Hi hangten1

My steps...

View Top Camera ->Parallel Projection Zoom Extents File -> Print Preview
Try with my settings.
Scale 1:5 will fit on A4 page.
Scale 1:1 will need 995.3mm x 532.8mm page or you can print few views on few pages to get the truss in desired scale.
PS. I have PDF Creator installed to test any printing scale and page format available.

20130413-SUFPrint.jpg

bridge1_beginner.skp

bridge1_beginner.pdf