Axial Bearing Capacity Research Articles

Seismic Soft Soil-Structure Interaction Using RLBRB-Equipped Strut in Deep Excavations

ABSTRACT This paper presents the applicability of Reduced Length Buckling-Restrained Braces (RLBRBs) in combination with strut elements in deep excavations. Strut members are used as part of the lateral load resisting system. By proposing a new type of RLBRB section, the advantages of RLBRBs are demonstrated in dynamic soft soil-structure interactions. A numerical investigation is carried out to clarify the behavior of RLBRB-equipped strut members in supported deep diaphragm walls in soft clayey soils. The validity of the numerical models is confirmed after comparing the results of the nonlinear dynamic analyses with those of the experimental evidences. Four different excavations with 8 m, 12 m, 16 m and 20 m of clear bay spans and an excavation depth of 14 m are numerically simulated. In order to investigate the seismic analysis under various circumstances, three different accelerograms with various frequency contents are utilized. In the current study, the damping mechanism and the axial load bearing capacity of the RLBRBs in seismic conditions are taken into account in order to dissipate the induced earthquake energy and consequently preserve the local and global stability of the supported deep excavation. In this regard, one- and two-sided RLBRB-equipped struts with pipe-shaped steel cores are applied in a lateral stiffening system. As a result, unlike the conventional struts, the sudden stress changes in the struts are removed. Furthermore, the parameters influencing deep excavation stability are investigated. Basal heave, surface settlement, and lateral deformation of diaphragm walls are determined during geostatic and seismic conditions. Findings of this study provide fundamental principles for designing deep excavations under seismic conditions with efficient strut members. The applicability and effectiveness of the obtained results are also illustrated.

Size effect on axial compressive failure of CFRP-wrapped square concrete columns: Tests and simulations

Carbon Fiber Reinforced Polymer (CFRP) has been widely utilized to wrap concrete column in order to improve the axial compressive bearing capacity. In this study, the size effect of CFRP-wrapped square concrete columns was investigated using both experimental and numerical approaches. A total of 30 geometrically-similar CFRP-wrapped concrete columns with a maximum cross-sectional width of 600 mm were designed and tested with repeated axial compression. The influences of loading type, structural size and reinforcement configuration on the failure of the columns were explored and measured. Moreover, a 3D meso-scale simulation approach considering the influence of concrete heterogeneity and CFRP-concrete interactions was utilized to furtherly investigate the size effect of CFRP-wrapped columns. In the 3D meso-scale simulations, the failure of columns with larger structural sizes and larger CFRP fiber ratios was analyzed. The size effect on the nominal compressive strength of CFRP-wrapped columns was examined and discussed in detail. Finally, an updated size effect law (SEL) was established to describe the size effect in CFRP-wrapped concrete columns. The updated SEL is proved to be reasonable, which shows good consistence with the present experimental data and simulation results.

Study on axial compressive properties of RC square columns strengthened with prestressed CFRP sheets

Carbon-fiber reinforced polymer (CFRP) has the advantages of high strength, high elasticity, light weight, corrosion resistance, high fatigue resistance, and ease of construction and has become the main seismic strengthening strategy for civil engineering structures. This paper presents a new technique to quickly strengthen reinforced concrete square columns using prestressed CFRP. The axial compression performance of three groups of 10 prestressed CFRP reinforced concrete square columns was tested. By observing the effects of different prestressed CFRP wrapping methods and the range and degree of prestressing on the axial compression, it was possible to analyze the mechanism by which CFRP actively restrains the reinforced columns. Changes in the ductility of the reinforced components were examined and their axial bearing capacity was studied theoretically. The test results and analytical studies show that, the larger the degree of prestressing and range of wrapping, the stronger the lateral deformation constraint placed on the core concrete, and the greater the bearing capacity and ductility. The increase in bearing capacity can reach 65.91%. Increasing the degree of prestressing of the CFRP is also more effective than increasing its reinforcement range. The axial bearing capacity of the reinforced columns was also calculated theoretically by establishing strength calculation models for the confined concrete for different methods and ranges of reinforcement. The predicted results were in good agreement with the test results, so, the models can provide a firm theoretical basis for practical applications.

Residual Properties and Axial Bearing Capacity of Steel Reinforced Recycled Aggregate Concrete Column Exposed to Elevated Temperatures

This paper presents an investigation on residual properties and axial bearing capacity of steel reinforced recycled aggregate concrete (SRRC) column exposed to elevated temperature. 48 specimens were designed for the static loading test after high temperature. The variables include replacement ratios, designed temperature, target duration ,thicknesses of concrete cover, steel ratios and stirrup spacing. From this test, the mass loss ratio and stress load-deformation curve were obtained, and the influences of various parameters on residual bearing capacity were analyzed. ABAQUS was used to calculate the temperature field of specimens to get temperature damage distribution on the cross section concrete. Based on the results from testing and finite element analysis, a method of calculating the residual bearing capacity of SRRC columns under axial compression after high temperature was presented. It is shown that the bearing capacity of specimens reduced as the heated time and exposure temperature increased while it decreased as the cover thickness and steel ratio decreased. The ductility increased with the increase of steel ratio and stirrup ratio but the opposite result appears if the temperature and coverage of concrete increased. The initial damage value increased as the temperature and fire duration increased; with the increasing of replacement ratio and the decreasing of temperature, the temperature of the cross section would increase gradually. Finally, comprehensive experimental research and numerical simulation analysis results show that the calculation results are in good agreement with the experimental results.

Fire Resistance Design of Concrete-Filled Steel Tube Stub Columns

This paper introduces simplified design methods for calculating the load bearing capacity of axially loaded concrete-filled carbon steel tubular (CFST) stub columns and concrete-filled stainless steel tubular (CFSST) stub columns. Refined finite element (FE) models are developed for capturing the fire performance of CFST and CFSST stub columns under ISO 834 fire. The accuracy of proposed FE models is validated by comparing with existing test data. By using the new developed FE models, the design equations suggested in Eurocode 4 for calculating the axial load bearing capacity of CFST and CFSST stub column in fire are evaluated. It is found that the Eurocode 4 generally provide an unsafe prediction due to the influence of unsuitable consideration on thermal expansion and adopted material strength values. In order to improve the equations in Eurocode 4, correction factors kc and ks for the concrete core and steel tube are defined and calibrated based on comprehensive parametric analysis, and refined equations for predicting the axial load bearing capacity of CFST and CFSST stub columns in fire are suggested. Finally, a design example based on the proposed simplified design methods is demonstrated in this paper.

Performance of Special-Shaped Concrete-Filled Square Steel Tube Column under Axial Compression

The axial compressive performance of novel L-shaped and T-shaped concrete-filled square steel tube (L/T-CFSST) column was assessed in this study. Ten L/T-CFSST columns were tested to failure under axial load. The experimental data were used to determine various failure modes, bearing capacities, and load-displacement curves. The test parameters included the section form, steel tube thickness, steel yield strength, and slenderness ratio. The axial compressive performance of the L/T-CFSST column proved favorable, and each square steel tube showed strong cooperative performance. The failure mode of the stub column specimen (H/D ≤ 3) was strength failure caused by local buckling of the steel tube and that of the medium-long column member (H/D > 3) was instability failure caused by overall bending of the specimen. A finite element analysis (FEA) model was established and successfully validated by comparison against the test results. Based on the FEA model, parametric analyses were conducted to investigate the effects of steel tube thickness, concrete strength, steel yield strength, and slenderness ratio. The ultimate loads obtained from the experiments and FEA were compared to the results calculated by the available design codes. A formula was established to calculate the axial compressive strength and stability bearing capacity of the L/T-CFSST column accordingly. The calculation results are in close agreement with the FEA and experimental results, and the proposed formula may provide a workable reference for practicing engineers.

Axial and Bending Bearing Capacity of Double-Steel-Concrete Composite Shear Walls

Double steel-concrete composite shear wall is a novel composite structure. Due to its good mechanical properties, it has been considered as a substitute for reinforced concrete walls in nuclear facilities, marine environmental structures, and high-rise buildings. However, the design method of the double-steel concrete composite shear wall is lacking. The purpose of this paper is to propose the bending capacity formula under large and small eccentric loads. By summarizing the test results of 49 steel-concrete composite double shear walls under cyclic loading from different studies, it was found that the bending failure of double-steel-concrete composite shear walls was featured by the concrete crushing at the bottom. A finite element model was established and it could simulate the axial and bending performance of double steel-concrete composite shear walls reasonably well. According to the experimental results and FE analysis, the primary assumptions for calculating the axial and bending bearing capacity of the double steel-concrete composite shear walls were proposed. Based on these assumptions, the bearing capacity formulas were derived according to the equilibrium theory of the cross section. The calculation results obtained by the bearing capacity formulas were in good agreement with the test results.

Experimental study of the behavior of prefabricated lightweight concrete shear walls with channel sections framing under axial compression

In order to satisfy requirements of fireproof and thermal insulation property of lightweight steel and lightweight concrete structures, an innovative prefabricated lightweight concrete shear wall with channel sections framing is developed. This paper focuses on axial compressive behavior of the wall. Two full-scale specimens are tested under axial compressive loads. The compressive strength of ceramsite-foamed concrete is varied to investigate their impacts on axial bearing capacity and axial compressive stiffness of the specimens. The failure modes, load-displacement curves, and deformability of the specimens are also investigated. Test results show that the failure modes of shear wall are mainly local bucking failure of channel sections framing and local crushing of ceramsite-foamed concrete plate. Compared with the specimen infilled C7-grade ceramsite-foamed concrete, the axial bearing capacity and the axial compressive stiffness of infilled C10-grade ceramsite-foamed concrete specimen are increased by 15.6% and 16.3%, respectively. Therefore, this study can provide a reference for further research on the axial compression performance of the prefabricated lightweight concrete shear walls with channel sections framing.

Numerical modeling and parametric analysis of grouted connections under axial loading

Abstract With the rapid development of the offshore wind power industry, large-diameter grouted connections (GCs) with high-strength grout have become a developing trend. Previous studies on ordinary-strength and small-scale GCs may not meet current engineering needs. A numerical study was carried out to investigate how the axial mechanical properties of a large-diameter GC that has high-strength grout are influenced by geometric parameters, such as radial stiffness, the height to space ratio (h/s) of shear keys, and the length to diameter ratio (Lg/Dp). The finite element model was verified against the results of the experimental test. The mechanical properties of ultimate bearing capacity, interface transfer strength, ductility, nominal average stress and grout contact pressure distribution are discussed in detail. The results suggest that the increase in radial stiffness can strengthen the axial ultimate bearing capacity and ductility of the GC. Besides, the h/s of the shear keys can affect the ultimate bearing capacity and ductility of GC by influencing the number of diagonal compression struts. Although the Lg/Dp can significantly improve the axial ultimate bearing capacity of GCs, conversely, the interface transfer strength is continuously reduced. The research results can provide technical reference for the design of GCs in the offshore wind turbine industry.

Axial Bearing Capacity Analysis of Pile Foundation using Nakazawa Method

Pile foundation serves to distribute all the loads in the building to the ground. There are several calculation methods for bearing capacity of pile foundation, one of them is Nakazawa method. Nakazawa method adapted from calculation used in Japan where it is relevant for soft soils. The aim of this research is to obtain axial bearing capacity of pile foundation that can withstand axial forces using Nakazawa method. The parameter that used for the calculation is modified or average N-value (). The analysis result shows the value is smaller than N existing, indicate that Nakazawa tend to use weaker value of N blows. It means the calculation is considered softer type of soils than the existing ones.The value of point bearing capacity, Rp, assimilate to the pattern of N-SPT. The result value of friction bearing, Rf, in respect of depth shows the linear trending. Rf along the pile depends on the friction interaction between soil and structure. This phenomena influenced by the soil type. The value of cohession along the pile augment, means the ability of soils to stick to the pile/structure is also high. It explains why the value of friction bearing is bigger in respect of depth.

Monotonic axial compressive behaviour and confinement mechanism of square CFRP-steel tube confined concrete

Steel tube confined concrete (STCC) is widely used in the vertical members of high-rise buildings such as columns. The axial load is not directly resisted by the steel tube in STCC, but is resisted via the interfacial frictional stress between steel tube and concrete core, which is different with that of concrete filled steel tube (CFT) members and would effectively suppress the outward local buckling of steel tube at early stage. Recently, fibre-reinforced polymer (FRP) confined STCC presents a potential to enhance the ductility and durability of such vertical elements. This paper presents an experimental study on monotonic axial compressive behaviour of carbon FRP (CFRP) confined STCC (CFRP-STCC) stub column and an analytical study on the confinement mechanism of and the ultimate axial bearing capacity of the elements. A three-stage confinement mechanism involving the different contributions of the steel tube and the CFRP wrap in CFRP-STCC elements was proposed based on the test results. A prediction model of the ultimate axial bearing capacity of CFRP-STCC stub columns was developed subsequently. Results show that the presence of CFRP wrap enhances effectively the load-bearing capacity and the ductility of steel tube confined plain concrete and reinforced concrete elements, and significantly prevents the local buckling of the steel tubes in the elements. The proposed prediction model of ultimate axial bearing capacity assesses test results with a great agreement.

Probabilistic Assessment of Model Uncertainty for Prediction of Pile Foundation Bearing Capacity; Static Analysis, SPT and CPT-Based Methods

Geotechnical designs, like other engineering disciplines, are always accompanied by uncertainties. Supplying continuous and reliable records and reducing the uncertainty associated with measurement errors, the cone penetration test (CPT) enhances the geotechnical designs to a more decent level. Deep foundation design, as an essential challenge of foundation engineering, is also involved with different sources of uncertainty. Moreover, the presence of various design methods, relying on different assumptions and requirements, introduces further complications to the selection of an appropriate method, which leads to the broad spectrum of the predictions. Hence, a database, including 60 driven pile load test results and CPT records in the vicinity of them, was compiled to investigate the model uncertainties embedded in various predictive approaches. Investigated approaches include two static analyses, five SPT, and five CPT-based methods, and were implemented to predict axial pile bearing capacity. The model parameters for these methods are investigated through seven statistical, probabilistic, and reliability-based criteria. Performance of the methods under these criteria is assessed by the use of radar charts. Moreover, the resistance factor, adopted in this study to estimate the efficiency ratio and actual factor of safety, is calibrated by four different prevailing methods. Eventually, among conventional available predictive methods, CPT-based methods perform better than others and result in cost-effective and optimized trends.

An efficient approach for numerical simulation of concrete-filled round-ended steel tubes

Concrete-filled round-ended (CFRE) steel tubes are widely used in civil infrastructures. Accurate and reliable numerical models of CFRE steel tube are significantly important to mimic the actual behavior. This study presents a fiber beam-column model to simulate nonlinear behavior of CFRE steel tubes. A group of uniaxial hysteretic constitutive models was defined for the properties of the material. To verify the reliability of the presented fiber model, a large number of numerical computations have been performed by the fiber model and a traditional refined finite element model. The results confirm that the proposed fiber model can accurately predict the nonlinear behavior of CFRE steel tubes. Finally, two empirical models for the prediction of the axial bearing capacity of CFRE steel tube columns were developed.

Experimental study on residual axial bearing capacity of UHPFRC-filled steel tubes after lateral impact loading

Concrete-filled steel tube (CFST) has been widely used in civil engineering. Numerous studies have shown that concrete-filled double-skin steel tube (CFDST) columns exhibit satisfactory mechanical properties under various loading conditions. Furthermore, ultra-high performance fiber-reinforced concrete (UHPFRC) has been developed as a prominent representative of new construction materials. This study investigates the residual bearing capacities of 10 concrete-filled steel tube specimens (three CFST columns and seven CFDST columns) after impact loading. The investigated parameters include the steel ratio, the concrete type, the section form, axial load ratio, the impact energy and the presence/absence of impact load. The results demonstrate that, when the inner steel tube thicknesses are identical, increasing the steel ratio from 0.296 to 0.467 (the outer steel tube thickness increases from 5 mm to 8 mm) can effectively improve the residual performance. For the non-impacted specimens, the bearing capacity of the CFDST columns is increased by 47.1% as the concrete type is changed from NSC to UHPFRC. For the impacted specimens, due to the influence of the test setup and other reasons, the concrete type has only a slight influence on the residual performance of CFDST columns; however, it has a substantial influence on the residual performance of the CFST columns. Furthermore, with the concrete type in the CFST columns changing from NSC to UHPFRC, the residual performance of CFST columns can be significantly enhanced.

Bearing capacity of welded composite T-shaped concrete-filled steel tubular columns under axial compression

The axial compressive experiments were carried out on 21 welded composite T-shaped concrete-filled steel tubular columns, and 395 finite element models were established for parameter calculation. The calculating formula of axial compressive bearing capacity of welded composite T-shaped concrete-filled steel tubular columns is established. The results show that three typical failure modes were found: middle buckling, end local buckling, and integral bending. When the slenderness ratio λ exceeds the elastic instability limit λp, the axial stress of steel is lower than yield strength fy, and the axial stress of core concrete is lower than axial compressive strength fc. Increasing the thickness of steel has a more obvious effect on increasing the axial compressive bearing capacity of specimen. The theoretical calculating formula can effectively predict the axial compressive bearing capacity, and the theoretical calculation is partial to safety. The average ratio of axial compressive bearing capacity of the theoretical calculation to the experimental is 0.909, and the standard deviation is 0.075. The average ratio of axial compressive bearing capacity of the finite element calculation to the experimental is 0.957, and the standard deviation is 0.045. The average ratio of axial compressive bearing capacity of the theoretical calculation to the finite element calculation is 0.951, and the standard deviation is 0.039.

Axial compression performance analysis and bearing capacity calculation on square concrete-filled double-tube short columns

The concrete-filled double-tube (CFDT) columns have been proposed in recent years. The existence of inner steel tube can not only increase the confinement on core concrete, but also increase its fire resistance and anticorrosion performance. This makes it have a great application prospect in the field of ocean structure engineering. In this paper, the axial compression performance of square CFDT short columns is comprehensively analyzed. The specimens studied consist of an external steel tube (square hollow section) and an inner steel tube (circular hollow section), in which concrete is completely filled. The fine finite element (FE) method is used to simulate the performance of this column. Two constitutive models of confined concrete for square CFDT core concrete are proposed. In order to ensure the correctness of the model, the verification analysis of the model is carried out based on the previous experimental results, and the whole process of axial compression performance of CFDT columns is analyzed in detail. The concrete strength (fc'), width-thickness ratio (B/to), diameter-thickness ratio (d/ti), diameter-width ratio (d/B) and yield strength (fy) of square CFDT columns are compared and analyzed. The performance of CFDT columns with the same steel content is also analyzed, it is of great significance to improve the application of CFDT columns in marine environment or high temperature environment. Finally, new formulas for calculating the ultimate bearing capacity of CFDT short columns under axial compression are proposed. The results show that the new formulas can predict the strength of CFDT short columns well.

Axial behaviour of concrete-filled corrugated steel tubular column embedded with structural steel

Concrete-filled galvanized corrugated steel tubular (CFCST) columns have been proposed as new composite members to improve the corrosion resistances and reduce the anticorrosion maintenance costs of concrete-filled steel tubular (CFST) structures. In this study, the axial behaviour of CFCST columns embedded with structural steel (CFCST-S) was investigated using comparative experiments and non-linear finite element analysis accompanied by multiple monitoring and in-depth discussions. The study revealed that, even when they are not configured with transverse reinforcements, the local stability and post-peak behaviour of the CFCST-S are competitive owing to the effectiveness of the confinements provided by the thin-walled corrugated steel tube (CSP). The unique local bending effect in the CSP was verified and discussed to reveal the mechanical nature of CSP-concrete columns. Next, a theoretical model of the non-uniform stress distribution, after fully considering the bidirectional curvature of the CSP, was developed. It is found that the CSP mainly provides hoop confinements for the infilled components instead of bearing the axial load owing to its “circumferential tight effect” and “vertical offset effect”. Based on equivalent simplifications and parametric studies, the current formula to calculate the nominal hoop stress in the CSP was modified. Finally, a design method was proposed for the prediction of the axial bearing capacity of the CFCST-S.

Setup of axial bearing capacity of open ended tubular steel piles driven in sand

Abstract This paper focuses on the setup of axial bearing capacity of open ended tubular steel piles that are used for offshore foundation systems such as those of wind turbines. A comparative evaluation of the most commonly used models for setup prediction shows an upper estimate bound and a lower estimate bound, which correspond approximately to a setup rate of 60% increase per log cycle of time and 20% increase per log cycle of time, respectively. This finding is validated with the results of case histories reported in literature, which show that the setup values of most case histories considered lie in the best estimate zone between the upper estimate zone and the lower estimate zone. The analysis results show a minimum setup factor of approximately 1.5 for 100 days following end of driving of open-ended tubular steel pile driven in sand.

Axial mechanical properties of concrete-filled GFRP tubular hollow composite columns

In this paper, a new type of concrete-filled Glass Fiber Reinforced Polymer (GFRP) tubular hollow composite column is tested and analyzed by finite element analysis. The axial pressure test of 27 concrete-filled GFRP tubular hollow composite columns is made to investigate the compressive properties of the specimens, including the failure mode, ultimate bearing capacity under axial compression, load-strain relationship and load-displacement relationship. The effects of the three parameters of hollow ratio, diameter-to-thickness ratio of GFRP tube and concrete strength grade on the axial compressive properties of concrete-filled GFRP tubular hollow composite columns are studied, and some key principles of designing concrete-filled GFRP tubular hollow composite columns are presented. The parameters of hollow ratio, diameter-to-thickness ratio of GFRP tube, and concrete strength grade are analyzed by using the verified finite element model. An ultimate bearing capacity adjustment coefficient is proposed, which takes into consideration the influence of hollow sections. A recommended formula is given for the axial bearing capacity of concrete-filled GFRP tubular hollow composite columns.

Prediction of Pile Axial Bearing Capacity Using Artificial Neural Network and Random Forest

Axial bearing capacity of piles is the most important parameter in pile foundation design. In this paper, artificial neural network (ANN) and random forest (RF) algorithms were utilized to predict the ultimate axial bearing capacity of driven piles. An unprecedented database containing 2314 driven pile static load test reports were gathered, including the pile diameter, length of pile segments, natural ground elevation, pile top elevation, guide pile segment stop driving elevation, pile tip elevation, average standard penetration test (SPT) value along the embedded length of pile, and average SPT blow counts at the tip of pile as input variables, whereas the ultimate load on pile top was considered as output variable. The dataset was divided into the training (70%) and testing (30%) parts for the construction and validation phases, respectively. Various error criteria, namely mean absolute error (MAE), root mean squared error (RMSE), and the coefficient of determination (R2) were used to evaluate the performance of RF and ANN algorithms. In addition, the predicted results of pile load tests were compared with five empirical equations derived from the literature and with classical multi-variable regression. The results showed that RF outperformed ANN and other methods. Sensitivity analysis was conducted to reveal that the average SPT value and pile tip elevation were the most important factors in predicting the axial bearing capacity of piles.