Showing papers on "Earthquake resistant structures published in 2002"

“Smart” Base Isolation Strategies Employing Magnetorheological Dampers

Abstract: One of the most successful means of protecting structures against severe seismic events is base isolation. However, optimal design of base isolation systems depends on the magnitude of the design level earthquake that is considered. The features of an isolation system designed for an El Centro-type earthquake typically will not be optimal for a Northridge-type earthquake and vice versa. To be effective during a wide range of seismic events, an isolation system must be adaptable. To demonstrate the efficacy of recently proposed ''smart'' base isolation paradigms, this paper presents the results of an experimental study of a particular adaptable, or smart, base isolation system that employs magnetorheological ~MR! dampers. The experimental structure, constructed and tested at the Structural Dynamics and Control/Earthquake Engineering Laboratory at the Univ. of Notre Dame, is a base-isolated two-degree-of-freedom building model subjected to simulated ground motion. A sponge-type MR damper is installed between the base and the ground to provide controllable damping for the system. The effectiveness of the proposed smart base isolation system is demonstrated for both far-field and near-field earthquake excitations.

Evaluating Strength and Stiffness of Unreinforced Masonry Infill Structures

Abstract: : Masonry has been used for hundreds of years around the world in construction projects ranging from simple roadways to complex arch designs. Masonry is also commonly used in frame building structures as infill to either protect the inside of the structure from the environment or to divide inside spaces. During the design and analysis of steel/reinforced concrete frame structures, infill has commonly been ignored. Contrary to common practice, masonry infills do influence the overall behavior of structures when subjected to lateral forces. The influence of infills on overall behavior of the structure has been found to change with the direction in which the load is applied. This report gives guidelines on evaluating the lateral load capacity of infilled panels for in-plane and out-of-plane loading. Further guidelines account for the effect of out-of-plane loading on in-plane capacity. This report is a complement to applicable provisions in FEMA 310 with respect to seismic evaluation of buildings. These guidelines should prove useful for engineering evaluations of the lateral strength of buildings with respect to wind or earthquake forces. The guidelines give the engineer a strength-based alternative to FEMA 273 a performance-based method, which should also result in safe and economical construction.

Assessment of performance of bolu viaduct in the 1999 duzce earthquake in turkey

Abstract: Nearly complete when hit by the powerful November 12, 1999 Duzce earthquake in Turkey, the Bolu Viaduct is a 2.3-km-long seismically isolated structure. The viaduct suffered complete failure of the seismic isolation system and narrowly avoided total collapse due to excessive superstructure movement. This report provides an evaluation of the design of the seismic isolation system of this structure and an assessment of the performance of the structure in the Duzce earthquake. The evaluation of design and assessment of performance are important in developing experience in the design of seismically isolated structures and in validating analysis and design specifications.

Seismic performance of precast segmental bridge superstructures with internally bonded prestressing tendons

Abstract: A research project is currently in progress to investigate the seismic performance of segment-to-segment joints of precast segmental concrete bridges. The paper presents the experimental and analytical results of two large scale tests which model the superstructure response of a prototype precast segmental bridge, post-tensioned with internally bonded tendons, under fully reversed vertical cyclic displacements. The joints of the first test unit were epoxy bonded with no reinforcement crossing the joints other than the prestressing steel. The second test unit had a reinforced cast in place deck closure with the remaining portions of the joints connected by epoxy. Both test units were subjected to fully reversed cyclic loads simulating earthquake vertical motions. The paper also presents results from nonlinear finite element modeling of the simulated seismic response of the test units.

Seismic Performance of Multisimple-Span Bridges Retrofitted with Link Slabs

Abstract: During earthquakes multisimple-span bridges are vulnerable to span separation at their expansion joints. A common way of preventing unseating of spans is to have cable or rod restrainers that provide connections between adjacent spans. Alternatively, dislocation of the girders can be controlled with a link slab that is the continuous portion of the bridge deck between simple spans. Seismic retrofit with link slab should be more cost-effective than the existing methods when it is performed during redecking or removal of expansion joints. Maintenance cost associated with expansion joints could also be reduced. This paper discusses the use of link slabs for retrofit of seismically deficient multisimple-span bridges with precast, prestressed concrete girders. The concept is equally applicable to bridges with steel girders. Analytical studies for typical overpasses were performed to investigate the effectiveness of the proposed link slab application. A simple preliminary design procedure was also developed.

Seismic performance and retrofit of steel pile to concrete cap connections

Abstract: This paper looks at the seismic-performance of steel pile-to-pile cap connections representative of construction practice in the eastern U.S. Two perspectives are considered. The first is the seismic vulnerability of existing pile cap connections, where the embedment depth of the pile inside the cap beam is small. An initial experimental study, therefore, was conducted for testing 2 specimens that represented existing exterior connections under cyclic lateral loading. The second perspective is the seismic design requirements for strong cap beam-to-pile connections. Hence, a theory assuming a linear distribution of stresses along the connection embedment depth was developed, and comparisons with a finite element model were performed. A second experimental program was conducted to evaluate the performance of specimens retrofitted in accordance with the theoretical model developed in this study. Results of the second experimental study validated the proposed retrofit strategy.

Pushover Analysis of Inelastic Seismic Behavior of Greveniotikos Bridge

Abstract: Nonlinear pushover analysis is a powerful tool for evaluating the inelastic seismic behavior of structures. The paper deals with the nonlinear analysis process followed during the independent design check of the Greveniotikos Bridge in Greece. The nonlinear response of the bridge was investigated from the first pier hinging to the inelastic equilibrium condition during the design-level earthquake and then up to the ultimate limit state. The effects on the seismic demand of period lengthening and damping increase produced by structural deterioration were evaluated. Onset and progression of plastic hinges were determined along with the pier stiffness distribution and the force reduction factors to be used in spectral analysis. The nonlinear loading conditions of plastic hinges were analyzed to assess their rotation capacity and shear strength. Finally, the safety factor from progressive collapse condition was evaluated. The parametric approach followed in this work permitted evaluation of the effects of several parameters on the inelastic structure response, thus enhancing confidence with result evaluation.

Hysteretic modeling of thin-walled circular steel columns under biaxial bending

Abstract: To ensure the safety of elevated highway bridges under major earthquakes, it is important to predict the ultimate behavior of columns used as bridge piers. After the Kobe earthquake, many analytical and experimental studies have been conducted to examine the ultimate seismic behavior of thin-walled steel columns. However, these studies are mostly restricted to the in-plane behavior of the columns. As observed in the Kobe earthquake, the damages to the columns are usually influenced by the two-dimensional horizontal seismic excitations. Therefore, it is more desirable to consider the effect of biaxial bending at the ultimate stage of earthquake response in the design of steel columns. Herein, we propose a hysteretic model of thin-walled circular steel columns under biaxial bending to predict the ultimate seismic behavior of cantilever-type thin-walled circular steel columns with constant axial load. The proposed column model consists of a concentrated mass and a rigid column with multiple nonlinear springs located at the column base. As the hysteretic constitutive relation for each spring, we adopt the Dafalias and Popov’s bounding-line model by modifying the original model in order to take into account the local buckling behavior. The material constants of the modified bounding-line model can be determined, based on the in-plane hysteretic behavior of the column obtained either by FEM shell analyses or by experiments. The validity of the proposed model is examined by comparing it with results of the two-dimensional horizontal earthquake-response analyses, using the FEM shell model.

Shear strength of circular reinforced concrete columns

Abstract: In considering the large number of circular concrete columns used to support buildings and bridges and the critical importance of ensuring that the shear strength of these members is adequate to survive a possible earthquake, relatively few studies have been conducted on the shear strength of circular reinforced concrete columns. This paper summarizes results of 3 experimental studies in which a total of 15 large circular specimens were tested in shear. The paper also explains how analytical models based on the modified compression field theory can be used to predict shear response of circular reinforced concrete columns.

Performance and Rehabilitation of Type L FAA Airport Traffic Control Tower at San Carlos, California, for Seismic Loading

Abstract: This paper presents a seismic evaluation of the San Carlos airport traffic control tower (ATCT) in San Carlos, California, that describes the tower, presents the seismic evaluation of the tower, and defines a rehabilitation approach that upgrades the structure to applicable life-safety standards. The San Carlos ATCT is a Federal Aviation Administration Type L tower, whose primary structure below the control cab (tower shaft) is four inverted L-shaped reinforced concrete members that frame together at the top of the tower shaft. The goal of this evaluation was to determine if life-safety performance could be demonstrated, and if not, to develop an upgrade approach to achieve this performance. The seismic hazard was based on the maximum considered earthquake defined in the National Earthquake Hazards Reduction Program (NEHRP) recommended provisions. The evaluation shows that the tower cannot achieve life-safety performance due to large deflections in the cab and the formation of a collapse mechanism. The connection base plates for the cab columns (corner window mullions) will form a collapse mechanism at very low seismic motions. Formation of the collapse mechanism is due to base-plate bending failure and subsequent hinging at the base of each column. The recommended rehabilitation approach is to upgrade the columns to reduce deflections to acceptable levels, and also to protect the vulnerable connections. Upgrading the columns consists of welding plates on the interior and exterior column faces and welding deep structural tubing members to the base of each corner column. The writers considered the evaluation of this particular control tower to be of interest to the technical community because of the unique failure mechanism and proposed upgrade approach.

A High Seismic Performance Shear Connector for Composite Steel-Concrete Structures Subjected to Strong Earthquakes

Abstract: This paper presents the final results of an experimental and analytical study designed to develop a new shear connector for composite steel-concrete structures. Innovative characteristic lies in the design features of the connector's base, which presents a special folded shape. A modified push-out test has been employed to assess the shear strength as well as the load-slip behaviour under cyclic loading. A remarkable strength and ductile behaviour have been observed. In this way, an optimised and economic shear connector was obtained.

Lessons From Recent Earthquakes in turkey and Seismic Rehabilitation of Buildings

Abstract: This paper discusses recent earthquakes in Turkey. Large-scale seismic rehabilitation projects carried out by the Middle East Technical University (METU) faculty and staff on moderately damaged reinforced concrete structures are summarized. Research at METU related to seismic rehabilitation is presented, emphasizing infilled frames, a system used extensively in Turkey.

Design, Construction, and Performance of Open Cell Sheet Pile Bridge Abutments

Abstract: Recent innovations in bridge abutment design have resulted in the development of open cell sheet pile bridge abutments. The open cell abutment structure is a cellular flat sheet pile structure driven in a partial circular shape when viewed from above. Open cell structures can easily resist very heavy loads such as extremely heavy drill rig vehicles and module loads, ice attack from arctic river breakup events and high seismic accelerations. Additionally, these abutments uniquely protect the bridge structure from the effects of extreme river scour. These abutment structures are easily constructed without the use of field welding, bolted connections or an independent tieback system, making them less expensive and easier to construct. The system functions as a membrane, relying solely on the resistance developed between the soil and the sheet pile tail wall. The system does not rely on toe embedment for stability. These structures have significant advantages over typical spill through or reinforced earth abutment structures, especially in arctic conditions. Over one-hundred open cell sheet pile structures (fifty-nine, of which are bridge abutments) have been built throughout Alaska and the rest of the United States, some in very active seismic zones. These structures have performed flawlessly in the twenty years of their history resisting hundreds of earthquakes. Details of seismic performance will be presented. This paper reviews the general theory, adaptability, construction, and seismic and ice load resistance of the open cell sheet pile abutment design. Examples and history of constructed open cell sheet pile abutments for heavy duty private installations and for public transportation systems will be presented.

Ground Improvement by Jet Grout Columns for the Foundations of an Automobile Plant in Turkey

Abstract: The aim of this paper is to review the performance of jet grouting after the Kocaeli Earthquake and to discuss the quality assurance during production. The jet grouting technique was implemented for soil improvement under several structures at the Ford Automobile Plant. The plant's production facilities have been in operation since April 2001 in Golcuk, Kocaeli, Turkey. The structures and their foundations were thoroughly checked and evaluated after the Kocaeli Earthquake on August 17, 1999. The earthquake epicenter was only 1 km away from the site. At the time of the earthquake, 90% of the foundation works were completed. An extensive testing and investigation program was adopted after the earthquake to verify the performance of the jet grouted system and to reassess the soil conditions. It was then decided to proceed with the construction in January 2000, with certain foundation design revisions.

An experimental study for seismic reinforcement method on existing cylindrical steel piers by welded rectangular steel plates

Abstract: A great earthquake occurred on Hanshin/Awaji, Japan in January 1995 causing severe damage to a lot of existing cylindrical steel piers This paper reports on a research that studied a reinforcing method to limit the enhanced horizontal bearing capacity of the existing piers to prevent the collapse of the anchor part of the pier and to improve the ductility in the plastic region The reinforcing method proposed will let local buckling to take place at the predicted point where the local buckling would take place due to the horizontal force at earthquake, and to improve the ductility at the same time Evaluation of the reinforcing effects was studied

Design Recommendations for Seismic Retrofit of Shear-Deficient Reinforced Concrete Bridge Columns with Advanced Composite Jackets

Abstract: A proposed design methodology for the seismic retrofit of shear-deficient reinforced concrete bridge columns by advanced composite jackets is presented. The proposed procedure is based partly on an extensive experimental investigation of half-scale bridge columns tested under cyclic lateral loads. A numerical prediction of the cyclic behavior of the tested samples was also performed using two displacement models and six different concrete confinement models. The recommended design procedure achieves both efficient and reliable seismic retrofit for shear enhancement

Strength and stress analysis of steel beam-column connections using finite element method

Abstract: Many studies, both experimental and analytical, have been carried out following the Northridge and Kobe earthquakes to get a better understanding of the seismic resistance of steel structures. Four types of steel web-bolted and flange welded (WBFW) beam-column connections with different details were analyzed by using nonlinear finite element method for the purpose of determining whether the improved connection detail can contribute to the seismic resistance of column-beam joints. The paper presents the calculations of the ultimate strength, the stress distribution and the development process of plastic zones of connections with the raising of applied loading. Also briefly reviewed are the modeling techniques used in the nonlinear finite element analysis of steel connections for obtaining information on stress fields, the loading capacity and ultimate strength.

Experimental and theoretical studies on steel-concrete hybrid structures

Abstract: The paper presents a study examining the behavior of steel frame and concrete tube hybrid structures for tall buildings. Since little research has been conducted on seismic behavior of hybrid structures, that specific area is the focus of this study. Presented is a scale-down model of a typical hybrid tall building that was designed and tested on the shaking table at Tongji University in Shanghai, China. The dynamic properties, seismic responses, damage features and displacement responses of the model were recorded and analyzed. Developed and proposed was a simplified approach for elasto-plastic response analysis of steel-concrete hybrid tall buildings. The effectiveness and reliability of the proposed analytical approach were verified by comparing the experimental and analytical results of the scale-down model subjected to simulated earthquakes.