Abstract: In order to study effectiveness of measures taken to protect mountain bridge piers against rockfall in the upper reaches of the Minjiang River in Sichuan, based on non-linear explicit dynamic analysis, a numerical model was established to analyze the effectiveness using Holmquist–Johnson –Cook(HJC) damage constitutive model .And the numerical stability of calculation was tested in accordance with energy conservation principle. Four working conditions of bridge pier, namely ordinary non-protection, encryption stirrups, thickening plain concrete protection layer, being wrapped in steel tube, had been analyzed.Then by studying the response characteristics of the pier including the maximum damage depth of concrete, stress of longitudinal rebar, failure volume of concrete, different effectiveness of the three protective measures was compared . The rationality of analysis was verified by comparing with experimental results.The study shows that the HJC constitutive model can simulate the behavior of concrete under impact load well, and respectively protective effect of being wrapped in steel tube , thickening plain concrete protection layer, encryption stirrups, is weaker than the previous one.
Abstract: Based on the data from dynamic analysis of a 40m-span multi-box steel-concrete composite bridge and the difference value of its modal curvature before and after the structural damage, this paper detects the damage locations in steel-concrete composite bridge by modal curvature difference method (MCDM). Here we adopt the updated finite element model in last work as analytical model, taking concrete density and elastic modulus as updating parameters and modal frequency+MAC as reference data. The results indicate that the modal curvature difference method can well locate the damages in steel-concrete composite bridge, especially the damage in concrete. But the change rate of frequency as damage index is insensitive to the bridge damage and the method can’t be applied solely for practical.
Abstract: Though seismic isolation technology has been applied widely in civil engineering and proved effective, it is not used in large aqueduct. Shaking table test experiment was made on anti-seismic problem of a large aqueduct in South-to-north Water Transfer Project. First, a single span aqueduct model is designed and made. Then, several isolation bearings are designed for experiment. At last, the structure system dynamic responses were presented with isolation bearing mounted and not under different period earthquake loads for different working conditions. The results show that by using isolation bearings, which can play an important role in large aqueduct anti-seismic problem, the structure dynamic response can be reduced effectively.
Abstract: With the mining depth increasing, the effect of temperature on coal mine is outstanding with each passing day. In order to enhance the tunnel insulating layer heat insulation effect, thermal insulation glazed hollow bead concrete will be used in tunnel wall thermal insulation layer, the characteristics of thermal insulation glazed hollow bead concrete will be discussed and the appropriate mixture ratio and coefficient of heat conductivity will also be determined, as well as in the basis of reasonable theoretical analysis and derivation, prediction of the thermal insulation material of surrounding rock after exhaust heat will drop significantly, and it is proved that the thermal insulation glazed hollow bead concrete used in deep mine roadway can produce the benefit and have broad prospects.
Abstract: Lauric acid(LA) and capric acid(CA) were mixed into binary mixture, whose melting temperature was predicted with Schroder’s equation and tested in step cooling curve method. Then latent heat was tested by DSC, and T-history method was used to test thermal conductivity of binary mixtures, heating and cooling characteristics were studied through expanded perlite(EP) adsorption of binary mixtures. Results show that Schroder’s equation can be used to predict melting temperature of fatty acid, and binary mixture prepared of 6:4 molar ratio has a high latent heat and its temperature is within a range that meets indoor comfort temperature. Thermal conductivity and the heating and cooling characteristics of the mixtures reveals that the thermal conductivity of fatty acid phase change material(PCM) is low, which restricts its latent heat release rate.
Abstract: This paper investigated the high temperature mechanical properties of the hybrid fiber reinforced high performance concrete (HFHPC) and normal concrete (NC) .After being subjected to different elevated heating temperatures, two kinds of concretes have been tested for the compressive strength, splitting tensile strength and flexural strength of test specimen at room temperature and 200 °C,400 °C,600 °C,800 °C.Microstructure changes of concrete were also observed by using Scanning Electron Microscopy (SEM) after high temperature. The results show that the hybrid fiber can significantly increase mechanical properties of the concrete at room temperature and high temperature. SEM and XRD analysis shows that there is a permeable diffusion layer in the steel fiber surface because of solid state reaction in the Interfacial Transition Zone of steel fiber and concrete. This permeable diffusion layer is white, bright, serrated and mainly consist of FeSi2 and the complex hydrated calcium silicate. The compounds of this layer change the Interfacial Transition Zone structure, enhance bonding capacity of the steel fiber and matrix, and increase the high temperature mechanical properties of concrete.
Abstract: The aim of this paper is to systematically investigate the alkali activity of the aggregate selected from a stockyard, and examine its supression method, before pouring roller compacted concrete into the hydro project in Lechang gorge. Samples of natural sand, sandstone and limestone will be analysed through comprehensive petrographic method and accelerate mortar bar method. The results showed that natural sand is the aggregate without activity; sandstone core contains some wave shape with extinction characteristics of deformation quartz, because of active alkali-aggregate and the harm expansion of mortar, which is the aggregate with potentially harmful alkali-silicate reaction; wave shape and elastic deformation of the alkali in limestone are also the harmful element in concrete. The addition of level 1 and level 2 fly ash both has the ability to inhibit the reaction between alkali and silicate, and can control expansion rate of sandstone under 0.1 %.
Abstract: The ultra-high strength quenched 22MnB5 steel is researched in this paper, the intermediate frequency inverter & electric servo welding gun system is used to weld the sheets, experiments included of tensile-shear with synchronous electrical testing, microstructure of the material and fractures analysis and the Vickers-Hardness testing. The results point out that the maximum hardness is located at weld nugget, and the minimum hardness is appeared in heat affected zone (HAZ). Fracture is formed under the combined effects of shear stress and normal stress, the shear stress contributes to interfacial fracture, and leads to rupture. Non-uniformity of the microstructure caused by spot welding, changed the property of the material in nugget, stress-strain relationship of this area is nonlinear. The results also show that the conventional weld size guidance of 4√t is not sufficient to produce nugget pullout failure mode for 22MnB5 UHSS spot welds.
Abstract: Based on the new simple third-order shear deformation theory, the deflections and stresses of the simply surported symmetrical laminated composite plates are obtained by using the principle of virtual work .The solutions are compared with the solutions of three-dimensional elasticity theory, the first-order shear deformation theory and the Reddy’s higher order shear deformation theory . Results show that the presented new theory is more reliable, accurate, and cost-effective in computation than the first-order shear deformation theories and other simple higher-order shear deformation theories.
Abstract: The early-age concrete properties are the basis for structure nonlinear analyzed under construction structure period. But at present the study on early-age concrete is lagging behind which there is not suitabel theory. This paper takes early-age C20 concrete as an example to analysis the early-age concrete properties. According to the distribution characteristics of early-age C20 concrete experiment data in the octahedral stress space, using section function expression form, by the method of mathematical derivation and linear fitting, the failure criterion and the elastic yield criterion of early-age C20 concrete materials in the octahedral stress space are established. By comparison between failure criterion and elastic yield criterion of C20 concrete, the subsequent yield criterion could be derived based on the non-uniform isotropic strengthening criterion.