• Steel and Composite Structures
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• v.50 no.1
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• pp.107-122
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• 2024

Following an internal column failure, adjacent double-span beams above the failed column will play a critical role in the load transfer and internal force redistribution within the remaining structure, and the span-to-depth ratios of double-span beams significantly influence the structural resistance capacity against progressive collapse. Most existing studies have focused on the collapse-resistant performances of single-story symmetric structures, whereas limited published works are available on the collapse resistances of multi-story steel frames with unequal spans. To this end, in this study, numerical models based on shell elements were employed to investigate the structural behavior of multi-story steel frames with unequal spans. The simulation models were validated using the previous experimental results obtained for single- and two-story steel frames, and the load-displacement responses and internal force development of unequal-span three-story steel frames under three cases were comprehensively analyzed. In addition, the specific contributions of the different mechanism resistances of unequal-span, double-span beams of each story were separated quantitatively using the energy equilibrium theory, with an aim to gain a deeper level of understanding of the load-resistance mechanisms in the unequal-span steel frames. The results showed that the axial and flexural mechanism resistances were determined by the span ratio and linear stiffness ratio of double-span beams, respectively.

• Steel and Composite Structures
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• v.52 no.2
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• pp.199-215
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• 2024

The Caynarachi Bridge is a 130 m long posttensioned steel-concrete composite bridge built in Peru. The structural performance of this bridge under construction loads is reviewed in this paper using numerical simulation. Hence, a numerical model using shell finite elements to trace its deformational behavior at service conditions is proposed. The geometry and boundary conditions of the superstructure are updated according to the construction schedule. Firstly, the adequacy of the proposed model is validated with the field measurements obtained from the static truck load test. Secondly, the study of other scenarios less explored in research are performed to investigate the effect of some variables on bridge performance such as time effects, sequence of execution of concrete slabs and type of supports conditions at the abutments. The obtained results show that the original sequence of execution of the superstructure better behaves mechanically in relation to the other studied scenarios, yielding smaller stresses at critical cross sections with staging. It is also demonstrated that an improper slab staging may lead to more critical stresses at the studied cross sections and that casting the concrete slab at the negative moment regions first can lead to an optimal design. Also, the long-term displacements can be accurately predicted using an equivalent composite resistance cross section defined by a steel to concrete modulus ratio equal to three. This article gives some insights into the potential shortcomings or advantages of the original design through high-fidelity finite element simulations and reinforces the understating of posttensioned composite bridges with staging.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.271-282
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• 2006

The behavior of the concrete slabs on grade considering the horizontal resistance at the slab bottom, which exists due to the shear resistance of the foundation and the friction between the slab and the foundation, has been investigated when the slabs-on-grade are subjected to the thermal load. Analytical formulations have been developed to include the effect of the horizontal resistance at the slab bottom employing the thin plate on an elastic foundation that is widely used for the analysis of concrete slabs-on-grade and rigid pavement systems. Finite element formulations have then been developed using the plate bending elements and the flat shell elements. The solutions from the analytical and numerical models have been compared and showed very good agreement. The sensitivity of the horizontal resistance to the stresses of the concrete slab has been investigated with various values of the slab thickness, elastic modulus, and vortical stiffness of the foundation when subjected to the temperature gradient between the top and bottom of the slab and the uniform temperature drop throughout the slab depth. The analysis results show that the horizontal resistance at the plate bottom can significantly affect the stresses of the slab when the thermal loads are applied.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.75-82
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• 2007

This paper addresses a method for shape optimization of a continuous elastic body considering stability, i.e., buckling behavior. The sensitivity formula for critical load is analytically derived and expressed in terms of shape variation, based on the continuum formulation of the stability problem. Unlike the conventional finite difference method (FDM), this method is efficient in that only a couple of analyses are required regardless of the number of design parameters. Commercial software such as ANSYS can be employed since the method requires only the result of the analysis in computation of the sensitivity. Though the buckling problem is more efficiently solved by structural elements such as a beam and shell, elastic solids have been chosen for the buckling analysis because solid elements can generally be used for any kind of structure whether it is thick or thin. Sensitivity is then computed by using the mathematical package MATLAB with the initial stress and buckling analysis of ANSYS. Several problems we chosen in order to illustrate the efficiency of the presented method. They are applied to the shape optimization problems to minimize weight under allowed critical loads and to maximize critical loads under same volume.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.233-245
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• 2007

Previous finite element studies have shown that AASHTO Standard load distribution factor (LDF) equations appear to be conservative for longer spans and larger girder spacing, but too permissible for short spans and girder spacing. AASHTO LRFD specification defines the distribution factor equation for girder spacing, span length, slab thickness, and longitudinal stiffness. However, this equation requires an iterative procedure to correctly determine the LDF value due to an initially unknown longitudinal stiffness parameter. This study presents a simplified LDF equation for interior and exterior girders of two-span continuous I-girder bridges that does not require an iterative design procedure. The finite element method was used to investigate the effect of girder spacing, span length, slab thickness, slab width, and spacing and size of bracing. The computer program, GTSTRUDL, was used to idealize the bridge superstructures as the eccentric beam model, the concrete slab by quadrilateral shell elements, steel girders by space frame members, and the composite action between these elements by rigid links. The distribution factors obtained from these analyses were compared with those from the AASHTO Standard and LRFD methods. It was observed through the parametric studies that girder spacing, span length, and slab thickness were the dominant parameters compared with others. The LRFD distribution factor for the interior girder was found to be conservative in most cases, whereas the factor for the exterior girder to be unconservative in longer spans. Furthermore, a regression analysis was performed to develop simplified LDF formulas. The formulas developed in this study produced LDF values that are always conservative to those from the finite element method and are generally smaller than the LDF values obtained from the AASHTO LRFD specification. The proposed simplified equation will assist bridge engineers in predicting the actual LDF in two-span continuous I-girder bridges.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.333-340
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• 2019

Tests using a middle velocity propulsion impact machine (MVPIM) were performed to verify the impact resistance capability of sandwich concrete panels (SCP) in a modular liquefied natural gas (LNG) outer tank, and numerical models were constructed and analyzed. $2{\times}2m$ specimens with plain sectional characteristics and specimens including a joint section were used. A 51 kg missile was accelerated above 45 m/s and impacted to have the design code kinetic energy. Impact tests were performed twice according to the design code and once for the doubled impact speed. The numerical models for simulating impact behaviors were created by LS-DYNA. The external steel plate and filled concrete of the panel were modeled as solid elements, the studs as beam elements, and the steel plates as elasto-plastic material with fractures; the CSCM material model was used for concrete. The front plate deformations demonstrated good agreement with those of other tests. However the rear plate deformations were less. In the doubled speed test for the plain section specimen, the missile punctured both plates; however, the front plate was only fractured in the numerical analysis. The impact energy of the missile was transferred to the filled concrete in the numerical analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.93-100
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• 2022

The collision behaviors of the tripod and jacket structures, which are considered as support structures for offshore wind towers at the Southwest sea of Korea, were compared by nonlinear dynamic analysis. These structures, designed for the 3 MW capacity of the wind towers, were modeled using shell elements with nonlinear behaviors, and the tower structure including the nacelle, was modeled by beam and mass elements with elastic materials. The mass of the tripod structure was approximately 1.66 times that of the jacket structure. A barge and commercial ship were modeled as the collision vessel. To consider the tidal conditions in the region, the collision levels were varied from -3.5 m to 3.5 m of the mean sea level. In addition, the collision behaviors were evaluated as increasing the minimum collision energy at the collision speed (=2.6 m/s) of each vessel by four times, respectively. Accordingly, the plastic energy dissipation ratios of the vessel were increased as the stiffness of collision region. The deformations in the wind tower occurred from vibration to collapse of conditions. The tripod structure demonstrated more collision resistance than the jacket structure. This is considered to be due to the concentrated centralized rigidity and amount of steel utilized.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.305-313
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• 2008

A reliability based calibration of dynamic load allowance (DLA) of highway bridge is performed by numerical dynamic analysis of various types of bridges taking into account of the road surface roughness and bridge-vehicle interaction. A total of 10 simply supported bridges with three girder types in the form of prestressed concrete girder, steel plate girder, and steel box girder is analyzed. The cross sections recommended in "The Standardized Design of Highway Bridge Superstructure" by the Korean Ministry of Construction are used for the prestressed concrete girder bridges and steel plate girder bridges while the box girder bridges are designed by the LRFD method. Ten sets of road surface roughness for each bridge are generated from power spectral density (PSD) function by assuming the roadway as "Average Road". A three dimensionally modeled 5-axle tractor-trailer with its gross weight the same as that of DB-24 design truck is used in the dynamic analysis. For the finite element modeling of superstructure, beam elements for the main girder, shell elements for concrete deck, and rigid links between main girder and concrete deck are used. The statistical mean and coefficient of variation of DLA are obtained from a total of 100 DLA results for 10 different bridges with each having 10 sets of road surface roughness. Applying the DLA statistics obtained, the DLA is finally calibrated in a reliability based LRFD format by using the formula developed in the calibration of OHBDC code.

• Journal of Food Hygiene and Safety
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• v.3 no.1
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• pp.7-18
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• 1988

In 1987, the level of heavy metals were determined ina total of 200 samples of 9 species of shellfish of Korea. The samples were collected at the fish. markets by 10 Public Institute of Health. The samples were whelk (Buccinum striatiBBimum), oyster (Crassostrea gigas), ark shell(Tegillarca granesa), shartnecked clam (Venerupis semidecussta), hard clam (Meretrix lusoria), top shell (Turbo cornutus), abalone (Haliotis gigantea), ark shell (Scapharea broughtonii), sea-mussel (Mytilus conuscus gould), respectively. The levels of total mercury, lead, cadmium, arsenic, copper, zinc and manganese were determined. The total mercury levels were determined by mercury analyzer using the combustion gold amalgamation method. The arsenic level were determined by spectrophotometry using colorimetric sil ver diethyldithiocarbamate method after dry ash dige8tion of the samples with magnesium oxide and magnesium nitrate. The levels of other metals were determined by inductively coupled pluma spectrophotometry after wet digestion of the samples with nitric acid and su1furic acid. The results were summerized as follows; 1. The overallranges and mean(ppm) were; Hg, ND-O.221 (0.036); Pb, 0.05-1.51 (0.37); Cd, 0.02-1.86 (0.61); As, 0.5-3.97 (1.22); Cu, 0.14-54.16 (4.93); Zn, 7.40-207.17 (30.09); Mn, 0.13-s.72 (3.40). 2. The levels of all 6 metals were found to be below the maximum permissible Iimits set by the Japan lor mercury, the Netherland for lead the Hong Kong for cadmium. The Finland for Arsenic no statutory Iimits for Zn and Mn in shellfish in any countries. 3. The results show that all the 9 species of shellfish studied, none have accumulated levels dangerous enough to pose a health problem.roblem.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.81-92
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• 2013

The ultimate flexural strength of HSB I-girders, considering the effect of local bucking, was investigated through a series of nonlinear finite element analysis. The girders were selected such that the inelastic local flange buckling or the plastic yielding of compression flanges governs the flexural strength. Both homogeneous sections fabricated from HSB600 or HSB800 steel and hybrid sections with HSB800 flanges and SM570-TMC web were considered. In the FE analysis, the flanges and web were modeled using thin shell elements and initial imperfections and residual stresses were imposed on the FE model. An elasto-plastic strain hardening material was used for steels. After establishing the validity of present FE analysis by comparing FE results with test results published in the literature, the effects of initial imperfection and residual stress on the inelastic flange local buckling behavior were assessed. The ultimate flexural strengths of 60 I-girders with various compression flange slenderness were obtained by FE analysis and compared with those calculated from the KHBDC, AASHTO LRFD and Eurocode 3 provisions. Based on the comparison, the applicability of design equations in these specifications for the flexural strength of I-girder considering flange local buckling was evaluated.