In this study, the structural performance of 15-year-old PC box-girder road bridge after reconstruction under severe chloride environment was evaluated. Since non-destructive test should be used for evaluating the structural performance of bridge in service, static and dynamic loading tests using dump trucks, impact vibration test by weight, and forced vibration test by vibration exciter were applied, focusing on the stiffness in whole superstructure, members, and local points in bridge. Also, by carrying out the FEM analysis considering the test results, it was verified the validity of consistency and test methods of various vibration test results with different inspection range. These field testing results reveal that the stiffness of whole superstructure is similar to the design value, the degradation of stiffness in a part of decks is indicated, and in some local points in deck, the stiffness is remarkably decreased.
Currently, very few studies have been published that aim to examine the seismic deformation performance of a steel-concrete sandwich member integrating shear reinforcing steel plates which, with no displacement stop, are placed perpendicular to the member's axis. Furthermore, as regards the member composed of steel elements connected with interlocking joints, there have been no studies that quantitatively evaluate bending deformation performance under axial forces. In order to investigate this problem, we conducted a cyclic loading test of a full-scale specimen, through which we confirmed that localized cracks develop in the concrete, and using a non-linear finite element method, clarified a mechanism in which bending deformation progresses along with opening of localized cracks. At the same time, we proposed a model able to evaluate the amount of deformation in a simple quantitative way by accumulation of rotational deformations of blocks sandwiched between shear reinforcing steel plates. The validity of this model was demonstrated with a loading test and a finite element analysis.
This paper shows fatigue evaluation method based on field measurements and FEM for RC foundation of wind turbine rated as 40 kW power class. First, field measurements for existing wind turbine were carried out to investigate the relation of action-response of tower-foundation system. Through a data analysis of the results of field measurement, multi-directional bending moment on foundation was expected. Next, a integrated model of tower-foundation system was built up for three dimensional nonlinear FE analysis. Damage process of reaching failure of the model was examined and limit state of concrete in the foundation was defined by numerical simulation. Furthermore, one of the indexes assessing damage state could identify a fatigue limit state of concrete subjected to repetition of loads. Consequently, the S-N diagram derived from the index indicated that the number of repetition of multi-directional loads reaching the fatigue limit state of concrete is much smaller than the number of repetition assuming single-direction loads, and experience of excessive load amplitude can affect the latter fatigue damage.
This study proposes a quantitative evaluation method of water migration in concrete. The threshold pore diameter (TPD) was obtained using the concept of critical volume fraction for percolation (CVFP; assumed to be 16%). This TPD had good correlation with the TPD obtained using another method which we had proposed in a previous study. The time required for water to penetrate in the concrete specimen by capillary action was calculated using the obtained TPD and compared with the measured time. The comparison yielded the tortuosity of six. Based on the concept of CVFP, the volume fraction of the pore whose size is greater than TPD can be constant. Permeated water volume in a water permeability test was calculated assuming tortuosity and effective area to be six and 16%, respectively, and the results agreed to some extent with the experimental ones. However, the calculation with the effective area of 16% overestimated the permeated water volume. We suggest that trapped air bubble during water infiltration can be the reason for the gap.
For the control of thermal cracking of concrete gravity dams in the design and construction stages, the effect of autogenous shrinkage of concrete on thermal cracking has been considered to be negligible from such that it is lean mix concrete. On the other hand, the effects of cement type and mix proportion on autogenous shrinkage of dam concrete have not been made clear. In this study, autogenous shrinkage strain of dam concrete using full-sized aggregate was experimentally investigated. Autogenous shrinkage characteristics of dam concrete with several types of cement, which have generally been used in Japan, was also investigated. In addition, the design values of autogenous shrinkage strain to be used for verification of thermal cracking in the construction stage of concrete gravity dams were proposed.
Chloride induced corrosion is one of the cause of deterioration reinforced concrete structures. In generally, as one of evaluation method of deteriorated situation caused by reinforcement corrosion in the concrete, drawing cores and chemical analysis are carried out. It is possible to perceive chloride content in the neighborhood of reinforcing bars. However, it is not possible to perceive only chloride ions at the position drawn cores and difficult to perceive about any corrosion of reinforcement unless corrosion induced cracks appear on the surface. Then, if it is possible to estimate the chloride ions in concrete using electromagnetic waves as a non-destructive method, it is possible to perceive the chloride ions in concrete without giving any damages. In addition, it is possible that this method conveniently evaluate the condition of degradation in respect of the wide area. From past studies, it was confirmed that the amplitude value of the electromagnetic waves decreases with increasing chloride ions within concrete. It is possible to estimate chloride ions by utilizing this characteristic. In this report, in order to improve the accuracy of this method, the theory construction and confirmation experiment were carried out. At first, the phenomenon of attenuation of electromagnetic waves by content of chloride ions in concrete was clarified by applying the electromagnetism and physicochemical theory. Next, each optimal solution was obtained by the result of measurement of radar, using specimens of concrete in which varied depth of concrete, temperature, water content and chloride content. As the results, it is possible that the attenuation characteristics to electromagnetic waves by material changes of properties of concrete and to obtain the principle equation which contribute to improve in accuracy of estimation of chloride ions in concrete using electromagnetic waves.
This study aims at investigating an influence of alkali-silica reaction (ASR) on fatigue resistance of RC bridge deck. Firstly, using full-sized RC deck specimens, two types of ASR accelerated tests were performed by varying the environmental condition of ASR. Then, a wheel load trucking test was conducted focusing on the presence or absence of water on upper-surface of the specimen. In this experiment, the deflection and crack patterns of RC deck specimen in each number of trucking were measured, and the degradation of stiffness due to ASR and fatigue was evaluated by forced vibration test using small vibration device. As a result, it was revealed that the fatigue resistance of RC bridge deck by ASR depended on the environmental condition of ASR, which was assumed due to the introduction of chemical prestress by ASR, and the interaction of crack propagation and water action. Furthermore, the vibration test proved useful in evaluating the fatigue resistance of RC bridge deck by ASR.
To establish a rational flexural reinforcing method for existing Reinforced Concrete (RC) beams using pretensioned Aramid Fiber Reinforced Polymer (AFRP) sheet, static loading tests on flexural reinforced RC beams were conducted taking sectional shape of beam, rebar ratio, sheet volume ratio, shear span ratio, and pretension force ratio as variables. In this study, the effects of these parameters on load-carrying capacity of the beams and debonding behavior of the sheet were investigated by comparing with between experimental results and analytical ones calculated by means of the multi section method. Furthermore, empirical prediction equations for failure mode of the RC beams reinforced with pretensioned AFRP sheet were developed. From this study, following results were obtained: 1) applying the pretensioned AFRP sheet bonding method proposed here, the load-carrying capacity of the RC beams can be upgraded irrespective of the magnitudes of design parameters of the RC beam; 2) introducing the pretension force to the AFRP sheet, sheet debonding due to peeling action of the critical diagonal cracks can be more restrained; and 3) an empirical prediction equation for failure mode of the flexural reinforced RC beam with pretensioned AFRP sheet was proposed which is composed of calculated two bending moments at rebar yielding and the ultimate state.
In order to examine safety over shear failure of RC beams subjected to impact loadings, it is essential to investigate the influence of loading rate on the shear resistance of RC beams and to develop an analytical model to evaluate it. Therefore, this paper initially presents an experimental investigation through rapid loading tests for RC beams with a shear span-to-depth ratio of 3.3 to clarify the effects of loading rates and shear reinforcement ratios on the failure modes and ultimate resistance of the RC beams. It was found that the RC beams without shear reinforcement exhibited diagonal tension shear failure under all the loading rates, while the failure modes were changed from brittle shear failure to ductile flexure failure by increasing the shear reinforcement ratios. The influence of loading rates on the ultimate resistance of the RC beams was more significant in shear failure than in flexure failure. Subsequently, well-known Modified Compression Field Theory (MCFT) developed under static loading was extended to the dynamic loading to evaluate the dynamic shear resistance of RC beams. The developed dynamic MCFT was justified by comparing with the experimental data. Finally it was found that the dynamic increase ratios in the shear resistance of RC beams calculated from the dynamic MCFT were consistent with those in the dynamic shear strength of concrete.
To establish a protective design for concrete structures, the explosive-resistant performance of concrete plates and the reinforced back surface of concrete plates were experimentally examined. In this study, explosion tests are conducted to examine the failure modes of concrete plates subjected to the contact explosion and the close-in explosion. Fiber sheet or polymer coating is used for the reinforcement of back surface of concrete plate. Generally, fiber sheet has high strength (high elastic modulus) and polymer coating has high braking strain. From test results, it is found that the reinforcement employed for these materials has remarkable effectiveness to reduce the local damage of concrete plates. Moreover, reinforcement of back surface can prevent the scattering of concrete fragment. The effect of reinforcement is formulated as a function of tensional stiffness of materials.