• Geomechanics and Engineering
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• v.12 no.6
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• pp.899-917
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• 2017

Sixty four tests were performed in a steel tank to investigate the axial responses of piles driven into organic soil prepared at two different densities using a drop hammer. Four different pile materials were used: wood, steel, smooth concrete, and rough concrete, with different length to diameter ratios. The results of the load tests showed that the shaft load capacity of rough concrete piles continuously increased with pile settlement. In contrast, the others pile types reached the ultimate shaft resistance at a settlement equal to about 10% of the pile diameter. The ratios of base to shaft capacities of the piles were found to vary with the length to diameter ratio, surface roughness, and the density of the organic soil. The ultimate unit shaft resistance of the rough concrete pile was always greater than that of other piles irrespective of soil condition and pile length. However, the ultimate base resistance of all piles was approximately close to each other.

• Computers and Concrete
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• v.33 no.5
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• pp.509-518
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• 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
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• v.31 no.1
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• pp.13-25
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• 2019

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.

• Steel and Composite Structures
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• v.27 no.6
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• pp.747-759
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• 2018

This study proposed a new type of concrete column that was confined with both steel angles and spiral hoops, named angle-steel and spiral confined concrete (ASCC) column. A total of 22 ASCC stub columns were tested under axial compression to investigate their behavior. For a comparison, three angle-steel reinforced concrete (ARC) stub columns were also tested. The test results indicated that ASCC column had a superior mechanical performance. The strength, ductility and energy absorption were considerably increased due to the improvement of confinement from spiral hoops. The confinement behavior and failure mechanism of ASCC column were investigated by the analysis of failure mode, load-deformation curve and section-strain distribution. Parametric studies were carried out to examine the influences of different parameters on the axial compression behavior of ASCC columns. A calculation approach was developed to predict the ultimate load carrying capacity of ASCC columns under axial compression. It was validated that the predicted results were in well agreement with the experimental results.

• Structural Engineering and Mechanics
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• v.55 no.5
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• pp.931-951
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• 2015

To improve the durability and service life of reinforced concrete column such as bridge piers, an advanced composite column made of Ultra High Performance Cementitious Composites (UHPCC) permanent form is proposed. Based on elasticity plasticity theory, axial compression behavior of the composite column was studied theoretically. The first circumferential cracking load and ultimate limit loading capacity are derived for the composite column. Short composite column compression tests and numerical simulations using FEM method were carried out to justify the theoretical formula. The effects of UHPCC tube thickness on the axial compression behavior were studied. Using the established theoretical model and numerical simulation, the large dimension composite columns are calculated and analyzed with different UHPCC tube thickness. These studies may provide a reference for advanced composite column design and application.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• Steel and Composite Structures
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• v.25 no.5
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• pp.603-615
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• 2017

This experimental research presents the seismic performance of steel reinforced high-strength concrete (SRHC) short columns. Eleven SRHC column specimens were tested under simulated earthquake loading conditions, including six short column specimens and five normal column specimens. The parameters studied included the axial load level, stirrup details and shear span ratio. The failure modes, critical region length, energy dissipation capacity and deformation capacity, stiffness and strength degradation and shear displacement of SRHC short columns were analyzed in detail. The effects of the parameters on seismic performance were discussed. The test results showed that SRHC short columns exhibited shear-flexure failure characteristics. The critical region length of SRHC short columns could be taken as the whole column height, regardless of axial load level. In comparison to SRHC normal columns, SRHC short columns had weaker energy dissipation capacity and deformation capacity, and experienced faster stiffness degradation and strength degradation. The decrease in energy dissipation and deformation capacity due to the decreasing shear span ratio was more serious when the axial load level was higher. However, SRHC short columns confined by multiple stirrups might possess good seismic behavior with enough deformation capacity (ultimate drift ratio ${\geq}2.5%$), even though a relative large axial load ratio (= 0.38) and relative small structural steel ratio (= 3.58%) were used, and were suitable to be used in tall buildings in earthquake regions.

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

• Steel and Composite Structures
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• v.19 no.4
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• pp.967-993
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• 2015

The aim of this paper is to investigate the appropriateness of current codes of practice for predicting the axial load capacity of high-strength Concrete Filled Steel Tubular Columns (CFSTCs). Australian/New Zealand standards and other international codes of practice for composite bridges and buildings are currently being revised and will allow for the use of high-strength CFSTCs. It is therefore important to assess and modify the suitability of the section and ultimate buckling capacities models. For this purpose, available experimental results on high-strength composite columns have been assessed. The collected experimental results are compared with eight current codes of practice for rectangular CFSTCs and seven current codes of practice for circular CFSTCs. Furthermore, based on the statistical studies carried out, simplified relationships are developed to predict the section and ultimate buckling capacities of normal and high-strength short and slender rectangular and circular CFSTCs subjected to concentric loading.

• Structural Engineering and Mechanics
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• v.40 no.2
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• pp.215-231
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• 2011

The axial compressive strength of unidirectional FRP is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. In order to restrain the lateral expansion and splitting of GFRP, and accordingly heighten its axial compressive bearing capacity, a project that to confine GFRP pole with surrounding CFRP sheet is suggested in the present study. The Experiment on the CFRP sheet confined GFRP poles showed that a combined structure of high bearing capacity was attained. Basing on the experiment research a theoretical iterative calculation approach is suggested to predict the ultimate axial compressive stress of the combined structure, and the predicted results agree well with the experimental results. Then the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure are also analyzed basing on this approach.