Ultimate Bearing Capacity Research Articles

Mechanical behavior of eccentrically loaded UHPC-encased CFST medium-long columns

To study the eccentric compression performance and failure mechanism of ultra-high performance concrete (UHPC) encased concrete-filled steel tubular (CFST) medium-long columns (UC-CFST medium-long columns), a total of 27 UC-CFST column specimens were tested under eccentric compression with eccentricity and slenderness ratio as the main parameters. After verified by experimental results, the finite element (FE) analysis of UC-CFST medium-long columns with actual structural cross-sectional size under eccentric compression was further carried out. It is found that as the slenderness ratio and eccentricity increased, the bending stiffness and the ultimate bearing capacity of the UC-CFST columns decreased gradually, and the failure mode changed from strength failure to instability failure, and the smaller the proportion of encasing UHPC area, the greater the upper-bound slenderness ratio of strength failure. Moreover, the influence of eccentricity was nonlinearly coupled with slenderness ratio on the eccentric compressive bearing capacity of UC-CFST medium-long columns. Finally, a calculation method of ultimate load-bearing capacity of UC-CFST medium-long columns considering the influence of eccentricity and slenderness ratio was proposed, which had good calculation accuracy with experimental and numerical results.

Application of the BP neural network algorithm to the ultimate bearing capacity test of building structures

The ultimate bearing capacity test effect directly influences the safety performance of the design of building structures. To enhance the safety of building structures, applying the BP neural network algorithm to their ultimate bearing capacity test is studied to improve the test effect. The shear wave velocity of the building structure during stress is collected using the static probing technique. The input samples of the BP neural network are the building structure’s shear wave velocity and construction parameters. They are processed by dimensionality reduction through principal component analysis. The firework algorithm is used to optimize the weight of the BP neural network. An early termination training method is designed, and the optimal weight is combined to train the BP neural network. After training, the samples are input after dimensionality reduction, and the building structure’s ultimate bearing capacity test results are output. Experimental results show that this method can effectively collect the shear wave velocity of building structures and complete the dimensionality reduction of samples. Under different coaxial stresses, this method can effectively measure the ultimate bearing capacity, about 3800 kN. After parameter optimization, the test value of this method is very close to the target value; that is, the ultimate bearing capacity test precision is high.

Influence of local scour on the evolution of the failure envelope for suction caisson foundation

Local scouring significantly undermines the load-bearing capacity of suction caisson foundations and poses a daunting challenge to the integrity of offshore structures. This study numerically addresses the impact that the size and shape of the local scour hole have on both the monotonic bearing capacities and failure envelopes of suction caisson embedded in sandy soil. Different loading conditions - individually and combined - by integrating local scour parameters such as scour depth (Sd), scour width (Sw) and scour angle (φ) while maintaining realistic scour proportions are carefully evaluated. The obtained results show that (1) scour depth has a stronger influence on the ultimate bearing capacity than the influences of scour width and angle; (2) the horizontal bearing capacity shows increased sensitivity to variations in scour depth; and (3) both the horizontal bearing capacity and the moment bearing capacity reach a plateau and a steady state manifest itself when the relative scour depth exceeds a threshold value of 0.9. An empirical formulation to characterize the failure envelope within the horizontal force-moment (H-M) plane is finally proposed, which properly considers the effect of scour depth. These findings provide a valuable reference for ensuring structural resilience to local scour phenomena.

Compressive axial load performance of GFRP–confined recycled aggregate concrete–filled steel tube stub columns

This study examined the axial compressive properties of glass–fiber reinforced plastic (GFRP)–confined recycled aggregate concrete–filled steel tube (RACFST) stub columns. The differences in the failure modes, load–displacement curves, and load–strain curves of the composite columns with different parameters were analyzed, including the number of GFRP layers, steel tube thickness, recycled aggregate substitution rate, and recycled aggregate concrete compressive strength. The results revealed a bulging failure mode in the middle of the GFRP–confined RACFST stub columns. With the increasing substitution rate of recycled aggregate, the bulging deformation of the specimen increased. This eventually resulted in a reduction in the stiffness and bearing capacity but an improvement in the ductility at a later stage. The early stiffness and ultimate bearing capacity of the specimen can be increased by thickening the steel tube or strengthening the recycled aggregate concrete. However, the ductility is greatly reduced in the later stage. Based on the axial compression test of GFRP–confined RACFST stub columns, the axial compression bearing capacity formula was derived. Compared with the existing formula, the formula presented in this paper has greater accuracy. In addition, a finite element (FE) model of the composite column was established to analyze the stress development during the compression process.

Axial compressive performance of thin-walled square steel tube concrete short column with built-in steel slag block

In the process of iron and steel production, steel slag is produced as waste. The steel slag processing method generally produces steel slag cement as a substitute for gravel and fine aggregates. Steel slag aggregates replace natural aggregate concrete used in concrete components. In addition, steel slag expansion can compensate for the shrinkage characteristics of concrete and steel pipes inside closed wet environments, and the outer steel tube hoop constraint can avoid late hydration expansion structure cracking. Through orthogonal testing, the wall thickness of the steel pipe (3 mm, 3.75 mm, 4.5 mm), content of the steel slag blocks (10 %, 15 %, 20 %) and particle size of the steel slag blocks (40–60 mm, 60–80 mm) were used as experimental variables to conduct axial compression tests on 9 groups of short columns made of slag aggregate concrete-filled thin-walled square steel tubes. Based on the analysis of the test process and displacement, strain, ductility and ultimate bearing capacity results, the failure pattern and mechanism of the short column specimens under axial compression were obtained, and a bearing capacity calculation formula was obtained according to the existing theoretical methods. The results indicate three failure patterns: local convexity, shearing and circumferential bulging. The factors influencing the bearing capacity, from most influential to least influential, are the particle size of the steel slag, the wall thickness of the steel pipe and the amount of steel slag. The Poisson's ratio of core concrete has an important effect on its passive binding force, which affects the longitudinal displacement and load-bearing capacity of the component. The deduced formula can be used to accurately calculate the ultimate bearing capacity of the square steel tube and steel slag concrete. This article transforms the drawbacks of steel slag concrete into advantages and, by combining the characteristics of steel tube concrete, proposes a new type of composite component that has a certain degree of innovation and application value.

Derivation of the Ultimate Bearing Capacity Formula for Layered Foundations Based on Meyerhof’s Theory

Derivation of the Ultimate Bearing Capacity Formula for Layered Foundations Based on Meyerhof’s Theory

Axial compressive performance and finite element analysis on spirally reinforced seawater sea-sand concrete-filled aluminum alloy tube columns

Axial compression experiment and finite element analysis were used in this research to explain the mechanical properties of spirally reinforced seawater sea-sand concrete-filled aluminum alloy tube (SR-CFAT) columns. The diameter and spacing of the spiral stirrup, the quantity and diameter of the longitudinal reinforcement, and the ratio of the spiral stirrup to longitudinal reinforcement (rhv) were used as the variation parameters in the design of 16 SR-CFAT columns and 1 seawater sea-sand concrete-filled aluminum alloy tube (CFAT) column. The results demonstrated that both the SR-CFAT columns and the CFAT column experience shear failure, while the former exhibited greater axial compression bearing capacity and deformation capacity. The ultimate bearing capacity, ductility, and energy absorption value of this composite column increase with an increase in rhv, then decrease under the same reinforcement content. The specimens perform best under axial compression when rhv is 2.20. Among the others, specimens with "fine and dense" spiral stirrups and "less and coarse" longitudinal reinforcement have higher ultimate bearing capacities, ductility, and energy absorption values. An FE model is created for the SR-CFAT columns, followed by a parameter extension analysis. Based on test and finite element results, a high-accuracy axial compression bearing capacity calculation algorithm is provided using cylinder theory.

Numerical analysis of soil–steel composite structure performance at ultimate load: impact of stiffening ribs and geotextile reinforcement

This study investigates soil–steel composite structures, emphasizing the role of stiffening ribs and geotextile reinforcement through comprehensive numerical modeling. This study presents a two-dimensional finite element analysis (FEA) and compares the influence of stiffening rib and geotextile on the ultimate bearing capacity of the soil–steel composite structures. The results of this study demonstrate a significant enhancement in load capacity. Specifically, a notable 47% improvement was observed with a stiffening rib, and a 26% increase was noted with the use of a single layer of geotextile. Under peak load, the vertical displacement at the crown exceeds the permissible standard for all models except for one model, while bending moments reach their limits, marking a failure mode of composite system considered. Structures with stiffened ribs reach their load capacity due to the creation of a plastic hinge around the shoulder and haunch of the shell. On the other hand, in structures without stiffening ribs, the crown and haunch section of the shell becomes fully plastic under peak load. The maximum axial thrust is shown in geotextile-reinforced structure, reaching 78% of the shell maximum capacity due to compression. Eventually, stiffening rib substantially improves overall load-bearing capacity of the soil–steel composite structures, and geotextile placement in the upper part of the backfill reduces shell deflection due to bending.

Shear behavior of thin-walled concrete-filled steel tubular columns

Shear failure is a brittle type of failures, which should be avoided in any structure as it could cause property loss and human casualties. The shear behavior of thin-walled concrete-filled steel tubular (CFST) columns was hence investigated in this study, involving the tests of 24 thin-walled CFST columns and considering the following parameters: shear span-to-depth ratios = 0.15, 0.3, 0.5, 1, 1.5, and 2; confinement factor = 0.63, 1.27, 1.44, and 1.70; and axial load ratios = 0, 0.2, 0.4, and 0.6. The test results revealed the insights of the initial shear stiffness, failure modes, ultimate bearing capacity, load-deflection curves, load-strain curves, and ductility of the specimens. Based on the failure modes, a method is proposed to evaluate the load resistance, and explain the relationship between the shear span-to-depth ratio and the peak bearing capacity. A compression strut mechanism considering the confinement provided by the steel tube flange is also proposed. The effect of axial load on the shear strength of the concrete core is negligible when the axial load ratio doesn’t exceed 0.4. The predicted results from using the proposed simple model agree generally well with the experimental results.

A novel crimped composite spline joint for pultruded FRP tubes: Conceptual design and tensile properties

Creating an effective composite joint between fiber-reinforced polymers (FRPs) and metallic profiles poses a significant challenge for heavy-loaded and lightweight emergency truss bridges. A novel crimped composite spline joint (CCSJ) was developed to achieve satisfactory engineering performance. Comparative tensile tests were conducted to evaluate the tensile properties and load-carrying mechanism of the CCSJ in comparison to those of joints without splines. Finite element (FE) analysis considering the crimping process and tensile loading was simultaneously executed and calibrated by experiments. Parametric simulation was supplemented to explore the key factors influencing the ultimate bearing capacity. The results indicated that the novel CCSJ features a simple preparation process, high connection efficiency, and large bearing capacity. A 60×6 mm hybrid FRP tube can withstand a maximum tensile load of 804 kN, achieving a connection efficiency of 61.3 % without the need for any secondary processing of the FRP tube. The CCSJ demonstrates a significantly higher connection efficiency of approximately 20 % compared to joints without splines. The ability of the CCSJ to effectively transfer significant axial loads through the interfacial friction effect is attributed to the increase in the interfacial contact area and preloading radial pressure resulting from the incorporation of pre-crimping splines. A typical failure mode involves interfacial slippage, resulting in satisfactory ductile behavior. The ultimate bearing capacity of the CCSJ is positively correlated with the crimping variables, friction coefficient, spline length, and number of splines. The FE model demonstrates sufficient accuracy in predicting the key behavioral indicators of the composite joint.

Mechanical properties of prestressed tendon-planted glulam beam-column connections under cyclic loading

Traditional glulam beam-column connections have the disadvantages of low bearing capacity, low stiffness, low ductility and poor energy dissipation ability. This paper proposed a new prestressed tendon-planted connection for glulam beam-column joints. Six groups of the connections were tested under reversed cyclic loading. The effects of the number and prestressed value of steel bars, tendon reinforcement ratio and tendon anchorage length on the performance of the connection were analyzed. The results indicated that the proposed connection showed ductile failure, involving the splitting failure of the beam and the bearing failure around the planting holes. The proposed configuration improves the ultimate bearing capacity, initial stiffness and energy dissipation performance, and slows down the stiffness degradation of the glulam beam-column connections. The number of steel bars and prestressed value have a positive effect on the initial stiffness of the joint, whilst the tendon reinforcement ratio has a significant positive influence on the bearing capacity of the joint. The bearing capacity of the joint no longer increases with the increase of the tendon anchorage length, when the anchorage length is 12.5 times greater than the tendon diameter. The prediction formula for the flexural capacity of the new joint is proposed, whilst the moment-rotation characteristics of the connection are also assessed.

Experimental study on the flexural performance of FRP grid-reinforced ultra-high-performance concrete I-beams with different steel fiber contents

To adapt to harsh engineering environments, the use of structural components with fiber-reinforced polymer (FRP) grid-reinforced ultra-high-performance concrete (UHPC) is considered a new development trend. Twelve FRP grid-reinforced UHPC I-beams are fabricated to investigate the effects of the thicknesses of FRP grids (0 mm, 1 mm, 3 mm, and 5 mm) and the steel fiber contents of UHPC (0%, 1%, and 2%) on their flexural performance. Four-point bending tests are conducted to obtain the failure modes, load-deflection characteristics, and strain responses of each testing beam, and a simplified calculation method for cracking loading and flexural bearing capacity is proposed. The results reveal that the increase in FRP grid thickness, the ultimate load bearing capacity of FRP grid-reinforced UHPC structural beams increases and the ductility also can be enhanced. The presence of steel fiber effectively inhibits the cracking and increases the first cracking load of the beam during the test process, although its influence on the ultimate bearing capacity is limited. Besides, until to the cracking stage, there is no noticeable change in the tensile strain of the FRP grids as the applied load increases. It has been used to simplify theoretical calculations, which shows good agreement with the experimental results.

Numerical Study of the Ultimate Bearing Capacity of Two Adjacent Rough Strip Footings on Granular Soil: Effects of Rotational and Horizontal Constraints of Footings

In this paper, the numerical study of the ultimate bearing capacity (UBC) of two closely spaced strip footings on granular soil is investigated using the finite element method (FEM) and upper bound limit analysis (UBLA). Although the UBC of two adjacent footings has previously been studied in other experimental and numerical research, in all the previously reported studies, the footings were not allowed to rotate and move horizontally freely. Due to the deformation of the soil medium, two closely spaced footings are subjected to horizontal movements and tilting, even under central vertical loads. When the two adjacent footings are not permitted to rotate and move in the horizontal directions, the unwanted bending moment and horizontal force act on the footings. Indeed, the UBC of two closely spaced rough footings is evaluated under incorrect constraints in earlier research. In the present research, the UBC of two adjacent rough footings is evaluated with and without these incorrect constraints. The key finding of this study is that constraining the horizontal and rotational movement of the foundation artificially increases the UBC, which does not reflect field conditions. When foundations are permitted to rotate and move horizontally, there is no increase in UBC; however, there is an increased risk of differential settlement and structural instability.

Bearing Capacity Equations for Intact Argillaceous and Arenaceous Rocks in Malaysia Derived from P-Wave Velocity

This paper presents the derivation of the bearing capacity equation of shallow foundations using P-wave velocity based on the seismic refraction method on argillaceous rocks (shale) and arenaceous rocks (sandstone). Various theories of bearing capacity equations were developed over the years for the calculation of bearing capacity under vertical central loading. But, the most widely used on rock is the Mohr-Coulomb failure criterion given by Meyerhof (1963). Based on this theoretical development, the empirical equation of ultimate bearing capacity was obtained. The detailed derivation of these parameters is comprised of the results from Uniaxial Compressive Strength (UCS) and P-wave velocity values. The proposed empirical equation of bearing capacity derived from P-wave velocity herewith can be used as an alternative method in designing shallow foundations. There is a good agreement on the bearing capacity determination from P-wave velocities.

Study on flexural property of glass fiber-reinforced polymer reinforced wood–plastic composite panels

ABSTRACT Fiber-reinforced polymers (FRPs) and wood–plastic composites (WPCs) have broad application prospects with the advantages of recyclability, lightweight, and corrosion resistance. However, WPCs cannot be used for bearing structures because of their poor mechanical properties. In order to improve the mechanical properties of WPCs, this study proposed a glass fiber-reinforced polymer (GFRP) to reinforce the tensile zone of WPCs. The failure mode, ultimate bearing capacity, and deformation of the panels were studied by four-point bending tests and finite-element simulations. The results showed that the failure modes of the panels were a mainly flexural failure, flexural shear failure, and interface debonding, and the optimal thickness of GFRP improved the ultimate bearing capacity of the WPC panel by 205% and the deflection by 55%. Finite-element simulations of WPC reinforced with GFRP were carried out, and the densities of WPC and the angles of glass fiber layup were considered. The results showed that the higher the density of WPC, the better the strengthening effect of the structure, and the fiber layup angles had less effect.

Flexural behavior of ECC reinforced RC beams under secondary load: Experimental, numerical simulation and theoretical analysis

The aim of this paper is to study the flexural behavior of reinforced concrete (RC) beams reinforced by engineered cementitious composite (ECC). The reinforcement effect of ECC on RC beam is studied by experiments, numerical simulation and theoretical analysis, considering the secondary load. Five beams were tested under static load, including two beams with ECC layers at the top and bottom (TBEB), two beams with ECC layers at the bottom (BEB) and one unreinforced beam. Different parameters in the test include reinforcement ratio, whether the top is equipped with ECC layer, and the thickness of the top ECC layer. The test data were used to validate the finite element model developed to simulate the bending response of the ECC layer reinforced beam. Then, a series of parameter studies were carried out to evaluate the effects of ECC layer thickness, reinforcement ratio and ECC elastic modulus on the reinforced beam. The experimental and numerical simulation results show that compared with other reinforced beams, TBEB equipped with 50 mm ECC layer at the top and bottom has better performance. Compared with the control beams, the ultimate bearing capacity is increased by 82.6 %, ductility and deformation capacity are increased by 2.38 times and 2.11 times, respectively. Finally, a calculation model for predicting the flexural capacity of TBEB is presented. The predicted flexural capacity is in good agreement with the experimental results.

The Seismic Performance of Self-Centering Ribbed Floor Flat-Beam Frame Joints

To achieve rapid post-earthquake repair of self-centering ribbed floor flat-beam frame structures, a ductile hybrid joint consisting of dog-bone-shaped, weakened, energy-dissipating steel bars connected to the upper and lower column sections through high-strength threads is proposed based on the damage control design concept. By moving the ductile energy-dissipating zone out to the locally weakened section of the energy-dissipating steel bars and the locally unbonded prestressed steel bars in the core area, the residual deformation was limited and the seismic performance improved. Based on the working principle of hybrid joints, low cycle loading tests were conducted on two joint specimens to analyze the influence of lateral prestress on the seismic performance of the hybrid joints. Numerical modeling methods were used to compare the position of the energy-dissipating steel bars in the composite layer and the friction performance of the joints. The research results indicated that the hybrid joint had stable load bearing, deformation, and energy dissipation capabilities, with damage being primarily concentrated in the energy-dissipating steel bars. Even at an inter-story displacement angle of 5.5%, the upper and lower column segments remained elastic. After unloading, the connection seam at the joint was closed, and the self-centering performance was good. When the inter-story displacement angle reached 5.5%, the lateral prestress increased from 150 kN to 250 kN, the ultimate bearing capacity of the joint increased by 16.3%, and the cumulative energy consumption increased by 30.0%. The influence of the friction coefficient of the joint surface on the structural performance was set at a threshold of 0.7. When it was less than the threshold, the ultimate bearing capacity and initial stiffness of the joint increased with the increase in the friction coefficient. After reaching the threshold, the increase in the ultimate bearing capacity of the joint slowed down, and the rate of stiffness degradation gradually accelerated. This joint showed excellent seismic performance and can thus achieve post-earthquake repair of structures.

Prediction of Ultimate Bearing Capacity of Soil–Cement Mixed Pile Composite Foundation Using SA-IRMO-BPNN Model

The prediction of the ultimate bearing capacity (UBC) of composite foundations represents a critical application of test monitoring data within the field of intelligent geotechnical engineering. This paper introduces an effective combinational prediction algorithm, namely SA-IRMO-BP. By integrating the Improved Radial Movement Optimization (IRMO) algorithm with the simulated annealing (SA) algorithm, we develop a meta-heuristic optimization algorithm (SA-IRMO) to optimize the built-in weights and thresholds of backpropagation neural networks (BPNN). Leveraging this integrated prediction algorithm, we forecast the UBC of soil–cement mixed (SCM) pile composite foundations, yielding the following performance metrics: RMSE = 3.4626, MAE = 2.2712, R = 0.9978, VAF = 99.4339. These metrics substantiate the superior predictive performance of the proposed model. Furthermore, we utilize two distinct datasets to validate the generalizability of the prediction model presented herein, which carries significant implications for the safety and stability of civil engineering projects.

Experimental study and theoretical prediction of axial compression behavior in PMC-reinforced CFST columns with void defects

Polymer-modified concrete (PMC) is a promising seismic reinforcement material to improve the ultimate load carrying capacity and ductility of structures. This study investigates the reinforcing effects of PMC on voided concrete-filled steel tube (CFST) columns through axial compression tests on 21 specimens. A meticulous analysis, incorporating void arch height, steel tube thickness, and PMC reinforcement, elucidates failure modes, load-deformation behavior, and strain characteristics. The experimental results demonstrate that PMC reinforcements significantly enhance the structural behavior and load-bearing capacity, improve ductility, and prevent material detachment from excellent bonding and collaborative working properties. A novel calculation model for ultimate load capacity and lateral pressure coefficient of voided CFST columns is developed and validated. Results reveal a distinct improvement in specimen performance post PMC reinforcement, with load-displacement curves resembling intact specimens, mitigating the impact of void defects. Furthermore, PMC-reinforced specimens exhibit effective recovery of load-bearing capacity and ductility, offering a cost-effective alternative to steel tube thickening. Changes in strain and Poisson's ratio curves underscore PMC's ability to restore biaxial compression stress, enhancing stability. Prediction models, rooted in the Double Shear Unified Strength Theory, accurately anticipate ultimate bearing capacity and lateral pressure coefficient, bolstering practical engineering design and repair endeavors. In summation, this study provides comprehensive insights into PMC-reinforced voided CFST columns, facilitating informed structural enhancements and repairs.

Eccentrically compressed behavior of UHPC columns considering the P-delta effect

Eccentric compression is a critical behavior observed in arches and columns, particularly in structures constructed with ultra-high performance concrete (UHPC). Compared to normal concrete structures, those made with UHPC exhibit distinct behaviors that need to be clearly investigated. This study comprehensively investigates UHPC columns under eccentric compression load through experimental study and theoretical analysis. Various experimental parameters, including slenderness ratio, eccentricity distance, fiber content, and stirrup ratio, were examined across 26 UHPC columns. Failure modes were evaluated using digital image correlation (DIC) methods. The load-displacement responses indicated that slender columns subjected to significant eccentricity exhibited load decreases during yielding stages, whereas short columns experienced load increases. This discrepancy in yielding stages was attributed to P-delta effects. In addition, theoretical models were developed to determine the ultimate bearing capacity of columns experiencing compression-controlled and tension-controlled failures, considering the P-delta effect caused by the different slenderness ratios. The moment magnifying coefficients for UHPC were calibrated based on theoretical analyses of the limit curvature of eccentric compression members. The proposed theoretical models agreed well with the experimental results, with an average ratio of 1.02. The second-order effect for the case of UHPC short column with a slenderness ratio of 5 can be ignored as per Eurocode 2, which is less than 10 % of the corresponding first-order effect.