A damage identification method for inner cracks of RC bridge deck was investigated. A local resonance of RC deck was excited by forced vibration test using a portable shaker, and local resonance frequencies could be measured. As the experimental results of the RC deck specimens, the local resonance frequencies were significantly decreased on the area including an inner void. Moreover, the damage estimating equation was proposed based on the linearity relation between the local resonance frequency and the void length. The RC deck was removed from the highway road bridge, and the distributions of local resonance frequencies were measured. It was indicated that the local resonance frequencies were decreased on the areas including inner cracks. Moreover, as the experimental results of field test on the highway bridge, it was shown that the areas including inner cracks were fairly identified based on the decrease of local resonance frequencies obtained by the forced vibration test.
The authors have proposed a method of joining the rebars of RC wall structures such as box culvert. It is effective for productive improvement of wall member with mechanical splices at the same section regardless of the plastic hinge zone. There are many reports where wall member's deformation capacity is raised by using mechanical splices at the same section. However, it's mechanism has not been completely explained yet. This report shows a buckling resistance test for main bars using Japanese class “A” mechanical splice in full scale sized wall specimen tested under cyclic seismic loading. As a result, mechanical splices at the plastic hinge zone of wall members effectively improved the buckling resistance of rebars, and the member's deformation capacity was superior than joint-less specimen.
The compaction for fresh concrete is very important work to control the quality of the RC structures. However, the judgments for compaction interval and time are often left to workers in the construction site, and therefore the compaction control is not performed enough. The main factor for this problem is that the quantitative controlling method for compaction effect by the internal vibrator is not yet established. In this paper, the authors suggest an easy and real time controlling method for compaction effect of the fresh concrete using the acceleration of the internal vibrator. This method can estimate viscosity, compaction range, compaction time for fresh concrete simultaneously with compaction work. As a result of comparison between the estimation and experimental value, the effectiveness of this method was confirmed.
In this paper, MPS method was applied to fluid analysis of fresh concrete with vibration. MPS method is one of the particle method, and it is suitable for the simulation of moving boundary or free surface problems and large deformation problems. The constitutive equation of fresh concrete is assumed as Bingham model. In order to set fluidity change of fresh concrete based on the decrement of the acceleration, the Bingham model is supposed to be the yield stress and the plastic viscosity of fresh concrete that decreased most in the neighborhood of the vibrator. To evaluate verification of compactability of fresh concrete, numerical analysis examples of compaction at the part of haunch section of wall were performed. As a result, it was found that the MPS method was suitable for the simulation of compaction of fresh concrete with vibration.
In order to establish evaluation method of flexural capacity for prestressed concrete (PC) beam structures deteriorated by Alkali-Silica Reaction (ASR), the evaluation method with the numerical analysis that can represent the static loading test following the long-term exposure test for 7.5 years was studied. For the input data of the analysis, the crack density and the drilled cores were used to estimate the mechanical properties of the ASR deteriorated concrete. As a result, it was found that the proposed evaluation method is effective to evaluate the flexural performance of the ASR deteriorated PC beam structure such as the load carrying capacity and the initial stiffness. In addition, the evaluation method for the real structures (ASR deteriorated PC beam) was also proposed.
The purpose of this study is to establish a method to measure fundamental frequency for the reinforced concrete of which thickness is around 2.5 meters by the Impact Elastic Wave Method. It is considered that earlier studies have not devised a practicable and reproducible method. In this study, passage and arrival time of the multiply reflected P-wave was validated by numerical analysis based on 2D elastic body wave equation and then measuring method and analysis method were proposed. In the result, the measuring method with multiple sensors on the surface of the measured concrete was devised, then the devised measuring method was tested on actual concretes of which thickness are 1.6 meters and around 2.5 meters. As a result, the fundamental frequency of the reinforced concrete is objectively determined by the Fourier Transform of the composed function from cross-correlation functions between the input waveform and measured waveforms by each sensor. In addition, the type of elastic waves is discriminated by measuring phase difference between measured waveforms by each sensor.
In this paper, the cathodic protection characteristics in seabed soil were investigated by monitoring the current density and the potential of the steel pipe pile in seabed soil. (1) In the seabed soil, as the depth from the seabed was deeper, the period until the potential of steel reach the protective potential was longer. However, the effect was fully obtained at the every depth of pile by the cathodic protection.(2) Regarding a cathodic protection mechanism in the seabed soil, the cathodic protection was considered to be achieved by continuing the protective current, even if feeble. (3) The supply of protective current was affected by the soil resistivity based on the ground survey. In addition, we proposed a design method of cathodic protection in consideration of the soil resistivity, based on the potential and current density distribution analysis using the finite element method.
In evaluation of imperfectly grouted part of tendon ducts in PC members, the influences given on vibration of sheath were investigated using a mechanical and a magnetical input method. These methods control the parameter of impact and generate elastic waves with high repeatability and accuracy. For this purpose, the specimens having a number of holes penetrating to the sheath were used, which enabled to observe the vibration directly on the sheath. As a result, it was found that the penetration and reflection properties of elastic wave at the sheath changed due to the existence of void in the sheath. Next, by defining “wave energy” of the detected signals at the grouted part and the ungrouted part, the detection capability of ungrouted part was made clear under the available placement of impact and detection. Thus, it was found that the magnetical input method has the larger detection capability of ungrouted part than the mechanical input method. By considering application of these methods at the concrete structures in use, a new inspection flowchart of evaluating ungrouted part was proposed.