Showing papers on "Earthquake resistant structures published in 2019"

Mechanical modeling of superelastic tensegrity braces for earthquake-proof structures

Abstract: This paper presents a novel application of tensegrity systems as lightweight and noninvasive braces for seismically resistant structures. The analyzed braces consist of D-bar systems equipped with shape memory alloy cables with superelastic response. These structures are able to markedly amplify the applied longitudinal displacements in the transverse direction, thus allowing for considerably large deformations of the SMA cables and high energy dissipation. The mechanics and the application of tensegrity braces for the reinforcement of anti-seismic structures are presented. A comparative study matches the seismic response of the analyzed systems with that of devices employing fluid viscous dampers. The results highlight the fact that D-bar units can be profitably employed as building blocks for innovative bracing systems, whose energy dissipation properties can easily surpass those of conventional anti-seismic braces.

Optimum design of viscous dampers to prevent pounding of adjacent structures

Abstract: This study investigates a new optimal placement method for viscous dampers between structures in order to prevent pounding of adjacent structures with different dynamic characteristics under earthquake effects. A relative displacement spectrum is developed in two single degree of freedom system to reveal the critical period ratios for the most risky scenario of collision using El Centro earthquake record (NS). Three different types of viscous damper design, which are classical, stair and X-diagonal model, are considered to prevent pounding on two adjacent building models. The objective function is minimized under the upper and lower limits of the damping coefficient of the damper and a target modal damping ratio. A new algorithm including time history analyses and numerical optimization methods is proposed to find the optimal dampers placement. The proposed design method is tested on two 12-storey adjacent building models. The effects of the type of damper placement on structural models, the critical period ratios of adjacent structures, the permissible relative displacement limit, the mode behavior and the upper limit of damper are investigated in detail. The results of the analyzes show that the proposed method can be used as an effective means of finding the optimum amount and location of the dampers and eliminating the risk of pounding.

A Study on Different Types of Base Isolation System over Fixed Based

Abstract: Based isolation is a technique which is used to prevent or reduce damage to a structure at a time of earthquake. It is a design principle by which flexible supports (isolators) are installed under every supporting point of a structure. It is generally located across a foundation (substructure) and superstructure. Seismic hazards are key concern for a earthquake prone areas of the world. Performance-based earthquake design has brought recent technological advances which has established new approach to construct earthquake resistant structure. Base isolation systems are progressively used technique for advanced earthquake resistance structure. The effect of different types of base isolator over earthquake resistant structures is studied in this paper. The work focuses on comparative study of different types of base isolators such as lead rubber bearings (LRB), friction pendulum bearings (FPB), elastomeric rubber bearing (ERB), high damping rubber bearings (HDRB), and low damping rubber bearing (LDRB) and compared for time period, base shear, fundamental period, frequency, storey drift, time history analysis, and displacement of the fixed base.

Repair Strategies for Earthquake-Damaged CFST Bridge Columns

Abstract: Concrete filled steel tubes (CFSTs) provide a unique, economical alternative to traditional reinforced concrete (RC) columns in highway bridges for their ease of construction and efficient structural properties. The steel tube provides optimal flexural resistance and continuous confinement to the infill concrete, while the concrete fill improves stiffness and strength of the column, and prevents inward local tube buckling of the steel tube. Recent research has developed a practical and structurally robust, column-to-foundation/cap-beam connection for use in mid-to-high seismic regions. This connection, referred to as the embedded ring (ER) connection, is a full-strength connection, where well-detailed, ER CFST columns exhibit local, outward tube buckling directly above the foundation/cap-beam when subjected to reverse-cyclic, lateral loadings. This typical ductile failure mode is readily identifiable post-earthquake events, and is uniquely advantageous compared to typical RC columns due to limited concrete spalling and the availability of the steel tube for welded connections. The main objective of this research was to develop practical repair strategies for ER CFST columns which exhibit this ductile failure progression, with the goal of reestablishing the original column strength and stiffness. Two strategies were developed: (1) a traditional plastic hinge relocation method that utilizes an enlarged, CFST pedestal that surrounds the damaged region, and (2) a performance-based repair that implements external energy dissipators and column-rocking to limit damage. A non-linear, numerical analysis approach was adopted to assess the hysteretic response of these repair methods in comparison to that of an undamaged, CFST column. Results indicated that both repair strategies successfully restored lost stiffness and strength, specifically peak strength values of 1.26Mp and 1.02Mp for the traditional and performance-based methods were observed, respectively, where Mp represents the plastic moment of the original column. Additionally, a limited experimental study was carried out on the proposed, bucking restrained, energy dissipator where, under cyclic-compressive loadings, compressive yielding (1.12Fy) and inelastic strains (9.0ey) were measured within the laterally-restrained, structural fuse of the dissipator.

A New Approach in Equivalent Spring-Dashpot Method for Seismic Soil-Structure Interaction Analysis of Long Bridges Including Non-uniform Excitations

Abstract: This paper is conducted on evaluating the seismic responses of long bridges under the effect of the soil-structure interaction (SSI) and spatially varying earthquake ground motions (SVEGM). The commonly used spring-dashpot method for analysis of the pile-supported structures under the effect of (SSI) improves to a more capable model. Also, a comprehensive investigation of the dynamic response of a long bridge subjected to spatially varying earthquake ground motions (SVEGM) is performed based on a proposed analytical model which includes the effect of (SSI). The modeling methodology is discussed in detail. To emphasize the importance of the SVEGM and SSI, bridge responses are also determined for the uniform ground motion and fixed base cases. This study proposing a compatible analytical model concerns the relative importance of the SSI and SVEGM and shows that these effects cannot be neglected in seismic analysis and design of long bridges.

New Structural Seismic Isolation System

Abstract: New structural seismic isolation system named Spherical Foundation Structural Seismic Isolation (SFSSI) system which has been discovered and first prototyped on a 104 m height (26 storey) building example is presented. Creation of SFSSI system aimed to build structural seismic isolation system, of which period must be more than the predominant period ground motion of majority existing earthquakes including near-fault zones also. As known, classical period-dependent isolation systems and not isolated (fixed base-FB) buildings are vulnerable under long-period earthquakes and it is required to design resistant structural system components. For this purpose, a system has been realised as a structure with inverse pendulum system’s behavior. Structure foot base and foundation contact surface are formed in spherical appearance and they are separated by known Lead Core Rubber Bearing (LCRB) or Laminate Rubber bearing (LRB) isolators which are installed through spherical contact surfaces. Dampers are installed through base (structure foot) plate counter for controlling system’s response. This allows spherical foundation’s turning around gyration center through rubber bearing contact and keeps the same behavior to superstructure. In the SFSSI system it is possible to keep the natural period of the structure in a large interval, which is much more than predominant period of ground motion of the majority of the existing earthquakes including near-fault zones also. In this study, behavior of the both classical base-isolated building using LCRB and not isolated-FB building has been investigated under long-period ground motion. Obtained results are compared with SFSSI system with the same stiffness and equivalent damping and number of LCRB which was installed on spherical foundation. It was shown that, SFSSI system deprived from known deficiency period-dependent isolation systems and it is the progress of the new type earthquake-resistant structures. SFSSI system exhibits improved Roly-poly (‘Haciyatmaz’, ‘Okiogary-Koboshi’) behavior. We believe that as Roly-poly, structures with SFSSI system will symbolize the ability to have success overcome adversity, and recover from misfortune.

Seismic Response Control of Unsymmetrical RCC Framed Building Using Base Isolation Considering Soil Structure Interaction

Abstract: In passive energy dissipation systems used for earthquake resistant structures, base isolation is one of the most powerful systems. For understanding the effect of base isolation system, G + 5 storey models are considered with planner asymmetry. Lead rubber isolator is used for controlling the response of building during earthquake effects and tremors. The paper deals with behavior of fixed base and isolated building in terms of natural time period, top floor acceleration, storey drift, base reaction and energy dissipation. The Non-linear Time history analysis has been performed by using FEM based software SAP2000. The paper also includes the effect of soil structure interaction on both fixed base and isolated base building. It was observed that with use of isolators, time period of structure becomes double as compared with the fixed base model. The soil parameters also plays vital role in performance of isolators.

Response of Self Centering Steel Moment Resisting Frames Against Cyclic Loading

Abstract: A Self Centering Moment Resisting Frame (SCMRF), an alternative to a conventional Moment Resisting frame, is characterized by gap opening and closing at the beam-column interface under earthquake loading. The beams are post tensioned to columns by high strength post tensioning (PT) strands oriented horizontally to provide self-centering forces when gap opening occurs. A Self Centering Moment Resisting Frame for earthquake resistant structures has the attributes of ductility, requires no field welding and returns the structure to its pre earthquake position which prevents permanent deformations when subjected to seismic loading. Energy dissipation is provided by supplemental elements that deform under the gap opening behavior. Unlike special steel moment resisting frame with welded connections a SCMRF can be designed to survive earthquake without much structural damage which provide immediate occupancy performance. Nonlinear static analysis is performed in ANSYS to investigate the effect of posttension load and bracing configuration on seismic performance of frame. The results indicated that an increase in PT force increases the residual drift and maximum load carrying capacity. Bracing in SCMRF is effective in increasing the load bearing capacity and energy dissipation. Bracing shifts the maximum stress position from beam column connection to gusset plate so that it act as sacrificial element which can easily be replaced without damaging the beams or columns.

Interaction Analysis of Long-span Bridges and Traffic System Subjected to Earthquakes

Abstract: 1 Long-span bridges support a large amount of traffic every day. Even when an earthquake strikes, a longspan bridge often still has many vehicles present due to the low predictability of earthquake events. To study the seismic performance of bridge and traffic systems, a new full-response prediction methodology for the coupled bridge-traffic interaction system under spatially varying earthquake excitations was developed by capturing the interaction effects not only between the bridge and moving vehicles, but also between earthquake excitations and the coupled bridge-traffic system. Different from existing bridge seismic analyses in which only traditional earthquake loads in terms of inertial forces are applied on the bridge structure, the new formulation can also incorporate coupled earthquake forces on the bridge and vehicles, which are expressed as functions of the bridge-traffic coupling matrices and earthquake displacement inputs. The proposed methodology was numerically demonstrated on a prototype long-span bridge and traffic system under spatially varying earthquake excitations. Responses of the bridge and vehicles were predicted when the bridge-traffic system was subjected to earthquake excitations. It was determined from the numerical analysis that the coupled earthquake force, as derived in this study, has notable influence on the dynamic performance of the bridge and vehicles under seismic excitations. 1 This study has been published as a journal paper: Zhou, Y. and Chen, S. (2018). “Full-response prediction of the coupled long-span bridge and traffic system under spatially varying seismic excitations”, Journal of Bridge Engineering, ASCE, 23(6): 04018031. TABLE OF CONTENTS

Review of IS 1893-1(2002): Effect of Unreinforced Masonry Infill Walls on Seismic Response of Framed Structures

Abstract: Earthquake, its occurrence and effects, its impact and structural response have been studied for many years in earthquake history and is well documented. The structural engineers have tried to examine the various method, with an aim to determine the complex dynamic effect of seismically induced forces in structures, for designing of earthquake resistant structures in a advanced and easy manner. From the study conducted it was found that more precise results are found from nonlinear static analysis method. An overview of the past researches conducted on the modelling of masonry infilled frame issues, it was found that macro model which consider the effect of masonry weak links is used for modelling the infill panels. Different factors governing the period of vibration was checked, and the result shows the effect of stiffness of the building is the most important factor influencing the period of vibration. Parametric study was conducted to determine the most influential factor that affects the period of vibration of a structure. From the observations it was clear that the effect of stiffness is the most important factor influencing the period of vibration. Therefore a curve with dimensionless height and lateral displacement were plotted using nonlinear static analysis obtained from SAP2000. From the above mentioned curve, the effective stiffness of the building under consideration is calculated, which route to find the period of vibration of the structure that is considered for the seismic analysis [1].