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API PUBL 937-A:2005 pdf download

API PUBL 937-A:2005 pdf download.Study to Establish Relations for the Relative Strength of API 650 Cone Roof Roof-to-Shell and Shell-to-Bottom Joints.
3.2 Full Tank (no buckling)
The response of a full tank is different at the shell-to-bottom joint. Because the product level does not affect the roof-to-shell joint. the failure pressure of the roof-to-shell joint will remain the same for both empty and full tanks, As for the empty tank, we will examine the response of the full tank to four cases:
• Zero internal gauge pressure
• The pressure required to just cause uplift of the tank
• The pressure at failure of the roof-to-shell joint
• The pressure at failure of the shell-to-bottom joint
These results are based on the elastic, large deformation, static finite element analysis in SafeRoof. Results for inelastic, large deformation, dynamic analyses are similar and are presented later in this report.
3.2.1 Zero Internal Gauge Pressure
Thc displacements for a full tank at zero internal gauge pressure are shown in Figure 3-15 and Figure 3-16. Figure 3-16 clearly shows the downward displacement of the bottom due to the pressure load of the product. The product also causes the circumferential stress to increase approximately linearly with depth. Figurc 3-17. However, at the shell-to-bottom joint. the bottom (which is relatively stiff in tension) constrains the radial displacement of the shell. decreasing the circumferential stresses near the joint.
As noted, buckling can reduce the strength of the joints. We will examine in detail the effect of buckling on the prcssurc at failure of the roof-to-shell joint. Buckling is approximatcd in thc elastic, large deformation, static finite element analyses by reducing the compressive strength of roof and floor when compressive stresses arc detected.
3.3.1 Roof-to-Shell Joint Failure Pressure
Buckling is approximated in the SafeRoof analysis by reducing the circumferential stiffness of the elements in compression in the roof or floor. Based on beam flange buckling practice. buckling effects are not included within a distance of 32 times the roof (or floor) thickness from the joint.
‘hen buckling is included, the pressure for failure of the roof-to-shell joint was calculated to he 0.724 psi as compared to 1.04 psi without buckling. These two values give a range at which the actual failure would be expected. Since both of these roof-to-shell failure pressures are greater than the balanced uplift pressure oiO.295 psi. significant Liplift occurs betbre the roof-to-shell fails, as shown in Figure 3-26.
Equivalent stresses for the middle surface arc plotted in Figure 3-27. Comparing these results to those without buckling (Figure 3-10) shows that buckling has significantly reduced the participation of the roof in resisting the circumferential compressive load. The load is being carried by hc angle and the short section of the roof near the joint. The circumferential and meridional stresses are shown in Figure 3.28 and Figure 3-29.


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