Trim shape? Am I using it correctly?

[KenS]

Hello,
I'm relatively new to Visio and am hoping someone can assist.  I have a shape that I need to edit.  In AutoCAD the function is called trim, and it deletes the portion of the shape which is hanging over a wall.  I have attached a screen shot which I hope shows what I am trying to do.  There are thin red lines perpendicular and crossing the ladder racks, I wish to end the ladder racks at those red lines and delete the portion after the red line. 

I have tried the trim function but it broke the shape apart into all its individual lines.  Am I using them wrong, or is there another function I should be using?   

I appreciate any help! 

Ken

[Surrogate]

Visio have same function. In Visio 2010 you can find it in Developer Menu

But you must turn on Developer Mode, because it is turn off by default!!!

In previous versions of Visio this function you can see in Shapes - > Operations -> Trim


But in Visio this function not so good as in AutoCAD. 
if you trim few thick black lines by thin red line. All lines became red and thin, same as edge line !!!