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On April 25, 2015, an earthquake of magnitude Mw 7.8 struck midwestern Nepal, followed by hundreds of aftershocks. The Government of Nepal Department of Archaeology estimates that one-third of the ...

A heritage building in Wellington, New Zealand (NZ) was classified as potentially earthquake-prone following an initial seismic assessment (ISA) by the Wellington City Council (WCC). The first four stories of the building were constructed originally in 1908 and an additional lightweight story was added in 1955 and altered in 1993. The building has a rectangular floor plan measuring 24 x 10.5 m. In the longitudinal direction, steel frame with solid unreinforced masonry (URM) infill walls provided resistance to seismic forces. In the transverse direction, perforated URM walls with large openings and nonductile concrete encased steel frames were used for both gravity and seismic load transfer. A detailed seismic assessment (DSA) of the building structure confirmed seismic capacity of the building in excess of 100% of New Building Standards (%NBS) in the longitudinal direction. However, in the transverse direction, the structure, secondary components and non-structural components had a seismic capacity less than 34%NBS, hence the building was confirmed earthquake-prone in its current state under the NZ Building Act. Performance-based engineering was used to devise the seismic retrofit for the principle structure. To retrofit the principle building structure to 100%NBS in the transverse direction, new Buckling Restrained Braced (BRB) frames were designed to carry seismic load. A geotechnical investigation showed that the underlying soil was competent and thus soil-structure interaction (SSI), tie foundation beams and nonlinear analysis were used to obtain realistic demand and capacity for the building after seismic retrofitting. The BRB manufacturer was consulted and the BRB size distribution along the height was optimized. The construction of the seismic retrofit is currently underway.

An innovative design using steel special moment frames sized per building code requirements for strength and viscous dampers to control story drift ratios results in longer period structures that limit floor accelerations with excellent performance in design-level earthquakes. However, the response of this design to extreme seismic events is not well understood. This is due to the lack of: a) limit state data for dampers, and b) data on the response of the system when subjected to large earthquakes. To address these issues, analytical investigation of the limit states of dampers was performed and the performance of the model was correlated with experimental data. This model was then implemented in a group of archetypes subjected to collapse-level loading. Analysis showed that this design had satisfactory performance when subjected to extreme seismic events. Additional significant improvement in performance was obtained with an enhanced damper design and with a damper safety factor of 1.3.

The January 2010 Haiti earthquake resulted in over 230,000 deaths, affected 3 million people, and damaged or collapsed over 200,000 structures. An unprecedented earthquake damage assessment project by a joint operation of the Haitian Ministry of Public Works, the United Nations Office of Project Services, the Pan American Development Foundation, and the authors was undertaken with three strategic goals: (1) rapid damage assessment, (2) reconstruction database development, and (3) upgrade the technical capabilities of Haitian engineers. A modified version of the Applied Technology Council's ATC-20 technical platform, accounting for Haitian building design, was developed. As part of this program, PDA-based data collection techniques and quality-assurance programs were implemented, and approximately 600 Haitian engineers were trained. As of March 2011, approximately 400,000 buildings had been inspected. This database was used to develop: (1) repair strategies for yellow-tagged structures, and (2) reparability, reconstruction, and demolition assessments or red-tagged structures. This program could also be extended as a platform for a seismic damage evaluation and reconstruction strategies in other parts of the world.

PurposeSchool buildings have suffered disproportionate damage during past and recent earthquakes. For example, during the 2008 Sichuan earthquake, many school buildings collapsed, resulting in loss of life. School buildings in many other parts of the world are also susceptible to this type of widespread damage because of inadequate design, detailing, or poor construction quality. The purpose of this paper is to show how these fatal flaws can be mitigated prior to future catastrophe by using good engineering practice to retrofit vulnerable schools.Design/methodology/approachConventional and innovative, cost‐effective, and reliable tools are available to prevent damage to schools. It is often necessary to examine a group of buildings or all structures in a locality and develop a comprehensive risk management plan for the vulnerable buildings. As an example, a comprehensive evaluation and retrofit project, under the auspices of the World Bank, is currently under way in Istanbul, Turkey, to address vulnerable school and hospital buildings as discussed in the paper. As part of this effort in Turkey, a guideline that relies on state‐of‐the‐art evaluation and retrofit methods has been developed to assist the local engineers.FindingsImplementation of the program based on the uniform standards developed in the retrofit guidelines, has significantly reduced the seismic risk to schools in Istanbul.Practical implicationsThe proposed evaluation and implementation technique can be utilized by governments worldwide to prevent further damage to key infrastructure and save millions of lives.Originality/valueInnovative retrofits can be used to provide enhanced performance and provide seismic resiliency for cluster of school buildings.

Past seismic events have demonstrated the vulnerability of suspended ceilings, classified as nonstructural components, to earthquake damage. Engineers, architects, and manufacturers all participate to help ensure that the units perform satisfactorily during earthquakes. To address the seismic susceptibility, the U.S. national codes and federal and regulatory guidelines recommend two distinct approaches. The first mandates capacity and installation requirements and the second addresses damage states, introducing performance based. Application of these methods entails either accurate structural analysis or seismic qualification by experimentation. Until recently, scant data were available to evaluate the adequacy of the required installations or the damage states. To address this issue, full-scale earthquake laboratory tests of suspended ceiling systems have been undertaken by researchers and manufacturers. Experimentation showed that ceilings meeting the code requirements performed well. The only mode of failure observed during the tests was the loss of panels. Laboratory data were also used to construct fragility curves for the specimen. Large vertical accelerations, typically not observed in the field, dislodged panels close to the center of the test frame. This type of response differs from that presented in past earthquake reconnaissance reports and thus necessitates further examination.

SUMMARY The design approach for tall steel moment frame structures with viscous dampers entails sizing steel members per code-level strength forces, and sizing viscous dampers to limit storey drifts. This method has been used extensively in new and retrofi t applications. This methodology has resulted in structures that have longer periods than those using the code-designed approach, are economically competitive and have excellent performance in design-level earthquakes. However, the effi cacy of this design in extreme events is not well understood because of the lack of limit states data for dampers and the absence of a fi eld or analytical database of such structures subjected to large earthquakes. Mathematical modelling of viscous dampers with limit states was developed, correlated with experimental results and then used to analyse 10-storey archetypes. This analysis showed that the design had satisfactory performance during extreme seismic events. There were signifi cant improvements in reducing collapse hazard by using an enhanced damper design with an increased damper safety factor. Copyright © 2010 John Wiley & Sons, Ltd.

Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design-level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures.

Performance based design with seismic protection devices such as viscous dampers have fundamentally altered the landscape of earthquake engineering and design. Structures designed and built without such devices typically use a codeprescribed design that implies extensive structural damage, loss of operation, and likely replacement at design-level earthquake. In contrast, performance based design incorporating earthquake protection devices leads to a combination of best engineering practice and reducing life-cycle costs. These devices are robust, costeffective, and have a proven exceptional performance record in past earthquakes. In most cases, initial cost of their utilization is neutralized by reduction in cost of other structural members. The long-term performance is the key parameter used for evaluation. Structures properly designed with these devices will likely only require minimum post-earthquake inspection and can be fully operational within hours of a seismic event. When utilized for critical structures, such performance reduces the need for use of natural resources by eliminating post earthquake repair or reconstruction and thus improving the community resiliency. Example cases are

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.

An advanced concept for design of steel moment framed structures, sizing steel members per code guidelines for strength and adding viscous dampers to limit story drifts, this results in robust structures with superior performance to that of conventional designs at the design and maximum considered earthquakes. However, the efficacy of such design at extreme events has not been well documented due to the lack of a comprehensive database detailing their responses and data on the structures with dampers subjected to very large earthquakes. The current research addresses the physical limit states of the dampers, and development of mathematical model of the viscous dampers incorporating such limit states. The adequacy of the model is then verified by correlating it with laboratory data. Next, nonlinear simulations of structures with viscous dampers are conducted to probabilistically determine the collapse performance of the buildings and draw conclusions about key factors affecting the response

A task committee comprised of local structural engineers and earthquake engineering experts from abroad was formed to assess the seismic performance of public schools in under auspices of this group; a guideline has been developed better assess the existing conditions and develop retrofit options for school and hospital buildings in Istanbul. The project is financed by a World Bank (WB) loan and is implemented through the Istanbul Special Provincial Administration (ISPA). The ISMEP project started on 1 February 1, 2006, and is expected to be completed by the end of 2010. The Istanbul Project Coordination Unit (IPCU), established under ISPA, is responsible for implementing the ISMEP. The Guideline is based on provisions of the ASCE 41 and Turkish earthquake code and is purposed to address the seismic design requirements for hospital and school facilities in Istanbul and recommends effective retrofit measures. Many such buildings were constructed prior to adoption of seismic codes and use non-ductile concrete moment frames and unreinforced masonry walls to resist earthquake loading. Recent earthquakes in Indonesia (2007) and China (2008) have shown that this type of construction is particularly sensitive to earthquake damage and even complete collapse due to the inadequate design and construction practices. Such vulnerability caused loss of life of thousands of students in China. The provisions of the guidelines are written to be easy to follow and implement. The engineer is charged with condition assessment, followed by analysis and determination of deficiencies. Both conventional and state-of-the-art retrofit measures are discussed in detail. The document also provides suggested retrofit measures for different building groups. It is hoped that the implementation of this guideline will drastically reduce the level of damage and loss of life in the public buildings during the next earthquake.

Fluid viscous dampers have been extensively used in new construction and seismic retrofit. They provide a reliable mean of dissipating seismic energy. In practice, the dampers are designed and sized using the procedures outlined on ASCE 7 for new structures and ASCE 41 for retrofit of existing buildings. These guidelines provide a factor of safety for damper design. In typical applications, the engineers analyze structures with dampers without consideration for the damper limit states and instead count on the abovementioned safety margins. However, the limit states of viscous dampers have a significant effect on the response of the building to which they are attached to. To address this issue, a refined model of viscous dampers has been developed based on the force-displacement-velocity constitutive relations of the damper components and incorporating the damper limit states. The model incorporates both displacement and force limit states. Simulations were conducted to check the limit state activation for the model. Experimental data were then used to verify the accuracy of such limit states. Finally, a sample structure was analyzed to assess the effect of limit states on the building response and to evaluate the safety margins.. INTRODUCTION Viscous dampers were originally developed as shock absorbers for the defense and aerospace industries. Figure 1 presents a photograph of a viscous damper. Viscous dampers have been used extensively for seismic application for both new and retrofit construction [Miyamoto and Gilani 2008]. During seismic events, the devices are activated and the seismic input energy is converted to the heat energy and is thus dissipated. Subsequent to installation, the dampers will not require maintenance [Taylor 2008]; and have been shown to possess stable and dependable properties for design earthquakes. 937 ATC & SEI 2009 Conference on Improving the Seismic Performance of Existing Buildings and Other Structures

Performance Based Design (PBD) and a system of steel Special Moment Resisting Frames (SMRFs) with Viscous Damping Devices (VDDs) were used for the seismic design of a new multi-story medical building in California. The five-story, 132,000 ft 2 office building is one of the first structures in the United States to apply 2005 ASCE 7 procedure to design with VDDs. In accordance with ASCE 7, the steel frames were sized and designed with strength requirements of the code level force. VDDs were provided to control displacement of the structure. Earthquake performance and cost effectiveness were the primary concerns in designing this building. Sitespecific response spectra and spectrum-compatible time histories, synthesized for 500-year and 2,500-year return events, were used for nonlinear response history analysis. Comparison analysis of the PBD design and conventional design (CD) showed that the PBD building had superior seismic performance. PBD lead to a long period, low frequency, structure with low acceleration. VDDs reduced the displacement level to less than a 1% story drift ratio. A cost study shows that much of the VDDs expense is offset by decrease in the weight of the steel members and reduction in foundation costs while providing a far superior performance.

Performance-based earthquake engineering was utilized to ascertain the seismic performance of an existing two-story non-ductile reinforced concrete building with a proposed new third floor steel-framed addition. The structure, hereafter referred to as the Capital Unity Center, is located in downtown Sacramento, California, and was designed and constructed in early 1940s per the applicable building codes at the time of construction. Capitol Unity Center is a remodel and addition to an existing warehouse structure and is an integral part of the city’s attempt to renovate the older downtown buildings. The new center will house a museum with space for exhibits, performing area, and workshops. Since the renovation constitutes major structural changes, the structure in the new configuration must comply with the current seismic provisions of the California Building Code [3]. In addition, since the facility and will be used by the California Department of Education, it must comply with the more stringent requirements of the California Division of State Architecture (DSA). Provisions of FEMA 356 [1], ACI 318 [2] and CBC 2001 [3] were used for a detailed investigation. Comprehensive material testing, detailed geotechnical investigations, site-specific seismic hazards, and state-ofthe-art nonlinear structural analysis were performed to assess the seismic performance of the building, identify deficiencies, and evaluate efficacy of seismic retrofit techniques. Analysis showed that the existing structural elements with the architectural renovations did not meet the required performance goals. To obtain satisfactory behavior, both the superstructure and substructure have to be retrofitted. In its retrofitted configuration, the building would then meet the performance objectives.

Analytical investigations were undertaken to assess the seismic performance of a hospital building located in Southern California in seismic zone 4. The structure consists of a eight-story steel, and a bottom story reinforced concrete superstructure constructed over four levels of sub-grade parking stories. The building is rectangular, is 125 ft tall, and has total floor area of 130,000 ft 2 . Steel and concrete moment-resisting frame along the grid lines of the building provide resistance to lateral loading. Project-specific design guidelines and FEMA, and SAC guidelines were used for evaluation. A comprehensive three-dimensional mathematical model of the structure was prepared. Nonlinear response history analysis of the existing building revealed that the performance was inadequate. In particular, story drifts and member nonlinear flexural rotations exceeded the limits specified in the design guidelines. The building rehabilitation consists of adding fluid viscous damper frames to the exterior faces of the building. The structure was then re-analyzed in the new configuration, and its performance was satisfactory.

Structural performances of two historic high-rise buildings, constructed in the early 1920s and located in seismic zone 3 in downtown Sacramento, CA were investigated. The objectives of this evaluation were to determine whether these structures met the current seismic criteria and to propose strategies to upgrade such performance to an acceptable level. Both structures, have fourteen main floors, are 200 ft tall, have an approximate floor area of 90,000-ft 2 . Performance-based procedures based on the Life Safety (LS) provisions of FEMA 356 for the Deign Basis earthquake (DBE). Detailed threedimensional mathematical models of the structures were prepared. Both structures performed better than expected when subject to seismic loading. A voluntary seismic upgrade using fluid viscous dampers (FVDs) and steel struts was utilized for one structure, whereas, for the second structure, structural modifications were undertaken to address some of the occupancy needs.

The purpose of this paper is to evaluate the effectiveness of Fluid Viscous Dampers (FVD) when used to control blast loading responses on lateral load resisting frames. In particular, this paper addresses the following issues: 1) Development of a blast loading time history for a 3,000 pound TNT blast, 2) Blast effects and performance comparisons of a conventional special moment resisting frame (SMRF), SMRF with FVD, and a conventional shear wall building. Nonlinear dynamic force history analyses were conducted on three different types of structures: 1) Conventional SMRF, 2) SMRF with FVD, and 3) Conventional concrete shear wall. The lateral load resisting frames of these structures were designed to conform to the 1994 Uniform Building Code, Zone 4 criteria. Nonlinear computer models with and without FVD were subjected to a dynamic blast loading from 3,000 pounds of TNT at 100, 40, and 20-foot standoff distances. Nonlinear analyses indicated that structures with FVD provided a cost effective way to control displacement and plastic hinge rotation of lateral load resisting frames under blast loading. Blast Loading Time Histories For A 3,000 Lb Charge Of Trinitrotoluene (TNT) The intent of this report is to study the relative performance of structures subjected to transient pulses caused by the detonation of explosives. Most explosives are developed and used primarily by the military and government agencies. Very little data is published in the public domain concerning blast pulse magnitudes and wave forms. The transient pulses presented here are for reference only. They were assembled entirely from an unclassified database of public domain material, and were appropriately scaled for use. In general, the frequency content from the time history of a detonation is at least an order of magnitude higher than the structural frequencies of a conventional building. Thus, it is not necessary to utilize high precision transients. Since only conventional buildings were to be studied, the extremely short explosive pulse durations also indicated that integrated pulse content was much more important than a highly precise wave form. For these reasons, all pulses were rendered generic by reducing them to an equivalent triangular wave form. The resultant time histories provide what