Design General Specification Structural Design Basis

Site Survey and Soils Report

Site survey

All design shall be in accordance with the horizontal and vertical controls contained in the survey report prepared by the survey consultant.

Soils report

Design and calculations

Prior to starting detailed design, a basic design shall be made consisting of:

Basic sketch

Loading Derivation

Calculation

Stability check

Main Structural members

Basic Sketch
The sketch shall show the proposed structure (in perspective and / or a series of cross sections).

Structural members may be shown as single lines.

The sketch shall include the foundations & all other parts of structures in structural steel or in structural concrete. All applied loads shall be shown on the skethch excluding the dead loads. Calculations The calculations shall give the design philosophy and all loads including the dead loads of the relevant structural components. The calculation shall state the loads in the main structural members (axial loads, bending moments, shear and possibly torsion, reactions, deflections) and shall include the upward reaction loads on the foundation (load per unit of area). The calculation shall take into account the soil investigation report. If any computer programs are to be used for the detailed design, these shall be identified during the basic design stage with all required documentation provided to demonstrate their adequacy & sufficiency.

Stability Check

Main Structural Members

Designer. Standard steel connection details may be designed by the Supplier but must checked by the Designer duly certified by a Professional Engineer. Or equivalent duly registered complying with international standards of EMF.

Detailed Design

The calculation shall clearly indicate:

1. The table of contents

2. Design philosophy employed on engineering assumptions

3. Applicable codes, formulas, graphs / tables

4. References to literature etc. for subjects not covered by applicable codes

5. Loading tables with loads location diagrams

6. If computer programs are used, the following information shall be supplied:

a. Logic and theory used

b. Analytical model of the structure used for computer analysis

c. Users manual

d. A hand calculation to prove the validity of the computer analysis except if validated by QA / QC system.

e. Loads and load combinations

Drawings and related documents

The preferred computer aided design system is the software used internationally as well as designer’s in house developed or other software approved by Company. These shall be suitably prepared to facilitate microfilming and incorporate a numbering and indication of revision system. Dimensions on the drawings shall be in the SI system unless otherwise specified. Levels shall be indicated in metres & all other dimensions in millimeters. Layout drawings shall show the highest point of grade as El. 100.00 and the reference of this level to the local datum level for Process Units, in offsites the actual level shall be indicated. All headings and notes shall be in English. Each drawing shall bear the following information in the title block.

Order number of the Company, Name of plant , Name of unit , Name of part of the unit , Example: Order number , Catalytic cracking unit , Compressor building

Portal frames

Only drawings marked "Released for Construction (RFC)" or “Approved for Construction (AFC)” shall be used for execution of works every where.

This mark "Released for Construction" can be given only by the Designer responsible for design and engineering. Drawings shall be submitted together with the relevant calculations including those required for submission to local authorities. Revisions to drawings shall be identified with symbols adjacent to the alterations, a brief description in tabular form of each revision shall be given and if applicable, the authority and date of the revision shall be listed. The term “Latest Revision” shall not be used. Claim to all drawings prepared by the Contractor under any order placed by the Company shall be vested in the Company and the later shall have the right to use these drawings for any purpose for this project without any obligation to the Contractor. The Contractor shall not disclose or issue to any third parties without obtaining written consent of the Company any documents, drawings, etc. provided at his disposal by the Company or any documents prepared by him in connection with inquiries and orders for purposes other than the preparation of a quotation or carrying out these orders.

Structural concrete

On this drawing, the general information / data shall be shown as General Notes on the right-hand side or any other suitable location of the drawing.

The general notes shall state that:

a. Levels are expressed in meters with reference to the highest point of grade

b. Dimensions are expressed in millimeters

c. Bar diameters are expressed in millimeters

Furthermore, the general notes shall list:

d. The quality (or qualities) of concrete

e. The quality (or qualities) of steel reinforcing bars

f. The quality (or qualities) of cement to be used

g. Concrete blinding (location, quality and thickness)

h. Polyethylene sheeting, if applicable (location and quality)

i. The concrete cover on bars (type of construction, location and thickness)

j. The list of reference drawings and related documents stating their title and number

k. The legend of the Contractor’s reinforcing bar call out

Including an indication for which part(s) each quality is to be used.

Detail drawings

On each of the detail drawings, the following information / data shall be listed:

a. For general notes, see Drawing No. ......

b. This detail drawing refers to Drawing No. ......

c. For bar bending list(s), see No. ......, sheet 1 to .......

d. For weight list(s), see No. ........, sheet 1 to ........

e. Quantity of concrete (for each quality of concrete separately)

Bending and weight lists

These lists shall always be made by the Designer unless explicitly stated otherwise. The lists shall be prepared on the detailed drawings or on separate sheets.

Scale of drawings

Plan drawings shall be made to a scale of 1:50 and detail drawings to a scale of 1:20.

Structural steel

General arrangement drawings

These drawing shall show the complete structure to be supplied. All main dimensions and the section to be used shall be included. All members to be fireproofed shall be marked with an appropriate symbol or FP designation. A fireproofing legend shall clearly identify the symbols and designations with the work to be performed. For the preparation of the general arrangement drawing, the Contractor may use a reproducible of the instruction drawing(s). For small and simple structures, this drawing may be combined with the base plate drawing.

Baseplate drawing

This drawing shall show all dimensions and details of the base plate including anchor bolts which be taken into account in the design of the (concrete) foundation. When the need for a slight adjustment of the anchor bolts during erection is expected, this shall be indicated on the drawing. The scale for details shall be at least 1:10. For small and simple structures, this drawing may be combined with the general arrangement drawing.

Construction drawings

These drawings shall clearly show all constructional details of the structure to be supplied. The location of the various parts in the structure shall be indicated.

Scale of drawings Drawings shall be made to an appropriate scale.

Bills of material

Bills of material shall show the weights of all large members from the viewpont of transportation and erection at site as well as the total weight of the structure.

Steel structures

Structural steel design shall be carried out in accordance with the relevant project, general specifications and international codes. The plastic design method in the AISC Manual shall not be used in steel design. Steel structures shall be designed for the loads and load combinations allowed In this specification. Normally, only pinned column bases shall be used in the design of steel structures. Use of fixed base plates for certain type of pipe racks and buildings may be necessary because of deflection considerations. Where headroom, access or equipment arrangement permit, wind and other lateral loads on a steel structure shall preferably be transferred to the foundations through vertical X-bracing or K-bracing included on the transverse and longitudinal column lines of the structure. As a second choice, wind and other lateral loads on a structure should be transferred to the foundations through moment resistant frames in one direction and vertical X-braced or K-braced frames in the other direction. Structures that resist lateral load with rigid frame systems in two directions should be avoided. The method of bracing selected for a structure should generally be used throughout the structure. Compression bracing for steel structures shall normally be designed with wide flange and structural tee shapes. For tension bracing, single angle or structural tees may be used. Double angle bracing because of maintenance difficulties shall not permitted for either compression or tension locations. When using structural tees in compression, the design shall include bending induced by eccentrically loaded connections. Braces for structures subject to vibration from equipment shall be designed as compression members. Horizontal bracing shall be provided in the plane of a floor, platform or walkway when necessary to resist lateral loads or to increase the lateral stiffness of the unit. Floor grating shall not be allowed to resist lateral loads in diaphragm action without investigated. In a floor system, beam compression flanges should be considered to be fully braced when a concrete slab is cast to match the bottom face of the compression flanges on both sides or when chequered plate is bolted or welded to the compression flanges or when grating or metal deck is welded to the compression flanges. Grating shall normally be clipped or bolted and therefore, shall not be considered as adequate compression flange bracing. In such cases, additional vertical and / or horizontal bracing in the floor system shall be provided. Bar joist floor and roof systems are generally considered to be too light for heavy industrial plant work. However, when approved by the Designer, bar joist systems may be used on a project.

Steel Structures shall be designed so that the surfaces of all parts be readily accessible for inspection, cleaning and painting. Pockets for depressions which would hold water shall be provided drain holes or otherwise protected.

Connections for steel structures shall conform to the following requirements:

Shop connections may be bolted or welded. Field connections shall normally be bolted however, when approved by the Designer, welded field connections may be used. Bolted connections for primary members shall utilize high-strength bolts conforming to ASTM A325 or A490. A minimum of 2 M20 bolts shall be used for all connections. These connections shall be designed as bearing type. Those connections subject to vibration or stress reversal shall be bearing type. Loads for bearing type connections shall be based on threads excluded from shear plane. Turn of the nut method or load-indicator washers shall be used for tightening all connections. Bolted connections for secondary members (e.g. purlins, girts, stair framing. etc.) shall be made with A307 bolts with the appropriate finish. Connections will normally be designed by the Supplier and checked by the Designer in accordance with the project construction specifications and loads shown on the drawings. Moment connections and special connections, however, shall be worked by the Designer duly shown on the engineering drawings.

Moment connections can be bolted or welded type depending on the type of structure and situation. The Designer will determine the type of connection to be used for each structure. All shear connections shall be designed and detailed by the Supplier and checked by the Designer. Reactions shall be shown on the engineering drawings or as per the calculation note provided by Designer. Plant area shall have the primary structural connections continuously seal welded except high strength bolted field connections. Primary structural connections include horizontal and vertical vessel supports, beams and columns on major pipe racks, inaccessible maintenance areas, etc. The forces in truss members and all main bracing shall be shown on the engineering drawings with plus signs indicating tension and minus signs indicating compression or as per the calculation note provided by Designer. The minimum thickness of any structural steel plate or bar shall be 10 mm. Gusset plates shall not be thinner than the members to be connected and shall have a thickness of at least 10 mm. Welded steel grating for platform covering shall be 30 mm x 6 mm bearing bars at 30 mm on center. Cross bars shall be twisted square 6 mm on each side and spaced not over 100 mm center to center, hot-dip galvanized in accordance with ASTM A123 and A143 for corrosive environment. E70xx welding electrodes shall be specified for all shop and field welding of structural steel. All welds shall be continuous. All bracing shall be arranged to minimize torsion and where practicable, be arranged concentrically about the resultant line of force. The connections wherever possible, shall be arranged so that their centroid lies on the resultant of the forces those members intended to resist. When the condition cannot be achieved, the members and connections shall be designed to resist any local bending due to the eccentricity of the force. In practice, it is noticed that corroded steel plates and bolts limit the expected movement which may result in additional stresses. The Designer should consider this point to include sequential additional stresses in their design consideration. Steel structures supporting equipment shall be fireproofed where required by risk & safety analysis.

Reinforced concrete structures and foundations

Cast-in-place or situ concrete structures shall be designed in accordance with ACI 318 except as indicated otherwise in this specification.

Cast-in-place or situ concrete structures shall be designed for the loads and load combinations required according to codes & description elsewhere in project documents. The working strength or limit state of serviceability design methods shall be used for the structural design of concrete members unless otherwise indicated. Load combinations and load factors for all concrete design shall be adopted in accordance with ACI 318. The design and details of cast-in-place concrete structures shall consider the monolithic nature of hardened concrete.

Construction joints in a concrete structure shall be located so as to least impair the integrity and unity of the structure. Construction joints in beams at column or pedestal faces should be avoided. The Designer / Contractor Site Management shall approve the location of all construction joints on site agreement. Moving concentrated loads on elevated concrete beams and slabs shall be treated in accordance with applicable recommendations of the referenced AASHTO specifications. Slabs at grade for buildings and process areas shall be designed in accordance with the publications ‘Concrete pavements for heavy storage areas’ Underground structures such as basements, rectangular tanks, sumps, and pits shall be designed in accordance with the latest referenced PCA bulletins and / or BS8007. The design of such structures shall include the effects of ground water pressures and buoyancy. A minimum factor of safety of 1.1 for buoyancy shall be used ignoring soil cohesion. Concrete process treatment structures shall be designed in accordance with ACI 350 R. For all liquid retaining structures, special precautions shall be taken for water tightness. All joints shall be fully detailed by Designer. A corrosion allowance of 3 mm shall be required for all anchor bolts. Bolts shall be hot-dip galvanized in accordance with ASTM A123 and A143. Foundation design in addition to the above applicable criteria shall meet the following requirements: Foundations shall be designed in accordance with the project geotechnical (soils) report. Foundations for structures shall be sized and stability determinations made using service loads only. Load factors shall not be included in these design operations. Unless there is a conflict with the project soils report, individual foundations shall normally be used for major equipment. If combined foundations are appropriate, the centroid of the bearing area should coincide with the resultant of the applied operating load (excluding live load). All foundations shall be placed on sealed blinding concrete on firm, undisturbed soil. Some seal slabs, however, may be placed on well-compacted earth fill, if approved by the Designer. In such cases, the engineering drawings shall specify the kind of fill material and the degree of compaction required for the fill material. Spread footings, combined footings and mats should be designed assuming linear soil pressure distribution. Where the rigidity of the foundation is questionable, an analysis considering the interaction between flexibility of the foundation and the subgrade soil reaction should be considered. For mats particularly, this method of analysis may be in order. ACI 336.2 R contains suggested design procedures. Foundations shall be proportioned so as to minimize general and differential settlements. In order to reduce the overturning moment on individual footings of buildings and process structures, the transfer of column base shears into the concrete grade slab should be considered. The frictional resistance provided by the grade slab shall equal at least 1.15 times the applied column base shears. For design purposes, a coefficient of friction of 0.2 may be assumed between the concrete slab and the membrane. If this design approach is used, the grade slab thickness and joint details shall be properly designed. Where seasonal changes in soil moisture content occur extremely, special details may be required to minimize foundation movements. Control of foundation movements is especially critical for masonry structures. The Designer shall determine design parameters to control such movements.

The stability ratio (SR) based on service loads for isolated spread footings shall not be less than 1.5 when determined as follows:

SR = D (P) / 2M = D / 2e Where: D = Diameter or width of footing, P = Minimum gravity load at bottom of footing (exclude equipment and live loads, include buoyancy), M = Maximum overturning moment at bottom of footing, e = Eccentricity = M / P

The uplift factor of safety based on service loads shall not be less than 1.25. This factor of safety must be maintained when 70 percent of dead load is combined with no reduction of wind load for uplift.

The stability ratio (SR) based on service loads for buildings, process structures and other framed structures shall not be less than 1.5 when determined as follows.

SR = Resisting Moment / Overturning Moment Where Resisting Moment = Moment due to dead load of foundation and structure (include buoyancy), Overturning Moment = Moment due to lateral loads

The overturning and resisting moments shall be computed about the most critical axis of rotation of the foundation block at the soil / concrete interface. There may be more than one axis of rotation.

The stability ratio (SR) of retaining walls based on service loads shall not be less than the following.

a. For sustained loading:

SR = Resisting Moment / Overturning Moment

= 3.5 for cohesive soils

= 2.0 for cohesionless material

b. For sustained loading combined with temporary loading:

SR = Resisting Moment / Overturning Moment

= 2.0 for cohesive soils

= 1.5 for cohesionless material

Where:

Resisting Moment = Moment due to dead load of wall and soil overburden (include buoyancy)

Overturning Moment= Moment due to lateral loads

Resisting moment and overturning moment shall be taken about the toe of the retaining wall and bottom of footing. For all service load conditions, the sliding resistance of foundations especially retaining walls, shall at least be equal to 1.5 times the applied lateral loads. Sliding resistance shall be developed by either friction between the footing and membrane or by passive resistance of shear keys extending below the bottom of the footing in the case of retaining walls. In cases where sliding resistance is developed by a combination of friction and passive resistance, it is recommended that a minimum factor of safety of 2.0 shall be provided. Stability calculations shall include the weight of the foundation concrete and the soil immediately above the footing(s). The effects of buoyancy on the concrete and soil weights shall be considered. Passive earth pressures shall not be included in stability calculations except in the design of retaining walls with keys. In this case, only that pressure acting on the key face shall be considered. Foundation bottom level shall be defined taking into consideration geotechnical (soil) report and other factors to be clearly noted on the drawings. Keep standard bottom of footing elevations where possible. Consideration shall be given to interferences with underground soil systems.

General

The Region has been defined as being in an Ultra Hot Climate t together with the extremely heavy concentration of chlorides in both the ground and atmosphere together with high humidity that result in the rapid degradation of Reinforced Concrete structures. The degradation of the concrete is principally caused by reinforcement corrosion due to the ingress of chlorides and other aggressive salts, the consequential increased volume of rust produced commonly breaks off the cover on the reinforcement. Failure of the R.C member then becomes imminent. The degradation of concrete arises also from the use of salt contaminated materials. The durability and quality of the concrete itself is of paramount importance. Factors to increase durability while designing shall be considered in concrete such as thermal insulation coating measures as recommended in the “CIRIA Guide to Concrete in The Gulf Region”. Quality of concrete is achieved by good engineering and detailing proper materials and proportioning good construction techniques and concrete curing. One of the main characteristics influencing the durability of concrete is its permeability to the ingress of chlorides, water, oxygen, carbon dioxide, wind blown chloride contaminated dust and other deleterious substances. Coatings shall be applied to all buried and exposed concrete surfaces as an essential protection against attack from chlorides, other harmful elements and to provide the concrete to develop a refined pore structure enhancing impermeability. Coatings shall have crack bridging properties on flexural members. Steel plates shall not be embedded in concrete. The Contractor shall develop a detail that allows attachment of the plates to inserts embedded in the concrete. A detail shall also be developed to ensure an effective seal from exterior moisture is achieved around the perimeter of the plates at the point of intersection between concrete and plate.

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