abstract:
The experimental equations under the simply supported condition has been used as the shear capacity of steel reinforced concrete (SRC) beams in Standard Specifications for Hybrid Structures. On the other hands, the support condition of members of the rigid frame viaduct is different from the simply supported because both ends are fixed. The study has evaluated the shear mechanism and shear capacity of SRC short beams under fixed both ends based on results of experiment and finite element analysis. The results indicated that the shear capacity was affected by support condition and increased with the decrease of the flange width of steel-frame. In addition, the effect of stirrup on the shear capacity was limited. Finally, the paper proposed calculation equation of shear capacity for SRC short beams under fixed both ends.

INVESTIGATION AND MODELING OF EFFECTS OF CHLORIDE ON DRYING AND WETTING BEHAVIOR OF CONCRETE

Kenji HARADA, Takumi SHIMOMURA
Vol. 72 (2016) No. 4 p. 427-439 (in Japanese)

Abstract:
Effect of chloride in liquid water on drying and wetting behavior of concrete was experimentally investigated. Experimental result showed that equilibrated water content increases and moisture transfer rate in concrete decreases with increasing of chloride content in concrete. Consequently, concrete tends to wet by the existence of chloride. Analytical method for coupled transport of water and chloride in concrete which effect of chloride on moisture transport is taken into account was proposed. Increasing of equilibrated water content due to chloride can be expressed by considering decreasing of saturated vapor pressure and change in physical property of liquid water. Decreasing of moisture transfer rate in concrete due to chloride can be expressed by considering decreasing in transfer rate of liquid water in accordance with chloride concentration.

STUDY ON FLEXURAL REINFORCING EFFECT OF SEISMIC RETROFITTING METHOD REINFORCING ONLY TWO-SIDES OF RC BRIDGE PIER WITH BAR CUT-OFF SECTIONS

Taichiro WATANABE, Kaoru KOBAYASHI, Takahiro KANNO, Shigehiko SAITO
Vol. 72 (2016) No. 4 p. 411-426 (in Japanese)

Abstract:
A new seismic retrofitting method reinforcing the termination zone of the longitudinal bars of RC bridge pier in which reinforcing members were placed only two-sides of the pier and enables to retrofit without removing machine room under viaduct was developed, and its flexural reinforcing effect was clarified. Beam tests were carried out using RC beam specimens in which two-sides of the existing beam were retrofitted by fixing RC reinforcing beams with anchor bars. From the beam test results, it was clarified that the ratio of the load carried by reinforcing beams to the load carried by existing beam was proportional to the products of the ratio of the rigidity of reinforcing beams to the rigidity of existing beam and the ratio of reinforced length within shear span to the effective depth of existing beam. Cyclic loading tests were also carried out using model pier specimens of the actual pier structures of the Touhoku-Shinkansen, in which the new seismic retrofitting method was expected to applicate. From the test results, it was clarified that the damage at the bar cut-off sections of the pier, in which failure mode factors S before retrofitting were under 1.0, could be avoided by reinforcing two-sides of the pier with RC reinforcing members such that the failure mode factors S' after retrofitting were about 1.3.

FLOW AND COMPRESSIVE STRENGTH OF GEOPOLYMER MORTAR USING FINE POWDER OF MELT-SOLIDIFIED SLAG FROM MUNICIPAL WASTE CHANGING STORAGE METHOD

Tohru KIMURA, Tatsuya NUMAO, Chihiro TOKUMOTO, Yuki YAMASHITA
Vol. 72 (2016) No. 4 p. 400-410 (in Japanese)

Abstract:
Geopolymer using fine powder of melt-solidified slag made from municipal waste as an active filler occasionally loses rapidly fluidity after mixing. The possibility of improving the fluidity were investigated for two methods, one is to use the stored fine powder of the slag and the other is to use fine powder of the stored slag. Influence of storage method and storage period on chemical ingredients was investigated using several chemical analyses. Influence of storage method and storage period on fluidity and compressive strength of the geopolymer were also investigated. It is revealed from the chemical analyses that hydrate and calcium carbonate are generated during storage when the slag is stored after grinding and that hydrate is generated during storage when the slag is stored before grinding. The experiments showed that the fluidity of the geopolymer mortar which use the slag powder as an active filler was improved. Compressive strength of air cured geopolymer mortar is decreased with the increase of storage period as generation amount of hydrate or calcium carbonate increases in the slag. It is confirmed that improvement of fluidity and reduction of compressive strength are caused to the change in the slag by storage. Meanwhile compressive strength of steam cured geopolymer mortar is not influenced by the change in the slag by storage. It is conceivable that this is caused to the restraint of reaction based on latent hydraulicity as condensation polymerization dominates under high temperature.

STUDIES ON PROGRESS ESTIMATION METHOD OF ABRASION DEPTH OF CONCRETE STRUCTURES

Toshiyasu TOYOFUKU, Takenori NAGAMATSU, Hiromi TSURUKUBO, Toshihide TOYOFUKU, Shinya NAKAYAMA
Vol. 72 (2016) No. 4 p. 380-399 (in Japanese)

Abstract:
In the maintenance of concrete structures whose degradation is produced by abrasion, it is necessary to predict an amount of abrasion quantitatively. Currently, however, the prediction method is not established. In this study, we examined effects of external force and factors of concrete quality (e.g. weight, speed, the number of blow, compressive strength) on the amount of abrasion using the shock abrasion examination device with the steel boll falling on a concrete surface. Based on the regression analysis of huge amount of experimental data, we developed the prediction method of abrasion depth development of concrete. The method was validated by applying the method to the abrasion of actual concrete structures.

DEFORMATION MECHANISM OF CEMENT PASTE AND EFFECT OF WATER

Yuya SAKAI, Toshiharu KISHI
Vol. 72 (2016) No. 4 p. 368-379 (in Japanese)

Abstract:
Triaxial compressive tests were carried out at different confining pressure and water content to understand the deformation mechanism of hardened cement paste. Results showed that stress did not decrease up to 10% strain, and macroscopic damage was not observed when tested under a certain confining pressure. This confining pressure differed depending on moisture content. Stepwise creep tests were conducted, and the slopes of the obtained differential stress-strain rate curves in a double logarithmic chart were around three, indicating that deformation was caused by dislocation creep. A sample saturated with sucrose solution exhibited more brittle behavior after the peak stress as compared to the behavior of the sample saturated with tap water. The results indicated that the deformation of cement paste was probably affected by dislocation, mechanical twinning, and pressure solution. Those mechanisms can affect cement paste and concrete deformation under low confining pressures.

EFFECT OF BLAST-FURNACE SLAG FINE AGGREGATE ON IMPROVEMENT OF PROPERTIES OF HARDENED CONCRETE

Kazuhide SAITO, Ryo YOSHIDA, Chiaki YOSHIZAWA, Hidetaka UMEHARA
Vol. 72 (2016) No. 4 p. 355-367 (in Japanese)

Abstract:
By replacing the blast furnace slag fine aggregate with natural fine aggregate, hardening properties improving effect, such as long-term strength enhancement, drying shrinkage reduction, and carbonation inhibition of concrete is known to be obtained. In this study, for the purpose of revealing the mechanism of hardening properties improvement of blast-furnace slag fine aggregate, we focused on the difference in particle size of the blast-furnace slag fine aggregate, and investigated the influence of each particle diameter on properties of hardened mortar. As a result, it was found that blast-furnace slag fine aggregate is effective in strength enhancement and drying shrinkage reduction as particle size is small, and particle size smaller than about 0.045 mm is more effective. Next, we confirmed the influence that content of the particle size smaller than about 0.045 mm gave to properties of hardened concrete. As a result, it was found that the compressive strength is remarkably enhanced, and effect on drying shrinkage and carbonation was small by adding about 5% of blast furnace slag powder as the particle size smaller than about 0.045mm.

SERVICEABILITY SIMULATION OF RC BRIDGE DECKS SUBJECTED TO COUPLED DRYING SHRINKAGE AND WHEEL-TYPE FATIGUE LOADS

Yoshisato HIRATSUKA, Koichi MAEKAWA
Vol. 72 (2016) No. 4 p. 343-354 (in Japanese)

Abstract:
As moving load testing of RC slabs of highway bridges takes several months, drying shrinkage of concrete progresses concurrently with fatigue-induced damage during this time. Further, as actual bridges are placed in service after drying shrinkage has progressed to some extent, RC slab fatigue life test results do not correspond with the actual life of RC slabs in service. This study investigated the effect of the combined action of drying shrinkage and fatigue-induced damage by using multi-scale analysis based on thermodynamics. The increase in deflection under fatigue load was found to be the result of the combined action of shrinkage and load-induced fatigue damage, and the process by which damage progresses through their interaction was elucidated.

FATIGUE-BASED STRUCTURAL BEHAVIOR OF RC BRIDGE SLABS WITH DIFFERENT LOADING HISTORIES

Yoshisato HIRATSUKA, Mineo SENDA, Chikako FUJIYAMA, Koichi MAEKAWA
Vol. 72 (2016) No. 4 p. 323-342 (in Japanese)

Abstract:
This paper discusses the path dependency of high cycle fatigue behaviors of RC bridge slabs under various loading histories in use of laboratory experiments and numerical behavioral simulation. A prototype standard RC slab and another two specimens, which were initially loaded statically in advance, were prepared for the subsequent wheel-type loading. All three of them were tested under a moving load of 160kN. Observed is the independency of the progressive mid-span deflection on the loading histories. Furthermore, the same trend is rather observed at a level of 220kN as well with another set of specimens of exactly the same shape and dimension. The observed phenomenon in the experiments was successfully simulated by direct path-integral 3D nonlinear FE analysis considering the varying boundary conditions from the preliminary loading state to the main one to introduce the high cycle fatigue damages.

EVALUATION OF RESISTANCE OF CONCRETE TO CHLORIDE INGRESS BY USING CHLORIDE PENETRATION DEPTH AFTER NON-STEADY-STATE MIGRATION EXPERIMENT

Eisuke NAKAMURA, Hiroshi MINAGAWA, Shintaro MIYAMOTO, Makoto HISADA, Hirohisa KOGA, Hiroshi WATANABE
Vol. 72 (2016) No. 3 p. 304-322 (in Japanese)

Abstract:
An experimental study was conducted to develop an evaluation method for the resistance of concrete to chloride ingress by using chloride penetration depths measured with a colorimetric method after non-steady-state migration experiments. The evaluation method was quicker and simpler than other existing laboratory-accelerated tests because the non-steady-state chloride penetration depths were utilized to evaluate the resistance of concrete to chloride ingress. An appropriate procedure to determine the applied voltage and the testing period was proposed on the basis of the experimental results obtained by using mortar and concrete specimens. The movement of chloride during the non-steady-state migration experiments was also clarified by analyzing the tested specimens. The test results derived from the evaluation method were compatible with those given by the immersion test; both test results accurately indicated the improvement of the resistance of concrete to chloride ingress due to mixing supplementary cementitious materials. Moreover, the evaluation method was found useful for measuring the time-dependent development of the resistance of concrete to chloride ingress.

A STUDY ON MODELING OF CLIMATE CONDITIONS FOR DURABILITY EVALUATION OF CONCRETE STRUCTURES

Akihiko NAKAMURA, Mitsuo KUNICHIKA, Kei KAWAMURA, Hideaki NAKAMURA
Vol. 72 (2016) No. 3 p. 288-303 (in Japanese)

Abstract:
Environment conditions are the external factor that affect the durability of concrete structures. Especially, early-age cracking such as thermal cracking and drying shrinkage cracking influences concrete durability. Therefore, it is important to understand this external factor accurately in order to evaluate the durability of a concrete structure. Meteorological conditions such as the ambient temperature and humidity are especially important in an external factor because meteorological conditions influence deterioration such as the crack and the steel corrosion. In this study, the seasonal fluctuation models of vapour pressure, ambient temperature and relative humidity were constructed by using the latest meteorological data.

PREDICTIONAL METHOD FOR REBAR CORROSION DEGREE EXISTING CAVITY CAUSED BY REBAR CORROSION IN RC STRUCTURE

Hideki OSHITA, Takayumi IMAI, Syogo HAYASHI, Yoshihiro FUKUOKA
Vol. 72 (2016) No. 3 p. 268-287 (in Japanese)

Abstract:
Simple modeling method of corrosion degree in rebar existing the cavity caused by the expansive stress in concrete due to the corrosion in rebar in RC structure is investigated. Employing the thermal on concrete surface by the thermography, heat stored in reinforcing steel-bar (rebar) due to electro-magnetic heating is applied to estimate qualitatively the thickness of cavity and the corrosion degree. The thickness of corroded layer in rebar is identified by the difference of the increased value of temperature on concrete surface between the measured value and the analyzed value assumed the rebar as non corroded state. On the other hand, the thickness of cavity is identified by the rate of the temperature increase on the concrete surface. An applicability of the analysis is demonstrated by the comparison between the analyzed and those measured value.

TENSILE FRACTURE ANALYSIS OF FIBER REINFORCED CEMENTITIOUS COMPOSITES WITH REINFORCING BAR AND FRACTURE BEHAVIOR EVALUATION FOCUSING ON BRIDGING FORCE

Hiroki OGURA, Minoru KUNIEDA, Hikaru NAKAMURA
Vol. 72 (2016) No. 3 p. 249-267 (in Japanese)

Abstract:
This paper introduces the results of tensile fracture analysis of Fiber Reinforced Cementitious Composites (FRCC) with reinforcing bar by means of meso-scale analysis concerning discretized short fibers. The effects of fiber volume fraction, steel reinforcement ratio, bond characteristic between steel reinforcement and FRCC, and fiber distribution on the tensile fracture are numerically investigated. The analytical result shows that there are cases in which cracks were localized in post-yield range of reinforcing bars. The localization mechanism was numerically explained and method for inhibiting the localization was demonstrated by focusing on the amount of bridging forces of fiber and steel bar. In the case of Strain Hardening Cementitious Composites (SHCC), it was clarified that the usage of steel reinforcement is effective to enhance strain capacity.

FUNDAMENTAL STUDY ON THE PRACTICAL APPLICATION OF SELF-COMPACTING CONCRETE USING SEAWATER AND UNWASHED SEA SAND

Takahiro SAKAI, Toru YAMAJI, Osamu KIYOMIYA
Vol. 72 (2016) No. 3 p. 196-213 (in Japanese)

Abstract:
The influence of NaCl on initial strength enhancement effect of concrete using seawater as mixing water is dominant, which is the main component of seawater. The initial hydration of the C3S is promoted by NaCl. Compared with the case of using tap water, it was confirmed that the formed tissue is denser. Previously, self-compacting concrete using sea water and unwashed sea sand for urgent restoration works as well as for construction work at isolated islands and other similar region where fresh water is not sufficient was developed. In this study, strength, drying shrinkage and thermal properties of concrete with sea water and unwashed sea sand are experimentally examined. It is found that initial strength development increased as compared with the control concrete made of tap water and land sand. Drying shrinkage strain and autogenous shrinkage strain of concrete were almost equal or higher than the control concrete, but the improvement of crack resistance was observed. Furthermore, in regard to the thermal properties, the rate of temperature rise due to the accelerated hydration reaction and the coefficient of thermal expansion was slightly larger. Considering these properties, the proposed concrete can possibly be used for un-reinforced concrete application.

SHEAR-RESISTING MECHANISMS OF PRE-TENSIONED PC BEAMS WITHOUT SHEAR REINFORCEMENT STRENGTHENED BY CFRP SHEETS

Thi Thu Dung NGUYEN, Koji MATSUMOTO, Yuji SATO, Masahiko YAMADA and Junichiro NIWA
Vol. 4, No. 1, pp. 59-71, Journal of JSCE (in English)

Abstract:
Although externally bonded carbon fiber-reinforced polymer (CFRP) sheets have been used more commonly for the strengthening of existing reinforced concrete (RC) structures, the effects of this strengthening method on prestressed concrete (PC) beams have not been well clarified. In this study, an experiment was conducted to investigate the behaviors of pre-tensioned PC beams without shear reinforcement strengthened in shear using externally bonded CFRP sheets with the consideration of CFRP reinforcement ratio, stiffness and prestressing level in strands. The results implied that the shear resistance in the strengthened PC beams depended on maintaining the combination of beam action, arch action, and the bonded sheets. The failures and the increase in shear capacity of the strengthened PC beams were strongly affected by the amount, thickness of the CFRP sheets, and the effective prestress in the strands. The higher effectiveness of strengthening could be obtained in the beams strengthened with a higher CFRP reinforcement ratio of the same thickness, higher elastic modulus sheets or having higher prestressing level. Nevertheless, the increase in the thickness of the sheets did not provide a better performance. Moreover, the high inaccuracy in the calculations using the equations stipulated in the recent design guidelines compared to the increment of the shear strength obtained by the experiment was explained by the shear-resisting mechanisms.

A NEW ALTERNATIVE SHEAR IMPROVEMENT OF CONCRETE BEAMS BY INTERNALLY REINFORCING PBO FIBER MESH

Sirapong SUWANPANJASIL, Koji MATSUMOTO, Junichiro NIWA
Vol. 3, No. 1, pp. 67-80, Journal of JSCE (in English)

Abstract:
This paper aims to develop a new method for shear reinforcing concrete beams by using the ultrahigh performance PBO fiber mesh as a replacement for conventional stirrups inside a concrete structural member. The elementary test was performed first to investigate the general behavior of the internal reinforcing PBO fiber mesh as a fundamental objective of this study. Then, nine RC beams with and without internal PBO fiber mesh were conducted in the RC beam test. The parameters in the RC beam test were the number of internal PBO mesh layers, the width of internal PBO mesh in the shear span, and the reinforcing configuration of the internal PBO mesh. The experimental results showed that the shear capacity and the shear carried by internal PBO fiber mesh increased significantly with a higher number of the internal mesh layers; however, the shear capacity decreased when the width of internal mesh in the shear span was expanded. Besides, the difference in reinforcing configuration of the internal PBO mesh showed a great impact on the shear capacity of concrete beams reinforced with internal PBO fiber mesh. Furthermore, an empirical method for evaluating shear carried by internal PBO fiber mesh was modeled and a moderate agreement between values from the model and values from the experiment was obtained.

SHEAR FAILURE MECHANISM OF REINFORCED CONCRETE HAUNCHED BEAMS

Chenwei HOU, Koji MATSUMOTO, Junichiro NIWA
Vol. 3, No. 1, pp. 230-245, Journal of JSCE (in English)

Abstract:
This study aims to clarify the shear resistance mechanism of reinforced concrete haunched beams (RCHBs). Four series of ten RCHBs with different parameters (positions of haunched portions, thickness of the concrete cover, presence of stirrups and the arrangement of the tensile rebar) were tested. The results demonstrated that the bending position of the tensile rebar as well as the different arrangement of the tensile rebar highly influenced the crack propagations which caused the variation in the shear capacities due to different contributions of the arch action. Different diagonal crack angles also resulted in different contributions by stirrups in RCHBs with stirrups. The thicker concrete cover at the mid span affected the crack propagation but had almost no effect on the shear capacity. Nonlinear FEM analyses were also conducted to complement the experiments and verify the results, which showed a good agreement including load-deflection curves, load capacities and crack patterns. The shape of the compression zone, which dominates the arch action in RC beams, was also evaluated by the analyses.

STUDY ON EVALUATION OF STRUCTURAL PERFORMANCE IN 15-YEAR-OLD PC ROAD BRIDGE AFTER RECONSTRUCTION UNDER SEVERE CHLORIDE ENVIRONMENT

Masaki MIYAMURA, Hideki NAITO, Satoshi NAKANO, Masuo KADO, Ichiro IWAKI and Motoyuki SUZUKI
Vol. 72, No. 2, pp. 41-55, Journal of JSCE (Division E2) (in Japanese)

Abstract:
In this study, the structural performance of 15-year-old PC box-girder road bridge after reconstruction under severe chloride environment was evaluated. Since non-destructive test should be used for evaluating the structural performance of bridge in service, static and dynamic loading tests using dump trucks, impact vibration test by weight, and forced vibration test by vibration exciter were applied, focusing on the stiffness in whole superstructure, members, and local points in birdge. Also, by carrying out the FEM analysis considering the test results, it was verified the validity of consistency and test methods of various vaibration test results with different inspection range. These field testing results reveal that the stiffness of whole superstructure is similar to the design value, the degradation of stiffness in a part of decks is indicated, and in some local points in deck, the stiffness is remarkably decreased.

SEISMIC DEFORMATION OF A STEEL-CONCRETE SANDWICH MEMBER COMPOSED OF STEEL ELEMENTS CONNECTED WITH INTERLOCKING JOINTS

Tomonori ABO, Tadayoshi ISHIBASHI, Shigeru MATSUOKA, Tatsuji NAGAO and Motoaki KURISU
Vol. 72, No. 2, pp. 56-67, Journal of JSCE (Division E2) (in Japanese)

Abstract:
Currently, very few studies have been published that aim to examine the seismic deformation performance of a steel-concrete sandwich member integrating shear reinforcing steel plates which, with no displacement stop, are placed perpendicular to the member's axis. Furthermore, as regards the member composed of steel elements connected with interlocking joints, there have been no studies that quantitavely evaluate bending deformation performance under axial forces. In order to investigate this problem, we conducted a cyclic loading test of a full-scale specimen, through which we confirmed that localized cracks develop in the concrete, and using a non-linear finite element method, clarified a mechanism in which bending deformation progresses along with opening of localized cracks. At the same time, we proposed a model able to evaluate the amount of deformation in a simple quantitative way by accumulation of rotational deformations of blocks sandwiched between shear reinforcing steel plates. The validity of this model was demonstrated with a loading test and a finite element analysis.

FATIGUE EVALUATION FOR RC FOUNDATION OF WIND TURBINE BASED ON FIELD MEASUREMENT AND NONLINEAR FE ANALYSIS

Kaoru YONETSU, Chikako FUJIYAMA, Masuo KADO, Takuya MAESHIMA and Yasuhiro KODA
Vol. 72, No. 2, pp. 68-82, Journal of JSCE (Division E2) (in Japanese)

Abstract:
This paper shows fatigue evaluation method based on field measurements and FEM for RC foundation of wind turbine rated as 40 kW power class. First, field measurements for existing wind turbine were carried out to investigate the relation of action-response of tower-foundation system. Through a data analysis of the results of field measurement, multi-directional bending moment on foundation was expected. Next, a integrated model of tower-foundation system was built up for three dimentional nonlinear FE analysis. Damage process of reaching failure of the model was examined and limit state of concrete in the foundation was defined by numerical simulation. Furthermore, one of the indexes assessing damage state could identify a fatigue limit state of concrete subjected to repetition of loads.Consequently, the S-N diagram derived from the index indicated that the number of repetition of multi-directional loads reaching the fatigue limit state of concrete is much smaller than the number of repetition assuming single-direction loads, and experience of excessive load amplitude can affect the latter fatigue damage.

QUANTITATIVE EVALUATION OF WATER MIGRATION IN CONCRETE WITH THRESHOLD PORE DIAMETER OBTAINED BASED ON CRITICAL VOLUME FRACTION FOR PERCOLATION

Yuya SAKAI and Toshiharu KISHI
Vol. 72, No. 2, pp. 83-96, Journal of JSCE (Division E2) (in Japanese)

Abstract:
This study proposes a quantitative evaluation method of water migration in concrete. The threshold pore diameter (TPD) was obtained using the concept of critical volume fraction for percolation (CVFP; assumed to be 16%). This TPD had good correlation with the TPD obtained using another method which we had proposed in a previous study. The time required for water to penetrate in the concrete specimen by capillary actioin was calculated using the obtained TPD and compared with the measured time. The comparison yielded the tortuosity of six. Based on the concept of CVFP, the volume fraction of the pore whose size is greater than TPD can be constant. Permeated water volume in a water permeability test was calculated assuming tortuosity and effective area to be six and 16%, respectively, and the results agreed to some extent with the experimental ones. However, the calculation with the effective area of 16% overestimated the permeated water volume. We suggest that trapped air bubble during water infiltration can be the reason for the gap.

STUDY ON EVALUATION METHOD OF AUTOGENOUS SHRINKAGE STRAIN IN DAM CONCRETE

Hideaki SATO and Shingo MIYAZAWA
Vol. 72, No. 2, pp. 97-108, Journal of JSCE (Division E2) (in Japanese)

Abstract:
For the control of thermal cracking of concrete gravity dams in the design and construction stages, the effect of autogenous shrinkage of concrete on thermal ceacking has been considered to be negligible from such that it is lean mix concrete. On the other hand, the effects of cement type and mix proportion on autogenous shrinkage of dam concrete have not been made clear. In this study, autogenous shrinkage strain of dam concrete using full-sized aggregate was experimentally investigated. Autogenous shrinkage characteristics of dam concrete with several types of cement, which have generally been used in Japan, was also investigated. In addition, the design values of autogenous shrinkage strain to be used for verification of thermal cracking in the construction stage of concrete gravity dams were proposed.

FUNDAMENTAL STUDY ON IMPROVEMENT OF ESTIMATION ACCURACY OF CONTENT OF CHLORIDE IONS IN CONCRETE USING ELECTROMAGNETIC WAVES METHOD

Junichiro NOJIMA, Mami UCHIDA, Junichi ARAI and Toshiaki MIZOBUCHI
Vol. 72, No. 2, pp. 109-125, Journal of JSCE (Division E2) (in Japanese)

Abstract:
Chloride induced corrosion is one of the cause of deterioration reinforced concrete structures. In generally, as one of evaluation method of deteriorated situation caused by reinforcement corrosion in the concrete, drawing cores and chemical analysis are carried out. It is possible to perceive chloride content in the neighborhood of reinforcing bars. However, it is not possible to perceive only chloride ions at the position drawn cores and difficult to perceive about any corrosion of reinforcement unless corrosion induced cracks appear on the surface. Then, if it is possible to estimate the chloride ions in concrete using electromagnetic waves as a non-destructive method, it is possible to perceive the chloride ions in concrete without giving any damages. In addition, it is possible that this method conveniently evaluate the condition of degradation in respect of the wide area.
From past studies, it was confirmed that the amplitude value of the electromagnetic waves decreases with increasing chloride ions within concrete. It is possible to estimate chloride ions by utilizing this characteristic.
In this report, in order to improve the accuracy of this method, the theory construction and confirmation experiment were carried out. At first, the phenomenon of attenuation of electromagnetic waves by content of chloride ions in concrete was clarified by applying the electromagnetism and physicochemical theory. Next, each optimal solution was obtained by the result of measurement of radar, using specimens of concrete in which varied depth of concrete, temperature, water content and chloride content.
As the results, it is possible that the attenuation characteristics to electromagnetic waves by material changes of properties of concrete and to obtain the principle equation which contribute to improve in accuracy of estimation of chloride ions in concrete using electromagnetic waves.

INFLUENCE OF ALKALI SILICA REACTION ON FATIGUE RESISTANCE OF RC BRIDGE DECK

Takuya MAESHIMA, Yasuhiro KODA, Ichiro IWAKI, Hideki NAITO, Ryo KISHIRA, Yasunori SUZUKI, Koji OHTA and Motoyuki SUZUKI
Vol. 72, No. 2, pp. 126-145, Journal of JSCE (Division E2) (in Japanese)

Abstract:
This study aims at investigating an influence of alkali-silica reaction (ASR) on fatigue resistance of RC bridge deck. Firstly, using full-sized RC deck specimens, two types of ASR accelerated tests were performed by varying the environmental condition of ASR. Then, a wheel load trucking test was conducted focusing on the presence or absence of water on upper-surface of the specimen. In this experiment, the deflection and crack patterns of RC deck specimen in each number of trucking were measured, and the degradation of stiffness due to ASR and fatigue was evaluated by forced vibration test using small vibration device. As a result, it was revealed that the fatigue resistance of RC bridge deck by ASR depended on the environmental condition of ASR, which was assumed due to the introduction of chemical prestress by ASR, and the interaction of crack propagation and water action. Furthermore, the vibration test proved useful in evaluating the fatigue resistance of RC bridge deck by ASR.

EXPERIMENTAL STUDY ON FLEXURAL LOAD-CARRYING BEHAVIOR OF REINFORCED RC BEAMS WITH PRETENSIONED AFRP SHEET

Norimitsu KISHI, Hiroshi MIKAMI and Yusuke KURIHASHI
Vol. 72, No. 2, pp. 165-180, Journal of JSCE (Division E2) (in Japanese)

Abstract:
To establish a rational flexural reinforcing method for existing Reinforced Concrete (RC) beams using pretensioned Aramid Fiber Reinforced Polymer (AFRP) sheet, static loading tests on flexural reinforced RC beams were conducted taking sectional shape of beam, rebar ratio, sheet volume ratio, shear span ratio, and pretension force ratio as variables. In this study, the effects of these parameters on load-carrying capacity of the beams and debonding behavior of the sheet were investigated by comparing with between experimental results and analytical ones calculated by means of the multi section method. Furthermore, empirical prediction equations for failure mode of the RC beams reinforced with pretensioned AFRP sheet were developed. From this study, following results were obtained: 1) applying the pretensioned AFRP sheet bonding method proposed here, the load-carrying capacity of the RC beams can be upgraded irrespective of the magnitudes of design parameters of the RC beam; 2) introducing the pretension force to the AFRP sheet, sheet debonding due to peeling action of the critical diagonal cracks can be more restrained; and 3) an empirical prediction equation for failure mode of the flexural reinforced RC beam with pretensioned AFRP sheet was proposed which is composed of calculated two bending moments at rebar yielding and the ultimate state.

STUDY ON DYNAMIC SHEAR RESISTANCE OF RC BEAMS BASED ON DYNAMIC MODIFIED COMPRESSION FIELD THEORY

Amornthep SOMRAJ, Kazunori FUJIKAKE and Bing LI
Vol. 72, No. 2, pp. 181-195, Journal of JSCE (Division E2) (in Japanese)

Abstract:
In order to examine safety over over shear failure of RC beams subjected to impact loadings, it is essential to investigate the influence of loading rate on the shear resistance of RC beams and to develop an analytical model to evaluate it. Therefore, this paper initially presents an experimental investigation through rapid loading tests for RC beams with a shear span-to-depth ratio of 3.3 to clarify the effects of loading rates and shear reinforcement ratios on the failure modes and ultimate resistance of the RC beams. It was found that the RC beams without shear reinforcement exhibited diagonal tension shear failure under all the loading rates, while the failure modes were changed from brittle shear failure to ductile flexure failure by increasing the shear reinforcement ratios. The influence of loading rates on the ultimate resistance of the RC beams was more significant in shear failure than in flexure failure. Subsequently, well-known Modified Compression Field Theory (MCFT) developed under static loading was extended to the dynamic loading to evaluate the dynamic shear resistance of RC beams. The developed dynamic MCFT was justified by comparing with the experimental data. Finally it was found that the dynamic increase ratios in the shear resistance of RC beams calculated from the dynamic MCFT were consistent with those in the dynamic shear strength of concrete.

EFFECTS OF REINFORCING BACK SURFACE OF CONCRETE PLATES ON LOCAL DAMAGE CAUSED BY EXPLOSIVE LOAD

Hiroyoshi ICHINO, Makoto NAGATA, Masuhiro BEPPU and Tomonori OHNO
Vol. 72, No. 2, pp. 146-164, Journal of JSCE (Division E2) (in Japanese)

Abstract:
To establish a protective design for concrete structures, the explosive-resistant performance of concrete plates and the reinforced back surface of concrete plates were experimentally examined. In this study, explosion tests are conducted to examine the failure modes of concrete plates subjected to the contact explosion and the close-in explosion. Fiber sheet or polymer coating is used for the reinforcement of back surface of concrete plate. Generally, fiber sheet has high strength (high elastic modulus) and polymer coating has high braking strain. From test results, it is found that the reinforcement employed for these materials has remarkable effectiveness to reduce the local damage of concrete plates. Moreover, reinforcement of back surface can prevent the scattering of concrete fragment. The effect of reinforcement is formulated as a function of tensional stiffness of materials.