Shakhzod M. Takhirov

Bolted large seismic steel beam-to-column connections Part 1: experimental study

Abstract Two large bolted steel moment-resisting connections were studied by experiments. These connections were single-sided beam-to-column assemblies that are representative of exterior beam-to-column connections, and they were composed of W36×150 Grade 50 beams and W14×283 Grade 50 columns. T-stubs were cut from W40×264 sections of Grade 50 steel. The T-stub stems were welded to the beams and prestressed by bolts to the beam flanges in the shop. Final beam-to-column assembly required no additional welding: the T-stub flanges were bolted to the column and the column shear tab was bolted to the beam web. The specimens had two symmetrically located T-stubs with different stem geometry: Specimen 1 had rectangular-shaped stems, whereas Specimen 2 had U-shaped stems. During the cyclic testing the beam deformation was minimal controlled by active participation of the T-stub flanges: a separation between T-stub flanges and the column flanges was observed. This separation was caused by bending plastic deformation in the T-stub flanges and plastic deformation in the high-strength bolts. This phenomenon allowed energy dissipation and prevented severe buckling of the beam flanges and beam web.

Bolted large seismic steel beam-to-column connections Part 2: numerical nonlinear analysis

Abstract A large bolted steel moment-resisting connection was studied by nonlinear numerical analysis. This connection was a single-sided beam-to-column assembly that is representative of exterior beam-to-column connections. It was composed of a W36 × 150 Grade 50 beam and a W14 × 283 Grade 50 column. The T-stubs were cut from W40 × 264 sections of Grade 50 steel. The T-stub stems were welded and prestressed by high-strength bolts to the beam flanges in a fabricating shop. Final beam-to-column assembly required no additional welding: the T-stub flanges were bolted to the column and the column shear tab was bolted to the beam web. During cyclic testing the beam deformation was minimal due to the active participation of the T-stub flanges. A separation was observed between the T-stub flanges and the column flange. The separation occurred due to plastic bending deformation in the T-stub flanges. This phenomenon allowed energy dissipation and prevented severe buckling in the beam flanges and beam web. The tests revealed the importance of the numerical analysis of the connection to obtain a better understanding of the critical performance parameters. A finite element analysis was conducted on a specimen with rectangular- shaped stems. The analysis consisted of two parts: a solid element analysis of the T-stub under tension load in the stem and a shell element modeling with buckling and instability analysis. The solid element analysis was conducted to study the local behavior of the T-stub, whereas the shell model analysis was performed to study the global behavior of the connection.

LASER SCANNING, MODELING, AND ANALYSIS FOR DAMAGE ASSESSMENT AND RESTORATION OF HISTORICAL STRUCTURES

High-definition laser scanning is rapidly becoming an essential tool for accurate non-destructive three-dimensional measurements of structures. This technology provides valuable information about an object which is discretized in space as “point clouds”. Two representative examples of current research activities on use of laser scanning in historic buildings in Uzbekistan and California are discussed. The first example is the Registan Square ensemble in Samarkand, Uzbekistan. The ensemble includes several heritage structures. Earthquakes, extreme seasonal temperatures, etc. have left the ensemble in a ruined condition. Domes and portals were partially or totally destroyed. The minarets were dangerously inclined, and some façades lost 70-80% of their ceramic tile coverings. Structural repairs and straightening of the minarets had been conducted over the years. In this study, the ensemble was scanned from about 70 positions to capture the current condition of the historic structures and to conduct structural assessment of the ensemble and its components. The scan data are expected to be used for monitoring of the ensemble’s structural condition. In addition to visual scan data inspection, detailed finite element model of the ensemble was generated from the as-found geometry captured by laser scans. This model allows detailed seismic analysis of the monuments and its components. The model developed for the Sher-Dor Madrasah, part of the ensemble, using the scan data and sample preliminary analysis results are presented in this paper. The research team also investigated several historic buildings damaged during the 2014 South Napa Earthquake, California, USA, as the second example. In that regard, structural damage assessment using laser scanning for several historic buildings, including three churches, were conducted. The results of one of the damaged churches are discussed herein.

Teaching Innovation through Hands-on-Experience Case Studies Combined with Hybrid Simulation

AbstractTeaching innovations in earthquake engineering with special attention to Bloom’s taxonomy is explored utilizing the versatility introduced by the hybrid simulation (HS) testing method. Such innovations focus on developing a variety of case studies with integrated earthquake and structural engineering concepts tailored for high school and first-year undergraduate students. The goal is to effectively guide students to understand the intricacies of real structural systems by visualizing their complex behavior when subjected to earthquake loading. A teaching activity involving theoretical and hands-on-experience components, in which a HS testing demonstration is used as a part of the activity, is described, and the results of this activity are presented. The experiences gathered from this activity and the developed HS experience at various laboratories are used to create new instructional case studies making use of HS.

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.

Numerical Study on Buckling of Elastomeric Seismic Isolation Bearings

1. ABSTRACT Seismic isolation allows the engineer to control damage in moderate and large earthquakes for both a building and its contents using low-cost structural systems. At the present time, there are several types of isolation system in use, many variants of existing systems are being developed, and new systems are being proposed and investigated. The most widely adopted system uses elastomeric bearings that decouple the building or structure from the horizontal components of the ground motion by interposing the structural elements with low horizontal stiffness between the structure and the foundation. This soft layer gives the structure a fundamental frequency that is much lower than both its fixed-base frequency and the predominant frequencies of the ground motion. One of the factors limiting further seismic application of bearings has been a general lack of knowledge regarding the buckling behavior of this type of bearing. The buckling of multi-layer elastomeric bearings under compression loads is a reasonably well-understood phenomenon. What is not well known is that theoretical buckling analysis for compression predicts that the isolator can buckle in tension at a load close to that for buckling in compression. The explanation of this rather counter-intuitive behavior is that the deformation in tension or compression is mainly shear and shear is inherently symmetric. The linear elastic model that leads to both compression and tension buckling is an extremely simple one and it might be argued that the tensile buckling may be an artifact of the model itself and not of the isolator. For this reason, the results of this simple model have been verified by a numerical simulation, using a finite element model of a multi-layer elastomeric bearing. The paper presents the major findings of the numerical analysis for the buckling of elastomeric bearings. The theoretical results are compared with a finite element analysis conducted on numerical models with various shape factors. The rubber material in the numerical models is assumed incompressible or almost incompressible and can undergo large deformations when the stress-strain relationship becomes significantly non-linear. The study shows that the prediction of tensile buckling by the simple linear elastic theory is, in fact, accurate and not an artifact of the model. The numerical study not only confirms the theoretical prediction but also shows an excellent correlation between theoretical and numerical buckling loads in both compression and tension and with other aspects of the behavior of multi-layer elastomeric bearings in tension and compression

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.

Assessment of Seismic Vulnerability and Retrofit Strategies of a Historic Building on the Great Silk Road Based on its Current Condition Captured by Laser Scans

ABSTRACT The technology of high-definition laser scanning is an essential tool for accurate non-destructive 3D measurements of structures. 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 monuments are from the Timurid Dynasty era and they are on the UNESCO World Heritage List. As a representative example, the research results obtained in Shakhrisabz (Uzbekistan) are discussed in detail. The Kok Gumbaz (Blue Dome) Mosque was scanned. It 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. The physical properties of the monument were investigated by material tests. Based on the results of numerical simulations, recommendations on further reinforcement of the historic monument were developed.

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

NONLINEAR SYSTEMS SUBJECTED TO MULTIPLE SEISMIC EXCITATIONS MATCHED TO THE SAME SPECTRUM: NUMERICAL PREDICTIONS VERSUS SHAKING TABLE TESTS

Abstract. The paper summarizes the results of an extensive study conducted at the University of California, Berkeley. A test article representative of a piece of high-voltage substation equipment was studied on a shaking table. It consisted of a support structure and an insulator installed on its top. The support structure was constructed from a HSS with well-separated natural frequencies in both horizontal directions. A porcelain insulator typically used on a 230-kV system was used in the study. A set of four wire ropes was used as a seismic isolation for the system. Two installation cases were considered in the study: (1) fixed base and (2) isolated by wire ropes. As required by the latest draft of IEEE693, a number of component tests was conducted to evaluate the performance of the wire ropes. Based on the results of component testing, detailed numerical models of the seismically protected equipment were generated. Each equipment configuration was subjected to seven time histories matched to the same IEEE693 spectrum. Four of them were modified from historical records and matched to the IEEE693 spectrum in the time domain. The other three excitations were synthetic strong motions matched to the same spectrum. The main objective was to evaluate the variability of the seismic response of the equipment subjected to seven time histories matched to the same response spectrum.