• Geomechanics and Engineering
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• v.28 no.2
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• pp.117-133
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• 2022

Determination of the mechanical behaviour of jointed rock masses has been a challenge for rock engineers for decades. This problem is more pronounced for non-persistent jointed rock masses due to complicated interaction of rock bridges on the overall behaviour. This paper aims to study the effect of a non-persistent joint set configuration on the mechanical behaviour of rock materials under both uniaxial and biaxial compression tests using a discrete element code. The numerical simulation of biaxial compressive strength of rock masses has been challenging in the past due to shortcomings of bonded particle models in reproducing the failure envelope of rock materials. This problem was resolved in this study by employing the flat-joint contact model. The validity of the numerical model was investigated through a comprehensive comparative study against physical uniaxial and biaxial compression experiments. Good agreement was found between numerical and experimental tests in terms of the recorded peak strength and the failure mode in both loading conditions. Studies on the effect of joint orientation on the failure mode showed that four zones of intact, transition to block rotation, block rotation and transition to intact failure occurs when the joint dip angle varies from 0° to 90°. It was found that the applied confining stress can significantly alter the range of these zones. It was observed that the minimum strength occurs at the joint dip angle of around 45 degrees under different confining stresses. It was also found that the joint orientation can alter the post peak behaviour and the lowest brittleness was observed at the block rotation zone.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.10
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• pp.162-169
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• 2004

High temperature uniaxial compression tests in the alpha single phase region were carried out on the Ti -43mo1%Al intermetallic compound, in order to obtain oriented lamellar microstructure. The compression deformation temperatures and strain rates are from 1573k to 1623k and 1.0x10$^{-4}$ s to 5.0x10$^{-3}$ s, respectively. Fully lamellar microstructure was observed after the uniaxial compression deformation in a single phase region followed by cooling to room temperature. Lamellar colony diameter depended on strain rates and test temperatures. The diameter varied between 8601m and 300fm. Stress-strain curve showed a work softening and the size of lamellar colony diameter varied depending on peak stresses. This shows the occurrence of dynamic recrystallization. Texture measurements after the uniaxial compression deformation, showed the development of fiber during dynamic recrystallization. It is seen that the area for the maximum pole density existed in 35 degrees away from the compression plane. The texture sharpens with a decrease in strain rate

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.993-998
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• 2009

This study was conducted to propose the model that is able to predict long-term settlement of sands containing carbonates. We can observe that in addition to the initial elastic compression, a considerable additional compression occurs with long-term period in some sands. The compressibility of sands is significantly dependent on particle characteristics. Some sands have many pores and particularly has an angular shape. To predict of long-term settlement of these sands which contain carbonates, first of all a variety of tests which are to assess chemical, physical and compression characteristics of these sands were conducted. Second, in order to know settlement with time, the time parameter was determined by analyzing the measured data obtained from $\bigcirc\bigcirc$ area. The measured settlement of this area shows that in addition to the initial elastic compression, a considerable additional compression occurring with time. It was caused by the crushing, shattering, and rearrangement of particles, which were real phenomena in sandy soils under loading condition. Based on this case study, we proposed that a simple method is able to predict settlement with time of sandy soil containing carbonates.

• Steel and Composite Structures
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• v.39 no.3
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• pp.319-335
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• 2021

This study proposes a new and highly-accurate artificial intelligence model, namely ANN-IP, which combines an interior-point (IP) algorithm and artificial neural network (ANN), to improve the axial compression capacity prediction of elliptical concrete-filled steel tubular (CFST) columns. For this purpose, 145 tests of elliptical CFST columns extracted from the literature are used to develop the ANN-IP model. In this regard, axial compression capacity is considered as a function of the column length, the major axis diameter, the minor axis diameter, the thickness of the steel tube, the yield strength of the steel tube, and the compressive strength of concrete. The performance of the ANN-IP model is compared with the ANN-LM model, which uses the robust Levenberg-Marquardt (LM) algorithm to train the ANN model. The comparative results show that the ANN-IP model obtains more magnificent precision (R² = 0.983, RMSE = 59.963 kN, a20 - index = 0.979) than the ANN-LM model (R² = 0.938, RMSE = 116.634 kN, a20 - index = 0.890). Finally, a new Graphical User Interface (GUI) tool is developed to use the ANN-IP model for the practical design. In conclusion, this study reveals that the proposed ANN-IP model can properly predict the axial compression capacity of elliptical CFST columns and eliminate the need for conducting costly experiments to some extent.

• Advances in concrete construction
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• v.10 no.6
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• pp.559-571
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• 2020

This study aimed to inspect the axial compression mechanical performance of basalt-fiber-reinforced recycled - concrete (BFRRC)-filled square steel tubular stub column. The replacement ratio of recycled coarse aggregate (RCA) and the basalt fiber (BF) dosage were used as variation parameters, and the axial compression performance tests of 15 BFRRC-filled square steel tubular stub column specimens were conducted. The failure mode and the load-displacement/strain curve of the specimen were measured. The working process of the BFRRC-filled square steel tubular stub column was divided into three stages, namely, elastic-elastoplasticity, sudden drawdown, and plasticity. The influence of the design parameters on the peak bearing capacity, energy dissipation performance, and other axial compression performance indexes was discussed. A mathematical model of segmental stiffness degradation was proposed on the basis of the degradation law of combined secant-stiffness under axial compression. The full-process curve equation of axial compressive stress-strain was proposed by introducing the influencing factors, including the RCA replacement ratio and the BF dosage, and the calculated curve agreed well with the test-measured curve.

• Advances in concrete construction
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• v.11 no.3
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• pp.261-270
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• 2021

In this study, a new understanding is presented on the microcracking behavior of high strength concrete (HSC) with steel fiber addition having prior compressive loading history. Microcracking behavior at critical stress (σcr) region, using seven fiber addition volume of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0% was evaluated, at two aspect ratios (60 and 75). The specimens were loaded up to a specified compressive stress levels (0.70fc-0.96fc), and subsequently subjected to split tensile tests. This was followed by microscopic analyses afterwards. Four compressive stress levels as percentage of fc were selected according to the linearity end point based on stress-time (σ-t) diagram under uniaxial compression. It was seen that pre-compression has an effect on the linearity end point as well as fiber addition where it lies within 85-91% of fc. Tensile strength gain was observed in some cases with respect to the 'maiden' tensile strength as oppose to tensile strength loss due to the fiber addition with teething effect. Aggregate cracking was the dominant failure mode instead of bond cracks due to improved matrix quality. The presence of the steel fiber improved the extensive failure pattern of cracks where it changes from 'macrocracks' to a branched network of microcracks especially at higher fiber dosages. The applied pre-compression resulted in hardening effect, but the cracking process is similar to that in concrete without fiber addition.

• The Korean Journal of Emergency Medical Services
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• v.26 no.2
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• pp.61-71
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• 2022

Purpose: This experimental study compared the chest compression quality, muscle activity, and subjective fatigue of paramedic students who did or did not wear a mask. Methods: The subjects of this study were 13 paramedic students at college D located in B city. Frequency percentages, mean standard deviations, and paired sample t-tests were conducted using the SPSS/WIN 23.0 program. Results: This study revealed that chest compression depths (t=-2.151, p=.053) and compression rates (t=-2.714, p=.019) were higher in mask-wearers, while muscle activity and subjective fatigue (t=2.382, p=.035) of the erector spinae (t=7.082, p=.001), rectus abdominis (t=4.776, p=.001), and pectoralis major muscles (t=3.193, p=.008) were lower in mask-wearers. Conclusion: The results of this study can be used as a basis to increase the resuscitation rates of cardiac arrest patients and provision of high-quality chest compressors to rescuers when infectious diseases recur in the future.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.101-109
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• 2008

In order to investigate the influence of the water on compression characteristic of decomposed granite soils, a single particle crushing test and one-dimensional compression tests were carried out on three decomposed granite soils and Silica sand. The initial fracture strength for single particle reduced and variability of the strength increases due to weakening by existing water. Moreover, it was recognized that one-dimensional compression characteristic was related to the initial fracture strength characteristic, and the initial fracture strength also has the effect of weathering.

• Computers and Concrete
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• v.29 no.5
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• pp.323-334
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• 2022

In order to study the axial compression performance of basalt-fiber reinforced recycled concrete (BFRRC) filled circular steel tubular short columns, the axial compression performance tests of seven short column specimens were conducted to observe the mechanical whole-process and failure mode of the specimens, the load-displacement curves and the load-strain curves of the specimens were obtained, the influence of design parameters on the axial compression performance of BFRRC filled circular steel tubular short columns was analyzed, and a practical mathematical model of stiffness degradation and a feasible stress-strain curve equation for the whole process were suggested. The results show that under the axial compression, the steel tube buckled and the core BFRRC was crushed. The load-axial deformation curves of all specimens show a longer deformation flow amplitude. Compared with the recycled coarse aggregate (RCA) replacement ratio and the basalt fiber dosage, the BFRRC strength has a great influence on the peak bearing capacity of the specimen. The RCA replacement ratio and the BFRRC strength are detrimental to ductility, whereas the basalt fiber dosage is beneficial to ductility.

• Steel and Composite Structures
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• v.44 no.6
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• pp.883-898
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• 2022

A hollow-core partially-encased composite beam, named HPEC beam, is investigated in this paper. HPEC beam comprises I-beam, longitudinal reinforcement, stirrup, foam formwork, and cementitious grout. The foam formwork is located on both sides of the web, and cementitious grout is cast within the steel flange. To investigate the shear performance of HPEC beams, static loading tests of six HPEC beams and three control beams were conducted. The shear span ratio and the number of studs on the shear behavior of the HPECspecimens were studied. The failure mechanism was studied by analyzing the curves of shear force versus both deflection and strain. Based on the shear span ratio (𝜆), two typical shear failure modes were observed: shear compression failure when 1.6 ≤ 𝜆 ≤ 2; and diagonal compression failure when 𝜆 ≤ 1.15. Shear studs welded on the flange can significantly increase the shear capacity and integrity of HPEC beams. Flange welded shear studs are suggested. Based on the deformation coordination theory and superposition method, combined with the simplified modified compression field model and the Truss-arch model, Modified Deformation Coordination Truss-arch (M.D.C.T.) model was proposed. Compared with the shear capacity from YB9038-2006 and JGJ138-2016, the calculation results from M.D.C.T. model could provide reasonable predictions.