Showing papers on "Earthquake resistant structures published in 2003"

Seismic Performance of Precast Reinforced and Prestressed Concrete Walls

Abstract: Two geometrically identical half-scale precast concrete cantilever wall units were constructed and tested under quasi-static reversed cyclic lateral loading. One unit was a code compliant conventionally reinforced specimen, designed to emulate the behavior of a ductile cast-in-place concrete wall. The other unit was part of a precast partially prestressed system that incorporated post-tensioned unbonded carbon fiber tendons and steel fiber reinforced concrete. Hysteretic energy dissipation devices were provided in the latter unit in the form of low yield strength tapered longitudinal reinforcement, acting as a fuse connection between the wall panel and the foundation beam. The conventional precast reinforced wall performed very well in terms of the ductility capacity and energy absorption capability, reaching 2.5% drift before significant strength degradation occurred. The precast partially prestressed wall unit achieved drift levels well in excess of 3% with no visible damage to the wall panel prior to failure. Test results and performance comparisons between the precast partially prestressed wall system and the precast conventionally reinforced unit are presented.

Effect of seismic retrofit of bridges on transportation networks

Abstract: The objective of this research is to determine the effect earthquakes have on the performance of transportation network systems. To do this, bridge fragility curves, expressed as a function of peak ground acceleration (PGA) and peak ground velocity (PGV), were developed. Network damage was evaluated under the 1994 Northridge earthquake and scenario earthquakes. A probabilistic model was developed to determine the effect of repair of bridge damage on the improvement of the network performance as days passed after the event. As an example, the system performance degradation measured in terms of an index, “Drivers Delay,” is calculated for the Los Angeles area transportation system, and losses due to Drivers Delay with and without retrofit were estimated.

Dynamic tests and simulation of magneto-rheological dampers

Abstract: Magneto-rheological (MR) fluid dampers are semi-active vibration devices that offer seismic response mitigation of civil engineering and building structures. This paper discusses the design of MR dampers with a bypass-type magnetizing orifice mechanism and verifies their performance by means of dynamic tests and dynamic analytical models. Their dynamic characteristics are also investigated experimentally to compare the performance of two different magneto-rheological fluids. Dynamic loading tests with various loading conditions show that MR dampers that do not have a magnetic field applied to them exhibit similar dynamic behavior to typical viscous dampers, but by applying the magnetic field, the generated force is increased according to the strength of the applied field and the behavior shifts to rigid-plastic hysteresis behavior like that of a friction damper. It is also shown that the increase in generated force has an upper limit, so that the range between the maximum force at the upper limit and the minimum force decided by the viscous force without the magnetic field is effective for variable dampers of semi-active vibration control systems. These results indicate that the MR dampers developed in this study do enable semi-active control of civil engineering and building structures.

Repair of new long-span bridges damaged by the 1995 kobe earthquake

Abstract: The 1995 Hyogo-ken Nanbu (Kobe), Japan earthquake provided the world’s first experience with earthquake damage to new long-span bridges designed to 1990s seismic standards. This paper reviews damage and describes techniques used to repair three major steel bridges along the Wangan route (Bayshore route) in Kobe—the 885 m Higashi-Kobe Bridge, the 217 m Rokko Island Bridge, and the 252 m Nishinomiya Port Bridge. These bridges, in service for less than three years, were essential components in the highway transportation system in the Kobe region. Extremely large ground motions, and failure of bearings, connections, and seismic restrainers were principal contributors to the damage sustained by these bridges. Repairs utilized heavy-lift floating cranes (up to 4,100 ton capacity) and various jacks to stabilize the structures and to realign spans. In one case, reconstruction of a collapsed span was required, with lifting weight a prime concern. Significant constraints on the repair included confined working space and requirements for maintaining maritime navigational clearances. The closure times for the repair of the bridges ranged from three to nine months.

Fault tolerance of semiactive seismic isolation

Abstract: A 6-story seismically isolated structure fitted with semiactive hydraulic devices is analyzed in order to study effects of time lag in the devices and mass eccentricity in the superstructure on the lateral-torsional behavior. The computer program 3DBASIS, which allows the nonlinear dynamic analysis of 3-D structures, is used in this work. Appropriate modifications were made to the program to incorporate behavior of semiactive hydraulic devices. Three different types of base isolation systems were considered: 1) lead rubber bearings (LRBs); 2) LRBs with supplemental viscous damping; and 3) LRBs with semiactive viscous damping. A comparison of these 3 base-isolation systems, considering both effects of eccentricity in the structure and differential time lags in semiactive hydraulic devices are studied. The peak isolator shear, isolation drift, rotation, and torsional moment, are reported. Three major earthquake motion records, namely, the El Centro record of the 1940 Imperial Valley earthquake, the Meloland record of the 1979 Imperial Valley earthquake, and the Sylmar free field record of the 1994 Northridge earthquake were used as inputs in the analyses.

Cyclic loading response of simple moment-resisting precast concrete beam-column connection

Abstract: This paper gives test results from 4 precast concrete beam-column connections and 1 monolithic concrete connection. The tests comprised the 2nd phase of an experimental program on a 2/5-scale model precast connection. The aim of the test program was to design a simple moment-resisting precast connection for regions of high seismicity. The connection transfers bending moment by a combination of lap-splicing and end anchorage of bars. The end portions of precast beams sit on the column bearing area at the beginning of subassemblage construction. Variables examined included the level of axial load on column, spacing of beam stirrups in the connection length region, gravity load on beam, and use of steel fiber in grout of connection region. Specimens were subjected to reversed cyclic loading in accordance with a prescribed displacement history. Connection performances were compared with prior tests based on ductility, energy dissipation capacity, flexural strength, and drift capacity. The simple precast connection matches the performance of monolithic connections indicating its suitability for seismic zones.

Evaluation of Seismic Performance for Tunnel Retrofit Project

Abstract: A seismic retrofit program at Yerba Buena Island Tunnel is presented as a case history. The studies include evaluations of portal stability under earthquake excitation and performance of the tunnel liner as a result of seismic induced deformation. Due to different potential failure modes at the two portal areas, two separate evaluation techniques were utilized. Key block theory in conjunction with a Newmark type analysis was used to assess movements of a potential failure wedge at the west portal slope, while discontinuous deformation analysis was utilized at the east portal slope to evaluate a rotational mode of failure. To assess the performance of the liner subjected to design earthquakes, a two-step analysis procedure was adopted. The first step was to compute seismic induced deformations of the tunnel subjected to seismic wave propagation through the island rock without the presence of the liner. The second step, not reported in this paper, involved imposing the deformations of the tunnel onto the structural liner through spring elements that accounted for interaction between the liner and the surrounding rock. From the studies, performance of the existing tunnel supports was found to be acceptable.

Earthquake-Resistant Property of Prefabricated High-Strength Concrete Pile

Abstract: This paper presents results from experimental studies of a prefabricated high-strength concrete (PHC) pile that suffered brittle failure at the pile head during the 1995 Hyougoken-Nanbu earthquake. The specimens, which were representative of typical pile heads, were tested under reverse cyclic loading and a constant axial load. Conclusions are provided, including the findings that: 1) when properly reinforced with longitudinal deformed bars and lateral reinforcement, PHC pile can exhibit stable hysteretic behavior and significant ductility, and 2) the deformation capacity can be evaluated using the section analysis, in which the concrete confinement provided by the lateral reinforcement is incorporated.

Seismic retrofit technology. in: bridge engineering: seismic design

Abstract: The seismic resistant retrofit design of bridges has been evolving dramatically in the last decade. Many of the retrofit concepts and details discussed in this paper have emerged as a result of research efforts and evaluation of bridge behavior in past earthquakes. This practice has been successfully tested in relatively moderate earthquakes but has not yet seen the severe test of a large-magnitude earthquake. The basic philosophy of current seismic retrofit technology in the U.S. is to prevent collapse by providing sufficient seat for displacement to take place or by allowing ductility in the supporting members. This paper's aim is to identify potential vulnerabilities to bridge components and to suggest practical retrofit solutions.

Performance and Analysis of Arifiye Overpass Reinforced Earth Walls During the 1999 Kocaeli (Turkey) Earthquake

Abstract: This chapter describes how, following the August 1999 earthquake in Kocaeli, Turkey, which had a 7.4 magnitude, the authors performed field investigation in the affected area in order to document the performance of improved soil sites and mechanically stabilized embankments. The seismic performance of a pair of conventional reinforced earth walls that were constructed of steel strips and compacted granular backfill is also described. The walls performed well and suffered only minor damage, despite being subjected to sever ground shaking and large ground displacements. Static and dynamic numerical analyses were performed to investigate the factors that contributed to this performance. The analyses were successful in predicting the observed wall behavior. The results suggest that conventionally designed reinforced earth walls perform relatively well during strong ground shaking and that displacement may be the controlling criterion as opposed to shear failure or collapse.

Retrofitting promotion system for existing low earthquake resisatnt structures using long-term earthquake prediction

Abstract: Among various issues on countermeasures for earthquake disaster reduction, retrofitting of existing low earthquake resistant structures, especially timber houses is the key issue in Japan, We propose a new methodology which encourages house owners to retrofit their own houses by using information on long-term earthquake prediction, earthquake resistance capacity of individual house and expecting ground motion of each site. With the methodology proposed, effect of retrofitting can be given to every house owner based on seismic capacity of his/her house and its location, probability of duration of earthquake prediction. This methodology is applied to discuss and evaluate the effects of retrofitting of structures using building stock data in Shizuoka-Prefecture, where 'Tokai Earthquake' is predicted to come. Language: ja

Seismic retrofit design of large cable-supported bridges in tokyo

Abstract: This paper describes the seismic retrofit of 3 cable-supported bridges in Tokyo: the Rainbow Bridge, the Yokohama Bay Bridge, and the Tsurumi Fairway Bridge. Site-dependent far-field ground motion due to possible maximum credible earthquake is calculated using a fault rupture model together with wave propagation techniques. The nonlinear seismic response of the bridges, including soil-structure interaction, is computed and it is found that all 3 bridges may suffer considerable damage. For the structural elements that receive severe damage, careful retrofit design is conducted. Taking into account that large bridges are complex structural systems, increase of the structural redundancy and fail-safe concept is emphasized in the retrofit design.

Performance of Interior Post-tensioned Concrete Wide Beams When Subjected to Lateral Earthquake Loading

Abstract: Concrete wide beam systems are widely used in Australia despite the fact that their performance under lateral earthquake loading is still uncertain. Moreover, the majority of the wide beams are in fact post-tensioned. In this research, an interior post-tensioned concrete wide beam sub-assemblage was tested under quasi-static cyclic loading to determine its performance under lateral loading. A special de-bonding strategy was implemented in the design of the sub-assemblage to improve the performance of the connection. The sub-assemblage was tested up to a drift ratio of 3.5% and was found to perform very well. Overall, the sub-assemblage was found to possess low energy dissipation capacity, good displacement capacity and small residual drift. Main issues investigated in the test were the formation and growth of cracks, behaviour of the hysteric response and the strain behaviour in the specimen. Finally the results from this investigation are compared with the results from a previous investigation on a similar reinforced concrete sub-assemblage.