Page 246 - Civil Engineering Formulas

180 CHAPTER SEVEN

For ordinary taping, a tape accurate to 0.01 ft (0.00305 m) should be used. The
tension of the tape should be about 15 lb (66.7 N). The temperature should be
determined within 10°F (5.56°C); and the slope of the ground, within 2 percent;
and the proper corrections, applied. The correction to be applied for tempera-
ture when using a steel tape is
C t 0.0000065s(T T 0 ) (7.6)
The correction to be made to measurements on a slope is
C h s (1 cos ) exact (7.7)
2
or 0.00015s approximate (7.8)
2
or h /2s approximate (7.9)
where C temperature correction to measured length, ft (m)
t
C correction to be subtracted from slope distance, ft (m)
h
s measured length, ft (m)
T temperature at which measurements are made, F ( C)
T temperature at which tape is standardized, F ( C)
0
h difference in elevation at ends of measured length, ft (m)
slope angle, degree
In more accurate taping, using a tape standardized when fully supported through-
out, corrections should also be made for tension and for support conditions. The cor-
rection for tension is
(P m P s )s
C p (7.10)
SE
The correction for sag when not fully supported is
2 3
w L
C s (7.11)
2
24P m
where C tension correction to measured length, ft (m)
p
C sag correction to measured length for each section of unsupported
s
tape, ft (m)
P actual tension, lb (N)
m
P tension at which tape is standardized, lb (N) (usually 10 lb) (44.4 N)
s
2
2
S cross-sectional area of tape, in (mm )
2
2
E modulus of elasticity of tape, lb/in (MPa) [29 million lb/in (MPa) for
steel] (199,955 MPa)
w weight of tape, lb/ft (kg/m)
L unsupported length, ft (m)
Slope Corrections
In slope measurements, the horizontal distance H L cos x, where L
slope distance and x vertical angle, measured from the horizontal—a simple