Abstract:The steel trusses can be used to replace the normal reinforcement to form the precast steel truss-concrete composite shear wall, which is conveniently prefabricated and installed and very suitable for prefabricated constructions.Seismic analysis model of steel-concrete shear wall was established by ABAQUS and validated by test data.Thus, the seismic performance of precast steel truss-concrete composite shear wall was studied by the model, and the cyclic loading simulation on five steel truss-concrete shear walls with different design parameters was carried out to investigate the influence of axial compression ratio and steel content on its hysteretic performance, deformation capacity, stiffness degradation and energy dissipation capacity. The results show that the increase of axial compression ratio is disadvantageous to the deformation capacity and energy dissipation capacity of the shear wall. Increasing the steel ratio of the truss chord can effectively improve the shear bearing capacity of the shear wall, and increasing the steel ratio of the truss web has significant effects on improving the energy dissipation capacity of the shear wall, but has little effect on the load bearing capacity.

Abstract:The seismic performance of frame-shear wall structure on the slope under frequent and rare earthquake was analyzed through a number of calculating examples with different floors and two fixed ends of the core shear walls. The effect laws of different fixed ends of the core shear walls for the shear distribution and seismic performance of the upper and lower grounding parts of the structures were discussed. It is found that the shear distribution of the upper and lower grounding parts of the structure is extremely uneven. The shear force ratio transmitted by each grounding part is affected by number of layers and the fixed end of the core shear wall. Selecting the fixed end of the core shear wall can coordinate the unevenness of shear transmission to some extent, and when there are a number of layers, it is more reasonable to embed the core shear wall on the upper ground, while when there is only a small amount of shear wall at the upper ground, plastic deformation is liable to be concentrated, and the design should focus on the ductility of such components.

Abstract:In order to solve nonlinear damage detection problem under the disturbance of some uncertain factors, a damage identification method based on probability theory and AR/GARCH hybrid model was presented. First, the combination theory of an autoregressive (AR) model and a generalized autoregressive conditional heteroskedasticity (GARCH) model was described and the corresponding formulas were given. Parameter estimation and order determination strategies were proposed. Then, acceleration responses were utilized to establish the AR/GARCH model and extract nonlinear damage feature factor. Finally, probability theory and confidence interval approach were adopted for calculating probability of damage existence and a basic probability index was employed to detect inter-storey stiffness damage. An improved probability index based on weighting technique was further presented to raise the identification reliability. Simulation and experiment results show that the damage identification method based on probability theory and the AR/GARCH model can solve the nonlinear damage problem with uncertain factor disturbance and the identification results of improved probability index are obviously superior to those of the basic one.

Abstract:In order to solve the existing problems in the practical engineering design method involving the second-order effect of staggered frame structure, by combining with The Concrete Structure Design Codes and through theoretical analysis and the example comparison, this paper proposed some feasible methods to simplify designation. The methods well reflect the law of the second-order effect of staggered frame structure, and it can be used to guide engineering design and to provide reference for regularizing the relevant provisions revision and subsequent research work.

Abstract:To study the frost resistance mechanism of multi-scale polypropylene fiber reinforced concrete(MPFC), crude polypropylene fibers in one size and fine polypropylene fibers in two sizes were selected to single-dope and mix-dope with concrete. The mass loss rate, the relative dynamic elastic modulus variation, and the tensile and compressive strength of the polypropylene fiber reinforced concrete before and after freeze-thaw cycle were analyzed based on the fast freeze-thaw cycle test and compression and splitting test. Mercury intrusion porosimetry(MIP) was carried out to study the relationship between frost durability degradation of cement concrete and pore structure. Besides, the influence of pore structure on the anti-frost performance is analyzed. The research indicates that adding polypropylene fiber into plain concrete can improve both the microstructure and the frost resistance of concrete. Under the condition of the same total fiber addition, crude polypropylene fiber and multi-scale polypropylene fiber can bring great improvement on frost resistance of concrete, and the effect of multi-scale polypropylene fiber on frost resistance of concrete is the best. Compared with the common concrete after freeze-thaw cycle, the compression and tensile strength loss of single-dope of fine fiber are reduceded by 9.95% to 11.94% and 4.29% to 7.62% respectively while the strength loss of single-dope crude fiber is reduced by 27.36% and 16.67% respectively, and that of MPFC decreases by 46.77% to 53.23% and 41.90% to 50% respectively.

Abstract:The stability of slopes and the position determination of sliding surfaces are always the hot spots in geotechnical engineering. The rotational failure mechanism in form of the logarithmic spiral is a potential slip surface of homogeneous slope. The slope with a weak interlayer is a common problem encountered in engineering practice, where the instability occurs easily and a loss of the life and property may happen. However, there is a lack of the relevant studies on destabilization and destructive mechanism of this type of damage. In this paper, based on the upper-bound limit analysis, the failure mechanism of translational movements is adopted to investigate the stability of slopes with weak interlayer under static or seismic load and the effects of the position of a single pile and the pile spacing on the stability of slopes is compared. A notable agreement between the results obtained from the proposed failure mechanism and the previous literature is observed for the static load. Under the seismic load, there is a failure slip extending from the top of the slope towards the outside. The mid-upper position of the slope is the most effective one for a pile. The factor of safety of the slope decreases with the increase of the earthquake acceleration and the pile spacing, and the failure slip extends along the weak interlayer.

Abstract:In order to explore the influence of steel on the seismic performance of full-length shear wall structure under different shear span ratio, a new form of steel-bolt-concrete shear wall is designed for super-high-rise buildings. Two full-scale steel reinforced concrete shear walls and two reinforced concrete shear walls were tested under low cyclic loading for comparison of hysteretic curve, stiffness degeneration and energy dissipation between them. The results show that bending failure occurs when the shear wall specimen has a large shear span ratio, while shear failure occurs when the shear span ratio is small. Compared with the reinforced concrete shear wall specimens, the shear walls with steel present slower development of cracks and slighter damage degree.The bearing capacity, deformation capacity, ductility, overall stiffness and energy dissipation capacity of shear wall specimens reinforced with steel have been improved.The shear wall specimens with small shear span ratio have higher bearing capacity, initial stiffness and energy dissipation capacity but the ductility is low. The steel, bolts and concrete work well together.

Abstract:Creep curve is fitted by MATLAB based on CEB-FIP(2010), and shrinkage and creep calculating program is designed by using ABAQUS. Based on parameter verification,vertical deformation component of column and frame beam models with rebar or without rebar under different parameters considering creep and shrinkage were obtained, deformation reduction factor considering the influence of steel bar is proposed and its influencing parameters are analyzed, and the column reduction coefficient formula under different factors is fitted. The results show that the relation between dimension, concrete strength, and reduction factor is quadratic curve, the relation between ratio of reinforcement in column, humidity and reduction factor is linear, while axial compression ratio has little effect on reduction coefficient. The relation between beam section height, concrete strength, ratio of reinforcement in frame beam and reduction factor is quadratic curve, the relation between humidity and reduction factor is linear, while the vertical load on beam has little effect on reduction coefficient. The column reduction factor formula can better consider the effect of steel bars on the shrinkage and creep of concrete.

Abstract:In order to study the force transfer performance of concrete filled steel tubular column-h-type steel beam with lower bolted and upper welded connecting joint under middle column failure, two specimens with round and long round holes at the web connection plate were designed. The static loading test was carried out to analyze the force transmission characteristics of steel beams and the sharing of vertical load resistance by different mechanisms. Results show that the far-end steel beam of the joint is always in the elastic state during the test and its internal force can be calculated by the relevant formula, and the steel beam within the scope of the perforation plate is greatly affected by its bending resistance. In addition, the vertical resistance is mainly provided by the steel beam bending mechanism firstly and then it is replaced by the catenary mechanism after beam yielding. The bending mechanism of the steel beam exists all the time and it is always in the bending state before the failure. The long round bolt holes can improve the rotation ability of the joint, so is more favorable for steel beam axial force providing vertical force. Meanwhile, the assumption of the rigid connection of the new joint form in the frame structure is proposed and verified, and the reference value of the limit surface load is given.

Abstract:An ultrasonic waves test scheme for three-point bending load of reinforced concrete I-beam was developed and implemented. Ultrasonic waves data were collected under 21 load levels, Taylor expansion was applied to eliminate the influence of high order signal and extract the multiorder content of amplitude change of wave, and an approximate linear curve between amplitude first-order change coefficient and stress change was established. The research shows that under the condition of three-point bending stress, the first-order change coefficient of the wave amplitude of reinforced concrete I-beam can be fitted linearly with its stress change, and the goodness of fit is higher than 0.99.

Abstract:In transportation engineering, it has been a focus to evaluate the resistance to water pressure of railway tunnel lining, especially in the southwestern region of China, where the hydrogeological conditions are complicated. When the water around lining does not fully drain away, high water pressure may cause the tunnel lining cracking, which will be a threat to tunnel safety. Therefore, it is very important to evaluate reasonably the anti-water pressure capability of the lining. In this paper, the continuous-discontinuous element method (CDEM) is used to simulate the progressive failure process of the tunnel lining under different water pressures. The relationships among the parameters such as displacement, stress, strain, interface crack factor and interface crack ratio are analyzed. Finally, the relationship between the interface crack ratio and the instability of the lining structure is obtained under the different water pressure conditions. The loading capacity of tunnel lining can be divided into four stages, i.e. safety stage, relative safety stage, critical instability stage and instability stage. Based on the interface crack ratio, a method for evaluating the current state and the loading capacity of tunnel lining is proposed, which is particularly valuable for designing the lining structure under water pressure.

Abstract:Most of the present studies on bridge damage identification using curvature modes only take one-dimensional single-beam structure as the research object. In this paper the idea of G-M method is put forward and the wide multi-beam structure is transformed into orthotropic plate based on thin plate vibration theory. The curvature expressions of the two orthotropic directions of the structure are obtained by analogy beam bending theory. In consideration of the deficiencies of the damage identification of the bridge by using single-order curvature mode difference index, two-direction multi-order curvature mode change rate superposition index for damage identification is used instead, and finally the finite element software Ansys is adopted to establish a bridge model to calculate the unit location, multi-location and different degree of damage under various working conditions. Matlab plotting results show that the index along the bridge longitudinal superposition is more accurate with less disturbance to the data of undamaged location and more index independence, and it can be used to locate the damage of wide multi-beam structure.