Damage Detection of Laminated Rubber Bearings Based on the Antiresonance Frequencies of Periodic Structure and Its Sensitivity Analysis

An isolation bearing consumes most of the seismic energy of a structure and is vulnerable to destruction. The performance of isolation bearings is usually evaluated according to the global stiffness and energy dissipation capacity. However, the early minor damage in isolation bearings is difficult to identify. In this study, a damage detection scheme for the isolation bearing is proposed by focusing on the antiresonance of the quasiperiodic structure. Firstly, a laminated rubber bearing was simplified as a monocoupled periodic rubber-steel structure. The characteristic equation of the driving point antiresonance frequency of the periodic system was achieved via the dynamic stiffness method. Secondly, the sensitivity coefficient of the driving point antiresonance, which was obtained from the first-order derivative of the antiresonance frequency, with respect to the damage scaling parameter was derived using the antiresonance frequency characteristic equation. Thirdly, the optimised driving points of the antiresonance frequencies were selected by means of sensitivity analysis. Finally, from the measured changes in the antiresonance frequencies, the damage was identified by solving the sensitivity identification equation via a numerical optimisation method. The application of the proposed method to laminated rubber bearings under various damage cases demonstrates the feasibility of this method. This study has proven that changes in the shear modulus of each rubber layer can be identified accurately.

Seismic Performance of Hybrid Corrosion-Free Self-Centering Concrete Shear Walls

Reinforced concrete (RC) walls are extensively used in high-rise buildings to resist lateral loads, while ensuring an adequate level of ductility. Durability problems, including corrosion of conventional steel reinforcements, necessitate exploring alternative types of reinforcement. The use of glass fiber reinforced polymer (FRP) bars is a potential solution. However, these bars cannot be used in seismic applications because of their brittleness and inability to dissipate seismic energy. Superelastic shape memory alloy (SMA) is a corrosion-free material with high ductility and unique self-centering ability. Its high cost is a major barrier to use in construction projects. The clear advantage of utilizing both SMA and FRP to achieve durable self-centering structures has motivated the development of a composite SMA-FRP bar. This paper investigates the hybrid use of FRP bars and either SMA bars or composite SMA-FRP in concrete shear walls. An extensive parametric study was conducted to study the effect of different design parameters on the lateral performance of hybrid RC walls. The seismic behavior of the hybrid walls was then examined. The hybrid walls not only solved the durability problem but also significantly improved the seismic performance.

Experimental multiblast craters and ejecta — seismo-acoustics, jet characteristics, craters, and ejecta deposits and implications for volcanic explosions

Blasting experiments were performed that investigate multiple explosions that occur in quick succession in the ground and their effects on host material and atmosphere. Such processes are known to occur during volcanic eruptions at various depths, lateral locations, and energies. The experiments follow a multi-instrument approach in order to observe phenomena in the atmosphere and in the ground, and measure the respective energy partitioning. The experiments show significant coupling of atmospheric (acoustic)- and ground (seismic) signal over a large range of (scaled)distances (30--330\m, 1--10\(\m\J^{-1/3}\)). The distribution of ejected material strongly depends on the sequence of how the explosions occur. The overall crater sizes are in the expected range of a maximum size for many explosions and a minimum for one explosion at a given lateral location. The experiments also show that peak atmospheric over-pressure decays exponentially with scaled depth at a rate of \bar{d}_0 = 6.47x10^{-4} mJ^{-1/3}; at a scaled explosion depth of \(4x10^{-3} mJ^{-1/3} ca. 1% of the blast energy is responsible for the formation of the atmospheric pressure pulse; at a more shallow scaled depth of 2.75x10^{-3 \mJ^{-1/3} this ratio lies at ca. 5.5–7.5%. A first order consideration of seismic energy estimates the sum of radiated airborne and seismic energy to be up to 20\% of blast energy.

Experimental and Numerical Investigation of a Dissipative Connection for the Seismic Retrofit of Precast RC Industrial Sheds

Past earthquakes have highlighted the seismic vulnerability of prefabricated industrial sheds typical of past Italian building practices. Such buildings typically exhibited rigid collapse mechanisms due to the absence of rigid links between columns, beams, and roof elements. This study aims at presenting the experimental and numerical assessment of a novel dissipative connection system (DCS) designed to improve the seismic performance of prefabricated sheds. The device, which is placed on the top of columns, exploits the movement of a rigid slider on a sloped surface to dissipate seismic energy and control the lateral displacement of the beam, and to provide a recentering effect at the end of the earthquake. The backbone curve of the DCS, and the effect of vertical load, sliding velocity, and number of cycles were assessed in experimental tests conducted on a scaled prototype, according to a test protocol designed accounting for similarity requirements. In the second part of the study, non-linear dynamic analyses were performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlighted the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

Updating Subsurface Image of Khashim Al-Ahmer Gas Field Using the Interpretation for Anisotropic Velocity Model North-Eastern Iraq

This research deals with structural interpretation of Khashim Al-Ahmer Gas Field North-Eastern Iraq in Diyala Province, using the interpretation of inhomogeneous velocity data. The specific target in this field is the gaseous Jeribe reservoir representing the L. Miocene-Tertiary period. A very thick layer of evaporates Al-Fatha Formation is overlap the Jeribe Formation in the gas field and play as a sealed bed and transition zone for faults movement as a thrust fault. The thrust fault with gas content negatively affected the seismic energy, causing a high attenuation below the level of Al-Fatha Formation in the dome of the Khashm Al-Ahmer structure. Using the interval velocities derived from the sonic logs of five surrounding wells that represent the inhomogeneous behavior of the seismic wave velocity within the rock layers, a model of the velocity behavior in the field was built and the extent of the Jeribe gas reservoir was reconstructed according to the new velocities interpretation data.

Vertical Seismic Isolation Device for Three-Dimensional Seismic Isolation of Nuclear Power Plant Equipment—Case Study

The purpose of this study was to develop a vertical seismic isolation device essential for the three-dimensional seismic isolation design of nuclear power plant equipment. The vertical seismic isolation device in this study has a concept that can be integrally combined with a conventional laminated rubber bearing, a horizontal seismic isolator with a design vertical load of 10 kN. To develop the vertical seismic isolation device, the vertical spring and the seismic energy dissipation device capable of limiting the vertical displacement of the spring were designed and their performances were verified through actual tests. In this study, the target elevation of the floor is 136 ft, where safety-related nuclear equipment, such as cabinet and remote shutdown console, etc., is installed. The sensitivity studies were carried out to investigate the optimal design vertical isolation frequencies for the target building elevation. Based on the results of the sensitivity study, a disc spring and a helical coil spring were selected for the vertical stiffness design, and the steel damper was selected for the seismic energy dissipation, and their performance characteristics were tested to confirm the design performance. For the steel damper, three types were designed and their energy dissipation characteristics by hysteretic behavior were confirmed by the inelastic finite element analyses and the tests in static fully reversed cyclic conditions. Through the study of the vertical seismic isolation device, it was found that 2.5 Hz~3.0 Hz is appropriate for the optimal design vertical isolation. With results of the vertical seismic isolation performance analysis, the appropriate number of steel dampers are proposed to limit the vertical seismic displacement of the spring within the static displacement range by the design vertical load.

Earthquake Relocation Studies near Local Scale Sources using Double-Difference Technique

Determination of the location of the hypocenter is very necessary to monitor the potential for seismic hazard. Positioning and seismic energy can help safety workers determine which areas can be mined or temporarily halted. Earthquakes in underground mines are caused by seismic induction due to mining activities such as blasting processes, hydrofracturing, vehicle activities, etc. Earthquakes that occur are generally clustering. Earthquake events generally occur in mine openings, this is caused by mass compensation taken. The data used in this study are synthetic micro-earthquake data around the mining area. To obtain a high level of accuracy and precision, especially in determining the location and depth in determining the hypocenter using the Double-Difference (DD) method. The results of the microseismic relocation in the study area are well covered, as evidenced by the residual histogram and shift distribution. The shift of the microseismic before and after being relocated spread in all directions with the dominant direction in the NE – SW direction. The value of the microseismic shift before and after being relocated ranged from 0.5 meters to 150 meters.

TERESVA-II EARTHQUAKE on July 19, 2015 with KR=11.1, МSH=3.4, I0=6 (Transcarpathia, Ukraine)

The instrumental and macroseismic data of the Teresvа-II earthquake on July 19, 2015 with the energy class KR=11.1, МSH=3.4 are considered. The earthquake occurred in the seismically active Tyachevo-Sigetskaya zone of Transcarpathia in the upper part of the Earth's crust and caused shaking intensity of I0=6 in the epicentral zone near the village of Teresva. The data on the focal mechanism solution, intensity distribution, parameters of the strongest aftershocks are presented. The release of seismic energy continued for 35 days. During this time, 306 earthquakes were recorded in a wide energy range. The space-time and energy properties of the complex sequence of the Teresvа earthquakes in 2015 have been investigated. The tectonics and previous seismi-city of the area are described.