• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.137-147
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• 2012

In the steel-free bridge concrete deck, steel straps are generally used instead of conventional steel rebar while laterally restrained in the perpendicular direction to the traffic in order fir the arching effect of concrete deck. In this paper, the minimum amount of FRP bar is to be suggested based on the structural strength, crack propagation, stress level and others in order to control cracks. As a result of laboratory tests, the structural strength of deck with 0.15 percentage of steel strap showed improved structural strength including ductility. The long-term serviceability of steel strap deck with FRP bar proved to satisfy the requirements and to be structurally stable while showing the amount of crack and residual vertical displacement within the allowable limits after two million cyclic loadings. The structural failure of RC bridge deck is generally caused from the punching shear rather than moment. Therefore, the ultimate load at failure could be estimated using the shear strength formula in the two-way slab based on ACI and AASHTO criteria. However the design criteria tend to underestimate the shear strength since they don't consider the arching effects and nonlinear fracture in bridge deck with lateral confinement. In this paper, an equation to estimate the punching shear strength of steel strap deck is to be developed considering the actual failure geometries and effect of lateral confinement by strap while the results are verified in accordance with laboratory tests.

• Earthquakes and Structures
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• v.15 no.6
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• pp.667-685
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• 2018

In eccentrically braced steel frames (EBFs), the links are fuse members which enter inelastic phase before other structure members and dissipate the seismic energy. Based on the force-based seismic design method, damages and plastic deformations are limited to the links, and the main structure members are required tremendous sizes to ensure elastic with limited or no damage. Force-based seismic design method is very common and is found in most design codes, it is unable to determine the inelastic response of the structure and the damages of the members. Nowadays, methods of seismic design are emphasizing more on performance-based seismic design concept to have a more realistic assessment of the inelastic response of the structure. Links use ordinary steel Q345 (the nominal yielding strength $f_y{\geq}345MPa$) while other members use high strength steel (Q460 $f_y{\geq}460MPa$ or Q690 $f_y{\geq}690MPa$) in eccentrically braced frames with high strength steel combination (HSS-EBFs). The application of high strength steels brings out many advantages, including higher safety ensured by higher strength in elastic state, better economy which results from the smaller member size and structural weight as well as the corresponding welding work, and most importantly, the application of high strength steel in seismic fortification zone, which is helpful to popularize the extensive use of high strength steel. In order to comparison seismic behavior between HSS-EBFs and ordinary EBFs, on the basis of experimental study, four structures with 5, 10, 15 and 20 stories were designed by PBSD method for HSS-EBFs and ordinary EBFs. Nonlinear static and dynamic analysis is applied to all designs. The loading capacity, lateral stiffness, ductility and story drifts and failure mode under rare earthquake of the designs are compared. Analyses results indicated that HSS-EBFs have similar loading capacity with ordinary EBFs while the lateral stiffness and ductility of HSS-EBFs is lower than that of EBFs. HSS-EBFs and ordinary EBFs designed by PBSD method have the similar failure mode and story drift distribution under rare earthquake, the steel weight of HSS-EBFs is 10%-15% lower than ordinary EBFs resulting in good economic efficiency.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.480-493
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• 2021

Since the generalized Hoek-Brown criterion (GHB) provides an efficient way of identifying its strength parameter values with the consideration of in-situ rock mass condition via Geological Strength Index (GSI), this criterion is recognized as one of the standard rock mass failure criteria in rock mechanics community. However, the nonlinear form of the GHB criterion makes its mathematical treatment inconvenient and limits the scope of its application. As an effort to overcome this disadvantage of the GHB criterion, the explicit approximate analytical equations for the minimum principal stress, which is associated with the maximum principal stress at failure, are formulated based on the Taylor polynomial approximation of the original GHB criterion. The accuracy of the derived approximate formula for the minimum principal stress is verified by comparing the resulting approximate minimum principal stress with the numerically calculated exact values. To provide an application example of the approximate formulation, the equivalent friction angle and cohesion for the expected plastic zone around a circular tunnel in a GHB rock mass are calculated by incorporating the formula for the approximate minimum principal stress. It is found that the simultaneous consideration of the values of mi, GSI and far-field stress is important for the accurate calculation of equivalent Mohr-Coulomb parameter values of the plastic zone.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.53-64
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• 2017

Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of such precaution, fault occurring is inevitable. Hence, there is a requirement for on-board fault recovery without significant degradation in the ALV performance. The present study develops an advanced fault recovery strategy to improve the reliability of an Aerospace Launch Vehicle (ALV) navigation system. The proposed strategy contains fault detection features and can reconfigure the system against common faults in the ALV navigation system. For this purpose, fault recovery system is constructed to detect and reconfigure normal navigation faults based on the sliding mode observer (SMO) theory. In the face of pitch channel sensor failure, the original gyro faults are reconstructed using SMO theory and by correcting the faulty measurement, the pitch-rate gyroscope output is constructed to provide fault tolerant navigation solution. The novel aspect of the paper is employing SMO as an online tuning of analytical fault recovery solution against unforeseen variations due to its hardware/software property. In this regard, a nonlinear model of the ALV is simulated using specific navigation failures and the results verified the feasibility of the proposed system. Simulation results and sensitivity analysis show that the proposed techniques can produce more effective estimation results than those of the previous techniques, against sensor failures.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.13-24
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• 1999

The external, unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of internal bonded PSC members because of eccentricity change and slip occurrence during loading process. The purpose of the present study is to propose the ultimate failure stresses of prestressing (PS) steels for those external unbonded PSC members. To this end, a comprehensive analysis has been made using the nonlinear finite element analysis program developed recently for external unbonded PSC members by authors. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, load geometry, amount of ordinary steel, and prestressing steel ration have great influence for the ultimate failue stress of PS steel is preposed and is compared with experimental dat as well as existing formulas for internal unbonded members. The Comparison indicates that the proposed equation agrees relatively well with experimental data and that existing formulas including ACI and AASHTO equations show some discrepancies from experimental ones. The present study allows more realistic analysis and design of prestressed concrete structures with external unbonded tendons.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.149-153
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• 2000

Substituting composite structures for conventional metallic structures has many advantages because of higher specific stiffness and specific strength of composite materials. In this work, one-piece propeller shafts composed of carbonfepoxy and glass/epoxy composites were designed and manufactured for a rear wheel drive automobile satisfying three design specifications, such as static torque transmission capability, torsional buckling and the fundamental natural bending frequency. Single lap adhesively bonded joint was employed to join the composite shaft and the aluminum yoke. For the optimal adhesive joining of the composite propeller shaft to the aluminum yoke, the torque transmission capability of the adhesively bonded composite shaft was calculated with respect to bonding length and yoke thickness by finite element method and compared with the experimental result. Then an optimal design method was proposed based on the failure model which incorporated the nonlinear mechanical behavior of aluminum yoke and epoxy adhesive. From the experiments and FEM analyses, it was found that the static torque transmission capability of composite propeller shaft was maximum at the critical yoke thickness, and it saturated beyond the critical length. Also, it was found that the one-piece composite propeller shaft had 40% weight saving effect compared with a two-piece steel propeller shaft.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.1-8
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• 1991

Recently the use of steel fibers has been increased in flexural members and columns of concrete structures subjected to cyclic loadings; such as bridge decks, highway roads, runway of airport, buildings, etc.. However only a few experimental tests have been carried out under fatigue loading. In the present study, the reinforced concrete beams with 1% and 2% steel fiber volume fraction are investigated with and without stirrups. It has been found that in fatigue tests, the failure of the beam is usually due to breaking of fibers rather than fiber pull-out. A comparison of experiments and numerical analysis using the nonlinear F.E.M. program (ADINA) is also presented herein.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.147-154
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• 1984

A numerical procedure based on the finite element method for the analysis of reinforced concrete beam-columns under uniaxial bending is presented. Material nonlinearities such as the cracking and crushing of concrete and the yielding of reinforcing steel as well as the geometric nonlinearity which is an important factor affecting the behavior of beam-columns are considered in the analysis. This method traces the behavior of reinforced concrete beam-columns up to failure by solving incremental equilibrium equations, Numerical examples are presented to demonstrate the validity and usefulness of the present method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1784-1797
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• 1996

The disk/blade assembly of a turbine engine is made in the shape of a dovetail type or a fir-tree type. Since disk fillet regions or contact surfaces undergo high stress comcentration, fatigue cracks frequentrly occur in the disk/blade assembly. Therefore, it is necessary to analyze the stress distributions in the fir-tree type disk/balde assembly and predict the region of fatigue failure. The stress distributions of the disk/blade assembly were investigated by using the photoelastic method and the finite element method. Two dimensional photoelastic techniques were used to investigate the stress distributions of contact surfaces and fillet regions. TH stress distributions were obtained by the shear-difference method and were compared to the finite element results. It was found that maximum tensile stresses were higher in the fillet region thatn in the contact surfaces of the fir-tree models. The finite element results showed good agreement with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1352-1358
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• 2004

The mechanical spring is one of widely used machine elements. Among various kinds, flat-type spring loaded by a rotating pin was studied. A flat spring was simplified to a cantilever beam, and numerical analysis was attempted. Since the loading pin rotates about a separate axis from the fixed spring or vice versa, the location, direction, and magnitude of the contact force including normal contact and friction loads vary accordingly. Meanwhile, the spring is deformed substantially as the relative motion progresses. Therefore, this problem needs to be formulated taking the follower loading characteristics and geometrical non-linearity into account. Derived nonlinear differential equation was solved to yield the spring deflection, contact force and the torque to rotate the pin, and the result was compared with a finite element solution. Also, the influences of principal design parameters were studied. The proposed methodology is expected to be useful for the design of pin-loaded flat spring and the prevention of mechanical failures in the form of yielding or fatigue failure of spring or severe wear of the components.