Abstract:To study the progressive collapse performance of fully assembled concrete frame structures, based on the static and dynamic tests of two fully assembled specimens (PC1 and PC2) and one cast-in-situ specimen (RC), three sub-structural macro-models were established by using OpenSees finite element software, and the results of model verification were compared with test results. Two seven-story fully assembled frame structures (PC1-Frame, PC2-Frame) and a cast-in-situ frame (RC-Frame) were designed. Progressive collapse analysis was conducted for the residual structure of which middle and exterior column at the bottom were removed by using column removal method, respectively. The results showed that removing exterior columns was more easier to cause collapse than removing middle columns, and the displacement time history curve amplitude of failure point of PC1-Frame was larger than that of RC-Frame; The ultimate bearing capacity of PC1-Frame and PC2-Frame was 30% and 20.5% lower than that of RC-Frame in the case of removing mid-column, 26.9% and 22.3% lower in the case of removing exterior -column, respectively. Finally, the validity of the simplified non-linear dynamic analysis method based on the principle of equal energy was verified, and it is found that the dynamic amplification factor decreased with the structure entering the plastic stage.

Abstract:Current Chinese design codes have not calibrated the reliable index of shear capacity of shear wall. In order to study the reliability level of shear bearing capacity of reinforced concrete shear wall, this paper collected and selected 74 shear wall specimens that are consistent with the ones based on the shear formulas of shear wall in terms of section type, concrete type, reinforcement type and failure mode. By analyzing the test and calculated values of shear capacity for the specimens, the statistical parameters of calculation model uncertainty were obtained, and then the statistical parameters and probability distribution types of resistance were obtained. The checking point method considering the probability distribution of basic variables was used to calculate the reliability index. The results show that the reliability index of shear capacity of shear wall in current code is lower than the target reliability index 3.7. Load effect ratio, shear span ratio, axial pressure, reinforcement ratio and concrete strength grade have little influence on the reliability index. The wind-to-dead load ratio has great influence on the reliability index. The reliability index of distributed rebar with HPB300 is small under the same conditions. In order to ensure that the reliability index of shear capacity of shear wall meets the requirements of target reliability index, a bearing capacity adjustment coefficient of 0.95 is introduced to modify the current calculation formula. The average value of reliable index in the revised formula is 3.738.

Abstract:This paper is to analyze the stability with anti-slide pile reinforced slope and determine the critical failure surface, optimal pile position and pile length. Firstly, a numerical model of slope was established based on the finite element limit analysis software OptumG2. Secondly, two cases were employed to verify the rationality of the numerical analysis. Then, the differences between two different analysis types (gravity multiplier and strength reduction) of OptumG2 were discussed based on the comparison results and the safety factor based on the strength reduction limit analysis was biased towards safety. Finally, the effects of slope angle and soil shear strength (internal friction angle and cohesion) on safety factor, optimal pile position and pile length were investigated. In addition, the variation law of the critical failure surface of anti-slide pile reinforced slope was analyzed and the fitting equation of safety factor was derived based on the parametric study results. Some regular conclusions were presented, and four common sliding surface forms and their forming conditions were summarized. The results can provide reference for the subsequent theoretical research of slope stability analysis.

Abstract:In order to analyze the failure mode and stability of block under complex surrounding rock，a numerical analysis method for block failure was proposed based on continuum mechanics. Firstly，based on the existing geologic plane modeling method of element reconstruction and node separation method，the grid-based block identification was carried out. Then，the expressions of contact force under various contact states were derived based on the explicit contact force method，and the contact analysis method of block and surrounding rock was proposed. Afterwards，the safety factor of block was calculated based on the strength reduction method. The numerical method can simultaneously calculate the deformation of surrounding rock and the deformation of block. A simple example of a double-plane sliding block also demonstrated that，under certain conditions，the numerical results are consistent with the results of rigid body limit equilibrium method. Finally，combined with a tunnel engineering across a fault，the stability of surrounding rock and blocks was analyzed. The results indicate that the numerical method effectively reflects the influences of stress and deformation form surrounding rock when evaluating the block stability. After failure of the key blocks，the potentially dangerous blocks occur in large deformation and the safety factor is low. This numerical method provides an effective analysis method for the stability evaluation of tunnel blocks under complex geological conditions.

Abstract:In order to evaluate the surface stability during the development of underground holes, the process of surface displacement change during the development of the hole is discretized, and the criterion of surface collapse analysis is established according to the catastrophe theory. The validity of the criterion is preliminarily verified by combining the consistency of the cover instability，the simultaneity of instability, the plasticity penetration criterion and the plastic zone cloud map analysis. The above method is used to quantify the determination process of the surface instability so as to obtain the critical hole radius and surface collapse range. The relationship among the critical thickness of the cover layer, internal friction angle, cohesion, elastic modulus and Poisson's ratio is discussed. The results show that the thickness of the cover layer, the internal friction angle and cohesion can be fitted into a linear relationship with good correlation. The thickness of the cover layer is not sensitive to Poisson's ratio and elastic modulus. The criterion of surface instability based on catastrophe theory can provide a useful reference for the study of surface stability above the developed pore.

Abstract:The force analysis of piles under complex loads is one of the important contents in the design and calculation of pile foundation. In this paper, a energy control differential equation of three-dimensional pile-soil system is established according to the energy principle, considering the special case of tilting and eccentricity of pile loads as well as the layering characteristics of soils. On this basis, combined with different boundary conditions of pile and displacement conditions of pile and soil, a semi-analytical solution of pile displacement under inclined and eccentric loads is obtained based on finite difference method. The solution can fully consider the P-Δ amplification effect of pile deformation. Then, an indoor model loading test of single pile under inclined eccentric load is carried out to validate the solution. The comparison results show that the theoretical solution and the experimental test results are in good agreement, and the P-Δ amplification effect of the pile deformation under combined load is well simulated. Finally, the influencing factors affecting the P-Δ amplification effect of the piles are analyzed. The results show that the relative magnitude of the axial and lateral loads, the length of the free section of the pile, the stiffness of the pile and the stiffness of the surface soil all have a significant impact on the P-Δ amplification effect.

Abstract:In order to study the longitudinal dynamic response of the sand-filled nodular pipe pile as a new type of composite pile foundation, the bi-directional inhomogeneity of medium around the pile is firstly simulated by multi-zone plane strain model and the complex stiffness transfer method. Then, considering the lateral inertia effect and the damping of the pile body，the analytical solutions of impedance and semi-analytical solutions of velocity response of the pile head are obtained by Laplace Transformation and Inverse Laplace Transformation. The validity of these solutions is verified by the existing analytical solutions afterwards. Finally, it is found that the properties of the sand-filled layer have great influence on the dynamic stiffness and damping by parameter influencing analysis. The proposed model and obtained conclusions provide a theoretical basis for the design, construction and low strain detection of the sand-filled nodular pipe pile.

Abstract:In order to study the shear performance of polypropylene fiber concrete beams under monotonic loading，nine polypropylene fiber concrete beams were constructed and tested considering the effect of fiber content, shear span ratio, stirrup ratio and concrete strength grade. According to the failure mode, load-deflection curve and shear bearing capacity measured by the test, the influence of different parameters on the failure mode, shear bearing capacity, stiffness and shear ductility of the specimen was analyzed. The results show that the fiber between concrete cracks can delay the development of cracks, reduce the inclination angle of diagonal cracks, and improve the shear performance of structures. The polypropylene fiber concrete beams had higher capacity, stiffness and shear ductility than the ordinary concrete beams. Based on the modified compression field theory，and considering the contribution of tensile strength of fiber concrete to the shear bearing capacity, a calculation formula of shear capacity for polypropylene fiber concrete beam was established and verified by the test data of the shear capacity for 26 sets of polypropylene fiber concrete beams. The mean，standard deviation and coefficient of variation of the calculated-to-tested value were 1.049, 0.107 and 0.102, respectively，which indicated that these two results were in good agreement.

Abstract:Taking the Second Bridge of Yueyang Dongting Lake as engineering background，wind tunnel test method was used to study the three-component force coefficients in horizontal direction and the drag coefficients along the bridge axis of a plate-truss composite stiffening girder（PTCSG） in service and construction stages under different attacks and yaw angles，respectively. The influence of compensation model with different length was also investigated. The expressions of longitudinal drag coefficients of the PTCSG in service and construction stage with yaw angles were fitted，respectively，based on the experimental data. The results show that，when the wind tunnel tests of longitudinal drag coefficients of PTCSG under skew wind are carried out，the accuracy requirements can be basically satisfied when the length of the compensation section model is about 30% of that of the force measurement model. The longitudinal drag coefficients of PTCSG increase first and then decrease with the increase of yaw angles，which reach the maximum at about 50° ~ 55° yaw angles. The drag coefficients in horizontal direction of PTCSG increase first and then decrease with the increasing yaw angles，reaching the maximum when yaw angle is about 5° ~ 10°，and the value is about 1.05 times the drag coefficient with 0° yaw angle.

Abstract:To optimize the shape of square cylinder, Large-eddy Simulation is applied in the study of flow past square cylinders at a high Reynolds Number Re of 22 000. The cylinders have various combinations of sharp/round corners and flat/concave/bulging edges. Particularly，the aerodynamic characteristics of cylinders with a combination of round corners and bulge edges are studied with the changing curvature radius of the edge. Besides, the flow patterns are discussed in detail to reveal the mechanism of aerodynamic optimization. The results show that corner and side modifications can significantly alter the structure of flow around cylinders and influence the aerodynamic performance of cylinders. In comparison to the concave modification, the round modification and bulge modification can reduce the aerodynamic forces, overall surface pressures and vortex shedding intensity of cylinders considerably. Among cylinders with various combinations of shape modifications, the cylinder with rounded corner and bulge edge leads to a thinner shear layer and a smaller recirculation region at the upper and lower sides of cylinder. Besides，it also causes a longer wake length, a weaker vortex shedding and reduces the aerodynamic forces. A further research shows that the aerodynamics of the round-bulge cylinder is extremely sensitive to the curvature radius of the edge. There exists an optimal curvature radius, which results in the lowest aerodynamic forces，the highest Strouhal number, the longest length of the recirculation region, and the weakest vortex shedding intensity.

Abstract:Wind tunnel tests on a aeroelastic model of steel angle transmission tower under typhoon wind field and terrain B wind field were carried out，and then the time series of wind velocity for different height of the transmission tower were simulated by Weighted Amplitude Wave Superposition（WAWS） method and the wind-induced responses were calculated with FEM in time domain. The comparisons of wind-induced response and wind vibration factor between typhoon wind field and terrain B wind field were conducted. The results indicate that the wind-induced acceleration responses enlarge significantly with wind velocity increase，the wind-induced acceleration response under typhoon wind field is more intensive than that under terrain B wind field，and the amplification is up to 20%~30% . The highly weighted wind vibration factor with value of 1.59 under terrain B wind field，and the value of 1.85 under typhoon wind field are found ，the amplification is up to 16% in total. The results from numerical simulation are in good agreement with that from the wind tunnel tests. Therefore，the design of transmission tower in typhoon-prone areas should take the fluctuating wind load magnification effect into consideration.

Abstract:To study the effect of corrosion on fatigue reliability of stay cables under random traffic and wind load, the fatigue life model for stayed cables considering corrosion is firstly built up based on accelerated corrosion and fatigue performance experimental results for high strength steel wires. Secondly, the fatigue reliability analysis procedure for stay cables under various corrosion levels and time-varying corrosion is established based on the linear cumulative damage theory considering the combination of vehicle and wind load. Finally, the influence of corrosion on fatigue reliability for the stay cable is studied considering the random traffic and wind combined action for a large span cable-stayed bridge. The research results indicate that the down rate of time-varying fatigue reliability increases with the aggravation of corrosion; the corrosion effect on fatigue becomes appreciable when corrosion is higher than level III, particularly for the cables closing to pylon and auxiliary piers; the maximum decreasing amplitude of cable fatigue life are 24% and 44% when corrosion condition changes from zero to level IV and V, respectively; the decrease of time-varying fatigue reliability index under time-varying corrosion is obviously larger than that just corresponding to corrosion level.

Abstract:The three-point bending tests were conducted to investigate the effects of various textile layers, steel fibers volume contents and prestress levels on the flexural behavior of Basalt Textile Reinforced Concrete（BTRC） plates. With the increase of textile layers, the flexural strength and toughness of BTRC plate are improved. Prestress on the textiles improves the first crack stress and the post-cracking flexural stiffness, but decreases the ultimate deflection of BTRC plate, while no obvious change occurs for the flexural strength. Adding steel fibers in matrix is revealed to positively affect the first crack stress, flexural strength and toughness of BTRC plate, and the effect of steel fibers on the flexural strength is more prominent after applying prestress on the textiles. Moreover, the increase of textile layers and the presence of steel fibers contribute to the crack pattern characterized by more and finer cracks; however, prestress on the textile reduces the crack number and increases the crack spacing.

Abstract:In order to apply the Void Growth Model (VGM) and Stress Modified Critical Strain model (SMCS) to predict the ductile fracture of Chinese structural aluminum alloys, uniaxial tensile tests on aluminum alloy 6061-T6, 6082-T6 and 7020-T6 were carried out, including smooth round bar specimens and notched round bar specimens. Besides, finite element analyses were conducted to calibrate the toughness parameters of three brands of aluminum alloys. The results show that the radius of the notch has slight influence on the toughness parameters of aluminum alloys, and the dispersion coefficients are all within 20%. It is indicated that the toughness parameter is an inherent attribute of the aluminum alloy material, and it can be used to predict the ductile fracture of Chinese structural aluminum alloys under various stress states. Compared with the SMCS model, the VGM model can predict the ductile fracture of aluminum alloys more accurately.

Abstract:The content of crushed brick affects the mechanical properties of cement stabilized recycled aggregates. The effects of cement content，crushed brick content and curing time on the mechanical properties of cement stabilized recycled aggregates were studied through tests in this paper. The relationships between the three variables and unconfined compressive strength，splitting strength，compressive resilient modulus and the frost resistance were established. The results show that，with the decreasing content of crushed brick，the maximum dry density of cement stabilized recycled aggregates increases，but the optimal moisture content decreases；the decrese of the cement content reduces the maximum dry density of cement stabilized recycled aggregates，but the optimal moisture content remains the same in general. The unconfined compressive strength，splitting strength，compressive resilient modulus and frost resistance of cement stabilized recycled aggregates decrease with the increase of crushed brick content，and go up with the increase of cement content for various curing time. Taking the contents of cement and crushed brick as variables，the calculation formulas of the unconfined compressive strength，splitting strength and compressive resilient modulus of cement stabilized recycled aggregate with crushed brick were established.