Heavy Hammer Research Articles

Modification of a wideband spectral-acoustic method for controlling stress state of a face space

To control and manage a stress state of an underground working face space it is important to measure the components of actual stresses. Traditional method for relieving a core-sample with central drill is time and labour consuming and is characterized by a lack of accuracy. To improve these issues geophysical methods which do not interfere with mining are to be used for controlling stress state. Acoustic methods are less time and labour consuming. Justification of spectral-acoustic method modification for controlling stress state of a face space is introduced. It is done on the basis of the dependence of the acoustic signal of the operating equipment amplitude-frequency response median on average stresses. The acoustic signal is recorded in the entire sensitivity band of the geophone. The description of a flow chart and operating principle of intrinsically safe portable device for implementing the modification in mines on the seams dangerous on gas and dust and prone to sudden coal and gas outbursts and rock bursts are given. The device operates in three modes: determining amplitudes of background noise and setting signal amplification coefficient; controlling stress state while generating continuous acoustic signal produced by operating mining equipment (combined machine, drilling device, plough-type machine) into the massif; control of stress state during generation a discrete acoustic signal produced by artificial source (heavy hammer strokes) into a massif.

From Cryptomania to Obfustopia Through Secret-Key Functional Encryption

Functional encryption lies at the frontiers of the current research in cryptography; some variants have been shown sufficiently powerful to yield indistinguishability obfuscation (IO), while other variants have been constructed from standard assumptions such as LWE. Indeed, most variants have been classified as belonging to either the former or the latter category. However, one mystery that has remained is the case of secret-key functional encryption with an unbounded number of keys and ciphertexts. On the one hand, this primitive is not known to imply anything outside of minicrypt, the land of secret-key cryptography, but, on the other hand, we do no know how to construct it without the heavy hammers in obfustopia. In this work, we show that (subexponentially secure) secret-key functional encryption is powerful enough to construct indistinguishability obfuscation if we additionally assume the existence of (subexponentially secure) plain public-key encryption. In other words, secret-key functional encryption provides a bridge from cryptomania to obfustopia. On the technical side, our result relies on two main components. As our first contribution, we show how to use secret-key functional encryption to get “exponentially efficient indistinguishability obfuscation” (XIO), a notion recently introduced by Lin et al. (PKC’16) as a relaxation of IO. Lin et al. show how to use XIO and the LWE assumption to build IO. As our second contribution, we improve on this result by replacing its reliance on the LWE assumption with any plain public-key encryption scheme. Lastly, we ask whether secret-key functional encryption can be used to construct public-key encryption itself and therefore take us all the way from minicrypt to obfustopia. A result of Asharov and Segev (FOCS’15) shows that this is not the case under black-box constructions, even for exponentially secure functional encryption. We show, through a non-black-box construction, that subexponentially secure-key functional encryption indeed leads to public-key encryption. The resulting public-key encryption scheme, however, is at most quasi-polynomially secure, which is insufficient to take us to obfustopia.

Simulation of dynamic compaction and analysis of its efficiency with the material point method

Dynamic compaction of rockfill is simulated by the material point method, and the compaction mechanism as well as the factors that influence the compaction efficiency are investigated. The rigid-flexible contact algorithm is further developed to simulate the dynamic contact of the hammer with soil. A density-dependent soil constitutive model for coarse grained soil is proposed, which is applicable for the analysis of soil subjected to high stress, as that under dynamic compaction. The simulation results are in good agreement with the experimental data from the construction site of the Chinese Chengde Airport. A new concept, the “effective energy ratio”, defined as the ratio of the plastic strain energy absorbed by volumetric compression deformation to the total tamping energy, is introduced to measure the effective proportion of the energy applied, which induces actual compaction of soil, and the influence factors on the effective energy ratio are studied. Especially, a comprehensive comparison is made between a low drop of a heavy hammer and a high drop of a light hammer. Moreover, an approximate formula for the effective improvement range of dynamic compaction is established, and an appropriate tamping point spacing is suggested through simulations of multipoint tamping.

A Comparative Test Study of the Impact Performances of Stainless-Steel Rebar Equal-Strength Replacement Piers

It has been found that there are rebar instability and construction complexity phenomena associated with the replacements of ordinary pier rebars with stainless-steel rebars of equal piece numbers and strength. Therefore, this study explored the issues of the equal-strength replacements of stainless-steel pier rebars with different distributions. The study utilized the most advanced domestic multi-function super-high heavy hammer impact test system available, and conducted a comparative test of the horizontal impact results of two groups of pier models with 1/5 contraction scales. The purpose of the testing was to analyze the impact force, impact displacement, strain time history curve, crack propagation and distribution, ultrasonic damages to the concrete, and so on. The test results showed the following: The original specimen displayed a consistent variation trend with the equal replacement specimen of the stainless-steel rebar of different distributions from the aspects of the maximum impact force, strain of the rebar and concrete, displacement peak, and so on, under the conditions of continuous multiple impacts. The relative variation rate was found to be within the scope of ± 10% under equal impact energy. The quantity and distribution of the cracks, as well as the concrete damages, were also found to be approximately consistent under equal impact energy. Therefore, in this study, it was considered to be feasible for the solution of the problems related to rebar corrosion, strength surplus, resource waste, and so on, to replace ordinary pier rebars with stainless-steel rebars with equal-strength and different distributions.

Analyzing chaotic effect of reinforced concrete pile driving in cohesive soil

This paper presents the chaos phenomenon in pile driving. Firstly, the pile wave equation that Smith put forward is used for painting Poincare section, and then the basic features of chaos are obtained. By analyzing the Poincare section, a point with which the ratio of penetration to velocity is the largest is discovered, and that is to say energy consumption is the lowest at this point. Moreover, the relationship between hammer weight and dropping height is proved to satisfy the construction experience of light blow with heavy hammer through curve fitting. So according to the theory, the value of impact force and initial value can change to get the hammer weight and dropping height for different square and circular piles under the lowest energy consumption. The results show it is better to use square piles during driving, and the relationships between square and circular piles with different cross-sections and its impact force on pile top, hammer weight and dropping height satisfy a certain function equation, respectively. Hence, the corresponding hammer weight and dropping height can be selected to save energy consumption and reduce the cost during construction according to their functional relation.

A Stereo-Vision System for Measuring the Ram Speed of Steam Hammers in an Environment with a Large Field of View and Strong Vibrations.

The ram speed of a steam hammer is an important parameter that directly affects the forming performance of forgers. This parameter must be monitored regularly in practical applications in industry. Because of the complex and dangerous industrial environment of forging equipment, non-contact measurement methods, such as stereo vision, might be optimal. However, in actual application, the field of view (FOV) required to measure the steam hammer is extremely large, with a value of 2–3 m, and heavy steam hammer, at high-speed, usually causes a strong vibration. These two factors combine to sacrifice the accuracy of measurements, and can even cause the failure of measurements. To solve these issues, a bundle-adjustment-principle-based system calibration method is proposed to realize high-accuracy calibration for a large FOV, which can obtain accurate calibration results when the calibration target is not precisely manufactured. To decrease the influence of strong vibration, a stationary world coordinate system was built, and the external parameters were recalibrated during the entire measurement process. The accuracy and effectiveness of the proposed technique were verified by an experiment to measure the ram speed of a counterblow steam hammer in a die forging device.

COMMUNITY-DRIVEN MODELS FOR SAFETY AND JUSTICE

AbstractThe U.S. criminal justice system is defined and fueled by foundations and principles that uphold harmful power dynamics such as white supremacy, further destabilizing communities that face intersecting structural barriers. This paternalistic system is characterized by the imposition of punishments—including fees, fines, penalties, and deprivation of freedom and even life—that are meted out disproportionally to people of color and people living in poverty. More often than not, policymakers and justice practitioners fail to solicit the views, experiences, and expertise of community members and justice system-involved individuals, leading to policies and practices crafted under the auspices of promoting safety that undermine community stability instead. Consistent with Square One ’s charge to “reimagine how we create justice,” this paper describes approaches that communities around the country employ to craft, lead, and participate in their own public safety strategies. The paper will offer examples of crime prevention work, investment and divestment efforts, and policy reform initiatives developed and guided by people most likely to experience crime and the heavy hammer of the traditional justice system. This paper will explore the promises, strengths, and challenges associated with each approach, presenting a range of creative strategies for residents—in partnership with the broader community of advocates, activists, and researchers—to adapt, own, and implement.

Bearded capuchin monkeys use joint synergies to stabilize the hammer trajectory while cracking nuts in bipedal stance.

The transition from occasional to obligate bipedalism is a milestone in human evolution. However, because the fossil record is fragmentary and reconstructing behaviour from fossils is difficult, changes in the motor control strategies that accompanied this transition remain unknown. Quadrupedal primates that adopt a bipedal stance while using percussive tools provide a unique reference point to clarify one aspect of this transition, which is maintaining bipedal stance while handling massive objects. We found that while cracking nuts using massive stone hammers, wild bearded capuchin monkeys (Sapajus libidinosus) produce hammer trajectories with highly repeatable spatial profiles. Using an uncontrolled manifold analysis, we show that the monkeys used strong joint synergies to stabilize the hammer trajectory while lifting and lowering heavy hammers. The monkeys stringently controlled the motion of the foot. They controlled the motion of the lower arm and hand rather loosely, showing a greater variability across strikes. Overall, our findings indicate that while standing bipedally to lift and lower massive hammers, an arboreal quadrupedal primate must control motion in the joints of the lower body more stringently than motion in the joints of the upper body. Similar changes in the structure of motor variability required to accomplish this goal could have accompanied the evolutionary transition from occasional to obligate bipedalism in ancestral hominins.

Experimental Study on the Impact Properties of Concrete Bridge Pier Reinforced with Stainless Steel Rebar

Abstract In this study, in order to examine the impact properties of a stainless steel reinforced concrete bridge pier under the conditions of horizontal impact load effects, a multifunction ultrahigh heavy drop hammer impact test system was utilized. The stainless steel reinforced concrete bridge piers had different impact energies, and the impact force time-history, displacement time-history, and strain time-history curves, as well as the crack developing state, were obtained during the testing. The test results showed that the peak values of the impact force, strain, and displacement increased with the increase of the impact energy under the impact load, and the fluctuation frequency also increased. The crack development was mainly concentrated in the lower frontal section of the bridge pier, as well as the middle and lower sections of the back of the bridge pier.

Prediction of pile running during the driving process of large diameter pipe piles

Offshore platforms in deep seas require extremely long large diameter pipe piles (LDPPs) to support the loads generated from the structure itself, wind and waves. One of the construction issues related to the installation of a LDPP into a seabed is pile running. Unexpected pile running during the LDPP driving process may break the steel wires connected to the heavy hammer or may cause the loss of the hammer into the sea. An analytical method to predict the occurrence of pile running is proposed in this paper. The framework for determining the calculation parameters from a laboratory or field test are established. The dynamic resistance of the surrounding soil during the pile driving process is considered through analysis of the soil sensitivity and the induced excess pore water pressure. Three case studies were conducted to verify the accuracy of the proposed method. Good agreement indicated that the proposed method is capable of predicting pile running during the driving process of LDPPs in layered soil deposits.

Beat map drawing method for large oriental bell based on operational deflection shape method

Oriental bells produce a peculiar sound in the form of beats, which are periodic repetitions of strong and weak sounds. A beating sound with a proper period gives the illusion of the bell being alive and breathing. To produce a good beating sound, appropriate modal parameters are required for beat tuning after casting the bell. Conventionally, modal parameters were extracted using frequency response functions of the excitation and response signals. However, a large oriental bell is usually struck by a heavy wooden hammer and hence, only the response signal can be measured. In this study, we extract the modal parameters using the response signal only and employ the data to predict the beat properties of the bell sound. Finally, the validity of the predicted beat properties is experimentally verified for a large oriental bell.

The Enduring Ambiguities of Antitrust Liability for Worker Collective Action

This Article examines the origins of the rule that antitrust law regulates and largely prohibits collective action by workers who fall outside the bounds of employment, and who therefore presumptively do not receive the benefit of the labor exemption from antitrust. The threat that organizing for decent wages and working conditions will be prosecuted as price-fixing is a powerful constraint upon such workers' ability to take action to change their circumstances. Antitrust has historically structured the nature and content of labor regulation in this country, and it is currently poised to do so again in a new form. It did so directly and punitively in the Gilded Age. During the New Deal era, the default rule that worker collective action is illegal under antitrust actually solidified its subterranean hold while the law of the labor exemption mostly blunted its practical effects. In today's deregulation era, it is of increasing significance in regulating workers who fall outside the bounds of the NLRA (and other employment and labor law); as a limit upon new forms of labor regulation that would bring these nontraditional workers within their scope; and as a potential baseline for labor law reform generally. Antitrust has irreducible political and normative content, despite its sometime claim of being justified on economic grounds that are independent of politics and moral norms. The key cases show that such extrinsic normative considerations operate, albeit tacitly, in antitrust's relationship to labor, which has changed over time according to the specific policy project embraced by decision-makers. The default rule that workers and other less-powerful economic actors are subject to the heavy hammer of the price-fixing doctrine for cooperation in pursuit of a decent livelihood ought to be revisited.

A universal rig for supporting large hammer drills: Reduced injury risk and improved productivity

Drilling holes into concrete with heavy hammer and rock drills is one of the most physically demanding tasks performed in commercial construction and poses risks for musculoskeletal disorders, noise induced hearing loss, hand arm vibration syndrome and silicosis. The aim of this study was to (1) use a participatory process to develop a rig to support pneumatic rock drills or large electric hammer drills in order to reduce the health risks and (2) evaluate the usability of the rig. Seven prototype rigs for supporting large hammer drills were developed and modified with feedback from commercial contractors and construction workers. The final design was evaluated by laborers and electricians (N=29) who performed their usual concrete drilling with the usual method and the new rig. Subjective regional fatigue was significantly less in the neck, shoulders, hands and arms, and lower back when using the universal rig compared to the usual manual method. Usability ratings for the rig were significantly better than the usual method on stability, control, drilling, accuracy, and vibration. Drilling time was reduced by approximately 50% with the rig. Commercial construction contractors, laborers and electricians who use large hammer drills for drilling many holes should consider using such a rig to prevent musculoskeletal disorders, fatigue, and silicosis.

Geological difficulties and countermeasures for socket diaphragm walls in weathered granite in Shenzhen, China

In Shenzhen, a complex series of folds and fractures, and intensive metamorphism took place during the pre-Caledonian, Caledonian, and Hercynian to Indosinian orogenies. Then, Yanshanian orogeny, with the most tectonic movement, occurred. Strong invasive activity of granitic magma, a massive blowout of acidic volcanic rock, and magmatism-related mineralisation are the features of Yanshanian orogeny. Moreover, deep faults were also developed and wide folds were formed. A large amount of granite rock was formed from the Yanshanian orogeny in Shenzhen. The outcrop area of the granite in Shenzhen reaches 760 km2, almost covers 50 % of Shenzhen land area. Granite is primarily susceptible to chemical weathering. Though weathered, granite and solitary granite boulders are of high uniaxial compressive strength (UCS). The weathered granite may be covered by Quaternary soil with low shear strength, such as backfill, sand, silty clay, and clay. The thickness of the Quaternary soil ranges from 0 to 40 m. Socket diaphragm walls are usually adopted during deep excavation construction in Shenzhen for their safety and low impact on the surrounding environment. When the excavation depth is increased, the socket diaphragm walls are embedded in weathered granite to a depth of between 3 and 10 m. However, the traditional socket diaphragm wall construction is only viable in soft ground, as it is not practical to penetrate hard weathered granite. As a consequence, difficulties arise during construction in the Shenzhen region, such as difficulty in breaking down the rock, socket diaphragm wall collapse and leakage. To solve these construction problems, countermeasures, such as monitoring, heavy hammer dropping, smooth blasting and a modified slurry, are proposed in this study. It can be concluded that the heavy hammer dropping method should be chosen to deal with weathered granite with a UCS of less than 50 MPa and the smooth blasting method should be adopted to deal with weathered granite with a UCS of more than 50 MPa. A case study of a metro station excavation using the smooth blasting method in Shenzhen is also introduced. The successful construction of the socket diaphragm walls demonstrates the applicability of the smooth blasting method.

Dynamic Characteristics of a Beam in an Existing Brick-concrete Structure

With heavy hammer hammering method and road roller vibrating fixed-point method, field tests on dynamic characteristics were conducted for the brick-concrete structure beam of a teaching building. The experiment results of heavy hammer hammering method show that the horizontal and vertical natural frequencies of the heavy hammer are respectively concentrated in 2.726 ~ 5.313 Hz and 3.596 ~ 9.104 Hz, horizontal and vertical peak acceleration values are respectively 489.56 ~ 532.05 m/s 2 and 248.77 ~ 494.61 m/s 2

Dynamic force calibration by impact excitation

Introduce a method of dynamic force calibration by impact excitation. An analysis of the 200kN standard dynamic force calibration equipment at NIM is presented. The heavy hammer and the force transducer under test are brought to collision, and the impact force is measured by laser-Doppler interferometer. Traceability of force is realized by the determination of mass and acceleration. Two experiments were introduced and a typical example of impact process was performed.

Buckling Analysis of Pile during Hammer Placement

Large diameter and thin thickness are the main characteristics of the steel pipe piles in offshore engineering. Before piling a pile, heavy hammer will be placed on the top of it, which may emerge a serious risk in pile buckling. A three dimensional finite element model of pile and soil was established for a case study. The modified Riks method which can automatically search a suitable increment factor of loads is adopted to assess the stability of the pile, and the geometric nonlinearity and pile-soil interaction were both considered. The practical example shows that the critical load considering pile-soil interaction is much smaller than that in a fixed constraint.

Consolidation Effect and Influencing Factors of Dynamic Compaction for Filling Subgrade

The parameters of dynamic compaction impacting on consolidation effect such as fall-height of hammer, impact mode, impact space, etc. are analysed by dynamic FEM method. The method of choosing parameters of dynamic compaction and consolidation effect of dynamic compaction on filling subgrade are illuminated by field test. Conclusions are drawn: with the increase of impact energy, the range of plastic deformation zone will extend to a certain depth in subgrade, which will certainly expand the effective reinforcement range of subgrade; optimal impact times of a subgrade is available; the consolidate depth and influencing area by light hammer with heavy impact is less than that by heavy hammer with light impact when impact energy is equal; with the increase of hammer diameter, both deformation and strain of subgrade reduce under the same impact energy.

Dynamic soil parameters and Case damping for high-capacity long H-piles

Uncertainty exists in signal-matching techniques. The quake and damping obtained may not be the actual response of the soil. In this paper, the final sets, strain gauge readings, pile driving analyzer, and Case pile wave analysis program of 12 high-capacity long H-piles at the end of initial driving as well as two of them at restrike are studied. Measured and deduced data show that the soil response underneath the pile toes has limited movement and yielding despite the piles being set using very heavy hammer rams and large ram drops. The quake and damping decrease with increased shearing strain and shearing stress, but are influenced by pile whipping, rebounded stress wave, and load-transfer mechanism. The lumped Case damping factor decreases with increased side resistance to total resistance ratio. This factor can decrease or increase with time due to changes in the load-transfer mechanism after set-up, thus affecting the proportion of viscous damping of soil along the pile shaft and at the pile toe. A Case damping model is proposed that approximates the lumped Case damping factor as the sum of hysteretic damping of the pile and viscous damping of the surrounding soil. The effects of variation in load distribution and set-up along the pile shaft in layered soils and incomplete mobilization of soil at the pile toe on the Case damping factors are explained.

Reliance

Reliance Catherine Reid (bio) I back the tractor out of the barn, get down on my hands and knees, and study the way the mower is attached. Two familiar messages sound equally loud in my head: I can do this. And, Can I do this? One of the blades had come off earlier in the week, when Holly was mowing, in a terrible grinding and strewing of metal parts. And now, though I’d rather be at the river or working in the garden, I kneel instead in gravel, remove the cotter pins, and free the bolts holding the main pulley in place. After dragging out the mower, I flip it over, a turtle on its back, missing one of its legs. The other is badly bent, and both it and the one still attached are so dull and pitted it’s hard to tell how the edges sliced grass. I take off the second blade and rue that I don’t have an anvil or large vise. I make do with a maul and a concrete block, slamming the heavy hammer against the bent blade a few times. Then I push a block of wood into the shade for a stool, sit down with the blade clamped between my feet and start filing, diagonal strokes toward the edge, black metal slow to yield silver. As sweat gathers on my back, I think how much easier it would be to borrow a truck, take the tractor to a repair shop, and let someone else deal with grease and scraped skin. But something insists that I do this myself, something that won’t relax its hold on me, and while often I like the stance such independence affords, it’s a trait that has also gotten me into trouble. An hour or so later, the pieces back together, I start the tractor, engage the mower, and shift into gear. The tractor bucks and shudders, and I know I didn’t reshape the blade quite right, but this time nothing flies off and I can see cut grass in my wake. I circle the lower field and head home for a beer. [End Page 17] “Why did you learn how to do that?” the horse whisperer asks. We’re eating pieces of yellow sheet cake in a room full of prisoners, and the best I can manage is a shrug. He deserved something better. We were, after all, the team that won at Pairs for Chairs, our arms linked together as we raced for a seat each time the music stopped. Elbow to elbow, we had had to find the right balance between caution and roughness—yank too hard and it might be misconstrued; don’t yank hard enough and you might miss a chair. We kept from getting tangled in each other’s legs and were the only ones left sitting when the game came to an end. But finding a better answer than “because I’m a dyke” or “self-reliance is in my genes” or “I drink of the same waters as did Emerson and Thoreau” requires too much explaining. I’m still not even sure why I’m spending a weekend in prison with men convicted of violent crimes. I do know it’s a good program—the Alternatives to Violence Project—co-led by outside facilitators and inmates who have already gone through the training. My role is similar to that of the twenty-odd prisoners, except that I get to go home to my lover at night. Like the men, however, I had much to surrender at the main entrance, including autonomy and a driver’s license; unlike them, I didn’t have to strip or get orifices checked, and the metal detector’s sweep around my body was brief. When the first session finally began—some of the men having waited months for this—we sat in a circle and learned about the games we would play, the exercises we would do, the times we would pair up or talk as a whole group. Then we were off at a pace that seemed edgy and fast, the inmates white and black and Hispanic, teenaged and...