Axial Bearing Capacity Research Articles

Mechanical performance of ocean concrete-filled circular CFRP-steel tube columns under axial compression

The axial compressive mechanical properties of ocean concrete-filled circular CFRP-steel tube columns were investigated in this paper. Eighteen specimens were designed for testing with the position and number of CFRP as the variation parameters. The results show that the final failure mode of the specimens was significantly correlated with the position of the CFRP. The ultimate bearing capacity of the specimens was positively correlated with the number of layers of CFRP. And the ultimate bearing capacity of the specimens containing inner CFRP was higher with the same number of layers. The initial elastic rigidity of the specimen is less correlated with CFRP. The ductility of the specimens based on energy dissipation showed a significant overall decreasing trend with the increase of the number of layers of CFRP. In addition, 139 axial compression data samples of concrete-filled circular CFRP-steel tube columns were collected to verify the axial compression ultimate bearing capacity calculation equation proposed in this paper, and the results indicated that the calculated values can well reflect the measured data. Finally, the finite element model for this test specimen was established and expanded parametric analysis was performed, and the results were in good agreement with the calculation equations.

Axial behavior of precast segmental hollow bridge columns confined by grouted steel tubes

To avoid the problems of the conventional precast segmental bridge columns (PSBCs) such as the concrete crushing at column ends, joint openings between segments, and torsional deformation under seismic attacks, a novel type of precast segmental bridge column confined by a grouted steel tube (TPSBC) was proposed, and herein the axial compressive behavior of the TPSBCs was investigated by testing of 14 specimens. The main parameters of the tested specimens included the diameter-thickness ratios of the steel tubes, the number of the precast segments, reinforcement arrangements in the precast hollow segments, initial prestress levels, sandwich concrete strengths, and loading forms. The effects of the parameters on the failure modes, loading bearing capacity, ductility, and steel strain development of the specimens were evaluated. The test results indicate that the proposed TPSBCs with proper configurations exhibited desirable compressive behavior with significantly improved load bearing capacity and deformability compared with the PSBCs. Based on the analysis of the confinement effects, analytical models were developed for predicting the axial bearing capacity of the TPSBCs under the different loading forms.

Effect of Filling Phosphogypsum on the Axial Compression Behavior of Cold-Formed Thin-Walled Steel Walls

To study the effect of filling phosphogypsum (PG) on the axial compression behavior of cold-formed thin-walled steel (CFS) walls, four full-scale test specimens were designed and fabricated, in consideration of the filling regions of PG as well as measures with or without wall sheathings. The fabricated specimens were tested under monotonic vertical loads, and the failure processes and failure modes of specimens were elaborated. Each specimen’s axial load-displacement curve, bearing capacity, strain curve, and energy dissipation capacity were investigated in detail. Furthermore, the internal force distributions of wall components and failure mechanisms were revealed. The test results indicated that the failure characteristics of specimens include the buckling of the steel tubes, cracking of wall sheathings, crushing of PG, and distorting of tracks. Compared with the cavity wall specimen, the axial bearing capacity of the specimen filled with PG in the studs only increased by 37.4%, and the bearing capacity of the specimen filled with PG in and between the studs increased by 115.7%. This indicates that filling PG can effectively improve the axial bearing capacity of CFS walls. The bearing capacity of the specimen without wall sheathings is lower than that of the specimen with wall sheathings, indicating that the wall sheathing has a beneficial effect on the bearing capacity of the specimen. In addition, the internal forces of components during the loading process were analyzed. It found that the steel tube and PG made a great contribution to the bearing capacity of the wall. Specifically, the steel tube played a leading role in the early loading stage, while the PG played a leading role in the later loading stage.

Perbandingan Kapasitas Daya Dukung Fondasi Tiang Pancang Berdasarkan Pengujian Data Sondir dan Data N-SPT

Rig was erected on a foundation that must be able to support the forces caused by the rig. The purpose of this research is to find out how big the difference between the axial and lateral bearing capacity of RIG ARJUNA #28 foundation. The research was conducted at RIG Arjuna #28 in Prabumulih City. In this research, an analysis of the carrying capacity of the pile foundation was carried out using Sondir and N-SPT data which will then be compared with the results of these calculations. It can be concluded that with data analysis using CPT/Sondir, the foundation will use 12 piles with a depth of 17 m, while using N-spt data the foundation will use 8 piles with a depth of 24 m.

Compressive behavior of double-skin composite walls considering local buckling and post-buckling effect

This paper presents axial compressive experiments of double-skin composite walls (DSCWs) with novel dumbbell-shaped connectors (DSCs) and traditional headed studs. The effects of the wall thickness, material strength, and diameter and number of the headed studs on the axial behavior of the DSCWs were analyzed. The failure modes of the specimens included the local buckling of the steel plates and compressive crushing of the concrete. The buckling position was between two adjacent rows of connectors. The experimental results demonstrated that the denser the arrangement of the connectors and the larger the diameter of the headed studs, the higher the critical buckling stress and axial bearing capacity of the specimens. The compressive stress–strain relationship of the steel material was determined considering the buckling and post-buckling behaviors of steel plates. According to the superposition principle, the theoretical load–displacement relationships of the five specimens were calculated, and the theoretical curves were in good agreement with the experimental results. The calculation formula for the axial bearing capacity of the specimens was introduced with some simplified assumptions, and the average value of the experiment/calculation ratio was 96.14%. ABAQUS software was used to simulate the DSCW specimens, and the failure modes of the models were in good agreement with the experiments. The average value of the experiment/simulation ratio for the peak load was 98.77%. Based on the verified benchmark model, the effects of four parameters on the compressive behavior of DSCWs were analyzed.

Prediction of axial load bearing capacity of PHC nodular pile using Bayesian regularization artificial neural network

Pre-stressed precast high strength concrete (PHC) nodular piles with hyper-MEGA construction method are favorably used in medium to high-rise building foundations. In this study, a feed-forward neural network (FFNN) was adopted to investigate the ultimate axial load bearing capacity of the PHC nodular pile. The network receives the composite pile and geotechnical conditions with eight input neurons and outputs the nodular pile's ultimate axial load bearing capacity. Among numerous possible FFNN network architectures, the most accurate one is determined by optimizing the hidden layer. Network training is conducted with Bayesian regularization backpropagation (BRB); the training datasets consist of static pile load test and standard penetration test index of soil profile collected from various projects in Vietnam. The significance of each input parameter is quantified with importance-based sensitivity analysis. An explicit function has been constructed from weights and bias values at each neuron in the FFNN to estimate the axial load bearing capacity. The excellent agreement of all output values by the proposed FFNN with the measured values proved the model’s robustness and reliability. The predictive capacity of the proposed FFNN model has significantly outperformed all current empirical formulas. The outcome of this study can be directly put into engineering practice to furnish an economically optimal design of the composite nodular pile.

Full-scale experimental study of the seismic performance of pretensioned spun high-strength concrete piles

Pretensioned spun high-strength concrete (PHC) piles have been widely used in the pile foundations of buildings in soft soil areas due to their high axial bearing capacity and good economic benefit. However, the behavior of PHC piles under lateral loading is generally poor and this restricts their application in high-intensity seismic regions, especially for high-rise buildings. The existing research on the performance of PHC piles under cyclic lateral loading and with the presence of axial force is scarce. In this paper, the seismic performance of PHC piles is systematically evaluated through full-scale tests and numerical simulations. Lateral cyclic loading tests for two full-scale PHC pile specimens were conducted under different axial force ratios, and their performances were examined in terms of cracking pattern, failure mode, hysteretic characteristics, lateral bearing capacity, ductility, stiffness degradation and energy dissipation capacity. A dedicated finite element (FE) model was then developed using the software DIANA to compute the cyclic behavior of PHC piles, and the model was verified against the experimental results. Using the verified FE model, parametric analyses have been carried out to study the effects of axial force ratio, prestressing level of prestressing tendons, longitudinal reinforcement ratio, concrete wall thickness of the pile body and distributed pattern of prestressing tendons on the seismic performance of the PHC piles. The results show that the axial force ratio has a significant effect on the cyclic behavior and failure mode of PHC piles; an increase in the axial force ratio leads to an increase in the lateral bearing capacity but generally a decrease in the deformation capacity. The failure mode of the PHC piles is controlled by the rupture of prestressing tendons under lower axial force ratios (less than 0.15) but crushing of concrete under higher axial force ratios (greater than 0.15). Increasing the concrete wall thickness tends to improve the overall performance of the PHC piles, especially under higher axial force ratios.

Experimental Study on Bearing Capacity of Compression Members of Space Grid Structures Reinforced by RPC

Insufficient bearing capacity of compression bars in space grid structures can significantly reduce the collapse resistance of structures and cause immeasurable losses. Reactive powder concrete (RPC) with high strength, micro-expansion, and good ductility is used to reinforce the compression members of grid structures by infilling steel tubes. Axial compression tests on five types of high-frequency welded pipes with different section sizes and initial stresses were carried out. The results showed that compared to steel tubes alone, the bearing capacity of steel tubes reinforced by RPC could be increased by 75.77 to 218.34%. With a decrease of either the initial stress or confinement coefficient, the contribution of the material reinforcement increased. The failure mode of the specimen after RPC grouting was the same as that of the non-reinforced steel pipe, which was dominated by elastic-plastic buckling. The grouting hole after reinforcement did not fail prior to the instability of the member, which suggests that necessary measures to repair the hole should be taken. Based on the design method of axial compression bearing capacity of concrete-filled steel tubular members in six codes in China and abroad, the test results of this paper and 242 RPC-filled steel tubes were compared and analyzed. Finally, an equation of nominal bearing capacity, which estimates the ultimate bearing capacity of compressive members strengthened by filled RPC in grid structures, was proposed.

EFFECT OF CLAY SHALE SHEAR STRENGTH DEGRADATION ON BORED PILE FRICTION IN CLAY SHALE

This research aims at investigating and modeling the axial bearing capacity degradation of a bored pile on clay shale due to the bored pile installation processes. Clay shale sample models were prepared to simulate the wetting and drying cycles through weathering process between 0 to 6 hours. All samples were tested in which every 1 hour of the weathering process representing 1 cycle of wetting and drying. The direct shear laboratory tests were performed to obtain the peak and residual shear strength parameters of the interface between the bored pile and clay shale. The peak and residual shear strength parameters were obtained after 6 hours of the weathering process. The residual shear strength parameters were measured by applying with and without stress release. This investigation showed that the shear strength degradation at peak, residual without stress release, and residual with stress release respectively reached 87-62%, 28-20%, and 25-14% after 1 to 6 hours of weathering process. This result is very useful for predicting the bored pile skin friction in clay shale soils.

Multiobjective optimization of 3-DOF magnetic bearing considering eddy current effects and saturation

The multiobjective optimization method of three-degrees-of-freedom hybrid magnetic bearings (3-DOF HMBs) is crucial compared to time-consuming finite element calculation due to their three dimensional magnetic field. Solid rotors are the first choice for high-speed applications because the yield strength of laminated rotors is lower. However, solid materials may induce eddy current effects and saturation problems. In addition, a 3-DOF HMB has solid and laminated materials and permanent magnet materials, and the material price presents a risk for the structure. In view of the above mentioned problems, a dynamic magnetic circuit model of the 3-DOF HMB with eddy current and saturation effects is initial given. Subsequently, a multiobjective optimization design method for maximum axial and radial bearing capacity and the lowest cost is proposed. Finally, the optimized parameters are given, and a prototype is manufactured. The range of all optimal solutions considering saturation is less than that without saturation, and the maximum reduction is 99%. The experimental results demonstrate the effectiveness of the optimized design results.

Experimental study on axial compression for composite hollow column of steel fiber, high-strength lightweight aggregate concrete and angle steel

In order to study the axial compression performance for composite hollow column of steel fiber, high-strength lightweight aggregate concrete and angle steel, the axial compression tests were carried out on five composite hollow columns of steel fiber, high-strength lightweight aggregate concrete and angle steel with the variation parameters of hollow ratio (0%, 15%, 16%, 32% and 36%) and the form of opening (round hole and square hole). The failure phenomena and failure forms of the specimens were observed, and their stress–strain curves were measured, and the axial bearing capacity formula suitable for composite hollow column of steel fiber, high-strength lightweight aggregate concrete and angle steel was established. The following conclusions may be obtained from the test results: the axial compression performance for the composite hollow columns of angle steel is influenced by the hollow ratio and opening form greatly. The axial compression performance for composite hollow columns of steel fiber, high-strength lightweight aggregate concrete and angle steel is almost close to that of composite solid columns when the hollow ratio is low; The higher the void ratio, the more the cracks at the surface of the concrete, some transverse cracks appear, the peak load decreases by about 5–38%, and the deformation ductility coefficient increases gradually; The deformation ductility coefficient of round-hole hollow column is lower than that of square-hole hollow column. Based on the test, the finite element software ABAQUS is used to simulate the SCAH column. The correctness of the model is verified via the comparison between the numerical simulation results and the test results. At the same time, the stress nephogram of concrete and steel at different stages and the stress nephogram at concrete restraint state are simulated. According to the finite element simulation results, Mander model is used to calculate the axial compression bearing capacity of composite hollow column of angle steel. The high calculation accuracy and suitable for popularization can be obtained.

Experimental investigation into FRP-confined concrete-filled steel tubular columns under axial compression

The mechanical behavior of 66 carbon-fibre-reinforced polymer (CFRP)-confined concrete-filled steel tubular (CFST) short columns and 42 non-CFRP-confined CFST short columns under axial compression are studied. The typical failure modes and load–displacement curves of the specimen are obtained, and the stress mechanisms of the specimen are analysed. The effects of fiber-reinforced polymer (FRP) layers, core concrete strength and cross-section forms on the axial mechanical properties of CFST short columns are discussed. The test results show that there is a positive correlation between the improvement coefficient of bearing capacity and the confinement effect coefficient of FRP. Based on the superposition principle, the bearing capacity calculation formulas of circular and square CFST columns without CFRP confinement are proposed. On this basis, taking the confinement effect of FRP into account, the calculation formula of axial bearing capacity of FRP-confined CFST short columns is proposed. The comparison between the calculated values of the model and the measured values of the experiments shows that the model has good prediction effect.

Grey Correlation Analysis of the Durability of Steel Fiber-Reinforced Concrete under Environmental Action.

The interface performance of steel fiber-reinforced concrete (SFRC) is a critical factor in determining mechanical properties and durability. The degradation of the concrete matrix and micro-structure interface is caused by environmental erosion, which shortens the service life of the structure design. Considering different volume contents of steel fiber (0%, 1%, 2%), the failure mechanism of SFRC under different environmental erosion conditions was studied through a laboratory test scheme. A total of six environmental factors are selected, including water, sodium chloride solution, sodium sulfate solution, dilute sulfuric acid solution, sodium hydroxide solution, and a freeze-thaw cycle. When subjected to different erosion concentrations and periods, micro-structure and axial bearing capacity deterioration laws are compared and analyzed. A durability equation related to fiber mixture ratio and strength is presented based on the experimental data and the numerical simulation method. The influence of different environments on steel fiber-reinforced concrete is analyzed, and the grey correlation degree of axial compressive strength is analyzed. The experimental results show that steel fiber can effectively improve the concrete axial bearing capacity, but different responses are observed under the various erosion conditions. A freeze-thaw cycle environment has the most significant impact on the axial compressive strength of concrete, followed by the sulfuric acid environment, and other environments have a weaker impact. The research results will provide a theoretical basis for predicting the performance deterioration of SFRC concerning other erosion conditions and periods.

ANALYSIS THE USE OF BORE PILE FOUNDATION ON ALLUVIAL SAND AND TUFFACEOUS SANDSTONES AT MARGATIGA DAM PROJECT

The elevation of the dam building foundation plan is at an elevation of +06.00 and +08.00, the results of sub-surface tests including the Standard Penetration Test (SPT) and Pressure Meter Test (PMT) show that at these elevations the SPT value is < 20 or categorized as loose rock and the PMT results shows a lateral pressure of <3 – 10 MPa or categorized as very soft rock - soft rock. The results of the sub-surface test show that the type of rock constituent in the dam building consists of layers of alluvial sand and tuffaceous sandstone. Based on the technical specifications, the foundation must be at SPT value > 50 or in very dense rock layer, if the dam building foundation is still built at the elevation of the foundation plan, it can cause the building to become unstable due to the rock layer at that elevation not able to support the weight of the building. SPT values >50 was found at an elevation of +01.00 - -02.00 or 7 to 10 meters from the design elevation of the foundation. Furthermore, an analysis is carried out based on the results of sub-surface test to determine the method of strengthen the foundation. The results of the analysis show that the bore pile foundation is effective as a method of foundation strengthen. The analysis includes the analysis of the ultimate bearing capacity, the axial allowance bearing capacity of the pile foundation and the bearing capacity of the pile group foundation. Based on the analysis, strengthening the foundation of intake area requires 156 piles with a depth of 19 meters, the spillway area requires 196 piles with a depth of 17 meters and the retaining wall area requires 64 piles with a depth of 15 meters. Keywords: Sub-surface test; alluvial sand; tuffaceous sandstone; bore pile; bearing capacity

Analytical model for concrete-filled double skin tube columns with different cross-sectional shapes under axial compression

The existing theoretical analysis models of concrete-filled double skin tube (CFDST) columns are limited to the analysis of CFDST columns with circular outer and inner tubes (CC-CFDST). The purpose of this paper is to propose a unified model for CFDST columns with different cross-sectional shapes, including CFDST columns with rectangular outer and inner tubes (RR-CFDST), CFDST columns with square outer and inner tubes (SS-CFDST), CFDST columns with square outer and circular inner tubes (SC-CFDST), CFDST columns with circular outer and square inner tubes (CS-CFDST), CC-CFDST columns. The CFDST columns with different shapes (original columns) are replaced with equivalent CC-CFDST columns by assuming that they have the same cross-sectional areas of the inner and outer steel tubes and concrete. The difference in mechanical properties between the original column and the equivalent column is attributed to the difference in the confining effect of the steel tube on the core concrete caused by the different shape, which is considered by the shape effect coefficient ke. The proposed model is verified by collected experimental data of CFDST columns with different cross-sectional shapes. The mean value and coefficient of variation of the ratio of the calculated bearing capacity to the experimental bearing capacity are 1.006 and 0.119, respectively. The results show that the proposed model can predict the axial compression bearing capacity and load–deflection curves of CFDST columns accurately.

Experimental Study on Compressive Strength of Ultrahigh Performance Concrete Prefabricated Wall Structure

In order to study the influence of two parameters, height-thickness ratio and reinforcement ratio, on the compressive performance of prefabricated recycled concrete block-filled core walls, the author proposes a test method for the compressive strength of wall structures. In this method, 9 walls of dry and full-fill masonry are used, and the test measuring device and the arrangement of measuring points are designed to carry out the loading test. The results showed that reinforcement can significantly improve the axial compressive bearing capacity of the wall, but the out-of-plane displacement of the unreinforced wall is smaller than that of the reinforced wall. The larger the height-to-thickness ratio, the better the ductility of the reinforced core wall; the measured value of the axial compressive bearing capacity of the core-filled wall and the mean and coefficient of variation of the ratio to the standard calculated value were 1.49 and 0.13, respectively. The measured value is 34% to 68% higher than the standard calculated value. In conclusion, based on the test data and GB 50003–2011 “Code for Design of Masonry Structures,” the theoretical calculation formula of the compressive bearing capacity of the prefabricated recycled concrete block-filled core wall is given.

Compressive behavior of reinforced steel-PVA hybrid fiber concrete short columns after high temperature exposure

To investigate the axial compression mechanical properties of steel-PVA hybrid concrete short columns after high temperature, three groups of 15 specimens (without or mixed with steel and PVA fibers) were tested in this paper. These specimens were subjected to quasi-static loading compressive loading after exposure to elevated temperature. The results indicated that as the temperature increased, the hydration reaction occurred in the concrete, and specimen surface color gradually changed from light gray to grayish white, and its mass loss rate gradually increased. The mechanical properties of short columns of hybrid fiber concrete were significantly affected by the elevated temperature. However, the compressive bearing capacity of specimens was increased by the mixed fibers after elevated temperatures, compared to the ordinary concrete. Meanwhile, specimen with more steel fibers performed better on bearing capacity. The PVA fiber effectively reduced the formation and expansion of cracks in hybrid fiber concrete after high temperature and enhanced its ductility. A suggested reduction coefficient was introduced by considering the influence of temperature and fiber volume ratio, and the calculated value of axial compression bearing capacity of the specimen was in good agreement with the experimental value.

Residual axial capacity of seismically designed RC bridge pier after near-range explosion of vehicle bombs

The terrorist bombing attacks on public transportation infrastructures, e.g., bridges, were increasing dramatically. Bridge pier damaged under the explosion will lose a portion of axial bearing capacity and may induce the partial and complete collapse of the whole bridge. This paper aims to numerically study the dynamic behaviors and post-blast axial capacity of the seismically designed RC bridge piers subjected to near-range blast loading of vehicle bombs. Firstly, by adopting the multi-material Arbitrary-Lagrangian-Eulerian algorithm, Fluid-Structure Interaction method, and erosion algorithm in LS-DYNA, a reliable and predictive finite element analysis (FEA) approach is established. Based on the existing three series of tests, the FEA approach is comprehensively verified by comparisons of blast overpressure, column deflection, spalling range of concrete cover, and residual axial bearing capacity. Secondly, the explosion scenarios of vehicle bombs on bridge piers are designed, in which the prototype bridge piers for three various earthquake intensity levels (EI7-EI9) are detailed according to the Chinese specification JTGT 2231-01-2020, and the compact and non-compact sedan bombs are concerned according to the requirements of FEMA-428, respectively. Then, the blast resistance of the above three seismically designed bridge piers under two typical vehicle bombs are evaluated based on the residual axial bearing capacity, and the influences of seismic detailing are further assessed quantitatively. Finally, a low-complexity engineering design approach is recommended based upon the seismic design and detailing provisions. The present work can provide helpful references for the damage assessment, blast-resistant design and further strengthening of RC bridge piers against the potential close-in explosions of vehicular bombs.

A novel direct SPT method to accurately estimate ultimate axial bearing capacity of bored PHC nodular piles with 81 case studies in Vietnam

Bored PHC nodular piles (BPNP) are an eco-friendly and advantageous option for pile foundations of medium-rise to high-rise buildings. As none of the current methods to estimate the ultimate axial load-bearing capacity is accurate enough for BPNP in engineering practice, this study aims to achieve that objective by developing a new direct SPT method. To that end, we use static pile load test and SPT data of 81 PHC nodular piles collected in Vietnam. The ultimate bearing capacity is interpreted from the load–displacement curve in pile static load tests by various methods to determine the most suitable method for the nodular piles. Furthermore, 8 methods to determine axial load pile capacity directly from the standard penetration test are examined. Each method’s effectiveness is evaluated by comparing its predicted values with the measured values. Finally, the genetic algorithm for function optimization is employed to develop a new direct SPT method that can accurately predict the ultimate axial load-bearing capacity of nodular piles. The reliability of the proposed formula is justified by comparing the proportion of end bearing capacity with other published works. It is verified that the developed directed SPT method outperforms all current methods and could be implemented directly in engineering practice.

Optimization of inter-helix spacing for helical piles in sand

The optimization of the inter-helix spacing is a key issue of the axial bearing capacity of helical piles. In this paper, based on the cavity expansion, an analytical approach considering the small-strain stiffness, strength, compressibility and stress level of sand around the helical pile was proposed to analyze the influence zone of the helices to determine the optimal inter-helix spacing in sand. The calculation results of the proposed method were verified using the centrifuge test data and finite element analysis for helical pile in Congleton HST95 sand. They were also compared with those using the Meyerhof pile foundation theory. The results show that the optimal inter-helix spacing based on Meyerhof pile foundation theory differs significantly from the measurement. The range of the influence zone for the helices in sand calculated by the cavity expansion theory matches with the data from literature. The calculation results with the proposed method are consistent with the range of the optimal spacing ratio inferred in the centrifuge tests. The results based on the two-dimensional (2D) finite element model (FEM) are also basically consistent with the calculated analytical solution.