Dynamic Response And Damage State Research On Steel Truss Bridge Structures And Components Under Near-field Explosion Loads

Steel truss bridge is a typical bridge that spans rivers.Its steel truss structure can be used for independent load-bearing structures,as well as for other structures,such as,the stiffening beams of long-span cable-stayed bridges and suspension bridges,arch ribs of arch bridges.It can be also used for roof trusses,crane beams and power transmission towers in other buildings.At present,the research on steel truss bridges mainly focuses on design,construction,retrofit and reinforcement,but the current bridge codes do not consider the impact of explosive loads.The results of the explosion study of the bridge structure show that under the explosion load,especially the near-field explosion load,the component is the weak part of the bridge structure.The damage of the bridge is mainly the component damage,and the component type of the bridge can also be used in other buildings.In view of the above situation,this paper studies the dynamic response and damage of the scale model of steel truss bridge structure and bridge components under near-field explosion load:(1)The series expansion method or the multi-point fitting method are used to derive equivalent single degrees of freedom(SDOF)load expression and load factor expression on_.basing on GB6722-2014,Brode and Henrych overpressure parameters and using the formula derived in this paper,the_of one-way component under different end constraints(simple-supported at both ends,fixed at both ends,and simply supported at one end and fixed at the other end)at elastic phase and plastic phase is derivesed at typical charge weight calledand typical component span calledrespectively,and the relationship curve between the_and the dimensionless parameter called(=?/,?is stand-off)is obtained.the_of the RC simply-supported beam under near-field explosion load is calculated using the theory of this paper,and is compared with the experimental_.The results show that the_is related to the span calledin the elastic stage,and the_is not related to thein the plastic stage;The_decreases with increasing of,eventually,it tends to a certain value.In the elastic stage,the value of the_of simply supported at both ends,fixed at both ends,and simply supported at one end and fixed at the other end,tend to 0.64,0.54,0.58,respectively,and in the plastic stage,the value of different end constraints tends to 0.5,within a certain error range,the case where?is equal to thecan be regarded as judgment criteria for near-field and far-field explosions;Basing on different overpressure parameters,the load factor of RC simply supported beam under near-field explosion obtained by the theory of this paper is very agreement with that of the experimental results,with a maximum error of 3.9%.(2)Taking a railway steel truss bridge in Taiyuan City as a prototype,the model is made at a scale of 1:16,and the location of two explosive charges is determined,one is over the crossbeam joints of the longitudinal and horizontal beams,the other is over the crossbeam at the mid-span,two charges expolsion is carried out.In the study of the steel truss bridge under two charge explosion load,the LS-DYNA software is used to simulate dynamics response and deformation of steel truss bridge under near-field explosion load.The results show that under two charge near-field explosion loads,the steel truss bridge is more severely damaged,mainly local damage;under the same condition,when the initiation time interval of the two charges is5000?s,The deformation of the steel truss bridge is different from the deformation with simultaneous detonation;The initiation sequence has a certain effect on the deformation of the steel truss girder bridge,compared with simultaneous initiation,the initiation sequences have a relatively greater effect on the deformation of bridge around the later initiating charge;The minimum charge weight for the invalidation of the steel truss bridge is obtained at a certain stand off;(3)Taking common I beam and steel pipe components in bridges and other building structures as the research object,combined with the use of GFRP for building structural components in the anti-explosion design,12 shots of near-field explosion on 12 specimens are carried out.The results show that when the explosion conditions and the cross-sectional area are same,the deformation of the I beam is the largest,followed by the square tube,and the circular tube is the smallest;The method of wrapping GFRP on I beam,circular tube and square tube can reduce the deformation of components and have a certain effect on improving the anti-explosive performance;When the stand-off increases,the deformation decreases;when I beam is added concrete outer or circular or square tube is filled with concrete,the deformation of the component is greatly reduced,and the deformation decreases with the increase of the concrete strength.The front surface and rear surface of the component deform oppositely in the axial direction.The rear surface is stretched(or first stretched and then compressed),and the front surface is compressed(or first compressed and then stretched),and the closer to the explosion center is,the greater the strain is,the stronger the response is;The component is axially stretched and transversely compressed on the rear surface;When the component is wrapped with GFRP or filled with concrete,the strain decreases,and the response decreases;When the strain is larger,the first peak of the strain is greater,the residual strain is larger.(4)Taking the reinforced concrete(RC)beams commonly found in bridges and other building structures as the research object,3 shots near-field explosion on 3 specimens are carried out.The results show that:the concrete on the front surface of the RC beam is compressed and destroyed,the side surface is broken down,and the rear surface is collapsed.Comprehensive comparison of the damage area and depth of the concrete on the four sides of three specimens,it can be found that the concrete damage on the back surface is the most serious,the side is more serious,and the front face is lighter;The double trapezoid failure mode with narrow trapezoid above and wide bottom trapezoid is the main failure mode on the side concrete;When the explosion conditions and rebar arrangement are same,the concrete strength is higher,the damage is less,and when the concrete strength is low,the whole concrete piece falls off from the damaged area,when the strength is higher,part of the concrete in the damaged area is intact or relatively intact,and the concrete falls off locally.(5)Taking the square tube as the research object,using numerical simulation method,by changing number of charge equal parts,charge mass ratio,charge distance and initiation time interval at the same total explosive charge,the dynamic response and damage of the steel tube under multiple explosion loads are studied.The results show that for multiple equal charge explosion load with simultaneous detonation,the deformation on the front surface and the deflection of the square tube are larger than that of single explosion load;For two explosion loads with simultaneous detonation,when the weight of the two charges is close,the deformation on the front surface and deflection of the square tube are larger than that of the condition that the weight of the two charges is quite different,the process of the mass ratio from 1:1 to 1:9 is the process of two equal charge explosion loads gradually tends to single explosion load acting on a square steel tube;For two equal charge explosion loads with simultaneous detonation at the same stand off,the distance between the explosives increases,and the deformation of the square steel tube on the front surface decreases,and within a certain distance,the deformation on the front surface and deflection of the square steel pipe are larger than that of the square tube under single explosion load.When the distance between all charge centers and the mid span of the square tube is equal and adoping simultaneous detonation,the deformation on the front surface of the square tube is the largest,and the longer the interval of initiation time is,the smaller the deformation on the front surface of the square steel tube is;When the distance between all charge centers and the mid span of the square tube is not equal,adjusting initiation time of each charge can make the deformation on the front surface at the mid span of the square tube larger than that of the condition with simultaneous detonation.The number of charge equal parts,charge mass ratio,and initiation time interval have a certain effect on the speed of the explosion shock wave at the same total explosive charge.