• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.6 s.58
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• pp.97-105
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• 2009

This study was conducted for the purpose of examinating the safety and economical efficiency of large high tension bolted joints. The specimen using F10T-M30 large high strength bolts has been selected and static tensile test has been conducted to evaluate the slip characteristics. In addition, finite element analysis has been carried out to estimate the number of required bolts. As a result, the average slip coefficient of M30 high strength bolts exceeded 0.4 - the standard in highway bridge design specification - and has satisfied the slip strength, which is the same as that of M22 high strength bolts. In addition, if F13T-M22 high strength bolts were applied, the number of required bolts decreased by 21%, and if F10T-M30 high strength bolts were applied, the number of required bolts decreased by 46%, that leads to the conclusion that the economical efficiency in accordance with diametering of high strength bolts was now verified.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.135-142
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• 2022

In this study, lap spliced ultra-high strength reinforced concrete beams were tested and the code criteria for calculating the lap splice length which was affected by the transverse reinforcement and concrete covering performance were reviewed. The main variables for test were set as fiber volume fraction and transverse reinforcing bar arrangement to improve the confining performance of the concrete cover. The change of the confining performance of concrete cover according to the increase in the fiber mixing amount at 1% and 2% volume ratio was examined, and D10 stirrups with a spacing of 100 mm were placed in the lap spliced region. As a result of the test, the specimens confined by the stirrups showed a sudden drop of load bearing capacity with horizontal cracking at the position of tensile longitudinal reinforcement. However, horizontal cracks were not appeared at the location of longitudinal reinforcement for the specimens with steel fiber. And these specimens showed gradual decrease of load bearing capacity after experiencing peak load. In particular, it was found that the strain at the position of the tensile longitudinal reinforcements of the specimens to which the mixing ratio of 2% was applied exceeds the yield strain. As a result of measuring the strain on the concrete surface, it was found that the fiber was more effective in preventing damage to the concrete surface than the stirrups for short lap spliced region.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4D
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• pp.483-489
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• 2009

The endurance of expansion joint manufactured the Fe-Mn damping alloy reducing noise and vibration is analyzed into FEM (Finite Element Method) and fatigue test. The fatigue test have been performed using the expansion joint manufactured Fe-Mn damping alloy and the hydraulic actuator (25tonf). And the results of fatigue test show that the maximum strength is 237.6 MPa. Also that is 56.6 percent of Fe-Mn damping alloy yield strength (420 MPa). The loading plate size is prepared $57.7cm{\times}23.1cm$ and the loading plate's set position is located on expansion joint. The expansion joint manufactured the Fe-Mn damping alloy had not presented breaking behavior against 2,000,000 times fatigue test and identified the fatigue endurance.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.375-384
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• 2005

The effects of bar deformation properties on bond of steel reinforcing bars to concrete are experimentally studied to predict the bond strength. Based on the previous research about high relative rib area, bond strength between reinforcing bars and concrete can be improved by the control of rib height and spacing. But, the equations in Korean code provisions to estimate development and splice length do not include these specifications of reinforcing bars. So the purpose of this paper is to determine the effect of relative rib area to the bond strength. This paper describes 2 kinds of experimental researches. Thirty beam-end specimens were tested to investigate the effects of bar size and relative rib areas ranging from 0.112 to 0.162. And, twelve lap-splice beam specimens were tested to the same variables. Each test results are normalized and compared with the proposed equations of ACI 408 committee. The results show that bond strength is increased as bar size and the relative rib area(Rr) increase. The distribution of flexural cracks and failure aspect do not appear to be affected by $R_r$.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.111-120
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• 2012

This paper is a report about lap splice performance of rebar embedded in the strain-hardening cement-based composites (SHCCs) under monotonic and repeated tension loading. Ten mix proportions of cement-based composites such as SHCCs and normal concrete were investigated. The study parameters are comprised of (1) types of reinforcing fibers (polyethylene and steel fiber), (2) replacement levels of expansive admixture (EXA, 0% and 10%), and (3) compressive strength (30 and 100 MPa) of cement-based composites. Lap splice lengths (ld) of rebars in SHCC materials and normal concrete were 60% and 100% of splice length calculated by code requirements for structural concrete, respectively. Test results indicated that SHCCs materials can lead to enhancements in the lap splice performance of embedded rebar. All of the fiber reinforcement conditions (PE-SHCC and PESF-SHCC) considered in this study produced considerable improvements in the tensile strength, cracking behavior, and bond strength of lap-spliced rebar. Furthermore, adding EXA to SHCC matrix improved the tensile lap splice performance of rebar in SHCC materials. However, for controlling crack behavior, the performance of PE-SHCC was better than that of PESF-SHCC due to its mechanical properties. This study demonstrated an effective approach for reducing required development length of lap spliced rebar by using SHCC materials.

• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.23-30
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• 2015

Developed in this study were Octagonal-hollow-section(OHS) struts, whose compressive strengths against flexural and local buckling is higher than H-shape or rectangular-hollow-section(RHS) struts with the same unit weight. OHS members are also advantageous in handling and storing compared to circular hollow sections(CHS). OHS members were fabricated from HR Plates by cold forming and fillet welding. 5 numbers of 20m long OHS struts were assembled, each of which consist of two 9.6m long OHS member and two end connection elements made of cast iron. The compressive strength of the OHS strut was evaluated by comparing the test results, design codes and FEM analysis each other. Test results show that all of the struts have almost same or larger compressive strength than Korean Road Bridge Design Code(KRBDC) (2012). The initial imperfections can be estimated by using measured strains and are turned out to be less than L/450 for all the struts tested. The results of FEM analysis show that the variation of initial imperfection has less effects on the compressive strength for struts with vertical surcharge than for those with self-weight only, while the strength decreases as the initial imperfection increases. As the result of this study, the allowable initial imperfection for 20m long OHS struts is recommended to be less than L/350 on job sites.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.53-61
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• 2013

A new deformation of reinforcing bar in coils was proposed to improve a machinability of straightening process, which has crescent-shaped transverse ribs with an inclination angle of 50 degrees, a crest width of $0.15d_b$, and a flank inclination of 55 degrees. The proposed deformation can increase contact area between a surface of re-bar and a groove of a roller during a straightening process and, therefore, it might reduce a damage of ribs, improve a final straightness, and enhance an efficiency of the straightening process. Splice tests were conducted to evaluate bond strengths of three types of re-bar in coils including the proposed re-bar, of which the inclination angles of transverse ribs were 50, 60, and 90 degrees, respectively. Test results show that the re-bars in coils have higher bond strengths than predicted strengths by equations of Orangun et al., ACI 408, and KCI by at least 10%. Correlation coefficients of bond strengths between a straight bar and re-bars in coils are 0.94 and more. Consequently, equations of the KCI code for determining development and splice lengths can be applied to the tested re-bars in coils.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1137-1143
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• 2010

This paper presents a fatigue design method for plug- and ring-type gas-welded joints, which takes into account the effects of welding residual stress. To develop this method, we simulated the gas-welding process by performing nonlinear finite element analysis (FEA) To validate the FEA results, numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. To evaluate the fatigue strength of plug- and ring-type gas-welded joints influenced by welding residual stresses, the use of stress amplitude $(\sigma_a)_R$, which includes the welding residual stress in gas welds, is proposed $(\sigma_a)_R$ on the basis of a modified Goodman equation that includes the residual stress effects. Using the stress amplitude $(\sigma_a)_R$ at the hot spot point of gas weld, the relations obtained as the fatigue test results for plug and ring type gas welded joints having various dimensions and shapes were systematically rearranged to obtain the $(\sigma_a)_R-N_f$ relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using $(\sigma_a)_R$.

• Journal of Korean Society of Steel Construction
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• v.9 no.3 s.32
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• pp.421-430
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• 1997

In this study, the static and the fatigue tests were performed with high tension bolted joints, of which the surfaces were spread with inorganic zinc-primer after shot-blast, and milling surface, and steel-natural surface, difference of friction surface condition were examined by comparing the esults of tests. From the result of synthetical investigation of this study. it is proper that using the torque management method in order to introduce design axial force to blots, and the provision of specifications that initial axial forces must be 110% of design axial forces is proper. Decreasing ratio of axial forces to initial force is proportional to common lorgarithms of time progress, it converge constant value after 20 hours, and decreasing ratio is little related to the roughness of friction surface. Sliding coefficient of milling, spreading inorganic zinc-primer, just producting is great in order and sliding forces are dependent on the applied axial forces, but if the applied axial forces are great, sliding coefficient become small by a loss of roughness. So it is confirmed that relation between the applied axial forces and the sliding forces are not proportional linearly. From the result of estimation on fatigue strength, all specimens satisfy the specifications with B-grade and milling surface is lower than the others about 14% in fatigue strength because in milling surface lose the function of friction-types joints at lower number of cycles. From the result of eximination for the distribution area of compressive force, friction area near to inside bolt is wider in the direction of stress than near to outside. It is guessed that this situation occurs because outside bolts firstly change from the friction connection to the bearing connection.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.195-204
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• 2012

In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.