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Fiber-reinforced polymer (FRP) composite has been widely applied to reinforce and rehabilitate concrete columns in civil engineering. It is necessary to deeply understand the ultimate deformation (i.e., the ultimate axial strain ε cc ) of FRP-confined concrete columns. A large database including different types of FRP (conventional FRP and large-rupture-strain FRP), concrete compressive strengths (19.4 MPa-169.7 MPa), and cylinder sizes (51 mm-508 mm), as well as various concrete types, is collected in this study. For this reason, several existing ultimate axial strain modes for FRP-confined cylinders have been evaluated via some statistical parameters based on the database. The verification results illustrate that the prediction accuracy of axial strain models is not good enough due to the intrinsic difficulty in predicting deformation and variability of data source, although the available models with better performance can achieve the average ratio between experimental and predicted strain value ( ε c c exp e / ε c c pred ) below 10%.

In recent three decades, fiber reinforced polymer (FRP) composites have been generally applied to strengthen concrete columns in infrastructure. It is necessary to grasp the ultimate axial strain ε cu of FRP-confined concrete square and rectangular columns which are more commonly used in civil construction. A database containing unconfined concrete compressive strengths(17.6~110.8MPa), section sizes (150~381mm), sectional aspect ratio(1.0~3.0), different types of FRP composites(conventional FRP and large-rupture-strain FRP), as well as confinement strategies(FRP wrap and FRP tube) is assembled in this investigation. To address the issue, some existing ultimate axial strain models of FRP-confined non-circular columns have been assessed according to this database. The verification results show that the predictive accuracy of available models can hardly perform very well by reason of the intrinsic difficulty in predicting deformation and diverse data source. However, the average experiment-prediction ratio and average absolute error can be below 35% and close to 1.0, respectively.

To overcome the lower bearing strength of coral concrete and the high cost of conveying raw materials from the mainland to the island, a new method was presented. This method suggested to apply the coral aggregate instead of the natural coarse aggregate (NCA) in seawater concrete, which was denoted as CAC. In this paper, 18 axial loading prism specimens and 90 cubic lateral loading specimens were cast. Two concrete strengths, three replacement ratios of coral coarse aggregate (CCA) (50%, 75% and 100%) and five biaxial stress ratios (0, 0.15, 0.3, 0.45 and 0.75) were designed. A Digital Image Correlation (DIC) system was used to investigate all the failure patterns and stress–strain curves, which were used to analyze the influence of the above parameters on the peak stress and the peak strain. In addition, the lateral–axial strain relationship and biaxial failure criterion were also established. After determining the biaxial failure surface, a hardening law and a softening law were proposed to describe the uniaxial stress–strain curves based on the Weibull distribution and Guo’s model, respectively. Finally, a new constitutive model for CAC under biaxial stress was developed using the two-dimensional incremental constitutive model. The results indicated that the crack development of CAC was similar to that of natural coarse aggregate concrete (NAC), and the failure patterns of biaxial specimens were related to the biaxial stress ratio. Furthermore, the biaxial stress showed an increase in the peak stress and the peak strain. The increase in CCA replacement weakened the enhancement effect on the peak stress, while it slightly influenced the peak strain. Additionally, the proposed lateral–axial strain model and biaxial failure criterion were in good agreement with the measured results. Through comparison, the proposed biaxial incremental constitutive model was verified using the tested curves.

The confinement of concrete enhances its strength and ductility by restraining lateral dilation. The accuracy of a confinement model depends on how well it captures the dilation of concrete. In the current paper, a mesoscale model is established to study the dilation properties of concrete in active confinement, where the heterogeneity of concrete is considered. The stress–strain and lateral–axial strain curves of concrete in active confinement were used to demonstrate the validity of the mesoscale model. Subsequently, the distribution of lateral strain and the influences of the strength grade and confinement ratio on the dilation of concrete were investigated in a simulation. The results show that the distribution of the lateral strain along the radial or longitudinal directions is not uniform on the specimen when compressive failure occurs. The confinement ratio has a more significant influence on the concrete’s transverse dilation than the strength grade. Finally, an expression of the lateral–axial strain relationship of concrete in active confinement is proposed. The proposed formula can reflect the simulation results of the mesoscale model and is in good agreement with the prediction of existing formulas.

In this paper, distributed fiber optic sensing (DFOS) was used to monitor indicators of track buckling, i.e., the axial strain, curvature, and lateral deflection along a 20-m section of curved track during the summer when ambient temperatures are highest. The objectives of the research were to (i) evaluate the performance of DFOS for this type of monitoring, (ii) develop an improved understanding of the lateral and longitudinal thermal response of a curved rail, and, (iii) create Gaussian process regression (GPR) models to assist in the prediction of the rail thermal response. The DFOS provided temperature measurements along the rail; however, local variations in temperature over the cross-section were not captured by the single temperature fiber installed. Multiple temperature fibers are required to correct each strain measurement for temperature to accurately capture the track behavior. The DFOS data were used to evaluate two of the critical parameters that indicate the potential for buckling due to temperature variation: the axial strain and lateral bending curvature. Gaussian process regression was used to predict the rail response to temperature and enable buckling assessment with uncertainty bounds.

In order to study the compression deformation characteristics of filling materials with gangue grouting, the compression test device for filling material with gangue grouting was made, and contrastive compression tests were carried out for different sizes filling materials with non-grouting of gangue and gangue grouting. Compared with the filling material with gangue non-grouting, the results showed that the axial strain-axial stress curves of filling material of gangue grouting was smoother, the slope decreased, the elastic modulus increased, compressibility reduced and the compression deformation decreased. During the compression process, the axial strain increasing rate of filling material of gangue with non-grouting and grouting gradually decreased with the increasing stress, and they can be divided into three stages, respectively, and the three stages was named speed compaction stage, stabilization compaction stage and steady compaction stage, respectively. In the steady compaction stage, when the axial stress applied to the filling material with gangue grouting is 11.5 MPa, as the diameter of gangue particles increased from 0 ~ 20 to 0 ~ 40 mm, the axial strain amplitude greatly, but when gangue particles increased from 0 ~ 40 to 0 ~ 50 mm, the amplification of axial strain decreased. When the gangue particles increased from 0 ~ 50 to 0 ~ 60 mm, the axial strain increased only by 0.009. Small particles gangue was mostly located at the bottom of filling materials, when the proportion was large, the filling effect and gangue cementation effect of the slurry in the gangue gap were affected. Considering comprehensively, the optimal particles of filling materials with gangue grouting selected in this paper was 0 ~ 40 mm. The results of this study are of guiding significance for the reasonable selection of filling materials with gangue particles to control surface deformation.

The fundamental understanding of the behavior of granular materials by the effect of vibration is necessary to properly address a number of engineering issues, such as long-term settlement of high-speed railway, vibratory pile driving in sandy stratum, and earthquake-induced geotechnical disaster. Triaxial compression tests of dry Pingtan sand were carried out by a modified triaxial apparatus, where axial high-frequency vibration was super-imposed on the specimen at pre-peak, peak, and post-peak stress states during monotonic shearing. The influences of vibration conditions, confining pressure, and the initial relative density on the vibration-induced responses of Pingtan sand are mainly considered. It is shown that the super-imposed vibration leads to significant deviatoric stress reduction and vibro-induced additional axial strain. This owes to the fact that the static inter-particle friction turns to dynamic friction, and consequently, the frictional resistance has a considerable reduction when vibration is applied to the sand specimen. The vibration-induced stress–strain behavior of sand specimen is characterized into three states by two thresholds concerning vibration intensity and confining pressure: (1) stable state, (2) vibro-compression state and (3) vibro-instability state. For the vibro-compression state, the deviatoric stress reduction has a positive linear correlation with the increase in vibration intensity, while the vibro-induced additional axial strain follows a power-law increase with vibration intensity. Given a vibration condition, the deviatoric stress reductions and the vibro-induced additional axial strains at pre-peak, peak, and post-peak stress state follow a descending order. Besides, the influences of vibration on shear strength and critical state were also discussed.

The cross-river subway in the Hangzhou Bay area often passes through deep, thick, soft soil at the bottom of the river. At the same time, overlying erosion, siltation, and changes in water levels adversely affect the deformation of the subway, thereby causing hidden dangers to its safe operation. Using two-way dynamic triaxial testing, the effects of cyclic loading of the cross-river subway on the soft clay foundation were investigated for the first time, using simulation methodology as the prime objective of the present study. A strain development curve for the soft clay was obtained as a result. Considering the effects of effective confining pressure (p′) and radial cyclic stress ratio (τr), an explicit model of accumulative strain on soft clay under cyclic loading of the cross-river subway was established. The results showed that the accumulative axial strain (εd) was closely related to p′ and τr. Under certain conditions, as p′ and τr increased, the εd produced by the soil tended to decrease. Furthermore, through non-destructive testing based on nuclear magnetic resonance (NMR), pore distribution and pore size changes in soft clay during cyclic loading were analyzed. It was observed that under the action of the cross-river loading, the large internal soft clay pores were transformed into small pores, which manifested as a significant decrease in the number of large pores and an increase in the proportion of small pores. Lastly, the macroscopic dynamic soil characteristics observed during triaxial testing closely correlated with the microscopic pore size of the soil obtained in the NMR test, which indicated that using pore distribution and pore size changes to describe microscopic changes was a valid method.

Subgrades may be subjected to intermittent cyclic loads such as traffic loads. Under these loading conditions, excess pore water pressure can accumulate in clayey soils during cyclic loading period and dissipate during resting time. The deformation behaviour of clayey soil after reconsolidation process may be different from that under consecutive cyclic loading. A series of undrained cyclic triaxial tests, including reconsolidation process between cyclic loading stages, were performed on kaolin clay. The axial strain accumulation, excess pore water pressure accumulation, deviatoric stress–strain loop and resilience modulus under different cyclic stress ratios, initial confining pressures and degrees of reconsolidation were discussed and presented. Test results show that the reconsolidation process has significant effects on the deformation characteristics of clayey soil. The coupling effects of change of void ratio and effective mean stress result in a non-monotonic relationship between normalised total axial strain and degree of reconsolidation. In addition, an increase in the degree of reconsolidation leads to an increase in the normalised excess pore water pressure increment during 2nd cyclic loading stage, regardless of cyclic stress ratio and initial confining pressure. Furthermore, the steady resilience modulus at the end of each cyclic loading stage depends on the effective cyclic stress ratio and initial confining pressure, irrespective of reconsolidation process.

The dilation of concrete in the radial direction is crucial in understanding the failure process and the key to predicting the confining level of passively confined concrete. To better understand this problem, we established a mesoscale model of concrete by considering the random distribution of coarse aggregate and the different properties between mortar and concrete. The model’s validity was demonstrated by comparing with the stress–strain curves in code and the lateral–axial strain curves in test. The simulation results show that the lateral dilation is non-uniformly distributed along the specimen height and the circumferential direction of sections. Moreover, the deformation mainly occurs in the middle part of the specimen ranging from 3/8 to 5/8. The strength of concrete influences the stress ratio at maximum compressive strain, while it slightly influences the stress ratio at zero volumetric strain. The secant strain ratio is about 0.5 as the compressive stress reaches the strength of concrete. Compared with the simulation, the relationship between lateral strain and axial strain proposed by Teng and Binici shows excellent performance on the dilation trend prediction of plain concrete.