Tetsuhiro Shimozato’s research while affiliated with University of the Ryukyus and other places

Corrosion in steel girder ends, progressing from localized thinning of the web and the lower flange to severe perforation in severe cases, can significantly affect structural integrity. This study evaluates the effects of severe corrosion, including web–lower flange disconnection and transverse flange perforation combined with web damage, on the residual shear strength of steel girder end web panels through experimental and numerical methods. Results indicate that when only the web is affected, post-buckling strength starts to decline by corrosion damaging the plastic hinge on the tension flange, disrupting the tension field action. Conversely, in cases involving simultaneous web and lower flange damage, localized yielding at fracture points near the flange damage leads to the abrupt rotation of the tension field inclination angle, causing an earlier and more pronounced decline in post-buckling strength compared to web-only damage scenarios.

Structures receive thermal energy from solar radiation, and temperature differences occur between structural members due to differences in solar exposure and heat capacity. This study attempted to generate electricity from this structural thermal energy, particularly targeting the temperature difference between the pavement and decks of steel deck bridges. The thermal environment of a full-scale steel deck bridge specimen was measured, and a thermal conduction analysis using a finite element model was conducted to explore the structural design for efficiently transferring heat to thermoelectric modules. The installation position that is advantageous for power generation in steel deck bridges was investigated through experiments and heat conduction analysis, followed by power generation simulations. Finally, prototype thermoelectric energy harvesters were installed on the target steel deck bridge and verification experiments demonstrated the potential for utilizing thermal energy in structures.

High-strength bolt attachment parts of steel bridges are prone to corrosion at an early stage, and blast nozzles and power tools cannot be inserted due to the structural shape during repairs, and there are many cases where rust remains partially. To solve such a problem, the Cold Spray technology, which uses a powder that mixes zinc and alumina, exhibits corrosion resistance by depositing a film even if rust remains. In this paper, first the anticorrosion mechanism on the residual rust was examined by focusing on the permeation prevention of the corrosion factor of the Cold Spray anticorrosion film and the adhesion of the residual rust boundary. Findings indicate that the Cold Spray anticorrosion film exhibits a porosity approximately one-tenth that of films engendered via the thermal spraying method, thereby constituting a denser film with heightened environmental barrier attributes. The firm adherence of the Cold Spray anticorrosion film to the residual rust interface is explained by differences in hardness between Cold Spray, residual rust, and zinc. Furthermore, the physical characteristics of zinc undergo modifications influenced by the temperature environment during construction, imparting a plasticity to zinc on uneven rust surfaces.

High-strength bolted joints are widely used in steel bridges since they have advantages to construction, maintenance, and replacement. On the other hand, bolt axial force may decrease after tightening due to tightening method, tightening order, relaxation, traffic load, or earthquake. The remaining axial force of high-strength bolts is a factor that includes uncertainty therefore, it is important to evaluate the remaining bolt axial force. In this study, in order to evaluate the remaining axial force of high-strength bolts non-destructively and simply, a new remaining axial force evaluation method based on eddy current measurement was constructed. In the eddy current measurement, the stress change can be obtained by using the relationship between the magnetic permeability and the stress. Therefore, authors proposed the method considering the stress state of the bolt head and simply install the eddy current probe on the bolt head. In addition, considering that the bolt head is deformed by the axial force, the relationship between the output signal and the gap between the probe and the measurement target, which is an important evaluation index in eddy current measurement, has clarified, and the influence of the axial force evaluation has also investigated.

p>High-strength bolted joints are widely used in steel bridges. However, bolt axial force may decrease during the service life of a bridge for many reasons including relaxation, traffic load, and earthquake. Consequently, the remaining bolt axial force is considered a factor with uncertainty that is important to evaluate. In a previous study, the authors proposed an axial force evaluation method using eddy current. In this study, to apply the proposed axial force evaluation method to the actual measurements, new evaluation indices with the possibility of reducing measurement errors and simplifying measurement have been considered. The applicability of the improved method for high- strength bolts using weathering steel has also been examined. An experiment using both high- strength bolts and weathering steel high-strength bolts was conducted to investigate the possibility of evaluating the stress change due to the axial force with the new indices.</p

Preflex beam girders with remarkable advantages are widely used in bridge structures. With aging, preflex beam bridges undergo concrete cracking and degrade as the cracks propagate and deteriorate due to repeated service load application and exposure to humid and saline environment. The objective of this study was to evaluate concrete cracking, changes in prestress, and consequent changes in sectional properties as the preflex beam undergoes deterioration in its concrete casing under cyclic loading. The experimental study investigated the behavior of a preflex beam specimen under multiple cyclic loading ranges, reproducing different deterioration levels in the concrete casing of the specimen. Relating concrete deterioration to resulting changes in the girder’s structural behavior, the study outlined recommendations for monitoring approaches in actual bridges. The study concluded that with advancement in concrete deterioration, the preflex beam girder loses prestress that results in reduced strength of the girder and remarkable changes in its sectional properties. The study also concluded to minimize prestress loss and changes in sectional properties of the girder, closer spacing for shear ribs welded to the lower flange can be helpful.

Preflex beam composite girders are widely used in the bridge industry. Understanding the post-cracking behavior of preflex beam girders under cyclic loading is essential to improve monitoring and maintenance. The aim of this study was to evaluate the relationship of the deterioration of the lower flange concrete under cyclic loading to the resulting changes in stiffness, neutral axis location, reinforcement bar stress, and steel-lower-flange stresses of the preflex beam. The study also compared the preflex beam behavior with a conventional girder without prestress under cyclic loading. The experimental study included two specimens of the same details, of which one was preflexed and the other was a conventional non-preflexed specimen. The cracking and post-cracking behavior of the specimens were investigated under multiple cyclic loading stages. The study concluded that changes in the concrete crack width can be used to fairly estimate changes occurring in the neutral axis location, rebar stress, and steel-lower-flange stress of the preflex beam under cyclic loading. The smaller width and shorter length of concrete cracks, implying smaller changes in the preflex beam girder, improved its behavior remarkably compared with the non-preflexed girder with wider and longer concrete cracks under cyclic loading. Furthermore, the study concluded that a closer spacing of the shear ribs reduces the crack width. However, the number of cracks would be larger.

p>Many bridges have been in service for over 40 years and face to the repapering or reinforcing period due to deterioration. Particularly, in a high-strength bolts used for joints may be loosened due to co-rotation, corrosion, or vibration caused by the vehicles. Thus, it is important to evaluate an axial force of the high-strength bolts. In this research, an axial force evaluation of high-strength bolt using eddy current that does not require measurement preparation has been investigated. The eddy current method is capable of capturing the change in permeability of steel members due to the stress change. Further, the stress distribution of the bolt head is assumed uniform without directionality. Therefore, a numerical simulation and an experiment that measures the output signal of the eddy current probe while introducing axial force to the high-strength bolt has conducted.</p

This paper describes an investigation of fatigue strength enhancement for transverse to longitudinal rib connections in orthotropic steel decks with open ribs by structural modification. A structural hot-spot stress approach was used to evaluate the fatigue strength. The results of a finite-element analysis revealed that the fatigue strength decreased with increasing span length of the longitudinal ribs. The structural modifications to the connection, which reduced the stiffness of transverse ribs due to section loss, absorbed the local deformation of the deck plate and consequently reduced the structural hot-spot stress.