Microsoft Word - SABPM006.Doc

Microsoft Word - SABPM006.doc

Previous Issue: 31 July 2002 Next Planned Update: 1 June 2009 of 39 Primary contact: Abu-Adas, Hisham on phone 874-6908

Best Practice

SABP-M-006 31 May 2005 Wind Loads on Pipe Racks And Open Frame Structures Document Responsibility: Onshore Structures Standards Committee

Wind Loads on Pipe Racks And Open Frame Structures

Developed by: Hisham Abu-Adas Civil Engineering Unit/M&CED Consulting Services Department

Document Responsibility: Onshore Structures Standards Committee SABP-M-006 Issue Date: 31 May 2005 Wind Loads on Pipe Racks Next Update: 1 June 2009 And Open Frame Structures

Table of Contents Page

1 Introduction .............................................................................................. 3

1.1 Purpose ............................................................................................ 3

http://dc166.4shared.com/doc/Gjn6CEmL/preview.html (1 of 10) [8/29/2012 7:16:10 PM]


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1.2 Scope ............................................................................................... 3 1.3 Disclaimer ......................................................................................... 3

1.4 Conflicts with Mandatory Standards ................................................. 4

2 References............................................................................................... 4

2.1 Saudi Aramco References................................................................ 4

2.2 Industry Codes and Standards ......................................................... 4

3 General .................................................................................................... 4

3.2 Wind Speed V................................................................................... 4

3.3 Importance Factor I .......................................................................... 4

3.4 Exposure Category ........................................................................... 4

3.5 Basic ASCE 7 Formulas ................................................................... 5

3.6 Velocity Pressure q z .......................................................................... 5

3.7 Gust Effect Factors G ....................................................................... 7

3.8 Force Coefficient C f .......................................................................... 7

3.9 Projected Area A e ............................................................................. 7

4 Wind Loads on Pipe Racks & Open Frame Structures ........................... 7

4.1 Pipe Racks ....................................................................................... 7

4.2 Open Frame Structures .................................................................. 10

ATTACHMENTS:

Attachment 1 – List of Tables TABLE 1 - Basic Wind Speed V for Saudi Aramco Sites TABLE 2 - Velocity Pressure q z (Customary Units) TABLE 3 - Velocity Pressure q z (Metric Units)

Attachment 2: ................................................................................................. 24

Example 1 – Wind Load on Pipe Rack

Attachment 3: ................................................................................................. 29

Example 2 – Wind Load on Pipe Rack

Attachment 4 .................................................................................................. 34

Example 3 – Wind Load on Open Frame Structure


1 Introduction

Most of the design practices in the petrochemical industry were based on the wind loading provisions of ASCE 7, “Minimum Design Loads for Buildings and Other



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Structures” or its predecessor (ANSI A58.1). ASCE 7 does not adequately address Pipe Racks and Open Frame Structures. It is the intent of this practice to provide uniform application of practices to all Piperacks and Open Frame Structures designed for Saudi Aramco projects.

1.1 Purpose

The purpose of this practice is to provide the engineer and designer with guidelines for wind load on Pipe Racks and Open Frame Structures for use by engineers working on Saudi Aramco projects and Saudi Aramco engineers.

1.2 Scope

This design guideline covers the minimum requirements and provides guidance for calculating wind load on onshore Pipe Racks and Open Frame Structures typically located in petrochemical facilities. Section 2.0 of this instruction includes reference codes, Saudi Aramco standards, and specifications. In cases where this guideline conflicts with these references, the conflict shall be immediately brought to the attention of the project engineer.

1.3 Disclaimer

The material in this Best Practices document provides the most correct and accurate design guidelines available to Saudi Aramco which comply with international industry practices. This material is being provided for the general guidance and benefit of the Designer. Use of the Best Practices in designing projects for Saudi Aramco, however, does not relieve the Designer from his responsibility to verify the accuracy of any information presented or from his contractual liability to provide safe and sound designs that conform to Mandatory Saudi Aramco Engineering Requirements. Use of the information or material contained herein is no guarantee that the resulting product will satisfy the applicable requirements of any project. Saudi Aramco assumes no responsibility or liability whatsoever for any reliance on the information presented herein or for designs prepared by Designers in accordance with the Best Practices. Use of the Best Practices by Designers is intended solely for, and shall be strictly limited to, Saudi Aramco projects. Saudi Aramco® is a registered trademark of the Saudi Arabian Oil Company. Copyright, Saudi Aramco, 2002.


1.4 Conflicts with Mandatory Standards

In the event of a conflict between this Best Practice and other Mandatory Saudi Aramco Engineering Requirement, the Mandatory Saudi Aramco Engineering Requirement shall govern.



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2 References

This Best Practice is based on the latest edition of the references below, unless otherwise noted. Short titles will be used herein when appropriate. Short titles will be used herein when appropriate.

2.1 Saudi Aramco References

Saudi Aramco Engineering Standards (SAES)

SAES-A-112 Meteorological and Seismic Design Data

SAES-M-001 Structural Design Criteria for non-Building Structures

2.2 Industry Codes and Standards

American Society of Civil Engineers (ASCE)

ASCE 7 – 02 Minimum Design Loads for Buildings and Other Structures

Wind Load and Anchor Bolt Design for Petrochemical Facilities

3 General

3.1 Wind loads shall be computed and applied in accordance with SAES-M-001, ASCE 7-, and the recommended guidelines for Piperacks, and Open Frame Structure in ASCE’s “Wind loads and Anchor Bolt Design for Petrochemical Facilities”.

3.2 Wind load calculations shall be based on basic wind speed V of 3-second gust speed at 33 ft (10 m) above the ground in Exposure C and associated with an annual probability 0.02 of being equaled or exceeded (50-year mean recurrence interval). The basic wind speed V for each site is defined in SAES-A-112, “Meteorological and Seismic Design Data” and Table 1 (Attachment 1).

3.3 The Importance Factor I shall be category IV .

3.4 Exposure Category C shall be used, except for structures close to the shoreline, as defined in ASCE, where Exposure Category D shall be used. Exposure D is defined as ‘Flat, unobstructed areas exposed to wind flowing over open water


for a distance of at least 1 mi 91.61 km). The Exposure category for each site is defined in SAES-A-112, “Meteorological and Seismic Design Data”.

3.5 Basic ASCE 7 Formulas



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The design wind forces for the main wind force resisting system shall be per Section 6.5.13 of ASCE 7-02 “Design Wind Loads on Open Buildings and Other Structures”. The applied wind force F shall be determined by the basic equation:

F = qz G C f Ae ASCE 7 (Eq. 6-25)

where

qz = Velocity pressure at height z above ground

G = Gust effect factor per Sect. 6.5.8 of ASCE 7

C f = Net force coefficient

A e = Projected area normal to wind

3.6 Velocity Pressure qz

The velocity pressure q z is determined in accordance with the provisions of Section 6.5.10 of ASCE 7.

qz = 0.00256 Kz K zt K dV2 I (lb/ft2) ASCE 7 (Eq. 6-15)

qz = 0.613 Kz K zt K dV 2 I (N/m2) [SI Units]

where

Kz is the velocity pressure exposure coefficient per Sect. 6.5.6.6 & Table 6-3 of ASCE 7.

Kz t is the topograhic factor per Sect. 6.5.7.2 of ASCE 7. K zt is equal to 1.0 for Pipe Racks and Open Frame Structures located in Saudi Aramco facilities.

Kd is the wind directionality factor per Sect. 6.5.4.4 and Table 6-4 (see below) of ASCE 7. When used with load combinations specified in SAES-M-001, K d is equal to 0.85 for Pipe Racks and Open Frame Structures.

V is basic wind speed of 3-second gust speed at 33 ft above the ground.

I is the Importance Factor set forth in Table 6-1 of ASCE 7. I equal 1.15 for Category IV structures. All Pipe Racks and Open Frame Structures at Saudi Aramco facilities are considered Category IV structures.


Velocity pressures qz are determined using ASCE 7, Eq. 6-25 shown above. Attachment 1 - Table 2 (Customary Units) and Table 3 (Metric Units) provides values for qz at several heights for most Saudi Aramco sites. These values are to be used for Pipe Racks and Open Frame Structures.



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TABLE 6-4 – Wind Directionality Factor, K d

(Adapted from ASCE 7– 02)

3.7 Gust Effect Factors G


The gust effect factor G is determined in accordance with the provisions of Section 6.5.8 of ASCE 7. For rigid structures, the gust effect factor shall be taken as G=0.85 per Section 6.5.8.1 of ASCE 7.This value should be used for all Pipe Racks and Open Frame Structures.



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For flexible or dynamically sensitive structures Gf is used in place of G. Flexible structures defined by ASCE 7 as those structures with a fundamental

natural frequency f < 1 Hz. G f shall be calculated per Section 6.5.8.2 or by a rational method as given in Section 6.5.8.3 of ASCE 7.

3.8 Force Coefficient Cf

The force coefficient C f for the various structures shall be as listed in the following sections of this guideline.

3.9 Projected Area Ae

The projected area A e normal to wind direction for the various structures in question shall be as defined in this guideline.

4 Wind Loads on Pipe Racks & Open Frame Structures

4.1 Pipe Racks

Wind on the piperack structure itself should be calculated based on no shielding. For all structural members C f = 1.8 shall be used, except Cf = 2.0 shall be used for columns.

4.1.1 Tributary Area for Piping

The tributary area for piping should be based on the diameter of the largest pipe plus 10% of the width of the pipe rack. This sum is multiplied by the length of the pipes (bent spacing) to determine the tributary area.

4.1.2 Tributary Area for Cable Trays

The tributary area for cable trays should be based on the height of the largest tray plus 10% of the width of the pipe rack. This sum is multiplied by the length of the pipes (bent spacing) to determine the tributary area.

4.1.3 Force Coefficients for Pipes

The force coefficient C f = 0.7 should be used as a minimum. The force coefficient C f is taken from ASCE 7, Figure 6-19 (see below) for a


round shape, with h/D=25, D √qz > 2.5 and a moderately smooth surface; that is C f = 0.7. If the largest pipe is insulated, then consider using a C f for a rough pipe dependent on the roughness coefficient of the insulation

(D ′/d).



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Figure 6-19 – (Adapted from ASCE 7)


4.1.4 Force Coefficients for Cable Trays

For cable trays the force coefficient C f = 2.0 shall be used. The force coefficient C f, for cable trays is taken from ASCE 7, Figure 6-19 for a square shape with the face normal to the wind and with h/D = 25; that is



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C f = 2.0.

4.2 Open Frame Structures

4.2.1 General

Wind loads should be calculated in accordance with the general

procedures and provisions of ASCE 7 for wind loads on “Other

Structures ”. 4.2.1.1 Main Wind Force Resisting System

Wind forces acting on structural frame and appurtenances (ladders, handrails, stairs, etc.) should be computed in accordance with 4.2.1.2 and 4.2.2.

Wind forces on piping and cable trays located on or attached to the structure should be calculated according to the provisions of 4.1 and added to the wind forces acting on the frames in accordance with 4.2.6.

4.2.1.2 Force Coefficients for Components

Wind loads for the design of individual components, cladding, and appurtenances (excluding vessels, piping and cable trays) should be calculated according to the provisions of ASCE 7. Force coefficients for several items are given in Table 4.1 below.

TABLE 4.1 Force Coefficients for Wind Loads on Components

(Adapted from ASCE – “Wind Loads and Anchor Bolt Design for Petrochemical Facilities”)

Item C f Projected Area

Handrail 2.0 0.80 sq. ft./ft. Ladder without cage 2.0 0.50 sq. ft./ft. Ladder with cage 2.0 0.75 sq. ft./ft. Solid Rectangles & Flat Plates 2.0 Stair w/handrail Side Elevation End elevation

2.0 2.0

Handrail area plus channel depth 50% gross area

Round or Square Shapes See ASCE 7 Figure 6-19


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