• Steel and Composite Structures
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• v.43 no.2
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• pp.165-183
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• 2022

Most transportation departments have recognized and developed procedures to address the ever-increasing weights of trucks traveling on bridges in a service today. Transportation agencies also recognize the issues with overheight vehicles' collisions with bridges, but few stakeholders have definitive countermeasures. Bridges are becoming more vulnerable to collisions from overheight vehicles. The exact response under lateral impact force is difficult to predict. In this paper, nonlinear impact analysis shows that the degree of deformation recorded through the modeling of the unprotected vehicle-girder model provides realistic results compared to the observation from the US-61 bridge overheight vehicle impact. The predicted displacements are 0.229 m, 0.161 m, and 0.271 m in the girder bottom flange (lateral), bottom flange (vertical), and web (lateral) deformations, respectively, due to a truck traveling at 112.65 km/h. With such large deformations, the integrity of an impacted bridge becomes jeopardized, which in most cases requires closing the bridge for safety reasons and a need for rehabilitation. We proposed different sacrificial cushion systems to dissipate the energy of an overheight vehicle impact. The goal was to design and tune a suitable energy absorbing system that can protect the bridge and possibly reduce stresses in the overheight vehicle, minimizing the consequences of an impact. A material representing a Sorbothane high impact rubber was chosen and modeled in ANSYS. Out of three sacrificial schemes, a sandwich system is the best in protecting both the bridge and the overheight vehicle. The mitigation system reduced the lateral deflection in the bottom flange by 89%. The system decreased the stresses in the bridge girder and the top portion of the vehicle by 82% and 25%, respectively. The results reveal the capability of the proposed sacrificial system as an effective mitigation system.

• Composites Research
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• v.35 no.4
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• pp.288-297
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• 2022

This study investigated the effect of addition of zirconia(zirconium oxide) powder on the curing behavior of phenolic resins. The heating rate controlled curing and isothermal curing behaviors of the phenol resin according to the content of the zirconia powder were analyzed. The viscosity and thermal decomposition characteristics of the phenolic resin with the zirconia content were also examind. From the DSC analysis, the degree of cure and the rate of cure were obtained. Finally, the activation energy for the cure reaction were calculated from the DSC data of the zirconia added phenolic resin. As a found, the higher the zirconia content, the longer the curing was delayed and the greater the activation energy required for curing. Additionally, the TGA result that as the content of zirconia increased, less weight loss was observed. The surface tackiness of the Carbon/Phenol prepreg was partially changed according to the zirconia content, but had no significant effect.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.125-132
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• 2007

The oedometer, radial CRS and Rowe cell tests, composite discharge capacity tests and smear effect tests are carried out to estimate the parameters for the reliability-based design of vertical drain method. Also the sensitivity analysis, the probabilistic and deterministic solutions of radial consolidation theory are presented. The result of probabilistic analysis was compared to that of deterministic analysis using the tested and estimated parameters. The results indicated that the drain spacing in the deterministic method is larger than that in the probabilistic method because the former does not consider the uncertainties in the geotechnical property. The divergence of two methods is dependent on the probability of achieving target degree of consolidation by a given time and the coefficient of variation (COV) of the coefficient of horizontal consolidation ($c_h$).

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.38.1-38.1
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• 2021

Dust polarization depends on the physical and mechanical properties of dust, as well as the properties of local environments. To understand how dust polarization varies with grain mechanical properties and the local environment, in this paper, we model the wavelength-dependence polarization of starlight and polarized dust emission by aligned grains by simultaneously taking into account grain alignment and rotational disruption by radiative torques (RATs). We explore a wide range of the local radiation field and grain mechanical properties characterized by tensile strength. We find that the maximum polarization and the peak wavelength shift to shorter wavelengths as the radiation strength U increases due to the enhanced alignment of small grains. Grain rotational disruption by RATs tends to decrease the optical-near infrared polarization but increases the ultraviolet polarization of starlight due to the conversion of large grains into smaller ones. In particular, we find that the submillimeter (submm) polarization degree at 850㎛(P850) does not increase monotonically with the radiation strength or grain temperature (Td), but it depends on the tensile strength of grain materials. Our physical model of dust polarization can be tested with observations toward star-forming regions or molecular clouds irradiated by a nearby star, which have higher radiation intensity than the average interstellar radiation field. Finally, we compare our predictions of the P850-Td relationship with Planck data and find that the observed decrease of P850 with Td can be explained when grain disruption by RATs is accounted for, suggesting that interstellar grains unlikely to have a compact structure but perhaps a composite one. The variation of the submm polarization with U (or Td)can provide a valuable constraint on the internal structures of cosmic dust

• Steel and Composite Structures
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• v.46 no.3
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Korean Journal of Materials Research
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• v.34 no.2
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• pp.85-94
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• 2024

The optimization of deacetylation process parameters for producing chitosan from isolated chitin shrimp shell waste was investigated using response surface methodology with central composite design (RSM-CCD). Three independent variables viz, NaOH concentration (X₁), radiation power (X₂), and reaction time (X₃) were examined to determine their respective effects on the degree of deacetylation (DD). The DD of chitosan was also calculated using the baseline approach of the Fourier Transform Infrared (FTIR) spectra of the yields. RSM-CCD analysis showed that the optimal chitosan DD value of 96.45 % was obtained at an optimized condition of 63.41 % (w/v) NaOH concentration, 227.28 W radiation power, and 3.34 min deacetylation reaction. The DD was strongly controlled by NaOH concentration, irradiation power, and reaction duration. The coefficients of correlation were 0.257, 0.680, and 0.390, respectively. Because the procedure used microwave radiation absorption, radiation power had a substantial correlation of 0.600~0.800 compared to the two low variables, which were 0.200~0.400. This independently predicted robust quadratic model interaction has been validated for predicting the DD of chitin.

• Steel and Composite Structures
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• v.51 no.2
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• pp.153-172
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• 2024

Due to the fast development of constructions in recent years, there has been a rapid consumption of fresh water and river sand. In the production of concrete, alternatives such as sea water and sea sand are available. The near surface mounted (NSM) technique is one of the most important methods of strengthening. Aluminum alloy (AA) bars are non-rusting and suitable for usage with sea water and sand concrete (SSC). The goal of this study was to enhance the shear behaviour of SSC-beams strengthened with NSM AA bars. Twenty-four RC beams were cast from fresh water river sand concrete (FRC) and SSC before being tested in four-point flexure. All beams are the same size and have the same internal reinforcement. The major factors are the concrete type (FRC or SSC), the concrete degree (C25 or C50 with compressive strength = 25 and 50 MPa, respectively), the presence of AA bars for strengthening, the direction of AA bar reinforcement (vertical or diagonal), and the AA bar ratio (0, 0.5, 1, 1.25 and 2 %). The beams' failure mechanism, load-displacement response, ultimate capacity, and ductility were investigated. Maximum load and ductility of C25-FRC-specimens with vertical and diagonal AA bar ratios (1%) were 100,174 % and 140, 205.5 % greater, respectively, than a matching control specimen. The ultimate load and ductility of all SSC-beams were 16-28 % and 11.3-87 % greater, respectively, for different AA bar methods than that of FRC-beams. The ultimate load and ductility of C25-SSC-beams vertically strengthened with AA bar ratios were 66.7-172.7 % and 89.6-267.9 % higher than the unstrengthened beam, respectively. When compared to unstrengthened beams, the ultimate load and ductility of C50-SSC-beams vertically reinforced with AA bar ratios rose by 50-120 % and 45.4-336.1 %, respectively. National code proposed formulae were utilized to determine the theoretical load of tested beams and compared to matching experimental results. The predicted theoretical loads were found to be close to the experimental values.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.4
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• pp.446-454
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• 2017

Recently, there have been many studies on bulk-fill resin composites. However, studies on the proper materials for pediatric patients are rare. The aim of this study was to compare the cavity wall adaptation of bulk-fill resin composites with conventional resin composite in class II cavities of primary molars using microcomputed tomography (micro-CT). Standardized class II slot cavities were prepared in 80 exfoliated primary molars and randomly divided into 4 groups. The control group was restored with conventional resin composite, Filtek Z-350 XT (FZ), and the three groups were restored with bulk-fill resin composites, Filtek bulk-fill posterior (FB), Tetric N-Ceram Bulk Fill (TNC), Filtek bulk-fill flowable (FBF). All specimens were thermocycled and then immersed in 50% silver nitrate ($AgNO_3$) solution. Micro-CT was used to measure the penetration volume of the total silver nitrate and the degree of cervical marginal leakage and the number, size, and position of the voids were evaluated. The results revealed that the volume of silver nitrate were significantly different between FB and FZ (p < 0.05). The results also revealed that the penetration length of silver nitrate FBF showed statistically lower than the FZ and FB (p < 0.05). There was no significant difference between the groups in number and size of voids. In conventional resin composite, most of the voids were present inside the restoration (83.3%), but the voids in the bulk-fill resin composites incidence were higher in the gingivoaxial angle. The cavity wall adaptation demonstrated in class II restorations of primary molar by new bulk fill resin composites was similar to conventional incremental technique. Bulk-fill resin composites might be an clinical option for a faster restoration in deciduous teeth.

• Geotechnical Engineering
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• v.14 no.5
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• pp.89-110
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• 1998

Variations of backfill load on the metal-polyethylene composite( MPC ) pipes buried in various trenches backfill afterward were investigated in this paper. The backfill loads obtained by the finite element method( FBM ) were compared with those calculated by the well-known MarstonBpangler(M-5) theory. The reliability of the finite element analysis used in this study was examined by an inaitu best for the buried pipe. The backfill lords and deflections on the real-size pipe buried on-site were measured while increasing the backfill height. In addition, further investigations were made for the variations of the backfill loads as a function of several important parameters such as the backfill soil type, bach. height$(\leq4.0m)$, diameter of the pipe$(B.$1.0m)$, and trench width($\leq 3.0 B_c$). It is confirmed that the M-S theory predicts reasonably well the backfill loafs of the MPC of the M-S backfill coils be 0.13 and 0.15 for the SC and SM coils in the D unman soil model, respectively. The load ratio, Wu-s/WwgM for a narrow trench varies negligibly with the back(111 height but fiends to increase for a wide trench. The ratio increases with increasing diameter of the pipe for a narrow trench while decreasing for a wide trench. It is also found that the ratio generally decreases as the degree of compaction increases and BM soil exhibits larger load ratio than that of SC soil.

• Asia pacific journal of information systems
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• v.19 no.2
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• pp.117-137
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• 2009

Recently, intelligent traffic information systems have enabled people to forecast traffic conditions before hitting the road. These convenient systems operate on the basis of data reflecting current road and traffic conditions as well as distance-based data between locations. Thanks to the rapid development of ubiquitous computing, tremendous context data have become readily available making vehicle route planning easier than ever. Previous research in relation to optimization of vehicle route planning merely focused on finding the optimal distance between locations. Contexts reflecting the road and traffic conditions were then not seriously treated as a way to resolve the optimal routing problems based on distance-based route planning, because this kind of information does not have much significant impact on traffic routing until a a complex traffic situation arises. Further, it was also not easy to take into full account the traffic contexts for resolving optimal routing problems because predicting the dynamic traffic situations was regarded a daunting task. However, with rapid increase in traffic complexity the importance of developing contexts reflecting data related to moving costs has emerged. Hence, this research proposes a framework designed to resolve an optimal route planning problem by taking full account of additional moving cost such as road traffic cost and weather cost, among others. Recent technological development particularly in the ubiquitous computing environment has facilitated the collection of such data. This framework is based on the contexts of time, traffic, and environment, which addresses the following issues. First, we clarify and classify the diverse contexts that affect a vehicle's velocity and estimates the optimization of moving cost based on dynamic programming that accounts for the context cost according to the variance of contexts. Second, the velocity reduction rate is applied to find the optimal route (shortest path) using the context data on the current traffic condition. The velocity reduction rate infers to the degree of possible velocity including moving vehicles' considerable road and traffic contexts, indicating the statistical or experimental data. Knowledge generated in this papercan be referenced by several organizations which deal with road and traffic data. Third, in experimentation, we evaluate the effectiveness of the proposed context-based optimal route (shortest path) between locations by comparing it to the previously used distance-based shortest path. A vehicles' optimal route might change due to its diverse velocity caused by unexpected but potential dynamic situations depending on the road condition. This study includes such context variables as 'road congestion', 'work', 'accident', and 'weather' which can alter the traffic condition. The contexts can affect moving vehicle's velocity on the road. Since these context variables except for 'weather' are related to road conditions, relevant data were provided by the Korea Expressway Corporation. The 'weather'-related data were attained from the Korea Meteorological Administration. The aware contexts are classified contexts causing reduction of vehicles' velocity which determines the velocity reduction rate. To find the optimal route (shortest path), we introduced the velocity reduction rate in the context for calculating a vehicle's velocity reflecting composite contexts when one event synchronizes with another. We then proposed a context-based optimal route (shortest path) algorithm based on the dynamic programming. The algorithm is composed of three steps. In the first initialization step, departure and destination locations are given, and the path step is initialized as 0. In the second step, moving costs including composite contexts into account between locations on path are estimated using the velocity reduction rate by context as increasing path steps. In the third step, the optimal route (shortest path) is retrieved through back-tracking. In the provided research model, we designed a framework to account for context awareness, moving cost estimation (taking both composite and single contexts into account), and optimal route (shortest path) algorithm (based on dynamic programming). Through illustrative experimentation using the Wilcoxon signed rank test, we proved that context-based route planning is much more effective than distance-based route planning., In addition, we found that the optimal solution (shortest paths) through the distance-based route planning might not be optimized in real situation because road condition is very dynamic and unpredictable while affecting most vehicles' moving costs. For further study, while more information is needed for a more accurate estimation of moving vehicles' costs, this study still stands viable in the applications to reduce moving costs by effective route planning. For instance, it could be applied to deliverers' decision making to enhance their decision satisfaction when they meet unpredictable dynamic situations in moving vehicles on the road. Overall, we conclude that taking into account the contexts as a part of costs is a meaningful and sensible approach to in resolving the optimal route problem.