ALBERT

Beschreibung: A postulated prediction of displacements in ductile reinforced concrete building systems is based on a redefinition of basic structural properties. Contrary to the ability of traditional techniques, the proposed approach permits displacement limits, relevant to ductile mixed systems, i.e., those with markedly differing components, to be established before details, such as strengths, are addressed. This should lead to significant benefits at the stage of preliminary design. Acceptable displacement limits, associated with currently introduced direct displacement-based seismic design strategies, can be readily and simply established. Similarly, limits of displacement ductility demands on components and the system, associated with current force-based approaches, can be estimated already as part of the preliminary design.

Beschreibung: This paper presents the dynamic analyses and seismic performance of a base-isolated demonstration building (BIDB). This building was designed and built in Indonesia in accordance with the Indonesian Seismic Code (ISC) and the Uniform Building Code (UBC) provisions for isolated buildings. The building is a four-story reinforced concrete frame with masonry infill walls supported on 16 high damping natural rubber (HDNR) isolators attached to the superstructure using recessed connections. The building superstructure was modeled using both three-dimensional (3-D) and two-dimensional (2-D) frame models. The isolators were modeled as a combination of linear springs and viscous dampers, whose properties were determined from testing. Time-history (TH) and response-spectra (RS) analyses performed on this building demonstrated that this newly developed isolation system, designed specially for low axial pressure applications, was effective in protecting the building superstructure from earthquake forces for all seismic risk levels being considered. The total isolator displacement obtained using the TH and RS approaches is also compared and discussed.

Beschreibung: The effect of damping on the response of elastic and inelastic single-degree-of-freedom systems was studied by nonlinear response-history analysis using earthquake histories that matched on average a 2000 NEHRP spectrum on a stiff soil site for a region of high seismic risk. New displacement reduction factors for levels of damping greater than 5% of critical are presented. New equations to relate inelastic and elastic displacements in the short-period range, for levels of damping greater than 5% of critical, are presented. The technical basis for reducing the minimum design base shear in damped buildings by a maximum of 25%, from that required for the corresponding undamped building, is derived based on comparable levels of damage in both the damped and undamped buildings.

Beschreibung: A freestanding rigid body under the action of base excitation can move in many different ways. In this study, the sliding response of a body is considered. The body is placed on a horizontal base that undergoes a one-dimensional horizontal motion. In 1965, Newmark (1965) gave a simple formula to determine the sliding distance of a freestanding body subjected to a single rectangular acceleration pulse of short duration at the base. The objective of this study is to see if this formula can be applied to estimate the sliding displacement of a body under the action of real earthquakes. Newmark's formula calls for the maximum velocity of the base which information is usually not directly available. To make use of the response spectrum commonly available to the engineers, Newmark's formula is first re-derived and expressed in terms of the maximum displacement of the base, which can be determined from the absolute displacement response spectrum in low frequency range. An ensemble of 75 real earthquakes is then employed, the equation of sliding motion is solved numerically and the average of the maximum sliding displacement of the body relative to the base is computed. The computed displacement is then compared with that obtained by Newmark's formula. This is done for a body placed on the ground as well as on the floors of a building. It is shown that Newmark's formula can be used if an adjustment factor, as suggested in this study, is applied. Key words: earthquake, sliding, unanchored body

Beschreibung: A base-isolated demonstration building (BIDB) was built in Indonesia as part of an ongoing effort by the United Nations Industrial Development Organization to promote the use of base isolation technology for common structures in earthquake-prone developing countries. The superstructure of the demonstration building is a four-story reinforced concrete frame with masonry infill walls, designed in accordance with the Indonesian Seismic Code. A specially developed isolation system for this project consisted of 16 high-damping natural rubber bearings, which were connected to the columns and foundation using recessed-type connections at the ground level. The seismic isolation provisions from the 1994 Uniform Building Code were adapted to complement the Indonesian Seismic Code requirements for this project, and site-specific spectra were developed and used for the design of the isolation system. This paper discusses the design considerations for the base-isolated demonstration building, the design and testing of the bearings and the cost-effectiveness of the isolation system. The seismic performance of the base-isolated building is discussed in the companion paper. It is expected that this newly developed isolation system, designed specifically for low-axial pressure applications, can be adopted for the earthquake protection of a variety of smaller public buildings—such as housing, schools, and hospitals—in developing countries.

Beschreibung: This paper concentrates on the rocking response of rigid equipment anchored on a foundation base with plan dimensions that are larger than the footprint of the equipment. With this configuration there are two distinct capacities to resist uplift and eventual overturning: (a) the equipment engages the base foundation into rocking motion, and (b) the restrainers fracture and the equipment subsequently rocks atop its foundation base. This study examines both moderate uplift (serviceability level) and overturning (ultimate state—failure). It is first shown that for specific equipment/base configurations, the high strength restrainers used in practice are sufficient to engage the foundation base into rocking motion for a wide range of recorded earthquake motions. Subsequently, the study uncovers that for earthquakes with long distinguishable pulses, the margin between exceeding the serviceability level of uplift and achieving overturning is minimal. None of the strong motions used in this study is capable of overturning the freestanding configurations examined. It is found that small values of the foundation protrusion from the footprint of the equipment reduces the uplift appreciably.

Beschreibung: This paper proposes a methodology by which probabilistic risk analysis methods can be extended to the assessment of urban lifeline systems. Probabilistic hazard information is commonly used for site-specific analysis. However, for such systems as highway networks, electric power grids, and regional health care delivery systems, the spatial correlation between earthquake ground motion across many sites is important in determining system functionality. The methodology developed in this paper first identifies a limited set of deterministic earthquake scenarios and evaluates infrastructure system-wide performance in each. It then assigns hazard-consistent probabilities to the scenarios in order to approximate the regional seismicity. The resulting probabilistic scenarios indicate the likelihood of exceeding various levels of system performance degradation. A demonstration for the Los Angeles study area highway network suggests that there is roughly a 50% probability of exceedance of Northridge-level disruption in 50 years. This methodology provides a means for selecting representative earthquake scenarios for response or mitigation planning.

Beschreibung: Efforts at improving earthquake recovery policies have been hampered by a lack of criteria and standards for evaluating and repairing damaged buildings. The Applied Technology Council has developed a performance-based methodology for the evaluation of earthquake-damaged concrete wall buildings and masonry wall buildings, recently published as FEMA 306/307/308. The methodology provides a way to quantify damage in terms of loss of seismic performance capability. It also provides guidelines for remedial measures to restore or improve seismic performance capability. In this methodology, the expected future seismic performance of a building is evaluated in its pre-event, damaged, and repaired conditions. Following the nonlinear static analysis procedure, displacement demands and capacities of the structure are used as indices of seismic performance. Identifying the governing mechanism of nonlinear deformation and the behavior mode of a structure and its components is shown to be a necessary first step towards evaluating expected seismic performance, interpreting indications of damage, and assessing their significance. The methodology provides a technical resource for understanding how buildings respond seismically on both global and component levels, and gives a basis for formulating post-earthquake policies.

Beschreibung: Site-response coefficients, Fa and Fv, used in U.S. building code provisions are based on empirical data for motions up to 0.1 g. For larger motions they are based on theoretical and laboratory results. The Northridge earthquake of 17 January 1994 provided a significant new set of empirical data up to 0.5 g. These data together with recent site characterizations based on shear-wave velocity measurements provide empirical estimates of the site coefficients at base accelerations up to 0.5 g for Site Classes C and D. These empirical estimates of Fa and Fv as well as their decrease with increasing base acceleration level are consistent at the 95 percent confidence level with those in present building code provisions, with the exception of estimates for Fa at levels of 0.1 and 0.2 g, which are less than the lower confidence bound by amounts up to 13 percent. The site-coefficient estimates are consistent at the 95 percent confidence level with those of several other investigators for base accelerations greater than 0.3 g. These consistencies and present code procedures indicate that changes in the site coefficients are not warranted. Empirical results for base accelerations greater than 0.2 g confirm the need for both a short- and a mid- or long-period site coefficient to characterize site response for purposes of estimating site-specific design spectra.

Beschreibung: The behavior of reinforced concrete walls that exhibit the shear mode of failure is studied, through the results of an experimental program that included the test of 26 full-scale specimens subjected to cyclic horizontal displacements of increasing amplitude. Test parameters were the aspect ratio of the walls, the amount of vertical and horizontal distributed reinforcement, and the compressive strength of concrete. The results include the cracking shear strength, the maximum shear strength, the drifts associated to these loads and the drift associated to a collapse limit state for each of the specimens tested. Conclusions are drawn concerning the deformation capacity, the energy absorption, the dissipation characteristics and the strength deterioration after maximum strength shown by the walls and the influence of vertical distributed reinforcement on the seismic behavior of walls.

Beschreibung: Recent code provisions for buildings and other structures (1994 and 1997 NEHRP Provisions, 1997 UBC) have adopted new site amplification factors and a new procedure for site classification. Two amplitude-dependent site amplification factors are specified: Fa for short periods and Fv for longer periods. Previous codes included only a long period factor S and did not provide for a short period amplification factor. The new site classification system is based on definitions of five site classes in terms of a representative average shear wave velocity to a depth of 30 m (V¯s). This definition permits sites to be classified unambiguously. When the shear wave velocity is not available, other soil properties such as standard penetration resistance or undrained shear strength can be used. The new site classes denoted by letters A - E, replace site classes in previous codes denoted by S1 - S4. Site classes A and B correspond to hard rock and rock, Site Class C corresponds to soft rock and very stiff / very dense soil, and Site Classes D and E correspond to stiff soil and soft soil. A sixth site class, F, is defined for soils requiring site-specific evaluations. Both Fa and Fv are functions of the site class, and also of the level of seismic hazard on rock, defined by parameters such as Aa and Av ( 1994 NEHRP Provisions), Ss and Sl ( 1997 NEHRP Provisions) or Z ( 1997 UBC). The values of Fa and Fv decrease as the seismic hazard on rock increases due to soil nonlinearity. The greatest impact of the new factors Fa and Fv as compared with the old S factors occurs in areas of low-to-medium seismic hazard. This paper summarizes the new site provisions, explains the basis for them, and discusses ongoing studies of site amplification in recent earthquakes that may influence future code developments.

Beschreibung: A modified version of seismic hazard assessment, directed toward planning of emergency relief efforts, is proposed. The method begins with a probabilistic hazard assessment to determine a reference peak ground acceleration (PGA) at a near site, rather than using a reference earthquake of a given magnitude. The reference PGA then serves as a basis for a probabilistic assessment of PGA at more distant sites. The ideas are illustrated by studying seismic hazard for Northern Israel from earthquakes on the northern section of the Dead Sea Rift (DSR). The reference PGA at a site 10 km from the DSR is taken to be 0.3 g, which has a return period estimated to be 320 years. Given an event with PGA of 0.3 g at 10 km, the subsequent analysis for distant sites shows that there is less than a 31% probability of PGA above 0.1 g at 30 km and an 8% probability that the PGA at 50 km will exceed 0.1 g.

Beschreibung: This paper examines the question of which sources of uncertainty most strongly affect the repair cost of a building in a future earthquake. Uncertainties examined here include spectral acceleration, ground-motion details, mass, damping, structural force-deformation behavior, building-component fragility, contractor costs, and the contractor's overhead and profit. We measure the variation (or swing) of the repair cost when each basic input variable except one is taken at its median value, and the remaining variable is taken at its 10th and at its 90th percentile. We perform this study using a 1960s highrise nonductile reinforced-concrete moment-frame building. Repair costs are estimated using the assembly-based vulnerability (ABV) method. We find that the top three contributors to uncertainty are assembly capacity (the structural response at which a component exceeds some damage state), shaking intensity (measured here in terms of damped elastic spectral acceleration, Sa), and details of the ground motion with a given Sa.

Beschreibung: The paper presents the methodology and findings from large-scale experiments conducted on reinforced concrete bridge subassemblies. Each subassembly consisted of the middle column/cap-beam joint of a three-column bridge bent and a large part of the monolithically cast-in-place box-girder of a typical California highway bridge. The subassemblies were subjected to constant gravity load and gradually increasing bidirectional cyclic lateral loading. One subassembly represented common practice in California and the other considered new design using headed reinforcing bars with reduced volume of transverse reinforcement to improve joint construction. When loading in the transverse direction, i.e., parallel to the cap-beam, the use of headed bars led to better global and local performances due to improved confinement of the joint region with less volume of reinforcement. On the other hand, when loading in the longitudinal direction, i.e., parallel to the box-girder, the headed bars were more engaged, as evident by their yielding, in confining the joint region than the conventional reinforcement. The effect of bidirectional loading on global damage of the box-girder slabs is presented as variation of the effective moment of inertia of the cap-beam cross section with displacement ductility indicating that Caltrans estimates are conservative up to displacement ductility of five. Key words: bidirectional cyclic loading, box-girders, bridge joints, headed reinforcement, reinforced concrete

Beschreibung: Caltrans' Seismic Design Criteria (SDC) has been adopted as the minimum seismic standard for ordinary bridges on California's highways. The SDC is a compilation of new and existing seismic criteria that had been previously documented in a variety of Caltrans documents. The SDC extends the capacity design philosophy introduced in the 1980 Caltrans Bridge Design Specifications. The most significant departure from the previous procedure is that ductile members are now designed by comparing the displacement demand to the displacement capacity. The demands are generated by a linear elastic analysis, and the capacities are determined from a curvature analysis that incorporates the nonlinear behavior of the structural elements. The demand/capacity methodology supplants the previous method based on reducing the elastic dynamic forces by a force reduction factor. In this paper, the significant features of Caltrans' SDC are described.

Beschreibung: Strong motion data from sites having both an instrumented structure and free-field accelerograph are compiled to evaluate the conditions for which foundation recordings provide a reasonably unbiased estimate of free-field motion with minimal uncertainty. Variations between foundation and free-field spectral acceleration are found to correlate well with dimensionless parameters that strongly influence kinematic and inertial soil-structure interaction phenomena such as embedement ratio, dimensionless frequency (i.e., product of radial frequency and foundation radius normalized by soil shear wave velocity), and ratio of structure-to-soil stiffness. Low frequency components of spectral acceleration recorded on shallowly embedded foundations are found to provide good estimates of free-field motion. In contrast, foundation-level peak ground acceleration (both horizontal and vertical) and maximum horizontal velocity, are found to be de-amplified. Implications for ground motion selection procedures employed in attenuation relations are discussed, and specific recommendations are made as to how these procedures could be improved.

Beschreibung: The building code development process has traditionally given little effort to developing the seismic design process of nonbuilding structures. This has created some unique problems and challenges for the structural engineers that design these types of structures. The intended seismic performance requirements for “building” design are based on life safety and collapse prevention. Structural elements in buildings are allowed to yield as a method of seismic energy dissipation. The seismic performance of nonbuilding structures varies depending on the specific type of nonbuilding structure. Nonlinear behavior in some nonbuilding structures is unacceptable while other nonbuilding structures may be allowed to yield during an earthquake. Nonbuilding structures comprise a vast myriad of structures constructed of all types of materials, with markedly different dynamic characteristics, and with a wide range of performance requirements. This paper discusses the development of codes, design practices, and future of the seismic design criteria for nonbuilding structures.

Beschreibung: This paper follows the evolution of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures from the development of ATC 3-06 to the 1997 edition of the document. The features of the 1997 NEHRP Provisions are described in detail. Complementary information about the NEHRP Provisions is found in several other papers in this volume of Earthquake Spectra. Subject areas covered elsewhere are specifically referenced in this paper.

Beschreibung: This paper evaluates the performance of a seven-story reinforced concrete frame building that was severely damaged during the 1994 Northridge, California, earthquake. The building was designed and constructed in the 1960s and contains details that are typical of that construction era in the western United States. The building sustained severe damage that included column shear failures. The building was analyzed independently by three research teams using analysis methodólogies that were similar in concept but different in details. An objective of each analysis was to correlate observed and calculated performance. The different analyses were successful to varying degrees. The results provide a test case of the effectiveness of various seismic performance assessment methodologies.

Beschreibung: Computer simulations are employed to assess the effects of near-source ground motions on base-isolated buildings that meet the provisions of the 1997 Uniform Building Code. A six-story base-isolated building designed for Nv = 1.6 exhibits essentially elastic structural behavior when subjected to six actual ground motions containing strong near-source effects. However, two simulated records, one intended to represent the most severe motions from the 1994 Northridge earthquake and the other a strong motion from a hypothetical Mw7.0 thrust earthquake produce larger responses well into the nonlinear range. In addition, a 113 cm ground displacement pulse of three-second duration, which is close to the period of the isolated buildings, causes story drifts of nearly 5% for the Nv = 1.6 design and over 2% for a stronger Nv = 2 design. Such drifts are effectively reduced when supplemental dampers are added alongside the isolators. The original Nv = 1.6 design with supplemental damping in the amount of 20% of critical experiences only 1.3% drift for the same three-second ground displacement pulse.

Beschreibung: The estimation of inelastic seismic demands using nonlinear static procedures, or pushover analyses, are inevitably going to be favored by practicing engineers over nonlinear time-history methods. While there has been some concern over the reliability of static procedures to predict inelastic seismic demands, improved procedures overcoming these drawbacks are still forthcoming. In this paper, the potential limitations of static procedures, such as those recommended in FEMA 273, are highlighted through an evaluation of the response of instrumented buildings that experienced strong ground shaking in the 1994 Northridge earthquake. A new enhanced adaptive “modal” site-specific spectra-based pushover analysis is proposed, which accounts for the effect of higher modes and overcomes the shortcomings of the FEMA procedure. Features of the proposed procedure include its similarity to traditional response spectrum-based analysis and the explicit consideration of ground motion characteristics during the analysis. It is demonstrated that the proposed procedure is able to reasonably capture important response attributes, such as interstory drift and failure mechanisms, even for structures with discontinuities in strength and/or stiffness that only a detailed nonlinear dynamic analysis could predict.

Beschreibung: U.S. seismic codes are undergoing profound changes as of this writing. Changes from the 1994 to the 1997 edition of the Uniform Building Code (UBC) (ICBO 1994, 1997) are many and far-reaching in their impact. The 1997 edition of the National Earthquake Hazards Reduction Program (NEHRP) Recommended Provisions for Seismic Regulations for New Buildings (BSSC 1998) contains further evolutionary changes in seismic design requirements beyond those of the 1997 UBC. The latter document will form the basis of the seismic design provisions of the first edition of the International Building Code (IBC), to be published in the spring of 2000. This paper first discusses the major changes that have been made in the concrete-related provisions from the 1994 to the 1997 edition of the UBC. The paper gives background to these changes, provides essential details on them, and indicates how they have been or how they are going to be incorporated (at times with significant modifications) into the 1997 NEHRP Provisions and the 2000 IBC. The newly published ACI 318-99, Building Code Requirements for Structural Concrete (ACI 1999), is going to be adopted by reference into the 2000 IBC. This entails further changes in concrete-related provisions beyond the 1997 UBC. Some of the more important of these changes are discussed here. A small number of amendments and additions to the ACI 318-99 provisions are going to be included in the 2000 IBC. The more important of these are also outlined in this paper.

Beschreibung: With the publication of the 1997 Uniform Building Code ( UBC) and the 1997 NEHRP Recommended Provisions for the Seismic Regulations for New Buildings and Other Structures, there has been a significant change in the earthquake design force provisions for buildings, structures, elements of structures and nonstructural components. Engineers and architects need to become informed regarding a variety of earthquake design force provisions, primarily those published in the UBC and those developed as part of the NEHRP Provisions. Both sources provide design force provisions for the building structural system and separate design force provisions for elements of structures and nonstructural components. This paper describes the development, evolution, and application of the earthquake design force provisions for elements of structures and nonstructural components.

Beschreibung: A new spectral representation of seismic demand is described for use in the seismic design of new structures and in the evaluation and rehabilitation of existing structures. Yield Point Spectra (YPS) retain the intuitive appeal of the Capacity Spectrum Method (Freeman 1978) and join the Nonlinear Static Procedures of FEMA 273/274 (1997) and ATC 40 (1996) for use in estimating displacement demands. YPS also may be used to establish admissible combinations of strength and stiffness for the design of new structures to limit system ductility and drift to arbitrary values. Graphical procedures allow admissible design regions to be established to satisfy multiple performance objectives. YPS computed for 15 ground motions classified as Short Duration, Long Duration, or as containing near-fault Forward Directivity pulses are presented for bilinear and stiffness-degrading hysteretic models.

Beschreibung: The U.S. Geological Survey (USGS) recently completed new probabilistic seismic hazard maps for the United States, including Alaska and Hawaii. These hazard maps form the basis of the probabilistic component of the design maps used in the 1997 edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, prepared by the Building Seismic Safety Council and published by FEMA. The hazard maps depict peak horizontal ground acceleration and spectral response at 0.2, 0.3, and 1.0 sec periods, with 10%, 5%, and 2% probabilities of exceedance in 50 years, corresponding to return times of about 500, 1000, and 2500 years, respectively. In this paper we outline the methodology used to construct the hazard maps. There are three basic components to the maps. First, we use spatially smoothed historic seismicity as one portion of the hazard calculation. In this model, we apply the general observation that moderate and large earthquakes tend to occur near areas of previous small or moderate events, with some notable exceptions. Second, we consider large background source zones based on broad geologic criteria to quantify hazard in areas with little or no historic seismicity, but with the potential for generating large events. Third, we include the hazard from specific fault sources. We use about 450 faults in the western United States (WUS) and derive recurrence times from either geologic slip rates or the dating of pre-historic earthquakes from trenching of faults or other paleoseismic methods. Recurrence estimates for large earthquakes in New Madrid and Charleston, South Carolina, were taken from recent paleoliquefaction studies. We used logic trees to incorporate different seismicity models, fault recurrence models, Cascadia great earthquake scenarios, and ground-motion attenuation relations. We present disaggregation plots showing the contribution to hazard at four cities from potential earthquakes with various magnitudes and distances.

Beschreibung: Currently the most widely accepted code regulations in the United States for seismic design of structures and nonstructural components are those found in the Uniform Building Code ( UBC). The UBC seismic requirements were significantly revised in the 1997 edition. Among the issues addressed in the UBC revisions are near-source effects and ground acceleration dependent soil site amplification factors for both short- and long-period structures. Also, the design force levels in the 1997 UBC are based on strength design rather than allowable stress design, as had been used previously. Other significant changes include introduction of a redundancy/reliability factor, a more realistic consideration of story drift and deformation compatibility, and new equations for equivalent static forces for both structural and nonstructural components. This paper traces the recent history of the code development and describes the major elements of the 1997 UBC seismic provisions.

Beschreibung: On January 25, 1999, an earthquake of magnitude ML = 6.1 occurred in central Colombia, which caused 1,200 deaths, 5,000 injuries, more than 250,000 people affected and economic losses estimated at US$1.2 billion. The earthquake left some important lessons that must be taken into account for the management of similar situations in the future. With respect to the behavior of buildings, the soundness and importance of the code of practice for buildings was demonstrated as a tool for the prevention of seismic disasters. The management of the emergency in cities such as Pereira and Armenia showed the need for planning, continued preparedness and mitigation awareness. The importance of the Colombian Prevention and Disaster Attention System (SNPAD) was demonstrated although the need to enhance organizational aspects, citizen awareness and participation was made evident. The characteristics of the disaster reflect a typical situation that can occur in many Latin American cities located in areas of high seismic risk. This article presents the main lessons learned from this event in the light of work performed by the research team for natural disasters from the Department of Civil and Environmental Engineering of the Universidad de Los Andes.

Beschreibung: This paper presents a revised method for estimating the seismic intensity (MMI or MSK scale) using Fourier amplitude spectra (FAS) of ground acceleration. The improvement of the recently proposed technique (Sokolov and Chernov 1998) has been made on the basis of the data, which were obtained recently during strong earthquakes that occurred throughout the world. The total amount of the used data (horizontal components of ground-motion recordings) is about 1,150 records, while the database of 300 recordings was used in the previous study. The method implies that the seismic intensity is determined by the level of ground motion spectral amplitudes in the frequency range of 0.4–13 Hz. The corresponding empirical relationships between FAS and each intensity level were developed. The method is validated by comparison of the results of the technique application with the empirical data, which have not been included in the database. The Romanian earthquakes (intermediate-depth events of 1977, 1986, and 1990) and the recent 1999 Hector Mine earthquake in southern California were used for this purpose. In general, the FAS intensity shows a good agreement with the reported intensity, and the average residuals do not exceed ±0.3 intensity units and standard deviation is about 0.4-0.6. Evaluation of seismic intensity distribution using region- and site-dependent spectral models, as well as calculation of instrumental intensity map for the recent 1999 Chi-Chi earthquake, Taiwan, show that the FAS intensity clearly reflects the regional (source scaling and attenuation relation) and local (soil response) peculiarities of ground motion.

Beschreibung: The circular, reinforced concrete (R/C) shaft-type support for elevated tanks lacks redundancy, damping and additional strength typically present in building framing systems and, therefore, should be designed for larger seismic resistance. However, the Indian seismic code IS:1893-1984 prescribes the same basic seismic force as that for the most ductile building framing system for which the design force is the least. Furthermore, the code-specified one-mass idealization of elevated water tanks is not appropriate for large (large width to depth ratio) and partially filled tanks. The low design forces lead to a weak and slender support—a very unfavorable feature in high seismic areas, as evidenced in the failure of two water tanks in the 1997 Jabalpur earthquake and a great many in the 2001 Bhuj earthquake. It is rather difficult to enhance the ductility and energy dissipation capacity of thin-walled, R/C shaft supports. Concrete jacketing is used as a retrofit measure to enhance the lateral strength and ductility by changing the failure mode of concrete crushing to a more ductile tension yielding. This scheme requires substantial strengthening of the existing foundation.

Beschreibung: The last two earthquakes in Marmara have been catastrophic disasters beyond all limits of perception. On 17 August 1999, there were 1 million people trapped under debris, eighteen thousand people had lost their lives, and hundreds of thousands had been evacuated from their homes. Roads had buckled and bridges had fallen down. On 12 November 1999 another earthquake hit Düzce. This earthquake also caused high casualties. There were 894 deaths and 4,948 injuries. Both of the disasters had social, technical, administrative, legal, economical as well as environmental consequences. This paper presents a brief overview of these earthquakes in terms of the six aspects mentioned above. Disaster management practices are also investigated. The authors are of the opinion that it is not only the buildings but also poor disaster management before, during, and after the disaster that kill people in severe earthquakes. The present disaster management system of Turkey is compared against professional standards of the United States and Japan. The authors systematically document where performance failed and offer proposals for change within the Turkish disaster management system.

Beschreibung: The 1997 NEHRP Recommended Provisions for Seismic Regulations for New Buildings use a design procedure that is based on spectral response acceleration rather than the traditional peak ground acceleration, peak ground velocity, or zone factors. The spectral response accelerations are obtained from maps prepared following the recommendations of the Building Seismic Safety Council's (BSSC) Seismic Design Procedures Group (SDPG). The SDPG-recommended maps, the Maximum Considered Earthquake (MCE) Ground Motion Maps, are based on the U.S. Geological Survey (USGS) probabilistic hazard maps with additional modifications incorporating deterministic ground motions in selected areas and the application of engineering judgement. The MCE ground motion maps included with the 1997 NEHRP Provisions also serve as the basis for the ground motion maps used in the seismic design portions of the 2000 International Building Code and the 2000 International Residential Code. Additionally the design maps prepared for the 1997 NEHRP Provisions, combined with selected USGS probabilistic maps, are used with the 1997 NEHRP Guidelines for the Seismic Rehabilitation of Buildings.

Beschreibung: The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. Synthetic seismograms are validated with the 1980 Irpinia earthquake, a good example of strong shaking for Naples, recorded 10km from the modeled sites. Realistic SH and P-SV wave seismograms are computed along geological cross sections representative of the area. As expected, the sedimentary cover causes an increase of the signal's amplitudes along the radial and transverse components. The spectral amplification of the vertical motion is generally negligible; instead, that of the horizontal motion ranges between 2 and 5 in the 0.7-2.2 Hz frequency range. Average and maximum spectral amplifications are considered along the different geological cross sections and acceleration response spectra for the Irpinia earthquake are evaluated in order to formulate appropriate design spectra and improvements to the building code.

Beschreibung: The Applied Technology Council (ATC), with funding from the California Seismic Safety Commission developed the document, Seismic Evaluation and Retrofit of Concrete Buildings, commonly referred to as ATC 40. This two-volume, 612-page report provides a recommended procedure for the seismic evaluation and retrofit of concrete buildings. Although the focus is specifically on concrete buildings, the document provides information on emerging techniques applicable to most building types. This paper provides an introduction and overview of the document. The conceptual basis of the procedures is performance-based design using nonlinear static structural analysis. The ATC 40 document comprises a practical guide to the entire evaluation and retrofit process. Topics include performance objectives, seismic hazard, determination of deficiencies, retrofit strategies, quality assurance procedures, nonlinear static analysis using the capacity spectrum method, modeling recommendations, foundation effects, and response limits.

Beschreibung: Traditionally, empirical formulas for building period recommended for code applications are intentionally calibrated to underestimate the period in order to estimate base shear conservatively. At a shorter period, the seismic displacements are smaller, however, and hence underestimated. This note discusses this issue and recommends formulas for estimating seismic displacements of buildings.

Beschreibung: Addition of dampers to a base isolator reduces base displacements but may increase floor accelerations and interstory drifts. This paper presents a “selective control approach” for the design of base-isolated active controlled structures with Controlled Stiffness Dampers (CSD). According to this approach the dampers are activated only within a given range of the base displacement. The optimal damping forces are calculated according to structure's displacements and velocities. However, because of the CS dampers' structure the actual application of the forces is independent of the displacement and the velocity that are transferred to the device. These forces depend only on the geometry and on the mechanical properties of the devices' springs. The efficiency of the proposed method is demonstrated in a numerical example.

Beschreibung: The effect of stiffness and strength degradation on the maximum inelastic displacement of single-degree-of-freedom (SDOF) systems was investigated. The SDOF model included strength and stiffness degradation with increasing deformation amplitude and upon reversal of loading cycles. Pinching of the hysteresis loops was also considered. Spectral displacements were calculated for oscillators with a myriad of degrading characteristics subjected to twelve ground motions on rock, firm and soft soils. The results show that the maximum displacements of degrading oscillators are, on average, larger than those of nondegrading systems. The displacement amplification varies significantly with the period, strength coefficient, degradation rate, and ground motion considered. Nonetheless, the amplification due to the degradation characteristics of the system is much more important in the short period range where average amplification factors of two or three are credible. The amplification factors proposed by ATC 33 provided conservative estimates for oscillators with periods greater than 0.3 seconds subjected to motions on rock or firm soil. On soft soils, a good correlation was found for periods greater than 1.5 seconds. At shorter periods, the ATC 33 factors underestimate the displacement amplification.

Beschreibung: Based on the conclusion that the primary barrier to widespread seismic rehabilitation of buildings in the United States was the lack of a consensus-backed, nationally applicable, professionally accepted rehabilitation standard, the Federal Emergency Management Agency supported the development of the NEHRP Guidelines and Commentary for the Seismic Rehabilitation of Buildings (FEMA 273 and 274). A six-year effort by a team of experienced professional practitioners and university researchers who were motivated to produce a standard that specifically addressed the differences in designing for seismic resistance in new buildings, as opposed to existing buildings, resulted in the NEHRP Guidelines and Commentary for the Seismic Rehabilitation of Buildings. These NEHRP Guidelines will provide the tools for design professionals of varying expertise in seismic design to design economical and appropriate seismic rehabilitation for buildings of essentially any size, commonly used building material and configuration.

Beschreibung: The main objective of this study is to assess the seismic vulnerability of a class of highway bridges existing in certain regions of the eastern and central states, where steel H-piles extends out of the soil to support the pier cap. During severe ground motions, the overall performance of the bridge will be governed by the local performance of the pile-to-cap beam connection. The scope of work was divided into several tasks as follows: (1) a theory was developed to predict the performance of the connection under lateral loading; (2) an initial experimental program was conducted to investigate the seismic behavior of the steel bents; (3) a retrofit strategy is proposed; (4) a second experimental study was carried out to validate the proposed retrofit method; and (5) fragility curves for such structures were developed. This paper deals with the first two tasks of the study. The other three tasks are the subject of a second companion paper (Shama 2002).

Beschreibung: This paper provides a literature review on the application of base isolation and supplemental damping systems for seismic protection of wood structures. The review reveals that both elastomeric bearings and sliding bearings have been considered for implementation within base isolation systems of wood-framed buildings. In addition, friction dampers, viscoelastic dampers, hysteretic dampers, and fluid viscous dampers have been considered for implementation within the framing of wood buildings. Although there are a number of impediments to the widespread implementation of such advanced seismic protection systems, the reviewed literature clearly demonstrates that advanced seismic protection systems offer promise for enabling light-framed wood structures to resist major earthquakes with minimal damage.

Beschreibung: One of the important surprises of the Northridge earthquake of January 17, 1994, was the widespread and unanticipated brittle fracture of welded steel beam-to-column connections. Although no casualties or collapses occurred during the Northridge earthquake as a result of these connection failures, and many WSMF buildings were not damaged at all, a wide spectrum of brittle connection damage did occur, ranging from minor cracking to completely severed columns. This paper summarizes two of the most important documents that have been developed in response to the damage suffered to steel moment frame buildings in the Northridge earthquake. The first, FEMA 267, Interim Guidelines: Evaluation, Repair, Modification and Design of Welded Steel Moment Frame Structures, was generated from studies undertaken as part of a project initiated by the U.S. Federal Emergency Management Agency (FEMA) to reduce the earthquake hazards posed by steel moment-resisting frame buildings. The second document addressed in this paper is the 1997 edition of the American Institute of Steel Construction (AISC) Seismic Provisions for Structural Steel Buildings (commonly referred to as the AISC Seismic Provisions) that incorporates the new information generated by the FEMA-sponsored project and other investigations on the seismic performance of steel structures, and has been adopted by reference into the 2000 International Building Code (IBC).

Beschreibung: A trilinear bending moment–curvature model is proposed for the nonlinear static (pushover) analysis of concrete walls. To account for the effect of cracking on the flexural stiffness of concrete walls in a simple yet accurate way, the elastic portion of the bending moment–curvature relationship is modeled as bilinear. To account for the influence of cyclic loading on tension stiffening of cracked concrete, the concept of upper-bound response for a previously uncracked wall, and lower-bound response for a severely cracked wall is introduced. To validate the proposed model, the results of a large-scale test on a slender concrete wall are compared with predictions from the model. The application of the proposed model in a pushover analysis of a 131-m-(430-ft) high coupled-wall structure demonstrates the importance of accurately modeling the nonlinear flexural stiffness of concrete walls.

Beschreibung: The purpose of this paper is to evaluate the earthquake performance of structures with passive energy dissipators. This paper addresses the following issues: (1) evaluation of seismic intensity levels at which frames incorporating the energy dissipating system (EDS) remain elastic; (2) performance evaluation of frames incorporating an EDS for high-intensity ground shaking; and (3) evaluation of SEAOC Blue Book provisions. Linear time-history analyses indicate that frames with an EDS generally remain elastic during earthquake events that do not greatly exceed the UBC Zone 4 response spectrum. Nonlinear time-history analyses indicate the following: (1) the frames with an EDS can provide “immediate occupancy performance” for high-intensity earthquakes; (2) the performance level of the frames with an EDS exceeds that of frames without an EDS; and (3) the performance of the frame with an EDS, which was designed per Blue Book provisions, can exceed life safety performance.

Beschreibung: This paper describes an experimental and theoretical study of the feasibility of using fiber reinforcement to produce lightweight low-cost elastomeric isolators for application to housing, schools and other public buildings in highly seismic areas of the developing world. The theoretical analysis covers the mechanical characteristics of multi-layer elastomeric isolation bearings where the reinforcing elements, normally steel plates, are replaced by a fiber reinforcement. The fiber in the fiber-reinforced isolator, in contrast to the steel in the conventional isolator (which is assumed to be rigid both in extension and flexure), is assumed to be flexible in extension, but completely without flexure rigidity. This leads to an extension of the theoretical analysis on which the design of steel-reinforced isolators is which accommodates the stretching of the fiber-reinforcement. Several examples of isolators in the form of long strips were tested at the Earthquake Engineering Research Center Laboratory. The tested isolators had significantly large shape factors, large enough that for conventional isolators the effects of material compressibility would need to be included. The theoretical analysis is extended to include compressibility and the competing influences of reinforcement flexibility and compressibility are studied. The theoretical analysis suggests and the test results confirm that it is possible to produce a fiber-reinforced strip isolator that matches the behavior of a steel-reinforced isolator. The fiber-reinforced isolator is significantly lighter and can be made by a much less labor-intensive manufacturing process. The advantage of the strip isolator is that it can be easily used in buildings with masonry walls. The intention of this research is to provide a low-cost lightweight isolation system for housing and public buildings in developing countries.