Amir S. J. Gilani

Seismic Evaluation and Retrofit of 230-kV Porcelain Transformer Bushings

Static and earthquake-simulator testing of two 230-kV, 3000A, Type-U transformer bushings manufactured in the mid 1980s by the General Electric (GE) Company was undertaken to evaluate both the seismic performance of bushings known to be vulnerable to damage from moderate earthquake shaking, and the efficacy of simple retrofit details. Both bushings survived earthquake shaking compatible with the IEEE spectrum for High Level qualification when mounted on a rigid frame. When mounted on a flexible frame, one 230-kV bushing was unable to sustain the High Level qualification shaking without oil leakage and slip of the porcelain units. Two retrofit details utilizing two semicircular ring plates and epoxy filler were prepared by utility representatives with the objective of limiting slip of the UPPER-1 porcelain unit over the gasket connection. The second detail, Ring-2, permitted the 230-kV bushing to sustain substantially larger accelerations and displacements than those of the unretrofitted bushing and eliminated the permanent slip of the UPPER-1 porcelain unit over the gasket connection for extreme earthquake shaking.

EVALUATION OF PRE-NORTHRIDGE STEEL MOMENT- RESISTING FRAME JOINTS

The 1994 Northridge earthquake caused widespread and unexpected damage to steel moment-resisting joints and connections. Shortly following the earthquake, the Federal Emergency Management Agency funded a series of full-scale tests of steel moment-resisting joints and connections to characterize the behavior of pre-earthquake connections and to evaluate the efficacy of a selected number of repair schemes. Twelve pre-earthquake connections were tested. Three of the twelve connections were tested by the authors to failure, and then repaired and re-tested. The response of the pre-earthquake connections was highly variable and uniformly poor. Premature fractures were observed in all twelve connections, and the types of fractures were similar to those observed in the field following the earthquake. The mean beam plastic rotation was 0.005 rad: one-sixth of the target value of 0.03 rad. The response of those moment-resisting connections that were repaired by replacing fractured weld and parent metal with toughness-rated weld filler metal was also poor. On the basis of the studies described in the paper, the rotation capacity of large-size moment-resisting connections built prior to the Northridge earthquake is smaller than the target values established following the earthquake; rehabilitation of earthquake-damaged moment-resisting connections by re-welding only will likely be ineffective; beam-column panel zones should be designed to remain elastic for the forces associated with plastic hinging in the beams; design equations for continuity plates should be revised; and design checks for flange compactness should be based on expected rather than nominal material properties. Copyright

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

Seismic Qualification Testing of Suspended Ceilings: Lessons Learned and the Requirements for a New Test Standard and Qualification Procedure

In recent years, three major ceiling grid manufacturers in the United States have conducted extensive earthquake simulator testing of suspended ceilings. The tests to date have followed the ICC-ES AC-156 protocol and have been performed on an elevated test frame of limited size. The test protocol was developed to be applicable for a wide array of nonstructural components and is referenced in the building codes as a standard when testing nonstructural components. The tests have provided researchers and engineers with invaluable data and have enabled manufacturers to assess the seismic performance of their components with a degree of reliability. However, the tests have also revealed shortcomings in the current experimental and evaluation procedures. It is proposed to develop a second-generation test protocol that takes into account the unique properties of suspended ceilings such as multiple attachment points and large floor plan, and to address evaluation questions including qualification levels and performance targets.

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.

Evaluation of seismic qualification procedures for high-voltage substation equipment

The standard industry procedures for the seismic qualification of substation equipment were assessed by analysis and triaxial experimentation using the earthquake simulator at the Pacific Earthquake Engineering Research Center, which is headquartered at the University of California at Berkeley. Information on the qualification of in-service high-voltage transformer bushings is presented. Two of the three classes of bushings performed substantially better in the laboratory than in the field during modest earthquake shaking. The excellent performance of these two classes of bushings calls into question the standard industry procedures for equipment qualification. Improved procedures that account for equipment interaction, permit uniaxial qualification, better address response amplification due to transformer tank and turret flexibility, and utilize standardized earthquake histories and filtering procedures, are needed.

Structural Health Monitoring and Assessment of Seismic Vulnerability of Historic Monuments on the Great Silk Road Based on Laser Scanning

The high-definition laser scanning technology is used in an extensive ongoing structural assessment of historic monuments in Uzbekistan. The laser scanning studies were conducted in Tashkent, Bukhara, Samarkand and Shakhrisyabz. As a representative sample, the research results based on data obtained in Samarkand and Shakhrisyabz are discussed herein. Samarkand is one of the oldest inhabited cities in Central Asia. Because of its strategic location on the Great Silk Road, an ancient trade route between China and the Mediterranean, Samarkand was one of the greatest cities of Central Asia. Shakhrisyabz is located in southern Uzbekistan approximately 80 km south of Samarkand, Uzbekistan. Once a major city of Central Asia, it is primarily known today as the birthplace of the 14th century Turco-Mongol conqueror Timur. The scanned monuments are on the UNESCO World Heritage List. To monitor the buildings’ possible settlement due to poor soil conditions, special high-resolution laser targets were permanently installed. A detailed finite element model of monuments was generated from the as-found geometry captured by laser scans. The physical properties of the monuments were investigated by material tests of the major components recovered from the historic sites. The calibrated numerical models were used for comprehensive seismic analysis of the monuments. To monitor the structural health of the monuments, they were repeatedly scanned in order to estimate whether the structural degradation is progressing. Based on the results of numerical simulations and health monitoring results, recommendations on further preservation of the historic monuments were developed.

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.

DETAILED NUMERICAL ANALYSIS OF A HISTORIC BUILDING BASED ON ITS CURRENT CONDITION CAPTURED BY LASER SCANS AND MATERAIL TESTS

The technology of high-definition laser scanning is an essential tool for accurate non-destructive three-dimensional measurements of structures. The object’s geometry is captured as a collection of points which is called a “point cloud”. The research team used this technology and conducted an extensive laser scanning program of many historic monuments in Uzbekistan. The program started in 2013 from scanning the famous Registan ensemble in Samarkand. Later in 2015, it was expanded to more cities and monuments and the laser scanning was conducted in Tashkent, Bukhara, Samarkand and Shakhrisyabz. The scanned monuments are from the Timurid Dynasty era and they are on the UNESCO World Heritage List. This paper summarizes some results of this extensive ongoing program. As a representative example, the research results based on data obtained in Shakhrisabz (Uzbekistan) are discussed in details. The city is located in southern Uzbekistan approximately 80 km south of Samarkand, Uzbekistan. Once a major city of Central Asia, it is primarily known today as the birthplace of 14th century Turco-Mongol conqueror Timur. The Kok Gumbaz (Blue Dome) Mosque was built in 1437 and underwent several restorations and reinforcement efforts. A detailed finite element model of the monument was generated from the as-found geometry captured by laser scans. To monitor the buildings’ possible settlement due to poor soil conditions, special high-resolution laser targets were permanently installed. The physical properties of the monuments were investigated by material tests of the major components recovered from the historic sites. The calibrated models were used for comprehensive seismic analysis Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2312-2322

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.