Bearing Capacity Coefficient Research Articles

Research on seismic behaviour of square steel tubular columns with deconstructable splice joints

In order to study the seismic performance of the square steel tubular column-to-column joints with a novel blind bolted connection, five specimens were designed. One specimen was tested under horizontal monotonic loading, and its failure mode was obtained. The mechanical performance including joint bearing capacity and displacement ductility coefficient were clarified through load versus displacement responses. The other four specimens with different design parameters were tested under cyclic loadings. Their bending moment-rotation curves, envelop curves and energy dissipation capacities were obtained. In addition, the deconstruction of the joints after their ultimate limit states being reached was validated. The finite element software ABAQUS was used to simulate the mechanical behaviour of the specimens, and the variation of the pretension within the high-strength bolts and of the friction force at the plate contact surfaces during the entire loading process were clarified. The results show that the square steel column-to-column splicing joint introduced herein is beneficial to simple configuration, convenience in installation as well as for deconstruction, and it possesses good slip-critical bearing capacity as well as ultimate bearing capacity. Good cyclic behaviour and energy dissipation capacity are also indicated. The research outcomes can provide an important basis for the subsequent research and application of deconstructable steel structures, and for further development of building industrialisation.

Structural Design and Optimization of Herringbone Grooved Journal Bearings Considering Turbulent

In order to improve the performance of the traditional constant-width herringbone grooved journal bearing in a computed tomography tube under a high-temperature environment, the present study designed a convergent herringbone grooved journal bearing (HGJB) structure lubricated by liquid metal. The bearing oil film thickness and the Reynolds equation considering the influence of turbulence are established and solved by using the finite difference method in the oblique coordinate system. The performance of the two bearings was compared, and the static and dynamic performance change trends of the two bearing structures under different eccentricities were systematically studied. The results show that the convergent herringbone grooved journal bearings are superior to the constant-width herringbone grooved journal bearings in terms of bearing capacity and stiffness coefficient. At the same time, the influence of structural parameters, such as the number of grooves, helix angle, groove to ridge ratio, groove depth on the performance of the constant-width herringbone grooved journal bearings, and the convergent herringbone grooved journal bearings was studied. Finally, we conclude that the performance of the convergent herringbone grooved journal bearings is optimal when the number of grooves is 15–20, the helix angle is 30°–45°, the ratio of the groove to ridge is 1, and the groove depth is 0.02 mm –0.024 mm. This research has provided the thinking and reference basis for the design of liquid metal bearings for high-performance CT equipment.

An attempt to apply the kinematic method of rigid solids in the study of bearing capacity of shallow foundations

Abstract In the geotechnical engineering field, shallow foundations are frequently needed to ensure good fieldwork stability. They are also intended to permanently and uniformly transmit all load pressure on the seating floor. However, numerous mechanical constraints, such as bearing capacity of foundations, durability, stability, design of shallow foundations, lead, unfortunately, to a serious realization challenge. Finding an adequate solution presents the main goal and effort of both scholars and professionals. Indeed, the corresponding drawback is observed through the high number of reported damages that occurred in the structure of foundations and the punching failure. The failure mechanisms of shallow foundations, verified in full size or on scale models, show “sliding surfaces” and rigid (solid) blocks, which can be described with the kinematic method of rigid solids. The main objective of this study is the application of the kinematic method of rigid solids in the study of the stability of shallow foundations with respect to punching, the purpose of which is to determine the bearing capacity factors Nc, N γ, and the passive earth pressure coefficient Kp of foundations. In this context, two mechanical models have been proposed with 5 and 7 rigid solids, and a program developed via the MathCAD environment is applied to check the validity of the two previous models. The kinematic method of rigid solids gives results very close and comparable with that of Caquot/Kerisel for the factors of the bearing capacity and passive earth pressure coefficient - the ratio Kp - according to the five- and seven-solid model.

Research on boundary slip of hydrostatic lead screw under different driving modes

The flow state of oil film in the hydrostatic lead screw directly affects the transmission performance of the screw pair. The static and dynamic characteristics of a new type of double driven hydrostatic screw-nut pair (DDHSNP) are studied under different motion modes. The boundary condition of navier slip model is introduced into the lubricating mathematical model of DDHSNP, and the influences of boundary slip on the axial bearing capacity, axial stiffness and damping coefficient in micro scale are researched by finite difference method. The results show that when the motor runs at high speed (the rotating speed range of the screw and nut driven motor is 1000–9000 rpm), the existence of boundary slip leads to a improvement of the axial bearing capacity and stiffness coefficient of DDHSNP in the case of single-drive operation and dual-drive differential feed (the range of rotation difference is 10–100 rpm), which is more obvious under the single-drive mode. The increase rate of stiffness coefficient induced by boundary slip is much larger than that of bearing capacity. In addition, the boundary slip has little effect on the damping coefficient of DDHSNP in either single drive operation or dual drive differential operation.

Progressive Collapse Safety Evaluation of Truss Structures Considering Material Plasticity.

Theoretical or numerical progressive collapse analysis is necessary for important civil structures in case of unforeseen accidents. However, currently, most analytical research is carried out under the assumption of material elasticity for problem simplification, leading to the deviation of analysis results from actual situations. On this account, a progressive collapse analysis procedure for truss structures is proposed, based on the assumption of elastoplastic materials. A plastic importance coefficient was defined to express the importance of truss members in the entire system. The plastic deformations of members were involved in the construction of local and global stiffness matrices. The conceptual removal of a member was adopted, and the impact of the member loss on the truss system was quantified by bearing capacity coefficients, which were subsequently used to calculate the plastic importance coefficients. The member failure occurred when its bearing capacity arrived at the ultimate value, instead of the elastic limit. The extra bearing capacity was embodied by additional virtual loads. The progressive collapse analysis was performed by iterations until the truss became a geometrically unstable system. After that, the critical progressive collapse path inside the truss system was found according to the failure sequence of the members. Lastly, the proposed method was verified against both analytical and experimental truss structures. The critical progressive collapse path of the experimental truss was found by the failure sequence of damaged members. The experimental observation agreed well with the corresponding analytical scenario, proving the method feasibility.

Seismic bearing capacity of shallow strip footing embedded in slope resting on two-layered soil

Abstract In this paper, the limit equilibrium method with the pseudo-static approach is developed in the evaluation of the influence of slope on the bearing capacity of a shallow foundation. Particle swarm optimisation (PSO) technique is applied to optimise the solution. Minimum bearing capacity coefficients of shallow foundation near slopes are presented in the form of a design table for practical use in geotechnical engineering. It has been shown that the seismic bearing capacity coefficients reduce considerably with an increase in seismic coefficient. Be sides, the magnitude of bearing capacity coefficients decreases further with an increase in slope inclination.

A New Method for Evaluating the Bearing Capacity of the Bridge Pile Socketed in the Soft Rock

Aiming at the rock-socketed pile in the soft rock area, this paper studies the inherent constitutive relationship between the vertical restraint stiffness at the pier bottom and the bearing capacity of the pile foundation. A new method to evaluate the bearing capacity of the pile foundation is proposed. Based on the Rayleigh energy method and the Southwell frequency synthesis method, the analytical expression of the vertical vibration fundamental frequency of the pier was calculated, and the constraint stiffness expression of the pier bottom was derived. By investigating the impact of parameters on the bearing capacity coefficient of the pile foundation, the fitting formula of the bearing capacity coefficient was obtained by multiple linear regression. Then, with this method, the vertical fundamental frequency of the pier was obtained through a field dynamic test to calculate the vertical constraint stiffness and evaluate the bearing capacity of the rock-socketed pile in the soft rock area. This method can overcome the shortcomings of the traditional static load test method, such as the high cost, long cycle, and poor representativeness. Finally, this method’s accuracy was verified by comparing field measurements and finite element simulation results. The results show that the difference between the code design constraint stiffness and the constraint stiffness by the frequency synthesis method was about 0.7%, and the bearing capacity difference between the analytical solution and the numerical simulation was small. The new method is accurate and effective.

QUASI-STATIC TEST STUDY ON PRECAST ECC CONCRETE-FILLED TUBULAR BRIDGE PIERS

A precast ECC concrete filled tubular pier is proposed. To investigate the seismic performance of the novel pier, 1 normal reinforced concrete pier specimen (RC) and 3 precast ECC concrete-filled tubular pier specimens (ECC1~ECC3) are designed and fabricated, among which specimen ECC1 is a reference, specimens ECC2 and ECC3 are employed to study the influence of the axial compression ratio and of the section in plastic hinge region, respectively. The specimens are tested under the action of a pseudo-static load to obtain crack propagations, failure modes and hysteretic curves. The indicators of seismic performance (bearing capacity, energy dissipation, ductility coefficient, stiffness degradation, residual displacement, etc.) are also analyzed. It can be observed that the reinforcement buckling after concrete broken in normal RC piers is prevented by the precast ECC tube, which enables the novel pier with an improved failure mode, enhanced deformation capacity and reduced damage severity. Compared with normal RC piers, the novel piers exhibit better energy dissipation capacity. The bearing capacity and ductility coefficient of specimen ECC1 are 16.66% and 42.15% higher than those of specimen RC, respectively. The novel pier with a lower axial compression ratio fails with less cracks in the ECC tube, and exhibits poorer energy dissipation, lower bearing capacity, better deformability, and slower stiffness degradation. Besides, casting ECC in a precast ECC tube in the plastic hinge region can enhances the energy dissipation, bearing capacity, and deformability, but has little influence on the crack propagation.

Study of the Bearing Capacity at the Variable Cross-Section of A Riser-Surface Casing Composite Pile

Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development. The offshore oil well structure includes a riser and a surface casing. The riser, surface casing and oil well cement can be considered special variable cross-section piles. Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production. In this paper, the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load. The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion, the influencing factors of the bearing capacity coefficient Nc are revealed, and the calculation method of Nc is proposed. By comparing the calculation results with the results of the centrifuge test, the accuracy and applicability of the calculation method are verified. The results show that the riser composite pile has a rigid core in the soil under the variable cross-section, which increases the bearing capacity at the variable cross-section.

How to Improve the Stability and Durability of Sand Castles

On the beach in midsummer, one of the favorite recreational activities for adults and children is to build the castle of the sea sand. However, the castles carefully built by the artists are often ruined by the inflow of waves or rising tides. We built the best 3D model of the sandcastle foundation. Moreover, we found the optimal essential moisture content. Due to the frequent precipitation in summer, our model also provides some reinforcement schemes. we compared the bearing capacity coefficients of several common foundation shapes and obtained the optimal shape on a plane. Then we compared the various indexes of the round table with different stacking angles in the vertical direction. We constructed the evaluation function using hierarchical analysis and then found the optimal stacking angle at the point where the first derivative of the function was zero. When calculating the thickness of the foundation based on a sandcastle with specific gravity, we chose the ordinary column foundation bearing capacity formula as the bearing capacity formula of the circular table foundation. Furthermore, we use this formula to find the corresponding thickness of the foundation in combination with the optimal stacking angle previously obtained.

Finite element analysis on the residual bearing capacity of axially preloaded tubular T-joints subjected to impacts

Understanding the dynamic behavior of tubular members is necessary for ensuring their safety, even when damaged after an impact. A nonlinear finite element analysis (FEA) was performed to evaluate the residual bearing capacity of axially preloaded square hollow section (SHS) T-joints subjected to impact loading. First, the Bao–Wierzbicki fracture criterion was used to simulate the failure modes and behavior of specimens subjected to static axial compression and impacts, and the numerical results were compared with experimental results in the literature. The bearing capacity error between the numerical and experimental results was within 10%, which verified the accuracy of the finite element (FE) model. Then, the local and global displacements of joints were distinguished with the central line displacement method, and 40 FE models were created. The dynamic responses of joints under impact loading were used to study the resistance mechanism. Joint deformation mainly manifested as outward buckling of the chord webs and indentation of the chord upper flange. The in-plane restraint and support by the brace of the chord increased with the brace–chord width ratio. Finally, the ultimate residual bearing capacity coefficient ψ was defined as the ratio of the ultimate bearing capacities of the impacted and reference specimen, and the influence of different parameters, including axial preloading, impact energy, brace–chord width ratio, and chord diameter, was explored. Axial preloading and impact energy showed a negative correlation with ψ, while the brace–chord width ratio and chord diameter showed a significant positive correlation with ψ.

Experimental study on flexural behavior of GFRP reinforced concrete slabs

Remarkable performance of glass fiber-reinforced polymer (FRP) bars make it an ideal candidate for prolonging the life of concrete structure. Although analytical and experimental research of concrete beams strengthened by FRP have flourished in recent decades, it is still in lack of research in comparison with traditional reinforced concrete structures, especially in case of the flexural behavior. In this paper, two groups of GFRP reinforced concrete slabs with different strength grades and reinforcement ratios were experimentally tested, and theoretical calculation method on their bearing capacities was explored. By comparing the deformation and bearing capacity characteristics, the test results were discussed in detail. The calculation formula of flexural capacity of GFRP reinforced concrete slab was derived and then verified against the experimental data. The test results show that the load deflection curve presents obvious double straight lines, and the reinforcement ratio is not closely related to the initial crack load. The cross section still obeys the plane section assumption and the crack distribution is sparse with large width. The flexural bearing capacity coefficient changes from 1.02 to 1.36. Therefore, the limitation of 1.4 times balanced reinforcement ratio in ACI is verified, which could apply a valuable reference for durability design of GFRP reinforced concrete slabs.

Effect of micro grooves on lubrication performance of friction pairs

The influence of micro-groove parameters on the lubrication performance of plane friction pair is studied, by combining theoretical analysis with experiment. The theoretical model of single-groove is established, the variation rules of bearing capacity, maximum pressure and friction coefficient are obtained by changing the number, width and depth of groove. At the same time, micro-grooves with different parameters are processed on the surface of friction pair, the variation rules of the average friction coefficient, friction coefficient under different lubrication conditions are obtained in experiment, and the wear condition of friction pair surface is observed. The results show that the lubrication performance of friction pair increases, with the increase of the micro-groove width. The numerical value of the groove width–depth ratio will influence the friction pair, when the width–depth ratio is greater than or equal to 2.5, the dynamic pressure effect of micro-groove occupies a dominant position, which can improve effectively the lubrication performance. When the width–depth ratio is less than 2.5, the micro-groove will have a negative impact, resulting in the increase of friction coefficient. The groove density will also influence the lubrication performance of friction pair, when the density is less than 10%, the spacing between the micro grooves is too large to collect wear particles, when the density is greater than 20%, the surface roughness of friction pair will be affected, leading to the increase of friction coefficient. The optimal parameters of the micro-groove obtained are as follows: the optimal density is 10%, the width is 0.1–0.2 mm, and the ratio of width to depth is greater than or equal to 2.5. In addition, by comparing the variation of friction coefficient under different lubrication conditions, it can be concluded that adding solid lubricant in lubricating oil, can not only reduce the friction coefficient value, but also decrease the variation fluctuation of friction coefficient.

Planning Research on Application of Nanomaterial Technology in Disaster Prevention and Reconstruction

An earthquake causes a huge loss of life and property. After an earthquake, many buildings are seriously damaged or collapsed. On the one hand, it is necessary to make full use of nanomaterials technology to improve seismic strength during reconstruction; on the other hand, scientific planning is needed to reduce pollution, carbon emissions, and energy consumption. This paper mainly studies the application of nanomaterial technology in disaster prevention and reconstruction. Through a series of planning safeguard measures, the overall seismic performance of the city is improved in order to provide theoretical guidance and technical support for disaster prevention and reconstruction. This paper mainly introduces the stress analysis of frame joints after earthquake and the planning of urban disaster prevention and reconstruction. In addition to the different types of concrete materials (ordinary concrete, nano silica fiber concrete, PVA fiber concrete), the fixed amount of water, superplasticizer, reinforcement, sand, and gravel, the concrete strength grade is C30. Then, three kinds of concrete frame joints are tested under low cycle cyclic loading to compare the seismic performance of the three kinds of concrete. The experimental results show that the fuzzy evaluation of urban disaster prevention and reconstruction planning has been carried out for 6 communities in this city. Among them, 4 communities are qualified and 2 communities are unqualified. Therefore, it is necessary to focus on seismic reinforcement or carry out urban planning research again. Compared with ordinary concrete, the bearing capacity and ductility coefficient of nano silica fiber concrete and PVA fiber concrete are increased by 37.8% and 15.6%, respectively. It is proved that the seismic performance of nano silica fiber reinforced concrete is far better than that of ordinary concrete.

Study on Bell solution of the ultimate bearing capacity for slope rock foundation and its application

Limited studies focused on the slope rock foundation, and the application results of several methods differ considerably. In this paper, the coefficients of the Bell solution are first reduced by the length ratio of the sliding failure plane and the vertical area ratio of the overloaded soil. Then, the Hoek–Brown criterion for nonlinear failure is introduced, and the tangential line tangent to the Hoek–Brown failure criterion curve is calculated to replace the original M-C failure criterion. A method for determining the instantaneous friction angle and instantaneous cohesion under normal stress with the Bell solution failure mode is established, and the relationship between the instantaneous friction angle, instantaneous cohesion, and normal stress are discussed. The instantaneous friction angle decreases with the increase in normal stress, whereas the instantaneous cohesion increases with normal stress. The influence of geological strength index (GSI) and rock empirical parameter mi on bearing capacity coefficients N σ, N q, and Nγ are also comprehensively analyzed. The coefficients increase with GSI and mi . In addition, the method is used to analyze the bearing capacity of rock foundation of a high and steep slope in an open-pit mine, and the results are compared with the slip-line method, which considers Hoek–Brown failure criterion and finite-element numerical simulation. The comparison demonstrates the acceptability of the proposed method.

Evaluating the efficiency of a composite geosynthetic reinforcement in container yard pavements via laboratory plate load test

ABSTRACT This paper experimentally studies the efficiency of a multi-task geosynthetic comprised of a geogrid and a nonwoven geotextile layer in diminishing the required thickness of base course constructed over different soft subgrades in container yards pavements. In this research, a total number of 24 laboratory static plate load tests (PLT) were conducted in a large-scale steel test box. In all tests, the reinforcement was embedded at the interface of the base course and subgrade to get both reinforcing and separation functions involved simultaneously. The investigated parameter was bearing capacity coefficient K30 obtained directly from the results of laboratory PLTs through a 305 mm-diameter circular steel plate. Results illustrated that in the case of composite-geosynthetic inclusion, the required thickness of the base course could be reduced from 17 to 23 percent depending on the strength of the underlying subgrade layer. This could be both economically and environmentally instrumental in real heavy-duty pavement design. Moreover, considering the geosynthetic end-fixation led to better functionalities of all reinforcements in fixed-end models compared to free-end ones. The results also demonstrated that the efficiency of the geocomposite is contingent on the thickness of the base course. As the thickness increases, the efficiency of the reinforcement reduces.

An analytical model for the loading capacity of splice-retrofitted slender timber columns

Retrofitting timber columns in traditional timber structures with a steel jacketed splice joint has advantages of aesthetic appearance and similar mechanic performance to the intact columns as compared to conventional simple splice columns. The axial compression behavior of such retrofitted splice columns has been studied experimentally in detail. However, there is still a lack of a calculation model for their axial compressive strength and general guideline for their design. The objective of this study is to establish a theoretical calculation model for this type of retrofitted splice columns. Firstly, a theoretical model for the axial compressive strength of splice columns retrofitted with a steel jacket is proposed considering the contact stresses at a splice joint and the relevant stability theory. Secondly, the buckling modes of splice columns and the actual stress distributions at the splice joints (i.e. the compressive stresses at the steel-timber and timber-timber interfaces) are thoroughly investigated. Finally, the theoretical model is validated by the experimental data and finite element analysis results with different splice parameters. Comparisons show that the theoretical calculations in terms of the bearing capacity and stability coefficient agree well with the experimental results. The proposed theoretical model is also shown to be suitable for predicting the axial compressive strength of a retrofitted splice column with the location of the splice from the column end ranging from 1/5 to 1/2 of the column length. The relative errors in the theoretical bearing capacities with respect to the finite element results are found to be less than that using the stability coefficient. From the analysis results, the length of the splice and the total length of the steel jacket are recommended to be in the range of 0.5~1.5 and 2~4.5 times of the column diameter, respectively. This proposed theoretical model can be applied in the retrofitting design of timber columns in historical timber structures, and it can also be applied in the development of new large-space timber structures where splice columns may be incorporated.

Evaluation of the Static Bearing Capacity Coefficients of Rough Strip Footing Using the Stress Characteristics Method

In this research, a numerical algorithm was proposed for evaluating the bearing capacity of rough strip footing rested on horizontal half-plane using the stress characteristics method. The bearing capacity coefficients, the layout of stress characteristic lines as well as the geometric specifications of the plastic and non-plastic regions beneath the footing for different values of internal friction angles have been calculated. The obtained results were in good agreement with those reported in the literature for $$\varphi \le {25}^{^\circ }$$ . The results revealed that by increasing the internal friction angle, the bearing capacity coefficients, as well as the depth of the plastic domain beneath the footing increase and the emergence point of the non-plastic curved wedge moves toward the footing edges. It was also shown that the roughness only affects the bearing capacity factor due to the unit weight and the maximum depth affected by the stress characteristic lines beneath the rough footing was almost $$0.62$$ times the footing's width which corresponds to $$\varphi ={25}^{^\circ }$$ .

Seismic Bearing Capacity of Strip Footings on Ground Reinforced by Stone Columns Using Upper-Bound Solutions

Abstract In this technical note, the seismic bearing capacity coefficients of shallow foundations placed on soft ground reinforced by stone columns are evaluated based on the upper-bound theorem of...

Field Test on Uplift Bearing Capacity of Rock-Socketed Belled Piles

The thick sandstone with an upper layer of clay (2 m to 3 m) was identified at the transmission line projects in western China. Tower foundations are affected by extreme weather such as strong wind and snow all the year round, so the research of foundation uplift is very significant. Belled piles are widely used in the area due to its high uplift bearing capacity, however, further research studies regarding the uplift bearing capacity of the belled piles in this special scenario still need to be conducted. The uplift bearing characteristics of five rock-socketed belled piles were studied by field testing method. The load-displacement curves, fitting analysis of load-displacement curves, change rate of pullout stiffness, distribution of axial force alone the pile, and pile side friction were analyzed. Observation results show that the load-displacement curves of rock-socketed belled piles are steeply changed. Moreover, we find that the hyperbolic model can provide a good fitting result for load-displacement curves, and the ultimate uplift bearing capacity is suggested to be predicted by using a reduction parameter of 0.64–0.85. Both uplift bearing capacity coefficient Nu and utilization ratio of pile material η increase with the increase of L/d under a same diameter, while the growth rate decreases. In this paper, the significant size effect is observed with increasing of pile diameter. The change rate of pullout stiffness-displacement curves are consistent with the trend of the safety factor-displacement curves, and can be fitted by power function model. Additionally, the change rate of pullout stiffness at the limit state will decrease to around 154 in this study, which can be used as the instability threshold for the rock-socketed belled piles in a similar soil foundation.