Axial Bearing Capacity Research Articles

Effect of crumb rubber on compressive behaviour of CRCFST stub columns

This paper investigates the effect of crumb rubber (CR) on compressive behaviour of crumb rubber concrete filled steel tube (CRCFST) stub columns. Therefore, experiments on 16 stub columns subjected to axial loading are carried out. The results show that the failure modes of CRCFST stub columns with different CR replacement ratios and CR size are similar, manifested the buckling of the outer steel tube. The axial bearing capacity and stiffness both decrease with an increase in CR replacement ratio, and with decreasing CR size.

Axial compressive performance of RAC-encased RACFST composite columns

A new type of composite column, recycled aggregate concrete (RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns, promotes the RAC extensive utilization considering synergistic effect between the RAC and the steel tube, which is an attempt to develop environmentally sustainable concrete in high-rise buildings. In this paper, experimental research investigated the axial compressive behavior of RAC-encased RACFST composite columns. Twenty 1:3-scaled specimens were fabricated to test until failure under axial compressive loading. The main variable parameters affecting the behaviour of specimens were recycled coarse aggregate replacement ratio (range from 0% to 100% with 10% increase), stirrup spacing (s = 50 mm, 70 mm, 100 mm, 120 mm), diameter of steel tube (D = 89 mm, 114 mm), concrete strength grade (RC40, RC60) and longitudinal reinforcement ratio (4▪12, 8▪12). The failure modes, the whole load-deformation curves and the mechanical performance of specimens were also obtained based on static loading experiments and theoretical analysis. It was found that RAC-encased RACFST composite columns, which were subjected to identical axial loads, exhibited more favorable bearing capacity and deformation than those of a comparative reinforced recycled aggregate concrete columns (RACC). The replacement ratio of RCA had a slight effect on the mechanical performance of RAC-encased RACFST composite columns, the optimal substitution ratio of RCA was 50–60%. Based on the previous theory of superposition, the concrete cover is considered, and a calculation formula with double reduction coefficients of the axial load-bearing capacity of composite columns is proposed. Compared to the simplified superimposition method and the Chinese code Technical specification for steel tube-reinforced concrete column structure (CECS188:2005), the calculated results of axial compression bearing capacity by the proposed formula are in more agreement with the experimental values, with errors no greater than 15%.

Post-blast performance and residual capacity of CFDST columns subjected to contact explosions

Contact detonations, even with a small charge weight, could cause severe damage to structural columns and result in devastating consequences, associate with significant casualties, economic losses and social impacts. Therefore, to prevent catastrophic structural collapse, the most critical requirement of a blast-damaged column would be the residual axial load bearing capacity. In this paper, the post-blast performance of concrete-filled double-skin steel tube (CFDST) columns subjected to contact explosions was studied by experimental tests and numerical simulations. The experimental study comprised of field blast tests and residual axial load-carrying capacity tests on four CFDST columns. A high-fidelity physics-based numerical model was then developed using the nonlinear dynamic analysis program LS-DYNA and was validated against the test results. It was then used to model the dynamic response and predict the residual axial load-carrying capacity of CFDST columns subjected to contact explosions. An extensive parametric study was then carried out to investigate the influence of charge weight, boundary conditions, axial loading level and column geometries on the column residual axial load-carrying capacity. An empirical formula was derived through multi-variable regression analysis to predict the residual axial bearing capacity of CFDST columns after contact explosions.

Developing a new hybrid soft computing technique in predicting ultimate pile bearing capacity using cone penetration test data

AbstractThis research intends to investigate a new hybrid artificial intelligence (AI) technique compared to some common CPT methods in estimating axial ultimate pile bearing capacity (UPBC) using cone penetration test (CPT) data in geotechnical engineering applications. A data series of 108 samples was collected in order to develop a new hybrid structure of an adaptive neuro-fuzzy inference system (ANFIS) network, and the group method of the data handling (GMDH) type neural network was optimized by applying the particle swarm optimization (PSO) algorithm over the hybrid ANFIS-GMDH topology, which leads to a new hybrid AI model called as ANFIS-GMDH-PSO. The derived database provides information related to pile load tests,in situfield CPT data, and soil–pile information for introducing the proposed hybrid neural system. The cross-section of the pile toe, average cone tip resistance along embedded pile length, and sleeve frictional resistance along the shaft had been considered as input parameters for the proposed network. The results of this research indicated that the proposed ANFIS-GMDH-PSO model predicted the UPBC with an acceptable precision compared to various CPT methods, including Schmertmann, De Kuiter & Bringen, and LPC/LPCT methods. Moreover, ANFIS-GMDH-PSO network model performance was compared to CPT-based models in terms of statistical criteria in order to achieve a best fitted model. From the statistical results, it was found that the developed ANFIS-GMDH-PSO model has achieved a higher accuracy level in terms of statistical indices compared to CPT-based empirical methods, such as Schmertmann model, De Kuiter & Beringen model, and Bustamante & Gianeselli for predicting driven pile ultimate bearing capacity.

Performance and design of partially CFRP-jacketed circular CFT column under eccentric compression

Nowadays, the carbon fibre reinforced polymer (CFRP) strengthening technology that uses the partial wrapping scheme is commonly applied in reinforcement engineering. Nevertheless, related investigations on partially CFRP jacketed concrete-filled steel tubular (CFT) columns under eccentric bearing forces are rarely reported. Herein, a series of experimental and analytical works on the eccentric behaviour of the partially CFRP jacketed circular CFT short and slender columns are presented. The influence of various parameters, in terms of steel yield stress, load eccentricity, number of CFRP layers, CFRP spacing, and column slenderness, on the eccentric compressive response of the specimens were analysed. Mechanical properties were evaluated by discussing the laws of the eccentric pressure (N)-vertical displacement (δ) curves, typical failure modes, strain responses, strength and ductility indexes, etc. Following these, a modified finite element model of the partially CFRP jacketed circular CFT column subjected to an eccentric bearing force was developed and validated against the existing experimental results. The contact stress and the effective jacketing scheme of the composite column were also discussed. Finally, based on an analysis of the confining stress transferring mechanism of the partial wrapping scheme, design formulae were proposed to assess the axial and eccentric load bearing capacity of the partially CFRP jacketed circular CFT column. The observations drawn from this study might provide a good basis for the future applications of CFRP strengthening CFT structures.

Application of Developed New Artificial Intelligence Approaches in Civil Engineering for Ultimate Pile Bearing Capacity Prediction in Soil Based on Experimental Datasets

In this study, a neural-fuzzy (NF) system is combined with group method of data handling (GMDH) in order to estimate the axial bearing capacity of driven piles. To reach optimum design of this conjunction (NF-GMDH) network, the metaheuristic techniques including particle swarm optimization (PSO) and gravitational search algorithm (GSA) were utilized. The datasets used for estimating pile bearing capacity were collected from the literature review. The parameters influencing the modeling and pile capacity analysis were taken into account as Flap number, surrounding soil properties, the pile geometric characteristics, and internal friction angles of the pile–soil interface. The efficiency of hybrid NF-GMDH networks in train and test phases was examined. Applying the PSO algorithm to the hybrid NF-GMDH model structure improved the model performance and achieved a higher level of accuracy in predicting the ultimate pile bearing capacity (RMSE = 1375 and SI = 0.255) compared to NF-GMDH model developed by GSA (RMSE = 1740.7 and SI = 0.357). In addition, based on achieved results, the developed NF-GMDH networks showed relatively better performances in comparison with gene programming and linear regression model methods considered in this study.

A novel five-degree-of-freedom AC-DC hybrid magnetic bearing

To reduce the volume, axial length and cost, a radial three-pole five-degree-of-freedom (5-DOF) integrated hybrid magnetic bearing (HMB) is studied, which the rotor can be levitated stably in one unit. Firstly, the configuration and suspension principle are introduced. The mathematical models of suspension forces are deduced by the magnetic circuit analysis. Then, according to radial and axial bearing capacity, the design method of main parameters is given. Finally, the magnetic circuit, suspension mechanism, air gap flux density, force-current relationships are calculated and analyzed by three-dimensional finite element method. The research results have shown that the structure of the 5-DOF integrated HMB is reasonable, and the suspension mechanism, mathematical model and design method are correct.

Effect of spalling thickness on transverse axial bearing capacity of pile foundation under different corrosion depths

The transverse and axial bearing characteristics of bridge pile foundation in salt marsh area are studied by numerical simulation. This paper mainly analyses the change of transverse and axial bearing characteristics of pile foundation caused by the change of spalling thickness of bridge foundation. The results show that the transverse and axial bearing capacity and displacement of pile foundation will be affected by the change of concrete spalling thickness under the condition of pile corrosion. When the peeling thickness is above 9.0cm, the transverse and axial bearing characteristics of pile foundation are obviously different with the change of corrosion depth of pile body. When the peeling thickness increases and the corrosion depth of the pile body is different, the negative displacement below the zero point of the first displacement of the pile body is continuously reduced, and the displacement curve above the first displacement zero point in the direction of the pile body begins to shift. When the peeling thickness reaches 15.0cm, the pile top displacement increases to 3.75mm. The research results are of great significance to the establishment of safety evaluation system of highway bridge pile foundation in alpine salt marsh area, and provide a basis for the structural design of highway bridge pile foundation in alpine salt marsh area.

Axial Load Monitoring for Concrete Columns Using a Wearable Smart Hoop Based on the Piezoelectric Impedance Frequency Shift: A Feasibility Study

Concrete columns are critical in supporting the weight of an entire structural frame and also play a key role in force transferring among structural members. Therefore, integrity of the columns, especially their axial load bearing capacity, directly affects the stability and safety of the entire structure. In this study, a wearable smart hoop is designed to monitor the axial load of the concrete columns. The smart hoop measures the shift in impedance frequency of its integrated piezoelectric transducer and correlates the frequency to the structural state of the column. In order to validate the feasibility of the smart hoop, an experiment on two concrete columns with different dimensions is carried out. The smart hoop is installed on each column. Then, an increasing axial load was applied onto the specimen, and the admittance of the PZT patch is acquired under different load levels by using an impedance analyzer. Finally, frequencies corresponding to the peak and trough in the susceptance of the admittance signal are collected as the monitoring index to estimate the axial load variation on the specimen. The experimental results demonstrated a downward shift in frequency corresponding to an increase of axial load. The results validate the feasibility of the wearable smart hoop in monitoring axial load for concrete columns and show potential for retrofit on existing columns.

Axial Compression Performance and Ultrasonic Testing of Multicavity Concrete‐Filled Steel Tube Shear Wall under Axial Load

In this study, the mechanical performance of multicavity concrete‐filled steel tube (CFST) shear wall under axial compressive loading is investigated through experimental, numerical, and theoretical methodologies. Further, ultrasonic testing is used to assess the accumulated damage in the core concrete. Two specimens are designed for axial compression test to study the effect of concrete strength and steel ratio on the mechanical behavior of multicavity CFST shear wall. Furthermore, a three‐dimensional (3D) finite element model is established for parametric studies to probe into compound effect between multicavity steel tube and core concrete. Based on finite element simulation and limit equilibrium theory, a practical formula is proposed for calculating the axial compressive bearing capacity of the multicavity CFST shear wall, and the corresponding calculation results are found to be in good agreement with the experimental results. This indicates that the proposed formula can serve as a useful reference for engineering applications. In addition, the ultrasonic testing results revealed that the damage process of core concrete under axial load can be divided into three stages: extension of initial cracks (elastic stage), compaction due to hooping effect (elastic‐plastic stage), and overall failure of the concrete (failure stage).

Influence of Red Mud Proportion on Circular Concrete‐Filled Steel Tubular Short Columns

Tests on twelve circular concrete‐filled steel tube stub columns with mixed red mud and three circular concrete‐filled steel tube stub columns to investigate the influence of the mixed proportion of red mud on the mechanical behavior of axial compressive circular concrete‐filled steel tube stub columns are reported. It is found that with the increase of red mud content, the ultimate load increases first and then decreases; on the contrary, the ultimate displacement decreases first and then increases; the specimen stress reaches the proportion limitation as the steel tube longitudinal strain is around 160 με and reaches the yield limitation as the steel tubes’ longitudinal strain is around 4400∼5000 με. The axial compressive bearing capacity empirical formulation of concrete‐filled steel tubes stub columns mixed with red mud is proposed. The theoretical calculation results agree well with those experimental data.

Compression Performance of Newly Designed Replaceable Tubular Steel Piers

To rapidly restore the seismic behaviour of a portal steel bridge column after an earthquake, the installation of replaceable tubular steel piers at the root of a portal steel bridge column is proposed herein. In this study, various tubular steel piers with different structural measures were designed; an axial compression test and a numerical simulation of the newly designed tubular steel piers were performed. The effects of parameters such as the structure of stiffening rib, the strength of LYP steel plate, the size of low‐yield‐point (LYP) steel plate, and the size of outer constrained steel plate were discussed. The results indicate that local buckling of steel tubular plates is likely to occur at the upper or lower end of those specimens, which belong to type II‐A specimens with stiffened LYP steel tubular plates or type III‐A specimens with T‐shaped LYP steel plates, respectively. This led to the LYP steel plate cannot fully display its function. For type III‐B and III‐C specimens with embedded LYP steel plates and constrained steel plates on both sides, when the outer steel tubular plates buckle, the internally constrained LYP steel plates provide support for the outer steel tubular plates. The plastic deformation of the specimens is sufficient, and the deformation performance is good. For type IV‐A specimens with LYP steel tubular plates and constrained steel plates on both sides, the mechanical behaviour of the new tubular steel piers is significantly improved, and increasing the height of the constrained LYP steel tubular plate can improve the compressive behaviour of the new tubular steel pier. Considering the effect of the steel plate thickness on bearing capacity and deformation performance, the thickness tw of the outer constrained steel plate should be equal to the thickness t of the common steel tubular plate, and the thickness tf of the LYP steel tubular plate should satisfy t ≤ tf ≤ 2t. Finally, a design formula is proposed to calculate the axial bearing capacity of newly designed tubular steel piers with constrained LYP steel plates.

Derivation of the unified equation of axial compression of CFST columns

The steel tube concrete columns with steel reinforcement cages, steel plates and steel tubes has been used in super high-rise buildings, which are called concrete-filled steel tubular (CFST) columns with internal stiffeners. Based on the theory of limit equilibrium, the unified equation for the axial bearing capacity of the CFST columns with internal stiffeners is obtained. The derived equation in this study can provide reference for the future engineering applications.

Experimental Study on Axial Compression Behavior of Masonry Columns’ Strengthening with Bamboo Scrimber Bar Mesh Mortar Layer

We propose a new method to strengthen structural masonry. To study on the axial compression behavior of masonry columns’ strengthening with a bamboo scrimber bar mesh mortar layer, axial compression tests of twelve masonry columns have been completed: nine strengthened columns and three unstrengthened columns. The failure process, bearing capacity, and failure mode are carried out. The strengthening method of bamboo scrimber bar mesh mortar layer permits the upgrade of the columns’ bearing capacity. The effects of bamboo bar ratio and mortar strengthening ratio on bearing capacity of the reinforced columns are compared. We propose the method for calculating the axial bearing capacity of such a reinforced column. The calculation results agree well with the experimental results, and the research results are available for engineering application.

Cold-formed elliptical concrete-filled steel tubular columns subjected to monotonic and cyclic axial compression

Concrete-filled steel tubular columns are widely used in structural systems, and elliptical concrete-filled steel tubular columns are receiving more and more attention. An experimental study on cold-formed elliptical concrete-filled steel tubular stub columns was carried out under monotonic and cyclic axial compression. The failure modes, axial load–displacement curves, ultimate loads, hoop strain–axial strain behavior, strength deterioration, and residual deformation were obtained and discussed. Complementary finite element models considering the complex non-uniform confinement between steel tube and concrete were developed and validated by experimental results. Then, the validated FE model was used to study the influence of aspect ratio, yield strength of steel, and compressive strength of concrete on the axial capacity of elliptical concrete-filled steel tubular stub columns. Finally, a relatively simple superposition method was put forward to predict the axial bearing capacity of elliptical concrete-filled steel tubular stub columns. Compared with the test data, both the numerical method and superposition method can generate accurate predictions.

Field trials on monotonic behaviour of a driven pile at an offshore wind farm in China

The existing database of the loading response of offshore pile foundations needs to be enriched, so that safety and economic considerations can be optimally balanced in design. This paper details a programme of field tests on an open-ended steel pile. The pile with a diameter of 2 m was driven to a depth of 72.8 m in a stratified soil site and then subjected to monotonic compressive, tensile and lateral loadings. Resting periods were allowed before each test to enable strength recovery, and a period of about one month was found to be sufficient (i.e., the axial bearing capacity increases from about 10 MN to 25 MN). The test results were interpreted in terms of the internal forces and displacements/deformations of the pile, and the more detailed pile-soil interactions (i.e., qs-s and p-y curves). It is found that, for cohesive soils, the unit shaft resistance qs remains constant through each soil layer regardless of the almost linearly varying undrained shear strength su obtained from CPTu tests, and the soil layer with overall higher su does not guarantee greater qs owing to different proportions of silty and clayey components. Upon reaching the ultimate uplift load, the shaft resistance within the cohesive soils shows a clear softening response. Extensive comparisons were made between these results and the predictions from existing design methods wherever applicable to discuss the accuracy of each.

Axial compressive behaviour of concrete-filled steel tubular columns with interfacial damage

In a previous study, 17 rectangular concrete-filled steel tubular columns were tested using a push-out test method to examine the interfacial bond behaviour. In this study, these specimens were subjected to axial compressive tests to study the effects of interfacial damage on the ultimate axial compressive capacity. The variations in both the load–axial displacement curves and load–strain curves were recorded and then compared to study the influences of both the steel tube fabrication method and the D/ B ratio on the axial load–carrying capacity. The axial compressive behaviour of rectangular concrete-filled steel tubular columns with no interfacial damage was then studied using a numerical analysis method. The contact stress distribution along the length and width of the face and at the height of the interface was obtained and discussed. In addition, the ultimate axial compressive capacity of rectangular concrete-filled steel tubular columns with no interfacial damage was calculated using the formulas from three international codes. The influence of interfacial damage on the axial compressive bearing capacity of a rectangular concrete-filled steel tubular column was discussed through a comparison of the results of the numerical simulation, formula calculation and experiments. The influence of the interfacial gaps caused by the push-out tests on the axial bearing capacity of the concrete-filled steel tubular columns can be ignored, because the core concrete was not destroyed and the outside steel tube can provide a sufficient constraint force on the concrete when the two materials yielded. Finally, the influences of the gap type and size on the bearing capacity were discussed.

Self-expanded piles: A new approach to unconventional piles development

In onshore and offshore fields of ocean engineering, piles are used as foundation systems for various structures. Piles are classified into different types depending on their materials, geometries, and particularly, installation methods, which have advantages or limitations. Companies and engineers have developed a new group of piles, because of necessity to improve their performance in terms of increasing the bearing capacity, reducing impacts of traditional installation procedures, implementing by low- torque power equipment, and utilizing them in widely different ground conditions, including in a marine environment. In the present study, three different models of a new pile with an expander body are introduced to increase the shaft and pile-toe diameters and its self-expansion in the embedment depth under the titles of the Bubble pile (BP), Self-Expanded pile (SEP) and Wing pile (WP). The main subject of this research is to achieve increased bearing capacity, reduced installation effects, and decreased required installation torque. The frustum-confining vessel of Amirkabir University of Technology (FCV-AUT) was employed for this purpose. Up to 14 axial compressive and tensile load tests were carried out on different model piles on sand collected from Anzali shore located on the northern coast of Caspian Sea in Iran, with relative densities of 45% to 50% within FCV-AUT. Comparing the performance of introduced pile with traditional pile corresponding to the same characteristics, the results indicated a significant increase in the axial bearing capacity and reduced disturbance effect of the pile. Also, a lower installation torque of the SE pile was required compared to the helical pile. The test results also demonstrated that the new pile could resist considerable compressive and uplift loads, and could be a possible alternative to traditional piles in the onshore sector.

Experimental investigation of the compression-bending property of the casing joints in a concrete filled steel tubular supporting arch for tunnel engineering

The concrete-filled steel tubular (CFST) arch is an effective new support form for mine/traffic tunnels in complex conditions, and the casing joints on the arch determine its global bearing capacity. Eighteen tests, including axial compression, eccentric-compression with different eccentricities, and pure bending tests, were carried out. The bearing behavior, failure mode and failure mechanism of the specimens with casing tubes were analyzed and compared with specimens without a casing tube. Failures are mainly caused by the local stress concentration on the CFST components or the casing tube at the contact positions. The compression-bending bearing capacities of the CFST casing joints were analyzed with the help of the Mu-Nu coordinate system. Each Mu-Nu relation is described by a straight line combined with a lateral parabola, and the Mu-Nu formulas were fitted. The bearing ability of a CFST casing joint is lower than that of a conventional CFST section, and the reduction rate of the square cross section is more obvious. The effects of the concrete grade, casing tube length, casing tube thickness and gap width on the compression-bending capacity were obtained through numerical simulation tests. The concrete strength is the main factor influencing the axial compression bearing capacity, while it is the casing tube length that mainly influences the bending bearing capacity. Suggestions for use in practice are finally proposed based on the above results.

Imperfection sensitivity analysis for a composite bowed-out shell under axial compression

In this article, we present a systematic work to investigate the imperfection sensitivity of composite bowed-out shells with different layup patterns under axial compression. Two types of geometric imperfections, including eigenmode-shaped imperfections (produced by a first-order eigenmode imperfection approach and an N-order eigenmode imperfection approach) and dimple-shaped imperfections (produced by a single perturbation load approach and a multiple perturbation load approach), are introduced into the finite element model to predict their knock-down factors. For the eigenmode-shaped imperfections, we show that the knock-down factors predicted by the first-order eigenmode imperfection approach are riskier than the ones predicted by the N-order eigenmode imperfection approach. When adopting the single perturbation load approach, we reveal that the direction of a dimple on the shell makes a negligible effect on axial pressure bearing capacity, while the amplitude of a dimple on the shell plays a significant role in affecting the knock-down factors. Using the multiple perturbation load approach as an extension of the single perturbation load approach, we uncover that the knock-down factors predicted by the multiple perturbation load approach are more conservative than these achieved by the single perturbation load approach. In addition, we also find that the composite bowed-out shells are more sensitive to dimple-shaped imperfection than eigenmode-shaped imperfections. This work provides helpful findings for designing an airplane body and marine risers.