When an ultra-high-speed train moves into a tunnel, a pressure wave is generated and propagates in the tunnel. At a side branch of the tunnel, a part of the pressure wave enters into the branch and discharges from its portal as a booming noise. In this study, we propose measures to suppress the booming noise and also the ventilation wind noise for the side branch in the Chuo-Shinkansen. First, to reduce the ventilation noise, we expand the cross-section of the side branch to slower the flow inside and install a flow outlet with guide vanes to flatten the velocity profile. The flow in the outlet is numerically simulated, and the result shows that the ventilation noise can be reduced below the standard level with these measures. The expansion of the side branch, however, increases the booming noise, and a conventional porous absorber is not sufficient to suppress it. Thus, we utilize the ventilation facilities including a ventilation fan and a silencer along with a porous absorber as measures to reduce the booming noise. The propagation of a pressure wave through the side branch with these measures is experimentally and numerically studied, and the result shows that the booming noise can be reduced to less than the standard noise level.
In this study, conducted are a uniaxial tensile test and FE analysis using GFRP plates bonded with repair plates. The tensile test was conducted with two types of GFRP plates that is intact case and damaged case with crack. It is known that the strength of the damaged GFRP plate can be enhanced by bonding repair plate, but it is still lower than the intact GFRP plate. It is also confirmed that bonding repair plate decreases the strength of the GFRP plate even if a GFRP plate has no damage. It is also shown that two types of failure mode classified into debonding of the repair plate and brittle failure of the GFRP plate. FE analysis concluded the reason why the tensile test showed two types of failure mode. FEA showed that bonding repair plate cause stress concentration on the surface of the GFRP plate. This is thought to be the reason why the GFRP plate cause brittle failure before the repair plate cause debonding. Finally, the applicability of failure criteria for composite materials is assessed with respect to the repaired test piece. It is obtained that these criteria underestimated the danger of failure when the fibre failure occurred.
A horizontal stiffener which prevents end plates’ deformation also has the effect of reducing the separation between end plates and the increment of bolts’ force by sharing the sectional force from lower flange. However, it is difficult to estimate the sectional force in horizontal stiffener from beam theory, and no calculation methods for this sectional force are proposed. Therefore, in this study, FE analysis of I girder was conducted to propose the estimation formula for sectional forces in horizontal stiffener and lower flange. From the analytical results, the estimation formula was proposed by using parameters of horizontal stiffener and I girder. In addition, the behavior of sectional forces in horizontal stiffener and lower flange with end plate connection is clarified.
The authors have proposed foundation composed of micropiles and soilbags as a new foundation type. The foundation is characterized by laying soilbags on the pile head and constructing structures on the soilbags. The expected effects are omission of junction structures of piles and footing, reduction of diameter of piles, and reduction of response acceleration of structures. In this study, seismic response evaluation method for the proposed structure of actual size was constructed, and the seismic responses of the proposed foundation and pile foundation were compared on the different conditions of input acceleration and height of pier. From analytical results, except for the case where the pier height is low, it was found that the prolonged period due to the lifting of the footing resulted in the effect of peaking the response acceleration of a pier and the effect of suppressing the flexural moment at the base of the pier compared to the pile foundation. It was also found that the response displacement of the proposed structure was almost the same as that of the pile foundation, and that the residual displacement of the proposed structure was smaller than that of the pile foundation. Moreover, it was clarified that the effect of suppression of flexural moment of piles was expected by laying soilbags.
In this study, stresses in the CFRP bonded steel tube under tensile or pure bending conditions by applying the shear lag theory are derived. The stresses in the steel tube and CFRP and the shear stress in the adhesive layer were in good agreement with that calculated by the finite element method. The required length of CFRP for CFRP bonded steel tubes can be calculated by the stress distribution in the steel tube. Additionally, it was shown that the stress intensity factors calculated by the shear stress in adhesive given by the shear lag theory under tensile or pure bending conditions show the same tendency as that given by the finite element method. Additionally, it was clarified that the stress intensity factors calculated by the strain energy of CFRP bonded steel tubes were also derived and they are corresponding with that given by the shear stress in the adhesive layer.
Cable-type seismic bridge restrainers are widely used to prevent unseating of superstructures during earthquakes. However, these bridge restrainers cannot be applied to the case when failure occurs in the entire superstructures. Therefore, a self-anchored cable-type collapse prevention device was newly proposed to prevent the entire collapse of bridge systems. This device makes use of the catenary action of the cables to support the overall length of the failed super-structures. Herein, the applicability of the cabletype collapse prevention device to an upper deck-type single span truss bridge was examined experimentally and numerically, assuming that seriously corroded lower chord members suddenly fail.
In this paper, the axial-force sharing of cross-sectional loss steel members repaired by patch plates with high-strength bolts under axial loading is estimated by applying the displacement conformance condition between cross-sectional loss steel members and patch plates among the distance of high-strength bolts. The estimated axial-forces of cross-sectional loss steel members with patch repair are in good agreement with that calculated by the finite element result as well as that given by the tensile test results. Additionally, when the cross-sectional loss was deep and its length was short, it fractured from the cross-sectional loss even after the repair by the patch plates.
This paper describes an investigation on vehicle stability when crossing a bridge under strong wind by Computational Fluid Dynamics (CFD) and vehicle dynamics stability model. Large Eddy Simulation (LES) was implemented in the CFD to compute time-histories of vehicle’s aerodynamic force coefficients when moving on the bridge at different traffic lanes. The aerodynamic force coefficients were later utilized to compute wind loads on the vehicle, based on which vibration and stability of vehicle were evaluated using vehicle dynamics model. Simulation results show that the flow fields around vehicle vary for each traffic lane and they were strongly influenced by the shear layer separated from leading edge of the bridge girder. As a result, the aerodynamic characteristics acting on the vehicle and the normal force on each wheel vary according to the traffic lane. Critical conditions of vehicle instability are defined as overturning and sideslip or yawing. The critical wind speed associated with each condition is defined as the wind speed that causes the normal force on one of the wheels becomes zero. Analyses demonstrate that the lowest critical wind speed occurs when the vehicle moves on the windward lane and it increases toward the leeward lanes. It is also observed that at any lanes, the critical condition for yawing instability occurs at a lower wind speed than the critical condition for overturning instability.
Metropolitan Expressway has been in service for over 50 years under heavy traffic, so that many fatigue cracks have been detected at web-gusset welded joints of steel I-beam bridges. Most of those cracks are shallow and staying along the weld toes. Commonly, these cracks are repaired by removing them with bar grinder. UIT (Ultrasonic Impact Treatment) has been used for enhancing fatigue strength by impacting weld toes with hard pins and inducing compressive residual stresses there. It was thought that the repair work loads would be much lighter, if UIT could be applied to the repair of those fatigue cracks instead of bar grinder method. For the purpose of verifying the repair effect of UIT on those fatigue cracks, fatigue tests using model specimens were performed. The results suggest that the fatigue life of welded joints with toe cracks is improved more than twice that of the original joints in conditions where the stress range is less than 65N/mm2 and the UIT groove depth exceeds 0.23mm.
In this research, the method of estimating the earthquake motion at seismic bedrock using seismic observation records at the surface was proposed by employing a nonlinear time domain analysis. Although proposed method uses a general optimization method, the perturbation waveform incorporating in a forward analysis is proposed, by which the convergence of calculation was drastically improved. In addition, the equivalent single-degree-of-freedom model of the ground was used when performing the nonlinear analysis in the time domain. As a result, the calculation time was decreased small enough to estimate the seismic motion with an economical cost while considering complex soil nonlinearity. In order to confirm the effectiveness of the proposed method, a series of calculation was conducted on the sample ground. As a result, it was confirmed that the proposed method successfully estimated the input motion with higher accuracy than the traditional frequency domain analysis. It was also confirmed that the appropriate input earthquake motion can be estimated even if the observation record was contaminated by noise. It follows that the proposed method is applicable for estimating the strong ground motion at bedrock from surface records, considering the nonlinear behavior of the surface soil layers.
Bridges that resonate under a passing a train disturb the passengers and degrade the sub-structures on the bridge. As serious resonance often requires counter measures, resonance phenomena must be properly detected. This study proposes a method that comprehensively and efficiently detects resonant bridges among a huge number of bridges from the carbody vertical accelerations measured at the head and tail of a train. After theoretically analyzing the vibration component peculiar to a given resonant bridge, the on-board resonant bridges detection method is proposed. The proposed method processes differences between filtered/ enveloped carbody vertical acceleration responses measured on the first and the tail vehicle. The detection accuracy of the method was verified through numerical simulations. Finally, the proposed method was applied to carbody vertical accelerations measured on a commercial train on a high-speed railway. The resonance states of the two resonant bridges identified by the proposed on-board resonant bridge detection method were verified by in-situ measurements.