Papers by Keyword: Dynamic Strength

Abstract: The results of experimental studies of the impact strength of samples of concrete and steel fiber concrete are presented. For dispersed reinforcement, three types of steel fiber were used - with bent ends, wave and flattened. Tests were conducted to determine the static and dynamic bending strength, and then - impact tests on the pendulum headstock MK-30. It was found that the impact strength increases significantly in the presence of fiber, but the type of fiber has almost no effect on it. Since specimens reinforced with a fiber content of 1.0 and 1.5% differ slightly in impact strength, 1.0% dispersed reinforcement in volume is recommended, both under static and dynamic loads.

Abstract: Currently, significant part of advanced air transport structural elements is made of fiber-reinforced polymer composite materials (PCM), in particular, carbon plastics. In order to increase the resistance of these materials to static electricity and lightning discharges while air transport passes through lightning fronts, lightning protection coatings in the form of copper grids are incorporated into PCM structure . For load-bearing structures and aircraft shells, the influence of dynamic loads in the form of low-cycle high-amplitude loading and hitting by solid objects is typical. The presence of inbuilt metal structure introduces additional uncertainty into the anisotropic PCM perception of these loads. Studies of the strength of carbon-fiber-reinforced plastics with built-in LPC at low-cycle loading and their perception of shock load has been carried out. It is established that short-term processing in the microwave electromagnetic field leads to an increase in the strength of the samples under low-cycle loading by 210%. CFR with LPC absorbs a part of the shock impulse and does not transfer it completely to subsequent structures. The microwave electromagnetic field helps to improve the damping properties of materials by 19.5% in average with a low impact energy. With an increase in the impact force energy, the effect of the microwave electromagnetic field is manifested to a less extent; further improvement of the damping properties does not occur. It increases the elastic characteristics of the material and practically does not lead to cracking and exfoliation of the surface layer in the impact area. The results can be used in the development of technologies for final processing of the products made of PCM in order to increase their resistance to dynamic loads.

Abstract: The features of the formation of the structure and physical and mechanical properties of all-in-one compounds of low-alloy steels are studied. It is shown that the quality and strength properties of permanent joints depend on the energy parameters of the technological process of their manufacture. The technological process is accompanied by melting, transfer and crystallization of the weld metal from the melt, which has a dominant effect on the structure, indicators of static and dynamic strength of welded joints. The ranges of welding modes that have the greatest impact on the structural and mechanical properties of the zone of permanent joints in the temperature range from +20 degrees to minus 60 degrees Celsius. The results of the research can be widely used in the practice of repair and installation works of structures of the Northern design, working in conditions of naturally low climatic temperatures.

Abstract: In the article the results of the eccentrically compressed reinforced concrete element calculation operating under the dynamic loading in fire conditions are shown. The calculation of the compressed reinforced concrete element was carried out, taking into account the conducted experimental studies. The calculation showed that, depending on the temperature effects, the curvature of the reinforced concrete element in stages I and II decreases while the class concrete, which varies from 28.9% to 55%, is increasing. When the temperature reaches 250⁰, the cracking moment and the moment of internal forces at the end of the stage II are reduced to 22% with respect to these forces at normal conditions. With increasing temperature, the dynamic stiffness of the element in the stage I is reduced by 29.3%.

Abstract: This article presents a study of the strength of a 25-storey reinforced concrete frame against progressive collapse in fire conditions. Taking into account the angles of disclosure of plastic hinges as norming for the strength of reinforced concrete elements, a computer technology program has been developed and included in PR Wolfram Mathematica 10 for the dynamic calculation of compressed reinforced concrete elements under fire exposure on the basis of the conducted experimental studies. Dynamic calculation of the strength of eccentrically compressed reinforced concrete columns was carried out, with operation in normal conditions and under high temperatures. The diagram «moment-curvature» and the graph of the change of the static and dynamic strength of the column depending on the temperature were developed. Nonlinear dynamic analysis of a 25-storey reinforced concrete frame was conducted, taking into account the changes of the dynamic characteristics of reinforced concrete elements in fire and, the estimation of resistance of the frame was given.

Abstract: Introducing research progress of rate-dependent tests by domestic and foreign scholars, strain-rate effect on dynamic mechanical properties of concrete are reviewed. Classified descriptions of research results on dynamic load tests of concrete at home and abroad are provided, including uniaxial compression tests, uniaxial tensile tests, and multi-axis tests; strain-rate effects on concrete strength and deformation properties in each test are respectively discussed; and strain-rate effect on concrete energy absorption capability are described.

Abstract: Research of influence of fire impacts on the dynamic strength of eccentrically compressed concrete elements requires a deeper consideration. The purpose of this article is the study of dynamic strength of eccentrically compressed concrete elements in fire conditions under rapidly increasing dynamic loading. It is done the analytical calculation of eccentrically compressed reinforced concrete columns under different thermo powers conditions, there are shown the results of calculations and experimental data. It is shown a graph of dynamic coefficient for concrete depending on the time of dynamic loading and temperature.

Abstract: Experiments on the dynamic behavior of ice in compression were carried out by means of SHPB apparatus. The specimens were to-10°C~-25°C and the tested strain rate ranged from 700/s to 1000/s. Strain-rate effects and the influence of freezing preserve time were studied. It was observed that the dynamic compressive strength of ice has an effect of strain-rate enhancement and the freezing preserve time has no influence to its dynamic compressive strength. In addition, a Pulse shaping technique to avoid the specimen failing before stress uniformity in ice specimen was presented.

Abstract: Based on the multi-body system dynamics in the ADAMS environment, a virtual prototype of the reel fulcrum of crane was developed. In this model, the whole system was disassembled lifting mechanism system with flexible body dynamics model of the wire rope. The virtual running environment was established according to the actual crane operation cases, which is designed the hanging & lifting working process. It is the key step to build the reel fulcrum dynamics model for performance analysis of system dynamics, which is the basis for the optimize design of the reel fulcrum of crane. Theoretical model analysis usually does not consider the coupling force status of the reel fulcrum of crane. It is a steady-state analysis to the reel fulcrum of crane models. These models have played an important role in the assessment of the reel fulcrum of crane performance and the system parameters, but do not reveal the interaction of the reel fulcrum of crane and the wire rope, which fail to be a comprehensive understanding practical system dynamics characteristic. Virtual prototype simulation results will be applied to prototype design and evaluation, and save a lot of manpower and material resources. At the same time,the method has an advantage for dynamics analysis to simulating some dangerous movement conditions, which is hard to be replayed or simulated at the test actual working condition site. In particular, some cases cannot be recurrence in the accident handling process. The simulation results show that the response value. Variable stiffness characteristics of wire rope of hoisting mechanism are implemented successfully through discrete multiple rigid body being applied to the wire rope in this paper. The establishment of the Reel fulcrum dynamic model is based on ADAMS, which realizes the reel fulcrum of crane system coupling modeling. These results show that the model reflects the actual dynamics of the reel fulcrum of crane, and also presents that some of the theoretical analysis results cannot be usually confirmed.

Abstract: In this paper, we conducted static push-out simulations of perfobond shear connectors (PBL) using SPH (Smoothed Particle Hydrodynamics), and validated their static strength and failure mechanism. In order to express hydrostatic pressure dependency of concrete in the analysis, The Drucker-Prager criteria with plane cap model and damage concept caused by compression fracture were applied. Appropriateness of constitutive model for concrete was confirmed on their static behaviors comparing with triaxial compression tests. Secondly, dynamic push-out test simulations were conducted using this model. The influence of input load velocity on strength and failure mechanism of perfobond shear connectors was examined.