Shigeki Unjoh

THE DAMAGE OF HIGHWAY BRIDGES IN THE 1995 HYOGO-KEN NANBU EARTHQUAKE AND ITS IMPACT ON JAPANESE SEISMIC DESIGN

The Hyogo-ken Nanbu Earthquake of 17 January 1995, caused destructive damage to highway bridges. Obviously, this was the first experience of such destructive damage since the Great Kanto Earthquake of 1923. Various tentative measures were taken for seismic design of repair and reconstruction of highway bridges which were damaged due to the earthquake. This paper summarises the damage feature of highway bridges and a series of actions taken for seismic design and seismic strengthening of highway bridges about half a year following the earthquake.

Damage of Bridges due to the 2010 Maule, Chile, Earthquake

This article presents the damage of bridges resulting from the 2010 Maule, Chile earthquake based on site investigations. Features of bridge damage are presented and discussed with emphasis on the effect of in-plane rotation of skewed bridges, insufficient seat support length, absence of integrity of prestressed concrete girder bridges without diaphragms, and lack of bearing capacity of foundations.

Development of shape memory alloy damper for intelligent bridge systems

The application of intelligent materials with self-diagnosis functions will provide more efficient and effective earthquake protective system to bridge structures. Shape memory alloys are possible candidates of intelligent materials that are applicable to bridge structures. The damping device made of shape memory alloys that can absorb seismic energy and reduce the seismic force by its pseudo yield effect was proposed. The device also enables the bridge to set again to the original position by its shape memory effects or self-centering effect even if residually displaced. This study focuses on the damping effect of shape memory alloys and verified its effect. First, the experiment to obtain the force-displacement relationship of the propose damping device was carried out in the Martensite and Austenite phases so that the effects were verified in the shape memory phase and super elastic phase. A series of shaking table test were also carried out in order to verify the effect under earthquake type shaking. As a result of this study, the shape memory alloy damper device performs its function more efficient and effective when designed in shape memory phase.

SEISMIC RETROFIT OF EXISTING HIGHWAY BRIDGES IN JAPAN

Abstract This paper presents the current technical developments for seismic design and seismic retrofit of existing highway bridges in Japan. At first, the histories of the past seismic design codes, past seismic evaluation investigation, and past seismic retrofit practices for highway bridges are described. Then the damage caused by the 1995 Hyogo-ken Nanbu Earthquake and the lessons learned from the earthquake are briefly described. Finally, the seismic retrofit program after the Hyogo-ken Nanbu Earthquake is described with emphasis on research and development as well as field practice of the seismic retrofit of existing reinforced concrete highway bridges such as single column bent, wall-type pier, and multicolumn bents.

Seismic Performance of a Full-Size Polypropylene Fiber-Reinforced Cement Composite Bridge Column Based on E-Defense Shake Table Experiments

E-Defense shake table experiments on a 7.5 m tall, 1.8 m by 1.8 m square bridge column using polypropylene fiber-reinforced cement composites (PFRC) at the plastic hinge region and part of the footing is presented. The column was excited using 80% of the original intensity of the near-field ground motion recorded at the JR Takatori Station during the 1995 Kobe, Japan earthquake. Use of PFRC mitigated cover and core concrete damage, local buckling of longitudinal bars, and deformation of ties even after six times of repeated excitation. The damage sustained was much less than the damage of regular reinforced concrete columns.

Earthquake Simulation Test of Circular Reinforced Concrete Bridge Column under Multidirectional Seismic Excitation

Structures behave multi-directionally when subjected to earthquake excitation. Thus, it is essential to evaluate the effect of multidirectional loading on the dynamic response and seismic performance of reinforced concrete bridge columns in order to develop more advanced and reliable design procedures. To investigate such effects, a 1/4 scaled circular reinforced concrete bridge column specimen was tested under two horizontal and one vertical components of a strong motion that has long duration with several strong pulses. Damage progress of reinforced concrete columns subjected to strong excitation was evaluated from the test. The test results demonstrate that the lateral force response in the principal directions become smaller than computed flexural capacity due to the bilateral flexural loading effects, and that the lateral response is not significantly affected by the fluctuation of the axial force because the horizontal response and axial force barely reached the maximum simultaneously due to difference of the predominant natural periods between the vertical and the horizontal directions. Accuracy of fiber analyses is discussed using the test results.

Seismic Isolation Design Code for Highway Bridges

This paper presents the seismic isolation design code for highway bridges. This is based on the 1996 Design Specifications for Highway Bridges, Part. V: Seismic Design, issued by the Japan Road Association in December 1996. This paper focuses on the outlines of the seismic isolation design code including the seismic design basic principles, design ground motion, and seismic isolation design.Copyright

Seismic damage sensing of bridge structures with TRIP reinforcement steel bars

Intelligent reinforced concrete structures with transformation-induced-plasticity (TRIP) steel rebars that have self-diagnosis function are proposed. TRIP steel is special steel with Fe-Cr based formulation. It undergoes a permanent change in crystal structure in proportion to peak strain. This changes from non-magnetic to magnetic steel. By using the TRIP steel rebars, the seismic damage level of reinforced concrete structures can be easily recognized by measuring the residual magnetic level of the TRIP rebars, that is directly related to the peak strain during a seismic event. This information will be most helpful for repairing the damaged structures. In this paper, the feasibility of the proposed intelligent reinforced concrete structure for seismic damage sensing is experimentally studied. The relation among the damage level, peak strain of rebars, and residual magnetic level of rebars of reinforced concrete beams implemented with TRIP steel bars was experimentally studied. As the result of this study, this intelligent structure can diagnose accumulated strain/damage anticipated during seismic event.

Development of an Earthquake Damage Detection System for Bridge Structures

After a large scale earthquake, evaluation of damage of highway structures such as bridge structures has great importance to assure the emergency route for rescue and transport of urgent supplies. Currently, the damage evaluation is basically conducted by means of visual inspection by bridge experts, but generally it takes so long time to collect whole damage information in the affected area. Therefore, the authors are developing a new damage evaluation system using advanced sensors, which can detect the damage level of structures more correctly and quickly just after the earthquake. This paper presents the proposed “Seismic Damage Evaluation System for Bridge Structures” and the effectiveness of proposed damage evaluation method is demonstrated through a series of shaking table tests. Also, the integration of proposed system to the SATURN system, which is practically used in Japan as a seismic damage information system, is discussed.

Nondestructive damage detection and evaluation technique for seismically damaged structures

The development of quantitative damage detection and evaluation technique, and damage detection technique for invisible damages of structures are required according to the lessons from the 1995 Hyogo-ken Nanbu earthquake. In this study, two quantitative damage sensing techniques for highway bridge structures are proposed. One method is to measure the change of vibration characteristics of the bridge structure. According to the damage detection test for damaged bridge column by shaking table test, this method can successfully detect the vibration characteristic change caused by damage progress due to increment excitations. The other method is to use self-diagnosis intelligent materials. According to the reinforced concrete beam specimen test, the second method can detect the damage by rupture of intelligent sensors, such as optical fiber or carbon fiber reinforced plastic rod.