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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.

Latex modified concrete (LMC) is used for a bridge deck pavement method that was introduced in Korea in the 2000s, and it is currently the concrete pavement method being used for most highway bridges. It has been recommended that mixing with latex approximately 15% in terms of polymer-cement ratio (P/C ratio) by weight showed no occurrence of cracks with sufficient tensile strength and bond strength of LMC. However, many cracks occur in the actual field mostly due to drying shrinkage of concrete, requiring frequent repair. Therefore, this study examined the feasibility of applying a shrinkage reducing agent(SRA) that could reduce plastic shrinkage cracks at early age as well as drying shrinkage cracks of LMC. Based on the test results, it was confirmed that adding a shrinkage reducing agent could secure the durability without affecting the fresh and hardened properties of LMC. The compression strength test results presented a 1.7–5.7% improvement in strength to the SRA mixture compared to the plain mixture. Length change test results indicated that SRA mix conditions presented more outstanding performance compared to mix conditions with the expansive admixture. The amount of shrinkage reducing agent suitable for achieving performance requirements in length change, crack resistance, chloride ions penetration resistance and scaling resistance, was evaluated as 3% by weight ratio of binding material under the limited condition of the present study.

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%.

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.

This paper presents the results of experiments carried out to evaluate the utilization of foundry sand (FS) as a substitute material for fine aggregate in concrete production. The physical and chemical characteristics of the FS were also addressed. FS obtained from the aluminium casting industry was used as a substitute for fine aggregate in five different substitution rates (10%, 20%, 30%, 40% and 50%). Several tests, including density, slump cone, split tensile strength, flexural strength; ultrasonic pulse velocity (UPV) and compressive strength tests were performed to understand the effects of FS on the behavior of concrete. The grain size distribution analysis of FS revealed that 8% of FS were less than 75 μm, and the water absorption of FS was about 1.13%. The test results revealed that the strength properties of the concrete mixtures containing FS up to 20% was relatively close to the strength value of the CM, and the average decrease in strength was only 2.1%. The decrease in the strength is attributed to the fineness of the FS and the presence of dust, clay and wood flour in the FS. From the test results obtained it was concluded that a substitution rate of up to 20% can be effectively used in good concrete production without affecting the concrete standards, and a substitution rate beyond 20% is not beneficial.

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.

Half cell potential is a widely adopted Non-Destructive Technique in field to evaluate the corrosion of steel in concrete structures qualitatively. If the concrete is exposed to chloride attack, the cracks on concrete surface will rapidly accelerate the steel corrosion due to the intrusion of chloride ions and water permeation. This paper presented the test results of half cell potential evaluation in cracked concrete exposed to chloride attack. The test parameters taken were cover depth (30 mm and 60 mm), w/c ratio (0.35, 0.55, and 0.70), and crack widths (0.0–1.5 mm). To accelerate corrosion cyclic salt spraying test was performed on reinforced concrete beams for the duration of 35 days. Half cell potential (HCP) and corrosion state of rebar were evaluated. From the test results, HCP evaluation technique was proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore required cover depths for anticorrosive condition were obtained through chloride penetration analysis and the results were compared with previous study.

Recently, in order to reduce a damage of chloride attack and hydration heat in marine concrete structures, blended cement in mixing the marine concrete is widely used. Long term strength development is distinct in concrete with blended cement and it also has excellent resistance to chloride attack and reduction of hydration heat. However, blended cement has a characteristic of relatively low compressive strength in early age of 28 days. On the other hand, a high level of compressive strength is required in the Standard Specification for marine concrete mix design. Such concrete mix design satisfying Standard Specification is effective to chloride attack but disadvantageous for hydration heat reduction due to large quantity of binder. In this study, the material properties of marine concrete considering water-binder ratio and binder type are experimentally investigated. Through the research results, compressive strength in blended cement at the age of 56 days is similar although it has smaller compressive strength at the age of 28 days compared with result of OPC (ordinary portland cement). Even though blended cement has a large water-binder ratio and small unit of binder content, chloride ion diffusion coefficient is still small and hydration heat is also found to be reduced. For meeting the required compressive strength in Standard Specification for marine concrete at 28 days, the increased unit content of binder is needed but the increased hydration heat is also expected.

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.

In this study, the physical, mechanical, structural, and environmental performances based on field measured data were evaluated to check the suitability of concrete for ecological preservation and cultivation of a hydrophilic environment. More specifically, the study is focused on developing an environmentally friendly functional concrete with river ecology restoration and natural river early formation capabilities. The mechanical performance evaluation results showed that the increase in mix rate of the PVA (Poly Vinyl Alcohol) reinforcement fibers and silica fume caused an increase in the strength. The optimal mix rate was found to be 0.05 volume % PVA fiber and approximately 10% silica fume. The frost resistance evaluation showed that superior performance was gained when 0.05 volume % PVA fiber and 15% silica fume was mixed simultaneously. In the structural per- formance evaluation, the bending strength was improved by 47.7% compared to plain concrete when mixed with 0.05 volume % PVA fiber. The flexural toughness also saw significant improvement. The environmental monitoring of field performance showed that grasses germinated most rapidly, but the growth of red poppies, a plant that germinates in the spring, was most active with passing of time. Coverage measurements in all of the monitoring locations found favorable coverage of over 95% after 12 weeks. The study results showed that the environmentally friendly functional concrete had outstanding environmental performance.

This study investigated the compressive strength, flexural strength, setting time, and rebound when blast furnace slag and anhydrite, which are widely used mineral admixtures for concrete, are applied to shotcrete. When Ordinary Portland Cement (OPC) was replaced at a rate of 10% with blast furnace slag and anhydrite, the initial and final setting time requirements were all satisfied. However, when OPC was replaced at a rate of 20%, final setting was delayed, revealing that this mixture was not suitable for shotcrete. Compressive strength test results showed that the mixture with 10% OPC replacement rate met the target strength at 1 day and 28 days for permanent tunnel support usage. Particularly, the mixture designed with OPC replacement by blast furnace slag and anhydrite at rates of 5% showed the highest compressive strength. Rebound measurements revealed that this mixture exhibited excellent performance with 23% reduction in the rebound compared to the shotcrete that was produced with only OPC binder.

In order to improve the shear strength of conventional pre-tensioned spun high strength concrete (PHC) pile, concrete-infilled composite PHC (ICP) pile, a PHC pile reinforced by means of shear reinforcement and infilled concrete, is proposed. Two types of specimens were cast and tested according to KS (Korean Standards) to verify the shear strength enhancement of ICP pile. Based on the test results, it was found that the KS method was not suitable due to causing shear failure of ICP pile. However, shear strength enhancement was clearly verified. The obtained shear strength of the ICP pile was more than twice that of conventional PHC pile. In addition, the shear strength of ICP pile reinforced with longitudinal reinforcement was estimated to be more than 2.5 times greater than that of conventional PHC pile. The allowable shear force of ICP pile, which was determined by the allowable stress design process, indicated a large safety factor of more than 2.9 compared to the test results.

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 describes results of an preliminary study to produce strain hardening cement-based composites (SHCCs)with consideration of sustainability for infrastructure applications. The aims of this study are to evaluate the influence of recycled materials on the mechanical characteristics of SHCCs, such as compressive, four-point bending, and direct tensile behaviors, and to give basic data for constitutive model for analyzing and designing infra structures with SHCCs. In this study, silica sand, cement, and PVA fibers, were partially replaced with recycled sand, fly-ash, and FET fibers in the mixture of SHCCs, respectively. Test results indicated that fly-ash could improve both bending and direct tensile performance of SHCCs due to increasing chemical bond strength at the interface between PVA fibers and cement matrices. However, SHCCs replaced with PET fibers showed much lower performance in bending and direct tensile tests due to originally low mechanical properties of own fibers, although compressive behavior is similar to PVA2.0 specimen. Also, it was noted that the recycled sand would increase elastic modulus of SHCCs due to larger grain size compared to silica sand. Based on pre-set target value to maintain the performance of SHCCs, it was concluded that the replacement ratio below 20% of fly-ash or below 50% of recycled sands would be desirable for creating sustainable SHCCs.

Prepackaged ECCs are rheologically designed by determining the amount of admixtures such that they are suitable for self-consolidating and shotcreting processes. Rheology is controlled such that it can be directly applicable to construction in the field, using prepackaged products with all powdered ingredients. To control the rheological properties of the composites, which have different fluid properties that facilitate two types of processing (i.e., self-consolidating and shotcreting processes), the viscosity change of the cement paste suspensions over time was initially investigated. The proper dosage of the admixtures in the cement paste was then determined. The two most appropriate mixture proportions were then selected by conducting self-consolidating and shotcreting tests. A series of self-consolidating and shotcreting tests demonstrated excellent self-consolidation properties and sprayability of the prepackaged ECC. Subsequent direct tensile tests also revealed hardened properties of prepackaged ECC comparable to those of normally cast ECC.

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.

The fiber dispersion performance in fiber-reinforced cementitious composites is a crucial factor with respect to achieving desired mechanical performance. However, evaluation of the fiber dispersion performance in the composite PVA-ECC (Polyvinyl alcohol-Engineered Cementitious Composite) is extremely challenging because of the low contrast of PVA fibers with the cement-based matrix. In the present work, an enhanced fiber detection technique is developed and demonstrated. Using a fluorescence technique on the PVA-ECC, PVA fibers are observed as green dots in the cross-section of the composite. After capturing the fluorescence image with a Charged Couple Device (CCD) camera through a microscope. The fibers are more accurately detected by employing a series of process based on a categorization, watershed segmentation, and morphological reconstruction.

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.

In the recent design of high ductile engineered cementitious composites (ECC), optimizing both processing and mechanical properties for specific applications is critical. This study employs a method to develop useful ECC produced with slag particles (slag-ECC) in the field, which possesses different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing while retaining the ductile material properties. To control the rheological properties of the composite, the basic slag-ECC composition was initially obtained, determined based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of the suspensions were then mediated by optimizing the dosage of the chemical and mineral admixtures. The rheological properties altered through this approach were revealed to be effective in obtaining ECC-hardened properties, represented by pseudo strain-hardening behavior in uniaxial tension, allowing the readily achievement of the desired function of the fresh ECC.

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.

Steel reinforced concrete(SRC) columns, which have been widely employed in high-rise buildings, exhibit a time-dependent behavior because of creep and shrinkage of concrete. This long-term behavior may cause a serious serviceability problem in structural systems, so it is very important to predict the deformation due to creep and shrinkage of concrete. However, it was found from the previous experimental studies that the long-term deformation of SRC columns was quite dissimilar from that of RC columns. A new method is required to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the discrepancy between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of reinforced concrete(RC) columns owing to the presence of a inner steel plate, which interferes with the moisture diffusion of concrete. This relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns. Therefore it is suggested that the differential moisture distribution should be taken into account in order to reasonably predict column shortening of SRC columns.

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength( MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.

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.

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. Especially at early ages, this nonlinear distribution has a large influence on the crack evolution. As a result, in order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the convection heat transfer coefficient which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, curing condition and ambient temperature. At initial stage, the convection heat transfer coefficient is overestimated by the evaporation quantity. So it is essential to modify the thermal equilibrium considered with the boiling effect. From experimental results, the convection heat transfer coefficient was calculated using equations of thermal equilibrium. Finally, the prediction model for equivalent convection heat transfer coefficient including effects of velocity of wind, curing condition, ambient temperature and boiling effects was theoretically proposed. The convection heat transfer coefficient in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with curing condition. This tendency is due to a combined heat transfer system of conduction through form and convection to air. From comparison with experimental results, the convection heat transfer coefficient by this model was well agreed with those by experimental results.

Sprayable high ductile fiber-reinforced cementitious composite (ECC), which exhibits tensile strain-hardening behavior in the hardened state, while maintaining sprayable properties in the fresh state, has been developed by employing parallel control of micromechanical design and rheological process design. Initially, micromechanical tools were adopted to properly select the matrix, fiber, and interface properties, and also to exhibit strain-hardening and multiple cracking behaviors in the ECC composites. Within the pre-determined micromechanical constraints, the fluid properties were controlled by the rheological process design to develop flocculations between cementitious particles at a proper rate. The sprayable properties of ECC mix were then developed by the controlled rheological properties of fresh matrix and the uniform dispersion of fibers. A series of spray tests showed the excellent pumpability, sprayability, and rebound property of tile sprayable ECC. Subsequent uniaxial tensile tests demonstrated that the mechanical performance of sprayed ECC is comparable to that of ECC cast with external consolidation, for the same mix design.

This paper presents an experimental study on the potential durability enhancement of infrastructures repaired by a sprayed high ductile fiber-reinforced cementitious composite (ECC). For this study, a PVA-ECC which exhibits sprayable properties in the fresh state and tensile strain-hardening behavior in hardened state was sprayed and tested. The experimental results show that the sprayed ECC exhibits mechanical properties with strain capacity comparable to the cast ECC with the same mix design. During loading, the crack widths of ECC are tightly controlled with an average of 30. It is also revealed that when sprayed ECC is used as a repair material, ductility represented by deformation capacity at peak load of repaired beams in flexure are obviously increased in comparison to those of commercial prepackaged mortar (PM) repaired beams. In addition to high delamination resistance, the significant enhancement of energy absorption capacity and crack width control in ECC repair system suggest that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

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.

V. 101, No. 1, January-February 2004.MS No. 02-473 received December 11, 2002, and reviewed under Institute publicationpolicies. Copyright © 2004, American Concrete Institute. All rights reserved, includingthe making of copies unless permission is obtained from the copyright proprietors.Pertinent discussion including authors’ closure, if any, will be published in the November-December 2004