• Computers and Concrete
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• v.20 no.4
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• pp.429-437
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• 2017

In this study, the effect of the tensile strength and ratio of disc spacing to penetration depth on the efficiency of tunnel boring machine (TBM) is investigated using Particle flow code (PFC) in two dimensions. Models with dimensions of $150{\times}70mm$ made of rocks with four different tensile strength values of 5 MPa, 10 MPa, 15 MPa and 20 MPa were separately analyzed and two "U" shape cutters with width of 10 mm were penetrated into the rock model by velocity rate of 0.1 mm/s. The spacing between cutters was also varied in this study. Failure patterns for 5 different penetration depths of 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm were registered. Totally 100 indentation test were performed to study the optimal tool-rock interaction. An equation relating mechanical rock properties with geometric characteristics for the optimal TBM performance is proposed. The results of numerical simulations show that the effective rock-cutting condition corresponding to the minimum specific energy can be estimated by an optimized disc spacing to penetration depth, which, in fact, is found to be proportional to the rock's tensile strength.

• The KIPS Transactions:PartD
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• v.14D no.7
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• pp.753-762
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• 2007

Traceability has been held as an important factor in testing activities as well as model driven development. Vertical traceability affords us opportunities to improve manageability from models and test cases to code in testing and debugging phase. Traceability also makes overcome to difficulties of going up-and-down abstraction level to find out error spot of faults discovered by testing This paper represents a vertical test method which connects a system test level and an integration test level in a test stage by using UML. Experiment of how traceability works and how effective focus on error spots has been included using concrete examples of tracing from models to the code.

• International Journal of Highway Engineering
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• v.15 no.6
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• pp.49-60
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• 2013

PURPOSES : The evaluation of the pavement condition of the asphalt concrete pavement of No. 2 runway of Inchon International Airport through PMS, a supporting system for making a decision of pavement, maintenance and repair, was made, and the proper time for repair according to the PCI reduction rate was suggested. METHODS : By comparing and analyzing the evaluation results of pavements built in 2009, 2010, 2011, PCI change in each facility (No. 2 runway, C parallel taxiway, connection taxiway) was calculated. By applying the calculated change to PCI deduction rate model, the pavement condition of the target sections was estimated, and then the necessary section and time for repair were chosen. RESULTS : After careful consideration of the time for pavement and maintenance, based on the result of PCI prediction, it was estimated that the southern takeoff and landing section of No. 2 runway was required to be repaired in 2012; connection taxiway in 2013; and C parallel taxiway in 2014; however, the section which is the main moving route of connection taxiway and C parallel taxiway was needed to be repaired in 2012. CONCLUSIONS : For maintenance and repair of airport pavements, the optimal alternative should be chosen by considering economics and operability, via examining the time for repair and the aspect of management all together on the basis of this study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.160-170
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• 2007

This study predicts Life Cycle Cost of RC Slab bridge case in maintenance and operation level and calculated economic efficiency by the avoidable costs of a bridge. This result of the study can be summarized as follow: (1) LCC analysis model on the bridge case is suggested. (2) Maintenance and operation level of a bridge have been divided, and LCC of the bridge case has been predicted at current maintenance and operation level and required maintenance and operation level. (3) Reduction costs is predicted by LCC of the bridge case, and its economic efficiency is calculated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.492-498
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• 2008

In this paper are described recent studies about variable nozzles, that are a rectangular type nozzle and an axisymmetric type nozzle, of the precooled turbojet engine(S-engine) which are developed for the demonstration of the key technologies for the propulsion system of the hypersonic airplane and the first stage propulsion of the TSTO space plane. For the rectangular nozzle, three types of C-shaped carbon/carbon composite cowls which includes subscale model of the precooled turbojet engine are fabricated and the fine attachment to the ramp is confirmed. For the firing of the S-engine, stainless steel cowl with concrete heat insulator are fabricated and tested for 20 sec. Axisymmetric variable plug nozzle which is made of C/C material is fabricated and pressurized by the cold flow test. The axisymmetric plug nozzle can be operative up to 0.57 MPa of nozzle inlet pressure.

• Structural Engineering and Mechanics
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• v.20 no.1
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• pp.1-20
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• 2005

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.211-229
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• 2004

The main purpose of this paper is the numerical analysis of the non-linear seismic response of a RC building mock-up. The mock-up is subjected to different synthetic horizontal seismic excitations. The numerical approach is based on a 3D-model involving multilayered shell elements. These elements are composed of several single-layer membranes with various eccentricities. Bending effects are included through these eccentricities. Basic equations are first written for a single membrane element with its own eccentricity and then generalised to the multilayered shell element by superposition. The multilayered shell is considered as a classical shell element : all information about non-linear constitutive relations are investigated at the local scale of each layer, whereas balance and kinematics are checked afterwards at global scale. The non-linear dynamic response of the building is computed with Newmark algorithm. The numerical dynamic results (blind simulations) are considered in the linear and non linear cases and compared with experimental results from shaking table tests. Multilayered shell elements are found to be a promising tool for predictive computations of RC structures behaviour under 3D seismic loadings. This study was part of the CAMUS International Benchmark.

• Structural Engineering and Mechanics
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• v.59 no.5
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• pp.803-820
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• 2016

In this study a direct displacement-based design (DDBD) procedure for a continuous deck bridge isolated with triple friction pendulum bearings (TFPB) has been proposed and the seismic demands of the bridge such as isolator's displacement and drift of piers obtained from this procedure evaluated under two-directional near-field ground motions. The structural model used here are continuous, three-span, castin-place concrete box girder bridge with a 30-degree skew which are isolated with 9 different TFPBs. By comparing the results of DDBD method with those of nonlinear time history analysis (NTHA), it can be concluded that the proposed procedure is able to predict seismic demands of similar isolated bridges with acceptable accuracy. Results of NTHA shows that dispersion of peak resultant responses for a group of ground motions increases by increasing their average value of responses. It needs to be noted that the demands parameters calculated by the DDBD procedure are almost overestimated for stiffer soil condition, but there is some underestimation in results of this method for softer soil condition.

• Computers and Concrete
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• v.17 no.6
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• pp.723-737
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• 2016

In this paper an approach was described for determination of direction of sliding block in rock slopes containing planar non-persistent open joints. For this study, several gypsum blocks containing planar non-persistent open joints with dimensions of $15{\times}15{\times}15cm$ were build. The rock bridges occupy 45, 90 and $135cm^2$ of total shear surface ($225cm^2$), and their configuration in shear plane were different. From each model, two similar blocks were prepared and were subjected to shearing under normal stresses of 3.33 and $7.77kg/cm^{-2}$. Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective joint surface that is in front of the rock-bridge and the total shear surface. In general, the failure pattern is influenced by the EJC while shear strength is closely related to the failure pattern. It is observed that the propagation of wing tensile cracks or shear cracks depends on the EJC and the coalescence of wing cracks or shear cracks dominates the eventual failure pattern and determines the peak shear load of the rock specimens. So the EJC is a key factor to determine the sliding direction in rock slopes containing planar non-persistent open joints.

• Smart Structures and Systems
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• v.5 no.1
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• pp.81-94
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• 2009

A vibration-impedance-based monitoring method is proposed to predict the loss of prestress forces in prestressed concrete (PSC) girder bridges. Firstly, a global damage alarming algorithm using the change in frequency responses is formulated to detect the occurrence of damage in PSC girders. Secondly, a local damage detection algorithm using the change in electro-mechanical impedance features is selected to identify the prestress-loss in tendon and anchoring members. Thirdly, a prestress-loss prediction algorithm using the change in natural frequencies is selected to estimate the extent of prestress-loss in PSC girders. Finally, the feasibility of the proposed method is experimentally evaluated on a scaled PSC girder model for which acceleration responses and electro-mechanical impedances were measured for several damage scenarios of prestress-loss.