• Earthquakes and Structures
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• v.16 no.4
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• pp.469-485
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• 2019

A numerical investigation regarding local (${\mu}_L$) and story (${\mu}_S$) ductility demand evaluation of steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (IGF), is conducted in this study. The interior connections are modeled, firstly as perfectly pinned (PP), and then as semi-rigid (SR). Three models used in the SAC steel project, representing steel buildings of low-, mid-, and high-rise, are considered. The story ductility reduction factor ($R_{{\mu}S}$) as well as the ratio ($Q_{GL}$) of $R_{{\mu}S}$ to ${\mu}_L$ are calculated. ${\mu}_L$ and ${\mu}_S$, and consequently structural damage, at the PMRF are significant reduced when the usually neglected effect of SR connections is considered; average reductions larger than 40% are observed implying that the behavior of the models with SR connections is superior and that the ductility detailing of the PMRF doesn't need to be so stringent when SR connections are considered. $R_{{\mu}S}$ is approximately constant through height for low-rise buildings, but for the others it tends to increase with the story number contradicting the same proportion reduction assumed in the Equivalent Static Lateral Method (ESLM). It is implicitly assumed in IBC Code that the overall ductility reduction factor for ductile moment resisting frames is about 4; the results of this study show that this value is non-conservative for low-rise buildings but conservative for mid- and high-rise buildings implying that the ESLM fails evaluating the inelastic interstory demands. If local ductility capacity is stated as the basis for design, a value of 0.4 for $Q_{GL}$ seems to be reasonable for low- and medium-rise buildings.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.1
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• pp.80-87
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• 2021

Most container ships are currently being constructed as Ultra-Large Container Ships. Hence, the equipment of the ships is also becoming relatively large. In particular, propellers, rudders, and rudder stocks are large in the stern structure, and in relation, efficient design of the hull structures to safely secure these parts is important. The bottom shell plate surface of a stern skeg is a perforated plate from which the rudder stock penetrates, so it is an important component for the stern structure. In this paper, to determine the critical buckling of the shell plate, an interaction curve equation for the two-axis compression of the shell plate was derived using the maximum value of the static structural stress multiplier in a load multiplier mode. This equation predicts the timing of the buckling occurrence. By analyzing this interaction curve equation, the buckling behavior of the plates subjected to a combination load was determined and the usefulness of applying it to ship building was investigated.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.873-882
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• 2012

Dual Phase (DP) steel which has a soft ferrite phase and a hard martensite phase reveals both high strength and high ductility and has received increased attention for use in automotive applications. To conduct structural analysis to verify vehicle safety, highly credible experimental results are required. In this study, tensile tests were performed in a strain rate range from $10^{-4}/s$ to 300/s for Sink Roll-Less (SRL) hot-dip metal coated sheets. Collision properties were estimated through simulation by LS-DYNA using the stress-strain curve obtained from the tensile test. The simulation results were compared with the actual crash test results to confirm the credibility of the simulation. In addition, a tensile test and a crash test with 2% prestrain and a baking (PB) specimen were evaluated identically because automotive steel is used after forming and painting. The mechanical behaviors were improved with an increasing strain rate regardless of the PB treatment. Thus, plastic deformation with an appropriate strain rate is expected to result in better formability and crash characteristics than plastic deformation with a static strain rate. The ultimate tensile strength (UTS) and absorbed energy up to 10% strain were improved even though the total elongation decreased after PB treatment, The results of the experimental crash test and computer simulation were slightly different but generally, a similar propensity was seen.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.115-135
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• 2021

This paper focuses on examining the effects of span arrangements on displacement responses of plan-symmetric RC frame buildings designed using the direct displacement-based design (DDBD) method by employing non-linear analyses and the skew seismic attack. In order to show the desired performance of DDBD design approach, the force-based design approach is also used to examine the seismic performance of the selected structures. To realize this objective, 8-story buildings with different plans are selected. In addition, the dynamic behavior of the structures is evaluated by selecting 3, 7, and 12-story buildings. In order to perform non-linear analyses, OpenSees software is used for modeling buildings. Results of an experimental model are used to validate the analytical model implemented in OpenSees. The results of non-linear static and non-linear dynamic analyses indicate that changing span arrangements does not affect estimating the responses of structures designed using the DDBD approach, and the results are more or less the same. Next, in order to apply the earthquake in non-principle directions, DDBD structures, designed for one-way performance, are designed again for two-way performance. Time history analyses are performed under a set of artificial acceleration pairs, applied to structures at different angles. It is found that the mean maximum responses of earthquakes at all angles have very good agreement with the design-acceptable limits, while the response of buildings along the height direction has a relatively acceptable and uniform distribution. Meanwhile, changes in the span arrangements did not have a significant effect on displacement responses.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.61-68
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• 2020

7-tonf turbopump real-propellant tests in Naro Space Center were conducted and high-frequency signals from an accelerometer and pressure sensors installed on the casing and the inlet/outlet pipeline of LOX pump were analyzed to estimate the structural and hydrodynamic stabilities. Waterfalls, frequency spectrums and RMS(Root Mean Square) values of the measured signals were calculated and characteristic instability frequencies by the rotating cavitation and the rear floating ring seal(F.R.S) were investigated. Static pressures of the inlet/outlet pipeline and an acceleration of the pump casing are strongly affected on pressure fluctuation induced by the rear floating ring seal in the leakage path. Despite the acceleration RMS value seems totally small, the rotating-speed-related synchronous frequency affecting the shaft instability is distinctly observed in the frequency contour.

• Structural Engineering and Mechanics
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• v.83 no.3
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• pp.327-340
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• 2022

The Collapse Margin Ratio (CMR) is a notable index used for seismic assessment of the structures. As proposed by FEMA P695, a set of analyses including the Nonlinear Static Analysis (NSA), Incremental Dynamic Analysis (IDA), together with Fragility Analysis, which are typically time-taking and computationally unaffordable, need to be conducted, so that the CMR could be obtained. To address this issue and to achieve a quick and efficient method to estimate the CMR, the Artificial Neural Network (ANN), Response Surface Method (RSM), and Adaptive Neuro-Fuzzy Inference System (ANFIS) will be introduced in the current research. Accordingly, using the NSA results, an attempt was made to find a fast and efficient approach to derive the CMR. To this end, 5016 IDA analyses based on FEMA P695 methodology on 114 various Reinforced Concrete (RC) frames with 1 to 12 stories have been carried out. In this respect, five parameters have been used as the independent and desired inputs of the systems. On the other hand, the CMR is regarded as the output of the systems. Accordingly, a double hidden layer neural network with Levenberg-Marquardt training and learning algorithm was taken into account. Moreover, in the RSM approach, the quadratic system incorporating 20 parameters was implemented. Correspondingly, the Analysis of Variance (ANOVA) has been employed to discuss the results taken from the developed model. Additionally, the essential parameters and interactions are extracted, and input parameters are sorted according to their importance. Moreover, the ANFIS using Takagi-Sugeno fuzzy system was employed. Finally, all methods were compared, and the effective parameters and associated relationships were extracted. In contrast to the other approaches, the ANFIS provided the best efficiency and high accuracy with the minimum desired errors. Comparatively, it was obtained that the ANN method is more effective than the RSM and has a higher regression coefficient and lower statistical errors.

• Journal of Korean Association for Spatial Structures
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• v.22 no.3
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• pp.25-32
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• 2022

In this paper, the instability of the domed spatial truss structure using wood and the characteristics of the buckling critical load were studied. Hexagonal space truss was adopted as the model to be analyzed, and two boundary conditions were considered. In the first case, the deformation of the inclined member is only considered, and in the second case, the deformation of the horizontal member is also considered. The materials of the model adopted in this paper are steel and timbers, and the considered timbers are spruce, pine, and larch. Here, the inelastic properties of the material are not considered. The instability of the target structure was observed through non-linear incremental analysis, and the buckling critical load was calculated through the singularities and eigenvalues of the tangential stiffness matrix at each incremental step. From the analysis results, in the example of the boundary condition considering only the inclined member, the critical buckling load was lower when using timber than when using steel, and the critical buckling load was determined according to the modulus of elasticity of timber. In the case of boundary conditions considering the effect of the horizontal member, using a mixture of steel and timber case had a lower buckling critical load than the steel case. But, the result showed that it was more effective in structural stability than only timber was used.

• Steel and Composite Structures
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• v.42 no.3
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• pp.407-426
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• 2022

Superior to traditional welded studs, high strength friction-grip bolted shear connectors facilitate the assembling and demounting of the composite members, which maximizes the potential for efficiency in the construction and retrofitting of new and old structures respectively. Hence, it is necessary to investigate the structural properties of high strength friction-grip bolts used in steel concrete composite beams. By means of push-out tests, an experimental study was conducted on post-installed high strength friction-grip bolts, considering the effects of different bolt size, concrete strength, bolt tensile strength and bolt pretension. The test results showed that bolt shear fracture was the dominant failure mode of all specimens. Based on the load-slip curves, uplifting curves and bolt tensile force curves between the precast concrete slab and steel beam obtained by push-out tests, the anti-slip performance of steel-concrete interface and shear behavior of bolt shank were studied, including the quantitative analysis of anti-slip load, and anti-slip stiffness, frictional coefficient, shear stiffness of bolt shank and ultimate shear capacity. Meanwhile, the interfacial anti-slip stiffness and shear stiffness of bolt shank were defined reasonably. In addition, a total of 56 push-out finite element models verified by the experimental results were also developed, and used to conduct parametric analyses for investigating the shear behavior of high-strength bolted shear connectors in steel-concrete composite beams. Finally, on ground of the test results and finite element simulation analysis, a new design formula for predicting shear capacity was proposed by nonlinear fitting, considering the bolt diameter, concrete strength and bolt tensile strength. Comparison of the calculated value from proposed formula and test results given in the relevant references indicated that the proposed formulas can give a reasonable prediction.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Steel and Composite Structures
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• v.43 no.1
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• pp.19-30
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• 2022

The static strength and fatigue crack resistance of the aircraft skin structures depend on the materials used and joint type. Most of the commercial aircraft's skin panel structures are made from aluminium alloy and carbon fibre reinforced epoxy. In this study, the fatigue resistance of four joint configurations (metal/metal, metal/composite, composite/composite and composite/metal) with riveted, adhesive bonded, and hybrid joining techniques are investigated with experiments and finite element analysis. The fatigue tests were tension-tension because of the typical nature of the loads on aircraft skin panels susceptible of experimenting fatigue. Experiment results suggest that the fatigue life of hybrid joints is superior to adhesive bonded joints, and these in turn much better than conventional riveted joints. Thanks to the fact that, for hybrid joints, the adhesive bond provides better load distribution and ensures load-carrying capacity in the event of premature adhesive failure while rivets induce compressive residual stresses in the joint. Results from FE tool ABAQUS analysis for adhesive bonded and hybrid joints agrees with the experiments. From the analysis, the energy release rate for adhesive bonded joints is higher than that of hybrid joints in both opening (mode I) and shear direction (mode II). Most joints show higher energy release rate in mode II. This indicates that the joints experience fatigue crack in the shear direction, which is responsible for crack opening.