Decrease In Bearing Capacity Research Articles

Assessing strength properties of stabilized soils using dynamic cone penetrometer test

Abstract The subgrade soil layer is the most essential part of the pavement system. Many pavement failures can be associated with subgrade weak strength and stiffness qualities. Therefore, it is necessary to strengthen this layer before building the other pavement layers. One of the essential methods utilized to enhance the engineering characteristics of this layer is soil stabilization. Stabilization methods are many and varied, but chemical and mechanical stabilization are the most common. This research aims to evaluate the strength of stabilized soils by using a dynamic cone penetration (DCP) test. To achieve this aim, subgrade soil was provided from a roadway project in Kerbala city and stabilized with 2.5 and 5% of Portland cement by weight of the dry soil. Then, the cemented subgrade soil was reinforced with 6 and 12 mm of polypropylene discrete fiber. The fiber was added to the soil with the following contents: 0.5, 1, and 2%. The characteristics of stabilized soils were evaluated by determining three parameters: dynamic cone penetration index (DCPI), in-situ California bearing ratio (CBR), and bearing capacity obtained from the DCP test. The results showed that when Portland cement was increased from 0 to 2.5% and then to 5% by weight of the dry soil, the DCPI value gradually decreased while increasing both CBR and bearing capacity. However, adding 6 and 12 mm fiber contents (0.5, 1, and 2) to the cement–sand mixture containing 2.5 and 5% cement led to increased DCPI and a gradual decrease in CBR and bearing capacity. Also, the results showed that the DCPI for a 12 mm fiber is lower than that for 6 mm fibers, while the CBR and bearing capacity for a 12 mm fiber are greater than those of 6 mm fibers for all ratios. Accordingly, the results of the DCP tests showed that the most significant support for the soil is obtained when the soil is stabilized using 5% cement with 12 mm of fiber by weight of dry soil.

Permafrost change and its engineering effects under climate change and airport construction scenarios in northeast China

Climate warming leads to the aggravation of infrastructures and environmental risks in permafrost regions. There are few reports about the interaction between airport runway and permafrost foundation. Based on long term field monitoring, remote sensing and comparative analysis approaches, our study quantitatively investigates the impacts of runway and climate on permafrost in northernmost China, and also the engineering problems are analyzed. Results show that the atmospheric inversion in winter controls the regional permafrost distribution in the study area. Ground surface warmed significantly after vegetation removal because of the runway construction. The maximum temperature difference among the forest, the swamp and the bared gravel can reach to 30 °C in summer. Such surface alterations caused abnormally rapid degradation of permafrost within the context of climate warming. The rate of permafrost table deepening varies from 0.461 to 0.590 m/a over the 2007–2017 periods. Also, the annual mean ground temperature at the 13 m depth increased at a rate of 0.054–0.130 °C /a. Its annual increase value is 0 ∼ 0.47 °C, with an average 0.108 ± 0.124 °C. In turn, permafrost degradation caused runway safety problems, such as the decrease of bearing capacity, increase of longitudinal slope, decrease of planeness, pavement cracks, density decrease of the foundation and cement concrete pavement cavity. However, in the natural places, the permafrost remained relatively stable and didn’t show a continued degradation trend. The permafrost table fluctuated with air temperature changes. Its interannual fluctuation range is 0 ∼ 0.25 m, with an average 0.08 ± 0.08 m. The interannual fluctuation range of ground temperature at the depth of 13 m is 0.01 ∼ 0.10 °C, with an average 0.06 ± 0.03 °C. In addition, the zero curtain phenomena were observed at the study site. Once the zero curtain periods were over, the ground temperature warmed rapidly. These findings have positive implication for new runway design in permafrost regions.

Behavior of large-scale concrete columns reinforced with high-strength and high-toughness steel bars under axial and eccentric compression

In this paper, combined with the current era background of energy saving and emission reduction, low carbon and environmental protection, the mechanical performance of new high-strength and high-toughness steel bars (HSHTSB) in concrete structural members is studied, and HSHTSB is expected to be popularized. To investigate the compression behavior of large-scale concrete columns reinforced with HSHTSB under axial and eccentric compression, thirteen reinforced concrete (RC) columns were designed in this paper, including the five columns under axial compression and the eight columns under eccentric compression. The effects of different types of steel bars, transverse steel bar spacing, the configuration of transverse steel bars, and eccentricity on failure modes, load-deformation curves, load-strain curves, ultimate bearing capacity, deformation capacity, and energy absorption capacity were studied in detail. The results show that the cracks are more uniform for concrete columns reinforced with HSHTSB. When the transverse steel bar spacing is less than 80 mm, concrete columns reinforced with HSHTSB with eccentricity ≤200 mm (including eccentricity = 0) have obvious secondary bearing phenomenon, and significantly improve ductility and energy absorption capacity; HSHTSB as longitudinal steel bars can reach yield strength for RC columns under axial compression. For RC columns under eccentric compression, HSHTSB could not reach yield strength on both the tensile and compression side. For the RC columns of Group II, III, and IV, when the eccentricity increases from 100 mm to 400 mm, the ultimate bearing capacity decreases by 76.1%, 75.2%, and 75.1%, respectively. Different from the ordinary RC columns, the ductility decreases with the increase of eccentricity for concrete columns reinforced with HSHTSB. Compared with ordinary RC columns, the energy absorption capacity and deformation capacity of concrete columns reinforced with HSHTSB under axial compression are increased by 120.9% and 116.9%, respectively. Compared with RC columns using transverse steel bars with single-leg, the energy absorption capacity and ductility for multiple-leg can be increased by 111.5% and 103.2%, respectively. When the eccentricity increases from 100 mm to 400 mm, the ductility for columns of Group II and III decreases by 73.5% and 65.9%, respectively. The use of HSHTSB can save the number of longitudinal steel bars and the transverse steel bar spacing while maintaining the bearing capacity, and further improve the deformation capacity. Based on the section strain analysis, the analytical models of the ultimate bearing capacity for the concrete columns reinforced with HSHTSB were established with high accuracy.

The influence of sizing on the compressive performance of foam-reinforced woven lattice sandwich panels

Woven lattice truss sandwich panels (WLTSPs) structure has excellent anti-stripping ability and energy absorption effect. The warp and weft distributions have an effect on the WLTSPs. Foam-filling technique and different heights of WLTSPs were double studied by the testing. Through the compression test and lateral compression test reveal the deformation, damage, failure and energy absorption. In the compression testing, the foam-filling can effectively increase peak force (PF) and energy absorption (EA), especially the weft distribution along the length direction-the specific energy absorption per unit mass of foam (△SEA) is 7.086 J/g. The foam filling transforms the piles from compression-shear coupled damage to progressive damage. In the lateral compression testing, when the WLTSPs at a low height the foam filling leads the load-displacement curve changes from brittleness to ductility. Foam filling improves the PF of PB by up to 459% at the height of 80 mm and restrain the decrease of bearing capacity with the increased height. The failure modes of the WLTSPs includes bending failure to progressive failure, concave, and the end fracture compression.

Prediction of Smear Effect on the Bearing Capacity of Driven Piles

This paper deals with prediction the effect of soil remoulding (smear) on the ultimate bearing capacity of driven piles. The proposed method based on detecting the decrease in ultimate bearing capacity of the pile shaft (excluding the share of pile tip) after sliding downward. This was done via conducting an experimental study on three installed R.C piles in a sandy clayey silt soil. The piles were installed so that a gap space is left between its tip and the base of borehole. The piles were tested for ultimate bearing capacity according to ASTM D1143 in three stages. Between each two stages the pile was jacked inside the borehole until a sliding of about 200mm is achieved to simulate the soil remoulding due to actual pile driving. The results of the tests exhibited that the pile might loss 14% of its ultimate capacity when it is loaded immediately after installation. Also, it was concluded that the pile may regain of about 9% of its original capacity after 30days of its installation.

Behavior of concrete-filled circular steel tubular stub columns exposed to corrosion and freeze–thaw cycles

This work experimentally and numerically studies the behavior of concrete-filled circular steel tubular stub columns experiencing corrosion and freeze–thaw cycles. The considered parameters are the corrosion rate, freeze–thaw cycles, and the number of alternations of the corrosion and freeze–thaw cycles. The failure modes and axial load–displacement curves are measured and discussed. The experimental results show that all the columns exhibit shear failure, and the core concrete suffers severe damage as the corrosion rate increases. The residual bearing capacity and ductility coefficient decrease with an increase in the corrosion rate and freeze–thaw cycles. A finite element (FE) model is also developed using the material thickness and strength reduction analysis method and validated using the experiments in this study. Further, a parametric analysis is conducted to identify the influences of the critical parameters on the load–bearing capacity of the columns. The finite element model results demonstrate that exposure to the alternations of corrosion and freeze–thaw cycles significantly influences the residual bearing capacity of the columns: the higher the number of alternations of corrosion and freeze–thaw cycles, the lower the residual bearing capacity of the columns. Finally, a simplified method is proposed for predicting the ultimate bearing capacity of concrete-filled circular steel tubular stub columns exposed to corrosion and freeze–thaw cycles.

Residual performance of compression stiffened welded hollow spherical joints after exposure to elevated temperatures

The post-fire residual behavior of the joints and their accurate identification are critical issues for the assessment of the fire damage in the commonly used grid structures. Accordingly, it will be determined, whether the structure is directly used, disassembled, or used after repair. In this paper, the residual performance of compression stiffened welded hollow spherical joints after a fire is studied using the methods of air cooling and water cooling. The failure mode, load-displacement curves, and residual mechanical properties of the joints are analyzed. The results show that the residual performance of the joints after a fire is mainly related to the exposure temperature and the cooling mode. In air-cooled joints, the initial axial stiffness and bearing capacity decrease with the increase of exposure temperature, while the ductility increases significantly. In water-cooled joints, the initial axial stiffness and ductility decrease with the increase of exposure temperature, and the bearing capacity shows a decreasing trend before 500 °C and gradually increases after 500 °C. When conducting the FEM simulation of the experimental specimens, three-dimensional hexahedral elements were adopted with the relationship of the steel material after elevated temperature consisting of a combination of straight lines. The validity of the FEM model was verified by comparison with the experimental results. Based on the results of the parametric analyses, a calculation formula is proposed for predicting the residual bearing capacity and initial axial stiffness of compression stiffened welded hollow spherical joints after a fire.

Terahertz Non-destructive testing and imaging of corrosion in coated steel plates

The corrosion will lead to the decrease of bearing capacity and durability of steel plate structures. Due to the limitations of the existing non-destructive testing (NDT) approaches, it is difficult to accurately evaluate the corrosion of steel plates, including the corrosion location, area, and thickness. In this paper, a method of extracting the delay time difference in the reflected terahertz (THz) signal is proposed to detect and image the corrosion in coated steel plates. The results from experiments and numerical modeling show that this THz method has a high measurement precision, and the thicknesses of coating and corrosion layers can be measured simultaneously. When the epoxy resin set as coating layer with a thickness of 1000 μm, the minimum thickness of corrosion layer that can be effectively detected in THz model is 25 μm, and the maximum thickness is 3700 μm. Meanwhile, the error percentage of the corrosion layer thickness in the range of 50 ∼ 3700 μm is less than 3%. In addition, a novel imaging technique to visualize the corrosion thickness of steel plates is developed by introducing the THz method. The three-dimensional (3-D) visual imaging directly describes the thickness and location distribution of the corrosion area while removing the effect of the coating layer. Those characteristic values, including the maximum, minimum, average, median, standard deviation, of the corrosion thickness, as well as the ratio of corrosion area/scanning area, can be extracted by this imaging method. In conclusion, the proposed THz technology can realize the NDT of the corrosion area, shape, and thickness, which serves as a guide to quantify the degree of corrosion for steel plate structures.

Modeling footing resting on anisotropic sand using material point method

Sand typically exhibits anisotropic internal structure which may significantly influence its mechanical behavior. The material point method (MPM) can eliminate mesh distortion and thus is suitable for investigating geotechnical problems with large deformation. In this study, an advanced anisotropic critical state theory (ACST)-based soil model is implemented in MPM to study the response of strip footing resting on anisotropic sand. The capability of the model is verified by simulating several element tests and strip footing tests with different soil densities and fabric bedding plane orientations. For the footing problem with a vertical load, as the fabric bedding plane orientation increases, the bearing capacity decreases and its corresponding settlement increases. The failure pattern becomes asymmetrical when the bedding plane orientation or the loading direction is inclined. A comparison between the simulation results predicted by the anisotropic and isotropic models is made, which demonstrates that neglecting the fabric anisotropy may lead to the overestimation of the bearing capacity.

Crossbars of frame buildings when changing the sign of forces

A large number of reinforced concrete frame buildings are located in seismically dangerous regions. In case of seismic impacts plastic strains and local destructions occur in elements of such buildings, which influence sufficiently on their bearing capacity and stress-strain state when changing the sign of internal forces. This fact is not taken into account in current Russian norms on earthquake-resistant construction. The numerical research of reinforced concrete beams behavior under action of alternating load with regard to elastic-plastic properties of concrete and reinforcement has been conducted. The evaluation of influence of plastic strain maximum value in tensed reinforcement on the relative bearing capacity of the beam when changing the force sign and on the limit value of coefficient of plasticity corresponding to the destruction of compressed zone of concrete has been made. The comparison of results of numerical simulation with the results of experimental tests of beams with the same parameters has been made, which has demonstrated good convergence of numerical calculations with experimental data both in terms of bearing capacity and deformations for plasticity coefficients less than 2.5. During the experiment it has been found that when changing the sign of internal forces the through cracks form in bending reinforced concrete elements throughout the entire section height, which close afterwards if the coefficient of plasticity for reinforcement deformations does not exceed 2.5. For greater values of coefficient of plasticity the through cracks closing doesn’t take place until the destruction of the specimens due to the rupture of reinforcement bars. According to the results of the study it was concluded, that the decrease by 40% of relative bearing capacity of beams compared with reference samples as the increase of coefficient of plasticity in the first semi cycle of loading takes place. Also with the increase of the coefficient of plasticity the three times decrease of the limit values of coefficients of plasticity, corresponding to destruction of compressed concrete, when changing the sign of forces is observed. The numerical calculations of beams models for 10 and 50 alternating load cycles have been conducted with cycle asymmetry coefficient equal to -1. The conclusion has been made that under the action of alternating load with the number of loading cycles not exceeding 50 and for maximum values of coefficient of plasticity not exceeding 1.62 the insignificant decrease of relative bearing capacity of beams, not exceeding 10%, takes place.

Seismic Performance of a New Assembled Bolt-Connected Concrete Beam–Column Joint: Experimental Test and Finite Element Modeling

A new assembled bolt-connected concrete beam–column joint is proposed, aimed at completing the repair of a post-earthquake node by replacing the bolts and precast beams. Low-cycle loading tests were performed on two new full-scale connections to investigate the effect of bolt strength on the seismic performance of the new connections. A finite element model was established based on the experimental node specimens and compared with the experimental results to verify the accuracy of the finite element simulation results. The seismic performance of the new joints under different axial ratios was studied using finite element software to determine the effect of the axial pressure ratio on the seismic performance of the new joints. Based on the research carried out, a new improved joint was designed, numerical models of the improved joint were established using finite element software, and the seismic performance of the improved joint was compared with the results of the experimental simulation to analyze the seismic performance of the improved joints. The results of the study showed that the bolts and precast concrete beams are the main load-bearing members in the period of service. The joint can be repaired by replacing the bolts and precast concrete beams under seismic action, which meets the new joint design concepts. The finite element simulation results are in good agreement with the experimental results. The larger the axial compression ratio, the earlier the failure stage of the concrete, and the faster the bearing capacity and ductility decrease. The larger the axial compression ratio, the higher the initial stiffness of the joints and the greater the rate of stiffness reduction. The bolt stress distribution of the modified and optimized joints is more satisfactory. This change in node form can improve the recovery efficiency of the joint to a certain extent.

Nondestructive testing and imaging of corrosion thickness of steel plates using THz-TDS

The corrosion of steel plates is one of the main reasons for the decrease of bearing capacity and structural durability. The existing nondestructive testing (NDT) approaches is difficult to accurately detect steel plate corrosion, including the location and degree of corrosion. Therefore, a non-contact nondestructive terahertz time-domain spectroscopy (THz-TDS) is utilized to evaluate the corrosion based on the properties of THz waves. The experimental results show that in the effective frequency range of 0.2–1.2 THz, the refractive index of corrosion products is around 2.8, and Fe3O4 has a significant impact on the optical parameters of the corrosion products mixture. The relative amplitude of the first signal from reflection THz-TDS exhibits a logarithmic relationship with the corrosion time of the steel plates and a linear relationship with the reciprocal of the corrosion time. By the method of extracting the delay time difference in the reflected THz signal, the THz-TDS can accurately measure the corrosion layer with a thickness larger than 40 μm, and the measurement accuracy is over 90 %. Meanwhile, the 3-dimensional (3D) visualization based on the THz method directly describes the true thickness and geographical distribution of the corrosion layer while removing the influence of coating materials. It provides a novel way to quantify corrosion degree of steel plate through NDT of corrosion under coating and extraction of corrosion thickness. The applicability and accuracy of non-contact THz-TDS for corrosion detection are therefore proved.

Plate armor foundation (PAF) - Innovative for intertidal wind turbines

The plate armor foundation (PAF) is an innovative type of foundation for intertidal wind turbines. A PAF consists of a top plate that is made of reinforced concrete and a side wall which is made of Larsen sheet piles. The steel tie rods are used to connect the top plate and the side wall. The Larsen sheet piles are interconnected using the edge locks. This connection mode is generally considered to be hinged connect. The PAF has significant advantages of cost effectiveness and fast installation. Model tests were conducted to investigate the monotonic lateral bearing capacity and its influence factors of the PAF in saturated marine fine sand. 3D numerical modeling was performed to explore the cyclic behavior of the PAF. Results show that the PAF with sheet pile hinged connection can provide higher lateral bearing capacity and effectively limit lateral deflection compared with no connection and welded connection between sheet piles. It was found that when the L'/L (L' is the length of the sheet pile edge lock and L is the height of the side wall) equals 1/3, there is no significant change in the lateral ultimate bearing capacity compared with the L'/L value of 1, while the lateral ultimate bearing capacity decreases by 14.3% when L'/L equals 2/3. Additionally, under a certain length of the sheet pile edge lock (L'/L value of 1/3), the sheet pile edge lock position (at the upper, middle, and lower part of the side wall) has a slight effect on the lateral ultimate bearing capacity. In addition, the lateral bearing capacity increases with increasing the aspect ratio of PAF; however, decreases with the increase of the loading eccentricity. During lateral loading, rotating behavior between neighboring sheet piles occurs. The incremental rate in the rotation angle decreases considerably with increasing the lateral load. Furthermore, the failure mode of the PAF changes from a combination of horizontal translation and rotation to pure rotation during loading. Numerical simulation results show that the PAF's accumulated deflection and accumulated rotation increase with increasing the loading cycle and loading amplitude. The excess pore pressure increases rapidly in the early stage of the cyclic loading.

Study on Mechanical Characteristics of Deformation and the Failure of Gas-Containing Coal in the Wuhai Mining Area of China under Different Gas Pressure Conditions

The mechanical properties of gas-containing coal and rock mass play important roles in controlling the occurrence and development of coal and gas outbursts. The gradual increase in mining depth will change the failure mechanism of gas-containing coal and rock mass. In order to further study the failure mechanism of gas-containing coal and rock mass, samples were taken from the gas-containing coal seam in the Wuhushan Coal Mine of the Wuhai Mining area of China. The mechanical parameters of coal samples during the failure process under different gas pressure conditions were measured and analyzed with the SAW-2000 rock mechanics testing machine, the gas-containing coal uniaxial compression device and inflation system. Meanwhile, the failure process and mechanical parameters of coal samples under different gas pressure were simulated by RFPA2D gas plate numerical simulation software. The results show that with increasing gas pressure in the coal there is decrease in Compressive strength, Elastic modulus, Strain, Peak strength and Bearing capacity and increase in Poisson’s ratio. When the failure state appears in the coal, the cracks are longer and wider, more random cracks are genareted, and the damage degree of the coal is greater. The numerical analysis’ results are in good agreement with experimental results. The research results are applicable to the gas bearing coal with the same or similar gas geological conditions. The tests can be carried out repeatedly and reasonable results can be obtained according to the physical and mechanical parameters of the actual coal seam and the occurrence of gas. On this basis, physical experiments and numerical simulations of triaxial compression can also be carried out to further study the mechanical characteristics of deformation and the failure of gas-containing coal under gas pressure and provide technical support for revealing the mechanism of coal and gas outbursts.

Experimental and Theoretical Study on Flexural Behavior of GFRP- and CFRP-Reinforced Concrete Beams after High-Temperature Exposure.

In this study, in order to study the flexural behavior of fiber-reinforced polymer (FRP) bars with reinforced concrete beams under static loads after high-temperature exposure, seven pieces of FRP-reinforced concrete beams were subjected to static bending tests and calculation model derivations. Four-point bending tests were carried out on FRP-reinforced concrete beams after high temperature treatment. The effects of high temperature and types of FRP bars on the cracking load, crack development, deflection and ultimate capacity, and failure mode of concrete beams were investigated. The test results show that the maximum crack width, deflection, and ultimate bearing capacity of GFRP- and CFRP-reinforced concrete beams decrease obviously with a rise in high temperature. After the exposure of 400 °C for 2 h, compared with the behavior of concrete beams at room temperature, the maximum crack width of GFRP and CFRP-reinforced concrete beams increased by 42.9% and 41.7%, respectively, the deflection increases by 103.6% and 22.0%, and the ultimate bearing capacity decrease by 11.9% and 3.9%. Meanwhile, through the analysis of the existing research results and test results, the calculation models for the maximum crack width, deflection, and residual ultimate capacity of FRP-reinforced concrete beams after exposure of high temperature were proposed. For FRP-reinforced concrete beams after high-temperature exposure, the errors between the measured maximum crack width, stiffness, residual bearing capacity, and their corresponding calculated values using the model were mostly less than 10%. The calculated value using the proposed model in this research is in good agreement with the measured value. The mechanical properties of FRP-reinforced high-strength concrete structures after high-temperature exposure can be preliminarily predicted, which provides a new theoretical basis for the application of FRP-reinforced concrete structures.

Frost Heaving Properties of Gravelly Soils in Alpine Seasonally Frozen Regions

To investigate the frost heaving properties of gravelly soil in alpine seasonally frozen regions and provide a foundation for the antifrost heaving design of the foundation tower in the Manzhouli 500 kV electrical transmission line. First, particle analysis and compaction tests were used to assess the basic characteristics of gravelly soil. Then, to investigate, a unidirectional freezing test of graded sand was performed to analyze the regularity and properties of the frozen process of graded sand. The test results demonstrate that the temperature gradient and the number of freeze-thaw cycles considerably affect the freezing of graded sand. The greater the temperature gradient and the number of freeze-thaw cycles, the greater the frost heave. In the freezing process, graded sand with zero fine-grain content exhibits obvious freezing shrinkage and thawing settlement. Still, the frost heave of sand is small. The frozen damage of graded sand is not caused by frost heaving deformation but by the deterioration of soil structure and the decrease of bearing capacity under hydrothermal coupling. Finally, experimental research is used to propose prevention and control measures for frost heave of power transmission and transformation projects.

Parameter analysis of coupling characteristics and load‐sharing law of arch‐chord coupled anti‐sliding structure

AbstractArch‐chord coupled anti‐sliding structure is a new type of anti‐sliding structure composed of multiple single piles in a specific form. The coupling effect of pile and soil is the most important key point. In this article, the factors that affect the coupling bearing capacity and load sharing ratio of the arch‐chord coupled anti‐sliding structure are screened out, and the rule that the evaluation index is affected by each factor is analyzed. The results show that, with the increase of pile diameter, the value of structural coupling ultimate bearing capacity increases exponentially, but the growth rate slows down gradually. With the increase of pile spacing, the value of structural coupling ultimate bearing capacity decreases. With the increase of soil cohesion around the pile, the value of structural coupling ultimate bearing capacity increases linearly. The coupling ultimate bearing capacity and load sharing ratio of the anti‐sliding structure are the most sensitive to the change of the internal friction angle of the soil around the pile, and the pile diameter has little effect on the evaluation indexes.

An Investigation of Compression Bearing Capacity of Concrete-Filled Rectangular Stainless Steel Tubular Columns under Axial Load and Eccentric Axial Load

In order to study the compression bearing capacity of concrete-filled rectangular stainless steel tubular columns, the influence of the stainless steel tube thickness, relative eccentricity, and slenderness ratio on the compression bearing capacity is analyzed, and then the calculation formula of compression bearing capacity is proposed. The results show that the finite element model can effectively simulate the compression bearing capacity, the mean of finite element calculations Nufem to the test Nuexp is 0.985, and the variance is 0.000621. The slenderness ratio and relative eccentricity have a great influence on the load–displacement curves. The thickness of the stainless steel tube has little influence on the load–displacement curves. With the increase in slenderness ratio and relative eccentricity, the compression bearing capacity decreases. With the increase in the slenderness ratio, the failure model of the specimen gradually changes from plastic failure to elastoplastic failure and then elastic failure. When the slenderness ratio is the same, if the relative eccentricity is larger, increasing the thickness of the stainless steel tube will be more effective in improving the compression bearing capacity. When the relative eccentricity is the same, if the slenderness ratio is smaller, increasing the thickness of the stainless steel tube will be more effective for improving the compression bearing capacity. The slenderness ratio and relative eccentricity have a great influence on the longitudinal stress distribution in the cross-section. When the slenderness ratio and relative eccentricity are greater, the longitudinal compressive stress in parts of the cross-section gradually becomes longitudinal tensile stress. The proposed formula can effectively predict the compression bearing capacity of concrete-filled rectangular stainless steel tubular columns. The mean of theoretical calculations to the test and the finite element is 1.054, and the variance is 0.0247.

Estimation of horizontal bearing capacity of mat foundation on structured and over-consolidated clays under cyclic wave loads

Bottom-supported platform with mat foundations is considered as a cost-effective option for offshore wind power installations due to its rapid installation and extraction period. However, the contact interface between mat foundation and soft seabed may undergo softening due to cyclic wave loads in operation, leading to bearing capacity losses especially in horizontal direction. In this study, the behavior of mat foundation on clay seabed under cyclic wave loads is investigated and the weakening effect on bearing capacity is presented. A unified elastoplastic constitutive model is adopted to consider the soil structure and over-consolidation in natural clay. Responses of excess pore water pressure, effective stress and horizontal bearing capacity for clays with various degrees of clay structures and over-consolidation ratios (OCR) are studied. Effects of wave frequencies and amplitudes on weakening effect of the interface are presented and discussed. Results indicate that the degrees of weakening effects of the normalized horizontal bearing capacity decrease with the increase of the degree of clays structure and OCR value. The clays structure is not easily damaged under the action of cyclic wave loads. The clay's over-consolidation state can be easily dissipated and transformed into normally consolidated clays under the action of wave loads with frequency equal to 0.4/s. The horizontal bearing capacity is basically consistent with the evolution tendency of the vertical effective stress at the interface of mat foundation and clay seabed, and it can be considered that the weakening effect of the horizontal bearing capacity is controlled by the interface.

ANALYSIS OF THE MOST COMMON DAMAGES IN REINFORCED CONCRETE STRUCTURES: A REVIEW

Reinforced concrete structures are often subjected to various negative environmental influences, reducing their reliability and durability. Main engineering tasks include extension of their life cycle, assessment of durability, reliability and residual service life. This requires reliable assessment of existing damages due to negative environmental impacts. Deterioration of RC structures is complex issue, which should be considered with the account of various factors. Damages and defects should be assessed, according to different criteria: degradation degree, type, time and cause of formation, etc. Article provides detailed analysis of the most common damages in RC structures on the basis of thorough literature review of this issue. Also, the classification of reasons for decrease of bearing capacity is proposed. Additionally, are discussed corrosion mechanisms and specifics of stress-strain state in corroded RC structures.