BCN 3281 Construction Layout

1
BCN 3281 Construction Layout

• Week 3

2
Chapter 3 Review

• Distance Measurement
• Today all of the countries in the world except
  Burma, Liberia, and the United States use the
  metric system for their measurements
• The meter is a unit of French origin supposedly
  equal to 1/10,000,000 of the distance from the
  equator to the north pole

3
Distance Measurement (cont.)

• Metric system
• Its application in the United States in the past
  has been limited almost entirely to geodetic
  surveys
• the meter is defined as being equal to 3.280833
  ft (or 39.37 in.)
• 1 inch is equal to 2.540005 centimeters.

4
Distance Measurement (cont.)

• Metric system (cont.)
• Since September 30, 1992, all federal agencies of
  the United States have been required to use
  metric units for procurement, grants, and
  business-related activities
• Since January 1994 the SI (System International)
  system must be used for the design of all new
  federal facilities. Exsurveys for highways,
  bridges, dams, utilities, and government
  facilities

5
PACING

• Accuracy Pacing ?
• Pacing is used to make approximate measurements
  quickly or to check measurements made by more
  precise means
• Pacing is used to detect large mistakes
• A person can determine the value of his or her
  average pace by counting the number of paces
  necessary to walk a distance that has been
  previously measured more accurately (e.g., with a
  steel tape)
• The pace is considered to be one step

6
PACING

• Downhill or Uphill ?
• Adjustments should be made when pacing on sloping
  ground
• Paces tend to be shorter on uphill slopes and
  longer on downhill ones
• Thus you would do well to measure your pace on
  sloping ground as well as on level ground

7
ODOMETERS AND MEASURING WHEELS

• Relation Distance/ Revolution !!
• Distances can be roughly measured by rolling a
  wheel along the line in question and counting the
  number of revolutions
• An odometer is a device attached to the wheel
  (similar to the distance recorder used in a car)
  which does the counting and from the
  circumference of the wheel converts the number of
  revolutions to a distance

8
ODOMETERS AND MEASURING WHEELS

• Accuracy ?
• Such a device provides a precision of
  approximately 1/200 when the ground is smooth,
  (along a highway )
• The results are much poorer when the surface is
  irregular !!!

9
Stadia

• What is Stadia ?
• Stadia is the plural of the Greek word stadium,
  which was the name given to a foot race track
  approximately 600 ft in length
• Transit and Theodolite telescopes are equipped
  with three horizontal cross hairs which are
  mounted on the crosshair ring. The top and bottom
  hairs are called stadia hairs

10
Stadia

• How does it work ?
• The surveyor sights through the telescope and
  takes readings where the stadia hairs intersect a
  scaled rod. The difference between the two
  readings is called the rod intercept
• The hairs are so spaced that at a distance of 100
  ft their intercept on a vertical rod is 1 ft at
  200 it is 2 ft

11
Stadia

• How does it work ? (cont.)
• When one is working on sloping ground, a vertical
  angle is measured and is used for computing the
  horizontal component of the slope distance.
• These measurements can also be used to determine
  the vertical component of the slope distance or
  the difference in elevation between the two points

12
Stadia

• Accuracy ?
• Precisions of the order of approximately 1/250 to
  1/1000 can be obtained with Stadia
• Such precision is not usually satisfactory for
  property surveys

13
ELECTRONIC DISTANCE MEASUREMENTS

• How does it work ?
• It is based on using the sound waves and the
  lapse between their emission and reception
• The speed of sound is 1 129 ft/sec at 70F and
  increases by a little more than 1 ft/sec for each
  degree Fahrenheit increase in temperature

14
ELECTRONIC DISTANCE MEASUREMENTS

• When is it used ?
• Usually EDM are used for distances greater than
  100.00 ft or greater distances.
• Though the precisions obtained for small
  distances (100 ft or less) are probably better
  when steel tapes are used
• The average surveyor today with EDMs rarely
  bothers to use tapes for any distances short or
  long.
• The supposed error occurring when an EDM is used
  is something in the order of (5 mm), and it is a
  fixed instrument error

15
ELECTRONIC DISTANCE MEASUREMENTS

• When is it used ? (cont.)
• The 5 mm part is much more important in its
  effect on precisions for short distances than for
  long ones, as is the error occurring due to the
  fact that reflectors cannot be set exactly over
  points

16
TAPING OR CHAINING

• Measuring with a tape
• For anybody watching surveyors measuring
  distances with a steel tape, might think
  "Anybody could do that. What could be simpler?"
• Measuring distance with a steel tape, though
  simple in theory, is probably the most difficult
  part of good surveying
• Precise distance measurement with a steel tape
  requires thought, care, and experience. In
  theory, it is simple, but in practice it is not
  so easy

17
Measurement Methods
18
EQUIPMENT REQUIRED FOR TAPING

• What equipment do you need ?
• A one 100-ft steel tape
• Two range poles
• A set of 11 chaining pins
• A 50-ft woven tape
• Two plumb bobs
• A hand level

19
Steel Tapes

• What you need to know ?
• The tapes are quite strong as long as they are
  kept straight, but if they are tightened when
  they have loops or kinks in them, they will break
  very easily
• If a tape gets wet, it should be wiped with a dry
  cloth and then again with an oily cloth

20
Range Poles

• What you need to know ?
• Range poles are used for sighting points
• For marking ground points
• For lining up tapemen in order to keep them going
  in the right direction

21
Range Poles

• What you need to know ?
• Range poles are used for sighting points
• For marking ground points
• For lining up tapemen in order to keep them going
  in the right direction
• Also the rods are used for rough distance
  measurements

22
Taping Pins or Chaining Pins

• What you need to know ?
• Taping pins are used for marking the ends of
  tapes or intermediate points while taping

23
Plumb Bobs

• What you need to know ?
• A plumb bob is suspended on a string or wire and
  used to establish a vertical line

24
Woven Tapes

• What you need to know ?
• They are commonly used for finding existing
  points, locating details for maps, and measuring
  in situations where steel tapes might easily be
  broken (as along highways) or when small errors
  in distance are not too important
• Their lengths should be checked periodically or
  standardized with steel tapes

25
Hand Levels

• What you need to know ?
• Used for taping and for rough determination of
  elevations
• Consists of a metal sighting tube on which is
  mounted a bubble tube
• The bubble tube is located on top of the
  instrument and its image is reflected by means of
  a 45 mirror or prism inside the tube so that its
  user can see both the bubble and the terrain
• If the bubble is centered while sighting through
  the tube, the line of sight is horizontal

26
Clamping Handles

• What you need to know ?
• Leather thongs are usually placed through the
  loops provided at the ends of the tapes
• With these thongs or with spring balances
  attached to the same loops, the tapes may be
  tensioned to desired values
• When only partial lengths of tapes are used, it
  is somewhat difficult to pull the tape tightly.
  For such cases clamping handles

27
TAPING OVER LEVEL GROUND

• What you need to know ?
• If taping is done on fairly smooth and level
  ground where there is little underbrush, the tape
  can rest on the ground
• The taping parry consists of the head tapeman
  and the rear tapeman.
• The head tapeman leaves one taping pin with the
  rear tapeman for counting purposes and perhaps to
  mark the starting point. The head tapeman takes
  the zero end of the tape and walks down the line
  toward the other end

28
TAPING OVER LEVEL GROUND (cont.)

• What you need to know ?
• When the 100-ft end of the tape reaches the rear
  tapeman, the rear tapeman calls "tape" or "chain"
  to stop the head tapeman.
• The rear tapeman holds the 100-ft mark at the
  starting point and aligns the head tapeman (using
  hand and perhaps voice signals) on the range pole
  which has been set behind the ending point.

29
TAPING OVER LEVEL GROUND (cont.)

• What you need to know ?
• Usually, this "eyeball" alignment of the tape is
  satisfactory, but use of a telescope is safer and
  will result in better precision
• Sometimes there are places along a line where the
  tapeman cannot see the end point and there may be
  positions where they cannot see the signals of
  the instrumentman. For such cases it is necessary
  to set intermediate line points before the taping
  can be started

30
TAPING OVER LEVEL GROUND (cont.)

• What you need to know ?
• It is necessary to pull the tape firmly
• This can be done by wrapping the leather thong at
  the end of the tape around the hand, by holding a
  taping pin that has been slipped through the eye
  at the end of the tape, or by using a clamp

31
TAPING OVER LEVEL GROUND (cont.)

• What you need to know ?
• After 1000 ft has been measured, the head tapeman
  will have used his eleventh pin, and he calls
  "tally" or some equivalent word so that the rear
  tapeman will return the taping pins and they can
  start on the next 1000 ft

32
TAPING ALONG SLOPING GROUND

• What you need to know ?
• When sloping distances are to be measured, there
  are three taping methods that can be used
• The tape may be held horizontally
• The tape may be held along the slope, the slope
  determined, and a correction made to obtain the
  horizontal distance
• the sloping distance may be taped, a vertical
  angle measured for each slope, and the horizontal
  distance later computed. The latter method is
  sometimes referred to as dynamic taping.

33
Holding the Tape Horizontally

• What you need to know ?
• The tape is held horizontally, but one or both
  tapemen must use a plumb bob
• If taping is being done uphill, the rear tapeman
  will have to hold his or her plumb bob over the
  last point, while the head tapeman may be able to
  hold his or her end on the ground
• If they are moving downhill, the rear tapeman may
  be able to hold his or her end on the ground
  while the head tapeman uses a plumb bob

34
Holding the Tape Horizontally (cont.)

• Limitations ?!!
• Please refer to page 44 in the surveying book. It
  is very important to know the level of accuracy
  and the different limitations to this method.

35
Taping on Slopes

• What you need to know ?
• Slope taping is quicker than horizontal taping
  and is considerably more precise because it
  eliminates plumbing with its consequent
  accidental errors
• Taping along slopes is sometimes useful when the
  surveyor is working along fairly constant, smooth
  slopes or when he wants to improve precision
• Limitations the method is generally not used
  because of the problem of correcting slope
  distances to horizontal values. This is
  particularly true in rough terrain where slopes
  are constantly varying and the problem of
  determining the magnitude of the slopes is
  difficult