Seismic testing of a static power static transfer switch

This test report documents seismic qualification testing of a Static Power Static Transfer Switch (STS). The STS is a mission-critical unit that will be installed at Eareckson Air Station (EAS), on the island of Shemya, Alaska. Two units were built, one of which was tested on the ERDC-CERL shake table on 10 November 2020, and the other delivered to EAS for installation. This report presents details on the STS configuration, seismic tests conducted, and the performance of the unit. The unit passed the final seismic test and can now confidently be installed at the EAS.

Improvement of operational exploration and mining safety using the shear-wave reflection method of mine seismology

During the whole life of mines, the geological survey departments are faced with the critical objectives of operational exploration. These objectives are sometimes impossible to be met adequately without geophysics. Neutrality of geophysical studies is often below the desired level. The shear-wave reflection method of mine seismology, with separation of reflections, which is developed by the present authors, allows: investigating the shape, thickness and dip angles of geologic beds and ore bodies, detecting geological discontinuities such as faults, joints and cavities, as well as determining physical and mechanical properties of rocks. The capacity of the shear-wave reflection method with separation of reflections is described in a case-study of the Upper Kama Potash Salt Deposit. The seismic tests were carried out in a few underground excavations. The developed method in the test conditions is accurate to the first meters at a spacing more than 300 m. Accordingly, it is possible to study the whole thickness of the salt strata in the Upper Kama Deposit, from the salt table to the anhydrous clay roof, specifically, to assess the structure and composition of the waterproof strata, to identify mine-threatening geological discontinuities, and to build the model of physical and mechanical properties of rock mass. Introduction of the newly developed method can greatly enhance efficiency of actual operational exploration. The method has yielded the best results during or immediately after heading of permanent and development openings. Considering similarity of surface and underground mineral mining in terms of access to solid rocks, it is expected to have the same outcomes in open pit mines.

Spectral ratio comparison between translation and rotational records from induced seismic events.

<p>The seismic observations of the rotational signals are a field of seismology that is constantly developed. The recent research concerns sensors technology and its potential application in seismic tests. This study presents the results of a comparative analysis of rotational and translational seismic records using the horizontal-to-vertical spectral ratio (HVSR) method. In terms of transitional signal ratio, we have used the name of HVSR, but in terms of rotational component spectra, we have introduced a torsion-to-rocking spectral ratio (TRSR) which corresponds to horizontal rotation spectrum to vertical rotation spectrum. It has to be noticed that rotation in the horizontal axes has a vertical character and rotation in the vertical axis has a horizontal character.</p><p>The comparison was carried out between velocity signals of translational and rotational records, as well as, between acceleration signals respectively. All seismic data were recorded by two independent sensors: the rotational seismometer and translational accelerometer at the Imielin station, located in the Upper Silesia Coal Basin (USCB), Poland. The seismic data composed of three-component seismic waveforms related to 56 recorded tremors which were located up to 1,5 km from the seismic station and they resulted from the coal extractions carried out in the neighboring coal mines. The rotational acceleration was obtained by numerical differentiation and the translational velocity was produced by numerical integration.</p><p>The conducted spectral analyses allowed to estimate the range of frequency in which the rotational HVSR and the corresponded translational HVSR are comparable. The analysis of HVSR/TRSR curves (in the selected frequency range of 1Hz to 10Hz) showed a strong correlation between the spectral ratios for the velocity signals (translational and rotational) in the frequency range of 1Hz to 2Hz. Respectively, the comparison of the accelerometer signals indicated the correlation between HVSR/TRSR curves in the frequency range of 1Hz to 3Hz. Moreover, both of the TRSR (for velocity and acceleration) showed additional maxima in the same frequency range of 3Hz to 5Hz. These relatively high-frequency maxima did not correspond to translational spectra.  </p>

Post-fire seismic performance of precast reinforced concrete columns

Quantifying the seismic resistance of reinforced concrete buildings after fire is difficult because of the lack of information regarding their strength and ductility under earthquake loads. In this study, four full-scale flexure-controlled reinforced precast concrete columns were subjected to quasi-static reversed cyclic lateral loading under constant axial load to examine the seismic response of reinforced precast concrete columns damaged by 30, 60, and 90 minutes of fire. For the first time, the impact of fire damage on force-displacement behavior, moment-curvature relationship, stiffness, energy dissipation capacity, and residual displacements was investigated through postfire seismic tests. Test results clearly indicated that the fire exposure did not significantly affect the lateral-load-bearing capacity, failure modes, and ductility of the columns, with the exception of the specimen subjected to 90 minutes of fire exposure. The analytical study consisting of thermal and fiber-based structural analysis demonstrated that conventional principles of structural mechanics are valid for estimation of the postfire seismic behavior of reinforced precast concrete columns when the deteriorations in materials are realistically taken into account and the given algorithm is followed.

Experimental seismic response of a resilient 3-storey post-tensioned timber framed building with dissipative braces

With the increased number of multi-storey buildings in seismic areas, research efforts have been focused on developing earthquake resilient systems, such as low-damage techniques based on the combination of post-tensioning and dissipating devices. This paper describes the experimental study performed on a 3-storey post-tensioned timber framed (Pres-Lam) building equipped with energy dissipating systems. The testing project consisted of three phases adopting different configurations of the experimental model: (1) post-tensioning to beam-column joints only, (2) post-tensioning and dissipative rocking mechanisms and (3) post-tensioning and dissipative braces. The main objective of this paper is to experimentally investigate on the seismic response of a large-scale specimen with dissipative braces located in high seismic area, considering construction details similar to those adopted in practical applications. During the experimental campaign, the test frame was subjected to more than one hundred ground motions considering a set of seven spectra-compatible earthquakes at increasing intensity levels. The dissipating bracing system with external replaceable hysteretic dampers improves the seismic resilience of multi-storey Pres-Lam buildings, showing inter-storey drift comparable to those with rocking walls, with full recentring capability and without structural damages or post-tensioning losses through seismic tests.