Mechanism Of Failure In Gate-closing And Structure Of Plain Gate Under High Water Head

Hydraulic gate is the "safe valve" of hydro-power station projects,the safety of gate is related to the safe,reliable and effective operation of the whole hydraulic project.In practical engineering,there are many gates which will produce vibration,failure in gate-closing and damage in structure under special hydro-dynamic loads.In the past,the engineering profession paid much attention to the vibration and reliability in the operation of radial gate with high water head,and systematic research are carried out.In recent years,there are few cases of problems in the operation of radial gate.However,due to the lack of attention to the reliability in the operation of the high head emergency plane gate in the engineering field,the failure of gate-closing of the high head emergency plane gate is becoming common in the existing projects,which seriously endangers the engineering safety.In this paper,based on the practical engineering cases of the gate-closing failure and structural failure of the high head plane gate,the theoretical analysis,model test,numerical calculation and prototype observation feedback analysis are carried out,the mechanism of the failure of the hydro-dynamic gate is revealed,the prevention and control measures for the failure of the gate are proposed,the continuous failure process of the gate structure is inverted,the failure mechanism of the gate structure is clarified,and the failure gate hole is proposed Mouth sealing scheme.The main research results are as follows:(1)The hydraulic characteristics of the plane gate are studied,the theoretical model of gate creepage vibration is established,the failure mechanism of the gate is revealed,and the prevention and control measures are put forwardThe research reveals the influence of upstream water level and the opening of working gate on the flow pattern,the change of panel and bottom girder,the fluctuating pressure and the holding force in the gate closing process.The "holes" of the main cross-beam will significantly reduce the pressure between its upper and lower surfaces,and that is to say,the holding force of the closed door will be reduced with the increase of the opening percentage of the hole.When the opening percentage is more than 30%,the effect is not so obvious.Through the geometric method of nonlinear dynamics,the theoretical model of creepage vibration of plane gate is established.The mechanism of the fail that gate can't fall completely and the creepage vibration is accompanied by is clarified.The verification of the factors through experiment that affect the creepage vibration is carried out.It is shown that the bearing friction coefficient is one of the main factors that affect the creepage vibration of gate,and the material of sliding block will also change the vibration characteristics of gate.In order to reduce the friction coefficient of the supporting structure,reduce the upstream water level and the opening of the working gate,and increase the balance weight of the gate.From the point of view of reducing the gate creepage,we should properly increase the counterweight,adjust the operation parameters,increase the diameter of the roller or slider,select the supporting structure with small friction coefficient,increase the elongation modulus of the wire rope of the winch hoist / adopt the hydraulic hoist,ensure the sealing is fine,optimize the flow pattern at the gate bottom and other failure prevention and control measures.(2)The feedback model for the continuous failure and collapse of the single section and the whole structure of the gate by numerical calculation is establishedThrough the numerical calculation,two kinds of structural failure modes of plane gate,namely,beam leading and weld leading are defined.Regardless of the failure of the main weld,through the study of the elastic-plastic ultimate bearing capacity and plastic zone expansion process of the main beams with different hole style under the overload water pressure and earthquake load,the main beams will have the ultimate bending failure mode in the span or the shear failure mode in the side span,without the overall instability.The continuous failure process of the single section of the gate is as follows:the plastic zone is formed at the lower left corner of the side span waist hole?the plastic zone is formed at the right side of the side span waist hole?the plastic zone is formed at the upper and lower sides of the side span waist hole section?the plastic zone is connected?the movable mechanism is formed?the web crack?the rear flange crack?the weld tear?the panel tear?the?shaped beam mid span crack?the side column is pulled out of the gate slot.When consider the weld failure,the continuous failure and collapse process of the single section structure of the gate is as follows:weld failure?front flange of the main beam and the panel are separated?the panel is split instantly?front flange of the main beam is broken?rear flange of the ? beam is broken?web of the main beam is broken?half span is twisted?side column is pulled out of the gate slot?gate failure.Through the comparative analysis of the site debris of a broken gate,the rationality of the numerical feedback deduction model proposed in this paper is proved.The failure mechanism of the gate accident is determined to be the failure mechanism of the main guide structure of the weld caused by the crack of the weld joint,the structural transformation of the beam system caused by the tearing of the panel,and the failure of the main guide structure from the bottom to the top.By tracking the continuous fall off of weld groups,the whole catastrophic process of the gate is as follows: the bottom section weld falls off?the bottom section panel is torn from one side to the middle?the bottom section main beam is broken in the middle of the span?the bottom section side column torsion drives the lower middle section left and right main beam to be broken in the middle?the top section panel is torn at 1/4 of the right side of the upper middle section?the upper middle section beam is broken ?the top section beam is twisted due to the pulling of the panel strong water pressure The top joint is out of the gate slot.(3)inversion analysis of other factors affect the failure of gate structureThe secondary cause of the gate structure damage is the abnormal flow through the vent hole and the additional hydro-dynamic load caused by the gap jet between the gate segments.The main cause of the continuous failure is the gate panel and the beam system disconnection caused by the insufficient height of the main weld,the lack of welding,and the poor welding quality.(4)Research on sealing scheme of the failure orificeUnder the same water level,the order of clapping door force is clapping door(middle door)?floating door > meter beam ball door?rubber coated ball door >herringbone door.According to the test and field practice,in order to systematically solve the problem of excessive impact force of flap door,the flap door can be made of herringbone flap door or composite material with small specific gravity.For different water levels,the ball shell or box girder flat gate can be used,and the hollow belly can be made in the middle.The sealing operation steps of the new floating box flap door are: flap door design and model test?flap door in Water?tap the door to the designated position?tap the door to inject water and exhaust gas and complete sealing?check the water sealing and tightness after tap the door is sealed?close the vent hole?repair the damaged part in the hole and construct the permanent block.