Ultimate Axial Load Capacity Research Articles

Response of Pile Groups Driven in Sand Subjected to Combined Loads

Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity.

EXPERIMENTAL STUDY ON CIRCULAR AND SQUARE CONCRETE FILLED STEEL TUBE COLUMNS SUBJECTED TO AXIAL COMPRESSION LOADS

D. R. Panchal1, V. P. Sheta2 1Assistant Professor, Department of Applied Mechanics, FTE-MSU, Vadodara, Gujarat, India panchaldr@gmail.com 2M.E. (Structural Engineering) Student, Department of Applied Mechanics, FTE-MSU, Vadodara, Gujarat, India vpsheta63@gmail.com Abstract This paper investigates the behaviour of concentrically axially loaded circular and square high strength steel tube (Fe310 grade) columns filled with different grades (M20, M30 & M40 etc.) of concrete. The effects of grade of concrete and composite action between the steel tube and the concrete core on axial load capacity are studied & graphs of Axial load v/s vertical deflection (axial shortening curves) are plotted experimentally. Some important performance indices entitled as Ductility Index (DI), Strength factor (SI) and Concrete Contribution Ratio(CCR) are also evaluated and compared between the circular and the square shaped Concrete Filled Steel Tube (CFST) columns.By referring many research works, we can know firmly that confinement effect is restricted to short column only. So, we choose 300mm length for all the specimens of 88.9mm dia and 80×80mm size, to keep the columns stub only for getting benefit of confinement effect especially in circular sections.From the results, it has been noted that square columns have higher axial capacity when compared with circular columns of same resisting area under compression. Hence, size reduction for square column is possible. While ductility index for circular columns are quite better than square ones. Ultimate failure patterns are obtained by applying axial compression loads concentrically up to ultimate stage on circular and square CFST stub columns. as expected, the results shows a Local buckling i.e. crushing of concrete type of failure at supports. Ultimate axial load capacity of Concrete filled steel tubular columns are evaluated and compared experimentally as well as by calculations also, as per the guidelines suggested by EC4(Eurocode part-4, British Standards Institutions) code, which is the best suitable code for design of CFST columns amongst all other international codes for composite structure design. From the study it is concluded that, loads obtained by EC4 fits nearer to perfection and depicts the behaviour well enough by 15-20% error with experimental ultimate loads. The results obtained by experimental and EC4 code are validated well with the previous scholar researchers too

A new sustainable composite column using an agricultural solid waste as aggregate

The agricultural industry is a source of many types of solid waste. For instance, oil palm shell (OPS), is a waste from the palm oil industry and is produced in enormous quantities in tropical countries. This waste material is considered to be a major problem in terms of pollution, while, on the other hand, normal concrete needs a large amount of the raw materials as coarse and fine aggregate. Due to the limitations of raw materials, the use of normal aggregate can have a negative effect on the environment. In addition, the high self-weight of raw aggregate in normal concrete is considered to be another disadvantage of this type of concrete for the construction of structural members. This paper presents a novel sustainable composite column by using of lightweight OPS concrete instead of conventional aggregate concrete. Composite columns in the form of concrete filled steel tubes (CFTs) are acknowledged to be a highly efficient group of columns with wide usage in different types of structure.In this study, the axial compressive behaviour of CFT columns constructed with conventional normal weight and OPS lightweight concretes was investigated. In the new composite column, 22% of the total volume of the composite was replaced with waste OPS aggregate. The test results showed that the CFT column containing OPS lightweight concrete had the same ultimate axial load capacity as the CFT column with conventional concrete. This new green composite column is about 15% lighter than a normal CFT column, with significantly higher specific energy absorption, structural efficiency and flexibility.

Effect of thickness of inner carbon fibre reinforced polymer tubes on axial compressive behaviour of steel-concrete-carbon fibre reinforced polymer-concrete columns

Steel-concrete-carbon fibre reinforced polymer-concrete columns (SCCC columns) have been introduced as a new form of hybrid columns by first author. An SCCC column consists of an outer steel tube, an inner carbon fibre reinforced polymer tube, an annular concrete between two concentric tubes and a core concrete encased in carbon fibre reinforced polymer tube. This paper presents the results of a test study that was conducted to investigate the effect of thickness of inner carbon fibre reinforced polymer tube on the axial compressive behaviour of SCCC columns. Four SCCC columns with carbon fibre reinforced polymer tubes of two different thicknesses of 0·167 mm and 0·334 mm in addition to two reference columns without carbon fibre reinforced polymer tube were prepared. All the six short columns, each 260 mm in diameter, 780 mm in height, were manufactured and tested to failure under pure axial compression. Test results demonstrate that the circular hybrid SCCC columns are of excellent axial compression behaviour, and that increasing the thickness of inner carbon fibre reinforced polymer tube can increase the ultimate axial load capacity and ultimate axial strain of SCCC columns remarkably.

Compression strength of hollow sandwich columns with GFRP skins and a paulownia wood core

This paper introduced a simple and innovative hollow sandwich columns with GFRP skins and a paulownia wood core (GSW columns), which were manufactured by vacuum assisted resin infusion process. Four full-scale GSW columns were fabricated and tested under axial compression loading to validate the effectiveness of this column. The ultimate axial load capacity, displacement ductility, failure mode and axial force distribution between GFRP skins and wood core were investigated. Meanwhile, the finite element analysis was conducted to extend to investigate the effects of wood density, GFRP skin thickness and hollow ratio on the axial strength which were not considered in the tests. The numerical results revealed that increasing GFRP skin thickness and decreasing the hollow ratio can enhance the ultimate axial load capacity of the columns. Furthermore, increasing the wood density can improve the initial stiffness significantly. The corresponding calculation formulae were also derived to predict the ultimate axial load capacity of sandwich columns.

PERFORMANCE OF AXIALLY LOADED TAPERED CONCRETE-FILLED STEEL COMPOSITE SLENDER COLUMNS

This paper focuses on the performance of a special kind of tapered composite columns, namely tapered concrete-filled steel composite (TCFSC) slender columns, under axial loading. These efficient TCFSC columns are formed by the increase of the mid-height depth and width of straight concrete-filled steel composite (CFSC) slender columns, that is, by the enhancement of the tapered angle (from 0° to 2.75°) of the tapered composite columns from their top and bottom to their mid-height. To investigate the performance of the columns, finite element software LUSAS is employed to carry out the nonlinear analyses. Comparisons of the nonlinear finite element results with the existing experimental results uncover the reasonable accuracy of the proposed modelling. Nonlinear analyses are extensively performed and developed to study effects of different variables such as various tapered angles, steel wall thicknesses, concrete compressive strengths, and steel yield stresses on the performance of the columns. It is concluded that increasing each of these variables considerably enhances the ultimate axial load capacity. Also, enhancement of the tapered angle and/or steel wall thickness significantly improves the ductility. Moreover, confinement effect of the steel wall on the performance of the columns is evaluated. Failure modes of the columns are also presented.

A mechanical model and experimental investigations for axially compressed sleeved column

This paper presents a combined study of theoretical solutions and experimental tests on the deformation processes of non-contact, point contact, line contact and secondary buckling of the sleeved column. In this study, a mechanical model based on the second order equilibrium differential equations with small deflection is developed, and two types of sleeved column are fabricated and tested using six specimens. And in the tests, it is observed that the ultimate axial load capacity and ductility of the sleeved column are substantially increased, and the axial load capacity will be reduced due to the small slenderness ratio of the inner core, large stiffness of the sleeved column and the large gap between the inner core and the sleeve. Furthermore, the study investigates the effects of the stiffness ratio of the inner core to the sleeve on the column's buckling mode transition process. Finally, a discussion on the comparison between the analytical results by the proposed mechanical model and the tested results is also presented.

INVESTIGATION OF CONCRETE-FILLED STEEL COMPOSITE (CFSC) STUB COLUMNS WITH BAR STIFFENERS

This paper is concerned with the investigation of concrete-filled steel composite (CFSC) stub columns with bar stiffeners. In order to study the behaviour of the columns, the finite element software LUSAS is used to conduct the non-linear analyses. Results from the non-linear finite element analysis and the corresponding experimental test are compared which reveal the reasonable accuracy of the three-dimensional finite element modelling. A special arrangement of bar stiffeners in the columns with various number, spacing and diameters of the bar stiffeners are developed and studied using the non-linear finite element method. Effects of various variables such as different number and spacing of the bar stiffeners and also steel wall thicknesses on the ultimate axial load capacity and ductility of the columns are examined. Moreover, effects of different diameters of the bar stiffeners, concrete compressive strengths and steel yield stresses on the ultimate axial load capacity of the columns are evaluated. It is concluded from the study that the variables significantly influence the behaviour of the columns. The obtained results from the finite element analyses are compared with those predicted values by the design code EC4 and suggested equations of the previous researches.

Experimental investigation of inelastic buckling of built-up steel columns

This paper experimentally investigated the buckling capacity of built-up steel columns mainly, Cruciform Columns (CC) and Side-to-Side (SS) columns fabricated from two Universal Beam (UB) sections. A series of nine experimental tests comprised of three UB sections, three CC sections and three SS sections with different lengths were tested to failure to measure the ultimate axial capacity of each column section. The lengths used for each category of columns were 1.8, 2.0, and 2.2 m with slenderness ratios ranging from 39-105. The measured buckling loads of the tested specimens were compared with the predicted ultimate axial capacity using Eurocode 3, AISC LRFD, and BS 5959-1. It was observed that the failure modes of the specimens included flexural buckling, local buckling and flexural-torsional buckling. The results showed that the ultimate axial capacity of the tested cruciform and side-by-side columns were higher than the code predicted design values by up to 20%, with AISC LRFD design values being the least conservative and the Eurocode 3 design values being the most conservative. This study has concluded that cruciform column and side-to-side welded flange columns using universal beam sections are efficient built-up sections that have larger ultimate axial load capacity, larger stiffness with saving in the weight of steel used compared to its equivalent universal beam counterpart.

Nonlinear analysis of concrete-filled steel composite columns subjected to axial loading

This paper investigates the nonlinear analysis of concrete-filled steel composite columns subjected to axial loading to predict the ultimate load capacity and behaviour of the columns. Finite element software LUSAS is used to conduct the nonlinear analyses. The accuracy of the finite element modelling is verified by comparing the result with the corresponding experimental result reported by other researchers. Nonlinear analyses are done to study and develop different shapes and number of cold-formed steel sheeting stiffeners with various thicknesses of cold-formed steel sheets. Effects of the parameters on the ultimate axial load capacity and ductility of the concrete-filled steel composite columns are examined. Effects of variables such as concrete compressive strength fc and cold-formed steel sheet yield stress fyp on the ultimate axial load capacity of the columns are also investigated. The results are shown in the form of axial load-normalized axial shortening plots. It is concluded from the study that the ultimate axial load capacity and behaviour of the concrete-filled steel composite columns can be accurately predicted by the proposed finite element modelling. Results in this study demonstrate that the ultimate axial load capacity and ductility of the columns are affected with various thicknesses of steel sheets and different shapes and number of stiffeners. Also, compressive strength fc of the concrete and yield stress fyp of the cold-formed steel sheet influence the performance of the columns significantly.

Finite Element Analysis of Ultimate Load Capacity of Slender Concrete-Filled Steel Composite Columns

Ultimate load capacity of slender concrete-filled steel composite columns is investigated in this paper. Nonlinear analyses are done by the use of finite element software, LUSAS, to study the ultimate axial load behaviour of the columns. Verification of the finite element modelling is done by comparing the result with the corresponding experimental result reported by other researchers. Analyses are carried out to assess different shapes and number of cold-formed steel sheeting stiffeners with various thicknesses of cold-formed steel sheets and their effects on the behaviour and ultimate axial load capacity of the columns. The results are presented in the form of axial load-normalized axial shortening plots. It is demonstrated that the ultimate axial load capacity of the slender concrete-filled steel composite columns can be accurately predicted by proposed finite element modelling. Obtained results from the study show that various thicknesses of cold-formed steel sheets, and different shapes and number of stiffeners influence the ultimate axial load capacity and behaviour of the columns. Also, the ultimate axial load capacity of the columns is improved by increase of number of stiffeners. Moreover, increase of thickness of cold-formed steel sheet enhances the ultimate axial load capacity.

Finite element prediction of the ultimate axial load capacity of V-section band clamps

Band clamps with a flat bottomed V-section are used to connect a pair of circular flanges to provide a joint with significant axial strength. Despite the wide application of V-band clamps, their behaviour is not fully understood and the ultimate axial strength is currently only available from physical testing. This physical testing has indicated that the ultimate strength is determined by two different types of structural deformation, an elastic deformation mode and a plastic deformation mode. Initial finite element analysis work has demonstrated that analysis of this class of problem is not straightforward. This paper discusses the difficulties encountered when simulating this type of component interaction where contact is highly localised and contact pressures are high.

A Study of the Factors Influencing the Penetration and Capacity of Vibratory Driven Piles

This study examined the factors influencing the vibratory installation of piles in drained granular soils. Several variables were examined to assess their relative importance in pile installation by simulating the pile-hammer-soil system using the finite difference program, FLAC. The soil was modeled using an elasto-plastic hyperbolic stress-strain model. The variables investigated include: soil strength, pile-soil interface friction angle, lateral earth pressure coefficient, hammer operating frequency, bias weight, hammer centrifugal force, and pile embedment. A simple empirical relationship was introduced to estimate the ultimate axial load capacity of vibratory driven piles based on hammer, pile and penetration characteristics. The capacities estimated using the proposed relationship are compared to other formulas using the results of this study and to data from two field test projects.

Biaxially Loaded Concrete-Encased Composite Columns: Design Equation

The main objective of the work presented in this paper is to propose a design equation to predict and check the ultimate load capacity of short and slender concrete-encased square and rectangular composite columns under uniaxial or biaxial bending moments and axial load. The proposed design equation satisfies basic analysis and design parameters of both the American Concrete Institute (ACI) and the American Institute of Steel Construction (AISC). It is simple to use, and is compatible with the principles of equilibrium—consistent deformation and structural stability. The second order effects on slender columns are considered by incorporating a moment magnification factor similar to the one used by the ACI for reinforced concrete columns, with the appropriate adjustments for rectangular composite columns. The proposed design equation was used to predict the ultimate axial load capacity of more than 80 square and rectangular composite column specimens. The analytical results were compared with the actual test results and current ACI and AISC design methods. The accuracy obtained in predicting the ultimate axial load capacity and checking the design of a composite section under uniaxial or biaxial bending moments and axial load confirms the validity of the proposed design equation.

An approximate numerical analysis of pile–raft interaction

AbstractThis paper presents an approximate method of numerical analysis of piled–raft foundations in which the raft is modelled as a thin plate and the piles as interacting springs of appropriate stiffness. Allowance is made for the development of limiting pressures below the raft and of the ultimate axial load capacity of the piles.Comparisons between this analysis and existing solutions verify that, despite the approximations involved, the analysis can provide solutions of adequate accuracy for the settlement and pile load distribution within a piled raft.Comparisons are also made with the results of a series of centrifuge tests and with measurements of the performance of a full‐scale piled raft. In both cases, the analysis predicts very well the settlement and proportion of load carried by the piles.

Ultimate axial load capacity of a delaminated beam-plate

The paper presents elastic buckling and postbuckling analysis of an axially loaded beam-plate with an across-the-width delamination symmetrically located at an arbitrary depth. It is found that, for a relatively short and thick delamination, the buckling load of the delaminated plate is a close lower bound of the ultimate axial load capacity. In the case of a relatively slender delamination, the postbuckling axial load can be considerably greater than the buckling load, while the failure of the plate may or may not be governed by delamination growth. The energy-release rate associated with delamination growth is systematically computed for various combinations of the delamination length and axial load. The resulting curves determine the possibility and the stability characteristics of delamination growth and provide a basis for finding the ultimate axial load capacity. Nomenclature = half-length of delamination = thickness of delamination = half-length of the plate = thickness of the plate =a/t = a/h = axial forces = bending moments w = transverse deflections = bending stiffnesses Young's modulus in the axial direction amplitude of deflection a h / t a a Pi Mf u, v,