Short-medium span steeleconcrete composite I-girder bridges are becoming more and more popular, because of the reduced construction time and costs. The light weight renders them particularly suitable also is seismic a...Short-medium span steeleconcrete composite I-girder bridges are becoming more and more popular, because of the reduced construction time and costs. The light weight renders them particularly suitable also is seismic areas, even though this advantage has not been yet adequately investigated. In fact, in case of seismic loading, significant tensile forces might be exhibited at the bottom flange of the steel girder, especially when monolithic connection between deck and pier is adopted, and the connection, conceived for sustaining prevailing hogging bending moments, could experience an excessive damage.With this aim, the cyclic behaviour of new pier-to-deck joints involving the use of concrete cross-beams(CCB) has been recently analysed within the European project(SEQBRI). This paper deals with the results of a wide experimental investigation of these new joints,performed with the aim of characterizing their hysteretic behaviour. Three different typologies were tested: one designed according to the German standard DIN-FB-104, generally utilized for gravity loads only, and other two types proposed for bridges located in low(VAR-1) and medium(VAR-2) seismicity. A series of displacement-imposed cyclic tests highlighted a good seismic behaviour of all the tested solutions. In particular, the DIN-FB-104 VAR C and VAR-2 displayed a similar global behaviour in terms of maximum force and displacement, but with a more pronounced crack development and buckling of steel girders of the first solution. The VAR-2 also avoids possible pull-out phenomena in the CCB thanks to the beneficial action of pre-stressing bars.A damage analysis of the proposed connections was finally performed in view of the application of the performance-based earthquake engineering methodology and the quantification the seismic performance of this bridge typology, which was among the aims of SEQBRI project.展开更多
The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the c...The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the cyclic modulus, the damping ratio, the accumulative deviatoric strain and the cyclic degradation parameter can be established if the cyclic stress ratio and initial shear stress ratio are used as normalized parameters. Thereby the reasonable method is supplied to measure and apply cyclic parameters of soft clay.展开更多
Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20&...Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20°C to 600°C for the steel tempered 2h at 350 °C, 460 °C, 560 °C and 600 °C. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10"2 strain rate, amax,A(T/2 decrease with the test temperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300°C to 600°C, but the maximal softening intensity occurs at room temperature. The strain rate influences notably the cyclic behaviour when T>500°C. The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.展开更多
In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone,at different confining pressures,using hollow cylinder specimens subjected to torsional monotonic a...In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone,at different confining pressures,using hollow cylinder specimens subjected to torsional monotonic and cyclic loading.Under monotonic loading a mixture of sand-ground rubber with 10% and 25% rubber content show more contraction behaviour than that observed in a pure sand specimen.Phase transformation point in these mixtures are located on a larger shear strain.As expected,the shear strength of specimens decreases with increase of ground rubber content.However,with increasing of effective confining pressure,the loss in shear strength of the mixture is decreased.In addition,a mixture with 25% ground rubber shows a smaller loss in shear strength compared to a mixture with 10% ground rubber mixture.Under cyclic loading mixtures with 10% and 25% ground rubber have similar liquefaction resistance,especially at confining pressures of 110 k Pa and 260 k Pa.Therefore,by using of the mixture with 25% ground rubber,a larger volume of scrap tires could be recycled.The addition of ground rubber to sand would affect the shear strain variation and excess pore water pressure trends,and this effect was further intensified with increasing ground rubber percentage.展开更多
基金the Research Fund for Coal and Steel of the European Community, within the SEQBRI project "Performance-based Earthquake Engineering Analysis of Short-medium Span Steeleconcrete Composite Bridges", Grant RFSR-CT-2012-00032
文摘Short-medium span steeleconcrete composite I-girder bridges are becoming more and more popular, because of the reduced construction time and costs. The light weight renders them particularly suitable also is seismic areas, even though this advantage has not been yet adequately investigated. In fact, in case of seismic loading, significant tensile forces might be exhibited at the bottom flange of the steel girder, especially when monolithic connection between deck and pier is adopted, and the connection, conceived for sustaining prevailing hogging bending moments, could experience an excessive damage.With this aim, the cyclic behaviour of new pier-to-deck joints involving the use of concrete cross-beams(CCB) has been recently analysed within the European project(SEQBRI). This paper deals with the results of a wide experimental investigation of these new joints,performed with the aim of characterizing their hysteretic behaviour. Three different typologies were tested: one designed according to the German standard DIN-FB-104, generally utilized for gravity loads only, and other two types proposed for bridges located in low(VAR-1) and medium(VAR-2) seismicity. A series of displacement-imposed cyclic tests highlighted a good seismic behaviour of all the tested solutions. In particular, the DIN-FB-104 VAR C and VAR-2 displayed a similar global behaviour in terms of maximum force and displacement, but with a more pronounced crack development and buckling of steel girders of the first solution. The VAR-2 also avoids possible pull-out phenomena in the CCB thanks to the beneficial action of pre-stressing bars.A damage analysis of the proposed connections was finally performed in view of the application of the performance-based earthquake engineering methodology and the quantification the seismic performance of this bridge typology, which was among the aims of SEQBRI project.
文摘The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the cyclic modulus, the damping ratio, the accumulative deviatoric strain and the cyclic degradation parameter can be established if the cyclic stress ratio and initial shear stress ratio are used as normalized parameters. Thereby the reasonable method is supplied to measure and apply cyclic parameters of soft clay.
文摘Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20°C to 600°C for the steel tempered 2h at 350 °C, 460 °C, 560 °C and 600 °C. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10"2 strain rate, amax,A(T/2 decrease with the test temperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300°C to 600°C, but the maximal softening intensity occurs at room temperature. The strain rate influences notably the cyclic behaviour when T>500°C. The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.
文摘In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone,at different confining pressures,using hollow cylinder specimens subjected to torsional monotonic and cyclic loading.Under monotonic loading a mixture of sand-ground rubber with 10% and 25% rubber content show more contraction behaviour than that observed in a pure sand specimen.Phase transformation point in these mixtures are located on a larger shear strain.As expected,the shear strength of specimens decreases with increase of ground rubber content.However,with increasing of effective confining pressure,the loss in shear strength of the mixture is decreased.In addition,a mixture with 25% ground rubber shows a smaller loss in shear strength compared to a mixture with 10% ground rubber mixture.Under cyclic loading mixtures with 10% and 25% ground rubber have similar liquefaction resistance,especially at confining pressures of 110 k Pa and 260 k Pa.Therefore,by using of the mixture with 25% ground rubber,a larger volume of scrap tires could be recycled.The addition of ground rubber to sand would affect the shear strain variation and excess pore water pressure trends,and this effect was further intensified with increasing ground rubber percentage.
