Showing papers on "Earthquake resistant structures published in 1996"

Seismic Isolation Retrofit of Large Historic Building

Abstract: Seismic isolation in the United States is gaining wide acceptance as an attractive and alternate means to upgrade historic structures seismically with minimal disturbance to architecturally significant features. One important historic-landmark structure that underwent such an upgrade is the Ninth Circuit U.S. Court of Appeals building located in San Francisco, which suffered damage during the 1989 Loma Prieta earthquake and was declared an unsafe building for further occupancy. The present paper summarizes the comprehensive approach adopted for implementation of the seismic-isolation technique for the seismic retrofit of this monumental structure. This historically significant structure is the first federal building to be retrofitted using seismic isolation. The paper discusses in detail the procedure adopted for evaluating the existing building strength, establishing the design approach, and evaluating and selecting the optimum isolator placement location and isolation system best suited for the building...

Horizontal connections for precast concrete shear wall panels under cyclic shear loading

Abstract: The performance of precast concrete loadbearing shear wall panel structures during an earthquake relies on the behavior and integrity of the connections between the panels. Design of these structures requires the ability to predict the behavior of the connections. This paper presents results of an experimental study of horizontal connections for precast wall panels subjected to reversed cyclic shear deformations combined with simulated gravity loads normal to the connection. The influence of mild steel reinforcement, post tensioning and shear keys was investigated. Experimental results were used to determine the cyclic behavior of the connections and to identify the contribution of the connections and to identify the contribution of the connection components. Simple rational models were proposed to predict the limit states of the connections. Two numerical design examples are included to illustrate the proposed models. Based on the study, design recommendations are presented.

Highway culvert performance during past earthquakes

Abstract: To assess performance of culverts during earthquakes, the authors reviewed reports from six earthquakes, interviewed highway officials in areas shaken by four earthquakes and conducted field investigations in epicentral regions of three earthquakes. Seventeen corrugated metal pipe (CMP), one thermoplastic pipe, five reinforced concrete pipe (RCP), and thirty reinforced concrete box (RCB) structures were specifically evaluated through field inspection of literature review. Five of these culverts (all CMP) were deformed into a dysfunctional condition; nine (three CMP, five RCP and one RCB) required major repairs or replacement; six RCB structures required minor repairs (epoxy of cracks). Primary causes of culvert damage were liquefaction-induced embankment penetration or spreading, slope instability, and fault rupture.

Seismic behavior of connections in precast concrete walls

Abstract: An experimental program is summarized which is aimed at enhancing the knowledge base regarding seismic behavior, analysis and design of precast concrete shear walls. The "emulation design" and "jointed construction" philosophies are described, and an idealization of the behavior of precast shear walls is presented. A compendium of connection details for precast concrete shear walls, seven for vertical joints and four for horizontal joints, is selected for further study and the selection process is described. The connection details are proportioned for a prototype shear wall that is designed as part of a six-story precast concrete office building. A description of all connection details and test procedure is given. Highlights from the cyclic load tests of the vertical joint specimens are documented, including connection resistance, displacement response, initial stiffness and energy dissipation capacity.

Ductile Connections for Precast Concrete Frame Systems

Abstract: This paper describes a research program to investigate the behavior of ductile connections between precast beam-column elements. Eight beam-column connections were tested to characterize the overall behavior of the connection details. Each connection specimen was designed to incorporate one of three behavioral concepts in the connection elements: tension/compression yielding, substantial energy dissipation, or nonlinear-elastic response. Based on the behavioral information collected during connection tests, analytical models were developed to investigate the behavior of complete precast frame systems. Results of the experimental study and preliminary results of the analytical work are presented. The objective of the program is to provide rational design recommendations for engineers to detail precast frame connections for use in regions of seismic risk.

Displacement-based assessment of reinforced concrete frames in earthquakes

Abstract: In this paper, a displacement-based approach to evaluating detailing requirements for frame elements is presented. Expressions are derived for the participation of beams, columns, joints and anchorages in overall story drift. Simple element models are presented for beam-column joints and anchorages, and guidelines for conventional sectional analysis of beams and columns are given. With an assessment of the local demand in each element type and mechanical models of element behavior, it is demonstrated that member variables normally considered as part of detailing can be accounted for in a quantitative supply-versus-demand fashion. A case study is made for an example in the ACI Committee 352. Recommendations to illustrate how a displacement-based frame evaluation is carried out and to provide a reference point for comparison with an existing design approach for beam-column joints.

Seismic design considerations for flat-plate construction

Abstract: Design algorithms expressed in current building codes and practiced in design offices focus attention on earthquake induced lateral forces, and away from earthquake induced lateral displacements. These procedures have led to development of structural systems in which a portion of the structural frame is designed to resist the total seismic design force while a substantial remainder of the structure is proportioned assuming it resists only gravity loads. This approach is commonly applied to design of slab-column systems in regions of high seismicity. For such systems, a displacement-oriented approach has advantages. Applications of the approach are described.

Simplified Response-Spectrum Seismic Analysis of Nonlinear Structures

Abstract: A method is presented for a simplified seismic analysis of nonlinear multidegree-of-freedom structures. The method represents an improvement over an earlier attempt to extend the use of the conventional response-spectrum method to nonlinear structures, and is also based on the use of a modal superposition in combination with nonlinear response spectra. It involves the computation of their natural frequencies and mode shapes on the basis of their initial elastic properties, the calculation of a yield deformation for each of their modes using formulas proposed here, and readings from a nonlinear response spectrum. The procedure is formulated for plane rigid frames, but limited to elastoplastic force-deformation behavior. Its application is illustrated by means of numerical examples with a three-story shear building and a six-story plane frame. In a comparison with solutions obtained with a step-by-step integration method, the proposed approximate method predicts the maximum displacements of these two structures with an average error of about 5%.

Seismic movement at bridge abutments

Abstract: For the Orange County Toll Roads in California seismic design criteria for bridges has been used which includes a requirement that expansion joints be designed for seismic movement. This departure from traditional practice is part of a design objective to avoid damage of any kind during moderate earthquakes. Practical limitations in expansion joint technology and conflicts with other design objectives have been encountered. Bridge expansion joint products currently available from industry are not designed for seismic movements. Large joints are complex and expensive to maintain. Bridge abutment participation is an important consideration in the overall structural system for resisting the effects of extreme seismic events, thus large joint openings can be counterproductive to the seismic system. Bridge bearings have been developed which make a positive contribution to seismic performance but expansion joints are more of a negative factor in seismic design.

Review of Current and Proposed Seismic Design Provisions

Abstract: Synopsis: This paper summarizes the findings of a research project performed by the American Iron and Steel Institute entitled "Technical Review of Current and Proposed Seismic Design Provisions." In the last several years, both New York City and the Building Officials and Code Administrators International (BOCA) have proposed and drafted seismic provisions for their respective building codes. The purpose of this study was to compare the pertinent provisions of these proposed provisions to each other and to existing building codes (UBC, SEAOC, NEHRP, and ASCE 7). In addition, the American Institute of Steel Construction has adapted seismic provisions in their Load and Resistance Factor Design Specifications. BOCA has proposed a method of adapting these LRFD Seismic provisions into its building code. This study also reviewed these proposed revisions with respect to applicability to East Coast earthquakes, especially in New York City. The impact of both the NYC and BOCA provisions on design and construction costs are also addressed.

Structural Parameter Analysis of U.S. Army Corps of Engineers Existing Intake Tower Inventory.

Abstract: : Existing Corps intake towers were designed using the seismic coefficient method which incorrectly estimates demands placed on an intake tower during a major earthquake. Lightly reinforced concrete structures, such as Corps' intake towers, may have sufficient inherent ductility to respond without failure. However, the success of the tower in resisting failure is dependent upon the magnitude of the earthquake loads and the structural details controlling the nonlinear dynamic response and failure mechanisms of the specific tower. Currently available analysis tools and engineering guidance for intake towers do not properly include these factors. The development and validation of better tools and guidance is the primary goal of Research Program 387- Earthquake Engineering - Structures, Work Unit 32911, Nonlinear Dynamic Response and Failure Mechanisms of Intake Towers. The research discussed in this report is an initial step in a planned 7-year effort to accomplish this goal. Specifically, the objective of this initial research was to quantify the distribution and variation of the structural characteristics of the Corps' inventory of existing intake towers, considering their earthquake location hazard. This was accomplished by the examination of the structural as-built drawings for 77 towers located in seismic zones 2 and above, the generation of a database containing 36 parameters for each of the towers, and a statistical analysis to summarize the distribution of these parameters. (MM)

On design requirements for reinforced concrete structural walls

Abstract: Following the strong earthquake in Chile on March 3, 1985, an intensive study was conducted to ascertain why the large inventory of moderate rise buildings in the coastal city of Vina del Mar performed so well during the earthquake. The major findings were that the vast majority of the buildings in this coastal city had a high wall area to total floor area ratio and that the reinforcement detailing in the boundaries of these walls were considerably less than required by U.S. codes. Analytical studies indicated that the high percentage of walls led to significantly lower drifts under severe seismic shaking, thus lowering the ductility demands on the walls. The findings of research following the Chilean earthquake have led to modified U.S. design procedures that relate the need for special detailing in wall boundary elements to expected strain levels along the compression edge of the wall.