Truss Bridge Diagram Quiz: Answers

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Photo by Ricardo Esquivel on

And now, after having done the Guessing Quiz, let’s have a look at the results. What I’ve done here is numbered the bridge types and pointed them out in the picture with an arrow.


The green line indicates the decking of the bridge, the red is the bottom chord. The bottom chord consists of a square-shaped panel with diagonal beams cris-crossing each other like the letter X. For the top chord of a through truss bridge, it’s the same as one can see in nr. 13. While the side view of the bridge doesn’t specifically show what the chords look like, another diagram, done in 3D and from a bird’s eye perspective shows the cross section of the bridge, including its decking.   The panels are the side chords where the vertical beams support the top and bottom chords. The diagonal beams, pending on the truss design, keeps the panel together and prevents it from folding.



What’s missing from this diagram are the lalley columns, which is nr. 16. Lally columns are cylindrical piers that are used to support the end post and the bottom bridge decking. Lallies, used up to ca. 1890, were the predecessor to concrete piers that were used when standardized trusses were built beginning between 1890 and 1900. The Henry Bridge has no lally column because the truss bridge is the lone span going across the river. It’s supported by the abutments alone, as marked with nr. 11.  Railings, marked with nr. 12 were once built using iron and steel; many of them had lattice bracing. In later bridge constructions and when rehabilitated, concrete railings and decking were used.

While I hope the answers and the supplemental diagram are of some help, a closer version of the bridge can be found through a series of drone videos one can find in the social media, including youtube. This one presented below is a series on historic truss bridges spanning the Bear River in the US state of Utah. There you can get a close-up of where the truss parts are.


After looking at the parts of the truss bridge, the next bridge will feature a similar bridge type but one that was more commonly built before the truss bridge itself. As a hint, the Kern and Blackfriars Bridges are the two longest of their kind.

bhc est 2010a