In this paper, a statistical pattern recognition method based on time series analysis is implemented in flexible risers. This method uses a combination of Auto-Regressive (AR) and Auto-Regressive with eXogenous inputs (ARX) prediction models. The flexible riser model used in this paper is experimentally validated employing a proposed numerical scheme for dynamic response of flexible risers. A modal-based damage detection approach is also implemented in the flexible riser model and its results are compared with the ones obtained from time series analysis. The numerical results show that the time series analysis presented in this paper is able to detect and locate structural deterioration related to fatigue damage in flexible risers. Finally, considering the case study results presented in this paper, the presented AR-ARX prediction model works better than the modal-based damage detection method.

View full abstract

The ultimate flexural strength of composite steel girders with compact sections is examined through experimental investigation and elasto-plastic finite displacement analyses to develop a reduction factor of the ultimate flexural strength. A two-point loading test of a composite girder was carried out to verify the numerical modeling by comparing the experimental and numerical results. Then, a parametric study was performed using finite element analyses to investigate the effect of concrete crushing on the flexural strength of composite girders constructed using SM570 grade steel. Observations made by comparison of the ultimate flexural strength obtained from the experimental and numerical results with that according to the AASHTO and Eurocode show that the existing reduction factor equations are conservative and can be relaxed when the strength is controlled by crushing of concrete slab. A new reduction factor for the ultimate flexural strength for composite I-girders under positive bending is proposed.

View full abstract

Presented in this paper is shaking table tests of bridges isolated by 4 different sliding bearings in order to identify the seismic response with emphasis on the frictional characteristics of the sliding bearings, effects of vertical and transverse excitation and the difference of frictional coefficient, and generation mechanism of vertical load at the sliding bearings. The test results showed that the combinations of vertical and horizontal excitation as well as longitudinal and transverse excitation generated larger responses compared with merely longitudinal excitation in case of sliding bearings with high frictional coefficient and high velocity-dependency, and that the effect of the 4 different frictional coefficients on the maximum and residual displacement became clear. Furthermore, it was found that shear keys at rubber buffers might affect vertical reaction force at the sliding bearings.

View full abstract

The impact responses of steel and reinforced concrete (RC) beams were previously analyzed. It was found that the decrease in the stiffness of concrete is a key feature to analyse RC beam. Consequently, introducing the damage model, analytical solutions are improved, and the applicability is demonstrated. Further, a new model is developed, estimating the residual impact resistance. Thus, the impact response of RC beam under cyclic loading is clarified.

View full abstract

It is important to know fatigue strength of weathered welded joints, when it is used in unpainted condition. Fatigue tests were carried out for 32 cruciform specimens and eight tensile plates with out-of-plane gussets after 25-year atmospheric exposure. Fifteen cruciform specimens were subjected to number of stress cycles corresponding to 25 percents of its fatigue life before weathering. The test data was compared with non-weathered, 2-, 4- and 10-year weathered specimens. Change in surface roughness and fillet weld toe profile was also measured for comparison. It was found that no reduction in fatigue life was observed after 25 years of atmospheric exposure in unpainted condition.

View full abstract

Liquid sloshing of oil storage tanks caused by Tokachi-Oki earthquake in 2003 gave severe damage to oil tanks in Tomakomai area. The purpose of our study is to verify sloshing behavior of floating roof tank and finally find out the method of sloshing damping. In this paper, we propose a vibration test by using φ4000 tank model and confirm sloshing behavior of floating roof tank. From these results, we have come to the conclusion that the first mode of sloshing may cause the higher modes and have significant influence on the deformation of single deck type floating roof tank.

View full abstract

It has been pointed out that ground with an irregular surface causes complicated seismic responses. However, the process of generating this complex response is not yet clear. In this study, it was pointed out that the mathematical expression of scattered-wave contribution has a form similar to that of the Huygens-Fresnel principle, and the expression consists of a wave function and an inclination factor. Next, the waveforms of the scattered waves from various parts of a ground surface were calculated and compared with those of the ground motions. This comparison showed that the waveforms of the ground motions at the surface can be decomposed into the waveforms of an incident wave and scattered waves, and the polarity and amplitudes of the scattered waves are primarily attributed to the inclination factor.

View full abstract

This paper presents a virtual crack closure-integral method (VCCM) using a generalized finite element with drilling degrees of freedom (DOF). So far, the finite element with drilling DOF has been applied to elastic stress analysis etc. It is has not been applied to fracture mechanics analysis. When VCCM is applied to the generalized finite element, the contributions of drilling DOF to the energy release rate need to carefully be examined in relation with the deformation modes of crack. In this paper, we propose a VCCM formulation and some numerical results. They are compared with the theoretical solutions and with some other numerical ones. Finally, the validity of proposed VCCM is discussed.

View full abstract

Fatigue durability assessment procedure is not well established for expansion joints of highway bridges, although they are subjected to wheel loads directly. First, basic information needed for fatigue assessment of expansion joints, such as axle loading and its number of cycles, ways to determine fatigue strength curves, i.e. S-N curves of the detail, and assessment procedure, is summarized. Then, the procedure is applied to modular type expansion joints, which consisted of center beams, which are supported by support beams with bearings. Wheel loads run on the center beams, of which the number can be changed according to bridge span. The modular type expansion joints thus can be used for medium to long span highway bridges. In this analysis, fatigue assessments of the joints is carried out for design wheel loading, as well as the wheel loadings in service of major highways in Japan, which were measured by Bridge Weigh-in-Motion system.

View full abstract

Tensile fatigue test of plates with fillet welded pipes and with out-of-plane gussets were carried out. Fatigue life became slightly shorter, as the diameter of pipes increased. Stress analysis by FEM showed that fatigue crack initiation points were within 30 degrees from the Crown, which coincided with the fatigue test results. Fatigue life was estimated by using one mm method, which takes reference stresses at 1 mm deep from the weld toe, and the result also coincided with the fatigue life obtained by the fatigue tests.

View full abstract

In this study, durability of A-, C- and I-paint systems was examined by salt water spray and acid rain spray combined cyclic corrosion tests. The differences of deterioration characteristics between the salt water spray and acid rain spray combined cyclic corrosion tests were investigated. As a result of the test, the blistering area of A-paint system by acid rain spray combined cyclic corrosion test was remarkably larger than the one by salt water spray test combined cyclic corrosion test. The C- and I- paint systems showed little difference between the salt water spray and acid rain spray combined cyclic corrosion tests.

View full abstract

Fatigue damage cases in steel bridge structures which were caused by weld defects due to inappropriate fabrication were studied in connection with the provisions of specifications for highway bridges. The most of fabrication faults and/or weld defects were resulted in violation of specifications, such as disapproved change of weld details to partial penetration or fillet welds instead of full penetration welds designed. The difficulty of fabrication and quality control caused these problems and these have to be considered in the design of joint details.

View full abstract

The authors developed a dynamic interaction analysis program coupling railway vehicles and structures. In the program, the vehicle is modeled by rigid bodies composed of a carbody, trucks and wheelsets spacially connected by nonlinear springs and dampers, and structures are modeled by the finite elements that can take into account their material nonlinearities. The fundamental performance of the program was verified by shaking table test results conducted with a full scale semi-vehicle model using an actual bogie. The behavior of vehicle subjected to the seismic motion produced on nonlinear structures was studied. The outlines of the formulation of the analytical model, the shaking table test and the results of analysis are presented in this paper.

View full abstract

The site amplification factors due to deep sediments are evaluated using earthquake motion records observed in the Kanto Plain. The observed amplification factors almost agree with the one-dimensional amplification factors computed from the deep underground structure when the earthquake source is located beneath the basin. On the contrary, in case that the source is situated outside of the basin, the observed amplification is much larger than the computed one. This is because that the mechanisms of seismic basin response depend on the location of earthquake sources.

View full abstract