1. Unit 10 -Surveying in Construction LINEAR MEASUREMENT Angelo Filomeno HEPS Higher Education & Access Studies angelo.filomeno@cnwl.ac.uk

2. Linear Measurement In these lectures we will cover : –The role of linear measurement –Equipment –Procedures and rules –Errors –Applications of linear measurement

3. What is linear measurement? Simply the measurement of distance : New building site - how big is it? 50.5 metres 27.9 metres

4. Distance measuring equipment and typical accuracies Pacing (1:100) Optical range finder (1:300) Trundle wheel (1:500) Stadia tacheometry (1:1000) Taping or chaining (1:10,000) Electronic distance measurement (1:50,000)

5. Some things to note… Equipment is fairly cheap (except EDM) Equipment is easy to maintain and adjust (!) Distances are easy to measure Very accurate results can be achieved (with care) Measurement line needs to be unobstructed Errors occur and need to be managed or minimised

6. Taping procedures Tape must always be straightstraight Tape must not be twisted Use chaining arrows for intermediate pointschaining arrows Tape horizontally if possible Tape on the ground if possible Slope taping needs to be reducedSlope taping Catenary taping requires correctionCatenary Step taping suits some applicationsStep taping

7. Tape must be straight… required distance measured obstruction measured distance  required distance

8. Use chaining arrows… required distance measured distance measured distance  required distance

9. Slope correction… For example : s = 30.589 m  = 2.5 o  H = 1.334 m then h = 30.589 cos(2.5) h = 30.560 m To calculate the horizontal distance : h = s cos  or h = (s 2 -  H 2 ) 1/2 measured (slope) distance = s  horizontal distance = h HH Or…. s = 30.589 m  H = 1.334 m then h = (30.589 2 - 1.334 2 ) 1/2 h = 30.560 m

10. Step taping… required (horizontal) distance

11. Catenary taping… measured distance measured distance  required distance required distance

12. Types of errors Blunders –mistakes and gross errors Systematic errors –repeated size and sign –affect accuracy Random errors –small and usually undetectable (noise) –affect precision These error types apply to any measurement technique used in surveying…

13. Accuracy and precision

14. Sources of error in taping Temperature correction L = L +L.c.  T where : L is the corrected distance L is the measured distance c = 1.15 x 10-5 m/ o C (for a steel band)  T =T actual - T standard

15. Sources of error in taping Standardisation –The tape is not of “true” length

16. Sources of error in taping Catenary (sag) –A suspended tape will measure too long where : M is the mass per unit length (0.011 kg/metre) g is gravity (9.8 metre/sec 2 ) T is the tension (50 Newton)  is the slope angle

17. Sources of error in taping Tension –Tape length will depend on applied tension Slope –Distances must always be reduced to horizontal

18. Applications Dimensions of building features Block dimensions Location and size of site features Setting out for construction Clearances and tolerances

19. An example road width building setbacks building dimensions side boundary clearances underground services block dimensions

20. Further Details on measuring for obstructed vision See word documents