• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.396-408
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• 2019

The tubes which are applied in jacket platforms as the supporting structure might be collided by supply vessels. Such kind of impact will lead to plastic deformation on tube members. As a result, the ultimate strength of tubes will decrease compared to that of intact ones. In order to make a decision on whether to repair or replace the members, it is crucial to know the residual strength of the tubes. After being damaged by lateral impact, the simply supported tubes will definitely loss a certain extent of load carrying capacity under uniform axial compression. Therefore, in this paper, the relationship between the residual ultimate strength of the damaged circular tube by collision and the energy dissipation due to lateral impact is investigated. The influences of several parameters, such as the length, diameter and thickness of the tube and the impact energy, on the reduction of ultimate strength are investigated. A series of numerical simulations are performed using nonlinear FEA software LS-DYNA. Based on simulation results, a non-dimensional parameter is introduced to represent the degree of damage of various size of tubes after collision impact. By applying this non-dimensional parameter, a simplified formula has been derived to describe the relationship between axial compressive residual ultimate and lateral impact energy and tube parameters. Finally, by comparing with the allowable compressive stress proposed in API rules (RP2A-WSD A P I, 2000), the critical damage of tube due to collision impact to be repaired is proposed.

• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.473-484
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• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.337-347
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• 2011

In this study, seismic resistance of concrete encased U-shaped steel beam-to-steel H-shaped column connections was evaluated. Three specimens of the beam-to-column connection were tested under cyclic loading. The composite beam was integrated with concrete slab using studs. Re-bars for negative moment were placed in the slab. The primary test parameter was the details of the connections, which are strengthening and weakening strategies for the beam end and the degree of composite action. The depth of the composite beams was 600mm including the slab thickness. The steel beam and the re-bars in the slab were weld-connected to the steel column. For the strengthening strategy, cover plates were weld-connected to the bottom and top flanges of the steel beam. For the weakening strategy, a void using styrofoam box was located inside the core concrete at the potential plastic hinge zone. The test results showed that the fully composite specimens exhibited good strength, deformation, and energy dissipation capacities. The deformation capacity of the beam exceeded 4% rotation angle, which is the requirement for the Special Moment Frame.

• Journal of the Korean Wood Science and Technology
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• v.35 no.3
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• pp.10-21
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• 2007

It is necessary to study about moment performance of glulam-dowel connections which had been applied rotation. To analyze and predict the moment performance, angled to grain load was replaced with parallel to grain load and perpendicular to grain load. The dowel bending strength and dowel bearing strength were tested. And tensile strength test for connections of two different end distances was performed. Specimens of rotation test were composed with different drift pin numbers and drift pin arrangement. Connection deformation was occurred by plastic behavior of drift pin after yield when tensile load applied at connection. And the absorbing drift pin deflection by end distance continued the connection deformation. When rotation applied at connection that 2 drift pins were arranged parallel to grain (b2h), it showed similar performance with tensile perpendicular to grain. And connection that 2 drift pins were arranged perpendicular to grain (b2v) showed similar performance with tensile parallel to grain. Connection capacity that 4 drift pins were arranged rectangular (b4) showed 1.7 times as strong as connection that 2 drift pins were arranged parallel to grain (b2h). These results agreed predicted values and it is available that rotation replaced with tensile load.

• Computers and Concrete
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• v.11 no.2
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• pp.123-148
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• 2013

The nonlinear finite element method with eight noded isoparametric quadrilateral element for concrete and two noded element for reinforcement is used for the prediction of the behavior of reinforcement concrete structures. The disturbed state concept (DSC) including the hierarchical single surface (HISS) plasticity model with associated flow rule with modifications is used to characterize the constitutive behavior of concrete both in compression and in tension which is named DSC/HISS-CT. The HISS model is applied to shows the plastic behavior of concrete, and DSC for microcracking, fracture and softening simulations of concrete. It should be noted that the DSC expresses the behavior of a material element as a mixture of two interacting components and can include both softening and stiffening, while the classical damage approach assumes that cracks (damage) induced in a material treated acts as a void, with no strength. The DSC/HISS-CT is a unified model with different mechanism, which expresses the observed behavior in terms of interacting behavior of components; thus the mechanism in the DSC is much different than that of the damage model, which is based on physical cracks which has no strength and interaction with the undamaged part. This is the first time the DSC/HISS-CT model, with the capacity to account for both compression and tension yields, is applied for concrete materials. The DSC model allows also for the characterization of non-associative behavior through the use of disturbance. Elastic perfectly plastic behavior is assumed for modeling of steel reinforcement. The DSC model is validated at two levels: (1) specimen and (2) practical boundary value problem. For the specimen level, the predictions are obtained by the integration of the incremental constitutive relations. The FE procedure with DSC/HISS-CT model is used to obtain predictions for practical boundary value problems. Based on the comparisons between DSC/HISS-CT predictions, test data and ANSYS software predictions, it is found that the model provides highly satisfactory predictions. The model allows computation of microcracking during deformation leading to the fracture and failure; in the model, the critical disturbance, Dc, identifies fracture and failure.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.71-84
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• 2003

The metallic shell of soil-steel structures are so weak in bending moment that it should sustain the applied load by the interaction of the backfill soil around the structures. The shell can be subjected to excessive bending moment during side backfilling or under live-load when the soil cover is less than the minimum value. The current design code specifies the allowable deformation and Duncan(1979) and McGrath et al.(2001) suggested the strength analysis methods to limit the moments by the plastic capacity of the shell. However, the allowable deformation is an empirically determined value and the strength analysis methods are based on the results of FE analysis, hence the experimental verification is necessary. In this study, the full-scale tests were conducted on the high-profile arch to investigate its behaviors during backfilling and under static live-loads. Based on the measurements, the allowable deformation of the tested structure could be estimated to be 1.45% of rise, which is smaller than the specified allowable deformation. The comparison between the measurements and the results of two strength analyses indicate that Duncan underestimates the earth-load moment and overestimates the live-load moment, while McGrath et al. predicts both values close to the actual values. However, as the predicted factors of safeties using two methods coincide with the actual factor of safety, it can be concluded that both methods can predict the structural stability under live-loads adequately when the cover is less than the minimum.

• Journal of Korean Association for Spatial Structures
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• v.8 no.2
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• pp.85-93
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• 2008

This study summarizes the results of a research project aimed at investigating the inelastic rotation capacity of beam-column joints of reinforced concrete special moment frames. All of the test specimens were classified as special moment frame (SMF), based on the design and detailing requirements of the ACI 318-02 provisions. The acceptance criteria, originally defined for steel moment frame connections in the 1997 edition of the AISC Seismic provisions, were used to evaluate the beam-column joints of the reinforced concrete moment frames. A total of 39 test specimens were examined in detail. Most of the joints that satisfy the design requirements for special moment frame structures were found to be ductile up to a plastic rotation of 3% without any major degradation in strength. This is mainly due to the stringent ACI 318-02 requirements for special moment frame joints. The presence of transverse beams increases confinement and shear resistance of joints, which results in better performance than for joints without transverse beams. All of the SMF connections that satisfy the ACI 318-02 limitations on joint shear stress turned out to meet the acceptance criteria.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.579-589
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• 2003

Most beam-to-column connections are symmetrically reinforced because of the reverse action caused by earthquakes. However, in weak-earthquake regions like Korea, asymmetrically reinforced connections could be used. In particular, the connections between concrete-filled tube (CFT) column and H-shape beam could be applied using a simplified lower diaphragm. The tensile capacity or Combined Cross Diaphragm for upper reinforcing was tested using a simple tension test. Four types for lower reinforcing combined Cross, none, horizontal T-bar, and vertical plate were tested using the ANSI/AISC SSPEC 2002 loading program. Horizontal T-bar and stud bolts in vertical flat, bar transmit tensile stress from the beam's bottom flange to filled concrete. All test specimens satisfied 0.01 radian inelastic rotational requirement in ordinary moment frame of AISC seismic provision. According to the results of the parametric studies simplified lower diaphragms demonstrated outstanding strength, stiffness, and plastic deformation capacity which could lead to more sufficient seismic performance in the field.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.201-209
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• 2010

Generally, PSC girder bridge uses total gross cross section to resist applied loads unlike reinforced concrete member. Also, it is used as short and middle span (less than 30 m) bridges due to advantages such as ease of design and construction, reduction of cost, and convenience of maintenance. But, due to recent increased public interests for environmental friendly and appearance appealing bridges all over the world, the demands for longer span bridges have been continuously increasing. This trend is shown not only in ordinary long span bridge types such as cable supported bridges but also in PSC girder bridges. In order to meet the increasing demands for new type of long span bridges, PSC hollow box girder with H-type steel as compression reinforcements is developed for bridge with a single span of more than 50 m. The developed PSC girder applies compressive prestressing at H-type compression reinforcements using unbonded PS tendon. The purpose of compressive prestressing is to recover plastic displacement of PSC girder after long term service by releasing the prestressing. The static test composed of 4 different stages in 3-point bending test is performed to verify safety of the bridge. First stage loading is applied until tensile cracks form. Then in second stage, the load is removed and the girder is unloaded. In third stage, after removal of loading, recovery of remaining plastic deformation is verified as the compressive prestressing is removed at H-type reinforcements. Then, in fourth stage, loading is continued until the girder fails. The experimental results showed that the first crack occurs at 1,615 kN with a corresponding displacement of 187.0 mm. The introduction of the additional compressive stress in the lower part of the girder from the removal of unbonded compressive prestressing of the H-type steel showed a capacity improvement of about 60% (7.7 mm) recovery of the residual deformation (18.7 mm) that occurred from load increase. By using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and rehabilitation of PSC girders are relatively easy, and the cost of maintenance is expected to decrease.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.271-280
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• 2010

This study was programmed to fabricate a beam-to-column connection that is limited to a steel-welded moment connection with full-scale members, using SN steel. A cyclic seismic test was conducted of the nine specimens that were fabricated by choosing the test variable for the weld access hole geometry, connection design method, and RBS. From the test results, failure modes, the moment-drift behavior, and the strain distribution were provided. From the specimen material properties, the beam's nominal plastic flexural capacity and classified qualified connection as a special moment flame were calculated. By analyzing the skeleton part and the baushinger part, a range of strength-raising effects, and deformation ratios were provided, with which the seismic performance of the specimens were evaluated. The test results showed that the specimens eliminated their weld access holes that demonstrated higher seismic performance than the specimens' existing weld access holes, and that the WUF-W connection that was reinforced by the supplemental fillet weld around the shear tap that was fastened by five bolts demonstrated superior seismic performance.