wooden warren truss rods question

[FJ and G]

got nearly half down, tho wood ties and rails not yet spiked and footers need some sheathing and tiny rails need to be placed between the bridge and its footing, but here's the progress thus far (it's just layed there for the photo and for measuring purposes). Used thin rebar from Lowe's (approx. gauge 12)







BB the beagle watches from nearby brambles

[larak]

What Jeffers said. However (just my preference) I would make the metal rods structural. I think it would make for a stiffer bridge and one more likely to hold together over the long haul (pun intended.).

Thirty feet long? Wow! I'd like to see some photos (with something or someone in them for scale) of the finished product.

Karl

[rrebell]

Put the rods and nut and bolt washers on it or it will not look real at all!!!!!!!!

[jeffers_mz]

In protptype applications, timber is tough to employ in tension, as fasteners concentrate the pull into point loads, which the wood fibers cannot resist well.

 

Tension rods pass clean through top and bottom chords, and the load is then spread out by using a plate washer and bolt. You can carry higher loads, using less timber, by replacing tension members of the truss with truss rods.

 

In model construction, you've already answered your own question. If model truss rods would be cosmetic only, and you'd rather not take the time, either way, you don't change the bridge's capacity. That makes it a question of appearance, which you've already decided.

[FJ and G]

I'm going to be making this bridge but in wood this weekend in 6 segments, totaling 30 or so feet long. It is for 7/8n18 scale on 32mm gauge track.

http://www.brantacan.org.uk/worcsr6X.jpg

The question I have is: are steel rod tensioners necessary in the bottom sides and top or have these wood trusses been designed without them?

The rods in photos I see run vertical, not diagonal.

Structurally, the wood should hold the truss together well, but the rods would be cosmetic. If I don't need to use them, that's one less thing to do.

Here's the bottom half brad nailed together. The outer longitudinal boards and the 2 upright diagonals on both sides are not nailed and are just there to show how the design will evolve.

The top portion of the truss will mirror the bottom that you see here. Additionally, the top portion will contain the longitudinal boards for the ties to reside upon.

Length of this span is 37.5 inches or nearly a meter.

I'll await any comments before continuing.

BTW, these things go together pretty quickly. My neighbors are learning to hate me with the loud noise of the table saw on my brick patio.