Dynamic Characteristics of Reinforced Concrete Beams Made of Carbonate Concrete

The ability of solid structures to absorb a certain part of the energy of dynamic impacts has not been properly reflected in impact theories. Meanwhile the effect of material properties on the various structures in the impact is so much that ignoring it when the solution of a large number dynamic problems makes it impossible to explain without distorting quantitatively and qualitatively, many of the actually observed phenomena, for example, equalization of dynamic stresses in places of their concentration and fluctuation of other parameters. In the article, two independent parameters for conventional reinforced concrete beams and those made of limestone concrete are compared, namely dynamic coefficient and the values of elastic rebound in impact. The effect of the reinforcement is not discussed in the paper.

UNFORMALIZED ASPECTS OF APPLICATION THE NON-DESTRUCTIVE METHODS FOR DETERMINATION OF CONCRETE QUALITY ON ROAD CONCRETE COATINGS

Formulation the problem. Experience with the use of non-destructive testing devices shows that theadjustment of calibration dependences in the conditions of damaged concrete surfaces is difficult. Usually quantitativeanalysis is replaced by qualitative, and methods that allow you to return to the quantitative assessment are notstandardized. That is, the adequacy of property definitions needs to be increased. The purpose of the study is todetermine the possibilities of increasing the adequacy in the using of non-destructive testing devices and to study theinfluence of the peculiarities of the technology of manufacturing concrete pavements on the measurement results.Results: It has been performed a visual inspection of the condition of the coating structure on the basis of currentregulations. The study was performed using an ultrasonic device "Novotest IPSM-U" and a device "Onyx 2.5" (shockpulse method). Measurements were performed both on the surface of the concrete pavement and on the samples takenfrom the structure. During the work, project materials and passports for the concrete mixture were used. Conclusions.Studies have shown that: to obtain evidence-based results in the application of non-destructive methods for determiningthe quality of concrete road pavements, existing methods need to be improved and formalized; it needs to be clarifiedand formalized the methods of providing acoustic contact of receivers − transmitters of ultrasonic vibrations with theconcrete surface and the conditions of interaction the indentors with the concrete surface during the implementation ofthe method of elastic rebound; it is necessary to develop and standartize a method for determining the properties of theconcrete mixture based on the properties of concrete.

Dynamics of Rubber Band Stretch Ejection

Why do stretched rubber bands not hit the hand after ejection? What is the mechanism behind the rubber band ejection dynamics? These questions represent a fascinating scientific problem. Because the size of a rubber band in the circumferential direction is much larger than that in the other two directions of its cross section, we regard the rubber band as a slender beam and establish a mathematical model of the dynamics of the rubber band stretching and ejection. Furthermore, we obtain the dependence of the dynamic curvature of the rubber band on the arc length and time. We used the finite element software ABAQUS to simulate the dynamic process of rubber band stretching and ejection. The simulation results and dimensional analysis were performed to examine the effect of the bending elastic rebound velocity. The mathematical model and simulation results revealed that the relationship between the curvature and time at the end of the rubber band ($s =0$) was as follows: $\kappa\sim t^{-{1}/{2}}$. This research has guiding significance for the design of rubber bands as elastic energy storage devices.

MODELING THE PROCESS OF INSPECTION OF REINFORCED CONCRETE SUPPORTS OF TECHNOLOGICAL OVERPASSES

The paper presents the process of assessing the technical condition of reinforced concrete supports of existing technological overpasses. The characteristics of overpasses are given. Defects identified in the process of assessing the technical condition are shown. The paper describes the control of concrete strength by the non-destructive method of elastic rebound using the Digi Shmidt 2000 device and the determination of the concrete cover thickness and the location of reinforcement by the magnetic method using the Profometer-5S device. The layout of the working reinforcement in the reinforced concrete supports of the overpass section has been determined. The results of verification calculations of the structures of technological ramps are given, taking into account the revealed defects and damages, the strength of materials and the specified actual loads. Proposals are given for improving the performance of concrete of reinforced concrete supports of overpasses.

Dynamics of Rubber Band Stretch Ejection

Why do stretched rubber bands not hit the hand after ejection? What is the mechanism behind the rubber band ejection dynamics? These questions represent a fascinating scientific problem. Because the size of a rubber band in the circumferential direction is much larger than that in the other two directions of its cross-section, we regard the rubber band as a slender beam and establish a mathematical model of the dynamics of the rubber band stretching and ejection. Furthermore, we obtain the dependence of the dynamic curvature of the rubber band on the arc length and time. We used the finite element software ABAQUS to simulate the dynamic process of a rubber band stretching and ejection. The simulation results and dimensional analysis were performed to examine the effect of the bending elastic rebound velocity. The mathematical model and simulation results revealed that the relationship between the curvature and time at the end of the rubber band ($s =0$) was as follows: $\kappa\sim t^{-{1}/{2}}$. This research has guiding significance for the design of rubber bands as elastic energy storage devices.

Activated Shale Creep and Potential Micro-Annulus Investigated in the Field

It has been demonstrated that creeping shales can form effective hydraulic well barriers. Shale barriers have been used for many years in P&A of wells in Norway. More recently, shale barriers for zonal isolation have also been used in new wells where shale creep was found to occur within days. In some cases, shale creep is activated by a reduction in annulus pressure, in other cases shale creep sets in without any active activation, possibly by time-dependent formation-pressure changes. However, the presence of thixotropic fluids (drilling muds) in the annulus may prevent full closure of the annulus as it requires large pressure differentials to squeeze the fluid out of a microannulus. Furthermore, elastic rebound of an actively activated shale barrier could result in a microannulus and hence a possible leakage pathway. Improved logging technology is needed for identifying shale barriers and the presence of micro-annuli in shale-barrier zones. We use cement bond log data and standard bond logging criteria to evaluate the quality of the shale well barriers (Williams et al., 2009). In addition, in order to detect microannuli on the outside of the casing, a new inversion algorithm for the bond logging data was developed and tested on field data. Later, we had the chance to apply the inversion algorithm to bond-log data obtained in the laboratory with a miniature bond-logging tool inside a cased hollow-cylinder shale-core sample place. It turned out that both the micro-annulus widths and shale velocities determined by the inversion technique were too high. By constraining the shale velocities to more realistic values, the updated microannulus widths were smaller and more consistent with the experimental results. Small microannuli may not cause any measurable leakage along the well, especially if filled with a thixotropic fluid. However, more studies are needed to quantify the impact of microannuli on the sealing capacity of shale barriers.

A transient in surface motions dominated by deep afterslip subsequent to a shallow supershear earthquake: the 2018 Mw 7.5 Palu case.

<div> <div> <div> <p>The 2018 <em>M<sub>w</sub></em> 7.5 Palu earthquake is a remarkable strike-slip event due to its nature as a shallow supershear fault rupture across several segments and a destructive tsunami that followed co-seismic deformation. GPS offsets in the wake of the 2018 earthquake display a transient in the surface motions of northwest Sulawesi. A Bayesian approach identifies (predominantly a-seismic) deep afterslip on and below the co-seismic rupture plane as the dominant physical mechanism causing the cumulative, post-seismic, surface displacements whereas viscous relaxation of the lower crust and poro-elastic rebound contribute negligibly. We confirm a correlation between shallow supershear rupture and post-seismic surface transients with afterslip activity in the zone below an inter-seismically locked fault plane where the slip rate tapers from zero to creeping.</p> </div> </div> </div>

Bridges maintainability evaluation peculiarities as part of hydraulic structures

Introduction: the article is dedicated to assessing the condition with respect to use for traffic methods of bridges as part of hydraulic structures (dams, hydroelectric power stations, locks). The main factors affecting the structural element’s durability included in the composition of the hydraulic structures are dynamic loads (applied repeatedly and repeated) affecting the bay due to the hydrodynamic effect; temporary, moving loads from passing highway transportation, along the top of the structure (along the roadway); harmful chemical impurities contained in the water passing through the structure. Under the influence of the above-mentioned factors, defects and damage occur in the hydraulic facilities’ structural elements. Methods: the authors assessed the actual state of the material of the operating structure. To assess structures and materials actual state during the bridge structure inspection work, the following instrumental measurements were performed on as-built structural elements: leveling the top of the sidewalks and the roadway; materials strength determination of the main supporting structures by nondestructive methods; thickness measuring the asphalt concrete pavement of the roadway; determination of the degree of carbonation of concrete; identification of defects in the elements of the bridge. The actual structure’s concrete strength was determined by nondestructive testing methods: (1) by the method of the elastic rebound; (2) by the shock pulse monitoring method; (3) an indirect method of concrete strength ultrasonic testing based on the revealed relationship between the method of separation with shear test and methods – shock pulse and elastic rebound. Results: technical condition and bridge safety indicators calculation as a hydraulic structure element was executed. Discussion: technical examination results of the bridge structural elements and instrumental studies confirm the conclusion about the repair measures need with high-strength concretes and protective coatings based on polymer composite materials. Final report: following the emergency scenarios a numerical estimate table for the quantitative and qualitative parameters list was made, parameters corresponding to a particular structure state. Thus, according to the scenario related to the 3rd accident group, the bridge technical condition is assessed as limited operable, and the safety level is reduced.