Going to build a trestle on a log pike, do I build the trestle first or the canyon it will cross? It makes no difference at this time as I can make the canyon fit the trestle or the trestle fit the canyon. Is there a strict rule of construction I’m unaware of ??? or am I making up problems that don’t exist ???
If I were trudging along a planned right of way, doing my locating surveys, and came upon an obstacle, I would have to consider bridging that obstacle…and so should you. In every instance, so far, I have visualized what I wanted, but when I had the terrain completed and ready to drop a bridge or trestle into the gap, I could see that what I had envisioned and what was before me were different in a number of ways. So, if I were you, I would go ahead and build terrain, and then build a trestle to fit. I make the bents a bit long and then trim each one until it will sit fairly snugly on a sill plate and not force the tracks overhead to lift, nor to let them sag even 1 tenth of a millimeter.
I make the gorge, draw it in profile, and make each bent about 3/4" longer than the drawn profile suggests is needed. Then, when I am ready to insert the trestle, I overlay the gorge with a section of track to meet tracks on either side of the gorge that I have already placed. Depending on the span, the section of unsupported track may dip a bit, but you will be fitting the trestle so that any grade is maintained between the already completed ends on either side. After a series of cut and fit, cut and fit, file and fit, sand and fit, the trestle will slide snugly under the span of track and support it to meet grade while each bent rests well on top of the sills.
Strictly speaking, the egg comes first. [;)]Then it hatches and grows up to be a chicken.[:-^]