Abstract:This paper presents a structural sub-pixel displacement measurement by using the digital image correlation technologies for structural displacement and deflection measurement. Pixel-based displacements of a monitored structural location were determined using an improved sub-pixel algorithm. To transform pixel-based displacements to engineering units, a camera calibration method was developed. The numerical simulation test was carried out based on digital image processing algorithm. The simulation results were in good agreement with theoretical value, which validated the reliability of systematic measurement accuracy. A machine vision-based displacement measurement system was developed. A steel frame model was established for conducting experiments to investigate the follows: (i) comparison study on the measurement results obtained by the vision-based system and the laser displacement sensor, (ii) the effect of the measurement distance on the accuracy of the vision-based system. The mid-span deflection of fire-fighting bridge was measured by the developed system. The experimental results show many advantages of vision-based method such as non-contact, low-cost and convenient to implementation in realizing the structural displacement measurement with the accuracy level of millimeter. The method has wide application prospects in the deformation detection of bridges and other structures.

Abstract:To study the progressive collapse resistance of reinforced concrete frame structures considering floor slab action, a finite element model for progressive collapse analysis of beam-slab structures was established using SAP2000. The accuracy and rationality of the analysis model were verified by 12 specimens from the existing progressive collapse tests. Then, we defined an increasing factor for assessing the compressive membrane mechanism based progressive collapse bearing capacity considering the action of the floor slab. The influence of parameters，such as concrete strength, slab thickness, and reinforcement ratio，on the increasing factor was studied. The results show that，after considering the action of the slab, the collapse resistance of the structure increases significantly，the compression arch effect of the beam near the side column beam also increases, and the displacement reduces when the bearing capacity rises again. The increasing factor of bearing capacity increases significantly with the increase of the concrete strength grade, the aspect ratio of the slab, the reinforcement ratio at the bottom of the beam, and the beam height. However, the increase factor of the bearing capacity decreases with the increase of the thickness of the slab, the reinforcement ratio at the top and bottom of the slab, and the reinforcement ratio at the top of the beam.

Abstract:A dry connection method for horizontal joints of fully assembled composite walls is proposed in this paper. The prefabricated wall and the upper and lower structure are connected by pre-buried steel parts, L-shaped steel plates and high-strength bolts. In order to study the seismic performance of the composite wall and the mechanical behaviour of the joints, 5 specimens were designed with the thickness of steel plate and the high-strength bolt specifications (diameter and pre-tension) as key parameters. A monotonic loading test was performed to study the failure mode, horizontal load-displacement curve, eigenvalue point, seismic performance index, strain of the joint, and relative slip of the joint and the wallboard of the test piece. The results of experimental research show that the specimens with bolted connections on horizontal joints have strong deformation ability, where the ultimate displacement angle is up to 1/25, and they still have high bearing capacity. Increasing the thickness of jointed steel plates can improve the bearing capacity and initial stiffness of the specimens, but the specifications of the high-strength bolt have no obvious influence on the bearing capacity and rigidity of the specimen.

Abstract:A quasi-static test was carried out on five corroded RC frame beams in general atmospheric environment to analyze the influence of corrosion degree on hysteretic behavior. Based on the test results and the characteristic point parameters of the intact RC frame beam’s skeleton curve, the skeleton curve model of corroded RC frame beams was obtained. The cyclic degradation index βi based on hysteresis energy dissipation was introduced, and the hysteretic rules considering the basic strength degradation, post-capping strength degradation, unloading stiffness degradation and reloading stiffness degradation of corroded RC frame beams were proposed. Then, the restoring force model applied to corroded RC beams in general atmospheric environment was established. The comparison of the established restoring force model and the experimental hysteresis curves was performed. The results showed that the agreement was good, and the established restoring force model has high precision, which can better reveal the hysteretic behavior of corroded RC frame beams in general atmospheric environment. This study can provide a theoretical basis for the elasto-plastic analysis of corroded RC structures.

Abstract:The one-point loading test was used to study the in-plane shear behavior of carbon textile reinforced mortar (CTRM) plate. The carbon textile layers and steel fiber content were used as the parameters to study the mechanical properties of the CTRM plate. The test results show that with the increase of the number of textile layers, the oblique section crack load, ultimate load, stiffness before cracking and stiffness after cracking of the specimens are significantly improved. Steel fiber content can effectively increase the oblique section bearing capacity, oblique section crack load and ultimate load of the specimens, and can effectively improve the interface performance between carbon textile and mortar, which can reduce the degree of peeling damage between carbon textile and mortar. Finally, a calculation method for the in-plane shear capacity of the CTRM plate is proposed.

Abstract:In order to study the effects of concrete strength, diameter-to-thickness ratio, CFRP (carbon fiber reinforced composite) layer number and CFRP cladding mode on the axial compression behavior of CFRP confined concrete-filled circular steel tube, the axial compression comparison tests of 6 concrete-filled circular steel tube short columns and 18 CFRP-concrete-filled steel tube short columns were carried out. It is found that the CFRP constraint significantly increases the bearing capacity of concrete-filled circular steel tubes, and the increasing range of the bearing capacity increases with the increase of CFRP layers. The failure pattern of high strength and ultra-high strength concrete-filled steel tube short column is shear failure with poor ductility. CFRP constraint can improve its ductility, and more CFRP layers result in better ductility. The performance of half-packaged CFRP specimens is close to that of full-packaged CFRP specimens. CFRP binding effect decreases with the increasing diameter - thickness ratio. If the bond is good, CFRP and steel tube can work together before the specimen fails. Finally, three classical formulas of axial bearing capacity of CFRP confined CFST are selected for calculation, and the formula based on the double restraint formula of CFRP and steel tube can better predict its bearing capacity.

Abstract:Based on the concept of physical neutral surface, the governing differential equations of free vibration of an axial-loaded functionally graded material (FGM) beam with the material properties varying along the beam height are derived by using Hamilton principle, and then the power series solutions of the differential equations are obtained. Then, the frequency equation is obtained based on the general boundary conditions expressed by elastic constraints. The effects of the parameters such as the length-height ratio, the gradient index, the axial force, and the section variation coefficient on the natural vibration characteristics of functionally graded beams are analyzed. The results show that the shear deformation affects not only the flexural vibration but also the axial vibration.

Abstract:Aiming at the problems such as the early damage accumulation of concrete structure, a detection and evaluation method for the damage of concrete specimens based on thermoelastic intensity modulation laser technique for excited narrow-band ultrasound is proposed in this paper. With the help of the finite element simulation method, the ultrasonic wave by laser excitation of nonlinear mesoscopic damage concrete model is obtained. The spectrum analysis of the displacement signal on the surface of the concrete model is carried out and the relative nonlinear coefficient is calculated. On this basis, the piezoelectric ultrasonic second harmonic system and the percussion resonance fundamental frequency detection system are built, and the exponential regression equation of the nonlinear coefficient β′ and the dynamic modulus of concrete Ed is established. The results show that the proposed method has the advantages of non-contact and high sensitivity, and can provide a strong basis for early damage assessment of concrete structures.

Abstract:In this test, 216 cement-based grouting test blocks with 3 different test models and 6 different ages were made using uniform raw materials, mixing ratios, and curing conditions. The compressive strength was measured under the same loading conditions. The effects of different test models on the early compressive strength of cement-based grout test blocks and the conversion coefficients of compressive strength under different test models were studied at six different ages. The conversion coefficients of early compressive strength of the standard test block with the size of 40 mm×40 mm×160 mm prism and the non-standard test block with the size of 150mm×150mm×150mm under standard curing conditions are obtained, and the conversion coefficients of early compressive strength of the standard test block with the size of 100 mm×100 mm×100 mm cube and the non-standard test block with the size of 150 mm×150 mm×150 mm under the standard curing conditions of the Class IV cement-based grout are obtained. The change rule of each early strength conversion coefficient was analyzed, and the conversion coefficient was obtained which can be used as a reference for practical engineering application.

Abstract:A total of 139 long-period ground motion（GM） records are selected to study the effects of the parameters of restoring force models（restoring force models, stiffness ratio η，damping ratio ξ，displacement ductility ratio μ） and GM characteristics （period T，earthquake magnitude MW，site，PGA） on the input energy spectra SEI，hysteretic energy spectra SEH and damping energy spectra SED of the long-period GMs. Therefore, it can be found that: 1） there is a significant（slight） influence of the restoring force model on the long-period (conventional) seismic energy spectra, while there is a slight influence of the restoring force model on the conventional one; there is a slight influence of η on the long-period and conventional seismic energy spectra; with the increase of ξ，the spectral values in the long-period region of the long-period SEI increases, but for the conventional one it decreases; with the increase of μ，the peak platform and peak value of the long-period SEH is prolonged and decreases, but for the conventional one they are shortened and increases，respectively. 2）the larger MW results in the greater structural damage，while the softer site soil leads to the larger energy spectra value；the seismic energy spectra with other PGAoth can be obtained by multiplying the known seismic energy spectra with the reference PGAref by the equation of （PGAoth /PGAref）2. Then，based on the above parametric studies，the elastic long-period input energy design spectra are established by using a three-segment fitting function, and the influence formulas of μ and ξ on the long-period spectra are fitted. And then the inelastic long-period input energy design spectra are obtained.

Abstract:A tunnel-bridge-tunnel (TBT) infrastructure along the high-speed railway in China is taken as the engineering background, based on the theory of CFD and porous media, a 3D CFD numerical simulation model of train-tunnel-bridge-wind barrier-air is established. The aerodynamic load variation characteristic of the train when running on the TBT is studied. Aiming at the process of train running on the bridge-tunnel connection section (BTCS) under crosswind environment, the influence of the existence of wind barrier on the transient change effect of the aerodynamic load is further revealed from the view of the flow field. The results show that: 1) Under the condition without wind barrier, the fluctuation amplitudes of aerodynamic loads of each carriage in the process of 'from bridge to tunnel' are 1.03~1.89 times of the corresponding values in the process of 'from tunnel to bridge', and the existence of wind barrier makes the fluctuation amplitudes of aerodynamic loads in the two processes basically equal. 2) The change of train aerodynamic side force is most sensitive to the influence of the wind barrier, while the sensitivity of aerodynamic lift force and pitching moment is relatively weak.

Abstract:In order to investigate the flexural behavior of Reactive Powder Concrete（RPC） beam with externally prestressed Carbon Fiber Reinforced Polymer（CFRP） tendons，four beams specimens with different shear-span to depth ratios, tension control stress of the tendons and partial prestressing ratios（PPR） were tested. Based on the experimental results，the failure patterns of the beams were clarified, and the equations for predicting the cracking and ultimate moments of the beams were proposed and verified. The results show that the failure mode is similar to the under reinforced RC beams for all fully prestressed beams of PPR 1.0 without any internal steel reinforcements. Increasing the tension control stress of the tendons could enhance the cracking load of the fully prestressed beams，but could not change the failure mode. Compared with the fully prestressed beams, the ultimate capacity and ultimate deformation of the partially prestressed beam with steel reinforcements（PPR 0.7） increase by 88.7% and 18.1%, respectively. The ductile failure mode with the yielding of steel bars followed by the crush of RPC in compression zone was observed in the partially prestressed beam. The steel fibers in RPC have a limited effect on the flexural performance of the fully prestressed beams, while the steel reinforcements might improve the behavior of the beams significantly. Therefore，it is not suitable to overestimate the role of steel fibers and remove the use of non-prestressed reinforcements in the RPC beams.

Abstract:Layered rock slope is a common geological body along the Sichuan-Tibet Railway. The seismic stability of slopes has an important effect on engineering construction. Numerical models of bedded and toppling slopes were established by using finite difference method software FLAC3D. By comparing and analyzing the dynamic acceleration response of two typical layered slopes, their dynamic response characteristics and deformation mechanism under earthquakes are studied. The results show that weak interlayer has an effect on the wave propagation characteristics in layered slopes, which results in a local amplification effect during the process of seismic wave propagation in the slopes. The dynamic response of the layered slope is amplified by the elevation and weak interlayer, and the amplification effect of the slope surface was greater than that of the internal slope under the same elevation condition. Compared with the toppling slope, the amplification effect of bedded slope shows a strong nonlinear increase trend with the increase of elevation. The dynamic amplification effect of the layered slopes increases with the increase of ground motion amplitude, and their dynamic amplification effect under horizontal seismic force is greater than that of the vertical seismic force. The weak interlayer controls the dynamic deformation characteristics of layered slopes, and the topmost weak interlayer is the potential sliding surface.

Abstract:The WHY-200/10 microcomputer-controlled universal testing machine was used to perform static and cyclic loading and unloading tests on cracked chevron notched Brazilian disc (CCNBD) of red sandstone, and the type I fracture mechanical characteristics and deformation feature of red sandstone under cyclic loading and unloading were studied. Based on the macro-mechanical parameters of red sandstone, PFC3D numerical simulation experiment was conducted to explore the law of microcrack propagation. The experimental results show as follows. Cyclic loading reduces the type Ι fracture toughness（KΙC） of sandstone, and with the increase of cycling times, the type Ι fracture toughness of sandstone decreases gradually until it reaches a certain threshold. The cyclic loading curve of CCNBD is strictly controlled by the static loading curve. The deformation at the failure point of the cyclic loading curve is similar to the post-peak deformation at the same load level as the static load curve. The process of radial displacement and deformation of the specimens under cyclic loading is related to the upper limit load ratio. There are mainly three stages: initial loading stage, middle stabilization stage and late acceleration stage. When the upper limit ratio is 0.95, the radial displacement deformation process and microcrack propagation of the sample occurred only in the initial and acceleration stages. When the upper limit ratio is 0.75, the displacement deformation process and microcrack propagation happen only in the initial and stable stages, and there is not fracture failure occurring. Under cyclic loading, the micro-cracks in the fracture process zone (FPZ) at both ends of the ligament of the sample were fully derived and expanded, and the number of final micro-cracks is significantly more than that under static loading.

Abstract:In order to study the influence of layered rock mass on tunnel seismic response, considering the oblique incident angles of seismic motion and the nonlinear contact characteristics at the interface, a numerical simulation method for seismic response of hydraulic tunnel in layered rock mass was proposed. First, based on the 3D viscoelastic artificial boundary conditions and the wave field decomposition theory, the input method of an obliquely incident earthquake in layered rock mass was put forward. It can transform the seismic waves into equivalent nodal forces acting on the nodes of artificial boundaries. In view of dynamic interaction characteristics between interlayers in layered rock mass under seismic action, a dynamic contact force algorithm considering the bond-slip characteristics of the interface was presented. Then, the methods were applied to the anti-seismic stability calculation of the hydraulic tunnel of AZAD PATTAN hydropower station in Pakistan. The calculation is divided into three different working conditions, with vertically incident earthquake, with obliquely incident earthquake but no dynamic contact force, with obliquely incident earthquake and dynamic contact force. The results indicate that the stress and displacement of the tunnel structure under seismic action are greatly affected by the angle of incidence. The existence of interlayer shearing and crushing fracture zone exacerbates the seismic response of the tunnel, resulting in the fact that the failure zone near the interface develops further. After considering the contact effect, the stress and displacement response of the haunch is larger than that of the vault, so that the haunch of lining where the cracking damage first occurs is the weak part of lining structure under the action of earthquakes. The damage zone of the lining mainly distributes in the place where the soft rock passes through and interlayer contacts.

Abstract:The stone filling rate and the strength index of individual structure for gabion net are the key indexes in studying the ecological revetment technology of gabion net cushion. Through the indoor filling rate test of gabion net, the correlation between the minimum dry density and grain size gradation of rockfill is studied, and the rockfill gradation curve of a single structure for gabion net is determined by a large-scale direct shear test. Using NHRI-4000 high-performance direct shear apparatus with large contact surface, the shearing comparison tests of rockfill are carried out for the specimens with or without a gabion net under the same particle size and shear conditions. The test results show that the filling rate of gabion net increases with the increase of inferior diameter particles content. When the P< 40 content is 60%, combined with certain compaction measures, the crushed stones in gabion net can reach the best filling effect（the filling rate is 72%），which meets the design requirements for revetment projects. The gabion net structure is a composite composed of rockfill and the gabion net. The shear strength of rockfill with gabion net is much greater than that of rockfill without gabion net. The elastic modulus of gabion net is much higher than that of the rockfill. The “hoop” effect of the gabion net restricts particle movement and increases the overall stability of rockfill. In terms of deformation characteristics, except for the overall ductility of the gabion structure, its strain softening and hardening are basically consistent with the deformation characteristics of general coarse-grained soil.

Abstract:In order to analyze the distribution characteristics of the modulus field of semi-rigid asphalt pavement in the time domain and spatial domain and to study the effect of the annual change of the modulus field on the fatigue life of the structural layers, the asphalt layers were subdivided into several sub-layers with a thickness of 1 cm. The modulus field distribution in the asphalt layers was obtained by iterative calculations based on the Odemark method, and the fatigue life correction factors of structural layers were obtained based on the Miner linear fatigue damage model as well as the mechanical responses of the pavement structure under 456 conditions throughout the year. The results show that the modulus field varies significantly with time. At the speed of 70 km/h, the ratio of the annual maximum and minimum values of the modulus at each depth of the asphalt layer reaches 20.1~34.9, and the modulus with the pavement depths are not equal at the same time. The ratio of the modulus at the speed of 120km/h to that at 10 km/h is in the range of 1.12 ~ 2.28, which means that the vehicle speed has a significant effect on the modulus field. The influence of the annual change of the modulus field on the fatigue life of pavement structures should be considered. The fatigue life of the upper base calculated under the standard conditions at 20 ℃ and 10 Hz is conservative, while the fatigue life of the lower base is dangerous. The calculation results under the standard condition should be revised by the fatigue life correction factor when checking the fatigue life of the pavement structures.

Abstract:Based on the theory of evidence-based design, the usage behavior of air conditioners by different occupants in a case building is measured, and the typical running modes in different operating periods are put forward in this paper. By the Monte Carlo method, the annual operation sequence of air conditioners is simulated. Taking the annual average operation time of air conditioner as a checking parameter, the simulation results are compared with the actual measured results of different room types under cooling and heating conditions, separately. The error rate of the simulation results is lower than 5.5%, and thus the rationality and practicability of the simulation method are verified. The input of the stochastic operation sequence of air conditioners is helpful to work out the energy-saving and thermal environment optimization strategies based on the actual operating characteristics in building energy simulation.

Abstract:Existing occupancy prediction models for residential buildings often lack the reasonable consideration of resident diversity, which generally results in poor prediction accuracy and limited applicability. To address this issue, this study proposes a Resident-differentiated, Markov Chain Occupancy Prediction Model with Cluster (RMCPMC) analysis to fully consider the resident diversity so as to improve the model predictive performance. First, Spearman correlation analysis is employed to identify the correlation between different influencing factors (i.e. resident characteristics) and total occupancy duration. The identified correlation coefficients are used as the weights for corresponding factors, and cluster analysis is subsequently performed to classify residents into different groups. Finally, RMCPMC models are established for obtained clusters to predict the occupancy pattern. To validate the performance of the proposed model, it is applied to the UK Time Use Survey (TUS) dataset and its performance is compared with the conventional Markov Chain（MC） model. Compared with the conventional MC model, the Mean Absolute Error and the Root Mean Square Error of the prediction accuracy decrease by 20.57% and 15.35%, respectively. The results indicate a significant improvement in model prediction accuracy through reasonably considering resident diversity and their impacts on occupancy patterns.