Repair and reconstruction of engineering structures - Assessment and Refurbishment of Steel Structures - page 294

the floating roof to move freely over the entire height of the tank. Although the shape of
the upper edge of the shell still deviated from the theoretical circular shape, it is very
important that the permitted negative deviation (towards the tank interior) is exceeded by
only 10 mm along an insignificantly short length of the perimeter in the area of bench-
mark 10. However, this did not endanger the smooth movement of the roof, which had
been proved by the second water test of the tank.
The difficulty in obtaining the correct circular shape of the upper edge of the tank is
related to significant deformations along the various generating lines of the cylindrical
shell. Two characteristic cross-sections of the shell illustrate this: the cross-section
between bench-marks 3 to 9 after the assembly of the tank had the smallest diameter
(Figure 6.134(a)). Cross-section 5 to 11 (Figure 6.134(b)) is close to the largest deviation
of the upper shell edge after assembly of the tank. Apart from the substantial
irregularities in the shape of the shell along the generating lines, Figure 6.134 also shows
the effectiveness of the repair method used. The range of deformation for different
heights of the shell at the various repair stages is shown for sections 3 to 9 and 11 (Table
6.2).
Figure 6.134 Deformations along the
characteristic generating lines of the
shell after completing the tank
assembly and after the third correction
test: (a) a cross-section at bench-marks
3 and 9 (b) a cross-section at bench-
marks 5 and 11