Damage Evolution and Acoustic Emission Character of Coalrock under Unloading Condition

The damage failure mechanisms of coalrock under unloading condition during deep mining is different from those under traditional loading condition, starting from the unloading condition position to study the dynamic disaster of coalrock has become a new direction in the disaster study. The rock mechanics electrohydraulic servo test system (MTS815) and acoustic emission system (8CHS PCI 2) are used to study the coalrock deformation damage and acoustic emission (AE) characteristics. The results show that the failure of coalrock under unloading condition exhibits strong brittleness and happens in sudden and is mostly of tensile shear failure type. The evolution curve of cumulative ring down count of acoustic emission can better reflect the coalrock unloading damage evolution process, and the whole unloading failure process can be divided into three stages: the stage of damage weakening, damage stably development stage and the stage of accelerated damage development. During the mining process the confining pressure of the coalrock is unloaded, the coalrock rapidly arrives at the third stage of the whole unloading failure process, and the damage is accumulated rapidly and the fracture failure of coalrok occurred suddenly, then follows the coalrock dynamic disaster.     

Experimental Analysis on Crack Initiation Stress and Rupture Energy of Marble Failure

Based on the marble conventional triaxial test data, the crack initiation stress and rupture energy under different confining pressures are analyzed. Results showed that the crack initiation position is gradually close to the peak strength point with the increase of the confining pressure. The location of the crack initiation occurs in 50% ~70% peak strength. The rupture energy and confining pressure are in positive linear relationship as well as the rupture energy and peak axial stress. And sudden increase of AE energy count corresponds with the crack initiation stress. AE energy count and cumulative energy increase quickly after the crack initiation position, which increase significantly in the crack initiation point. The crack initiation point of theoretical calculation is in good agreement with acoustic emission monitoring. Mogi-Coulomb criterion is in keeping with experimental results.     

Numerical Simulation of Microcrack Toughening in Particulate Composite

The crack tip region in an elastic composite can be divided into three different zones. The constitutive equations corresponding to these zones and the extent of the saturated damage zones are derived. The damage isotropy in the largest saturated damage zone is expressed by utilizing the Monte Carlo technique to create uniform distribution microcracks. The interaction between the main crack and microcracks can be evaluated by an alternating iteration scheme. In the assumption of a dilute concentration of microcracks, the interaction among microcracks is neglected, and the stress intensity factor produced by interaction between the main crack and each microcrack can be superposed. Two sources of loading are analyzed: one is for the main crack microcrack interaction under an applied remote load, and the other is for the main crack microcrack interaction accompanied by the relief of residual stresses on the microcrack surfaces. The results show that two sources of loading can shield the main crack tip, and microcracks behind the main crack tip can create the most shielding whereas the micro cracks ahead of the main crack tip play no role in shielding.     

Shear resistant performance of RC columns subjected to vertical near-fault velocity pulse-like earthquake actions

The aim is to evaluate the seismic properties of ancient timber structure after strengthening and analyze the failure process and corresponding failure state. Based on the hysteretic behavior and energy dissipation principle of the dovetail column-frame strengthened with CFRP and Arches Brackets under the low reversed cyclic loading, the “potential of destruction-resisting” of the two energy-consuming components is obtained. The dissipated energy of each energy-consuming component under the various earthquake conditions is calculated combining with the shaking table test of ancient timber structure. The model of seismic damage evaluation of the two energy-consuming components is established on the basis of the “potential of destruction-resisting” and the dissipated energy. By means of the energy distribution coefficient, the relationship of the failure state between energy-consuming components and overall strengthened structure is discovered, and the model of seismic damage evaluation of the overall structure under the various earthquake conditions is presented. With the derived model of seismic damage evaluation, the failure coefficient of the energy-consuming components and the overall strengthened structure is quantitatively calculated. According to the failure state, the corresponding damage grade of overall strengthened structure is obtained. The results can provide a reliable theoretical basis for predicting the destruction before earthquake and re-reinforcement to the strengthened ancient timber structures after earthquake.     

Application of Fracture Mechanics in Explosion of Large Iron and Steel Wastes

The ex plosio n process a n d paramete rs in the blast of large iron a nd steel wastesare analysed by using the theory of fracture mechanice.A three-dimensional model is established us-ing pressurised cylinder with multiple semi-elliptical surface cracks.Reasons are given for the expla-nation that the dynamic fracture toughness for iron and steel is generally lower than the correspond-ing static value during the blast.The importance is emphasized of the critical duration time of the dy-namic stress intensity factor for crack extension.     

Elastic_Brittle Fracture Analysis of Micro_Crackin Concrete Loaded by Stretching Stresses

The concrete is a typical brittle material.The fracture and propagating failure of the micro-crack in loaded concrete are very important problem in civil engineering.In this paper,from the equilibrium differential equations and failure criterion,the elastic-brittle static fracture analysis of the plane stress micro-crack in concrete loaded by stretching stresses was done near crack line.The relations between the stretching stresses and the length of brittle fracture zone on the crack line were obtained.     

Experimental Analysis of Pre-cracked RC Beams Strengthened with EB-FRP and HB-FRP

On the basis of the crack characteristics of aging RC beam bridges, the cross-section of RC simple beams with different pre-cracking levels were strengthened by the externally bonded FRP（EB-FRP）and the FRP-bolt hybrid bonding（HB-FRP）respectively to check the strengthening characteristics of HB-FRP. The flexural test with symmetrical loading on two points was conducted to study the mechanical behavior and failure mode of pre-crack beams strengthened with EB-FRP and HB-FRP. The influence of pre-cracking level on the FRP initial debonding load and FRP utilization ratio was assessed respectively. The test results show that the flexural capacity of pre-cracking beam strengthened with HB-FRP can be improved by 30%~44% compared with the one with EB-FRP. The failure mode has been changed from FRP brittleness debonding of beam strengthened with EB-FRP to obvious ductility failure of beam strengthened with HB-FRP. Furthermore, the crack distribution of RC beam has obvious influence on the FRP initial debonding load, the FRP utilization ratio and the failure mode of strengthened pre-crack beams.     

Analysis on mechanical properties evolution ofoutburst coal under cyclic loading

Briquette specimens made of outburst coal are taken as research objects, and both mechanical properties evolution under cyclic loading and law of hysteretic curve evolution under different loading level are studied. The results show that hysteretic loop is composed of load-unload curve when briquette specimens are studied under cyclic loading, and secondary hysteretic loop is produced from the second cycle. The area composed by hysteretic curve becomes smaller with the addition of cycle numbers. The relation between deformation response and loading level is very close. Load-unload curve of hysteretic curve is expressed by conic, and the change law of fitting parameters of conic is very regular with the addition of cycle numbers, but the regularity of the law with loading level isn’t very obvious; the minis sign of fitting parameters of conic is opposite.     

TENTATIVE INVESTIGATION OF THE BEHAVIOR OF REINFORCED CONCRETE FRAME CORNER JOINTS UNDER LOW CYCLE LOADING

In this pager, four full-scale corner joint assemblies of reinforced concrete frame beam and column with different detail structure are tested under low cycle loading, The process of damage development and the characteristics of break of the assemblies in the course of alternately increasing positive and negative bending deformation are learned Strength, stiffness and ductility of assemblies and the various regulations of energy consumption are also studied. Compared with these properties, the anti-seismic behavior is tentatively commented. Besides, the test results of the strain distribution of beam and column longitudinal bars and stress state of joint stirrups are analyzed.     

Effect of outburst coal’s gas seepage properties under stage cyclic loading

Experiments of outburst coal’s gas seepage and deformation under cyclic loading of the stationary gas pressure and different confining pressures are made by “fluid-solid-heat coupling with axis servo seepage system of coal”. The results show that loading route has a significant effect on mechanical properties of coal sample. Although the complete stress-strain curves and one cyclic loading curve present similarity in the overall trend, the stress peak value of coal sample under cyclic loading is lower. Under cyclic loading, the stress-strain curves during loading and unloading don’t overlap. They connect to form a hysteretic loop. The permeability is in close relation with the damage deformation process of coal sample. Under cyclic loading, permeability is increasing during the unloading and decreasing during the loading. The permeability-strain curves during loading and unloading form a hysteretic loop, which is corresponding with the hysteretic loop of stress-strain curves of coal sample.     

Analysis on AE characteristic and its confining pressure effect of outburst coal containing gas

Briquette samples made of outburst coal are taken as study objects to study AE characteristic and its confining pressure effect by using self-developed equipment, Shimazu servo test machine and AE monitor system, and the characteristic of AE parameters are analyzed, too. The results show that in the process of outburst coal containing gas triaxial compression, there is no serious dense or sparse area of AE events, but three relative dense appear in compression phase, middle area of linear elastic stage and near peaking phase area so that the characteristic of AE events look like three peaks. But the amplitude of AE events is small and the good consistency between energy change and amplitude change is showed. Microstructure change caused by external stress field change, fracture and fragmentation of particle of samples, movement besides particle of samples and microstructure change caused by dissipation of gas are the sources of AE events. The number of AE events is reduced as the confining pressure is increased, but the influence on total number of AE events caused by confining pressure show nonlinear, expressed by quadratic function. The number of larger amplitude of AE events show decreasing tendency as the confining pressure is increased, the relation between numbers of AE events whose amplitude is more than certain value and confining pressure is expressed by quadratic function.     

Average Constitutional Relationship of Unanchored Zone of RC Structure with Considering Bond and Slip

Based on the equilibrium of static forces and coordination of deformations, with considering the effects of bond strength variation and crack width development at different stress stage of reinforcement in tension cracks, the average stress strain relationship of unanchored zone of RC structure under bond and slip action has been derived. The typical test on reinforced concrete beams was simulated with average constitutional relationship and the result was compared with that of real test. The analytical results show that the model using average constitutional relationship with considering bond and slip in unanchored zone of RC structure can give a result close to that of test and simplify the nonlinear analysis.     

Performance of New-type Steel Tube Buckling-Restrained Brace with Reinforced Concrete Outside

A New-type Steel Tube Buckling-Restrained Brace with Reinforced Concrete outside (ST-BRB-RC) was introduced in this paper. Six specimens of the ST-BRB-RC were designed and cyclic loading test were carried out to study the hysteretic energy dissipation performance of the six specimens. And then, ABAQUS finite element analysis was used to study the performance of four specimens. The results indicated that the ST-BRB-RC had stable and full hysteretic curve. The bearing capacity of the ST-BRB-RC was stable and the hysteretic behavior was excellent. And the analysis model of ST-BRB-RC could be described by a bilinear model. The construction of the ST-BRB-RC was reasonable, and the energy dissipation mechanism of the ST-BRB-RC was clear. It is proved that the design philosophy of using reinforced concrete for exterior restrained element was available.     

A Mesoscopic Simulation Analysis of Interface Transition Zone Characteristics Effect on Mechanical Properties of Concrete

The concrete was equivalent to a three-ingredient compound material, which was composed by aggregate, mortar and interface transition zone (ITZ). The random aggregate model was established using the Monte Carlo method. The relation between linear stress and crack was analyzed, which was used to describe the mechanics of concrete ingredients. The extended finite element method was used to simulate the failure response to various ITZ characteristics of concrete under uniaxial tension. With the tensile strength of ITZ increasing, the tensile strength, fracture energy and ductility of concrete are enhanced. The fractured modes are altered. The concrete’s elastic modulus increases with the elastic modulus of ITZ. With the thickness of ITZ decreasing, the tensile strength, elastic modulus and fracture energy of concrete increase. The interface thickness effect on concrete is reduced.     

Life cycle assessment in large air-conditioning system and evaluation framework model of energy utilization

Based on central air conditioning system of Xi'an-Xianyang international airport, energy efficient utilization with life cycle theory and analytic hierarchy process was conducted. Firstly, the application of life cycle and analytic hierarchy process to building energy was deeply studied. Secondly, life cycle inventory analysis was conducted combined with the practical cases data. And the data resource is related to the proposed model. Thirdly, On basis of analytic hierarchy framework model and analysis of energy consumption as well as potential environmental impact on air-conditioning project, the study on how to evaluate energy-consumption project with the use of life cycle impact assessment is done. Based on the life cycle assessment of practical cases data, a new hierarchical evaluation model of energy utilization is put forward. And in view of the model, several suggestions are given such as establishing energy utilization process monitoring and evaluation from the point of whole life cycle assessment. This provides a theoretical basis for policies about enormous quantity of building energy and energy saving of air conditioning system.     

Analysis of Damage Localization in Crack Weakened Rock Mass

Damage localization in crack weakened rock mass is closely related to the crack growth pattern. Bifurcation of the alternative evolution of cracks occurs when the cracks grow to some extent, then some cracks keep on growing while other ceased evolving. It is found that damage localization in crack weakened rock mass is caused by bifurcation of the crack growth pattern, and the initial location is also determined by the crack growth pattern. Based on the analysis on the bifurcation of crack growth pattern, the critical length of wing crack and the critical stress of damage localization in crack weakened rock mass are obtained. Subsequently, the onset location of damage localization is determined by using the eigenvalue and eigenvector of coefficient matrix, and crack interaction is also taken into account in this model. Finally, the relationship between the interval between columns and rows, the orientation of crack, confining stress and the critical stress of damage localization is defined in the example.     

Quantitative analysis of damage extent of transmission tower by using strain energy method

In order to solve the structural damage identification problem of transmission tower, a two-step identification method based on change rate and dissipation rate of modal strain energy is proposed. The damage location is identified by the change rate of modal strain energy method. Then, the modal strain energy dissipation rate theory is analyzed further by using the element stiffness matrix after injury. As a result, a more accurate damage quantification equation method is introduced. This method requires only several modals of vibration. The numerical simulation results show that this two-step method can find the damage location and damage degree of transmission towers effectively.     

Thermogravimetric study on the pyrolysis performance and its impactfactors of several kinds of typical industrial sludge

Thermogravimetric analysis is used to determine the pyrolysis performance of three types of industrial sludge and their mixed samples at different pyrolysis temperature,sample diameter,heating rate,pyrolysis pressure and adding different metal element compounds.At the same time,the pyrolysis mechanism equations and pyrolysis reaction parameters are obtained.The results indicate that the pyrolysis temperature,sample diameter,heating rate,pyrolysis pressure play an important role in the pyrolysis process for industrial sludge.The metals element compounds can improve the pyrolysis performance of industrial sludge.The pyrolysis reaction progression is respectively 1,1.5,and 2.0 in low,medium and high temperature segment for three types of industrial sludge,the pyrolysis character of mixed sludge isn't obviously changed.The pyrolysis characters of the industrial sludge are alike as the coal residue,the activation energy and the frequency factors are smaller at the initial pyrolysis process,they are increased with the increase of the pyrolysis temperature.The activation energy and the frequency factors are enhanced at the end of pyrolysis.     

Experimental Analysis on the Deformation of Sandstone underPore Pressure and Constant Time

In order to discuss the deformation characteristics of rock mass under different water levels changing between 145 and 175 meter in the Three Gorges reservoir area, an experiment was carried out for the studying sandstone deformation under the conditions of three different axial stresses(σ1=55.54,34.18,12.82 MPa), two cyclic pore pressures(Pmin=2 MPa,Pmax=6 MPa) and two kinds of constant time(the upper limit time and the lower limit time(ΔT=120,240 s).With ε1-T curves and p-T curves, as well as p-ε1  hysteresis curves, it was found that the curves were continuous sine wave-shaped curves.At first, the strain decreased with loading pore pressure.And then, it decreased to valley value with pore pressure at stable upper limit.Next, it increased with unloading pore pressure and increased to peak value with pore pressure at stable lower limit.The p-ε1  hysteresis curves of the sandstone had two typical stages.And one was caused by the closure of some primary pores and crack under increasing compaction, in which the strain did not form obviously hysteresis curves, and the other was pore pressure coupling stage which showed obvious hysteresis curve in form of the anti-clockwise from the dispersed to the dense.In addition, Δε-n curves in four sections (loading, unloading, steady upper limit, steady lower limit) of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time .     

THE THEORETICAL DERIVATION FOR C-M FORMUJA

Form the crack propagation rate and the cyclic stress-strain respon- dence of low cycle fatigue, the C-M formula is theoretically derived by using the correcting factor. The constants in this formula are also estimaled and discussed.