6.5　Strength Calculations for Packing Support Grids and Packing Support Beams

6.5.1　Packing support grids

In sizing the packing support grid(flat bar),the strength of the longer flat bar shall be calculated.The flat bar is assumed as a simply supported beam carrying uniform load(see Figure 2),and the frictional resistance of the packing to column walls shall be omitted.Strength calculations for flat bar are as follows:

a)Uniform load applied on flat bar,q,shall be calculated by equation(6).

mp=(HLtγ)×10-4

Unless otherwise specified,mL may be approximately calculated by the following equations:

For random packing,mL=0.35HLtγL×10-4

For wire wave packing,mL=0.05HLtγL×10-4

where　q—uniform load applied on the flat bar,N/cm;

mL—mass of the liquid holdup in packing,kg;

mp—mass of the packing,kg;

H—height of the packing,m;

L—length of the flat bar,cm;

t—spacing between flat bars,cm;

γ—bulk density of the packing,kg/m3;Y may be selected from Appendix C of this Specification unless otherwise specified;

γL—liquid density,kg/m3.

b)The maximum bending moment for a simply supported beam carrying uniform load shall be calculated by M=qL2/8,N·cm.However,loads on the packing support grid are not uniformly distributed and the weight of wet packing will be somewhat increased,thus,the maximum bending moment for a simply supported beam shall be calculated by Equation(7).c)The bending stress shall be calculated by equation(8).

where　W—coefficient of the cross section,cm3;

S—thickness of the flat bar,cm;

C—corrosion allowance,cm;

h—height of the flat bar,cm.

Therefore,

d)The bending stress shall be checked by the Expression below:

σ≤[σ]t

where　[σ]t—allowable stress for the packing support grid(flat bar)at design temperature,MPa;Which shall be selected in accordance with GB 150.

6.5.2　Packing support beams

Where packing support beam is required for a large diameter packing column,its strength and stability shall be calculated.

6.5.2.1　Strength calculations for packing support beam

a)Unless otherwise specified in project design documents,the design load for packing support beams shall be as specified in Table 8.For the packing with support rings,loads on the packing support beam from the total mass of packing,grid and liquid holdup should be converted into a uniform load applied on the packing support beam per unit length using the following methods:

1)Where a single packing support beam is used,the uniform load applied on the packing support beam shall be 65% of the total mass of packing,liquid holdup and grid.

2)Where two packing support beams are used,the uniform load applied on the packing support beams shall be 45% of the total mass of packing,liquid holdup and grid.

b)The stress and deflection of packing support beam shall be calculated in accordance with Table 9;

c)The allowable deflection values for packing support beam shall be as specified in Table 10.6.5.2.2　Overall stability calculations for packing support beam

As specified in GB 50017-2003,Article 4.2.1,if the overall stability of packing support beam(e.g.,I-shaped steel,H-shaped steel or channel steel)is required for calculation,it shall be calculated by Equation(10).

where　ϕb—overall stability coefficient of the packing support beam;ϕb shall be selected from GB 50017-2003,Appendix B;

[σ]t—allowable stress of the packing support beam at design temperature,see Note 2 in Table 9.