New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake res...New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake resisting systems are idealized as prismatic cantilever flexural-shear beams. Floor masses are considered as lumped masses at each story level and masses of columns are evenly distributed along the cantilever beam. Soil-structure interaction is considered as axial and rotational springs, whose potential energy are formulated and incorporated into overall potential energy of the structure. Subsequently, natural frequency equations are derived on the basis of energy conservation principle. The effect of axial forces on natural frequency is also considered in the proposed formulas. Using the method presented in this study, natural frequencies are computed using a simplified method with no complex numerical modeling. The proposed formulas are verified via experimental and numerical methods. Close agreement between the results from these three approaches are observed. Furthermore, the effects of panel zone flexibility, continuity plates and doubler plates on the natural frequencies of buildings are investigated.展开更多
Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with ...Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method （FEM） respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.展开更多
This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel.Based on the g...This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel.Based on the geological condition in an island longwall panel in the Tangshan Coal Mine,Tangshan,China,a numerical FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps.The results of the numerical modeling show that the roof deformation starts to occur at more than 30 m ahead of the longwall face and the deformation starts to accelerate after a distance of 10 m in front of the longwall face.Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel.Based on the numerical results,a stress–relief technology using boreholes,which was employed to release abutment pressure,was investigated through numerical methods.The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps.The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing.展开更多
This study presents a novel approach using theoretical analysis to assess the risk of rock burst of an island longwall panel that accounts for the coupled behavior of stress distribution and overlying strata movement....This study presents a novel approach using theoretical analysis to assess the risk of rock burst of an island longwall panel that accounts for the coupled behavior of stress distribution and overlying strata movement. The height of destressed zone(HDZ) above the mined panel was first determined based on the strain energy balance in an underground coal mining area. HDZ plays a vital role in accurately determining the amount of different loads being transferred towards the front abutment and panel sides. Subsequently, based on the load transfer mechanisms, a series of formulae were derived for the average static and dynamic stresses in the island pillar through theoretical analysis. Finally, the model was applied to determining the side abutment stress distribution of LW 3112 in the Chaoyang Coal Mine and the results of ground subsidence monitoring were used to verify the predicted model. It can be concluded that the proposed computational model can be successfully applied to determining the safety of mining in island longwall panels.展开更多
文摘New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake resisting systems are idealized as prismatic cantilever flexural-shear beams. Floor masses are considered as lumped masses at each story level and masses of columns are evenly distributed along the cantilever beam. Soil-structure interaction is considered as axial and rotational springs, whose potential energy are formulated and incorporated into overall potential energy of the structure. Subsequently, natural frequency equations are derived on the basis of energy conservation principle. The effect of axial forces on natural frequency is also considered in the proposed formulas. Using the method presented in this study, natural frequencies are computed using a simplified method with no complex numerical modeling. The proposed formulas are verified via experimental and numerical methods. Close agreement between the results from these three approaches are observed. Furthermore, the effects of panel zone flexibility, continuity plates and doubler plates on the natural frequencies of buildings are investigated.
文摘Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method （FEM） respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.
基金financially supported by the Major State Basic Research Development Program Fund of China(No.2010CB226801)State Key Laboratory for Coal Resources and Safe Mining+5 种基金China University of Mining&Technology(SKLCRSM11KFB07)China Postdoctoral Science Foundation(Nos.2011M5004482012T50161)the National Natural Science Foundation of China(No.51174213)the New Century Excellent Talents in the Ministry of Education Support Program of China(No.NCET10-0775)the Fundamental Research Funds for the Central Universities
文摘This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel.Based on the geological condition in an island longwall panel in the Tangshan Coal Mine,Tangshan,China,a numerical FLAC3D(Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps.The results of the numerical modeling show that the roof deformation starts to occur at more than 30 m ahead of the longwall face and the deformation starts to accelerate after a distance of 10 m in front of the longwall face.Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel.Based on the numerical results,a stress–relief technology using boreholes,which was employed to release abutment pressure,was investigated through numerical methods.The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps.The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing.
基金Project(2017CXNL01) supported by the Fundamental Research Funds for the Central Universities,China
文摘This study presents a novel approach using theoretical analysis to assess the risk of rock burst of an island longwall panel that accounts for the coupled behavior of stress distribution and overlying strata movement. The height of destressed zone(HDZ) above the mined panel was first determined based on the strain energy balance in an underground coal mining area. HDZ plays a vital role in accurately determining the amount of different loads being transferred towards the front abutment and panel sides. Subsequently, based on the load transfer mechanisms, a series of formulae were derived for the average static and dynamic stresses in the island pillar through theoretical analysis. Finally, the model was applied to determining the side abutment stress distribution of LW 3112 in the Chaoyang Coal Mine and the results of ground subsidence monitoring were used to verify the predicted model. It can be concluded that the proposed computational model can be successfully applied to determining the safety of mining in island longwall panels.
