Effect of Compression Overload on Fatigue Strength Improved by ICR Treatment

Toshiyuki Ishikawa,Masaru Shimizu,Hajime Tomo,Hirotaka Kawano,Kentaro Yamada 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.1

ICR (Impact Crack-closure Retrofit) treatment was developed for extending fatigue life of cracked steel structures by closing the fatigue crack opening. By applying the ICR treatment to as-welded condition, compressive stress remains at weld toe. Therefore, ICR treatment can be used for the improvement of fatigue strength of welded joint at the same level of the other fatigue strength improved techniques. If a compression overload is subjected after ICR treatment, however, the residual compressive stress at weld toe will shift the tensile stress region. Accordingly, improved fatigue strength of welded joints by ICR treatment will be reduced after the compression overloaded. In order to investigate the effect of the compression overload on fatigue strength improved by ICR treatment, fatigue tests of out-of-plane gusset specimens were carried out. As the results,fatigue strength improved by ICR treatment was hardly reduced under the compression overload condition of nominal stress of −190 MPa.

Reduction of Stress Concentration at Stop-Hole by Bolting a Crack

Toshiyuki Ishikawa,Shogo Kiyokawa,Wataru Nakatsuji 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.6

A stop-hole, which is drilling at the crack tip, is one of the famous tentative repairs of fatigue cracks in steel structures. When the crack becomes longer, the stress concentration of the stop-hole also increases. Therefore, during the tentative repair of long fatigue cracks, the chances for re-initiation of the fatigue cracks from the stop holes are high. The bolting stop-hole method is a useful technique against fatigue cracks. In this technique, bolting is applied only for the stop-holes at the crack tips. Therefore, as the crack length increases, the eff ect of the bolting stop-hole method decreases. In this paper, the authors propose a stress concentration reduction technique for a stop-hole by bolting the fatigue crack between stop-holes. The eff ect of the proposed technique was verifi ed by tensile and bending tests of specimens as well as fi nite element analysis. From the tensile and bending tests, it was clarifi ed that the stress concentration of the stop-hole was drastically reduced by bolting a crack under the condition before the slippage of bolts. Additionally, multi-bolting cracks have the advantage of improving the slippage load of the bolts in a crack. Furthermore, fi nite element analysis verifi ed the reduction in stress concentration of the stop-hole by bolting a crack, and the eff ectiveness of bolting cracks and stop-holes was also shown.

Simultaneous Assimilation Model of Drifting Buoy and Altimetric Data for Ocean Surface Circulations

Awaji, Toshiyuki,Ishikawa, Yoichi,Akitomo, Kazunori 대한원격탐사학회 1996 International Symposium on Remote Sensing Vol.12 No.1

A simultaneous assimilation model of drifting buoy and altimetric data is proposed to determine the mean sea surface height(SSH) as well as the temporal evolution of the surface circulation on synoptic scales. The result shows that realistic buoy deployment (32 in a 40° square) ca.n effectively constrain the model variables; that is, both the absolute (mean plus time varying) velocity and SSH (interface depth) fields are significantly improved. Successive correction of the mean SSH is made with the simultaneous assimilation of drifting buoy and altimetric data. Consequently, a better correction of the mean SSH is obtained: The initial error of the mean SSH is reduced by approximately 40% after the 1-year experiment. These results clearly show that simultaneous assimilation of drifting buoy and altimetric data into the dynamical model is a very useful tool for improving the model's realism.

Air-Sea Heat Flux Estimation by Ocean Data Assimilation Using Satellite and TOGA/TAO Buoy Data

Awaji, Toshiyuki,Ishikawa, Yoichi,Iida, Masatora,In, Teiji 대한원격탐사학회 1999 International Symposium on Remote Sensing Vol.15 No.1

A data assimilation system for a 1-dimensional mixed layer model has been constructed using the adjoint method. The classical adjoint method does not work well for the mixed layer variabilities due to the occurrence of spikes in the gradient of the cost function. To solve this problem, the two techniques of scaling the cost function and optimization in the frequency space are used. As a result, the heat flux can be reliably estimated with an accuracy of 8Wm^(-2) rms error in the identical twin experiments. We then applied this system to the tropical Pacific TOGA-TAO buoy data. The air-sea heat flux as well as the mixed layer variability were estimated in close approximation to the buoy data, particularly on time scales longer than the seasonal one.

GLOBAL OCEAN STATE EATIMATION BY 4D-VAR DATA ASSIMILATION USING SATELLITE DATA

Awaji, Toshiyuki,Sugiura, Nozomi,Baba, Kinji,Masuda, Shuhei,Horiuchi, Kazutoshi,Jiang, Qin.,Ishikawa, Yoichi,Toyoda, Takahiro,Komori, Nobumasa 대한원격탐사학회 2001 International Symposium on Remote Sensing Vol.17 No.1

By using a free-surface ocean general circulation model and the variational adjoint method, our joint group has constructed a global ocean data assimilation system capable of providing a comprehensive 4-dimensional dataset from many of the available observational data such as satellite data and thereby estimating ocean circulation processes with high accuracy and good dynamical consistency. The system was applied to an experiment to define the climatological seasonal state of a global ocean. The result showed the efficiency of our assimilation system in reproducing the detailed features similar to those of ocean circulations reported so far. For example, a low salinity distribution associated with the North Pacific Intermediate Water is reproduced much better than in other simulations. The accuracy of estimated heat and freshwater fluxes is also better than that by the flux correction method currently used in most of ocean-atmosphere coupled models. These results suggest that our data assimilation system is a very powerful tool for ocean climate researches.

Stop-hole conditions to prevent re-initiation of fatigue cracks

Ichiro Okura,Toshiyuki Ishikawa 국제구조공학회 2002 Steel and Composite Structures, An International J Vol.2 No.6

In steel bridges fatigue cracks are sometimes repaired by placing drilled holes at the crack tips. From the meaning that the drilled holes stop the propagation of cracks, they are called stop-holes. Since stopholes are regarded as an emergency measure to delay crack propagation, usually some substantial repair follows. However, if the stress at the stop-holes is below their fatigue limit, fatigue cracks would not be expected to occur. The purpose of this study is to present the conditions under which stop-holes prevent the reinitiation of fatigue cracks. The fatigue limit of stop-holes and the equations necessary to estimate the maximum stress on the circumference of the stop-holes are provided.

Risk factors for severity of colonic diverticular hemorrhage

Ken Kinjo,Toshiyuki Matsui,Takashi Hisabe,Hiroshi Ishihara,Toshiki Kojima,Kenta Chuman,Shigeyoshi Yasukawa,Tsuyoshi Beppu,Akihiro Koga,Satoshi Ishikawa,Masahiro Kishi,Noritaka Takatsu,Fumihito Hirai,K 대한장연구학회 2018 Intestinal Research Vol.16 No.3

Background/Aims: Colonic diverticular hemorrhage (DH) was a rare disease until the 1990s, and its incidence has increased rapidly since 2000 in Japan. In recent years, colonic DH has been the most frequent cause of lower gastrointestinal bleeding (LGIB). Nearly all cases of DH are mild, with the bleeding often stopping spontaneously. Some cases, however, require surgery or arterial embolization. In this study, using a cohort at Fukuoka University Chikushi Hospital, we investigated factors associated with severe colonic DH. Methods: Among patients with LGIB who underwent colonoscopy at our hospital between 1995 and 2013, DH was identified in 273 patients. Among them, 62 patients (22.7%) were defined as having severe colonic DH according to recurrence of bleeding in a short period, and/or the necessity of transfusion, arterial embolization, or surgery. We then evaluated risk factors for severe DH among DH patients in this retrospective cohort. Results: Among the 273 patients with DH, use of non-steroidal anti-inflammatory drugs (NSAIDs) (odds ratio [OR], 2.801; 95% confidence interval [CI], 1.164–6.742), Charlson Risk Index (CRI) ≥2 (OR, 3.336; 95% CI, 1.154–7.353), right-sided colonic DH (OR, 3.873; 95% CI, 1.554–9.653), and symptoms of cerebral hypoperfusion (such as light-headedness, dizziness, or syncope) (OR, 2.926; 95% CI, 1.310–6.535) showed an increased risk of severe DH even after controlling for other factors. Conclusions: Severe DH occurred in 23% of DH patients, and NSAID use, CRI ≥2, right-sided colonic DH, and symptoms of cerebral hypoperfusion are suggested to be predictors of severe DH.

Extending Fatigue Life of Out-of-plane Gusset Joint by Bonding CFRP Plates Under Bending Moment

Risa Matsumoto,Toshiyuki Ishikawa,Manabu Takemura,Yoshisato Hiratsuka,Hirotaka Kawano 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

Carbon fiber reinforced plastic, CFRP, plates bonding method is one of the new repair methods for fatigue cracks. In this method, propagation of fatigue crack will be delay because of the suppression of crack opening by crack bridging and stress reduction by composite effect of bonding CFRP plates. In this study, to clarify the effect of bonding CFRP plates on fatigue life extension, bending fatigue tests were carried out. First, fatigue tests on the specimens in as-welded condition were conducted until fatigue crack propagated to 10mm away from the weld toe. Then, fatigue crack was covered by CFRP plates and the specimens were re-tested until fatigue crack penetrated through the base plate. As the results of bending fatigue tests, the fatigue test data of the specimens repaired by bonding CFRP plates showed much longer fatigue life compared with that in as-welded condition, under stress ratio, R=0 and -infinity.

Experimental Study on Ultimate Strength of Concrete Filled Double Tubular Steel with Shear Connector

Masaru Shimizu,Fumihito Tatsumi,Toshiyuki Ishikawa,Atsushi Hattori,Hirotaka Kawano 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.1

Concrete Filled Tubular steel (CFT) member, which represents a superb deformability due to well-known confined effectbetween steel tube and concrete, has been used mainly as bridge pier. As a progressive composite member, Concrete FilledDouble tubular steel (CFDT), which is consist of double skin steel tubes and filled concrete between them, has been proposed. Although a lot of reports on mechanical characteristics of the CFDT member are presently published, the necessity of shearconnector for the CFDT member has not been addressed. In this research, the shear connector was installed at the interfacebetween tubes and concrete in the CFDT member. To investigate the effect of the shear connector on the bending characteristics,the four points bending test were carried out. The results show that integrating the steel tubes and concrete enhances its bearingcapacity. Furthermore, the strains of outer and inner tubes were also discussed in this paper.

Prediction of Bending Fatigue Life of Cracked Out-of-Plane Gusset Joint Repaired by CFRP Plates

Risa Matsumoto,Takafumi Komoto,Toshiyuki Ishikawa,Atsushi Hattori,Hirotaka Kawano 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.4

Carbon fi ber reinforced polymer (CFRP), plates bonding repair method is one of the simple repair methods for cracked steel structures. In this study, the infl uence of width of CFRP plates on bending fatigue life of out-of-plane gusset joint strengthened with CFRP plates was investigated from the experimental and numerical point of view. In the bending fatigue test of cracked out-of-plane gusset joint strengthened with CFRP plates, the eff ect of width of CFRP plates on crack growth life was clarifi ed experimentally. Namely, it was revealed that the crack growth life becomes larger with increasing the width of CFRP plates. In the numerical approach, the stress intensity factor ( SIF ) at the surface point of a semi-elliptical surface crack was estimated based on the linear fracture mechanics. Furthermore, the extended fatigue life of cracked out-of-plane gusset joint strengthened with CFRP plates was evaluated by using the estimated SIF at the surface point and the empirical formula of the aspect ratio of semi-elliptical crack. As the results of numerical analysis, the estimated fatigue life of the specimen strengthened with CFRP plates showed the good agreement with the test results.