H. Kit Miyamoto

Design of a New Steel-Framed Building Using ASCE 7 Damper Provisions

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.

Identifying the Collapse Hazard of Steel Special Moment-Frame Buildings with Viscous Dampers Using the FEMA P695 Methodology

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.

Massive Damage Assessment Program and Repair and Reconstruction Strategy in the Aftermath of the 2010 Haiti Earthquake

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 Councils 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.

Probabilistic Evaluation of Seismic Performance of Steel Moment Framed Buildings Incorporating Damper Limit States

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

Development of Guidelines and Effective Retrofit Strategies for Public Schools and Hospitals in Istanbul, Turkey

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.

Design of Structures with Dampers per ASCE 7-16 and Performance for Large Earthquakes

An impediment to the use of seismic protection devices has been the difficulty for practicing engineers to design buildings with isolation system or damping devices. ASCE/SEI task committees charged with the development of a new generation of codes for seismic design and retrofit of buildings have updated the relevant code sections with one goal being to encourage the use of such devices. An effort was undertaken to develop a step-by-step design guideline for such design. Following the preparation of guideline, incremental analysis of four steel SMF building models was undertaken. The benchmark model was designed using the strength and drift requirements of ASCE 716. The other models were based on provisions of Chapter 18 of ASCE 7-16. For one model the lower base shear value was used, and for a third model, the drift ratios were further limited to obtain enhanced performance. Lowerand upper-bound analyses as required by ASCE 7-16 were conducted to size the dampers. The models were then subjected to incremental nonlinear analysis and key response parameters were evaluated. In all cases, the use of dampers resulted in reduction in the hinging of SMF members. It was noted that the best performing model was the model designed for 100% of nominal base shear and above minimum effective damping had superior performance, remaining elastic at design earthquake, and having almost no residual displacement at very large earthquakes.

Seismic Retrofit of a Heritage Building in Wellington Using Buckling Restrained Braces

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.

Cost-Effective Seismic Isolation Retrofit of Heritage Cathedrals in Haiti

Historic and heritage have sustained severe damage and collapse in recent earthquakes, including in Italy (2009), Haiti (2010) and New Zealand (2011). The main vertical and lateral load bearing members for these buildings are typically comprised of unreinforced masonry stone/rubblewalls. These walls have experienced both in plane and out-of-plane failures leading to the collapse of the structures. Given that the walls have little lateral capacity, it is critical to limit the input forces acting on them. In addition, these structures do not have a well-defined load path or diaphragm for seismic loading. A proposed mitigation strategy combining seismic isolation and superstructure intervention is discussed to address these deficiencies. Advanced nonlinear global and local finite element analysis is used to assess the efficiency of the proposed retrofit. The proposed method significantly reduces the level of seismic excitation acting on the existing walls and limits the superstructure retrofit, and thus preserves the historical features of the structures. Application of this technique to Miragoane Cathedrals in Haiti is presented construction.

Seismic Viscous Dampers: Enhanced Performance and Cost Effective Application of PBE

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

Damage mitigation for school buildings in seismically vulnerable regions

Purpose – School 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/approach – Conventional 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 vuln...