# I am trying to analyze a bridge truss. The geometry includes truss members, cables and a pulley. I have attached the geometry (Truss.jpg) for your reference. The bridge design has a cable passing over a pulley. The objective is to avoid tension in the bottom chord members of the truss by pretensioning the cables. The pretension cables should produce a compressive stress in the bottom chord members and thus balance the existing tension developed in them under a live load. How do I model the pulley and apply the load?

 Please see the ANSYS 9.0 input below. BEAM189 elements were used for the truss structure, LINK10 elements were used for the cable, CONTA175 elements were used for the nodes to surface contact between the cable and the pulley, and a TARGE170 rigid target cylinder was used to model the pulley. By including an initial strain (1%) in the LINK10 cable elements, the bottom members of the bridge truss were put in compression to begin the analysis. In a second load step, the live load was added. All of the dimensions, section properties, loads, etc., were made up, so please only use this example for procedural purposes...= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =fini/clear/title, Truss Design/RGB, INDEX, 100, 100, 100, 0/RGB, INDEX, 80, 80, 80, 13/RGB, INDEX, 60, 60, 60, 14/RGB, INDEX, 0, 0, 0, 15/plopts,info,1/view,,1,2,3/pnum,line,1/dscale,,1/eshape,1/prep7et,1,BEAM189 ! truss memberskeyopt,1,4,2 ! combined shear stress outputsectype,1,beam,isecdata,0.1,0.1,0.2,0.01,0.01,0.01 ! w1, w2, w3, t1, t2, t3, metersmp,ex,1,2.07e11 ! Young's modulus, Pa (N/m^2)mp,prxy,1,0.30 ! Poisson's ratio, unitlessmp,dens,1,7.83e3 ! mass density, kg/m^3et,2,LINK10! cablekeyopt,2,2,0 ! no stiffness when cable slackkeyopt,2,3,0 ! tension-only cabler,2rmodif,2,1,0.0004909 ! area (m^2) for 0.025m diameter cablermodif,2,2,0.01 ! initial strain (1%)mp,ex,2,2.07e11 ! Young's modulus, Pa (N/m^2)mp,dens,2,7.83e3 ! mass density, kg/m^3et,3,CONTA175 ! node-to-surface contactkeyopt,3,5,3 ! "Adjusted to Touch" ...keyopt,3,7,1 ! automatic bisection of incrementkeyopt,3,10,2 ! update contact stiffness each iterationr,3rmodif,3,1,0.50 ! rigid cylinder radius, metersmp,mu,3,0.01 ! small amount of frictionet,4,TARGE170 ! rigid target cylinder (pulley)keyopt,4,2,1 ! user-specified constraintset,5,BEAM188 ! pulley supportkeyopt,5,3,2 ! internal mid-node usedkeyopt,5,4,2 ! combined shear stress outputsectype,5,beam,rectsecdata,0.05,0.05 ! width and height, metersmp,ex,5,2.07e11 ! Young's modulus, Pa (N/m^2)mp,prxy,5,0.30 ! Poisson's ratio, unitlessmp,dens,5,7.83e3 ! mass density, kg/m^3k, 1, 0.0, 0.0, 0.0k, 2, 3.0, 0.0, 0.0k, 3, 6.0, 0.0, 0.0k, 4, 9.0, 0.0, 0.0k, 5, 12.0, 0.0, 0.0k, 6, 3.0, 3.0, 0.0k, 7, 6.0, 3.0, 0.0k, 8, 9.0, 3.0, 0.0k, 9, 6.0, -1.0, 0.0l,1,2l,2,3l,3,4l,4,5l,6,7l,7,8l,1,6l,2,6l,2,7l,3,7l,4,7l,4,8l,5,8larc,1,9,7,18.5 ! arcs for cable ...larc,5,9,7,18.5lsel,s,line,,1,6,1lsel,a,line,,7,9lsel,a,line,,11,13latt,1,,1,,9,,1lsel,s,line,,10latt,1,,1,,1,,1lsel,allesize,1.0lmesh,1,13,1 ! mesh truss with I-beam sectionsnsel,nonelsel,s,line,,14,15lesize,all,,,24,0.25latt,2,2,2,,7lsel,alllmesh,14,15 ! mesh cablesmat,3type,3real,3*get,ncount,node,0,countncurr=0*do,i,1,ncount ncurr=ndnext(ncurr) e,ncurr ! create node-to-surface contact*enddonsel,nonen,, 6.0, -0.5, -0.1n,, 6.0, -0.5, 0.1npilot=node(6.0,-0.5,-0.1) ! pilot node for rigid cylinder (pulley)n2=node(6.0,-0.5, 0.1)mat,3type,4real,3tshap,cylie,npilot,n2 ! rigid target cylinder (pulley)tshape,piloe,npilot ! pilot node elementnsel,allesel,allmat,5type,5real,5secnum,5ntruss=node(6.0,0.0,0.0)e,ntruss,npilot ! pulley support ...! e,ntruss,n2/pnum,type,1/num,1eplotfini/soluantype,staticoutres,all,allnlgeom,on ! large displacement solutionnfix=node(0,0,0)d,nfix,all,0.0 ! fix left end of trussnroll=node(12,0,0)d,nroll,uy,0.0 ! allow right end of truss to rolld,all,uz,0.0 ! make problem 2D ...d,all,rotx,0.0d,all,roty,0.0time,1.0nsubst,5,100,2solve ! establish initial strain in cablesavetime,2.0nsubst,1,10,1f,node(3,3,0),fy,-50000.0 ! downward concentrated loads ...f,node(6,3,0),fy,-50000.0f,node(9,3,0),fy,-50000.0acel,0.0,9.8,0.0 ! add gravitational load, m/sec^2solvesavefini/post1/edge,,1set,1,last/title, Bottom Beams in Compression from Cable Preload (Initial Strain)plnsol,s,x/wait,3set,2,last/title, Bottom Beam Compression Reduced form Additional Loading ...plnsol,s,x/eof.