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External bonding of carbon-fibre-reinforced polymer composites has been proposed as an innovative technique to strengthen steel structures. This paper discusses an experimental study carried out to investigate the feasibility of using carbon-fibre-reinforced polymer composite strips for strengthening concrete-filled steel tubular columns. In this study, columns were strengthened using polymer composite strips 50 mm wide at two different spacings. They were then tested under compression until failure. The test results are discussed in terms of failure modes, stress–strain behaviour, load-carrying capacity and ductility. The results show that externally bonding composite polymer strips is an effective approach to restraining axial deformation and enhancing the ultimate capacity of columns under compression. By bonding the strips, the deformation of the columns was restricted to a maximum of 141·2% and 69·75% compared to the reference column when set at spacings of 20 mm and 40 mm, respectively. The capacity of the columns increased by about 30% for a 20 mm spacing, whereas no significant increase in capacity was observed for a 40 mm spacing. It is therefore recommended to apply this technique for strengthening and rehabilitating concrete-filled steel tubular columns and to use a 20 mm spacing.

The carbonation of concrete is one of the factors influencing the durability of reinforced concrete members or structures. Manual measurements can reportedly induce low reproducibility when measuring carbonation depths. This study presents a new image-processing algorithm for the automatic detection of carbonated regions of concrete sprayed with a phenolphthalein solution. The proposed image-processing algorithm consists of a primary detection process based on binarization and a morphology analysis and a secondary detection process based on a convex hull. A series of tests of images of carbonated concrete sprayed with the phenolphthalein solution is conducted to assess the validity of the proposed image-processing algorithm. The validation test results showed that the proposed image-processing algorithm is capable of the accurate detection of carbonated concrete regions compared to direct visual inspections.

The pile-cap connection part which transfers foundation loads through pile body is critical element regarding flexural and shea r force because the change of area, stress, and stiffness occurs in the this region suddenly. The purpose of this study is to investigate the s tructural behavior of pile-cap connection dependent on fabrication methods using conventional PHC pile and composite PHC pile. A series of test under cyclic lateral load was performed and the connection behavior was discussed. From the test results, it was found that the initial rotational stiffness of pile-cap connection was affected by the length of pile-head inserted in footing and the location of longitudinal reinforcing bars. The types of pile an d location of longitudinal reinforcing bars governed the behavior of pile-cap connection regarding load-carrying capacity, ductility, and energy dissipati on.Keywords: Pile-cap connection, Cyclic lateral load, PHC pile, Composite PHC pile 1 정회원, 충남대학교 건설방재연구소 박사후 연구원

This article presents the test results of an investigation carried out on the reuse of coal bottom ash aggregate as a substitute material for coarse aggregate in porous concrete production for marine ranch applications. The experimental parameters were the rate of bottom ash aggregate substitution (30%, 50% and 100%) and the target void ratio (15%, 20% and 25%). The cement-coated granular fertiliser was substituted into a bottom ash aggregate concrete mixture to improve marine ranch applications. The results of leaching tests revealed that the bottom ash aggregate has only a negligible amount of the ten deleterious substances specified in the Ministry of Environment – Enforcement Regulation of the Waste Management Act of Republic Korea. The large amount of bubbles/air gaps in the bottom ash aggregate increased the voids of the concrete mixtures in all target void ratios, and decreased the compressive strength of the porous concrete mixture; however, the mixture substituted with 30% and 10% of bottom ash aggregate and granular fertiliser, respectively, showed an equal strength to the control mixture. The sea water resistibility of the bottom ash aggregate substituted mixture was relatively equal to that of the control mixture, and also showed a great deal of improvement in the degree of marine organism adhesion compared with the control mixture. No fatality of fish was observed in the fish toxicity test, which suggested that bottom ash aggregate was a harmless material and that the combination of bottom ash aggregate and granular fertiliser with substitution rates of 30% and 10%, respectively, can be effectively used in porous concrete production for marine ranch application.

The prestressing force has not been managed after construction nevertheless it is one of the importrant factors that maintain the structural safety of PSC girder bridges. The prestressing force is just measured during construction using jacking device and after that, it can not be managed practically. For this reason, this study investigated the measurements of prestress using embedded sensors that can be available now with an ultimate goal to propose smart prestressed girders that can measure the prestress from the birth to the end of service life. 4 types of sensors were installed on the small prestressed girders, and the applicability and the accuracy of those sensors were tested while the prestress was applied to the girders. The results show that a center-hole type loadcell has a tendency to measure a prestressing force higher than a reference value, especially when it is loaded with an eccentricity. a EM sensor shows several advantages that has a good practical accuracy, that can be installed anyplace along the tendons.

Prestressed concrete girder bridges are one of the most widely used bridges in the world because of their excellent construction feasibility, economic efficiency, serviceability, and safety. In certain situations, however, the prestressing tendon is supposed to be bent locally, and this leads to the loss of prestress force. This kind of prestress loss is not considered in the design and construction processes. This study shows that prestress loss occurs at the locally bent tendon, and that a 2% maximum of prestress loss occurs at the locally bent tendon, due to eccentricity.

Over the last several decades, various approaches to strengthening steel structures through the use of Carbon fibre reinforced polymer (CFRP) composites have been investigated; however, most of the studies have been focused on the steel tubes. This paper presents the feasibility analysis on the application of CFRP composite strips to strengthen the CFST column member under axial loading. CFRP strips having a width of 50 mm were used to confine the columns. The experimental parameters were the spacing between the CFRP strips (20 and 30 mm) and number of CFRP layers (one, two and three layers). All columns were tested under axial compression until failure. The experimental results revealed that bonding of CFRP composites effectively delayed the local buckling of the columns and also reduced the axial deformation by providing a confinement/restraining effect against the elastic deformation at both spacings. The confinement effect provided by CFRP composites was increased with the increase in the number of layers; however, the enhancement in buckling stress was not proportional. The load carrying capacity of the column increased with the application of CFRP strips, by up to 30% compared to the of un-strengthened column. From the test results it is suggested that the application of CFRP strips at a spacing of 20 mm or 30 mm is suitable for strengthening of a CFST circular column member; however, the application of strips at intervals of 30 mm recommended as an economical approach to strengthening compared to the 20 mm spacing. Finally, an analytical equation was proposed to predict the load carrying capacity of the CFRP strengthened CFST column, and the average difference between the calculated and experimental value was only ±5%.

The potential for monitoring the construction of post-tensioned concrete beams and detecting damage to the beams under loading conditions was investigated through an experimental program. First, embedded sensors were investigated that could measure pre-stress from the fabrication process to a failure condition. Four types of sensors were installed on a steel frame, and the applicability and the accuracy of these sensors were tested while pre-stress was applied to a tendon in the steel frame. As a result, a tri-sensor loading plate and a Fiber Bragg Grating (FBG) sensor were selected as possible candidates. With those sensors, two pre-stressed concrete flexural beams were fabricated and tested. The pre-stress of the tendons was monitored during the construction and loading processes. Through the test, it was proven that the variation in thepre-stress had been successfully monitored throughout the construction process. The losses of pre-stress that occurred during a jacking and storage process, even those which occurred inside the concrete, were measured successfully. The results of the loading test showed that tendon stress and strain within the pure span significantly increased, while the stress in areas near the anchors was almost constant. These results prove that FBG sensors installed in a middle section can be used to monitor the strain within, and the damage to pre-stressed concrete beams.

Concrete infill and reinforcement are one of the most well-known strengthening methods of structural elements. This study investigated flexural performance of concrete infill composite PHC pile (ICP pile) reinforced by infill concrete and longitudinal rebars in hollow PHC pile. A total four series of pile specimens were tested by four points bending method under simply supported conditions and investigated bending moment experimentally and analytically. From the test results, it was found that although reinforcement of infilled concrete on the pure bending moment of PHC pile was negligible, reinforcement of PHC pile using infilled concrete and longitudinal rebars increase the maximum bending moment with range from 1.95 to 2.31 times than that of conventional PHC pile. The error of bending moment between experimental results and predicted results by nonlinear sectional analysis on the basis of the conventional layered sectional approach was in the range of -2.54 % to 2.80 %. The axial compression and moment interaction analysis for ICP piles shows more significant strengthening effects of infilled concrete and longitudinal rebars.

Prestressed concrete girder bridge has been one of the most widely used bridges in the world because of its excellent construction feasibility, economic efficiency, serviceability, and safety. In certain situations, the prestressing tendon is supposed to be bent by the construction error and the radius of curvature at the continuous joint of PSC girders, and this leads to the loss of prestressing force. However, this kind of prestress loss is not considered in the design and construction processes. This study proves that the prestress loss occurs at the continuous joint due to the local bending of tendon by the construction error or the radius of curvature. Also, a method that can reduce this type of prestress loss is proposed, and proved by the experiment. The result shows that maximum 10% of prestress loss occurs at the continuous joint and the proposed block-out method can reduce the prestress loss ratio by maximum 5%, approximately. This means that the block-out method can enhance the prestressing efficiency of continuous PSC girder bridges.

The conventional PHC pile-footing connection is the weak part because the surface area and stiffness are sharply changed. The Composite PHC pile reinforced with the transverse shear reinforcing bars and infilled-concrete, hereafter ICP pile, has been developed for improving the flexural and shear performance. This paper investigates the cyclic behavior and performance of the ICP pile-footing connection. To investigate the behavior of the connection, one PHC and two ICP specimens were manufactured and then a series of cyclic loading tests were performed. From the test results, it was found that the ICP pile-footing connection exhibited higher cyclic behavior and connection performance compared to the conventional PHC pile-footing connection in terms of ductility ratio, stiffness degradation and energy dissipation capacity.

Prediction of concrete cracking due to hydration heat in mass concrete such as reactor containment building (RCB) in nuclear power plant is a crucial issue in construction site. In this study, the numerical analysis for heat transfer and stress development is performed for the containment wall in RCB by considering the severe weather conditions. Finally, concrete cracking risk in hot and cold weather is discussed based on analysis results. In analyses considering severe weather conditions, it is found that the through-wall cracking risk in cold weather is high due to the abrupt temperature difference between inside concrete and the ambient air in cold region. In hot weather, temperature differences between inner and outer face is relatively small, and accordingly the relevant cracking risk is relatively low in contrast with cold weather.

Bending of a prestressing tendon by construction error or the radius of curvature at the continuous joint of PSC girders cannot be avoided. However, this kind of prestress loss is not considered in design and construction processes. This study proves that prestress loss occurs at the continuous joint due to local bending of the tendon which is induced by construction error or the radius of curvature. The result shows that a maximum 3 % of prestress loss occurs at the continuous joint for a single tendon.

The cracking and strength improvement in beams are one of main issues in the area of architecture and civil engineering. This paper presents the experimental and numerically predictive studies on the flexural performance of reinforced concrete (RC) beams strengthened with a strain-hardening cementitious composite (SHCC) and high strength reinforcing steel bar (HSRS bar) as a new strengthening method for beams. In order to investigate the effects of SHCC and HSRS bar on the control of cracking and load bearing capacity, four types of beam specimens were manufactured and a series of flexural bending tests were performed. The test results showed that the crack width can be controlled by applying SHCC and the load-bearing capacity of beams improved by applying the SHCC and HSRS bar.

Steel corrosion in reinforced concrete (RC) structure is such a critical problem to structural safety that many researches have been performed for maintaining required performance during intended service life. This paper is for a numerical technique for obtaining optimum concrete mix proportions through genetic algorithm (GA) for RC structures under carbonation which is considered as a serious deterioration in underground sites and big cities. For this study, mix proportions and CO2diffusion coefficients are analyzed through the previous studies, and then the fitness function of CO2diffusion coefficient is derived through regression analysis. The fitness function from 69 test results includes 5 variables of mix proportions such as w/c (water to cement) ratio, cement content, sand content percentage, coarse aggregate content, and R.H. (relative humidity). Through GA technique, simulated mix proportions are obtained for 12 cases of verification and they show reasonable results with average relative error of 4.6%. Assuming intended service life and design parameters, intended CO2diffusion coefficients and cement contents are determined and then related mix proportions are simulated. The proposed technique can provide initial concrete mix proportions which satisfy service life under carbonation.

Semi-rigid pavement, which mitigates the drawbacks of cement concrete and asphalt concrete pavements, is being widely used, but the body of research on enhancing the performance of cement grout remains limited. This paper discusses basic research on the development of a rapid hardening cement grout for semi-rigid pavement that meets chloride resistance, rheological property, and strength requirements. Evaluation results indicate that with up to 10% addition of expansive additive, in terms of the weight fraction of cement particles, the rheological property and strength requirements were satisfied. Examination of the chlorine ion penetration resistance revealed that an increase of expansive additive content yielded lower numbers of charged chlorine ions, resulting in 75.5 times higher resistance over a plain mix designed without expansive additive. In contrast, it was found that excessive addition of expansive additive, that is, beyond 10% in terms of the weight fraction of cement particles, was detrimental to achieving the desired rheological property.

In the present work, an image processing technique that automatically detects and analyses cracks in the digital image of concrete surfaces is proposed. The image processing technique automates the measurement of crack characteristics including the width, length, orientation and crack pattern. In the proposed technique, a morphological technique was applied to correct the non-uniform brightness of the background, and enhanced binarisation and shape analysis were used to improve the detection performance; furthermore, detailed algorithms to calculate the crack width, length, orientation and an artificial neural network to recognise crack patterns including horizontal, vertical, diagonal (−45°), diagonal (+45°), and random cracks are proposed. An image processing program was developed for the proposed algorithm and a series of experimental and analytical investigations were performed to assess the validity of the algorithm. Then, the crack characteristics measured using the proposed technique were compared ...

A research was conducted to develop a 2-D nonlinear Galerkin finite element analysis of reinforced concrete struc- tures subjected to high temperature with experiments. Algorithms for calculating the closed-form element stiffness for a triangular element with a fully populated material conductance are developed. The validity of the numerical model used in the program is established by comparing the prediction from the computer program with results from full-scale fire resistance tests. Details of fire resistance experiments carried out on reinforced concrete slabs, together with results, are presented. The results obtained from experimental test indicated in that the proposed numerical model and the implemented codes are accurate and reliable. The changes in thermal parameters are discussed from the point of view of changes of structure and chemical composition due to the high tem- perature exposure. The proposed numerical model takes into account time-varying thermal loads, convection and radiation affected heat fluctuation, and temperature-dependent material properties. Although, this study considered standard fire scenario for rein- forced concrete slabs, other time versus temperature relationship can be easily incorporated.

The brittleness of concrete raises several concerns due to the lack of strength and ductility in the plastic hinge region of reinforced concrete columns. In this study, in order to improve the seismic strength and performance of reinforced concrete columns, a new method of seismic strengthened reinforced concrete composite columns was attempted by applying High Performance Fiber Reinforced Cementitious composites (HPFRCs) instead of concrete locally in the plastic hinge region of the column. HPFRC has high-ductile tensile strains about 2–5% with sustaining the tensile stress after cracking and develops multiple micro-cracking behaviors. A series of column tests under cyclic lateral load combined with a constant axial load was carried out. Three specimens of reinforced concrete composite cantilever columns by applying the HPFRC instead of concrete locally in the column plastic hinge zone and one of a conventional reinforced concrete column were designed and manufactured. From the experiments, it was known that the developed HPFRC applied reinforced concrete columns not only improved cyclic lateral load and deformation capacities but also minimized bending and shear cracks in the flexural critical region of the reinforced concrete columns.

A model for the nonlinear flexural analysis of extruded Enginee red Cementitious Composite (ECC) panel reinforced concrete (RC) composite slab has been newly presented. From direct tensile test, ECC panel has been modeled to have the high-ductile tensile behavior after cracking. The developed mod el was compared with bending test results of two specimens, a conventional RC slab and a ECC panel RC composite slab. The predicted results were well patched with the experimental results, and the ECC panel RC composite slab system had advantages in crack control and improving flexural load-carrying capacity and deformation-capacity.

The nature of civil infrastructure projects can be described as complex and large-scale systems that are dynamically associated with diverse organizations and participants. Large budgets, collaboration efforts, and IT strategies are involved in major projects to increase the efficiency and effectiveness of all site activities involved. Emerging IT-based computational environments are providing a feasible vision of ubiquitous computing for the improvement of productivity and efficiency. This paper introduces the serviceability criteria of wireless sensor network to investigate the practical and technical considerations. Among the criteria, reliability issue was chosen for experimental analysis to analyze the equivalent distance between receiver and transmitter. The performance measurement indicates that the degraded ratio compared with the line-of-sight condition increases in accordance with the thickness and dielectric constant of construction material.

ECC is a micro-mechanically designed cementitious composite which exhibits tightly controlled crack width and strain hardening behavior in uniaxial tension while using a moderate amount of reinforcing fiber, typically less than 2% fiber volume fraction. Recently, a variety of applications of this material ranging from repair and retrofit of structures, cast-in-place structures, to precast structural elements requiring high ductility are developed. In the present study, a retrofitting method using ECC reinforced with high strength rebar was proposed to enhance load-carrying capacity and crack control performance of deteriorated reinforced concrete (RC) beams. Six beam specimens were designed and tested under a four-point loading setup. The flexural test revealed that load-carrying capacity and crack control performance were significantly enhanced by the use of ECC and high strength rebar. This result will be useful for practical field applications of the proposed retrofitting method.

Fibre distribution characteristics were evaluated to investigate their effect on the flexural strength of steel fibre-reinforced ultra high strength concrete in conjunction with the direction of placement. For this purpose, an image processing technique developed in this study was employed. Flexural tests were carried out to quantify the effect of fibre distribution characteristics on flexural strength. It was found that the image processing technique developed in this study could quantitatively evaluate the fibre distribution property by the use of the distribution coefficient, the number of fibres in a unit area, the packing density of the fibre image, and fibre orientation. It was also found that the fibre distribution characteristics were dependent on the direction of placing. Fibre distribution characteristics were revealed to strongly affect the ultimate flexural strength, while hardly affecting the first cracking strength. The validity of the current test results was verified through comparison with a theoretical model of flexural strength.

This paper presents a prediction and simulation method of tensile stress-strain curves of Engineered Cementitious Composites (ECC). For this purpose, the bridging stress and crack opening relations were obtained by the fiber bridging constitutive law which is quantitatively able to consider the fiber distribution characteristics. And then, a multi-linear model is employed for a simplification of the bridging stress and crack opening relation. In addition, to account the variability of material properties, randomly distributed properties drawn from a normal distribution with 95% confidence are assigned to each element which is determined on the basis of crack spacing. To consider the variation of crack spacing, randomly distributed crack spacing is drawn from the probability density function of fiber inclined angle calculated based on sectional image analysis. An equation for calculation of the crack spacing that takes into quantitative consideration the dimensions and fiber distribution was also derived. Subsequently, a series of simulations of ECC tensile stress-strain curves was performed. The simulation results exhibit obvious strain hardening behavior associated with multiple cracking, which correspond well with test results.

In the current research, a displacement-based seismic design scheme to retrofit reinforced concrete columns using FRP composite materials has been proposed. An accurate prediction for the nonlinear flexural analysis of FRP jacketed concrete members has been presented under multiaxial constitutive laws of concrete and composite materials. Through modification of the displacement coefficient method (DCM) and the direct displacement-based design method (DDM) of reinforced concrete structures, two algorithms for a performance-based seismic retrofit design of reinforced concrete columns with a FRP jacket have been newly introduced. From applications to retrofit design it is known that two methods are easy to apply in retrofit design and the DCM procedure underestimates the target displacement to compare with the DDM procedure.

Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, KoreaABSTRACT To evaluate the fiber orientation characteristics and estimate its effect on the flexural strength of steel fiber rein-forced ultra high strength concrete with directions of concrete placing, we developed an image processing technique and carriedout the flexural test to quantify the effect of fiber orientation characteristics on the flexural strength as well. The image processingtechnique developed in this study could evaluate quantitatively the fiber orientation property by the use of dispersion coefficient,the number of fibers in a unit area, and fiber orientation. It was also found that the fiber orientation characteristics were dependenton the direction of concrete placing. Fiber orientation characteristic was revealed to strongly affect the ultimate flexural strength,while hardly affecting the first cracking strength. Theoretical model for flexural strength was applied to compare with test results,which exhibited a good agreement.Keywords : ultra high strength concrete, steel fiber, fiber orientation, image processing, flexural strength

The purpose of this study is to suggest a method of quantitatively predicting long-term deformation of walls under an axial load concentrated on a part of the entire width of the walls. Four wall specimens were tested and three-dimensional finite element analyses were performed for these specimens. The test results verified the finite element models. On the basis of this verification, analysis parameters were selected with respect to various dimensions of the walls and the sectional area of the concentrated load, and finite element analyses for these parameters were carried out. The novel concept of the effective width coefficient was introduced as a method of predicting the long-term behaviour of walls. Furthermore, from the regression analysis, a function is suggested that can optimally fit the effective width coefficients that were calculated from the analysis results for the selected parameters. The suggested function can be conveniently used to predict the long-term behaviour under loads concentrated on a local area for the entire width of walls.

A number of studies have suggested that the use of high ductile and high shear materials, such as Engineered Cementitious Composites (ECC) and High Performance Fiber Reinforced Cementitious Composites (HPFRCC), significantly enhances the shear capacity of structural elements, even with/without shear reinforcements. The present study emphasizes the development of a nonlinear model of shear behaviour of a HPFRCC panel for application to the seismic retrofit of reinforced concrete buildings. To model the shear behaviour of HPFRCC panels, the original Modified Compression Field Theory (MCFT) for conventional reinforced concrete panels has been newly revised for reinforced HPFRCC panels, and is referred to here as the HPFRCC-MCFT model. A series of experiments was conducted to assess the shear behaviour of HPFRCC panels subjected to pure shear, and the proposed shear model has been verified through an experiment involving panel elements under pure shear. The proposed shear model of a HPFRCC panel has been applied to the prediction of seismic retrofitted reinforced concrete buildings with in-filled HPFRCC panels. In retrofitted structures, the in-filled HPFRCC element is regarded as a shear spring element of a low-rise shear wall ignoring the flexural response, and reinforced concrete elements for beam or beam-column member are modelled by a finite plastic hinge zone model. An experimental study of reinforced concrete frames with in-filled HPFRCC panels was also carried out and the analysis model was verified with correlation studies of experimental results.

An experimental program to apply a new retrofit technology using high performance carbon fiber reinforced polymer (CFRP) bars with a trapezoidal cross section to reinforce concrete beams has been investigated. The proposed method has two important advantages in the retrofit of concrete beams: the failure mode of the beam is controlled by flexural failures before reaching local failures and the retrofitting process in the construction field is simple and easy to apply in aged reinforced concrete beams or beam–column members. The new methodology has been proposed based on a system where geometrically modulated CFRP trapezoidal bars are embedded into grooved concrete with additional assistance from externally applied U-type metal fittings. The proposed retrofit method is validated by comparing it with the experimental results of conventionally strengthened beams and showing that the proposed method gives good improvement in ductility and load-carrying capacities of concrete beams. When compared with conventional retrofit methods using steel plates or FRP sheets, the proposed method is effective in preventing local failures before reaching the flexural failure of retrofitted beams, due to the superior composite action between the concrete and embedded CFRP trapezoidal bars.

This paper presents experimental and analytical studies on the long-term behaviour of rectangular concrete-filled steel tubular (CFT) columns under central axial loading. Four loading cases are considered in this study: (a) a load applied simultaneously on both the inner concrete and steel tube (SCE); (b) a load applied only on the inner core concrete (CE); (c) a load applied on the steel tube and three quarters of the inner concrete (SCQ); and (d) a load applied on the steel tube and half of the inner concrete (SCH). The last two loading cases (SCQ and SCH) simulate a diaphragm installed in the steel tube. Specimens measuring 600 mm in length were tested for the first two loading cases (SCE and CE), and specimens of three different lengths, 600, 900 and 1200 mm, were tested for the last two loading cases in order to investigate the effect of the diaphragm size and the length of the specimen on the long-term behaviour of rectangular CFT columns. In addition to the experimental study, three-dimensional finite element models for each specimen were established and verified from a comparison of the test data and the analysis results. From the test and analysis results, a number of conclusions can be drawn. The magnitude of long-term deformation of a CFT column with a diaphragm that covers more than a half of the cross-sectional area of the inner concrete is identical with that of a column under a load applied simultaneously on the entire section of the steel tube and the inner concrete. The diaphragm confines the lateral deformation of the end surface of the column, and its influence range is limited only to the end part of the column, meaning it is limited only from the surface to a depth as long as the width of the CFT column. The confinement effect and stress variation along the longitudinal axis do not occur except in the influence range of the diaphragm. In the case of loading only at the inner concrete, the inner concrete is confined at the corner by the steel tube, and the slip between the inner concrete and the steel tube increases over time.

This paper presents an experimental study on the repair performance of sprayed engineered cementitious composites(ECC) serving as a repair material. Sprayable ECC, which exhibit tensile strain-hardening behavior in the hardened state and maintain sprayable properties in the fresh state, have been developed by using a parallel control of micromechanical design and rheological process design. The effectiveness of sprayable ECC in providing durable repaired structures was assessed by spraying the ECC and testing them for the assessment. The experimental results revealed that, when sprayed ECC were used as a repair material, both load carrying capacity and ductility represented by the deformation capacity at peak load of the repaired flexural beams were obviously increased compared to those of commercial prepackaged mortar(PM) repaired beams. The significant enhancement in the energy absorption capacity and tight crack width control of the ECC repair system treated with wet-mix spraying process suggests that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

The purpose of this study is to suggest a method to quantitatively predict long-term deformation of walls under an axial load concentrated to a part of the whole width. Four wall specimens were tested and three-dimensional finite element analyses were performed for these specimens. The finite element models established in this study were verified from the test results. On the basis of this verification, analysis parameters were selected considering various dimensions of walls and sectional area that a concentrated load is acting on, and finite element analyses for these parameters were carried out. The concept of the effective width coefficient was newly introduced as a method to predict the long-term behavior of walls, and a function that is able to optimally fit the effective width coefficients calculated from the analysis results for the selected parameters was found from regression analysis. The found function can be conveniently used in practice to predict the long-term behavior under loads concentrated to a local area of the whole width of walls.

This paper presents experimental and analytical studies on long-term behavior of square CFT columns with diaphragm. In order to investigate the effect of the diaphragm on the long~term behavior, experiments for six specimens with two diaphragms and three different column length, and three-dimensional finite element analysis for each specimen have been performed. The finite element models considering the interface behavior between the steel tube and the inner concrete were verified from comparison of the test results with the analysis results. From the test and the analysis results, the following conclusions were obtained. The confinement effect created by the diaphragm does not depends on column length and influences only a part of the whole column that is from the end to the depth which is the same to the width of the column. The shortening of the column with diaphragm which covers more than a half of the cross sectional area of the inner concrete is the same as that of the column under a load applied on the steel tube and the entire section of the inner concrete.

In this study, a wedge-splitting testing was carried out for the investigation of fatigue crack growth behavior of high strength concrete. Selected test variables were concrete compressive strength (28, 60, and 118 MPa) and stress ratio (6, 13%). In order to apply the target stress ratio, the maximum and the minimum fatigue loadings were 75–85 and 5–10% of ultimate static load, respectively. Fatigue testing was preceded by crack mouth opening displacement (CMOD) compliance calibration, and then the fatigue crack growth was computed by crack length vs. the CMOD compliance relations acquired by the CMOD compliance calibration technique. In the fatigue test, the frequency of loading cycle was 1 Hz, and the initial notch length a0 was 30% of specimen height. To verify the applicability of the CMOD compliance calibration technique to wedge-splitting testing, the crack lengths measured by this method were compared with those predicted by linear elastic fracture mechanics (LEFM) and dye penetration testing. On the basis of the experimental results, an LEFM-based empirical model for fatigue crack growth rate (da/dn − ΔKI relationship) that takes strength into account was suggested. The fatigue crack growth rate increased with the strength of concrete. It appeared that the da/dN − ΔKI relationship depended on stress ratio, and the effect was evaluated by the proposed equation. In addition, the comparisons between the CMOD compliance calibration technique and the other methods supported the validity of this technique in the wedge splitting test.

The distribution of fiber orientation is an important factor in determining the mechanical properties of fiber-reinforced concrete. This study proposes a new image analysis technique for improving the evaluation accuracy of fiber orientation distribution in the sectional image of fiber-reinforced concrete. A series of tests on the accuracy of fiber detection and the estimation performance of fiber orientation was performed on artificial fiber images to assess the validity of the proposed technique. The validation test results showed that the proposed technique estimates the distribution of fiber orientation more accurately than the direct measurement of fiber orientation by image analysis.

This paper presents an innovative approach to designing the transition zones between concrete deck slab segments and an adjacent highly deformable link slab on a steel girder composite bridge deck. (A link slab provides a special class of jointless bridge for which only the bridge deck is made continuous rather than both the deck and girders). The transition zones represent a fraction of the ends of the link slab introduced to divert stress from the potentially weak link slab/deck slab interface. The link slab studied herein is built with an engineered cementitious composite (ECC), an ultra ductile concrete, adopted in a recent demonstration project in Southeast Michigan. Conventional design of concrete link slabs leaves the old/new concrete interface as the weakest part of the bridge deck system. Due to the presence of a link slab debond zone (part of the link slab is debonded from bridge girder to provide hinge flexibility), this interface also experiences high stress concentrations. In addition, the effectiveness of the link slab design depends on the integrity of the interface so that imposed rotation and tensile deformation will be accommodated within the highly deformable ECC link slab. The basis of the suggested approach is to isolate the concrete/ECC interface away from the structural interface between the debond zone and composite zone to prevent interfacial cracking. The shear studs and lap-spliced reinforcement located within transition zones facilitate load transfer between the concrete deck and the ECC link slab. These modifications are expected to cause a shift of the stress concentration from the concrete/ECC interface to the bulk part of the ECC link slab. In support of this new design concept, experimental tests are carried out on the behavior of the ECC link slab-bridge deck-girder connection. Detailing of the transition zone, that is, spacing of shear stud and development length/lap splice length requirement is then laid out in a design procedure based on results of shear stud/ ECC pushout and reinforcement pullout tests.

Reinforced concrete (RC) shield tunnel lining must be designed for fireproof performance because the lining is sometimes expose d to very high temperature due to traffic accidents. Both experimental and numerical studies are carried out to evaluate fire resistance performance of precast RC tunnel lining systems. In the experimental studies, six full-scale precast RC tunnel segments are exp osed to fire in order to examine the influence of various parameters on the fire resistance performance of precast RC tunnel lining. We used the temperature curve of the RABT criteria, which are severe conditions of fire temperatures. The fire test showed that the explosive spalling was not observed by substituting concrete to PP fiber reinforced concrete. A transient heat flow analysis was carried out in consideration of the material properties that change with temperature, and the results showed good agreement with the test results.Key words : Fire resistance, Precast segment, Concrete lining, Heat flow analysis, RABT criterion초 록철근콘크리트 쉴드 터널 라이닝은 대형화재 등과 같은 고온에 노출될 경우 , 구조체에의 급격한 온도 전달 및 내하력 저하로 구조체 붕괴의 원인이 될 수 있기 때문에 내화성능을 확보해야 한다. 이 연구는 쉴드터널의 프리캐스트 RC 세그먼트 라이닝에 대한 내화성능을 평가하고자 실험/해석적 연구를 수행하였다. 실험적 연구에서는 프리캐스트 RC 세그먼트내의 열적 취약부위를 실험변수로 하여 6개의 실 대형 실험체에 대한 내화실험을 실시하였으며, 화재조건은 RABT 곡선에 의한 온도이력을 이용하였다. 내화실험결과 이 연구에서 제시된 쉴드형 터널의 PP섬유 혼입콘크리트 충전부위는 폭렬이 발생하지 않는 우수한 내화성능을 나타내었다. 해석적 연구에서는 온도의존성을 고려한 재료의 열특성을 고려하여 비정상 유한요소 온도분포해석 기법을 이용하였는데, 실험결과를 잘 모사하는 것으로 검증되었다.검색어 : 내화성능, 프리캐스트 세그먼트, 콘크리트 라이닝, 열전달해석, RABT 시간가열곡선