Sensitivity of response of isolated bridges to modeling and design parameters : A case study

The concept of base isolations in bridges implies that structural components should experience limited inelastic behavior associated only with minor damage. Most isolation systems are designed to eliminate altogether inelastic behavior. The estimation uncertainties during the design process of the future ground motions, associated with the uncertainties involved in the constructed practice, leave the possibility that the entire system will ecperience inelastic behavior with permanent deformations and damage.(AU)

Implications of spatial variation of ground motion on the seismic response of bridges : Case study

Linear and non-linear analytical studies were conducted for evaluating the performance of the southbound separatin and overhead bridge at the SR14/15 interchange during the Northridge earthquake of January 17, 1994. The analyses are focused on potential implications of the spatial variability of ground motion on the collapse of the structure. The influences of vertical ground motion, soil-structure interaction and non-linear contact effects at the expansion joints and abutments, are also examined. The parameter studies help to determine some of the causes of collapse and offer insight on the complex seismic behavior of long multi-span concrete bridges. (AU)

Inelastic analysis techniques

The current seismic design procedures imply that structures will respond with inelastic deformations during the design seismic event. An inelastic time history analysis is usually necessary to determine the structure's response. The response demands obtained from this method are used along with a composite energy displacement spectrum to determine the seismic performance of a structure by monitoring the damage levels and states. Vulnerability functions can be determined using appropriate probability distribution of the main structural parameters and ground motions.(AU)

IDARC2D version 4.0 : A computer program for the inelastic damage analysis of buildings

This report summarizes the modeling of inelastic structures and enhancements to the program series IDARC developed for analysis, design and support experimental studies. This report presents a synthesis of all the material presented in previous reports NCEER-87-0008, NCEER-92-0022 (and in other related reports). This report presents also the new developments regarding modeling of inelastic elements and structures with supplemental dampimg devices, infill panels, etc. (AU)

Experimental and analytical investigation of seismic retrofit of structures with supplemental damping : Part.1 - Fluid viscous damping devices

The need for structures which function more reliably without damage during severe earthquakes was reemphasized by the behevior of structures during recent earthquakes (Loma Prieta 1989, Northridge 1994, Kobe 1995, etc.) The existing structures and often new ones must rely on large inelastic deformations in hysteretic behavior to dissipate the motion's energy, while the capacity to sustain such deformation is limited by precious non-ductile design or limitations of materials. An alternative method to reduce the demand of energy dissipation in the gravity load carrying elements of structures is the addition of damping devices. This report. first in a series, presents the evaluation of fluid viscous dampers used as additional braces in reinforced concrete frame structures.(AU)

Evaluation and retrofit of lightly reinforced concrete buildings

One of the major areas of research in the buildings project has been the evaluation of the perfomance and study of the rehabilitation of existing concrete buildings. Most of these structures were designed only for gravity loads, without any consideration of seismic forces. The seismic behavior of typical gravity load designed (GLD) buildings has been studied through a coordinated program of full-scale component tests, reduced-scale shake table model tests, and analytical simulation. Guidelines have been developed and a monograph has been drafted to asist engineers in evaluating gravity-load designed buildings. The rehabilitation study has concentrated on simple techniques especially suited to regions of moderate seismicity.(AU)

IDARC : Computer program for inelastic damage analysis of reinforced concrete structures

The need to evaluate structures which experience behavior as designed by current seismic codes motivated the development of a specialized computer program which models such behavior in an efficient way. The primary modeling technique employed in the computer program IDARC (Inelastic Damage Analysis of Reinforced Concrete Structures) is the representation of the overall behavior of components in terms of macromodels. Each component of the structural system is discretized into a series of macroelements: beam-column elements whose inelastic behavior is characterized by a primarily flexural response, shear-wall elements that may deform inelastically in flexure or shear, floor-slabs that are capable off deforming inelastically in the plane of the diaphragm, and inelastic rotational springs that may be attached at any node. Special-purpose elements, such as viscoelastic braces and other friction devices for hysteretic energy dissipation were also developed.(AU)

3D = tres d- Basis - Tabs : Version 2.0 computer program for nonlinear dynamic analysis of three dimensional base isolated structures

This report describes the development of computer program 3D-BASIS-TABS Version 2.0. The new program is an enhanced version of 3D-BASIS-TABS. The report should be viewed as a continuation and addition to previous reports NCEER-93-0011 and NCEER-91-0005. The enhancements that have been made include (i)addition of new isolation elements; (ii)models of nonlinear dampers and other hysteretic elements; (iii) additional verification; (iv) addition of several new example problems; (v) new input/output format for easier usage; (vi) updated user's manual.(AU)

3 D-BASIS-ME : Computer program for nonlinear dynamic analysis of seismically isolated single and multiple structures and liquid storage tanks

3D-BASIS-ME is a special purpose program for the nonlinear dynamic analysis of seismically isolated multiple buildings and liquid storage tanks. New features of this program, which do not exist in the currently available class of 3D-BASIS programs, are new elements for modeling hysteretic stiffening behavior, for modeling the behavior of spherical sliding isolation systems and for modeling linear and nonlinear viscous fluid dampers. Furthermore, the effects of vertical ground motion and overturning moment on the behavior of sliding bearings have been included.(AU)

3D = tres d - Basis - Tabs : Computer program for nonlinear dynamic analysis of three dimensional base isolated structures

This report describes the development and verification of the new computer program 3D-BASIS-TABS, an enhanced version of 3D-BASIS, which includes linear beam, column, shear wall and bracing elements to model the elastic three dimensional superstructure and inelastic/nonlinear elementss to model the isolation system. The superstructure member forces are computed in 3D-BASIS-TABS by back substitution, after the nonlinear time history analysis completed, and peak member forces are output to facilitate the design of members The verification of the program 3D-BASIS-TABS is presented in two case studies, i.e., three-story and eight-story buildings with various isolators. These case studies serve also as examples of use if this computer program. A comprehensive user's manual input/output files is presented.(AU)

Inelastic response of reinforced concrete structures with viscoelastic braces

The adition of viscoelastic braces in structures for vibration reduction was proposed and implemented in the past decade in metal models or full-scale structures. Viscoelastic braces provide energy dissipation, while the structures remains by-and-large elastic. In reinforced concrete structures, the seismic response in by-and-large inelastic, which is often accompanied by permanent deformations and damage. The addition of viscoelastic dampers can dissipate energy at the early stages of cracking of the concrete elemnts and reduce the development of damage. With proper selectio of dampers, this damage can be substantially reduced or even eliminated. However the addition of viscoelastic dampers may stiffen the structure unnecessarily producing increased inertial forces and base shears when subjected to seismic motion. The quantification of the influence of viscous and elastic stiffness properties of dampers during the inelastic response of reinforced concrete structures is the subject of this invetigation. Models for analysis of inelastic response with damege indexing for reinforced concrete structures that include viscoelastic braces are developed and calibrated using experimental data produced by shaking table tests. These models are then used to determine the variation of expected damage in the presence of damping and quantify the hysteretic energy dissipation along with the damping energy (AU)

Seismic retrofit of gravity load designed reinforced concrete buildings

The performance of Gravity Load Designed (GLD) building has been studied at severalinstitutions over the past five years, It has been fount that under earthquake loads, extensive damage occur in the frame joints and the flexibility of these structures are of primary concern. However, relatively inexpensive retrofit techniques for such structures might suffice for regions of low the moderate seismicity, Several local and integrated global techniques are suggested and studied (AU)

Hybrid isolations systems for sensitive equipment and secondary systems

The seismic response of sensitive equipment and secondary systems can be improved by isolating them with aseismic sliding bearings. Historicallysuch isolation system have been complemented by passive devices, to control relative displacement of the system during large magnitude seismic events and restrict a build - up of drift. Active servo - hydraulic actuators are suggested herein to supplement the conventional sliding bearings, creating a hibrid active - passive protective system. This control system is capable of minimizing the inertial forces in the equipment, while providing higher damping ratios and better displacement control when necessary. This paper presents to control algorithms for the proposed hibrid isolation system. These algorithms were verified experimentally. The results of the experimental tests show thatthe hybrid systms is capable of significantly improving the seismic response of sensitive equipment. Most notably, the hibrid system minimizes the energy transmitted to the secondary system, reducing the possibility of damage to sensitive equipment (AU)

Seismic resistance of reinforced concrete frame structures designed only for gravity loads : Part III - Experimental perfomance and analytical study of a structural model

A series of varying intensity simulated ground motion tests were perfomed on the one-third scale building model using scaled accelerograms on the shaking table to represent minor, moderate, and severe earthquakes. The dynamic characteristics of the model ofter each seismic event were identified from white noise shaling table tests. The results of this expiremental investigation are presented in this report.(AU)

Evaluation of seismic retrofit of reinforced concrete frame structures : Part II-experimental perfomance and analytical study of a retrofitted structural model

This report is Part II of a two part series on the evaluation of seismic retrofit methods for concrete frame structures. It deals with the behavior of the entire structural system when several retrofit techniques are applied to individual components. An analytical and an experimental study was done on a scaled model of a structure and several retrofit techniques were evaluiated. Pat I describes the evaluation of individual components retrofitted and tested with cyclic loading, that provided the base for modeling of the entire structure presented in this report.(AU)

Evaluation of seismic retrofit of reinforced concrete frame structures : Part I-Experimental performance of retrofitted subassemblages

This report is Part I of a two part series on the evaluation of seismic retrofit methods for reinforced concrete frame structures. It deals with the experimental behaviour of retrofitted reinforced concrete column elements and beam-column joint subassemblages under reversed cyclic lateral loading. A seismic retrifit/rehabilitation redesign methodology was developed, and validated in the present experimental study. Part II describes the application of this method to a one-third scale model building.(AU)

Seismic resistance of reinforced concrete frame structures designed only for gravity loads : Part I - design and properties of a one-third scale model structure

This report is part I of a three-part series prepared fpor a comprehensive Evaluation of typical gravity load designed low-rise reinforced concrete frame buildings (lightly reinforced concrete structures) for seismic adequacy. The study was done at State University of New York at Buffalo -Earthquake Simulation Laboratory on a 1:3 scale building model designed for gravity loads only. No considerations were made for seismic resistance and the general non-seismic detailing provisions of ACI-318-89 were used for the design. The one-third scale three story model, one-bay by three-bay, of a typical office building was constructed to represent the critical interior bay of a prototype structure.(AU)

Seismic resistance of reinforced concrete frame structures designed only for gravity loads : Part II - Experimental perfomance of subassemblages

This report is Part II of a three part series on the evaluation of seismic resistance of reinforced concrete frame structures designed only for gravity loads. It is concerned with the experimental behavior of gravity load designed reinforced concrete columns and subassemblages under reversed cyclic lateral load. This report presents the study of four column specimens (with ans without lap splice), and two beam-column (exterior and interior) subassemblages of a one-third scale model of a prototype designed for gravity loads according to ACI 318 non-seismic detailing were subjected to axial load and cyclic lateral displacements.(AU)

IDARC version 3.0 : A program for the inelastic damage analysis of reinforced concrete structures

This report summarizes the significant modeling and program enhancements to the computer coe, IDARC (see Technical Report NCEER-87-0008) for inelastic damage analysis of reinforced concrete frame-wall structures. The base program is capable of analyzing structures in the inelastic range subjected to combined horizontal and vertical excitations, quasi-static cyclic loading, and incrementally applied static loads.(AU)