• International Journal of Highway Engineering
• /
• v.8 no.1 s.27
• /
• pp.1-13
• /
• 2006

This paper is one of the studies for developing new methodologies for improving performance of hot-mix recycled asphalt mixtures. The objective of this study is to evaluate rut-resistance characteristics of recycled asphalt mixture which was prepared by newly developed mixing method. The new mixing method provided more sufficient rejuvenation of old binder of reclaimed asphalt pavement (RAP), making homogeneous binder viscosity level in a recycled mixture. Two aggregates (gneiss and granite), two RAP contents (15% and 30%) and two contents (none and 6%) of polymer modifier (LDPE) were used. Recycled mixture was prepared with two methods; method A and method F. To examine difference of binder oxidation level by type of material within a recycled mixture, Gel-permeation chromatography(GPC) analysis was performed on the binders mixed with coarse aggregates and matrix separately. Laboratory tests were performed for evaluation of rut resistance characteristics of each recycled mixture and these includes wheel tracking (WT) test and Kim test. Rut depth and dynamic stability were obtained from WT test and deformation strength $(S_D)$ was obtained from Kim test. The results of regression analysis was shown that correlation $(R^2)$ of F mixing mixtures was higher than one of A mixing mixtures. Therefore, F mixing mixtures showed more consistent rut resistance than h mixing mixtures.

• Composites Research
• /
• v.20 no.3
• /
• pp.43-49
• /
• 2007

Dynamic instability of rotating disks is the most significant factor to limit its rotating speed. Application of composite materials to rotating disks may enhance the dynamic stability leading to a possible design of rotating disks with lightweight and high speed. Whereas much work has been done on the effect of transverse shear and rotary inertia, called Timoshenko effect, on the dynamic behavior of plates, there is little work on the correlation between the effect and the rotation of disk, especially nothing in case of composite disks. The dynamic equations of a rotating composite disk are formulated with the Timoshenko effect and the vibrational analysis is performed by using a commercial package MSC/NASTRAN. According to the results, the Timoshenko effect goes seesaw in some modes, unlike the well-known fact that the effect decreases as the rotating speed increases. And it can be concluded, based only on the present results, that decrement of the Timoshenko effect by disk rotation grows larger as the thickness ratio decreases, the diameter ratio increases, the modulus ratio increases, and the mode number increases.

• The Journal of Korean Academy of Prosthodontics
• /
• v.30 no.2
• /
• pp.286-318
• /
• 1992

The objective of preventive dentistry is the maintenance of a healthy dentition for the life of a patient. Unfortunately, if an individual has not received the benefit of a comprehensive program of preventive dentistry and has finally reached the edentulous state, as a consequence, he receives a set of complete denture. Dentures are mechanical devices and subject to the principles of mechanics. In some cases, the general health and nutritional status of the patient are felt to be the causative factors. But, the most important thing in residual ridge resorption is felt to be caused by the unequal distribution of functional forces. This study was to analyze mandibular stresses of complete denture occlusion by three dimensional finite element method. The results were as follows ; 1. As deformation and stress distribution of the complete denture of the mandible were concentrated on the upper lingual side of the mandible, alveolar ridge resorption of the mandible occurred from lingual side to labio-buccal side. 2. Analyzing by three dimensional F. E. M., the mandible is a very effective form for tolerating stress and deformation biomechanically. 3. According to the concentration of stress distibution in the upper buccal side of the lower posteriors, buccal shelf area must be a primary stress bearing area in the lower complete denture. 4. Lower complete denture moved horizontally to the balancing side under lateral occlusal force. 5. Bilateral balanced occlusion should be constructed in the complete denture for denture stability, especially in the protrusive movement. 6. Physical property of the denture base material was as important for stress distribution in the denture base as or even more than that in the mandible. 7. Impression technique is very important because of most of stress was concentrated between them due to close contact of the mandible and the denture base.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.2
• /
• pp.161-173
• /
• 2013

When the ground is excavated near the pre-existing structures due to the region restricted condition such as urban area, the ground will be released by the excavation and the temporary wall will be deformed depending on the earth pressure. In this case, issues can be created in terms of stability of pre-existing structures. Firstly, the laboratory model tests were carried out to investigate the ground surface settlement due to the ground excavation according to the excavation methods in this study. Using the ground surface settlement results from model tests, numerical analyses were carried out to study the structure deformation due to the ground excavation according to the excavation methods. Finally, using the structure deformation results from numerical analysis, the damage assessment of structures was carried out by using the strain damage estimation criterion.

• Structural Engineering and Mechanics
• /
• v.37 no.3
• /
• pp.309-320
• /
• 2011

As a new type of large-span space structure, suspendome is composited of the upper single-layer reticulated shell and the lower cable-strut system. It has better mechanical properties compared to single-layer reticulated shell, and the overall stiffness of suspendome structure increases greatly due to the prestress of cable. Consequently, it can cross a larger span reasonably, economically and grandly with high rigidity, good stability and simple construction. For a better assessment of the advantages of mechanical characteristic of suspendome quantitatively, the static behavior of Kiewitt6 suspendome was studied by using finite element method, and ADINA was the software application to implement the analysis. By studying a certain suspendome, the internal forces, deformation and support constrained forces of the structure were obtained in this paper. Furthermore, the influences of parameters including prestress, stay bar length, cross-sectional area and rise-to-span ratio were also discussed. The results show that the increase of prestress and vertical stay bar length can improve the stiffness of suspendome; Cross-sectional area has nearly no impact on the static behavior, and the rise-to-span ratio is the most sensitive parameter.

• Steel and Composite Structures
• /
• v.34 no.5
• /
• pp.715-732
• /
• 2020

High-strength steel composite Y-eccentrically braced frame (Y-HSS-EBF) is a novel structural system. In this study, the spatial substructure hybrid simulation test (SHST) method is used to further study the seismic performance of Y-HSS-EBF. Firstly, based on the cyclic loading tests of two single-story single-span Y-HSS-EBF planar specimens, a finite element model in OpenSees was verified to provide a reference for the numerical substructure analysis model for the later SHST. Then, the SHST was carried out on the OpenFresco test platform. A three-story spatial Y-HSS-EBF model was taken as the prototype, the top story was taken as the experimental substructure, and the remaining two stories were taken as the numerical substructure to be simulated in OpenSees. According to the test results, the validity of the SHST was verified, and the main seismic performance indexes of the SHST model were analyzed. The results show that, the SHST based on the OpenFresco platform has good stability and accuracy, and the results of the SHST agree well with the global numerical model of the structure. Under strong seismic action, the plastic deformation of Y-HSS-EBF mainly occurs in the shear link, and the beam, beam-columns and braces can basically remain in the elastic state, which is conducive to post-earthquake repair.

• Tunnel and Underground Space
• /
• v.11 no.2
• /
• pp.109-119
• /
• 2001

Up to now single large cavern was excavated for each undergroud hydraulic powerhouse in Korea. But the Yangyang underground hydraulic powerhouse consists of two large caverns; a powerhouse cavern and main transformer cavern. In this carte, the structural stability of the caverns, especially the rock pillar formed between two large caverns, should be guaranteed to be sound to make the caverns permanently sustainable. In this research, the Distinct Element Method(DEM) was used to analyze the structural stability of two caverns and the rock pillar. The Barton-Bandis joint model was used as a constitutive model. The moot significant parameters such as in-site stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. In addition, two different cases; 1) with no support system and 2) with a support system, were analysed to optimize a support system and to investigate reinforcing effects of a support system. The results of analysis horizontal displacement and joint shear displacement proved to be reduced with the support system. The relaxed zone in the rock pilar also proved to be reduced in conjunction with the support system. Having a support system in place provided the fact that the non zero minimum principal stresses were still acting in the rock pillar so that the pillar was not under uniaxial compressive condition but under triaxial compressive condition. The structural stability f an approximately 36 m wide rock pillar between two large caverns was assured with the appropriate support system.

• Earthquakes and Structures
• /
• v.18 no.5
• /
• pp.637-648
• /
• 2020

In this study, a new steel cylindrical shell configuration of the dissipative energy device is proposed to improve lateral ductility and to reduce the damage of the structures against seismic forces. Four nested-eccentric- cylindrical shells are used to constructing this device; therefore, this proposed device is named nested-eccentric-cylindrical shells damper (NECSD). The particular configuration of the nested-eccentric-cylindrical shells is applied to promote the mechanical characteristics, stability, and overall performance of the damper in cyclic loads. Shell-type components are performed as a combination of series and parallel non-linear springs into the in-plan plastic deformation. Numerical analysis with respect to dimensional variables are used to calculate the mechanical characteristics of the NECSD, and full-scale testing is conducted for verifying the numerical results. The parametric study shows the NECSD with thin shells were more flexible, while devices with thick shells were more capacious. The results from numerical and experimental studies indicate that the NECSD has a stable behavior in hysteretic loops with highly ductile performance, and can provide appropriate dissipated energy under cyclic loads.

• Geomechanics and Engineering
• /
• v.33 no.6
• /
• pp.529-542
• /
• 2023

Wave propagation with high transverse deflection could affect the stability of the ball in its trajectory. For low stiffness balls similar to soccer and volleyball balls, the waves are more noticeable in comparison to other balls like ping-pong ball. On the other hand, the soccer balls are under heavy impact loads from shoots and contacting different objects in the field. The maximum recorded speed of a soccer ball after kicking is the 211 km/hr and the average maximum speed is around 112 km/hr. Therefore, in such speeds the aerodynamic forces become important which are directly related to geometrical shape of the ball. In this regard, the wave propagation in soccer ball is examined in the current study using large deformation shear deformable formulations. Classical relations of stress-strain components are taken into consideration along with minimum total energy principle. The final derived relations were solved by using harmonic differential quadrature method. The results are generally presented ion term of phase velocity as function of different influencing parameters of the materials, geometry and mass of the ball.

• Geomechanics and Engineering
• /
• v.35 no.5
• /
• pp.539-554
• /
• 2023

This article is dedicated to the pursuit of establishing a robust empirical relationship that allows for the estimation of in-situ modulus of deformations (E_m and G_m) within sedimentary rock slope masses through the utilization of Q_slope values. To achieve this significant objective, an expansive and thorough methodology is employed, encompassing a comprehensive field survey, meticulous sample collection, and rigorous laboratory testing. The study sources a total of 26 specimens from five distinct locations within the South Pars (known as Assalouyeh) region, ensuring a representative dataset for robust correlations. The results of this extensive analysis reveal compelling empirical connections between E_m, geomechanical characteristics of the rock mass, and the calculated Q_slope values. Specifically, these relationships are expressed as follows: E_m = 2.859 Q_slope + 4.628 (R² = 0.554), and G_m = 1.856 Q_slope + 3.008 (R² = 0.524). Moreover, the study unravels intriguing insights into the interplay between in-situ deformation moduli and the widely utilized Rock Mass Rating (RMR) computations, leading to the formulation of equations that facilitate predictions: RMR = 18.12 E_m0.460 (R² = 0.798) and RMR = 22.09 G_m0.460 (R² = 0.766). Beyond these correlations, the study delves into the intricate relationship between RMR and Rock Quality Designation (RQD) with Qslope values. The findings elucidate the following relationships: RMR = 34.05e^0.33Qslope (R² = 0.712) and RQD = 31.42e^0.549Qslope (R² = 0.902). Furthermore, leveraging the insights garnered from this comprehensive analysis, the study offers an empirically derived support system tailored to the distinct characteristics of discontinuous rock slopes, grounded firmly within the framework of the Q_slope methodology. This holistic approach contributes significantly to advancing the understanding of sedimentary rock slope stability and provides valuable tools for informed engineering decisions.