6.2　Calculations of Wind Load and Seismic Load

6.2.1　The wind load and seismic load applied on the column shall be calculated in accordance with JB/T 4710.

6.2.2　The reference wind pressure shall be determined according to the project site information provided by the Owner,but it shall not be less than the value specified in GB 50009,and shall not be less than 300N/m2.

Note:The 50-year-return reference wind pressures for the cities in China are provided in GB 50009,Appendix D.

6.2.3　The design seismic precautionary intensity shall be determined according to the project site information provided by the Owner,but shall not be less than the value specified in GB 50011.

Note:The design seismic precautionary intensities,seismic accelerations and design seismic groups for the main cities and towns in China are provided in GB 50011,Appendix A.

6.2.4　The site soil categories shall be determined according to the project site information provided by the Owner,and shall not be less than the categories classified in GB 50011.

6.2.5　In calculating the natural vibration period,wind load and seismic load for column,both column shell and skirt shall be divided into several sections based on the following principles:

a)Each section for calculation shall have no sudden geometry change,diameter and thickness change;

b)The conical shell(or the intermediate transition)should be assumed as one single section(or several sections)for calculation;

c)Each section for calculation shall have no sudden mass distribution change,e.g.,the section loaded with packing(or catalyst)shall be assumed as one single section,the section with trays and the section without trays for tray columns shall be assumed as individual sections;

d)Each section for calculation shall be made of the same material.

6.2.6　In calculating the equivalent width of the platform,K4,the projected area of the platform members,􀰐A,(excluding the projected area of the open spaces)may be approximately calculated by Equation(4).

where　􀰐A—projected area of the platform and handrail,mm2;

W—width of the platform,mm;

H—height of the platform handrail,mm.

6.2.7　Loads of column platforms,ladders,trays and packing(or catalyst)may either be determined based on the specific project design requirements,or estimated according to the data given in Appendix B and Appendix C of this Specification.

6.2.8　The critical cross sections of the column shell(including skirt)required for stress calculation include:

a)The cross section of the skirt shell above the top surface of skirt base ring plate;

b)The cross section of the skirt shell at the largest opening;

c)The cross section at the welded joint between skirt and column shell;

d)The cross section of the column shell at the junction between column sections with different diameters;

e)The cross section of the shell at the junction between cylinders with the same diameter and different thickness i.e.,the bottom cross section of the section with same thickness;

f)The cross section at the tangent line of column bottom head;

g)The bottom cross section of the skirt transition section.

6.2.9　If the wall thickness of a column is governed by pressure load(internal or external pressure),and the column is designed with same temperature,same diameter and same material,the column shell(excluding skirt)may be designed in same wall thickness.Where static head of liquid is considered,the required pressures at different elevations shall be used to determine shell sections with different thicknesses.

6.2.10　If the wall thickness of a column is governed by wind load or seismic load(e.g.,a tall,slender column),as the bending moment due to wind load or seismic load varies with height,the column shell shall be designed with incremental wall thickness from top to bottom to achieve equal strength and proper structural design.The principle for determining column sections with different wall thicknesses are as follows:

a)Considering the fabrication and cost effectiveness factors,the maximum number of sections with different wall thicknesses of a column(excluding skirt shell)should not exceed 5;

b)The wall thickness difference between adjacent sections should not be too large,and it should be 2mm-4mm for carbon steel and low alloy steel,and 2mm for stainless steel;

c)The length of a section with same wall thickness should not be less than 4m,and should be an integral multiple of the nominal width of steel plate.

6.2.11　For the columns with height-to-diameter ratio(H/D)greater than 15 and height(H)greater than 30m,resonance in transverse wind direction shall be determined and calculated in accordance with JB/T 4710-2005,Appendix A.Precautions against column failure due to resonance in across wind are described in Appendix F of this Specification.

6.2.12　The deflection at the top of column and its controlled value shall comply with the following requirements:

a)The deflection at top of column shall be calculated in accordance with Appendix C of JB/T 4710-2005;

b)The controlled value of deflection at the top of column shall be determined according to specific project design requirements,and may also be selected from the values recommended in Appendix D of this Specification.