alan Wrote:
The track is built in sections varying around 300m in length with the beams sitting on bearings that allow expansion / dynamic movement. Each section is buttressed by a thrust block which resists the downwards pull of gravity on the superstructure supporting the track. Expansion joints in the track are situated on some of these.
Not talking about the beam to pier expansion...I'm talking about the beam expansion along its length...& by joining the pre-cast beams together by casting insitu at the sections/joints between each pre-cast beam section they are making the effective total length of the beams much greater by adding the precast sections together with insitu cast infill
Thus you have forces of expansion & load deflection from the pre-cast section interacting with the insitu cast section which has a different set of forces....thus the weak point is the cast joint....& here you get failure...
They should have cast with vertical expansion joints at every section thus every pier to pier section can move differently to the next one...to accommodate ground heave due to frost etc. & also the train loads as the angle of the train on each section causes different loading as it passes over each section...think of the flat sections where the weight is more distributed between the two piers...then the steeper sections where the downhill pier will always carry more weight...
Basic structural & foundation/load design..
...& I have noticed these joints when I have been ski-ing & have wondered at their suitability before...
PPS...as this work to fix is not accounted for in costings as too young in the life span...I bet NR will want nothing to do with it as this is design failure from the start when HIE contracted it...therefore HIE problem..I hope NR want "out"...
---That was not a fall, I intended to do that!---
Edited 1 times. Last edit at 17.45hrs Wed 3 Oct 18 by SnowmanDave.
