Hiroshi Katsuchi

Full-scale measurement of Akashi–Kaikyo Bridge during typhoon

Abstract Full-scale measurement data observed on the Akashi–Kaikyo Bridge during strong typhoons were analyzed. Power spectral density and spatial correlation of longitudinal velocity fluctuations were analyzed. PSD was well represented by Hino’s formula by changing the scaling parameter. Spatial correlation at two points was well represented not by the exponential formula but by an alternative coherence function based on isotropic turbulence theory. Decay factor in the exponential formula showed a weakly increasing trend with the increase in distance and wind speed. Bridge response of deck lateral deflection was also analyzed. Static deflection at winds with normal to the bridge axis was in good agreement with the analytical value. Gust factors of deck lateral deflection were mostly less than design specification.

A study on spatial correlation of natural wind

Abstract In the design of aeroelastic structures, the effect of gust response is taken into account. When the structure is long and has low natural frequency, the spatial correlation of the wind in the low-frequency range affects the gust response. However, data from field measurement about spatial correlation of natural wind are generally not available. Therefore, data concerning the spatial correlation of the natural wind were measured on two Honshu-Shikoku Bridges. The results show that the spatial correlation of the natural wind is lower than that specified in the wind-resistant design manual in the low-frequency range. In order to evaluate the effect of the difference of the spatial correlation of the wind on gust responses, a gust response analysis was conducted. The results show that gust responses calculated using measured spatial correlation is much smaller than the ones calculated using spatial correlation specified in design manual. This means that there is a possibility to be able to ease the design specifications of long span bridge concerning gust response.

Analytical demonstrations to assess residual bearing capacities of steel plate girder ends with stiffeners damaged by corrosion

Many field surveys depict that steel plate girder ends tend to corrode due to the leakage of water from construction joints and/or detention of rain water near bearing regions. In many cases, buckling failures of plate girders were observed due to the excessive loss of material at the bottom portion of bearing stiffeners. In this study, the effect on the buckling strength of steel plate girder due to the corrosion damage at bearing stiffeners was investigated. Full-scale experimental tests were performed on two plate girder ends to determine the bearing capacity. Bearing capacity and failure modes were also verified by numerical analyses. Initial imperfections and welding residual stresses were also taken into account in analytical models. The simulation of the model was extended to the various corrosion damages, considering different damaged heights and thicknesses of the bearing stiffener near weld seam. All results were plotted in terms of remaining bearing capacity versus damage thickness ratio keeping the damage height of the stiffener constant. In this study, a damage parameter Reduced Thickness Ratio was used to assess the ultimate capacity and buckling of steel plate girder end with various corrosion levels.

Aeroelastic complex mode analysis for coupled gust response of the Akashi Kaikyo bridge model

Abstract An analytical approach for the coupled gust response of long-span bridges is presented. The calculation scheme is based on the direct complex eigenanalysis of the integrated system of three-dimensional FEM model of a long-span bridge and the aeroelastic forces. Actual vibration modes of the bridge in wind flow, which are called aeroelastic complex modes, are appropriately determined at each mean wind speed. A complex modal analysis scheme is then formulated for gust response analysis in either time or frequency domains. By using the aeroelastic complex modes, the aeroelastic coupled gust responses are effectively captured and interpreted. A numerical example is given for the Akashi Kaikyo Bridge model. The calculated results agree very well with the experimental ones. Parameter studies on the effect turbulence properties and the advantages of using the aeroelastic complex modes are then addressed.

Present condition of highway bridges in Vietnam: an analysis of current failure modes and their main causes

This paper reports on research conducted to evaluate the current status of highway bridges in Vietnam. The adopted approach included literature reviews to identify common failure modes and causes, together with site inspections to ascertain their validity. Interviews were also conducted with the various stakeholders to further understand the current condition of the inspected bridges. Results show an overall picture of existing bridges in poor physical condition, thus providing poor service to users. Defects that have previously been identified in the literature include corrosion, settlement, fatigue damage, obsolescence, scouring and aging. New problems identified were human invasions and missing elements. Previous literature identifies traffic overload and jams, collision, adverse environmental conditions and poor maintenance as causes for these problems. Additionally, this paper considers war, improper data retention and other country-specific causes. The authors suggest that maintenance efforts should be prioritized to remedy and eliminate serious failures. Properly trained maintenance crews need to be established and further research carried out to establish adequate bridge maintenance systems.

Flow field analysis of a pentagonal-shaped bridge deck by unsteady RANS

ABSTRACT Long-span cable-stayed bridges are susceptible to dynamic wind effects due to their inherent flexibility. The fluid flow around the bridge deck should be well understood for the efficient design of an aerodynamically stable long-span bridge system. In this work, the aerodynamic features of a pentagonal-shaped bridge deck are explored numerically. The analytical results are compared with past experimental work to assess the capability of two-dimensional unsteady RANS simulation for predicting the aerodynamic features of this type of deck. The influence of the bottom plate slope on aerodynamic response and flow features was investigated. By varying the Reynolds number (2 × 104 to 20 × 104) the aerodynamic behavior at high wind speeds is clarified.

Nonlinear features for damage detection on large civil structures due to earthquakes

This article proposes the degree of nonlinearity as a feature for damage detection on large civil structures due to earthquakes. The degree of nonlinearity, which is a numerical value, represents how nonlinear structures behave during earthquakes. The degree of nonlinearity is computed directly from the data of the ground motion and vibration of the structure. The computation of the degree of nonlinearity uses a Hilbert transform and does not require any other nonlinear structural or mathematical models. Therefore, the damage detection process is very fast. Thus, an immediate decision about the condition of structures after strong earthquakes is possible. This article shows theoretically that a plot between the degree of nonlinearity against the magnitude of the ground motion represents the behavior of a structure. This plot is considered the signature of that structure. A structure that is healthy will have its specific healthy signature. If a new earthquake strikes and the new degree of nonlinearity deviates from its healthy signature, the structure may be damaged by that earthquake. To verify the validity of the degree of nonlinearity, numerical studies of nonlinear systems are presented. Although the application of degree of nonlinearity on a real civil structure is still not totally conclusive due to the limitation of data, the results from currently available data are encouraging. With more investigation, the degree of nonlinearity could be an additional or alternative feature for vibration-based structural health monitoring.

Involvements of stress triaxiality in the brittle fracture during earthquakes in steel bridge bents

Stress triaxiality is proposed as one of the key parameters to discuss the cause of brittle fracture during earthquakes in steel structures. This study analytically investigated the features of stress triaxiality in steel bridge bent subjected to earthquakes. The target structure is a steel bridge bent actually fractured during the South Hyogo prefecture Earthquake. From the investigations, it was confirmed that high stress triaxiality was generated at a point supposed as fracture origin. There is a possibility that the triaxiality was involved in the fracture strongly through the increase of maximum principal stress. Moreover, from the analyses accounting for several kinds of large earthquake waveforms, it was indicated that threre is possibility that the distribution of triaxiality around the fracture origin was not affected by significantly by each cycle and each waveform.

Investigation of Flow Fields Around Rectangular Cylinder Under Turbulent Flow by Les

Abstract In the atmospheric boundary layer turbulent flow is continuously interacting with structures. Recently it has been found that properties of natural wind turbulence are anisotropic in nature in terms of turbulence intensity and length scale. It is important to know the bluff body response under this anisotropic turbulent flow. In the present work, anisotropic turbulence effect was investigated numerically on rectangular cylinders of varying side ratios (R=d/h), R=0.1875 to 1. Four different properties of anisotropy were considered and anisotropy of the turbulence was altered by changing the vertical wind turbulence intensity and length scale. Numerical simulations were performed employing large eddy simulation (LES) with smagornisky subgrid-scale model. Turbulence effects were discussed in terms of mean drag and base pressure coefficients. Time averaged flow pattern was plotted to understand the flow field around the rectangular cylinders. After body vortex strength was also checked for turbulent flow. It was found that the anisotropy of turbulence alters bluff body responses considerably.

Structural monitoring and design verification of Akashi Kaikyo bridge

Bridge monitoring is conducted at the Akashi Kaikyo Bridge which is the world ’s longest span suspension bridge. The purposes of the monitoring are for daily traffic control, real -time mon itoring during extreme events, long -term monitoring for bridge health indices and design verification. The paper presents a couple of examples of bridge monitoring and design verification results. The results showed that short - and long -term monitoring giv es possible health indices to detect structural damages. In addition , study on design verification identifying vibration characteristics such as natural frequency and structural damping showed that structural damping greatly affecting flutter stability is larger than the design value.