• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.281-288
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• 2014

As a gas explosion is the most fatal accident in shipbuilding and offshore plant industries, all safety critical elements on the topside of offshore platforms should retain their integrity against blast pressure. Even though many efforts have been devoted to develop blast-resistant design methods in the offshore engineering field, there still remain several issues needed to be carefully investigated. From a procedure for calculation of explosion design pressure, impulse of a design pressure model having completely positive side only is determined by the absolute area of each obtained transient pressure response through the CFD analysis. The negative pressure phase in a general gas explosion, however, is often quite considerable unlike gaseous detonation or TNT explosion. The main objective of this study is to thoroughly examine the effect of the negative pressure phase on structural behavior. A blast wall for specific FPSO topside is selected to analyze structural response under the blast pressure. Because the blast wall is considered an essential structure for blast-resistant design. Pressure time history data were obtained by explosion simulations using FLACS, and the nonlinear transient finite element analyses were performed using LS-DYNA.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.92-103
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• 2015

Box-Wilson experimental design method, known as central composite design, is the design of any information-gathering exercises where variation is present. This method was devised to gather as much data as possible in spite of the low design cost. This method was employed to model the effect of mixing factors on several performances of 60 MPa high strength self compacting concrete and to numerically calculate the optimal mix proportion. The nonlinear relations between factors and responses of HSSCC were approximated in the form of second order polynomial equation. In order to characterize five performances like compressive strength, passing ability, segregation resistance, manufacturing cost and density depending on five factors like water-binder ratio, cement content, fine aggregate percentage, fly ash content and superplasticizer content, the experiments were made at the total 52 experimental points composed of 32 factorial points, 10 axial points and 10 center points. The study results showed that Box-Wilson experimental design was really effective in designing the experiments and analyzing the relation between factor and response.

• Earthquakes and Structures
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• v.12 no.4
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• pp.397-407
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• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.

• 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.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.4
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• pp.73-86
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• 1998

The purpose of this paper is to evaluate the shear stiffness, hysteretic behavior, and ultimate behavior of HDRB(High Damping Rubber Bearing), which will be included in the seismic isolation design guideline as requirements. To do this, two 1/8 scaled HDRB are designed, fabricated, and tested to show the mechanical characteristics. The shear stiffness obtained from the proposed equation of the shear stiffness shows a good agreement with those of the experiments. For analysis of the hysteretic behavior of HDRB using the modified rate model, the parameter equations are obtained from the experiments. Using the obtained parameter equations for the modified rate model, the seismic response analyses are carried out for 1-D system. The results of analysis well follow the hysteretic behavior of HDRB obtained from the experiments. To evaluate the ultimate behavior of HDRB used in this paper, the analyses are carried out using the modified macro model, which can consider the large shear deflection. The critical shear strain(CSS) is defined to express the maximum allowable shear strain and vertical load. From the analyses, the CSS, showing the instability, decreases significantly as increased the vertical loads. The CSS is not appeared for the design vertical load in the used HDRB. In analysis using about 5 times of design vertical load, the HDRB start to show the instability transient and for about 7 times, the CSS is about 350%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.130-137
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• 2017

The purpose of this study is to provide a reasonable analytical method for the reinforced concrete beams which shows failure mode of shear and flexure-shear by proposing a modified formulation to consider the effect of shear deformation on the beam-column fiber element based on the flexibility method and a new constitutive law of inelastic shear response history for the section. A total of 6 specimens of reinforced concrete beams which is designed to cause shear failure before yielding longitudinal reinforcement to investigate the influence of the main experimental variables on the shear behavior characteristics and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the newly modified constitutive equation by the authors. The failure mode and the overall behavior characteristics until fracture are predicted appropriately for all specimens and the results are expected to be useful enough for the 3 - D analysis to carry out reliable results of large-scale and complicated structures in the future.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.49-56
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• 2024

An automated dynamic structural analysis module stands as a crucial element within a structural integrated mitigation system. This module must deliver prompt real-time responses to enable timely actions, such as evacuation or warnings, in response to the severity posed by the structural system. The finite element method, a widely adopted approximate structural analysis approach globally, owes its popularity in part to its user-friendly nature. However, the computational efficiency and accuracy of results depend on the user-provided finite element mesh, with the number of elements and their quality playing pivotal roles. This paper introduces a computationally efficient adaptive mesh generation scheme that optimally combines the h-method of node movement and the r-method of element division for mesh refinement. Adaptive mesh generation schemes automatically create finite element meshes, and in this case, representative strain values for a given mesh are employed for error estimates. When applied to dynamic problems analyzed in the time domain, meshes need to be modified at each time step, considering a few hundred or thousand steps. The algorithm's specifics are demonstrated through a standard cantilever beam example subjected to a concentrated load at the free end. Additionally, a portal frame example showcases the generation of various robust meshes. These examples illustrate the adaptive algorithm's capability to produce robust meshes, ensuring reasonable accuracy and efficient computing time. Moreover, the study highlights the potential for the scheme's effective application in complex structural dynamic problems, such as those subjected to seismic or erratic wind loads. It also emphasizes its suitability for general nonlinear analysis problems, establishing the versatility and reliability of the proposed adaptive mesh generation scheme.

• Computers and Concrete
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• v.22 no.3
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• pp.337-353
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• 2018

The present study focuses on examining the structural behaviour of steel-fibre-reinforced concrete (SFRC) beams under high rates of loading largely associated with impact problems. Fibres are added to the concrete mix to enhance ductility and energy absorption, which is important for impact-resistant design. A simple, yet practical non-linear finite-element analysis (NLFEA) model was used in the present study. Experimental static and impact tests were also carried out on beams spanning 1.3 meter with weights dropped from heights of 1.5 m and 2.5 m, respectively. The numerical model realistically describes the fully-brittle tensile behaviour of plain concrete as well as the contribution of steel fibres to the post-cracking response (the latter was allowed for by conveniently adjusting the constitutive relations for plain concrete, mainly in uniaxial tension). Suitable material relations (describing compression, tension and shear) were selected for SFRC and incorporated into ABAQUS software Brittle Cracking concrete model. A more complex model (i.e., the Damaged Plasticity concrete model in ABAQUS) was also considered and it was found that the seemingly simple (but fundamental) Brittle Cracking model yielded reliable results. Published data obtained from drop-weight experimental tests on RC and SFRC beams indicates that there is an increase in the maximum load recorded (compared to the corresponding static one) and a reduction in the portion of the beam span reacting to the impact load. However, there is considerable scatter and the specimens were often tested to complete destruction and thus yielding post-failure characteristics of little design value and making it difficult to pinpoint the actual load-carrying capacity and identify the associated true ultimate limit state (ULS). To address this, dynamic NLFEA was employed and the impact load applied was reduced gradually and applied in pulses to pinpoint the actual failure point. Different case studies were considered covering impact loading responses at both the material and structural levels as well as comparisons between RC and SFRC specimens. Steel fibres were found to increase the load-carrying capacity and deformability by offering better control over the cracking process concrete undergoes and allowing the impact energy to be absorbed more effectively compared to conventional RC members. This is useful for impact-resistant design of SFRC beams.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.377-387
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• 2014

This study mainly treats a new type of the bracing friction damper system, which is able to minimize structural damage under earthquake loads. The slotted bolt holes are placed on the shear faying surfaces with an intention to dissipate considerable amount of friction energy. The superelastic shape memory alloy (SMA) wire strands are installed crossly between two plates for the purpose of enhancing recentering force that are able to reduce permanent deformation occurring at the friction damper system. The smart recentering friction damper system proposed in this study can be expected to reduce repair cost as compared to the conventional damper system because the proposed system mitigates the inter-story drift of the entire frame structure. The response mechanism of the proposed damper system is firstly investigated in this study, and then numerical analyses are performed on the component spring models calibrated to the experimental results. Based on the numerical analysis results, the seismic performance of the recentering friction damper system with respect to recentering capability and energy dissipation are investigated before suggesting optimal design methodology. Finally, nonlinear dynamic analyses are conducted by using the frame models designed with the proposed damper systems so as to verify superior performance to the existing damper systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1055-1067
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• 1994

This paper is presented to perform linear dynamic analysis of bridges due to vehicle moving on bridges. The road surface roughness and bridge/vehicle interaction are also considered. The bridge and vehicle are modeled as 3-D bridge and vehicle model, respectively. The road surface roughness of the roadway and bridge decks are generated from power spectral density(PSD) function for good road. The PSD function proposed by C.J. Dodds and J.D. Robson is used to describe the road surface roughness for good road condition. The vehicles are modeled as two nonlinear vehicle model with 7-D.O.F of truck and 12-D.O.F of tractor-trailer and the equations of motion of the vehicles are derived using Lagrange's equation. The main girder and concrete deck are modeled as beam and shell element, respectively and rigid link is used between main girder and concrete deck. The equations of motion of the vehicles are solved by Newmark ${\beta}$ method and the equations of the motion of the bridges are solved by mode-superposition procedures. The validity of the proposed procedure is demonstrated by comparing the results with the experimental data reported by the AASHO Road Test. The comparison shows that the agreement between experiment and theory is quite satisfactory.