Forecasting research of overpressure of explosive blast in subway tunnels

In case of an explosion happening inside the subway tunnel, blast waves interacts with the structure in an enclosed space. Both the overpressure and duration of blast increase. On the basis of experimental research, we establish a calculation model of blast effects in a tunnel. Its applicability has been verified by comparing the numerical results and the experimental findings. Then the blast effects in subway tunnel have been analyzed. It has been found out such factors as the tunnel shape, charge position, and distance to the explosion center all have a great influence on blast effects. The overpressure of blast in the subway tunnel is summarized and the formula is proposed. Compared to data of explosion tests at home and abroad, the formula has been proven to have some applicability. It may be provide some reference to the design of antiknock loads of subways and evaluation of casualties

Bearing capacity and failure mechanism of strip footings on anisotropic sand

Sand typically exhibits anisotropic internal structure (or fabric), and the fabric anisotropy has a dramatic influence on the mechanical behavior of sand. Meanwhile, the fabric evolves when sand is subjected to external loading. This eventually makes the response of strip footings on sand dependent on fabric anisotropy and fabric evolution. A numerical investigation on this effect is presented using a critical state sand model accounting for fabric evolution. The model parameters are determined based on plane strain and triaxial compression test data, and the model performance is validated by centrifuge tests for strip footings on dry Toyoura sand. The bearing capacity of strip footings is found to be dependent on the bedding plane orientation of dense sand. However, this effect vanishes as the sand density decreases, though the slope of the force-displacement curve is still lower for vertical bedding. Progressive failure is observed for all the simulations. General shear failure mode occurs in dense and medium dense sand, and the punching shear mode is the main failure mechanism for loose sand. In general shear failure, unsymmetrical slip lines develop for sand with an inclined bedding plane due to the noncoaxial sand behavior caused by fabric anisotropy. For strip footing on sand with horizontal bedding, the bearing capacity and failure mechanism are primarily affected by the sand density. The bearing capacity of a strip footing is higher when the sand fabric is more isotropic for the same soil density. An isotropic model can give significant overestimation on the bearing capacity of strip footings

Numerical investigation on seismic performance of base-isolation for Rigid Frame Bridges

Rigid Frame Bridge was widely used while the according seismic design was quite difficult and worth of discussion. Section sizes of piers were increased when elasticity seismic theory was adopted; plastic hinges were designed on the top or bottom of piers when ductility seismic theory was employed; and isolation bearings were installed when seismic isolation theory was applied. However, larger size may neither be cost-effective nor meet the requirements of seismic design. Furthermore, seismic rehabilitation would be extremely difficult when plastic hinges were employed, and isolation bearings were not applicable to Rigid Frame Bridge as there was nowhere to place them. A new method was proposed for Rigid Frame Bridge referred as base-isolation design. Based on introducing base-isolation concept, base-isolation design of Rigid Frame Bridge was achieved by setting seismic-isolation layer in cap. There were four kinds of base-isolation systems widely adopted in numerical investigation of base-isolation for Rigid Frame Bridge, i.e., laminated elastomeric bearings (EB) system, lead rubber bearings (LRB) system, EB and liquid viscous dampers (EB-LVD) system, and LRB-LVD system. It was found that: i) seismic effect transmitted to superstructure and substructure of bridge could be dramatically reduced by seismic-isolation layer; ii) efficiency of base-isolation system could be significantly promoted by using EB and LVD together; iii) mechanical parameters of isolation devices should be determined according to the actual situation of the bridge

The State and the Arts of Research on Foundation Buried Depth Effect on Building Structure

The state and the arts of research on foundation buried depth effect on building structures are reviewed and summarized in detail from such aspects as static response property and dynamic response property, and a brief discussion is carried out on the future developments and studies. Different scholars have conducted research for this aspect of the issue; the conclusions vary because of differences in the conditions of the upper structure stiffness. Superstructure should consider different stiffness conditions a lot of numerical calculations, foundation depth summary obtained reaction influence on the dynamic characteristics and dynamic soil structure interaction system of law

Nonlinear response of continuous girder bridges with isolation bearings under bi-directional ground motions

The isolation seismic technology has been developed during the past three decades, but it is a current focus in bridge seismic research and practice. In order to investigate the nonlinear seismic responses of isolated bridges and evaluate the effects of seismic isolation on the peak response of the bridges with lead rubber bearings (LRB) under bi-directional horizontal earthquake excitation, an analytical method of nonlinear seismic responses of continuous multi-span girder bridges with LRB and its solving method are presented considering the interaction between the restoring forces of the bearings. Shaking table test of 1/10 the scaled model of two-span girder isolated bridge with LRB have been conducted to verify effectiveness of the LRB as a seismic isolation device and peak response of isolated bridges. Experimental results well agreed with the results obtained from analytical results of peak displacement and acceleration of deck, displacement and force-displacement hysteresis loops of isolators. It is verified that analytical method given this paper is right and effective when analyzing nonlinear earthquake response of continuous girder isolated bridges with LRB. Moreover, the bi-directional coupled interaction of the restoring forces of LRB should be taken into account, which has considerable effects on the peak seismic responses of the isolated bridge

Multiple shaking tables tests of seismic pounding effect of reinforced concrete bridge model

In order to investigate the longitudinal pounding effect of highway bridges with high-piers under strong ground motions, multiple shaking tables tests of a 1/10 scaled continuous rigid frame and simply-supported girder bridge with high-piers were carried out. The pounding responses of the bridge model under different earthquake excitations including the uniform excitation and the traveling wave excitation were studied, and the effectiveness of the dampers and isolation bearings for reducing the seismic pounding effect were analyzed and discussed. Test results indicate that the traveling wave effect is the important factor in seismic pounding response of high pier bridges. Additional dampers can mitigate the pounding effect apparently and play a role in reducing seismic response for bridge superstructures. Compared with conventional rubber bearing (RB), the decreases in the relative displacement and the pounding force between adjacent girders were 30 % and 55 % with lead rubber bearing (LRB) in this experiment, respectively. Seismic pounding effect of bridge superstructures depends on different structural dynamic properties of adjacent girders and characteristics of ground motions

Hysteresis behavior of reinforced concrete bridge piers considering strength and stiffness degradation and pinching effect

In order to effectively simulate the nonlinear hysteresis behavior of reinforced concrete (RC) bridge piers under strong earthquake excitation, an improved nonlinear hysteresis model for RC bridge piers was developed and its controlling parameters were determined considering stiffness and strength degradation and pinching effect based on classical Bouc-Wen model. The improved model can be carried out to predict the nonlinear hysteresis behavior of RC bridge piers under various failure modes using MATLAB/ Simulink program. Cyclic tests of different failure mode bridge column specimens were performed under constant axial load with lateral bending. The results did show that force-displacement relationship curves of bridge column specimens derived from theoretical analysis agree well with experimental results. The nonlinear hysteresis behavior of bridge column specimen was simulated under 2008 Wenchuan earthquake excitation and its failure modes were identical with real earthquake damage of bridge column. The improved analytical models in the paper were applied to accurately predicting the nonlinear hysteresis behavior of RC bridge columns with strength and stiffness degradations and the pinching effect subjected to strong earthquake motion

Test on dynamic performance of silt-concrete structure system under cyclic loading with different frequency

In order to study the dynamic response of the soil-structure system and the contact performance between soil and structure under cyclic loading, a Suspensory Ring Test Apparatus was designed by the authors, and a series of tests had been carried out. The physical properties of the test silt were that ρ=1.59g/cm3, ωP=14.26%, ωL=21.77%. In the paper, The Suspensory Ring Test Apparatus was introduced firstly. Then, the test data were analyzed in two aspects, that was (1) the damage mechanism of the soil-structure system, (2) the factors which affected on contact performance between silt and concrete structure under cyclic loading, such as moisture content, loading frequency, roughness, and so on. Finally, some conclusions were also proposed

Fractional elastoplastic constitutive model for soils based on a novel 3D fractional plastic flow rule

A novel three-dimensional (3D) fractional plastic flow rule that is not limited by the coordinate basis of the differentiable function is proposed based on the fractional derivative and the coordinate transformation. By introducing the 3D fractional plastic flow rule into the characteristic stress space, a 3D fractional elastoplastic model for soil is established for the first time. Only five material parameters with clear physical significance are required in the proposed model. The capability of the model in capturing the strength and deformation behaviour of soils under true 3D stress conditions is verified by comparing model predictions with test results

Evaluation the Impact of Flexible Joints and Deck on the Seismic Response of Bridges

Bridges have undeniable importance at different parts of urban areas. In this study the influence of various forms of bridge decks, flexible joints and other elements of concrete bridges with diverse size have investigated, because of high rate of popularity of concrete bridges in construction project. Due to the significance of plastics in analyzing the seismic response of bridges, finite element model is chosen in this project. In the present study, two types of hinges, including fiber hinge and the force moment interactive hinge (PMM), have been selected to indicate the ductility of the columns in the lower and upper regions of the abutments and in the length of the plastic hinge. A huge decrease can be seen in dissipation of energy through pier, by interpreting the data of designed models and effect of dedicated earthquake force. Therefore, to reach better efficiency, it is suggested strengthening the seismic behavior of traditional bridges. To assess short bridges, roller model is not a reliable way to get accurate results, but in long bridges with the length of more than 95m, a simple model can be set to evaluate bridge response