Abstract:Reinforced concrete（RC） frame beams will undergo large deformation stages in the process of collapse. In order to study the influence of bond-slip effect of reinforcing bars on the progressive collapse resistance of RC frame beams, especially in the suspension stage, the beam-column joint element was used to numerically validate the experimental results of a restrained beam substructure on the basis of OpenSees nonlinear finite element analysis platform and a set of parameters in the bond-slip model of reinforcing bars. The analysis results effectively reflect the elastic and plastic deformation, arch-compression effect and mechanical characteristics of the suspension stage of the structure, which are in good agreement with the experimental results. On the basis of the above analysis results, further simulations were conducted in a single-story plane RC frame structure and a three-story plane RC frame structure. In addition, the effects of number of stories and spans on the collapse-resistant performance of the plane frame structure were investigated. The force mechanism was also analyzed.

Abstract:To analyze the vertical collapse robustness of isolated structures, considering double randomness of structure and seismic wave, a random robustness index was proposed based on the reliability theory. Through analyzing and contrasting the random robustness indexes of different randomness, the influence of randomness on the vertical progressive collapse robustness of isolated structures was revealed. In addition, the influence of PGA on the vertical progressive collapse robustness of isolated structures was studied. And the following results were obtained: The random robustness index can be effectively used for quantitative evaluation of the vertical progressive collapse ability of isolated structures. If only considering random ness of structures or seismic wave, it may overestimate the ability of the structure. The robustness of the isolation structure decreases with the increase of PGA. Under strong seismic, isolation structures are more prone to vertical progressive collapse.

Abstract:For the bearing capacity design of RC crane beams, the crane load action partial coefficients are determined by engineering experience for lacking the probability models of the crane load and combination actions. So the design reliability level of the beams is unknown. For the bending and shearing capacity design method of the RC crane beams, the probability model and the statistical results of crane load were introduced, and the design reliability indicators were calibrated with the basic variables non-dimension. The design reliability indicators were 5.79 and 5.87 respectively for the one and two-way bending design, and 5.31 for the oblique section shear design. The reliability index was high and conservative for the bearing capacity design of the crane beams. It quantitatively analyzed the different influence of each factors on the reliability of the crane beams, and gave some reasonable suggestions for the design and maintenance.

Abstract:In order to investigate the in-plane stiffness and bearing capacity of cold-formed thin-walled steel composite floor, a floor model was established through ABAQUS software and verified by the in-plane cyclic loading test results. Further, the effect of different parameters on the in-plane stiffness and bearing capacity of the floor model was studied. The results showed that the influence of the joist size，the opening area and spacing of joist web, flat strap and blocking layout on the in-plane stiffness and bearing capacity of composite floors was insignificant. The in-plane stiffness and bearing capacity of composite floors can be improved by decreasing the screw spacing and the length-to-width ratio of floor. The change of slab thickness in the range of 20~40 mm had a certain effect on the in-plane stiffness and bearing capacity of composite floors. Based on the failure modes and mechanical behavior of composite floors, the ultimate bearing capacity of floor can be estimated by the load-carrying capacity of the single self-tapping screw and the number of self-tapping screws connected on both sides of floor. The calculation method for in-plane stiffness of composite floors was established based on the degenerate quadri-polyline model, which provided a theoretical basis for engineering design and application of thin-walled steel floors.

Abstract:To study the mechanical properties of Q235 steel frame girder in different corrosion degrees, low frequency cyclic loading test on steel frame girders of six trusses in different corrosion degrees was carried out on the basis of seismic performance test of steel frame girders. The hysteresis curve, skeleton curve and rigidity degeneration rule were obtained based on the text results. The effect of different corrosion degrees on seismic performance of steel frame beams was acquired by analyzing text data. The cyclic degradation index was introduced, and the characteristic point (yield point, limit point and breaking-down point) formula with cumulative damage effect was fitted. The hysteretic rule applied to rusted steel frame girders was put forward，and then the restoring force model of steel frame with the consideration of corrosive action was established. The comparison between the simulation curve and text curve for the samples of three trusses was performed, and the comparison between the simulation curve and finite element analysis for other samples of three trusses was implemented. The comparison results show that the restoring force model has high precision and better tally, the established restoring force model can provide theoretical basis for the analysis on steel frame girders in different degree of corrosion and lay a foundation for elastic-plastic analysis steel frame girder in different degree of corrosion

Abstract:To reveal detailedly the strength and stiffness characteristics of biaxial warp-knitted fabrics，which contain multi-layered composite structures，high performance biaxial warp-knitted fabric Seaman PVDF8028 was taken as the research object，and seven tensile tests of off-axis angles with a gradient of 15° were performed. Based on the obtained stress-strain relationship, strength and deformation data of different angles, the relationship between elastic modulus and strain was deduced, and its evolution was analyzed minutely. The results show that biaxal warp-knitted fabric PVDF8028 is a typical nonlinear and anisotropic material. Stiffness characteristics of different angles present obvious differences and evolve regularly. In the whole tested strain range, the stress-strain relationship and elastic modulus-strain relationship exhibit three distinct sections, including the initial linear elastic section，strain hardening section, and stress hardening section. Additionally，there is a “W” shaped relationship between tensile strength and off-axis angles, which is different from the “U” shaped relationship of Tsai-Hill strength criterion. The results can provide some useful references for strength prediction and deformation analysis of biaxial warp-knitted fabrics, as well as the design and analysis of membrane structures.

Abstract:In order to study the bearing capacity of the occlusal part of interlocking compressed earth block (ICEB) masonry under shear-compression composite action, shear-compression composite test was performed on 18 ICEB masonry specimens under various vertical loads. The mechanical properties, failure mechanism and correlation between compression and shear stress were investigated. The results show that the interlocking of the brick can play a pinning effect，showing a better shear capacity. The main causes of the three types of failure mode of masonry were analyzed and summarized, and shear-compression strength formula was proposed compared with the formula by maximum tensile theory. It is found that the shear strength of the masonry calculated by the maximum tensile stress failure theory is safe and reliable, but conservative. The results of the study can provide the experimental results and theoretical basis for further research and design, as well as the application of the masonry mechanical properties.

Abstract:Considering the three dimensional unsteady compressible turbulent characteristics of the flow field when a high-speed train (HST) enters the tunnel, a refined 3D CFD numerical model of tunnel-train-air was built to analyze the transient flow field structure and pressure distribution in the process of HST entering into tunnel under the conditions of crosswind and without crosswind comparatively. The transient change characteristics of the five aerodynamic loads (i.e. aerodynamic side force, lift force, rolling moment, yawing moment and nodding moment) of the train body under crosswind and the influence of wind and vehicle speeds on its maximum variation amplitudes were studied. The main results can be summarized as follow: When a HST enters into tunnel under crosswind environment, flow field structure and pressure distribution on both sides of the train body outside the tunnel have an obvious dissimilarity, and it's smaller inside the tunnel, which causes the sudden change of the train body pressure difference before and after the HST entering the tunnel. In the process of HST entering the tunnel, there are transient change effects in various aerodynamic loads of the train body, and the tail carriage presents capsizing，“jumping”，“snake-like” swing and “nodding” behavior at the same time. The change of the wind speed has a significant effect on the variation amplitude of the tail carriage yawing moment, while the change of the train speed has a significant effect on the variation amplitude of the head carriage yawing moment.

Abstract:To study the effect of actual operational condition on the fatigue damage of lateral connection structure for fabricated concrete girder bridges, a fatigue damage assessment framework for the steel plate connection structure of this bridge type was presented based on linear Miner cumulative damage criterion. The influence rules of dynamic impact effects from stochastic traffic, traffic condition and progressive deterioration of bridge deck roughness on the fatigue damage of lateral connections were studied through an actual bridge example. The results show that the fatigue life of the transversal beam is obviously underestimated when considering the vehicular impact effect under Chinese specification compared with that of stochastic traffic with 95% confidence level. Traffic condition also has a significant influence on the fatigue damage, and the structural fatigue cumulative damage under intensive traffic condition is smaller than that of general one. Progressive deterioration of bridge deck condition has an obvious effect on the fatigue damage. The fatigue life of lateral connection decreased by 60.01% and 34.88% under general and intensive traffic conditions considering bridge deck degradation. When designing a new bridge, the impact factors from specification and general traffic condition should be considered in the fatigue calculation for lateral connection structure. It is suggested that considering the influence of stochastic traffic dynamic impact，operation traffic status and progressive deterioration of bridge deck was necessary when evaluating lateral connection fatigue damage for the existing bridges.

Abstract:This paper regarded the force and deformation characteristics of geocell reinforcement，as a small deflection of an elastic circular thin plate. Taking into account the deformation compatibility between the geocell and pile-soil reinforced area，horizontal-vertical coupling deformation of the geocell-reinforced mattress，as well as the horizontal friction effect of the top and bottom plate-soil interface，the governing differential equations of the geocell flexural deformation were established under symmetric load. The analytic expressions of vertical and horizontal displacement were constructed by the Bessel complex-variable functions，from which the calculation formulas were deduced for pile-soil stress ratio below the net, settlement and differential pile-soil settlement. To verify this method, an existing case was employed. Finally，the effects of various factors were discussed, which show that it is beneficial to modify the pile-soil stress ratio below the net and to reduce the embankment settlement by changing the composite elastic modulus, the pile-soil stiffness ratio and horizontal frictional coefficient ratio to some extent.

Abstract:The influence of the length of prestressed reinforcement on the distribution of horizontal earth pressure and the prestress mechanism of prestressed reinforcement were studied by using scale model test and three-dimensional finite element simulation. The study showed that the value and distribution of the earth pressure on the panel were independent on the length of prestressed reinforcement. With the action of prestress, the horizontal earth pressure value of prestressed reinforced layer was large at ends and small in the middle along the direction of reinforcement. The increase range of the pressure at middle of the layer decreased with the increase of the length of the prestressed reinforcement. With the increase of prestress, the horizontal stress value of filler can exceed the vertical stress value and coincide with the large principal stress value completely. The average failure ratio coefficient of filler decreased with the increase of prestress, and the stress level of filler presented an optimal safety state for the filler under the action of prestress.

Abstract:In order to solve the punch-through problem of the Jack-up platform in the soft clay area such as the South China Sea, the punch-through phenomenon of the Jack-up platform when penetrating in clay was verified by experiment, and the mechanism and solution for the punch-through were explored. In this paper, an experimental set for single leg penetration test under discontinuous loading was designed to simulate the preloading process of a real Jack-up platform with large spud-can, and a series experiments were performed to investigate the effect of the water jetting process for eliminating the risk of punch-through. The results show that the punch-through can occur in the clay layer under discontinuous loading, and the risk of the punch-through can be mitigated by reducing the loading rate or performing water jetting process. Thus, the present investigation is beneficial for safety operation of the jack-up platform in practice.

Abstract:To analyze the settlement of bearing structure of the cement concrete pavement of highway under traffic loads, pavement structure was regarded as a viscoelastic foundation beam. The interfacial friction effect between the foundation beam and soil below was introduced into the Kelvin foundation beam model. Based on the Kelvin model and taking the interfacial friction forces into consideration, an analytical solution of settlement for the viscoelastic foundation beam under traffic load was proposed by using trigonometric series, Laplace - Fourier transform and inverse transformation. Influence parameter study was presented to quantify the effects of various factors, such as the interfacial friction of subgrade and pavement, velocity of moving load, pavement structure stiffness, the coefficient of vertical soil reaction and viscous damping of subgrade. The results show that the settlement of pavement increases with the decrease of moving load speed，deformation decreases with the increase of viscous damping or subgrade stiffness, and deformation decreases with the increase of pavement stiffness or height of pavement structure. Meanwhile, the wave phenomenon of pavement decreases with the increase of the pavement structure stiffness.

Abstract:This paper focused on the improvement of the current pile-supported embankment calculation model from three aspects: soil arching effect，geotextile deformation and pile-soil load transfer due to the deficiency of the embankment- reinforcement- composite pile foundation interaction model. Firstly，considering the influence of foundation stratification, buried depth and overlying load on pile-soil load transfer，the vertical deformation function of pile and soil was derived. Secondly, the empirical model of the membrane effect was introduced to analyze the influence of the lateral deformation of the embankment and the foundation on the tensile force of the geotextile. Finally, based on the soil column model, this paper analyzed the relationship between load distribution and differential settlement at the bottom of the embankment in consideration of the influence of relative displacement on the interface friction. On the basis of the above work, the improved model of embankment, geotextile, pile and inter-pile soil interaction was established on the premise of the equal relationship between pile-soil settlement and load distribution，from which the calculation method was deduced of pile-soil stress ratio of pile-net composite foundation under the embankment. The rationality of the method mentioned was validated by practicable engineering examples.

Abstract:The shear wave velocity of slag-cement-bentonite （S-CB） samples by piezoelectric bending element was tested to study the influence of cementitious material content，slag substitution rate and age on shear wave velocity （Vs） and shear modulus （G0）. The test results showed that, with the increase of age, decrease of slag substitution rate and increase of content of cementitious material, shear wave velocity （Vs） of S-CB increased. In the tests, Vs of S-CB is significantly lower than that of cemented clay at the same age. This is mainly due to the higher water content of S-CB than cemented clay. It is observed that the development tendency of S-CB is closely related to the slag substitution rate of cementitious material, and it is not obviously correlated with the content of cementitious material. Based on the test results, the prediction formula for shear modulus of cement-bentonite with age was proposed. If the normalized formula of S-CB with one kind of cementitious material content is obtained by test, the shear modulus of S-CB with other composite cementitious materials content and the same slag replacement rate can be speculated.