How To Make a
Steel Bridge Framework

Objects: Round_Box, cylinder.
Methods: #local, #declare, union, #macro, #while loops, #if, shearing by matrix.

This example shows how to make the framework of a truss bridge for railroad / railway (Warren or Neville type). It is possible to use variable sizes for the dimensions of the bridge.

The Construction in details:
 
Step 0: First we declare the basic variables for the dimensions of the bridge (textures are up to you!):

#local L =10.00; // bridge length . #local H = 2.50; // bridge height #local W = 1.50; // bridge width #local BD = 0.50, // beam diameter #local BR = 0.10; // beam border radius

Step 1: Then we calculate the number of subdivisions and their lenght for an equidistance distibution of the segments. We also declare the shearing factor (How to calculte see the opposite image):

// number of subdivisions: #local NSub = int(L/H); // distance for equidistant distribution: . #local SubDistance = L/NSub; // shearing factor: #local S_Factor = 0.5*SubDistance/H;

Step 2: Now we make a pair of diagonal beams:

union{ // pair of diagonals object{ Round_Box(<-BD/2,0,-BD/2>,<BD/2,H,BD/2>,BR,0) matrix< 1, 0, 0, // matrix-shear_y_to_x S_Factor, 1, 0, 0, 0, 1, 0, 0, 0> } // ----------------------------------------- object{ Round_Box(<-BD/2,0,-BD/2>,<BD/2,H,BD/2>,BR,0) matrix< 1, 0, 0, // matrix-shear_y_to_x -S_Factor, 1, 0, 0, 0, 1, 0, 0, 0> translate<SubDistance,0,0> } // ----------------------------------------- }// end union pair of diagonals

Step 4: The macro Steel_Bridge_Framework_1
Two side beam, some floor beams and diagonals and some additonals stringers complete the bridge. We add all together in a macro to keep the construction as flexible as possible!

//--------------------------------------////////// #macro Steel_Bridge_Framework_1( Len, // bridge length H, // bridge height W, // bridge width BD,// beam diameter BR,// beam border radius )// ------------------------ // ----------------------------------------------- // ------------------------------- default texture #ifndef( Steel_Bridge_1_Texture_1 ) #declare Steel_Bridge_1_Texture_1 = texture { pigment{ color rgb<1,1,1>*0.5} normal { bumps 0.25 scale 0.35 } finish { phong 1 } } // end of texture #end // ------------------------------------------ #local L = Len-BD; // inner bridge lenght //------------------------------------------------ // number of subdivisions: #local NSub = int(L/H); // equidistant distribution: #local SubDistance = L/NSub; // shearing factor: #local S_Factor = 0.5*SubDistance/(H+2*BR); //------------------------------------------------ #local Side_Beam = union{ #local Nr = 0; // start counter at zero! #while (Nr < 2*NSub ) object{ Round_Box(<-BD/2,0,-BD/2>, <BD/2,H+2*BR,BD/2>,BR,0) texture{ Steel_Bridge_1_Texture_1 } matrix< 1,0,0, // matrix-shear_y_to_x S_Factor, 1, 0, 0,0,1, 0,0,0> #if( Nr/2 != int(Nr/2 )) // uneven numbers scale<-1,1,1> translate<SubDistance/2,0,0> #end translate<Nr*SubDistance/2+BD/2,-2*BR,0> } // ------------------------------------- #local Nr = Nr + 1 ; #end // end // bottom strut object{ Round_Box(<0,-BD,-BD/2>,<L+BD,0,BD/2>,BR,0) texture{ Steel_Bridge_1_Texture_1 } } // top strut object{ Round_Box(<SubDistance/2,-BD,-BD/2>, <L-SubDistance/2+BD,0,BD/2>,BR,0) texture{ Steel_Bridge_1_Texture_1 } translate<0,H,0> } } // end of union // ----------------------------------------------- // ---------------------------------- final union: #union{ object{ Side_Beam translate<0,0,-W/2+BD/2> } object{ Side_Beam translate<0,0,-W/2+BD/2> scale<1,1,-1> } object{Round_Box(<0,-BD/2,-BD/3>,<L+BD,0,BD/3>,BR,0) texture{ Steel_Bridge_1_Texture_1 } translate<0,0,-W/4+BD> } object{Round_Box(<0,-BD/2,-BD/3>,<L+BD,0,BD/3>,BR,0) texture{ Steel_Bridge_1_Texture_1 } translate<0,0, W/4-BD> } #local Nr = 0; // start counter at zero! #while (Nr <= NSub ) // foot traversals object{ Round_Box(<-BD/2,-BD,-W/2>, <BD/2,0,W/2>,BR,0) texture{ Steel_Bridge_1_Texture_1 } translate<Nr*SubDistance + BD/2,0,0> } // foot diagonals #if( Nr < NSub ) object{ Round_Box(<-BD/4,-BD,-W/2+BD/2>, <BD/4,-BD/2,W/2-BD/2>,BR,0) texture{ Steel_Bridge_1_Texture_1 } matrix< 1,0,0, // matrix-shear_y_to_x 0,1,0, 1*(SubDistance-BD)/(W-BD),0,1, 0,0,0> #if((Nr/2) = int(Nr/2)) // even numbers scale<1,1,-1> #end translate<(Nr+0.5)*SubDistance+BD/2,0,0> } #end // end diagonals #local Nr = Nr + 1 ; #end // end loop } // end final union #end // ----------------------------- end of macro //--------------------------------------////////// //------------------------------------------------ object{ Steel_Bridge_Framework_1( 10.00, // bridge length 2.00, // bridge height 4.00, // bridge width 0.30, // beam diameter 0.05,// beam border radius )// ------------------------ rotate<0, 0,0> translate<0,0.0,0> } //----------------------------------------------

Note: For a more comfortable use of this as a ready-made object it should be put in an include file as demonstrated in the opposite sample files!