This paper presents damage assessment schemes by using 2-dimensional nonlinear finite element analyses. The second strain invariant of deviatoric strain tensor and consumed strain energy are calculated by local strain at each integration po int of finite elements. Those scalar values are averaged over certain region. The produced nonlocal values are used for indices to verify structural safety by confirming which the ultimate limit state for failure is reached or not. Flexural and shear failure of reinforced concrete beams are estimated by us ing the proposed indices.
The size effect on flexural fatigue strength of concrete was experime ntally investigated. For this purpose, specimens of two sizes were prepared: 150mm x 150mm x 530mm (span=450mm) and 200mm x 450mm x 1800mm (span=1350mm). The stress levels were set at 70%, 80% and 90% of the compressive strength. Experimental results showed that the number of loading cycles at failure increased with the enlargement of specimens. Based on a fracture mechanics approach, with a stress level of 70%, this dependence of flexural fatigue strength on size was explained by the difference in the stress distributions in the sections of small and large sized specimens. A te nsion softening stress region was formed in the section of the small specimen, whereas elastic stress was produced over the full section in the large specimen.
The aim of this research is to clarify the mechanism of controlling plastic shrinkage crack by adding small amout of synthetic short fiber, and to propose optimum polypropylene short fiber to control plastic shrinkage crack. In this research, the effect of the hydrophily of polypropylene fiber was investigated in the amount of plastic shrinkage of mortar, total area of plastic shrinkage crack, and bond properties between fiber and mortar. The plastic shrinkage test of morar was conducted under high temperature, low relative humidity, and constant wind velocity. When polypropylene fiber had hydrophily, the amount of plastic shrinkage of mortar was restrained, which was because cement paste in morar was captured by hydrophilic fiber and then bleeding of mortar was restrained. With hydrophily, plastic shrinkage of mortar was restrained and bridging effect was improved due to better bond, which led to remarkable reduction of plastic shrinkage crack. Based on experimental results, the way of developing optimum polypropylene short fiber for actual construction was proposed. The fiber should have large hydrophily and small diameter, and should be used in as small amount as possible in order not to disturb workability of concrete.
The shear-resisting mechanism of solid circular RC lin ear members is different from that of rectangular RC members. The objective of this re search is to propose the equation fo r evaluating the shear capacity of reinforced concrete (RC) beams of solid circular cross section. The bending tests of solid circular RC beams were conducted under simply-supported condition. A series of experimental results indicated that conventional evaluation methods were difficult to predict the shear capacity of solid circular RC beams. Distributed longitudinal bars, angle of diagonal crack, shape of stirrups were taken into account. Finally, the paper proposed the equations that can predict the shear capacity of solid circular RC beams accurately.
Recycled aggregates have brittle defects such as cracks, pores, and voids, which comes from the residue of paste in original concrete. This report presents a method of improving the quality of recycled fine aggregate by a producing method of selectively removing the defects. Fourteen different kinds of recycled fine aggregates were manufactured by three different griding machines: joe crusher, ball mill and granulator. The influences of the characters on the recycled fine aggregates on the flowability and strength of the recycled mortar was evaluated using multiple linear regression analysis. From the results obtained in this study, it is clear that the flowability was mainly affected by both the filling fraction of recycled fine aggregate and the amount of fine powder, whereas both the compressive strength and bending strength of mortars were affected not by the filling fraction, but by the fraction of defects and the surface smoothness of the aggregates. Compareing the properties of mortar with grinding machine, it is evident that the polishing action, which is such as the ball mill or the granulator is effective both to increase the filling fraction of recycled fine aggregate and to reduce the fraction of defects in the aggregate. It was also found that the surface of grain was more irregular when the granulator was used compared with the ball mill, and hence the strength of the recycled mortar was increased.
In applying the glulam timber to the large-sized structures, the new types of connections have been developed. In presence, there are a few joint systems using steel plates and bolts. However, those systems are not always adequately satisfied with durability. Therefore, the new joint system by prestressing was developed. In Nagano prefecture, the timber-concrete composite bridge was provided as the standard design of timber bridges, and the joint system is by prestressing. In case of concrete girder, work of prestress decrease by elastic strain, creep, and etc. However, timber-concrete composite girder is not cleared numerically. In this study, we discussed the effective prestress on timber-concrete composite girder based on time-dependent of prestress checked in existing bridge, and we suggest the evaluation method of it.
A simulation model to estimate the pore structure of cement hydrates by curing in arbitrary relative humidity is presented. This paper describes procedures for predicting phase compositions based on the classical hydration model of Portland cement, calculating the particle size distribution of constituent phases and evaluating the pore size distribution by stereological and statistical considerations. And to estimate the water content in pore structure under any relative humidity, we proposed the simulation model of adsorption isotherm model based on the pore structure. To evaluate the effectiveness of this model, simulation results were compared with experimental results of the pore size distribution measured by mercury porosimetry. As a result, it was found that the experimental and simulated results were in close agreement, and the simulated results indicated characterization of the po re structure of cement hydrates.
There is a need to develop the generalized bond stress-slip relationship since bond characteristics between steel reinforcing bars and concrete may be influenced by various parameters. Although one of the reliable approaches is to consider the influence of steel strain in the bond model, the existing model is only based on the pull-out tests of a deformed bar embedded in massive concrete. This paper presents bond stress-slip-strain relationships of deformed bars including the effect of concrete cover thickness. The proposed model represents the post-peak behavior of bond shown in bars with small cover thickness. The model performance is demonstrated through finite element analyses of bond tests with different boundary conditions.
Impact Elastic Wave Method is a non destructive test method for concrete structures. In Impact Elastic Wave Method, Fast Fourier Transform (FFT) has mainly been used for measuring the frequency with which elastic wave is reflected between the opposite su rfaces of a concrete plate, and if the velocity of elastic wave is known, the thickness of concrete plat e can be calculated by this measured frequency. In this paper limitation of measuring by using FFT is discussed and other frequency analysis method that uses cross-correlation function and FFT is studied. As a result, the attenuation of reflected elastic wave was found to be the major drawback to determination of the frequency. In concrete plate whose thickness is 2m or greater, the thickness of concrete plate can not be measured by using FFT. On the other hand, the cross-correlation function that is cal culated by the initial portion of the waveform relate to the arrival time of the reflected elastic wave without influence of the attenuation. It was concluded that the frequency analysis method using cross-correlation function and FFT can be an effectual method for measuring the frequency and the thickness of concrete plate.
In this study, the durability evaluation of concrete and mortar that mixed fly ash was done through the measurement of the diffusion co efficient of the chloride ion and the electrical resistivity. To evaluate the durability in the initiation stage, the statistical analysis of the diffusion coefficient of the chloride ion of the offshore structure was done. It was clarified that the initiation stage until the reinforcement corrosion began elongated by mixing fly ash. Moreover, durability in the acceleration stage was eval uated by the electrical resistivity that is the index that showed resistance to the reinforcement corrosion and impermeability. As the result of the concrete and mortar tests, it was clarified that the durability was improved by mixing of fly ash.
This research proposed a framework for assessing c oncrete sustainability which is based upon the concept that technology is defined by stakeholders' perspectives and which applied Analytic Hierarchy Process to translate these perspectives into quantifiable assessment values. A survey was conducted to identify important criteria, and several "design scenarios" were introduced which represent different value systems by varying criteria importance. Concrete materials with varying environmental impact were then assessed to observe the effect of different value systems and material properties, and it was found that the concrete with better properties was generally selected as most sustainable regardless of the design scenario.
When a reinforced concrete member having cracks at the anchorage zones is loaded, diagonal crack is formed from the tip of the exsisting crack, and it lead s to brittle shaer failure. A reinforced concrete beam containing corrosion cracks at the anchorage zone were strengthened with sheets at the expected damaging zones, and tested in 3-point loading. Th e test result shows that the load capacity of the strengthened beam was the same to that of the repli cate beam with no damage at the anchorage zones and contained enough shear reinforcement to develop flexural failure. It means that strenghtneing at the expected damaging zone with keeping corrosion cr acks along to the tensile reinforcements at the anchorage zones may improve the load capacity of the damaged reinforced concrete.
This paper presents a comprehensive review on the available prediction models in the literature to estimate shear crack width in reinforced and prestressed concrete members by comparing shear crack openings calculated from prediction model with those obtained from seven experimental investigations to evaluate their accuracy together with effectiveness of factors considered. As a result of this study, the models for the prediction of shear crack spacing and width in reinforced and prestressed concrete beams are proposed. The proposed models show a better correlation with all the test results compared to the other prediction models. The models can predict both average and maximum shear crack width and are applicable to fatigue loading.