Abstract:Building structures will suffer different degrees of damage, or even progressive collapse when subjected to blast loading. The performance evaluation of building structures after the explosion is to analyze the residual resistance of the building structures considering the effects of blast damage, which is essential for selection of structural disposal and retrofitting techniques in the reconstruction stage. Explosion-proof research of building structures has become a popular research field during the past decades. Extensive studies have been conducted by numerous scholars, but most studies have focused on protective design and analysis before explosions. In order to promote in-depth investigation in this field and provide technical support for post-blast reconstruction, several key issues related with structural performance evaluation of buildings after explosion event were introduced and summarized in detail, and feasible repair and reinforcement techniques were also summarized and commented. After years of development, pressure-impulse curves and correlations for evaluating residual bearing capacity of blast-damaged structural components have been established. Methods for blast damage grading of buildings and affected areas division have been proposed. Besides, experience in reinforcement and repair of reinforced concrete structures using carbon fibre reinforced polymer has been continuously accumulated. However, current study on performance evaluation and post-blast repair of building structures is still in its infancy, and there is still a huge gap from perspective of engineering practice and application.

Abstract:In order to reduce the vibration impact of tunnel blasting on adjacent structures and improve the quality of tunnel blasting, a new method for evaluating and optimizing adjacent existing structures tunnel blasting schemes is proposed based on numerical simulation and nonlinear fuzzy analytic hierarchy process (FAHP). Firstly, the method uses Midas/GTS NX software to apply the equivalent blasting time-history load of the blasting plan to the excavation profile for dynamic response analysis. Combined with blasting vibration safety criterion, the vibration influence of simulated monitoring points is evaluated and vibration control parameters are optimized. Secondly, the blasting parameters that meet the vibration speed control standards are comprehensively evaluated for rationality using nonlinear FAHP, and the index parameters that affect the evaluation results are optimized. Finally, the rationality criteria of each stage met the blasting parameters determine the blasting scheme. In engineering applications, the solution optimized by this method reduces the maximum dose of the original solution by 25%, and the peak value of the simulated vibration velocity at the measuring point is therefore reduced by 41.2%. After implementation of the solution, the attenuation trend and peak size of the on-site monitoring and simulation results are basically the same. Effect of light blasting meets the relevant technical requirements of smooth blasting, which verifies the rationality of the evaluation criteria established at each stage of the method and the feasibility of program evaluation and optimization.

Abstract:Drop hammer test was carried out on five reinforced concrete (RC) beams which include one as-built RC beam, two reinforced with basalt fiber rebar (BRRC) and two reinforced basalt textile (BTRC) by using drop hammer impact testing machine. The damage process, impact force time-history curve, reaction force time-history curve, deformation time-history curve, impact force-deformation curve and reaction force-deformation curve were analyzed to study the impact characteristics of the RC beams reinforced with BTRC or BRRC. Results indicate that BTRC and BRRC can significantly increase the impact load-carrying capacity, thus decreasing the peak deformation and residual deformation of the beams. The reinforcement layouts and FRP amount have marginal influence on the deformation of the beams. Part of the kinematic energy of the drop hammer can be dissipated due to the fracture of fiber net or debonding of anchor end of fiber reinforcement, resulting in lower internal energy of the reinforced beams in comparison with that of the as-built RC beam.

Abstract:The effect of blast wave with different duration on building structure and protection engineering are obviously different, long duration blast wave is generally essential in experimental studies and numerical simulations. However, it is difficult to prolong the duration of the positive pressure in the practice experiment of studying the structural responses under long duration blast load. A multi-point delayed detonation model with multiple small charge TNT explosives in a long tube explosion chamber is established by computational fluid dynamics software AUTODYN. The propagation law of blast wave in the long tube is analyzed. On this basis, the influences of length of explosion chamber, the delay detonation time and the initiation sequence on the blast wave form are further investigated. The results show that, as the distance increases, the peak value of overpressure decreases and the duration of positive pressure increases. The overpressure time-history curve with full and continuous attenuation of the wave form can be obtained by selecting the delay detonation time rationally according to the amount of explosive and the length of the explosion chamber. Detonating from the bottom of the explosion chamber and controlling the delay detonation time interval reasonably can form a long-duration blast wave which is equivalent with the continuous attenuation produced by a large equivalent charge long distance explosion. The parameters such as the length of explosion chamber, amount of explosive and delay detonation time are adjusted repeatedly, and the detonation schemes of 100 ms explosion duration and 200 ms explosion duration are provided, providing technical support for design of long duration explosion simulation device.

Abstract:To investigate the enhancement effect of polyurea coating on the blast-resistance capacity of steel storage tanks, two ground explosion experiments were carried out in this study via the scale model steel tanks with polyurea coating sprayed inside and uncoated steel tanks, and the response data such as displacement time-history and residual deformation of the measuring point of the tanks were collected. Meanwhile, ALE fluid-solid coupling analysis method in LS-DYNA software was used to simulate the explosion response process of the tanks, and the influence of different coating connection settings, tank materials and coating thickness on the coating protection effect was investigated. The test results show that the inner spray polyurea coating can significantly reduce the maximum displacement and residual deformation of the tanks. The numerical simulation results show that the influence of different connection settings between the polyurea coating and the steel plate on the peak displacement of the tanks is negligible, while the influence on the residual displacement of the tanks is great. At the same time, with increase of steel yield strength, the displacement reduction ratio of polyurea coating decreases gradually. Increasing the coating thickness can reduce the deformation of tank. Howerer， the enhancement effect decreases continuously.

Abstract:To further elucidate the mechanical properties of fiber-reinforced concrete, carbon fiber was added to modify polymeric concrete, and the impact resistance of polymeric concrete reinforced by various contents of carbon fiber was studied. Impact compression test was carried out using a split Hopkinson pressure bar (SHPB) test system to investigate the influence of carbon fiber content on the impact resistance of polymeric concrete in terms of the stress-strain curve, strength, deformation characteristics and impact toughness. The results show that with continuous increases in carbon fiber content, the impact resistance of the polymeric concrete first increases and then decreases. When carbon fiber content increases to 0.2%, the dynamic compressive strength of the concrete, as well as the deformation capacity under high strain rate compression load, is at the maximum. Consequently, 0.2% is the optimal content of carbon fiber.

Abstract:In order to solve the problem that it is difficult to control the deflection in high liquid limit soil subgrade filling, according to the stiffness compensation theory and deflection equivalent principle, taking the deflection as the control objective, the deflection control method is proposed. In this method, the resilient modulus of lower embankment, the resilient modulus of each layer top surface in subgrade and the filling thickness were taken as the calculation parameters. The material modulus required for fillers in each layer was obtained by theoretical calculation, and the appropriate filler was selected according to laboratory test results. The filling scheme of subgrade deflection control can be determined, and it can be dynamically adjusted according to subgrade construction effect. Taking Hainan National Highway G360 as case history, the test road was paved according to the proposed method, and the field test was carried out. The results show that the subgrade top deflection meets the acceptance requirements and the discrepancy is marginal. This method can effectively control the subgrade deflection, and guide the construction and quality control of high liquid limit soil subgrade.

Abstract:The mesoscale mechanism of the interface behavior of different geomembranes was analyzed systematically combining with the mechanical model test of the Horizontal-Vertical (H-V) three-dimensional (3D) and traditional horizontal geomembrane by using the Particle Flow Code (PFC) based on the discrete element theory. The mesoscale characteristics such as the displacement variation， contact force distribution between the different kinds of geomembrane liners and soil particles, the stress distribution on the geomembrane, and the vertical stress distribution in the liner system were analyzed by comparing with the macroscopic mechanical characteristics obtained from the model test. The results show that the horizontal-vertical three-dimensional geomembrane provided similar friction as the traditional horizontal geomembrane. The vertical membrane of the H-V 3D geomembrane provided additional side friction and confine force. The vertical element not only confined the displacement and contact force of the partial transferring from the center to the two sides of the footing, but also provided the squeezed region between the H-V geomembrane and soil. This delayed the happening of the continuous slip surface and homogeneously distributed the stress in the H-V geomembrane lines. Therefore, the overall and uneven settlement of the H-V 3D geomembrane liner are smaller than the traditional under the same overburden load.

Abstract:The load-transfer modelling of soil mixing anchor is regarded as taking the coupling of dual-interface slip into account. It is essentially caused by the mobilization of bond strength for both the reinforcement-binder and the binder-matrix interfaces, and the impact of stress and strain conditions of materials adjacent to the interfaces on the propagation of interface shear stress. A recently developed load-transfer modelling framework of soil mixing anchor accounting for coupling of dual-interface slips was presented in this work based on interface characterization. This framework was established by integrating load-transfer method and shear displacement method, conventionally used in anchor behavior analysis, to solve for the straining of soil mixing anchor induced by interface shear stress in axial and radial directions, respectively. Laboratory testing including mechanical characterization of cemented soils, pullout tests on soil mixing anchor using elementary specimen and model specimen were carried out to calibrate the parameters in modeling and to validate the predictive capability for the pullout response of the presented modelling framework.

Abstract:The carbonaceous shale is widely distributed in the weak intercalated layer of high mine slopes in southwest China, the stability of which would be affected by the rain infiltration induced delegation of the carbonaceous shale. Carbonaceous shale can be regarded as a typical elastro-plastic material as ductile failure can be observed under complex loading conditions, which is similar with the over-consolidated clays. This paper developed a modified unified hardening model for carbonaceous shale to account for the strain-softening and dilatancy features. Besides, a β-yield function was adopted to better capture the negative dilatancy deformation. Moreover, the proposed model is able to account for the effect of the shape of yield locus on the model predictions, and the model performance can be then improved. Model predictions were compared with the drained triaxial test results of carbonaceous shales, form which a well-agreement was achieved, and consequently the model's performance was verified.

Abstract:Since the complex chemical substances in the waste permeate can affect the water-absorbing swelling performance of the sodium bentonite cushion, this paper studies the influence of different valences and concentrations of chlorine salt solutions on the swelling index of bentonite. At the same time, the influence of pH value and temperature on the swelling performance of bentonite was explored, and the bentonite treated with chlorine salt solution was characterized and analyzed by X-ray diffractometer and scanning electron microscope. The test results show that the high-valence and high-concentration chlorine salt solution inhibits the swelling performance of bentonite, and the swelling index is at least 5 mL/2 g. The monovalent low-concentration NaCl solution improves the swelling performance of bentonite, and the swelling index reaches a maximum of 56 mL/2 g. XRD test shows that the bentonite layer spacing after chlorine salt solution treatment decreases from 12.512 ? to 11.856 ?. SEM test analysis find that the morphology of bentonite in the high-valence chlorine salt solution changes from regular scaly to irregular flocculation. In 0.01 mol/L NaCl solution, 0.02 mol/L NaCl solution and 0.01 mol/L CaCl₂ solution, the gel state part of the bentonite in the process of absorbing water and swelling conforms to the Fickian diffusion model, it shows that the diffusion rate of water molecules in the solution is less than the relaxation rate of the gel state of bentonite. The gel part of bentonite in the swelling process of water absorption and swelling in chloride salt solutions of other concentrations conforms to the non-Fickian swelling process, and the diffusion rate of water molecules in the solution is approximately the same as the relaxation rate of the gel part of bentonite.

Abstract:Saturated sandy soil ground under earthquake is easy to reach liquefaction state which is of great threat. Soybean-urease induced carbonate precipitation (SICP) cement solidification was conducted using standard sand. Medium dense sand in the relative density of 30%, 40% and 50% was respectively solidified by the cementing fluid once, twice and three times, followed by a dynamic triaxial test under different CSR (ratio of cyclic shear stress to confining pressure). By analyzing dynamic strain, excess pore water pressure and the number of dynamic cycles, the effect of liquefaction resistance of the SICP-method in the treatment of saturated sand was evaluated. The results show that the pore pressure and strain development of the sample both show the characteristics of staged growth. The pore pressure will increase sharply to a certain level at the moment of loading, and then increase at a stable rate with the plastic strain until failed. The SICP-method can effectively enhance the liquefaction resistance of sandy soil and slow down the increasing trend of excess pore water pressure. And the more the number of treatments and the higher the compactness, the better the effect of liquefaction resistance.

Abstract:This paper takes Yunnan laterite as the research object, takes the wet-dry cycle as the control condition. The indoor unconfined compressive strength test is carried out considering the three influencing factors of wet-dry cycle times, initial moisture content and dry density. The relationship between the unconfined compressive strength of dehumidified laterite under wet-dry cycle and the wet-dry cycle times, initial moisture content and dry density is studied. The results show that the stress-strain relationship curve of the dehumidified laterite presents typical strain-softening characteristics after the wet-dry cycle. Compared with that before the wet-dry cycle, the strain softening characteristics of the stress-strain curve of the laterite after the wet-dry cycle are more obvious, and the unconfined compressive strength increases, and with the increase of the number of wet-dry cycles, the unconfined compressive strength decreases. Under different initial moisture content and dry density, the stress-strain curves of dehumidified laterite are strain softening. With the increase of initial moisture content, the unconfined compressive strength of laterite decreases and the corresponding peak strain increases before the wet-dry cycle, and after the wet-dry cycle, the unconfined compressive strength and the corresponding peak strain of dehumidified laterite increase. With the increase of dry density, the unconfined compressive strength of laterite increases before and after the wet-dry cycle, and the corresponding peak strain also increases.

Abstract:It has been gradually recognized of the existing of initial hydraulic gradient（i₀）during water seepage in soft clay and the necessity of considering continuous drainage boundary is being accepted more and more. However, the analytical solution of one-dimensional consolidation under variable load, considering both continuous drainage boundary condition and initial hydraulic gradient has rarely been reported. Based on the actual situation that the external load increases with time, taking variable load into account, a consolidation model considering both continuous drainage boundary and initial hydraulic gradient is established. The approximate analytical solution of the one-dimensional consolidation model is obtained by using Fourier transform and Laplace transform, from which, the moving law of dynamic boundary, dissipation law of excess pore water pressure as well as the growth characteristics of average consolidation degree are analyzed. The results show that, with the same loading rate, the influence of permeability of drainage surface under initial hydraulic gradient on consolidation behavior is just the same with that according to Darcy's law. The better the permeability is, the faster the dissipation rate of pore water pressure comes, and conversely, the worse the permeability is, the slower the dissipation rate of excess pore water pressure becomes. The effect of initial hydraulic gradient on consolidation behavior under continuous drainage boundary presents consistent with that under fully permeable boundary, of which the fact is, a larger value of i₀ may lead to, larger residual excess pore pressure when consolidation is completed, and smaller average degree of consolidation defined by pore pressure. On the other side, the smaller value of i₀ is, the shorter time it takes for the moving boundary reaching to the bottom of soil layer, the smaller the residual excess pore pressure becomes, and the larger the average degree of consolidation defined by pore pressure is. When under the same initial hydraulic gradient case and boundary drainage conditions, the peak value of excess pore water pressure decreases with the growth of loading time, and correspondingly takes longer time for the excess pore water pressure reaching to the peak value. However, the loading time has no influence on the residual value of excess pore water pressure and the final average cohesion defined by pore pressure.

Abstract:The dredged soil of waterway is increase day by day, and the utilization of dredged soild to make spray seeding matrix for slope greening can realize the resource utilization of dredged soil. The L₂₅(5³) orthogonal test design was adopted with dredged soil as the main test material, and different proportions of PAM, SAP and straw were added to the dredged soil for improvement, and tall fescue was planted for pot experiment. The physical structure characteristics, moisture characteristics, chemical properties and tall fescue emergence rate of each test group were measured. The effects of PAM, SAP and rice straw on the dredged soil were analyzed. Through the comprehensive evaluation of the principal component analysis method, the ratio of the green spraying substrate based on the dredged soil was obtained. The results show that adding SAP to the dredged soil can significantly improve the pore characteristics of the dredged soil, reduce the soil bulk density, and increase the water holding capacity of the dredged soil; an appropriate amount of PAM can increase the retention of ammonium nitrogen in the dredged soil and promote tall fescue seeds. Excessive PAM will inhibit the germination of tall fescue seeds; straw can significantly increase the nutrient content of the dredged soil and reduce the pH value of the dredged soil; the optimal ratio of the substrate is 6 g of sap, 0.5 g of PAM and 35 g of straw per kg of dredged soil.

Abstract:The vulnerability assessment of diversion dike was studied in order to provide an effective method for the determination of the rank of prevention and control engineering and the assessment of disaster prevention and mitigation capability of diversion. By taking Queer Gully diversion dike of Yalu Road suffered debris flow disaster as engineering background, referring to previous research results on vulnerability, the concept of vulnerability of diversion dike has been proposed in this paper. According to the characteristics of debris flow to cause disaster and the characteristics of the diversion dike bearing the disaster, the engineering vulnerability evaluation method of diversion dike suffering from debris flow is established, and the combination hierarchy method is used to solve the problem of index weight. The established evaluation method is applied to assess the diversion dike of Queer Gully and the result is highly vulnerable, which shows that the overall operation of the project in the study area is poor and the protection ability is weak. It is necessary to take measures in time to ensure its normal service. The evaluation results are consistent with the field investigation and quantitative calculation results, which verifies the feasibility of the method.

Abstract:Energy pile combines the ground source heat pump system with the traditional pile foundation, which has the advantages of high heat exchange efficiency, less space occupation and low cost. This paper summarizes the latest research results on heat transfer and bearing performance of energy piles at home and abroad, and analyzes the influencing factors and mechanism of heat transfer performance, structural response under thermal-force coupling and numerical models of heat transfer and structural response of energy piles. Based on this basis, the next research suggestions and prospect of energy pile are put forward. The analysis indicates that the largest heat exchange area of the spiral tube and the best heat exchange efficiency; under the action of cyclic shear at the pile-soil interface, the lateral friction resistance attenuates, which continuously weakens the bearing capacity of the energy piles. Moreover, the uneven refrigeration/heating demand in one cycle may cause the surface temperature imbalance, thus affecting the heat exchange efficiency. Therefore, the optimized design of energy piles and the reliability of long-term service will be the focus of future research.

Abstract:Modal parameters reflect structural dynamic properties, and damage indexes based on modal parameters can reflect changes in structural dynamic properties and can be used for bridge structural damage identification. There are many damage indexes composed of modal parameters, and each damage index identifies damage by its own changes, but it is difficult to quantify and compare the identification effect of different damage indexes by a unified standard. In view of the hinge joint damage of hollow slab bridge, this paper proposes a consistency quantification index to quantitatively describe the indication effect of damage indexes for hinge joint damage of hollow slab bridge, which is convenient for the comparison and application of various damage indexes. First, according to the damage indexes of moda parameters, the consistency quantification indexes are constructed to quantitatively describe the identification effect of different damage indexes. Then, a solid model of hollow slab bridge and hinge joint damage is established based on ANSYS, the damage conditions at three different hinge joint locations are simulated, and six different damage levels are set for each damage location. Finally, the consistency quantification index is applied to compare the identification effects of each damage index, and the change law of the identification effect of each damage index under different damage conditions is summarized. The analysis shows that the consistency quantification index can quantitatively describe the identification effect of different damage indexes under different damage conditions.

Abstract:The stress increment of the in vitro prestressing tendons is of critical importance in the theory of waveform steel web girder bridges. Among the existing stress increment calculation methods, there are relatively few methods suitable for corrugated steel web girder bridges, especially considering the slip effect of prestressed tendons. In order to study the calculation formula for the external prestressed tendon stress increment of composite beams with corrugated steel webs, this paper consider the influence of the slip effect between the external prestressed tendons and the concrete at the steering block. By analyzing the geometric relationship between the deformation of the prestressed tendons and the overall deformation of the structure, the calculation formula of stress increment under symmetrical loads is deduced. Combined with the existing test data, an entity model was established using Ansys, and the nonlinear spring unit Combin39 was used to realize the slip effect of the prestressed tendons; the calculated value obtained was compared with the experimental value and the model value for analysis. The results show that: 1) The calculated value of the deduced stress increment formula is in good agreement with the test value of the corrugated steel web composite beam, which verifies the applicability of this method.2) When considering the influence of the slip effect, the overall deflection and stress increment of the structure increase, and the bearing capacity decreases.

Abstract:The fabricated H-shaped steel web opening energy dissipation support is a new type of energy-consuming support composed of web opening H-shaped steel and force transmission channel steel connected by bolts, which can effectively avoid the instability of supporting members. In order to study the energy dissipation capacity and failure mechanism of this support, low-cycle reciprocating loading tests and finite element simulation analysis were performed on the specimens. The results show that the fabricated H-shaped steel web opening energy dissipation support has a full hysteresis curve, strong energy dissipation capacity and good deformability. Under the action of axial load, the test piece mainly relies on the short columns between the holes of the open web to enter the plastic energy dissipation. The ends of the short columns between the holes are the weak parts,which first enters the plastic during the loading process, and the fracture occurs first. With the deepening of loading, the plastic area in the middle part of the short column between holes becomes large and large. During the loading process, the bolts and channel steel are always in an elastic state. The specimen is eventually damaged due to the fracture of the short column between the holes. When the length of H-shaped steel energy dissipating web is the same, the wider the web width, the greater the height-width ratio of the short column between the holes, the smaller the bearing capacity and stiffness of the energy dissipation support, the better the deformation ability, and the short column height-width ratio between the holes in the range of 5-8 is more reasonable. It is recommended that the shortest distance from the arc at the end of the oblong hole to the center of the bolt hole be controlled between 1.2d₀ and 1.5d₀. Changing the arc radius of the oblong hole has little effect on the mechanical properties of the support. When the width of the H-beam web is the same, the greater the web length, the greater the bearing capacity and stiffness. The design method and ultimate bearing capacity formula of fabricated H-shaped steel web opening energy dissipation support are give.

Abstract:A GFRP-RPC composite beam bridge for double deck traffic is designed. The bridge is composed of two GFRP trusses and ribbed plates, which are connected by glue bolts. The composite beam bridge is formed by pouring self compacting RPC concrete. The scale model (1:8) of composite beam bridge is tested and analyzed by quasi-static loading test and finite element method, and its elastic performance is studied. The results show that: After pouring RPC, the stiffness of the beam bridge increases about 2.6 times, which indicates that the combination of GFRP and concrete is conducive to the reasonable stress of the structure, and the deformation of the beam bridge increases about 10% when the lower part is loaded, which is unfavorable to the structure; the chord stress accords with the assumption of plane section, and the stress of composite structure is more reasonable; the upper and lover chords are in the force state of compression bending and tensile bending respectively, when the upper and lower chords are loaded, the tensile stress of the lower chords is about 1.5 and 2.5 times of that of the upper chords, and the lower chords are weak chords; when the diagonal web member is in tension, the straight web member is basically in compression state, and the loading mode of up and down affects the stress form of the straight web member. The design with larger local tensile and compressive stress should be considered for the lower bearing; the concrete on the side of the top plate is compressed, while the concrete on the side of the bottom plate is tensioned, indicating that the setting of the web member is conducive to the uniform stress of the slab concrete.

Abstract:Brick and stone are widely used as building material in the world. Masonry structure composed of brick, stone and mortar has low tensile and shear strength, insufficient seismic resistance, and is prone to damage or even collapse under earthquake action. Therefore, strengthening is needed to improve the mechanical properties of masonry structure. Due to high tensile strength, light weight, easy installation and corrosion resistance, fiber reinforced polymer(FRP) has been widely used to strengthen the masonry structure. Near-surface mounted FRP(NSM-FRP) has more advantages in strengthening historic masonry buildings because it has little influence on the weight and appearance of the structures. In this paper, the research progress of masonry structures strengthened with NSM-FRP is summarized, and the development of masonry structures strengthened with NSM-FRP is prospected.

Abstract: