Saiji Fukada

Experiments and Dynamic Finite Element Analysis of a Wire-Rope Rockfall Protective Fence

The imperative need to protect structures in mountainous areas against rockfall has led to the development of various protection methods. This study introduces a new type of rockfall protection fence made of posts, wire ropes, wire netting and energy absorbers. The performance of this rock fence was verified in both experiments and dynamic finite element analysis. In collision tests, a reinforced-concrete block rolled down a natural slope and struck the rock fence at the end of the slope. A specialized system of measuring instruments was employed to accurately measure the acceleration of the block without cable connection. In particular, the performance of two energy absorbers, which contribute also to preventing wire ropes from breaking, was investigated to determine the best energy absorber. In numerical simulation, a commercial finite element code having explicit dynamic capabilities was employed to create models of the two full-scale tests. To facilitate simulation, certain simplifying assumptions for mechanical data of each individual component of the rock fence and geometrical data of the model were adopted. Good agreement between numerical simulation and experimental data validated the numerical simulation. Furthermore, the results of numerical simulation helped highlight limitations of the testing method. The results of numerical simulation thus provide a deeper understanding of the structural behavior of individual components of the rock fence during rockfall impact. More importantly, numerical simulations can be used not only as supplements to or substitutes for full-scale tests but also in parametric study and design.

Numerical study on the vibrational serviceability of flexible single span bridges with different structural systems under traffic load

Bridge vibration is the major focus of environmental issues, especially in urban areas where the ground is soft. The structural system of the bridge greatly influences the ergonomic serviceability of the bridge, infrasound and ground vibration by vehicular live load. This paper discusses the vibrational serviceability of bridges, considering the interaction between vehicular live load and the structural systems of the bridge. The numerical approach with Finite Element Analysis was conducted to understand and evaluate the fundamental dynamic behaviour of flexible single span bridges under vehicular live load for four types of different structural systems, including the adjacent approach parts of the bridges.

Experimental Study on the Biaxial Loading Effect on Group Stud Shear Connectors of Steel-Concrete Composite Bridges

Abstract Clustering stud shear connectors with minimized spacing based on specifications to form group studs are useful for concrete slab prefabrication and prestress installation efficiency in steel-concrete composite bridges. To date, many long-span composite bridge girders have been designed with wide transverse cantilevers and web spacing, and most of these girders use group studs. The concrete’s self-weight and the weight of moving loads result in a significant transverse bending-induced effect generally consisting of bending stresses and tensile concrete cracks. In this sense, the studs are actually under longitudinal interlayer shear force that is influenced by the transverse bending-induced effect. This biaxial loading effect has not been investigated experimentally. Thus, standard and newly designed push-out tests and corresponding analyses were carried out. In addition, the stud arrangement effect also was of concern. In this study, the ratio of stud height to shank diameter was approximately 6....

Relation of the infrasound characteristics and the continuous steel bridge vibration modes generated by the vibration of moving heavy trucks

As heavy trucks pass over highway bridges, bridge vibration occurs and generates infrasound. General trucks in Japan with rear leaf suspension have whole body vibration (suspension spring vibration) frequencies of about 3 Hz. Also, the frequencies of the wheel vibration (tire spring vibration) are about 10–20 Hz. The continuous steel highway bridges with middle span length have vibration modes with the same phase in each span at the frequencies of about 3 Hz and also have those with the secondary mode shape at the frequencies of about 10–20 Hz. Truck vibrations and bridge vibrations are closely related. In this work, vibration tests are conducted using a heavy test truck for two cases of infrasound complaints in order to investigate the relation between the continuous steel bridge vibration modes generated by the vibration of moving heavy trucks and its infrasound characteristics. As a result of the examination, two types of bridge vibration modes are caused by the vibrations of a moving heavy truck. Moreover, the bending vibration modes with the same phase in each span have the most powerful infrasound pressure, since each span vibrates with the same phase. Two countermeasures, including viscoelastic damper at the end of the girders and extended deck method, are proposed to reduce the amplitude of bridge vibration and its infrasound.

Load Bearing Capacity of PC Girders with and Without Fly Ash Affected by ASR Deteriorations

Alkali-silica reaction (ASR) is one of the prominent explanations of concrete degradation. Many reactive aggregates are widely distributed to various places in Japan. Especially, in Hokuriku region along the Sea of Japan, there is a wide spread of andesite which accelerates the ASR-induced expansion of concrete. The aim of this study is to investigate how the structural behavior and the load bearing capacity of prestressed concrete (PC) girders, which were affected by varying degrees of ASR-induced damages, change with and without of fly ash. In order to achieve the above purpose, this study conducted full-scale destructive tests of prestressed concrete girders. Specifically, two PC girders, which were constructed and placed outside the laboratory, had been exposed to weather conditions. The first girder was affected by alkali-silica reaction while the second one was kept at an inactive state with ASR acceleration due to the addition of fly ash. As an outcome, it was noticed that the elastic and ultimate states of the full-scale PC girders were well illustrated by the experimental data. In addition, since difference behaviors were well observed, fly ash played significant effects on the performance of the PC girders subjected to ASR deteriorations.

Current Status of Degraded Road Bridge Slab Located in Mountainous Area

In the mountainous area of the Hokuriku region, bridges are suffering early deterioration caused by salt damage, alkali-silica reaction (ASR) and frost damage. Under such a regional situation, the load carrying capacity evaluation of these bridges has become an urgent issue. In this study, a statistical method–survival analysis–was carried out by using inspection data for bridges in the Hokuriku region, and the relationship between degradation tendency of bridges and regional characteristics causing salt damage, ASR and frost damage has been studied. In addition, the degradation causes of the reinforced concrete deck of a road bridge which deteriorated early in the mountainous area of the Hokuriku region were investigated. Cylindrical core extraction was carried out to analyze the degradation causes. Polarizing microscopic observation of specimens collected from RC slabs confirmed that cracks developed from the andesite particles and cracks were confirmed to be filled with ASR gels. Therefore, ASR was a cause of the deterioration. Moreover, the degradation in the mechanical properties of concrete due to ASR was also studied and reported. The results show that the reduction in compressive strength and static elastic modulus of both dry and leakage-water parts affected the load bearing capacity of the structure.

Long-Term Vibration Monitoring of the Effects of Temperature and Humidity on PC Girders with and without Fly Ash considering ASR Deterioration

Structural responses have been used as inputs in the evaluation procedures of civil structures for years. Apart from the degradation of a structure itself, changes in the environmental conditions affect its characteristics. For adequate maintenance, it is necessary to quantify the environment-induced changes and discriminate them from the effects due to damage. This study investigates the variation in the vibration responses of prestressed concrete (PC) girders, which were deteriorated because of the alkali–silica reaction (ASR), concerning ambient temperature and humidity. Three PC girders were exposed to outdoor weather conditions outside the laboratory, one of which had a selected amount of fly ash in its mixture to mitigate the ASR. The girders were periodically vibration tested for one and a half years. It was found that when the temperature and humidity increased, the frequencies and damping ratios decreased in proportion. No apparent variation in the mode shapes could be identified. A finite element model was proposed for numerical verification, the results of which were in good agreement with the measured changes in the natural frequencies. Moreover, the different dynamic performances of the three specimens indicated that the fly ash significantly affected the vibrations of the PC girders under ASR deterioration.

ESTIMATION OF UNACCEPTABLE EXPRESSWAY ROAD ROUGHNESS WITH SHORT WAVELENGTH DETECTED BY TRUCK DRIVERS

This study estimated unacceptable expressway road roughness with short wavelength, which was detected by truck drivers, using IRI (International Roughness Index) 10 analysis. As the results of the IRI 10, unacceptable roughness is over IRI 10 [4]. In order to confirm the unacceptable roughness, running tests using test trucks with leaf or air suspension were carried out at Meishin, Sanyo and Cyugoku Expressway. According to the running tests, truck driver detected the unacceptable roughness when maximum acceleration of tire spring is over 1.5G. Moreover, dynamic running analysis using test truck model with leaf suspension was carried out. It is clear that between IRI 10 [4] and maximum acceleration of tire spring 1.5G are correlated. This study investigated a new evaluation for detecting the unacceptable road roughness with a short wavelength which affects the tire vibration of the truck. 本研究では，高速道路を走行する大型車のドライバーをモニターとしたアンケート調査を行い，大型車ドライバーの乗り心地が優れない，または積荷の損傷が心配されるなどの苦情を受けた路面（苦情路面と称す）を抽出することにより，苦情路面の路面特性を把握した．また，リーフサスペンションまたはエアサスペンションを有する3軸トラックとトラクタ+セミトレーラを4台用いて走行試験を行い，アンケートによって得られた苦情路面の確認と新たな苦情路面を抽出した．その結果，苦情路面の特徴として評価基準長10m のIRI値が4（以下，IRI_10「4」）以上，大型車のばね下最大加速度1.5G以上（ただし，瞬時値ではなく繰り返しの振動）であった．さらに，試験車をモデル化した走行解析から，IRI_10「4」とばね下振動の最大加速度1.5Gに相関があることを明らかにした．

Ground Vibration Measures for the Rocking Vibration of the Piers with Two-Box Girders Bridge

Vibration caused by running vehicles on a highway bridge is spread to the superstructure, substructure s and ground. The ground vibrates both in horizontal and vertical direction. When vehicles load at the tip of the cross beam in the T -shape d pier , rocking vibration of the pier occurs. Its ground vibration in transverse direction is the biggest. In the two -box gi rders bridge, which bearings are installed at the tip of the cross beam of the T -shape d pier , the ground vibration has greatly occurred due to the rocking vibration of the pier. Two measures to mitigate the vibration are propose d in t his study. The evaluat ion the change of the vibration characteristics and effects of the measures to mitigate the vibration are also discussed in the study .

THE STRENGTHENED EFFECT OF ENDURANCE IN EXISTING STEEL BRIDGE

耐力不足となっている既設鋼橋の補強工法として, カバープレート工法と外ケーブル工法がある. その耐力的な補強効果は確認されているが, 耐久的な補強効果については明確になっていない. 特に, 疲労損傷の原因となることの多い二次応力の動的荷重下での挙動については, ほとんど研究されていない. そこで本研究では, 車両の大型化対策として外ケーブル補強された単純活荷重合成Iげた橋を対象に, 数値解析によって算出する動的荷重下での橋梁部材に作用する一次応力および二次応力の妥当性の検証を行い, その数値解析を用いて, カバープレート工法と外ケーブル工法の疲労から決まる耐久性に対する補強効果について検討するものである.