curious how modern engineers do this?
Fonzie
| Posted in Tools for Home Building on
I heard this week about a guy pouring concrete for 2 – 50 ft diameter grain bins and having the engineers come out during the pouring and locate the anchor bolts with their transit.
He said they had the locations programmed in, established 2 reference points and easily told them exactly where to put the bolts such that the bins dropped right on.
He didn’t think they even had to plumb up from the locations. I’m just curious how they do this and pretty sure somebody on here knows? tx
Replies
Too little information, I'm afraid.
Trimble¯ makes a variety of electronic survey equipment.
They are trying to sell us one that locates sleeves for high rises without having to lay out grids & tape measures.
It's a little too slow for my likes since I usually have about 300 to 500 sleeves per deck to set.
They used a total station wnich is a fancy name for an electronic transit/ distance measurer. The two reference points were probably already established and will be bench marks for the whole job. They had already established north and west from those 2 points and with that they can shoot any point on site. I'm not sure if this is the answer your looking for but I cant help much further than that. When I worked for a surveyor I was only a teenager so thats pretty much all I can remember.
Due to the recent state of the economy, the light at the end of the tunnel has been turned off
"Total Station" as others mentioned.
http://www.topconpositioning.com/products/optical/total-stations/general-construction/cts-3000.html
Hey if I could just push the question a little further - thanks by the way - what do they see when they look at the "screen" of their "total station"? Or is the message in the "reader" - does the main transit send out all the co-ordinates for the reader? I get the picture that it's like a localized gps system anchored to the two bench marks? The guy said he didn't think they used a plumb to locate the bolts so I wonder how the transit could be on the tripod and the locations be down from that but still accurate....(I'm with the cardboard template but this new equipment is fascinating - the disto d3 for one)
I am not sure. I was working the target when it was being used. I believe the machine displays the distance and direction to the ideal "Set point".
You start with a known point that you reference the machine to , then enter the measurements from that point to the point you want to find
Since it measures in three (horizontal, vertical and distance) dimensions using triangulation it can spot the "Set Point" without using a plumb line. brownbag may know for sure just what the display is.
They can't get your Goat if you don't tell them where it is hidden.
Fonzie,
There was a series on National Geographic Channel awhile back call "LA Hardhats" that told the story of buiding a residential high rise.
One of the episodes followed the plumbers and other pipe trades, and they had a few minute segment that featured the total station to lay out the sleeves and threaded inserts for pipe hangers.
Try this link if your interested:
http://channel.nationalgeographic.com/series/la-hard-hats/2990/Overview#tab-Videos/05590_00
That video was interesting - tx. I like what that guy was saying about holding back pressure - not letting them rush him. The thousands they were talking about (having to move a can) helps pay for the "total station" transit.
its works off the PFM system, Pure F*&^%* magic
Fonzie,
The total station is set on the tripod over a control point. Although they don't have to plumb down to the control point with a plumb bob, they do level the instrument and look through an "optical plummet" (basically a right angle prism with crosshairs) to align the instrument directly over the control point (plumb). The Instrument man will sight a target on the other control point, called a backsight. Usually you set Zero degrees on the instrument while sighted on the backsight target. All control points and construction points for the project will be in a coordinate system. Using the two control points the total station, or data collector attached to it, can calculate an angle and distance to any point you want, in this case the anchor bolt locations (which are predetermine in the office). You punch in the point you want to stake out and the data collector will tell you to turn to angle ####.xx.xx. degrees/minutes/seconds. You line up your rodman on this line and take a distance measurement. The data collector then says "go back x.xx feet", or "come forward x.xx feet." If they're good it only takes a few shots to get your point within a few hundredths of a foot.
The "screen" on a total station varies by make and model.
What they do is to establish the coordinates for stakeout in an electronic model in a computer. You can do them by hand, but most people are using some form of computer program.
I start with an initial site survey, based on two points, I arbitrarily set. Depending on how big the site survey gets, and how much stuff is in the way, I set more control points, as I go to allow me to move the instrument and see everything. The control points are typically 5/8-inch rebar driven several feet into the ground, with fancy little plastic caps driven on. The caps, have a little hole in the middle, that shots are taken to, and which is used when you set the instrument over it if you occupy that point.
The points are then downloaded into the survey and design software and the digital model of the site is developed.
From there I do the design work, and locate the improvements. Any points that I need to set out the improvements get developed, and named. A list containing the data (Northing, Easting, and elevation) for each point is made up, and that list is then uploaded into the instrument.
When you get to the site, you set up the instrument over any control point that will let you see where you need to stake out the improvement points, and at least one other control point.
When you select a point to stake out, the instrument will tell you where to aim, and how far out the point is. The guy with the prism, gets on line, and you move him in or out, until he is on the point you want.
Does the prism have to be on a level plane with respect to the instrument, or can the instrument calculate the z coordinate as well?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
The instruments measure three things: vertical angle, from either the horizon, or plumb, depending on how you set it up; horizontal deflection from the backsite point; and distance. When you set up on a point, the instrument will query you for the point number, and the height of the instrument above the point. It then knows where it is, because it knows the Northing, Easting, and elevation of the point, and adds the vertical correction to the points to determine it's elevation. You then take a shot on the prism, held on another point, which is called the backsite. And the instrument will ask what point you are shooting, and what the rod height is. The instrument will then calculate the elevation of the backsite point, and the distance to it. If there is any error it will alert you and ask if you want to continue. It also, determines it's angular orientation to the model world, by calculating the azimuth between the two points, and setting itself to match that. When you are taking shots, you are asked what the rod height, or distance from the prism to the bottom of the pole is. Since the prism rods are generally adjustable, you can move up and down to clear obstacles to the line of site. But, the instrument needs to know what the height is because it is calculating the coordinates of the points as you go. When you are in the stake out mode, the instrument calculates the coordinate of the prism, and adjusts for the rod height to determine the coordinates of the ground point. It then compares those coordinates to those of the point you are trying to set, and gives you the distances in or out, and left or right to the point, and the cut or fill to the design grade. If you have been doing it for a while, and have any natural sense of space and distance you rapidly get skilled enough to be on the point within a couple of shots. Many of the newer instruments are prismless, meaning that the laser / laser sensor system, is good enough it can generate a strong enough pulse to measure the bounce back with out the prism. The prismless units work well on open ground. But, for work in rough vegetated terrain, the prisms work better, because they lessen the chance of accidentally reading a wet leaf, or some other slightly reflective thing that happens to be there. There are also robotic units out now that have the controls mounted on the prism rod, and a radio frequency tracking system, so the instrument follows the rod, and the operator can take the shots, and see the results while at the rod. They cost about $40,000 to $60,000, as compared to $20,000 to $40,000 for a standard system that requires a minimum of two people. But, since you only have one person in the field, the pay off time can be quite short.
That's some pretty cool stuff.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
They show up with all their fancy, expensive gadgetry and then, when nobody's looking, they break out the cardboard template and make all thier marks.
~ Ted W ~
Cheap Tools! - MyToolbox.net
See my work at TedsCarpentry.com
IIRC some of the total stations are close to $20,000. A little more than my Hilti laser. :o)
What Doobz24 said, and a little more. You can locate any point in space through X,Y, and Z coordinates. The "engineer" (most likely a poor underpaid techie) establishes a coord system on each piece with an easily definable POB (point of beginning) and a reference line or bearing. Then, on the computer, he will be able to generate coords of all points, and then calc the angles and distances to each to .00001" accuracy. You can't set'em that close, but it makes the calcs look pretty. The interesting thing is, that you don't even need an instrument. Any point may be positioned from another point by calcing the distances between by "inversing.". Pull one distance and strike an arc, pull the other, and where they intersect, set the point.
Total stations will generate their own coords and calc the course (angle) and distance and display it on the screen...and the data recorder.
There are pitfalls though. If you need to check your work as the gunner may have busted an angle, somebody held or set the wrong distance, or just read it wrong. Shid happens, so double checking is smart...