• Magazine of the Korea Concrete Institute
• /
• v.10 no.6
• /
• pp.261-268
• /
• 1998

Deflections due to shrinkage are frequently ignored in design calculation. Especially for thin member, shrinkage often causes considerable deformations as wellas appreciable stress changes. Several methods for computing shringkage curvature have been proposed by many researchers. Some of the approximte methods widely used in the recent years are the equivalent tensile force method, Miller's method and Branson's method. These methods were, however, somewhat oversimplified and could be too conservative in the case of well cured concrete structure. In this paper, an approximate method for computing shrinkage curvature and deflection is proposed. Curvature due to shrinkage is derived from the requirements of strain compatibility and equilibrium of a section and the age-adjusted effective modulus method. The proposed method is verified by comparison with several experimental measurements. The correlations between calculated and measured curvatures is very good.

• Magazine of the Korea Concrete Institute
• /
• v.6 no.2
• /
• pp.118-128
• /
• 1994

There have been conducted a lot of works on shear behavior of steel fiber reinforced concrete beams. Fiber reinforced concrete beams without shear reinforcement were tested to determine their cracking shear strengths and ultimate shear capacities. Results of tests on 14 reinforced concrete beams (including 11 containing steel fibers) are reported. Two parameters were varied in the study, namely, the volume fraction of fibers and shear span-to-depth ratio.The effects of fiber incorporation on failure modes, deflections, cracking shear strength, and ul~imate shear strength have been examined. Resistance to shear stresses have been found to be improved by the inclusion of fibers, The mode of failure changed from shear to flexure when the shear span-to-depth ratio exceeds 3.4. Based on these investigations, a method of computing the shear strength of steel fiber reinforced concrete beam is suggested. The comparisons between computed values and expenmentally observed values are shown to verify the proposed theoretical treatment and steel fibers efficiency.

• Journal of Aerospace System Engineering
• /
• v.12 no.4
• /
• pp.18-25
• /
• 2018

The head frame structure of a machine tool for aircraft parts, which requires machining precision and machining of difficult-to-cut materials is required to be light-weighted for precision high-speed machining and to minimize possible deformation by cutting force. To achieve high stiffness and for light-weight structure optimization design, a preliminary model was designed based on finite element analysis. The topology optimization design of light-weight, high stiffness, and low vibration frame structure were performed by minimizing compliance. As a result, the frame weight decreased by 17.3%, the maximum deflection was less than 0.007 mm, and the natural frequency increased by 30.6%. The static stiffness was increased in each axis direction and the dynamic stiffness exhibited contrary results according to the axis. Optimized structure with the high stiffness of low vibration in topology optimization design was confirmed.

• Journal of Korean Society of Steel Construction
• /
• v.12 no.1 s.44
• /
• pp.17-28
• /
• 2000

The current specifications for bridge decks requires the same amount of upper and lower reinforcement mats. There have been many empirical activities that the partial elimination of upper reinforcing bars was not caused the structural integrity of a deck. A simplified method is derived based on thin plate theory for three and four-girder-span bridge decks. A simplified method for bridge deck considering the effect of girder deflection is proposed based on a closed-form solution that shows good agreement with the results of finite element models. In this research, a new design approach for deck slabs is proposed based on the simplified method. The negative bending moments in a deck can be evaluated with the simplified method based on the position of a wheel load, the aspect ratio and relative stiffness and the span length. This new approach can lead to a significant reduction of the quantity of the top reinforcing steel bars in a deck. Reducing the quantify of the top reinforcement not only reduces the construction costs for bridge decks, but also reduces the corrosion of reinforcement to a minimum.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.2
• /
• pp.281-291
• /
• 2002

This paper describes the minimum cost design of prestressed reinforced concrete (PRC) hem with rectangular section. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non prestressing steel, and formwork is minimized. The design constraints include limits on the minimum deflection, flexural and shear strengths, in addition to ductility requirements, and upper-Lower bounds on design variables as stipulated by the specification. The optimization is carried out using the methods based on discretized continuum-type optimality criteria(DCOC). Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables - effective depth, eccentricity of prestressing steel and non prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. In this paper the effective depth is considered to be freely-varying and one uniform for the entire multispan beam respectively. Also the maximum eccentricity of prestressing force is considered in every span. In order to show the applicability and efficiency of the derived algorithm, several numerical examples of PRC continuous beams are solved.

• Journal of the Korea Concrete Institute
• /
• v.14 no.6
• /
• pp.900-909
• /
• 2002

Fibers play a role to increase the tensile strength and cracking resistance of concrete structures. The post cracking behavior must be clarified to predict cracking resistance of fiber reinforced concrete. The purpose of this study is to develop a realistic analysis method for the post cracking behavior of synthetic fiber reinforced concrete members. For this purpose, the cracked section is assumed to behave as a rigid body and the pullout behavior of single fiber is employed. A probabilistic approach is used to calculate effective number of fibers across crack faces. The existing theory is compared with test data and shows good agreement. The proposed theory can be efficiently used to describe the load-deflection behavior, moment-curvature relation, load-crack width relation of synthetic fiber reinforced concrete beams.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.5
• /
• pp.39-52
• /
• 1993

For the lateral-torsional buckling analysis of the thin-walled space frame and circular arch with the unsymmetric cross section, the tangent stiffness matrices are derived by introducing Vlasov's assumption for the thin-walled beam and using the principle of virtual displacement. In the cases of the unrestrained torsion and the restrained torsion, the elastic and geometric stiffness matrices corresponding to semitangential rotation and semitangential moment are evaluated by using the Hermitian polynomials as the shape function. In order to illustrate the accuracy and convergence characteristics of the derived formulations, numerical examples for the lateral-torsional buckling analysis of the hinged circular arch under pure bending and uniform compression are presented and compared with the analytic solutions of references.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.6
• /
• pp.201-212
• /
• 2007

This study presents experimental results of Steel-PSC mixed structural system having front-rear plate connection between Steel and Prestressed Concrete. Two kinds of Steel-PSC mixed structural system of 5.4m length were tested to evaluate flexural behaviors under four point loading, and 4 kinds of specimens with and without prestressing force at R & L type connection were tested to observe the shear behavior. Based on the test results of load-deflection curves and failure modes of specimens, it is found that the proposed L shape connection with front-rear plate connection between Steel and Prestressed Concrete has higher strength and stiffness. From the study, Steel-PSC mixed structural system with L shaped connection has a better structural performance in connection part.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.2 s.54
• /
• pp.122-128
• /
• 2009

This study is to improve constructability of LB-DECK construction in site such as inconvenience of main and distribution bars in arrangements LB-DECK Panel which is work is applied to many bridges these days as a permanent formwork. So, the constructability is improved by changing the method of allocation of main reinforcing bar and distribution bar which is reviewed for improving efficiency of design and construction process among the suggested methods. The crack shapes, deflections, and strains under static load of the improvement of LB-DECK Panel are compared and analyzed to former LB-DECK Panel. As a result, 13% of strength compared to before the improvement of LB-DECK Panel, and 10% of strength is increased in the case of slab.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.1
• /
• pp.30-39
• /
• 2017

This paper concerns flexural strength of reinforced concrete beams containing recycled coarse aggregate (RCA) with compressive strength ranging from 31 to 38 MPa. The experimental parameters were replacement ratio of RCA and rebar ratio. Replacement ratio of RCA was 0, 30, 50 and 100%, and rebar ratio was 0.50, 0.79 and 1.14%. The RCA concrete beams were tested by using four-point bending test, and experimental results were discussed regarding crack and failure patterns, load-deflection relationship. Crack pattern of concrete beams with RCA was similar to that of concrete beams with natural coarse aggregate (NCA) but overall crack spacing of concrete beams with RCA was smaller than that of concrete beams with NCA. The crack width of RCA and NCA concrete beams was similar to each other. In addition, the test results of flexural strength were compared to the design code predictions. The design code predictions for flexural strength underestimated the experimental results. Therefore, the design code predictions for flexural strength of RCA concrete beams would offer conservative design.