• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.95-104
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• 2016

Flexural strength of concrete ground slab reinforced with steel fiber is evaluated using the equivalent flexural strength ratio of steel fiber reinforced concrete based on the yield line theory. Recently, the European standard specifies that the tensile performance of the steel fiber reinforced concrete be evaluated directly from the residual flexural strength after the cracking of concrete. Thus, in the study, an experiment was carried out to evaluate the conventional equivalent flexural strength ratio and the residual flexural strength of the steel fiber reinforced concrete. Then the design flexural strength was investigated according to the location of a point load, based on the ratio of the radius of contact area of the load to the radius of relative stiffness. Design flexural capacity obtained from ACI 360R-10 was smaller than that from TR 34 (2003 & 2013). In addition, TR 34 (2013), which evaluates the design flexural capacity based on the residual flexural strength, showed slightly smaller value than TR 34 (2003).

• Journal of Navigation and Port Research
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• v.35 no.10
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• pp.823-827
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• 2011

The present Common Structural Rules for double hull oil tanker is not included the residual strength, which is one of the functional requirements in design part of Goal-based new ship construction standards (GBS). The GBS will be enforced after July 1, 2016. The requirement related residual strength has the goal to build safe ship even if she has the specified damages due to marine accidents including collision and grounding. In order to assess the residual strength based on risk for structural damages according to GBS, tons of nonlinear FE analysis work taking into account various types of damage will be needed. The Smith's method, a kind of simplified method for the strength analysis is very useful for this purpose. In this paper, the residual strength assessments based on ultimate strength using Smith's method were carried out. The objected ship is VLCC with stranding damage in bottom structures. Also, the results were compared with that of nonlinear FE analysis using three cargo hold model.

• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.23-34
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• 2012

In this study, stub columns subjected to concentrical and eccentrical loads were tested to check the applicability of the current local stability criteria (KBC2009, AISC2005) to 800MPa high-strength steel (HSA800). The key test variables in the concentrically loaded tests included the plate-edge restraints and the width-to-thickness ratio normalized by the yield strength of steel. Specimens made of ordinary steel (SM490) were also tested for comparative purposes. Eccentrically loaded stub column tests were conducted for a range of the P-M combinations by controlling the loading eccentricity. All the concentrically loaded specimens with non-compact and slender sections developed sufficient strengths according to the current local stability criteria. All the eccentrically loaded specimens with non-compact H sections also exhibited a sufficient P-M interaction strength that was even higher than that of compact H- section counterparts. Residual stresses were also measured by using the non-destructive indentation method to demonstrate their dependency or independency on the steel material's yield strength. The measured results of this study also indicated that the magnitude of residual stresses bears no strong relation to the yield strength of the steel material.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.377-386
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• 2015

In this study, inelastic buckling strength of HSA800 steel columns were tested to investigate the applicability of current column curve (KBC2009, 2010 AISC-LRFD) to HSA800 steel. Key test variables included width-thickness ratio, plate-edge restraints, and column slenderness ratio. Specimens made of ordinary steel (SM490) were also tested for comparison purposes. All the concentrically loaded HSA800 specimens exhibited sufficient buckling strength compared to the current column curve, but some of SM490 specimens showed understrength. This difference can be explained by the lower residual stress present in HSA800 specimens.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1900-1907
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• 2012

Since the subpanels of polygonal-section shell have the corners of an obtuse angle larger than 90 degree unlike general plate or box-section structures, this could have an influence on forming nodal lines against local plate buckling or stress distributions. However, there is not sufficient material in the relevant study results or design recommendations. The very feasible models of the initial imperfections were acquired through the literature studies and then the parametric studies were conducted along with the initial imperfection models by using the finite element method. The parameters like the size of residual stresses, the portion of compressive residual stresses, and steel grades were considered. From the parametric studies, it was found that the maximum residual stress is more influential factor than the distribution pattern of residual stresses. In addition, The design strength equations for the simply supported plates can be applicable to the determination of the local buckling strength of the polygonal cross-section shell structures.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.321-330
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• 2009

This paper presents numerical analysis results for the lateral-torsional buckling (LTB) strength of steel I-girder bridges. Current Korean and AASHTO design specifications for LTB consider the buckling strength of a single girder with both its ends constrained. The I-girder bridges are composed of more than one girder, and the girders are interconnected with intermediate cross-beams or cross-frames. Therefore, it should be required to evaluate the effects of cross-beam stiffness and the interactionof girders on LTB strength. It is also necessary to consider the effects of transverse web stiffeners on LTB strength. By considering these parameters, a series of four-girder systemswere numerically modeled using 3D shell elements to estimate the LTB strength while considering initial imperfections and residual stresses.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.33-42
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• 2004

Making use of SN steel in the building structure should be a prerequisite to adopt the design strength of said steel. As a preceding study, the material properties of STKN400B/490B tubes and SPAP235/325 and SPAR295 square pipes manufactured using SN400B/490B plates were evaluated. Compared with the yield and ultimate strengths of SN400B/490B plates, those of STKN400B/490B tubes increase. Nonetheless, the yield and ultimate strengths of STKN400B/490B tubes satisfied the design codes of STKN400B/490B tubes even though the tubes were fabricated via roll bending or press forming. On the other hand, the yield and ultimate strengths at the edges of SPAP235/325 square pipes did not satisfy the design codes based on the values at the sides. The maximum tensile and compressive residual stresses at the SN490B tube were equal to and 40% of the yield strength of the SN490B plate, respectively, In the case of the SPAP325 square pipe, both the maximum tensile and compressive residual stresses were 80% of the yield strength of the SN490B plate. The axial compressive loaded column test results snowed that the buckling strengths were not very different regardless of the mode of fabrication of STKN490B tunes. i.e., through roll bending or press forming. On the other hand, the buckling strength of the SPAP325 square pipe was higher than that of the built-up square pipe.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1179-1185
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• 2011

Cold and hot-rolled carbon steel sheets are commonly used in railroad cars or commercial vehicles such as the automobile. The sheets used in these applications are mainly fabricated by spot welding, which is a type of electric resistance welding. However, the fatigue strength of a spot-welded joint is lower than that of the base metal because of high stress concentration at the nugget edge of the spot-welded part. In particular, the fatigue strength of the joint is influenced by not only geometrical and mechanical factors but also the welding conditions for the spot-welded joint. Therefore, there is a need for establishing a reasonable criterion for a long-life design for spot-welded structures. In this thesis, ${\Delta}P-N_f$ relation curves have been used to determine a long-life fatigue-design criterion for thin-sheet structures. However, as these curves vary under the influence of welding conditions, mechanical conditions, geometrical factors, etc. It is very difficult to systematically determine a fatigue-design criterion on the basis of these curves. Therefore, in order to eliminate such problems, the welding residual stresses generated during welding and the stress distributions around the weld generated by external forces were numerically and experimentally analyzed on the basis of the results, reassessed fatigue strength of gas welded joints.

• 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.25 no.2
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• pp.141-151
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• 2013

In this paper, lateral-torsional buckling(LTB) strength of HSB800 steel plate girder under uniform bending moment was estimated by the nonlinear analysis. Doubly symmetric sections with slender, noncompact and compact webs were considered and the LTB strength in the inelastic range was estimated by taking initial imperfection and residual stress into account. For the numerical analysis, single-panel model and three-panel model were considered and analysis of SM490 steel plate girder was performed to judge the validity of the constructed models by comparing the results with AASHTO, AISC, Eurocode and KHBDC(LSD) codes. By using the same models, LTB strength of HSB800 girder was evaluated and it was acknowledged that the current codes can be applied to HSB800 girders with doubly symmetric section in the inelastic LTB range.