• Steel and Composite Structures
• /
• v.34 no.3
• /
• pp.377-391
• /
• 2020

A concrete filled steel tube (CFT) column with stiffeners has preferable behavior subjected to axial loading condition due to delay local buckling of the steel wall than traditional CFT columns without stiffeners. Welding lines in welded built-up steel box columns is expected to behave as longitudinal stiffeners. This study has presented a numerical investigation into the behavior of built-up concrete filled steel tube columns under axial pressure. At first stage, a finite element model (FE) has been built to simulate the behavior of built-up CFT columns. Comparing the results of FE and test has shown that numerical model passes the desired conditions and could accurately predict the axial performance of CFT column. Also, by the raise of steel tube thickness, the load bearing capacity of columns has been increased due to higher confinement effect. Also, the raise of concrete strength with greater cross section is led to a higher load bearing capacity compared to the steel tube thickness increment. In CFT columns with greater cross section, concrete strength has a higher influence on load bearing capacity which is noticeable in columns with more welding lines.

• Structural Engineering and Mechanics
• /
• v.70 no.3
• /
• pp.269-277
• /
• 2019

Using the non-local elasticity theory, Timoshenko beam model is developed to study the non- local buckling of Triple-walled carbon nanotubes (TWCNTs) embedded in an elastic medium under axial compression. The chirality and small scale effects are considered. The effects of the surrounding elastic medium based on a Winkler model and van der Waals' (vdW) forces between the inner and middle, also between the middle and outer nanotubes are taken into account. Considering the small-scale effects, the governing equilibrium equations are derived and the critical buckling loads under axial compression are obtained. The results show that the critical buckling load can be overestimated by the local beam model if the small-scale effect is overlooked for long nanotubes. In addition, significant dependence of the critical buckling loads on the chirality of zigzag carbon nanotube is confirmed. Furthermore, in order to estimate the impact of elastic medium on the non-local critical buckling load of TWCNTs under axial compression, the use of these findings are important in mechanical design considerations, improve and reinforcement of devices that use carbon nanotubes.

• Steel and Composite Structures
• /
• v.16 no.5
• /
• pp.455-480
• /
• 2014

Sixteen concrete filled square CFRP-steel tubular (S-CFRP-CFST) stub columns under axial compression were experimentally investigated. The experimental results showed that the failure mode of the specimens is strength loss of the materials, and the confined concrete has good plasticity due to confinement of the CFRP-steel composite tube. The steel tube and CFRP can work concurrently. The load versus longitudinal strain curves of the specimens can be divided into 3 stages, i.e., elastic stage, elasto-plastic stage and softening stage. Analysis based on finite element method showed that the longitudinal stress of the steel tube keeps almost constant along axial direction, and the transverse stress at the corner of the concrete is the maximum. The confinement effect of the outer tube to the concrete is mainly focused on the corner. The confinements along the side of the cross-section and the height of the specimen are both non-uniform. The adhesive strength has little effect both on the load versus longitudinal strain curves and on the confinement force versus longitudinal strain curves. With the increasing of the initial stress in the steel tube, the load carrying capacity, the stiffness and the peak value of the average confinement force are all reduced. Equation for calculating the load carrying capacity of the composite stub columns is presented, and the estimated results agree well with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.5
• /
• pp.586-593
• /
• 2007

This paper proposes closed-form plastic limit load solutions for elbow with local wall thinning at extrados under internal pressure. This work was performed using 3-dimensional, small strain FE analyses based on elastic-perfectly plastic materials. The wide range of elbow and local wall thinning geometries are considered. For systematic analyses for effect of axial thinning extent on limit loads, two limiting cases are considered; a sufficiently long thinning, and the circumferential part-through surface crack. Then, the closed-form plastic limit load solutions for intermediate thinning are obtained by using result of two limiting cases. The effect of axial thinning extent for elbow on plastic limit load is highlighted by comparing with that for straight pipes. Although the proposed limit load solutions are developed for the case when local wall thinning exist in the center of elbow, it is also shown that they can be applied to the case when local wall thinning exists anywhere within elbow.

• Journal of Korean Society of Steel Construction
• /
• v.27 no.6
• /
• pp.525-536
• /
• 2015

An experimental study was performed to investigate the axial-flexural load-carrying capacity of concrete-encased and-filled steel tube (CEFT) columns. To restrain local buckling of longitudinal bars and to prevent premature failure of the thin concrete encasement, the use of U-cross ties was proposed. Five eccentrically loaded columns were tested by monotonic compression. The test parameters were axial-load eccentricity, spacing of ties, and the use of concrete encasement. Although early cracking occurred in the thin concrete encasement, the maximum axial loads of the CEFT specimens generally agreed with the strengths predicted considering the full contribution of the concrete encasement. Further, due to the effect of the circular steel tube, the CEFT columns exhibited significant ductility. The applicability of current design codes to the CEFT columns was evaluated in terms of axial-flexural strength and flexural stiffness.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.1126-1131
• /
• 2010

Experimental studies for the high damping rubber bearing, lead rubber bearing and natural rubber bearing, those are often used to improve the seismic capacity if the structure recently, are conducted to evaluate the seismic capacity of the seismic isolation bearings. The shear stiffness of the bearings decrease and the shear strain amplitude or the constant axial load level increase, but not sensitive to the strain rate effect. Bearings are strong for the axial compression but weak for the axial tension.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.8
• /
• pp.69-76
• /
• 2007

Axial behavior of tapered piles is affected by taper angle, stress state of soils, soil frictional angle and pile-soil interface friction angle. In this paper, a series of model pile load tests were performed using a calibration chamber in order to investigate the effect of taper angle on the axial response of cast-in-place tapered piles in sand. According to results of the tests, as taper angle of piles increased, the shaft load capacity of piles increased but its base load capacity decreased. The unit base load capacity of piles increased with increasing taper angle for medium sand but decreased for dense sand. The ratio of shaft to total load capacity increased with increasing taper angle and with decreasing relative density of soils. The test results also showed that total load capacity per unit pile volume increased with increasing taper angle for medium sand, but it decreased for dense sand. Therefore, it can be stated that tapered piles are economically more beneficial for medium sand than for dense sand.

• Computers and Concrete
• /
• v.33 no.5
• /
• pp.509-518
• /
• 2024

In this study, we investigated the effect of shear-key placement on the performance of grouted connections in offshore wind-turbine structures. Considering the challenges of height control during installation, we designed and analyzed three grouted connection configurations. We compared the crack patterns and strain distribution in the shear keys under axial loading. The results indicate that the misalignment of shear keys significantly influences the ultimate load capacity of grouted connections. Notably, when the shear keys were positioned facing each other, the ultimate load decreased by approximately 15%, accompanied by the propagation of irregular cracks in the upper shear keys. Furthermore, the model with 50% misalignment in the shear-key placement exhibited the highest ultimate strength, indicating a more efficient load resistance than the reference model. This indicates that tensile-load-induced cracking and the formation of compressive struts in opposite directions significantly affect the structural integrity of grouted connections. These results demonstrate the importance of considering buckling effects in the design of grouted connections, particularly given the thin and slender nature of the inner sleeves. This study provides valuable insights into the design and analysis of offshore wind-turbine structures, highlighting the need for refined design formulas that account for shifts in shear-key placement and their structural implications.

• Steel and Composite Structures
• /
• v.21 no.3
• /
• pp.605-628
• /
• 2016

The energy absorption characteristics of diamond core sandwich cylindrical columns under axial crushing process depend greatly on the amount of material which participates in the plastic deformation. Both the single-objective and multi-objective optimizations are performed for columns under axial crushing load with core thickness and helix pitch of the honeycomb core as design variables. Models are optimized by multi-objective particle swarm optimization (MOPSO) algorithm to achieve maximum specific energy absorption (SEA) capacity and minimum peak crushing force (PCF). Results show that optimization improves the energy absorption characteristics with constrained and unconstrained peak crashing load. Also, it is concluded that the aluminum tube has a better energy absorption capability rather than steel tube at a certain peak crushing force. The results justify that the interaction effects between the honeycomb and column walls greatly improve the energy absorption efficiency. A ranking technique for order preference (TOPSIS) is then used to sort the non-dominated solutions by the preference of decision makers. That is, a multi-criteria decision which consists of MOPSO and TOPSIS is presented to find out a compromise solution for decision makers. Furthermore, local and global sensitivity analyses are performed to assess the effect of design variable values on the SEA and PCF functions in design domain. Based on the sensitivity analysis results, it is concluded that for both models, the helix pitch of the honeycomb core has greater effect on the sensitivity of SEA, while, the core thickness has greater effect on the sensitivity of PCF.

• Journal of Navigation and Port Research
• /
• v.31 no.3 s.119
• /
• pp.235-245
• /
• 2007

Stiffened steel plates are basic structural members on the deck and bottom structure in ship, offshore. It has a number of one sided stiffeners in either one or both directions, the latter structure was called grillage structure. At the ship structural desgn stage, one of the major consideration is evaluation for ultimate strength of the hull girder. In general, it is accepted that hull girder strength can be represented by the local strength of the longitudinal stiffened panel. In case of considering hogging condition in a stormy sea, stiffened panel was acting on the bottom structure under axial compressive load induced hull girder bending moment, also simultaneously arising local bending moment induced lateral pressure load. In this paper, results of the structural analysis have been compared with another detailed FEA program and prediction from design guideline and a series analysis was conducted consideration of changing parameters for instance, analysis range, cross-section of stiffener, web height and amplitude of lateral pressure load subjected to combined load (axial compression and lateral pressure load). It has been found that finite element modeling is capable of predicting the behaviour and ultimate load capacity of a simply supported stiffened plate subjected to combined load of axial compression and lateral pressure load It is expected that these results will be used to examine the effect of interaction between lateral pressure and axial loads for the ultimate load-carrying capacity based on the Ultimate Limit State design guideline.