Axial Bearing Capacity Research Articles

Experimental and Computational Study on Conductors Bearing Capacity in Offshore Drilling.

The height of the cementing cement sheath of the conductor for offshore drilling is the key factor affecting wellhead stability. For the influence of the insufficient return height of cement slurry on the mechanical behavior of the conductor after running the conductor by shallow water exploration well drilling, the axial load distribution characteristics and bearing capacity mechanism of conductor were first analyzed from the perspective of operation characteristics of the drilling method. Second, a calculation model of axial bearing capacity of the conductor with the size of the conductor and the return height of cement slurry as variables was established on the basis of the hole enlargement that often occurs during drilling. In addition, the law of the influence of the return height of cement slurry on the ultimate bearing capacity of conductor and the strength difference of the two cementing surfaces between conductor and cement ring and between the cement sheath and submarine soil layer and its changing rules with time were explored and studied by field experiment. It was concluded that the friction between the cement sheath and the soil layer is the key factor that decides the main bearing capacity of the conductor.

Axial Compression Prediction and GUI Design for CCFST Column Using Machine Learning and Shapley Additive Explanation

Axial bearing capacity is the key index of circular concrete-filled steel tubes (CCFST). A hybrid PSO-ANN model consisting of an artificial neural network (ANN) optimized with particle swarm algorithm (PSO) was proposed to reliably and accurately predict the axial bearing capacity in this paper. The predictive performance of the model was evaluated and compared with the EC4 code and original ANN based on a dataset of 227 experiments, and a graphical user interface (GUI) was developed to achieve the automatic output of the results. The influence of each design parameter on the bearing capacity was analyzed and quantified using the Shapley additive explanation (SHAP) method and sensitivity analysis. The results show that the prediction performance of the PSO-ANN model is superior, and can be recommended as a candidate for the prediction of axial compression bearing capacity of the CCFST column in terms of performance indices. Shapley additive explanation-based parameter analysis indicated that the diameter and thickness of the steel tube are the most two important parameters to the bearing capacity; in particular, the fluctuation of the diameter under the stochastic environment leads to the variation of the axial compression bearing capacity beyond the diameter itself.

The analysis of pile-pile cap behavior under static loading test using distributed fiber optic sensor

Pile-Pile cap behavior was investigated in this study through the utilization of fiber optic sensors to continuously transmit information along the bored pile at a reading interval of 40 mm during each cycle of the static loading test. It is important to note that the fiber optic cables were installed on the two sides of the bored pile connected up to the pile cap to monitor the stress distribution beneath the pile cap while fiber optic sensors were installed under the pile cap. The ultimate axial bearing capacity expected to be achieved using the pile-pile cap configuration was 190 tons x 250% but failure occurred when the load used was increased to 190% of the design load. Therefore, the strain measurement obtained from the Distributed Fiber Optic Sensor Technology was analyzed to obtain information on the load transfer, pile shortening, mobilized unit skin friction, and mobilized end bearing at the pile-pile cap. The load portion carried out by pile cap was approximated at 6% to 23% from the actual top load applied. It was also discovered that the fiber optic sensors initially installed were able to record the strain caused to the soil by the load on the pile cap. The strain measurements on the soil made the zone of influence due to the loading of the foundation to reach two times the length of the pile while the biggest zone of influence lies at the end of the foundation. From recorded strain, show higher strain from one side compared to the other, this may indicate eccentricity of the load.

Experimental study on dynamic response and residual mechanical behavior of SRC columns under repeated lateral impacts

The steel reinforced concrete(SRC) column is a key bearing part of some kinds of buildings and bridges, and its failure is usually the main cause of progressive structural collapse. To evaluate the column as-built performance, this paper reports the impact behavior of seven SRC columns with built-in L-shaped steels under out-of-plane lateral multiple impacts and the corresponding residual axial mechanical properties. The column is first subjected to three repeated impact loading under the same impact energy to study its impact resistance. Subsequently, the axial compression test is carried out to explore residual behavior. The influences of impact height, stirrup ratio and axial compression ratio on its performance are considered and discussed in detail. Results indicate that the column does not collapse or perforate after three times of impact, showing good impact resistance. Flexural-shear failure is the main failure mode under the first impact. And columns with large axial pressure gradually experience local punching failure from overall failure because the axial pressure inhibits the oblique crack. With the increase of impact times, the peak impact loads of the hammer reduced while the mid-span displacement of the specimen increased continuously. And the performance of column deteriorates sharply after two impact damages. The static tests showed that the residual axial bearing capacity was deeply influenced by the induced residual deformation. Both the impact behavior and residual mechanical properties were improved with the increase of stirrup ratio. In addition, the deformation of specimen after impact damage caused the constraint effect of stirrup in the initial stage of axial compression test, leading to the difference in the ascending stage of load displacement curves.

Prediction of axial compressive capacity of CFRP-confined concrete-filled steel tubular short columns based on XGBoost algorithm

Carbon fiber reinforced polymer (CFRP) is widely used in the field of strengthening concrete-filled steel tubular (CFST) columns due to its excellent performance. However, the interactions between steel tube and concrete, and between steel tube and CFRP are very complex, which make it difficult to predict the strength. To solve this problem, a new method using an advanced machine learning algorithm, XGBoost, to predict the axial compressive capacity of CFRP-confined CFST short columns is proposed. The data set for training and testing contains 379 pieces of data out of two parts: 271 from the literature and 108 from our experiments presented in this paper. Firstly, the typical failure modes and stress mechanisms of the specimens and the effects of the number of CFRP layers, the strength of core concrete and section forms on axial compressive capacity are analyzed through experiments. Then, the machine learning is carried out with the material strengths (concrete, steel, CFRP), the cross-sectional areas of the materials (concrete, steel tube, CFRP) and the cross-sectional shapes of the specimen as the features, and the axial compression bearing capacity of the specimen as the labels. Eight algorithms: Linear Regression (LR), K-Nearest Neighbor (KNN), Support Vector Machine (SVM), and typical ensemble learning models such as Random Forest (RF), Adaptive Boosting (AdaBoost), Gradient Boosting Decision Tree (GBDT), Extreme Gradient Boosting (XGBoost), LightGBM Regressor (LGB) are selected for calculations. Based on RandomizedSearchCV and 5-fold cross validation, the performance of the eight algorithms is compared. It is found that XGBoost has the best prediction performance, with the coefficient of determination R2 = 0.9719. Finally, based on the learning curves and grid search, nine hyperparameters of XGBoost model are adjusted, the optimal combination of hyperparameters of XGBoost model is obtained. The results show that the performance of XGBoost model is improved, with the coefficient of determination R2 = 0.9850.

Analytical study on the composite behavior of rectangular CFST columns under combined compression and torsion

In this paper, a total of 44 rectangular CFST column finite element models are established and verified. The effect of loading path, the working mechanism and the constraint interaction of rectangular CFST column under compression-torsion loading are discussed. The obtained results show that the ultimate axial bearing capacity of CFST column is decreased when the torsional moment is applied first, and the ultimate torsional capacity is increased when the compression force is applied first. The working mechanism of the compression-torsion CFST column can be simplified as unity of “pulling/compressive torsion” of the steel tube and “compressive torsion” of the core concrete. Finally, the torque-axial force correlative formula of rectangular CFST column is proposed, and is verified well with the test results and finite element results with higher accuracy and less dispersion.

Uncertainty Analysis of Axial Pile Capacity in Layered Soils by the Piezocone Penetration Test

This study presented a framework for uncertainty analysis of the ultimate axial bearing capacity of piles evaluated by the UniCone method in layered soils. The UniCone method by Eslami and Fellenius (1997) is a direct piezocone penetration test (CPTU) method for evaluating the ultimate axial capacity of piles in the reliability design. The spatial variability of CPTU data is modeled as a random field for each soil unit in the soil strata. The empirical correlation coefficients of the UniCone method are assumed to follow lognormal distributions. On the basis of uncertainties of CPTU data and empirical correlation coefficients, the first-order reliability method (FORM) is then applied to the reliability analysis of ultimate axial bearing capacity of piles. The effects of spatial variability of CPTU data and variations of empirical correlation coefficients on the ultimate axial bearing capacity of piles are evaluated by an Excel spreadsheet-based framework. Seven case studies show that the proper identification of different soil units from soil profiles is crucial for estimating the failure probability of pile capacity in the reliability analysis. Uncertainties of CPTU data and empirical correlation coefficients would be over-estimated unless different soil units in soil profiles are identified properly from each other. The over-estimated geotechnical parameters contribute to a higher failure probability of pile capacity. The proposed framework can evaluate the uncertainty of the ultimate axial bearing capacity of pile foundations more rationally.

Numerical and theoretical analysis of beam-to-column connections with ECC ring beams subjected to local compression loading

Engineered cementitious composite (ECC) is a kind of high performance cement-based composite materials with strain hardening and multiple cracking behaviour. Replacing concrete with ECC in the beam-to-column connection with ring beam may effectively improve the load-carrying capacity and ductility, as well as prevent cracks and solve durability problems caused by the brittleness of concrete. In this paper, the failure mechanism of beam-to-column connection with ECC ring beam subjected to local compression loading was investigated with the nonlinear finite element (FE) method. The results indicated that continuous lateral pressure was provided by the ECC ring beam, which improved the local compression performance of the ring beam connection. Extensive parametric studies on the local compression behavior of connections with ECC ring beams were also conducted. According to the simulation results, the peak strength of ECC connections was 13.0%–24.2% higher than that of concrete specimens. Increasing the ECC compression strength or ring beam width can effectively increase the load-carrying capacity of the connection, but the ECC tensile strain can only affect the ductility of the connection when the ultimate tensile strain was lower than 1.5%. Based on the FE analysis, an effective restraint width of the ECC ring beam was proposed, and theoretical models were established to predict the axial compressive bearing capacity of the beam-to-column connection with ECC ring beam.

Lightweight design of arcuately stiffened cylindrical shells based on smeared stiffener method and active learning strategy

The lightweight design of stiffened cylindrical shells has always been a key area of research for the aerospace industry, owing to its considerable economic benefits. In this study, a novel arcuately stiffened cylindrical shell, which aims to utilize the potential of the axial bearing capacity effectively, is proposed based on the concept of synchronous failure. Subsequently, the smeared stiffener method is derived by using the equivalent stiffness, and the critical buckling load is predicted accurately. Furthermore, the lightweight designs for the perfect and imperfect stiffened cylindrical shells are established, and an objective-pursuing learning method is proposed to reduce the computational cost by combining the advantages of the smeared stiffener method and Kriging model. The results showed that the arcuately stiffened cylindrical shell is very efficient, and the proposed objective-pursuing learning method exhibited high efficiency for optimization design.

Design method of fire-resistance capacity of reinforced-concrete-filled steel tube column under axial compression

Concrete-filled steel tube (CFST) columns are widely used in high-rise and superhigh-rise buildings because of their good mechanical properties, and the fire protection design of building structures must be considered. Under the same conditions, reinforced-concrete-filled steel tube (RCFST) columns show better fire-resistance performance than CFST columns. The theoretical calculation formula of its axial compressive fire-resistance capacity was derived in this study. The current structural design method adopted in China is a partial factor method based on reliability, in which the partial factors at room temperature are generally used for structural design at high temperatures. The strength of materials has greater dispersion at high temperatures, and it is necessary to develop reliability design methods for CFST columns at such temperatures. To consider this change fully, reliability theory was used to obtain the material partial factor at high temperatures. Then, based on the calculation theory of the axial bearing capacity of the RCFST column at high temperatures, a fire-resistant design method for the RCFST column was developed.

Experimental study on bearing capacity of corroded Q345 H-shaped steel column under axial compression load

In order to investigate the effect of corrosion damage on the bearing performance of H-shaped steel columns under axial compression, experimental study was carried out on specimens obtained from artificial accelerated corrosion. Firstly, the cleaned corroded surface morphologies were scanned by a 3D laser profiler. The volume loss ratio, residual cross-sectional area, centroid coordinate, and other parameters of the corroded specimens were calculated and analyzed, and the material properties of the corroded steel were obtained. Then, an uncorroded steel column and four corroded steel columns were subjected to the axial compression test, and it was found that corrosion damage significantly reduced the axial compression bearing capacity of the steel column and the degree of bearing capacity degradation was negatively correlated with its volume loss ratio. In addition, the failure mode of the axially compressed steel column changed from the overall buckling of the uncorroded specimen to the local-overall interactive buckling because of corrosion. Moreover, the final failure location was in the height range with the most serious volume loss of the corroded specimen. Finally, based on the directly scanned corroded morphology, an innovative modeling method using shell elements was proposed and verified.

Developing random forest hybridization models for estimating the axial bearing capacity of pile.

Accurate determination of the axial load capacity of the pile is of utmost importance when designing the pile foundation. However, the methods of determining the axial load capacity of the pile in the field are often costly and time-consuming. Therefore, the purpose of this study is to develop a hybrid machine-learning to predict the axial load capacity of the pile. In particular, two powerful optimization algorithms named Herd Optimization (PSO) and Genetic Algorithm (GA) were used to evolve the Random Forest (RF) model architecture. For the research, the data set including 472 results of pile load tests in Ha Nam province-Vietnam was used to build and test the machine-learning models. The data set was divided into training and testing parts with ratio of 80% and 20%, respectively. Various performance indicators, namely absolute mean error (MAE), mean square root error (RMSE), and coefficient of determination (R2) are used to evaluate the performance of RF models. The results showed that, between the two optimization algorithms, GA gave superior performance compared to PSO in finding the best RF model architecture. In addition, the RF-GA model is also compared with the default RF model, the results show that the RF-GA model gives the best performance, with the balance on training and testing set, meaning avoiding the phenomenon of overfitting. The results of the study suggest a potential direction in the development of machine learning models in engineering in general and geotechnical engineering in particular.

Study on axial compression bearing capacity of novel concrete-filled square steel tube columns

The way that strengthening the bond effect between the concrete and the inner steel by welding technology can effectively improve the axial bearing performance of the concrete-filled square steel tube (CFSST) column. However, this method requires high welding quality. In order to simplify the construction and reduce the difficulty of construction, two kinds of novel section forms of CFSST column without welding have been proposed. One is CFSST column reinforced with rhombic stirrups (specimens in SSSC group), the other is double-skin CFSST column (rhombic inside & square outside) (specimens in SSC group). A total of 21 specimens were fabricated for axial compression test, including 10 specimens in SSSC group, 7 specimens in SSC group, 1 CFSST column reinforced with inclined I-steel, 1 CFSST column reinforced with I-steel, 1 CFSST column reinforced with circle steel tube, and 1 CFSST column. The axial load-displacement curves of the specimens were obtained, and the failure modes and the influence parameters of specimens with different sections were analyzed and compared. The results show that the failure modes can be divided into local buckling failure and instability failure during plastic loading according to the aspect ratio. The specimens in SSC group have the highest average peak load, and the best residual bearing capacity, and the most eximious plastic strengthening characteristics in the later stage than other specimens. The decreasing rate of unit peak load of SSSC group was the slowest when the steel content was increased, which improves the bearing capacity overall. Increasing the core concrete area (inner steel tube side length) can enhance the bearing capacity of the specimens with longitudinally continuous build-in steel (reinforced with steel tube). While, it is not economical to improve the peak load of the specimens with large section (side length >200 mm) by increasing the thickness of the outer steel tube when the build-in steel is longitudinally discontinuous (reinforced with rhombic stirrups). Based on the result analyses, the calculation formulas considering the stability of axial compressive bearing capacity of specimens in SSSC and SSC group have been derived by superposition method. And the calculated results are in good agreement with the test results.

Axial compression behaviour of cruciform cold-formed steel built-up columns: Shape optimization and experimental study

In this paper, the cruciform CFS built-up cross sections are formed through four identical multi-roll lipped channels connected at their webs with high-strength bolts and filler plates. An optimization algorithm is primarily proposed that integrates sequential quadratic mathematical programming methods and finite strip analysis. It is desirable to effectively improve the buckling behaviour of cruciform CFS built-up columns without increasing the material volume. Eight different areas of built-up sections were optimized, each built-up open section was formed by fold-lines of the steel plate, and the width and angle of the constituent elements of the built-up section were selected as the main design variables. To simplify the optimization task and provide more practical structural components, usage constraints and practical manufacturing limits were imposed on the selected built-up sections during the optimization process. The results show that the adopted optimization process significantly increased the critical local buckling stress of the cruciform CFS built-up columns by 26.2%–58.9%. The design strength calculated according to the AISI standard was increased by 2.76%–18.15%. The axial compression bearing capacity tests with two different optimized cross sections were conducted, and the test loading capacities and failure modes of each specimen were obtained. The test results show that the failure modes were mainly driven from local and distortional buckling to torsional and flexural buckling with increasing slenderness, and the deformations were concentrated in the region near the end of column. Finally, the axial compression strengths of such cruciform CFS built-up columns obtained from the tests were used to assess the applicability of AISI standards. For columns failed by local and distortional buckling, AISI standard were un-conservative, whereas for torsional and flexural, AISI standard were conservative.

Investigation on Mechanical and Microstructure Properties of Steel Fiber Reinforced Concrete

This paper studied the microscopic and mechanical property degradation of axially compressed concrete with different steel fiber content under chemical erosion and freeze-thaw environment. Concrete cylinders with three types of steel fiber contents (0%, 1%, 2%) were selected to study the durability behavior concerning different environmental effects up to 28 days, which included tap water, 3.5% sodium chloride solution, 10% sodium sulfate solution, 5% sulfuric acid solution, 2 mol/L sodium hydroxide solution, and 100 freeze-thaw cycles. The variation of specimens’ microstructure and axial bearing capacity with different fiber content was studied with the chemical erosion cycle increase, and the mass and pH variations of the specimen were measured. According to the law of micro-cracks, the deterioration degree was judged, and a numerical analysis model was established to quantify the reliability of the structure with different fiber content. The results show that the addition of steel fiber can effectively improve the axial bearing capacity of concrete, and a freeze-thaw environment and chemical erosion can accelerate fiber-reinforced concrete’s failure. The optimal content of steel fiber was determined, which is 1% for sodium chloride and sodium sulfate environments, and 2% for the freeze-thaw cycle, dilute sulfuric acid, and sodium hydroxide environments. The finite element software Abaqus was used to simulate and analyze the freeze-thaw cycle and mechanical test of concrete, which verified the rationality of the test results. Research results will provide a theoretical basis for predicting the performance deterioration of steel fiber reinforced concrete under different erosion conditions and periods.

Bearing Strength of Concrete-Filled Steel Tube Reinforced with Internal Transverse Stiffened Bars under Axial Compression.

A new type of square concrete-filled steel tubular (SCFST) column is proposed, which is characterized by transverse stiffened bars inside the steel tube to improve the effective constraint performance of the concrete core. The experiment of this kind of composite material under axial compression was carried out. The results showed that the bearing capacity of the SCFST column reinforced by internal transverse stiffened bars increased by 4.5%-15% than that of the ordinary SCFST column. The transverse strain is smaller than the SCFST column. As the diameter of the reinforcement increases and decreases the spacing of bars, the axial load bearing capacity increased. The transverse strain of the member decreased obviously. It is noted that the confinement performance of the concrete core of this type was improved to some extent. At the same time, based on the unified theory, the simplified calculation formula of axial compression bearing capacity is derived.

Axial Compression Behavior of Symmetrical Full-Scale Concrete Filled Double Skin Steel Tube Stub Columns

To investigate the bearing behavior of symmetrical full-scale different strength concrete filled double skin steel tube (CFDST) stub columns, 19 full-scale specimens were designed, considering the slenderness ratio (λ); the compression strength of core concrete and sandwich concrete (fcki, fcko), the thickness of the inner and outer steel tubes (ti, to); the diameter of inner and outer steel tubes (Di, Do); and the tensile strength of the inner and outer steel tubes (fyki, fyko) as the main parameters. Nonlinear constitutive models for concrete considering constraint effect were adopted, and a finite element (FE) model was established using ABAQUS software. By comparing the results between simulations and experiments, the rationality of the modeling method was verified. Based on the FE model, the parameter analysis for CFDST columns were conducted, and the force mechanism, stress distribution, and deformation process were analyzed. The results showed that the axial compression bearing capacity (Nsu) increased significantly with an increase in fcki, to, Do, and fcko, while Nsu decreased gradually with an increase in λ. Finally, according to the calculated results of the specimens, the calculation formula for Nsu of full-scale composite columns was statistically regressed using 1stOpt software and showed a good agreement with the FE.

Axial compression capacity analysis of prefabricated steel reactive powder concrete columns in prefabricated modular buildings

This article proposes a prefabricated steel reactive powder concrete (PSRPC) component. Axial compression tests are conducted with five 3m full-scale column specimens to investigate the specimen damage and failure process and to measure the axial displacement, strain and ultimate bearing capacity in order to study the influences of the RPC strength and the section steel flange thickness on the mechanical properties of the PSRPC. The tests show the following. The ultimate failure mode of the PSRPC is column end splitting. During the loading process, the RPC and the section steel work compatibly, and their strengths are given full play. The lateral effect of the RPC on the section steel and the composite confinement effect of the stirrups and section steel on the RPC core significantly increase the ultimate bearing capacity of the PSRPC, and these effects increase with an increase in the RPC strength. The confinement effect on the RPC core in the enclosed region increases with an increase in the section steel flange thickness, that is, the thicker the section steel flange, the larger the portion of the load taken by the RPC core and the higher the ultimate bearing capacity of the PSRPC. The finite element analysis of PSRPC specimen is carried out by ANSYS software, and the simulation results are in good agreement with the test results. A method for calculating the axial bearing capacity of a full-scale column is proposed, taking the confinement effect of the stirrups and section steel on the RPC core into account.

ANALYTICAL STUDY ON AXIAL AND ECCENTRIC COMPRESSIVE BEHAVIOR OF POPLAR COLUMN STRENGTHENED BY BFRP

In this work, the compression behaviour of the Xinjiang poplar column was reinforced by basalt fibre reinforced polymer (BFRP) strips with different reinforced configurations, and thenumerical simulations were performed on the axial and eccentric compressions of poplar columns unreinforced and reinforced with BFRP to assess the effect of the bearing capacity and deformation of the columns. The results show that the use of BFRP to reinforce the Xinjiang poplar column effectively improves its axial compressive bearing capacity (axial compression) andbending bearing capacity (eccentric compression), and at the same time, the bearing capacity and stiffness of the columns strengthened by BFRP increased with the bonding area of BFRP.

Experimental investigation on behavior of splicing glass fiber–reinforced polymer-concrete–steel double-skin tubular columns under axial compression

Splicing glass fiber–reinforced polymer (GFRP)-concrete–steel double-skin tubular column (DSTC) is to set connection component at the joint of two or more separated GFRP tubes, and then pour concrete in the double-tube interlayer to form a continuous composite member. In this paper, the splicing DSTC composite members based on steel bar connection were designed and tested under axial compression to determine its mechanical performance. The main parameters include the connection steel ratio, the hollow ratio, and the thickness of GFRP tube. The results show that the GFRP tube presents apparent constraint effect on the concrete at about 60% of the ultimate load. The failure of splicing specimen occurred in the non-splicing section at a certain distance from the splice joint, and the stirrups at the splice joint provide effective constraint effect on the internal concrete. The proposed DSTC splicing method based on steel cage connection can satisfy the strength requirements of splice joint. Nevertheless, the increase of axial steel bar ratio cannot improve the bearing capacity of the splicing column, and the steel ratio of 2.44% is suggested for the splice joint of DSTCs under axial compression. The axial bearing capacity of splicing DSTCs significantly increases with the increase of GFRP tube thickness, but the amount of stirrups should be increased properly when a larger tube thickness is used. Two models were selected to calculate the bearing capacity of splicing members and it is found that Yu’s model is more accurate in predicting splicing DSTCs.