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A new theoretical calculation method for the load-slip curve and the shear stiffness of the stud based on Winkler’s elastic foundation beam theory and deflection differential equation of the stud is proposed. Different stress characteristics of the elastic and plastic zones of the concrete are considered in the proposed method. The accuracy of the theoretical calculation method is validated by the test results. Moreover, the effect of concrete strength, stud diameter, and yield strength on the stud load-slip curve is analyzed. The results show that the proposed model can effectively reflect the change process of the load-slip curve of the test specimen stud connector. The stud diameter, stud yield strength, and concrete strength affect the peak slip, shear stiffness, and shear capacity of stud shear connectors. With an increase in stud diameter, the peak slip, shear stiffness, and shear bearing capacity of the stud are all increased. An increase in the yield strength of the stud increases its elastic slip, peak slip, and shear capacity. Lastly, with an increase in concrete strength, the elastic slip and peak slip of the stud both decrease, whereas the shear stiffness and shear bearing capacity are increased.

The mechanical properties of reinforced concrete (RC) structures are closely related to the bond stress-slip relationship of rebar-concrete interface. In this paper, a novel bond stress-slip model under monotonic and cyclic loading is proposed. For interfacial behaviour under monotonic loading, an innovative micro-element model, consisting of a spring element, a friction element and a switch element, is proposed to effectively characterize the interfacial micro-damage mechanical behaviours in a physical sense. By adopting a parallel system of micro-elements and setting the fracture threshold of individual spring element as a random variable, the expressions of the bond stress-slip relationship and interfacial damage variable are derived. Subsequently, succinct practical expressions for the bond strength, peak slip under monotonic loading are formulated. The bond stress-slip model for rebar-concrete interface under monotonic loading are further established. For cyclic constitutive model of rebar-concrete interface, a new method of cyclic correction factor for the degradation law of bond strength is developed. The bond strength degradation under cyclic loading affected by the number of cycles, maximum slip value and opposite loading can be reflected with reasonable accuracy. Furthermore, the predictions calculated by the proposed model under monotonic and cyclic loading are in favorable agreement with experimental results. All parameters in the model have clear physical meaning.

In order to evaluate the effect of seismic isolation on random seismic response characteristics of a track-bridge system, in this paper, a three-dimensional detailed nonlinear dynamic model consists of rail, CRTS II slab ballastless track, high-speed railway simple supported bridges, isolated bearings, piers, pile foundations from top to bottom, is established by OpenSEES. The stochastic process of ground motion constructed by the random harmonic function is taking as random excitation, and the probability density evolution method (PDEM) is applied to investigate and analyze the system from the random perspective. On this basis, the influence of FPB bearing and the different FPB parameters (such as equivalent radius) on the random seismic response of the track-bridge system is studied. Thereby, aplenty probabilistic information (probability density evolution function, mean value and standard deviation) can be gained of seismic response of isolated bridges with different isolation parameters and non-isolated bridges of the high-speed railway track-bridge system under the excitation of random earthquakes by case study. Through the comparison of random seismic responses of non-isolated bridge and isolated bridges with different parameters under random ground motions, the favorable and unfavorable effects of seismic isolation for high-speed railway bridges are explored and demonstrated from a random point of view. The comparison of the random seismic response under different cases are discussed and significant outcomes are drawn. Results show that: The use of isolation bearing can reduce the response of track structure and pier, but meanwhile, increase the response of bearings. The change of the equivalent radius of the isolation bearing has no obvious influence on the random response of the pier and the track structure, but will to some extent bring the change of the bearing response. The results can be used for the seismic design and maintenance of the railway high-speed bridge.

Steel-reinforced concrete-filled circular steel tubular (SRCFT) stub columns is a novel type of composite columns, which have a great potential to be used as piers or columns in practical engineering. Hence, it is essential to comprehend the compressive performance of SRCFT stub columns and suitably predict the compressive strength for the engineering design and applications. This paper aims to investigate the compressive behavior of SRCFT stub columns through combined experimental and numerical studies. A total of 8 specimens were tested to investigate the compressive performance of SRCFT stub columns in detail, in terms of the axial load-strain curve, ultimate bearing capacity, ductility, strength-weight-ratio and strain ratio. The SRCFT stub columns exhibited better ductility than CFT stub columns. The inserted steel section can effectively prevent shear cracks in the core concrete from propagating quickly. Furthermore, finite element model was established and verified by comparing the experimental and FE results. Then, the complex composite action among the steel tube, core concrete and steel section was discussed and clarified comprehensively. In addition, the capacity of the energy dissipation for SRCFT stub columns was discussed. Finally, a novel simplified formula was proposed to predict the ultimate bearing capacity of SRCFT stub columns. The studies may provide a considerable reference for designing this type of structures in engineering practice.

To study the effects of concrete creep and temperature gradients on the cooperative working performance of a longitudinal slab ballast-less track prestressed concrete simply supported box girder system (girder-rail system), a girder-rail system model was established based on the ANSYS software. Then, the deformation of the girder-rail system caused by concrete creep and temperature gradient was studied in addition to the normal stress redistribution of the sliding layer and the normal stress variation of the interface between the cement asphalt mortar (CA mortar) and track slab. The results showed that the mid-span creep camber of the box girder under the girder-rail system was smaller than that of the single box girder, to which a uniform load (converted from the ballast-less track system) was applied. Concrete creep and temperature gradients led to the camber deformation of the ballast-less track, and then caused a redistribution of interlayer stress. At 1500 days, the creep camber of the box girder caused the appearance of a void in the sliding layer close to the end of the box girder (approximately 2 m). Voids appeared in the sliding layers at the middle and edge of the base plate under positive and negative temperature gradients, respectively. Under the creep camber of the box girder, tensile stress at the interface between the CA mortar and track slab appeared at the end of the box girder. This tensile stress appeared at the interface in the middle and edge of the track slab under positive and negative temperature gradients, respectively. Under the effects of creep camber of the box girder and temperature gradient, the maximum normal tensile stress of the interface was 264.8 kPa at day 1500, which was less than the normal cohesive strength of the interface and indicated that there was no interface separation.

The influences of temperature, relative humidity (RH) and carbon dioxide (CO2) concentration on concrete carbonation in a simulated environment were investigated. The carbonation depth, compressive strength and surface strain of concrete under different simulated environments were tested. The results showed that the effects of temperature, RH and carbon dioxide concentration on carbonation depth and compressive strength were significant. There was a linear relation between temperature and carbonation depth as well as compressive strength of concrete. A power function existed between carbon dioxide concentration and carbonation depth, and there was an exponential function between carbon dioxide concentration and compressive strength. The carbonation of concrete was more significant when the RH was within the range 60­–80%. Significant differences of phase composition and hydration products were observed before and after the carbonation, mainly manifested as attenuation and disappearance of diffraction peaks of hydration products.

A framework is developed in this article to predict the nonstationary random ground vibrations induced by high-speed trains, by combining the pseudo-excitation method with the two-and-a-half-dimensional finite element method. This development contains two steps. First, the power spectral density of the wheel–rail dynamic force is accurately obtained through the combination of the pseudo-excitation method and a vehicle–slab-track–ground theoretical model. Second, the nonstationary random ground vibrations are efficiently solved by combining the pseudo-excitation method and the two-and-a-half-dimensional finite element method, where the power spectral density of the wheel–rail dynamic force obtained in the former step is used to constitute the pseudo-loads. In the numerical examples, the accuracy and efficiency of the proposed approach are validated through the comparison to the fast three-dimensional random method for train–track–soil system developed previously. The results show that the proposed approach can predict the train-induced random ground vibrations with sufficient accuracy and has three-to-five times increase in efficiency in comparison to the fast three-dimensional random method.

A new nonlinear track-bridge random model was established based on OpenSEES, of which the random seismic responses is systematically studied by using probability density evolution method (PDEM). First, a three-dimensional detail nonlinear random dynamic model of the track-bridge coupled system in high-speed railway is established considering the earthquake as the random excitation. The dynamic model is composed with the rail, CRTS II slab ballastless track, the simple supported bridges, bearing, pier and the pile foundation, from which the random dynamic equation of the random model is formulated. In order to evaluate the seismic performance of track structures from a random perspective, the random seismic responses of high-speed railway bridge under random seismic excitations are investigated and analyzed by using the PDEM. Eventually, the Newmark β integration method and the double edge difference method of TVD format are adopted to obtain the random responses involving the probability functions, which can be translated to get the mean value and the standard deviation of responses. Thus, the abundant probability information of seismic responses of the high-speed railway bridge under random seismic excitations can be obtained. The PDF and CDF of the sliding layer are obtained; thus, the failure probability and reliability of different damage grades of sliding layer are obtained. Discussions and significant conclusions on the random dynamic responses are presented.

The main goal of this paper is to perform the safety assessment of high-speed trains (HSTs) on the simply supported bridges (SSBs) under low-level earthquakes, which are frequently encountered by HSTs, utilizing spectral intensity (SI) index. First, the HST’s limit displacements, which are calculated by using the multi-body train model with detailed wheel–rail relationship, varying with train speed, frequency and amplitude of a sinusoidal base excitation are obtained. Then, based on the obtained HST’s limit displacements, the spectral intensity limits (SIL) graded by the train’s running speed are calculated, and the relationship between the bridge seismic dynamic responses and the train’s running safety was established. Next, the method that utilizes the SI and the SIL indexes to evaluate the HST’s running safety was proposed and verified by comparing with the evaluation result of the train–track–bridge interaction model. Based on the proposed SI index, the HST’s running safety on the SSBs was evaluated under earthquakes, considering different pier heights and site types. The results showed that the low-frequency components of the ground motions are unfavorable to the HST’s running safety, and the height of bridge piers has a significant impact on running safety.

The objective of this paper is to investigate the behaviors of concrete-filled circular stainless steel tubular (CFCSST) stub columns under axial loading. A fine finite 3D solid element model was established, and the FE results revealed that the increased ultimate bearing capacity of CFCSST stub columns compared with their carbon steel counterparts was mainly due to that the confinement effect of CFCSST stub columns was stronger than that of carbon steel counterparts and the stress contribution of stainless steel was higher than that of carbon steel. The stress nephogram was simplified reasonably in accordance with the limit state of core concrete and a formula was proposed to estimate the ultimate bearing capacity of CFCSST stub columns using superposition method. Finally, the difference of the experimental and predicted results using the proposed formula and the existing codes were illustrated.

Through-beam connections offer the effective performance in developing the rigid connection, but the practical applications often encounter concrete pouring difficulties at the through beam region. Then an advanced through-core connection between concrete-filled steel tubular (CFST) columns and steel-concrete composite (SCC) beams is proposed in this study. The modification emphasizes the reduced beam flange width to convenient the concrete pouring, and the penetrated slab reinforcement into the CFST column to make up the strength loss from flange reduction. To investigate the seismic behavior of the connection, quasi-static cyclic loading tests on four specimens are conducted, and corresponding finite element analyses are also performed. The failure modes, hysteretic response, skeleton curve, ductility, stiffness degradation, ultimate bearing capacity, and energy dissipation of these connections are all discussed in detail. The results indicated that the proposed new connection has a favorable seismic performance. Then with FE simulations, the varying trends of the seismic behaviors, including the strain at the core area, plastic damage at core concrete and the energy dissipation proportions in the connections are all analyzed. Moreover, the influencing patterns of axial load ratio and the flange reduction degrees (RD) are also investigated through FE simulations. To ensure a good seismic performance, the maximum flange reduction degree (RD) of the steel girder is suggested to be 0.4 for the upper flanges and the ratio of the flange reduction between the lower and the upper flanges should not exceed 0.8.

This paper experimentally investigates the seismic behavior of tie bar stiffened round-ended concrete-filled steel tube columns. A total of 16 specimens were tested. The test parameters in...

A series tests on concrete and mortar cylinders under cyclic uniaxial loading were carried in this study to investigate the effect of internal stress-induced cracks on their mechanical properties. It was found that the radial strain cannot be changed continuously because the internal circular cracks appear firstly inside the specimens. Moreover, a unified approach for calculating the apparent volumetric strain of the cylindrical specimens at both elastic and inelastic stages was proposed. Additionally, the Acoustic emission (AE) experimental result shows that the AE hits rate can well reflect the crack formation and propagations of the concrete specimen under the cyclic axial compression.

This paper mainly presents a pseudo-static test program on 12 terminal stirrup-confined square concrete-filled steel tube (SCFT) columns and 14 rectangular SCFT columns under constant axial pressure. The effects of various factors on the hysteretic behavior of specimens are investigated. These factors include with or without stirrups, height of terminal stirrup region, equivalent stirrup ratio, stirrup form, loading direction, height-length ratio (L/B), length-width ratio (B/D), axial compression ratio (n) and sliding support. The failure mode, strain ratio, hysteretic curve, skeleton curve, ultimate bearing capacity, ductility, stiffness degradation, energy dissipation, as well as the residual deformation of the specimens are analyzed. The results indicate that: (1) When n is relatively larger, the bidirectional stirrups can effectively delay the local buckling of steel tube and greatly increase the ultimate bearing capacity, stiffness, equivalent damping viscosity index, residual deformation rate and ductility index, and further significantly improve the seismic behavior of the rectangular SCFT columns; (2) Axial pressure can improve the confinement effect from the steel tube to the core concrete, also bidirectional stirrups can directly confine the core concrete to decrease strain ratio of the steel tube; (3) With the same value of n, increasing the height of terminal stirrup region or increasing the equivalent stirrup ratio can effectively improve the seismic behavior of the rectangular SCFT columns; (4) The influence of loading direction, L/B and B/D on the ductility of rectangular SCFT columns are not obvious.

This paper presents an experimental and theoretical study of CFRP-confined concrete-filled circular steel tube (CFT) stub columns, which aims at investigating the effects of different numbers of CFRP layers and concrete strengths on the mechanical performance of CFRP-confined CFT stub columns. Based on continuum mechanics, a mechanical model of concentric cylinder consisting of CFRP, circular steel tube and concrete core under concentric loading was established and the corresponding elasto-plastic methods were obtained through a FORTRAN program. The influence of the number of CFRP layers on the ultimatecapacity, ductility and confinement effect of the steel tube on the core concrete wasdiscussed and identified. Finally,based on the limit equilibrium and elasto-plastic methods, a simplified formula for the ultimatecapacity of CFRP-confined CFT stub columns was proposed. Good agreement of the ultimate capacity was found between the elasto-plastic methods and the proposed formula, with the maximum discrepancy less than 12%.

This paper mainly presents a combined experimental, numerical and theoretical study on the mechanical behaviors of both conventional concrete-filled rectangular steel tubular stub columns (RST) and stirrup-confined concrete-filled rectangular steel tubular stub columns (SST) under compressive load. 16 RST stub columns and 16 SST stub columns were tested, with consideration of parameters including internal stirrup, concrete strength, and cross-sectional aspect ratio B/D. The failure patterns, bearing capacity, stiffness and ductility of specimens were analyzed based on the experimental results. A 3D finite element (FE) model was established for numerical simulation and parametric study to investigate the composite action among the steel tube, stirrups and the core concrete. The improvement of energy dissipation capability due to the stirrups confinement on the core concrete is also discussed. In addition, a unified theoretical formula to predicted ultimate bearing capacity for SST stub columns and RST stub columns subjected to compressive load was developed according to the superposition principle with rational simplification. It is shown that the proposed formula for these columns has a higher accuracy compared with the existing formulas in current literatures and codes.

As a new member of concrete-filled steel tube (CFT) structural families, concrete-filled elliptical steel tubes (CFETs) have great potential to be used as piers and columns in bridges and airport terminals because of its low flow resistance coefficient and reasonable distribution of major–minor axis. Hence, the main objective of this paper presents an experimental investigation on the seismic behavior of terminal stirrup-confined concrete-filled elliptical steel tube (TS-CFET) columns. Pseudo-static tests were tested to investigate the seismic performance of TS-CFET columns, including 3 concrete-filled elliptical steel tube (CFET) columns and 11 terminal stirrup-confined concrete-filled elliptical steel tube (TS-CFET) columns. Those key parameters varied in the experiments included the stirrups, height of terminal stirrup region, equivalent stirrup ratio, loading direction, slenderness ratio and axial load ratio. Then, based on the experimental results, the complete curves analysis on the load (P) vs. deflection ( Δ ) hysteretic curves were analyzed in detail, and the failure modes and composite action between the steel tube and core concrete were discussed and clarified. Furthermore, six indexes were employed to quantify the effect of varied parameters. The experimental results indicated that using stirrups in the CFET columns can directly confine the core concrete, and then considerably enhance the seismic behavior of CFET columns especially under higher axial load ratio. With the increase of axial load ratio, the energy dissipation capacity increased, while the displacement ductility decreased. The seismic performance of TS-CFET columns under major axis loading was obviously superior to that under minor axis loading. Additionally, the slenderness ratio had significant influence on the ultimate bearing capacity, stiffness and ductility of composite columns.

Concrete-filled elliptical steel tube (CFET) is a novel type of composite member, which has great potential to be used as piers and columns in bridges and airport terminals because of its low flow resistance coefficient and reasonable distribution of major-minor axis. Pure bending loading conditions are not frequently occurred in practical engineering, but the flexural researches are important since it's the basis of mechanical property researches under complex loading. However, little attention to the flexural behavior of CFETs has been paid at present. Hence, the main objective of this paper presents a combined experimental and numerical investigation on the flexural behavior of CFETs. Flexural tests were carried out to investigate the behavior of CFETs under bending. The moment vs. curvature curves during the whole loading process was analyzed in detail, and all the specimens behaved in a very ductile manner. Besides, the composite action between the steel tube and core concrete was discussed and clarified based on experimental results. Furthermore, FE (Finite element) model with precise material constitutive models was established to investigate the flexural mechanical of CFETs comprehensively, in terms of the full curves analysis on the moment vs. curvature curves, development of the stress and strain distribution in the steel tube and core concrete, and composite action. It should be noted that there existed bond slip in the interface between the core concrete and steel tube during the loading process. Then, the parametric studies with various factors were performed. Finally, design formulas were proposed to predict the ultimate moment and flexural stiffness of CFETs. The predicted results showed satisfactory agreement with the experimental and FE results . Moreover, the difference among the experimental, FE and predicted results using the related design codes were illustrated. The results of this study are expected to provide a reliable reference for design and application in concrete-filled elliptical steel tube (CFST) structures.

The migration and transport of water in the hydrophilic porous structure of cement-based materials are the main reason for the durability degradation. Hydrophobic cement-based materials have been developed to prevent water penetration and hence greatly improve the durability. This paper aims to present a comprehensive review on the latest advances of hydrophobic cement-based materials. Firstly, the assessment and test methods of hydrophobic cement-based materials, including surface wettability, water absorption and impermeability are introduced. Secondly, the strategies of surface and integral hydrophobic modifications are introduced, and the effects of different strategies are holistically evaluated. Thirdly, the durability and mechanical properties of cement-based materials affected by surface and integral hydrophobic modifications are summarized. Finally, the key scientific problems and challenges in this field are concluded and future research directions are proposed. It is expected that this review can guide further research on the design, preparation and characterization of hydrophobic cement-based materials.

This study investigates a novel prefabricated concrete frame beam with an innovative assembly pattern that is cost-effective, reliable, practical, and has a good fault-tolerance. Quasi-static cyclic experiments were carried out on a cast-in-place (CIP) beam and three precast concrete (PC) beams with different lengths or widths of protruding beam stumps. The cracking propagation mode , load-bearing capacity, beam ductility, beam stiffness , and plastic energy dissipation ability were comparatively analysed. It is concluded that the hysteretic behaviour of the PC beams with the innovative assembly pattern suggested in this study was similar to that of the CIP. Moreover, PC beams with a wider protruding beam stump displayed better seismic performance . In particular, development curves of crack width with cyclic load were obtained, which showed that the cracks widened gradually as the number of load cycles increased, and the main crack width increased significantly around the peak load. A finite element model (ABAQUS) was established to further reveal the working mechanisms and conduct a parametric investigation of the PC beams. Parametric simulations indicated that a reasonable and relatively larger thickness of the U-shaped beam shell and higher post-pouring concrete strength are recommended for practical applications of the proposed novel prefabricated concrete frame beams.

Track–bridge interaction under the seismic excitation is a dominant factor to the design and operation of railway bridges. A spatial model integrating rails, deck system, stringers, cross beams, suspenders, main trusses, piers and foundations was established in this paper, adopting non-linear springs to simulate the longitudinal resistance between the track and the bridge. The improved Penzien model was utilised to simulate the soil-pile interaction effect and a computer program was developed to generate artificial seismic waves. Comparison of natural vibration characteristics for the track–bridge system with and without considering the track constraint was made. Furthermore, the effects of sensitive parameters were investigated, including the ballast resistance, friction of movable bearings, location of rail expansion joint (REJ), etc. Present study results indicate that the track–bridge interaction enhances the structural integrity and induces relatively higher natural frequencies of the bridge....

Compressive tests of the CFST stub columns with artificial notches in the steel tubes were conducted in this paper to investigate the effects of the material imperfections of steel tubes on column performances. The load-strain responses, column strength and confining effects were discussed in detail. A parametric study, including the notch length, notch orientation, notch location and ductility, was also conducted. The results indicate that the notched CFST specimens have quite different failure modes from the intact CFST specimens. A notched CFST specimen may fail by bulging or closing of the notch, which was determined by the notch orientation. The results also show that the notched CFST specimens had lower mechanical performances than the intact CFST specimens because the notch steel tube could not offer sufficient confining effect on the concrete core inside it. Based on the experimental results, a practical calculation formula for the bearing capacity of notched CFST columns was proposed, which gave well agreement with the experimental results.

China’s high-speed railway (HSR) construction industry has been experiencing a golden period of opportunities in the recent decades. Due to the necessity of protecting arable lands and the advantage of rapid construction, bridges (elevated structures) are predominantly used in China’s HSRs, which must meet the critical small settlement requirement. This article first reviews the main technical standards of small- to medium-span HSR bridges, where their comparison with the Japanese standard and International Union of Railway standards is highlighted. Then, the long-span HSR steel bridges are described and discussed case by case. Based on the engineering practice of HSRs, the main achievements and key technologies of HSR bridges in China are provided, followed by the opportunities and challenges of the current and future developments of HSR bridges.

The high-speed maglev vehicle-guideway coupled system (MVGCS) is a complex system, whose random vibration characteristics have not been well studied due to a limited number of examples. To address this issue, a new efficient approach is proposed for the random vibration analysis of the MVGCS, which combines the probability density evolution method and multi-time step method with multiple random loads considered. The random model established for 10-degree-of-freedom maglev vehicles and guideway is time-dependent, considering two different supporting conditions. The Monte Carlo method is used to assess the accuracy and efficiency of the proposed approximate approach, and the random model is verified through comparison with available results. The stochastic dynamic responses of the vehicles, guideway, and electromagnetic levitation forces, including the mean values and standard deviations, are determined in a case study. The results show that the proposed method is feasible for the dynamic analysis of maglev systems with a reasonably good efficiency in computation. Furthermore, critical parametric analyses involving vehicle speed, irregularity, and cut-off wavelength are performed with the results discussed.

Based on the fractal theory, the fractal dimension model of coarse aggregate gradation in concrete was proposed, and the fractal dimension of coarse aggregate gradation in concrete was calculated based on the measured data. The variations of the micro structure, composition distribution and porosity to paste ratio of concrete surface layer were investigated by the methods of X-ray computed tomography (XCT) and profile grinding technology (PGT). Moreover, the content variations of coarse aggregate and paste with depth in concrete surface were also studied. The results show that the coarse aggregate content in concrete surface layer increases but the porosity decreases with increase of depth from concrete surface. Finally, they all tend to be a constant when the depth is larger than a certain value. The porosity to paste ratio of concrete surface decreases with increase of concrete strength. The major composition is cement paste within 0.1 mm of concrete surface, which turns into mortar within 0.1 mm ~ 0.4 mm. The volume fractal dimension of coarse aggregate and the fractal dimension of coarse aggregate gradation in concrete is about 1.35 and 2.68, respectively.

Four groups of axial compression tests on hexagonal CFT stub columns have been carried out aiming to investigate the effects of the concrete strength and steel ratio on the behaviour of hexagonal CFT stub columns. Studies on parametric analysis and composite action between core concrete and steel tube have been carried out using FE modelling which had been benchmarked using the test data. Based on the essential data obtained in this paper, the ratio of axial stress-yield strength of steel tube was determined at the ultimate state. The stress contour of core concrete was simplified to an unconfined area without constraint and a confined area with uniform constraint imposed by hexagonal steel tube. Eventually, a practical design equation of the ultimate bearing capacity of hexagonal CFT stub columns was proposed based on the superposition principle. An excellent agreement between the proposed equation and the experimental results was observed, with an average ratio of predicted to measured capacity of 1.08 and a standard deviation of 0.05.

Based on the assumption that chloride concentration and water influential depth change linearly in convective zone, the chloride convection zone depth is used in Fick’s diffusion law to investigate the chloride diffusion characteristic of concrete at tidal zones. In this study, an artificial simulation environment and field tests were carried out to validate and calibrate the rationality of the chloride convection zone depth model. The distribution model of surface chloride concentration in concrete was determined by exploring the correlations among chloride concentration, elevation, time and linear distance from seaside. The results illustrated that the depth of chloride convection zone on the concrete surface varied and manifested in terms of a function of water influential depth. The relation between the surface chloride concentration and the linear distance from the seaside followed an S-curve function equation. The similarities and differences regarding the characteristic of chloride diffusion in concrete between experimental and in-situ test were discussed for surface chloride concentration, chloride convection zone depth and chloride diffusion coefficient.

This paper investigates the flexural capacity of simply supported steel-concrete composite I beam and box beam under positive bending moment through combined experimental and finite element (FE) modeling. 24 composite beams are included into the experiments and parameters including shear connection degree, transverse reinforcement ratio, section form of girder, diameter of stud and loading way are also considered and investigated. ABAQUS is employed to establish FE models to simulate the behavior of composite beams. The influences of a few key parameters, such as the shear connection degree, stud arrangement, stud diameter, beam length and loading way, on flexural capacity are discussed. In addition, three methods including GB standard, Eurocode 4, and Nie method are also used to estimate the flexural capacity of composite beams and also for comparison with experimental and numerical results. The results indicate that Nie method may provide a better estimation in comparison to other two standards.

The objective of this work was to study the fatigue and post-fatigue monotonic behaviour of partially prestressed concrete (PPC) beams with a high degree of prestress. Eleven large PPC beams were tested under fatigue and monotonic loading. The effects of applied load level and severity of fatigue damage on the beams' fatigue and post-fatigue monotonic behaviour were studied and analysed. The results indicated that the fatigue behaviour of beams with a high degree of prestress was dependent on the applied load level. For an optimum and safe design, the applied load level should be less than 1·28 times the cracking load, the maximum crack width should be limited to 0·20 mm and the initial maximum stress range of non-prestressed reinforcing bars before repeated loading should be less than 170 MPa. The post-fatigue monotonic behaviour of beams was related to the severity of fatigue damage prior to the monotonic test. Low fatigue damage was found to have only a slight impact on the monotonic behaviour of the beams, whereas medium and high fatigue damage respectively reduced the ultimate strength by up to 15·2% and 18·0% and increased the deformability ductility index by up to 18·6% and 41·0%.

This paper presents a comparative study and a 3D finite element (FE) model of square stirrup-confined concrete-filled steel tubular (stirrup-confined CFT) stub columns. The FE results agreed well with the experimental results. The results indicated that: (1) The ultimate load-bearing capacity of CFT stub columns with internal studs was no improvement; (2) All three forms of stirrup confinement effectively reduced local bucking of the steel tube, and the cross ties was optimal, followed by spiral stirrups; (3) With the same overall steel ratio, the behavior of the square stirrup-confined CFT stub columns was considerably higher than in the square CFT stub columns.

The moisture in interior concrete is the primary factor directly influencing the deterioration phenomena of concrete structures. In this study, a method for predicting the moisture of the natural environment and the interior concrete was proposed based on the relative humidity (RH) and water vapor density (WVD) concepts using meteorological data. The variations of the moisture in the environment and the interior concrete were measured and modeled. After experimental validation, the moisture model was extended to investigate the action spectrum of humidity in the environment and the reaction spectrum of moisture in the interior concrete based on monthly and annual meteorological data. The results show that the characteristics of the RH and WVD differ from one another in both the environment and the interior concrete as a result of the intrinsic properties of the concrete. In the atmosphere, the RH fluctuates periodically with the diurnal cycle, whereas the WVD shows only slight fluctuations. In the interior concrete, the WVD fluctuates periodically, whereas the RH is relatively steady and tends towards a constant beyond a critical depth. Thus, it is proposed that the WVD, supported by the RH, be used to quantitatively characterize the moisture and the RH be used to qualitatively characterize the moisture.