scholarly journals An Energy-Based Safety Evaluation Index of Blast Vibration

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Mingsheng Zhao ◽  
Dong Huang ◽  
Maosen Cao ◽  
En-an Chi ◽  
Jun Liu ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Failure Modes ◽  
Guizhou Province ◽  
Damage Potential ◽  
Blast Vibration ◽  
Restoring Force ◽  
Safety Criterion ◽  
Plastic Damage ◽  
Field Investigations ◽  
Blast Vibrations

The combined peak particle velocity (PPV) and frequency safety criterion for blast vibration is widely used in blasting engineering. However, some field investigations are inconsistent with this criterion. On the basis of field investigations, it is found that there are two failure modes of structures subjected to blasting seismic waves, that is, first-excursion failure and cumulative plastic damage failure. Moreover, the nature of structural responses under blast vibrations is a process of energy input, transformation, and dissipation. Therefore, an energy-based dual safety standard is proposed in this work to more comprehensively explain all failure modes of structures under blast vibrations. To this end, structures are simplified into elastic-plastic single degree of freedom (SDOF) systems with bilinear restoring force models, and energy responses of SDOF systems are then determined using theNewmark-βmethod. From the energy responses, the maximum instantaneous input energy and hysteretic energy are selected as the basis of the dual safety criterion, because they can reflect first-excursion failure and cumulative plastic damage failure, respectively. Finally, field investigations in a blasting site in Zunyi, Guizhou province, China, are used to prove that compared to the PPV-frequency criterion the proposed energy-based dual safety criterion is more capable of assessing the damage potential of blast vibrations.

Study on Failure Mode for Power Intake Structure under Seismic Action

2013 ◽  
Vol 438-439 ◽  
pp. 1537-1541
Author(s):  
Lin Gang Tian ◽  
Bin Bin Zhen ◽  
Hu Huang ◽  
Jing Shen
Keyword(s):  
Failure Mode ◽  
Seismic Waves ◽  
Failure Modes ◽  
Seismic Analysis ◽  
Failure Process ◽  
Early Period ◽  
Seismic Load ◽  
Seismic Action ◽  
High Intake ◽  
Ultimate Failure

This paper studies on the ultimate failure modes and bearing capacity of high intake tower under the action of seismic load based on nonlinear concrete model. By monitoring the way of crack development and failure process of the tower to study failure mode under the action of various seismic wave, we can conclud that the regional distributions of the structural crack of tower body vary with the duration of an earthquake. In the early period of earthquake, the crack has little effect on the whole structure. After duration of the earthquake, the structure forms penetrable cracks. By studying the cracks development and distribution on the structure of tower body under the action of various seismic waves, we know the failure process and failure mode of high intake tower. The conclusions provide evidence for engineering design and seismic analysis of pertinent engineering.

An Estimation Method for First Excursion Probability of Nonlinear System Using Maximum Response

2004 ◽  
Author(s):  
Shigeru Aoki
Keyword(s):  
Failure Modes ◽  
Damping Ratio ◽  
Estimation Method ◽  
Maximum Response ◽  
Estimation Methods ◽  
Mechanical Equipment ◽  
Primary System ◽  
Secondary System ◽  
Restoring Force ◽  
Excursion Probability

The secondary system such as pipings, tanks and other mechanical equipment are installed in the primary system such as building. The important secondary systems should be designed to maintain their function even if they are subjected to destructive earthquake excitations. First excursion failure is one of the most important failure modes. The secondary system has many nonlinear characteristics. In this paper, an estimation methods of the first excursion probability of the secondary system with gap and friction subjected to earthquake excitation is proposed. Restoring force with gap and friction force is equivalently linearized. When the tolerance level is normalized by the maximum response of the secondary system without gap and friction characteristics, variation of the first excursion probability is very small for various values of mass ratio of the secondary system to the primary system, the damping ratio and the natural period.

Development of design spectra for long-duration ground motions from Cascadia subduction earthquakes

1998 ◽  
Vol 25 (6) ◽  
pp. 1078-1090 ◽  
Author(s):  
R Tremblay
Keyword(s):  
Subduction Zone ◽  
Failure Modes ◽  
Ground Motions ◽  
Damage Index ◽  
Cascadia Subduction Zone ◽  
Damage Potential ◽  
Design Spectra ◽  
Subduction Earthquakes ◽  
Long Duration ◽  
Short Period

There is now growing evidence that large-magnitude earthquakes have occurred and could occur again along the Cascadia subduction zone located west of Vancouver Island, Bristish Columbia. Numerical simulations indicate that these earthquakes would produce long-duration ground motions and would thus be capable of inducing a large number of reversals of inelastic deformations in engineered structures. Efforts have now been undertaken to account for this damage potential in building codes. In this paper, inelastic design spectra are developed for Cascadia subduction earthquakes for four sites in British Columbia. These spectra are compared with elastic design spectra that have been developed recently for the same sites based on empirical attenuation relationships for Cascadia events. The approach used to develop the inelastic spectra aims at providing the same level of protection against structural failure for both subduction events and crustal or subcrustal earthquakes. Force modification factors are first determined for structures exhibiting various failure modes and ductility levels when subjected to representative crustal and subcrustal earthquake ground motions. Thereafter, design spectra are developed for the same structures to prevent structural collapse under simulated Cascadia subduction ground motions. The study reveals that the elastic spectra do not reflect adequately the damage potential of Cascadia earthquakes. These elastic spectra generally are unconservative for Tofino and Victoria. For Vancouver and Prince George, the elastic spectra overestimate the demand, especially for short-period structures.Key words: collapse, crustal earthquakes, damage index, design spectrum, ductility, duration, ground motion, subduction zone.

Blast Induced Damage Due to Repeated Vibrations in Jointed Gneiss Rock Formation

2010 ◽  
Vol 1 (1) ◽  
pp. 110-134 ◽  
Author(s):  
M. Ramulu ◽  
T. G. Sitharam
Keyword(s):  
Rock Mass ◽  
Dynamic Loading ◽  
Seismic Waves ◽  
Damage Zone ◽  
Research Work ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Rock Blasting ◽  
Hydroelectric Power ◽  
Blast Vibrations

Blasting is the most common method of rock excavation technique in mining and civil construction and infrastructure projects. Rock blasting produces seismic waves similar to those produced by earthquakes, but with relatively high frequency and low amplitude. General blast induced damage was extensively studied by researchers globally, but the studies on damage due to repeated blast vibrations is not yet reported, quantitatively, on underground openings. This paper deals with the research work carried on the effect of repeated dynamic loading imparted on the jointed rock mass from subsequent blasts in the vicinity, on the jointed rock mass at Lohari Nag Pala Hydroelectric Power Construction Project. The blast induced damage was monitored by borehole extensometers, borehole camera inspection surveys and triaxial geophones installed at three test sites of different joint orientations at the Main Access Tunnel of power house. The study reveals that there was extra damage of 60%, exclusively due to repeated blast vibrations. The results of the study indicate that repeated dynamic loading, resulted in damage even at 33% of the conventional damage threshold vibrations (Vc) in case of favorable joint orientations and 23% of Vc in case of unfavorable joints. The paper concludes in quantification of effect of repeated blast loading and the orientation of joints on the extension of damage zone in jointed rock mass of underground excavations.

scholarly journals Numerical Test Study of the Microscale Failure Modes and Fractal Analysis of Lower Cambrian Shale Based on Digital Images

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Hengtao Cui ◽  
Zhonghu Wu ◽  
Liping Li ◽  
Jing Wang ◽  
Shuguang Song ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Failure Modes ◽  
Fractal Theory ◽  
Failure Process ◽  
Numerical Test ◽  
Confining Pressure ◽  
Guizhou Province ◽  
Internal Damage ◽  
Damage And Fracture ◽  
Confining Pressures

To reveal the effect of confining pressure on the mechanical properties and rupture modes of quartz-bearing shale, the shale core of the no. 3 block of Fenggang, Guizhou Province, China, was analyzed by nuclear magnetic resonance, polarized light microscope thin section observation and identification, and core X-ray whole-rock minerals diffraction analysis to determine the distribution of shale minerals in the Niutitang Formation. On the microscale, based on digital image processing technology, this paper characterizes the nonuniformity of minerals in shale, a numerical model that can reflect the true microstructure of shale. Then, the failure process of shale under different confining pressures was simulated. The results show that when the shale is loaded with vertical displacement under different confining pressures, the compressive strength and elastic modulus of the sample change significantly. The failure mode can be roughly divided into three types: the inverted V-shaped (0 MPa, 2 MPa, and 4 MPa), V-shaped (6 MPa and 8 MPa), and inverted Z-shaped (10 MPa). Since the development of fractal theory provides a new space for studying the damage and fracture of rocks, the damage evolution and failure process of shale can also be regarded as the fractal process of cracks, in which the fractal dimension is the core parameter. The calculation is different under different stress levels. The fractal dimension under the condition of confining pressure shows that the value of the fractal dimension is greatly affected by the effect of confining pressure. When the fractal dimension is higher, the fracture mode is more complicated, and the internal damage degree is more serious. The research results provide important theoretical guidance for shale gas fracturing production.

scholarly journals Tribology Issues in the Operation of a Microswitch: A Tutorial

2009 ◽  
Author(s):  
George G. Adams
Keyword(s):  
Contact Resistance ◽  
Failure Modes ◽  
Impact Force ◽  
Electrostatic Force ◽  
Beat Frequency ◽  
Actuation Voltage ◽  
Thermal Response ◽  
Steady Increase ◽  
Restoring Force ◽  
The Impact

Microswitches have the potential to be used in numerous applications [1]. Microswitches are slower and currently less reliable than semiconductor switches. However they have the advantage of reduced power consumption, less insertion loss, and better isolation. The operation of a microswitch involves many interesting phenomena which will be reviewed. In an electrostatically actuated switch a voltage difference is applied between the beam and the gate. The resulting electrostatic force pulls the beam toward the gate such that its tip contacts the drain and completes the circuit. However the momentum of the beam causes it to deflect further, even after the tip is in contact with the drain. This stored elastic energy can be sufficient to cause the tip to separate from the drain resulting in what is often referred to as “contact bounce” [2]. Contact bounce causes several problems. First the switch cannot be used until the bouncing has stopped, thus increasing the effective time-to-closure. Second the tip and drain are subjected to more mechanical open-close contacts than are intended. Third the impact force between the tip and drain can be several times greater than the force in the closed position. These last two phenomena can prematurely degrade the contact surfaces. Attempts have been made to tailor the actuation voltage in order to reduce both the impact force and contact bounce [3]. Switches can fail in either of two failure modes. In one mode the contact resistance decreases with cycling. This behavior, while seemingly not a problem, is symptomatic of the contact being cleaned due to repeated contacts (i.e. “contact scrub” as it is known in the industry). As the resistance decreases the force of adhesion increases between these clean metal-to-metal contacts, eventually causing the switch to stick shut when the restoring force in the beam is insufficient to pull the contacts apart [4]. Another failure mechanism is a steady increase in contact resistance until the point at which the switch is no longer useable. These failures are attributable to the growth of contamination in the form of a friction polymer on the contacting surfaces [5]. Another measure of switch performance is intermodulation distortion which quantifies the distortion of a pair of harmonic RF signals with nearly equal frequencies. The beating between two such components causes the power to vary relatively slowly, i.e. at the beat frequency. This beat frequency may be sufficiently close to the thermal response time of the switch leading to distortion and false signals in the frequency range of interest [6].

scholarly journals The FAST/SKA Site Selection in Guizhou Province

2001 ◽  
Vol 182 ◽  
pp. 213-218
Author(s):  
B. Zhu ◽  
Y. Nie ◽  
R. Nan ◽  
B. Peng
Keyword(s):  
Remote Sensing ◽  
Information System ◽  
Geographic Information System ◽  
Site Selection ◽  
Guizhou Province ◽  
Radio Telescopes ◽  
3 Dimensional ◽  
Gis Technologies ◽  
Spherical Antenna ◽  
Field Investigations

AbstractMany karst depressions with diameters of 300 m to 500 m, suitable for constructing Arecibo-style radio telescopes, were identified in the south of Guizhou Province by Remote Sensing (RS) and Geographic Information System (GIS) technologies together with field investigations. Fundamental topography and landform databases were established for 391 candidate depressions, and using GIS the 3-dimensional images of depressions, at a scale of 1:10000, were then simulated to fit a spherical antenna.

Dynamic Mechanical Behavior of Aluminum Alloy Mortise-and-Tenon T-Joints

2018 ◽  
Vol 777 ◽  
pp. 533-537
Author(s):  
Hui Yuan Xiong ◽  
Zhi Peng Luo
Keyword(s):  
Experimental Investigation ◽  
Aluminum Alloy ◽  
Failure Modes ◽  
Bending Moment ◽  
Restoring Force ◽  
T Joints ◽  
Failure Characteristics ◽  
Dynamic Mechanical Behavior ◽  
Rigid Connection ◽  
Mortise And Tenon

An experimental investigation was conducted on aluminum alloy mortise-and-tenon T-joints (MT-joints) under dynamic cyclic loading. The MT-joints strengths, stiffness, failure characteristics, hysteresis curves, skeleton curves, restoring force models and energy dissipation curves of the joints have been reported. It’s shown from the experiment that main failure modes of the MT-joints are plastic deformation of squeezing area and tenon divorced from joint. And MT-joints structure is a typical semi-rigid connection that can withstand both rotation and bending moment.

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