RMweb Gold Captain Kernow Posted June 18, 2015 Author RMweb Gold Share Posted June 18, 2015 In the meantime, here's a nice picture of the bridge: Link to post Share on other sites More sharing options...
RMweb Gold Captain Kernow Posted June 18, 2015 Author RMweb Gold Share Posted June 18, 2015 Oh, and here are a couple of photos of an old nut and screw thread taken from the bridge during the refurbishments, and replace with modern equivilents. These are big items and very heavy! Note the way the pin has been worn down over the years by the metal hawsers attached to it. Shortly after I too these photos, a chap from Taziker popped up into the office and took them away to be shot-blasted clean! Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted June 18, 2015 RMweb Gold Share Posted June 18, 2015 Presumably if it's inside the tower, with a vertical line painted behind it and a marked position to sight from, it would show any movement of the tower? I think we now know that you get the prize. It wouldn't need a vertical line behind it, just some marks on the floor below it. Martin. Link to post Share on other sites More sharing options...
RMweb Gold Enterprisingwestern Posted June 18, 2015 RMweb Gold Share Posted June 18, 2015 In the meantime, here's a nice picture of the bridge: IMG_6187.jpg Would look better with a hydraulic on it. Cue......................................... Mike. Link to post Share on other sites More sharing options...
RMweb Gold Worsdell forever Posted June 18, 2015 RMweb Gold Share Posted June 18, 2015 Would it have been at the bottom of a rope/chain mechanism to indicate the volume of water in a column or tank? I.e it would have pointed to a scale of gallons. You ain't pointing that thing at me sonny... I think we now know that you get the prize. It wouldn't need a vertical line behind it, just some marks on the floor below it. Martin. No need for marks or lines, go inside the tower, if the thing swings over and clobbers you the bridge is swaying... Link to post Share on other sites More sharing options...
RMweb Premium rab Posted June 18, 2015 RMweb Premium Share Posted June 18, 2015 In the meantime, here's a nice picture of the bridge: IMG_6187.jpg Any chance you can get something done about all that vegetation spoiling the veiw of the bridge Cap'n. Name your price, pasties or sausages.We'll have a whip round, or as I believe it's now called, cloud fund it Link to post Share on other sites More sharing options...
RMweb Gold Stubby47 Posted June 18, 2015 RMweb Gold Share Posted June 18, 2015 Any chance you can get something done about all that vegetation spoiling the veiw of the bridge Cap'n. Name your price, pasties or sausages. We'll have a whip round, or as I believe it's now called, cloud fund it. Or take the photo from the other side... Link to post Share on other sites More sharing options...
woodenhead Posted June 18, 2015 Share Posted June 18, 2015 Well, we've now come up against the limitations of an operator pretending to be an engineer. All I know is that the line was inside the structure of the bridge, and was used to measure wind deflection of the main structure. Next time I get a chance to speak to the (real) engineer that showed me, I'll ask for more information on how it was set up. If you heard a bong in the wind you knew the bridge was leaning too far! Link to post Share on other sites More sharing options...
muddys-blues Posted June 18, 2015 Share Posted June 18, 2015 Well that was enlightening, thank god the answer came out earlier than my suggestion I was going to say a plug of some sort ... but I didn't want to be butt of many jokes Link to post Share on other sites More sharing options...
RMweb Premium rab Posted June 18, 2015 RMweb Premium Share Posted June 18, 2015 Well that was enlightening, thank god the answer came out earlier than my suggestion I was going to say a plug of some sort ... but I didn't want to be butt of many jokes Or make an ass of yourself! Link to post Share on other sites More sharing options...
RMweb Premium St Enodoc Posted June 18, 2015 RMweb Premium Share Posted June 18, 2015 In the meantime, here's a nice picture of the bridge: IMG_6187.jpg I clicked 'like' but I would like to 'unlike' the very badly photoshopped building at the bottom left. Link to post Share on other sites More sharing options...
BG John Posted June 18, 2015 Share Posted June 18, 2015 I clicked 'like' but I would like to 'unlike' the very badly photoshopped building at the bottom left. That's not the Cornish side is it? If so, the house must belong to someone with a death wish. Or a UKIP member! Link to post Share on other sites More sharing options...
RMweb Gold Captain Kernow Posted June 19, 2015 Author RMweb Gold Share Posted June 19, 2015 That house has been painted like that for many years. Link to post Share on other sites More sharing options...
RMweb Premium rab Posted June 19, 2015 RMweb Premium Share Posted June 19, 2015 That house has been painted like that for many years. I think it's a pub. Link to post Share on other sites More sharing options...
Pacific231G Posted June 19, 2015 Share Posted June 19, 2015 We don't seem to be much further forward. A plumb line hangs vertically. Winds blow sideways. A plumb line can be used to check verticals, but in order to measure deflection it needs a solid surface below it as reference. I suspect the River Tamar doesn't count. I can imagine it mounted somewhere on the bridge and used as a sighting target for measuring deflections. But that wouldn't be called a plumb line. More information and diagrams please. Martin. Surely a tower is a vertical beam fixed at its base so the floor of the tower would provide a fixed reference. The force of a wind blowing past it would create a bending moment that would cause it to lean slightly and the top of the tower would be deflected sideways relative to its base. So, If you hang a plumb line from the top of the tower then at the base the plumb bob will be deflected sideways by the same amount as the top of the tower. If the point at the bottom of the bob is hanging just above the floor then if you mark its position when there's no wind you can directly measure the the deflection of the top of the tower from its base. I'd guess that there was something like a brass plate mounted on the base immediately under the pointer of the bob with the deflections marked in inches. That could have been converted into an angle of lean but the deflection itself was probably more relevant in terms of bridge security. It would also tell you if the tower had developed a permanent lean after a particularly powerful storm and that may have been its main purpose. It does occur to me though that the plumb bobs may have been set up not to measure deflections caused by high winds but rather those created by misadjustments of the bridge members. The Royal Albert Bridge is unusual in combining a bowstring with a suspension design to create two self balanced spans that don't exert significant horizontal forces on the towers. The suspension chains of a suspension bridge tend to pull its towers together while the arch of a bowstring tends to push them apart. Those two forces have to be kept well balanced. The plumb bobs would indicate any imbalance and allow the chains to be tightened or loosened accordingly. There probably would be slight stretching of the suspension chains over time and that would have to be adjusted for. Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted June 19, 2015 RMweb Gold Share Posted June 19, 2015 Surely a tower is a vertical beam fixed at its base so the floor of the tower would provide a fixed reference. The force of a wind blowing past it would create a bending moment that would cause it to lean slightly and the top of the tower would be deflected sideways relative to its base. So, If you hang a plumb line from the top of the tower then at the base the plumb bob will be deflected sideways by the same amount as the top of the tower. I think if you had read on a bit further you would have realised that we had all arrived at that conclusion. The missing piece of information for me was that the towers have a straight hollow shaft from top to bottom. Obviously a plumb line outside the tower would be useless in a howling gale. I'm still thinking that movement of the tower in a strong gusty wind would cause the line to start swinging like a pendulum, making it very difficult to get any useful information from it. That's why I'm waiting for a bit more info from CK. regards, Martin. Link to post Share on other sites More sharing options...
RMweb Gold Captain Kernow Posted June 19, 2015 Author RMweb Gold Share Posted June 19, 2015 I was specifically told that it hung down to measure movement of the bridge in high winds. I will supplement this as and when I can, but I'm not due to see the engineer again for a while. Link to post Share on other sites More sharing options...
RMweb Premium 47137 Posted June 19, 2015 RMweb Premium Share Posted June 19, 2015 It might have been at the bottom of a long metal rod, fixed high up inside the tower. A plate with some concentric rings underneath it, most usefully on the floor/ground. Then it could measure deflection during a high static load (e.g. broken-down train) as well as dynamic loads. The brass boss on the end would support this. It was a plumb bob it would have a loop for a rope or wire. - Richard. Link to post Share on other sites More sharing options...
RMweb Gold Stubby47 Posted June 19, 2015 RMweb Gold Share Posted June 19, 2015 I think it was orientated as shown in the first photo, and was a screw fitting to the top of Brunell's head to keep his top hat on. Link to post Share on other sites More sharing options...
RMweb Gold Captain Kernow Posted June 19, 2015 Author RMweb Gold Share Posted June 19, 2015 The item was definitely attached to a long piece of string, that was how it was described to me. Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted June 19, 2015 RMweb Gold Share Posted June 19, 2015 The item was definitely attached to a long piece of string, that was how it was described to me. So it was used finally to answer the question "How long is a piece of string?" Link to post Share on other sites More sharing options...
RMweb Gold Stubby47 Posted June 19, 2015 RMweb Gold Share Posted June 19, 2015 So it was used to finally answer the question "How long is a piece of string?" If it's still there, quite long... Link to post Share on other sites More sharing options...
Pacific231G Posted June 19, 2015 Share Posted June 19, 2015 I think if you had read on a bit further you would have realised that we had all arrived at that conclusion. The missing piece of information for me was that the towers have a straight hollow shaft from top to bottom. Obviously a plumb line outside the tower would be useless in a howling gale. I'm still thinking that movement of the tower in a strong gusty wind would cause the line to start swinging like a pendulum, making it very difficult to get any useful information from it. That's why I'm waiting for a bit more info from CK. regards, Martin. I did read on Martin but, as people were still referring to inclinometers, it didn't seem entirely clear that the plumb line, which would of course have had to be inside the tower or in a special vertical shaft, was directly measuring the total deflection of the top of the towers. I'm not sure whether the oscillating swaying of the tower in a high wind would cause a pendular oscillation of the plumb line; I think that depends on their relative natural frequencies but it's an awfully long time since I studied this. I don't know how common it was to fit permanent plumbs to structures like bridges; all the references I've found to plumb lines with bridges relate to their construction or to later individual measurements using a temporary plumb line and not to permanent monitoring of the completed structure. Modern large bridges are though often fitted with accelerometers and displacement sensors to measure the effects of "wind excitation" The only references I can find to the use of permanently installed plumb lines relate to monitoring longer term movements in structures rather than measuring the immediate effects of winds or trains. Modern electronic counterparts to plumbs have been used a lot to monitor the effects of for example the Cross-Rail tunneliing on adjoining buildings or the sinking of the new Westminster Underground Station on the Palace of Westminster but I did find a detailed description from 1980 by the US Army Corps of Engineers of the fitting of permanent traditional plumb lines in structures such as dams. http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-4300.pdf The relevant stuff is in section 4 and the plumb lines were mounted in vertical pipes embedded in the concrete with a measuring station at the bottom. These plumb lines were damped by immersing the plumb bob in an oilbath to prevent any pendular oscillation but the movement they were designed to detect required microscope micrometers so probably very much smaller than those used for the Royal Albert Bridge. I'll be very interested to see whatever else Captain Kernow is able to find out. I wonder if IKB fitted anything like this to the Clifton Suspension Bridge? Link to post Share on other sites More sharing options...
RMweb Premium Gwiwer Posted June 20, 2015 RMweb Premium Share Posted June 20, 2015 In the meantime, here's a nice picture of the bridge: IMG_6187.jpg Time for the photographic mob to attend with their loppers perhaps? And about time that house on the Cornish side was repainted and stopped displaying the enemy flag as one enters the Holy Principality of Pastygonia. Link to post Share on other sites More sharing options...
RMweb Premium St Enodoc Posted June 20, 2015 RMweb Premium Share Posted June 20, 2015 Time for the photographic mob to attend with their loppers perhaps? And about time that house on the Cornish side was repainted and stopped displaying the enemy flag as one enters the Holy Principality of Pastygonia. Promoted from a Duchy to a Principality? Won't that upset Stubby47 and his compatriots? And was it a Captain's Call (Australian in-joke)? Link to post Share on other sites More sharing options...
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