First Web Edition 2006, Devoted to Engineering Community

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Crack prevention

Crack widths shall be controlled by an expeditious use of combinations of reinforcement sizes, spacing and cover.

Crack widths shall be calculated using the applicable formula in BS 8007.

The calculation shall be based on the long term, steady state loading. For durability it is not necessary to consider peak loadings although this may affect coating selection for the requirement for crack bridging and flexural performance.

Crack widths apply at the surface of the concrete i.e. the full depth of cover shall be utilized in the calculation.

Calculation of crack widths shall consider both load (flexural) and restraint (due to thermal and shrinkage effects) induced cracking.

In order to reduce flexural cracking to acceptance limits, it will be necessary to use reduced allowable stresses in the reinforcement.

Calculation of crack widths shall not use ‘deemed to satisfy’ options of BS 8007, i.e. do not calculate crack widths on PC and minimum reinforcement ratios.

The minimum external restraint factor (R) shall be 0.5.

Methods of calculating crack widths in relation to temperature and moisture effects are given in Appendix A - BS 8007.

The minimum fall in temperature between hydration peak and ambient (T1) shall not be less than 31° C for walls and 21° C for ground slabs.

Seasonal temperature fall (T2) shall be considered where continuous construction is used - BS 8007 - Table 5.1 - Option 1. This shall be not less than 30° C.

Crack widths shall be limited as follows.

Crack width shall be = 0.15 mm for all buried, submerged and exposed concrete.

Crack width shall be = 0.30 mm for all concrete located in an air conditioned and sealed environment.

Crack widths shall be = 0.10 for all liquid retaining structures.


Use smaller diameter re-bar at closer centers.

For sections = 500 mm thick and for the outside 300 mm of large sections, reinforcement shall not be less than 0.35% of the applicable gross cross-sectional area of the concrete section.

Maximum spacing of reinforcement shall be 150 mm in any direction.

Use fabric reinforcement where possible (‘nested’ where necessary) as this gives better crack control.

Do not bunch reinforcement or use in vertical or horizontal pairs.

Reinforcement shall be adequately detailed to eliminate congested areas i.e. laps to be staggered.

Place reinforcement nearest to the surface where it is the greatest restrained length which means horizontal wall reinforcement will be on the outside of the vertical reinforcement.

Ensure additional diagonal reinforcement is placed at each re-entrant opening to prevent cracks emanating from corners.

All reinforcement shall be fully detailed by the Designer on bar bending schedules BBS for fabrication.

All concrete sections with a thickness of 250 mm or more, reinforcing bars shall be placed on both faces over the full section. In addition, minimum reinforcement shall be placed in the other two faces.

Concrete Cover

Adequate cover to the outside of all reinforcement is essential for resistance to corrosion for all types of sections & situations whatsoever..

Minimum Concrete Cover (mm) Concrete cast against or permanently exposed to earth (all below grade structures) and all marine facilities over or in contact with water 75

Concrete exposed to weather (all above grade structures not enclosed by a temperature and humidity controlled building) 60

Concrete not exposed to weather and located within a temperature and humidity controlled building 50

Where any individual structural element falls within two or more categories then the most stringent criteria shall apply for the entire element.

Horizontal re-bar in walls and faces of large elements shall be on the outside of the vertical reinforcement for more effective crack control.

All concrete cover shall conform strictly with values given above unless noted otherwise on design documents or in the applicable standards.

Required covers shall not be reduced by provision of protective coatings, membranes or by membrane protective screed.

If fire resistance of more than 2 hours is required, cover shall be as determined in Table 3.5 in BS 8110 Part 1 for the particular element under consideration.

Concrete Grades

Concrete shall have a minimum compressive strength as given in Specification for Concrete

Externals Features

Features which collect sand and dust that can form with rain or dew into a corrosive pollutant shall be avoided i.e. decorative patterns with holes and pockets, gutters, ledges and exposed aggregate finishes. Top surfaces shall be designed with falls to encourage run-off drainage.

Tops of all pedestal heads shall be sloped 1:20 away from the base plate grout.

Top of pedestal shall project a minimum of 100 mm from the edge of the column base plate grout. Dimensions of the concrete columns or foundations are designed taking into account loads applied to & not by reference to geometric dimensions of base plate.

Minimum pedestal heights excluding grout above top of adjacent paving shall be as follows:

Structural Steel columns: 150 mm to 200 mm

Equipment (general): 100 mm to 300 mm

Equipment (pumps): 100 mm to 300 mm

Grout is to be sloped 1:1 away from the bottom outside corner of the column base plate grout.

Shear keys shall not be used on pedestals / plinths.

Stress Raisers

Complicated plan shapes which produce stress shall be avoided.

Large and sudden changes of cross-section i.e. wall junctions and counterforts in the middle of bay lengths shall be avoided. Locate joints adjacent to these stress producers or cast in two separate sections.

Provide appropriate extra reinforcement where stress producers are unavoidable.

Casting-in pipes, box-outs, notches in the middle of bay lengths shall be avoided, Locate joints adjacent to these stress producers if possible.

Anchor Bolts

For small diameters, Chemical type anchors or cast-in anchors are preferred. Where chemical anchors are used, the hole must be properly cleaned according to Manufacturer’s instructions. Anchor bolts shall be designed for combined tension and shear as per BS5950. Minimum edge distance measured to outside of tube shall be 100 mm or 4 times the bolt diameter whichever is greater.

Shear Keys

For standard conventional structures, shear keys shall not be used.

For situations where shear keys are required, back up design calculations and justification shall be given for approval.

Pits and Tanks

As a minimum requirement, the recommendations of BS 8007 - Section 5 ‘Design, Detailing and Workmanship of Joints’ shall be adhered to regardless whether or not, the structure is liquid retaining.
All construction joints shall be designed, detailed and shown on the drawings by the Designer or Subcontractor for Construction with approval of Contractor.

Where continuous construction is necessary, the method of ‘Temporary Open Sections’ as specified in BS 8007 C1.5.5 shall be used. Such open sections shall not be more than 1.0 m containing the “Lapped’ section of reinforcement. The use of sequential bay wall construction shall not be permitted. Unless roofs are insulated, these sections are subject to extremely high daytime temperatures and lower night temperatures. Consideration shall be given to the use of insulation or reflective coatings (e.g. aluminum). All such structures (other than blast resistant structures) shall have an isolated roof slab on a sliding bearing (slip strip or equal approved). Monolithic construction with the supporting wall shall not be considered in such design.


For ground slab paving construction, the method used for design and construction shall be by the alternate ‘long strip method’ using a combination of transverse contraction joints (induced or formed). Adjacent longitudinal strips shall be cast with longitudinal tied joints between each strip.

The recommendations for slab design and construction shall be complied with the provisions in the following publications:-

Design of Floors on Ground by Cement and Concrete Assoc. Tech. Report 550.

Concrete Industrial Ground Floors by U.K. Concrete Society Technical Report #34.

The Design of Ground Supported Concrete Industrial Ground Floors by British Cement Assoc. Interim Note 11.

Guide for Concrete Floor and Slab Construction by ACI 302.1R.

The location of all joints shall be shown on the drawings with accompanying details of each joint type. Isolation joints are to be provided around all equipment foundations and pedestals.

Concrete Masonry Structures

The design of concrete masonry structures shall conform to ACI 530 and the UBC. Concrete masonry structures shall be designed for the loads and load combinations specified


All grout materials and application procedures shall be approved by the Designer and the Manufacturer. Sand-cement grout shall not be used for any project. All grouting shall be in accordance with the defined project specifications as well as proprietary standards. Epoxy-based non-shrink grout shall be evaluated by Contractor and the Manufacturer for each application for temperature creep as well as strength and applied in accordance with Manufacturer's specification.

Grout material used below base plates for machinery, pipe racks, pumps, pipe supports, etc. shall not be placed higher than the bottom of plate level and sloped outward at a 1:1 slope away from the bottom of the base plate to prevent water accumulation near the base plate as well as to prevent cracking of the grout as a result of corrosion around base plate edge. Contractor shall develop a detail to ensure an effective seal from exterior moisture is achieved around the perimeter of the base plates at the point of intersection between grout and base plates.


Fireproofing zones

Only specific structures and equipment located within a Fire Proofing Zone (FPZ) shall be fireproofed as described in Specification for Fireproofing


Buildings, Process Structures, Pipe Racks, Miscellaneous Plant Structures, Vessels, Exchangers and Tanks

The following loads shall be considered:

Dead Load

a. Soil Load (Include as part of Dead Load)

Operating (Product) Load

Test Load

Live Load

a. Sand Load (Include as part of Live Load)

b. Surge Load (Include as part of Live Load)
Truck Load

Wind Load

Earthquake Load

Crane / Impact Load

Dynamic Load

Thermal Load

Erection Dead Load

Maintenance Load

Miscellaneous / Differential Settlement Load

Earth / Hydrostatic Load and Buoyancy

Blast Load

Future Load

The above loads are defined as follows.

Dead Load

Dead load is defined as the weight of all permanent construction including walls, foundations, floors, roofs, ceilings, partitions, stairways and fixed service equipment. For heavy industrial work, this would include equipment, vessels & internals, pipes, valves, accessories; electrical and lighting conduits, switchgear; instrumentation, fireproofing; insulation; ladders; platforms; and all other similar items. Weight of equipment shall be extracted from the Manufacturer’s data sheets and include auxiliary machinery, piping. Equipment and piping should be considered empty of product load when calculating dead load. The gravity weight of soil overburden shall be considered as dead load
a. Soil Load (Dead Load)

Soil loads shall consist of lateral earth pressures. Active and passive coefficients for lateral pressures shall be obtained from the project soils report.

Operating (Product) Load (Live Load)

The load shall be defined as the gravity load imposed by liquid, solid or viscous materials in vessels, tanks, equipment or piping during operation. Unusual loading that occurs during regeneration or upset conditions shall also be considered.

Test Load (Live Load)

The test load shall be defined as the gravity load imposed by any method necessary to test vessels, tanks, equipment or piping. When more than one vessel etc. is supported by one structure, the structure need only be designed on the basis that one vessel will be tested at any one time and that the others will either be empty or still in operation.

Live Load

Live load is defined as the weight superimposed by the use and occupancy of the building or other structure but not permanently attached to it. For industrial design, live load can be defined as the load produced by personnel, moveable equipment, tools and other items placed on the structure but not permanently attached to it. Unless specified otherwise, use the minimum live load values given in the table below. Uniform loads and concentrated loads do not occur simultaneously.

Types of Structures Load (kN/m2)
Walkways (not used as operating) 2.0 (or 3.0 kN point load)

Operating platforms (other than compressor and generator platforms 5.0 (or 5.0 kN point load)

Trench covers (non vehicular) 5.0

Roof (min) 1.0 (or 3.0 kN point load)

Sand on roof (min.) 0.75

Light Storage 6.25

Heavy Storage 12.5

Compressor and generator platforms;

Floor framing (Determine from use but never less than) 5.0

Floor Grating and Slabs 10.0*

For floor grating and slabs being subjected to a concentrated load from either the installation or removal of equipment
Office first aid buildings, guards houses, control room, computer room, electrical

equipment room, laboratory room locker room 3.0

Canteens, Lunchrooms, Stairs, Halls 4.0

Library 5.0

Battery rooms 10.0

Mechanical, electrical, instrument workshop building 20.0

Bulk storage 40.0

Stairs and Ramps 2.0 (or 3.0 kN point load)

Handrailing ** ** 0.75 kN per linear meter applied horizontally at the top of railing, or a horizontal force of 0.9 kN at any one point.

a. Sand Load (Live Load)

Sand load shall be additive to live loads only when the area under consideration is used as a ‘work area’. A 0.75 kN/m2 load shall be used in the design of flat roofs. The effect of sand accumulating behind walls and upstands shall be considered in the design of the walls and roof (treat similar to snow loading).

b. Surge Load (Live Load) Surge loads may occur in some vessels or equipment such as fluid cokers, hydroformers, crackers etc. In such cases, the magnitude and direction of the load will be given in the equipment specification. The project process engineer shall furnish a list of equipment having surge loads and the designer make allowance for such loadings in relevant calculations.

Truck Load (Live Load)

Structures accessible to trucks shall be designed to withstand the gravity, lateral and impact effects of truck loading. Truck loading shall be HS20 or HS20-44 wheel loading as defined by the AASHTO specifications. It shall be checked where applicable whether maintenance and / or construction equipment loads are governing over HS20 wheel loading. At least one road leading to the main process area(s) shall be designated as a heavy equipment route. Bridges, culverts and other underground facilities shall be designed for the maximum expected loading condition caused by transportation of heavy equipment

Wind Load (Live Load) The design wind loads shall be calculated based on a basic wind speed of 145 km per hour at a height of 10 m above the ground for terrain exposure C and a mean recurrence interval of 50 year. For this exposure and recurrence, the value of the importance factor of (I)=1.1. The Designer shall

develop specific wind load calculation criteria and procedures using ASCE 7 for various types of structures and equipment for the project.

For overhead pipe tracks 4m wide or less, the wind load on the three largest pipes shall be taken into account. For overhead pipe tracks of over 4m wide, the wind load on the four largest pipes shall be taken into account.

The following tabulated velocity pressures shall be used for calculating design wind forces for the design of all structures, buildings and equipment and their parts, portions and appurtenances for the project. Pressure coefficient Cf = 0.8.

Pipe racks 4 m wide or less: Wp = 0.8 qh (D1+D2+D3) or pipe racks wider than 4 m: Wp = 0.8 qh (D1+D2+D3+D4) Where

Wp = Unit design wind load on piping

qh = Velocity pressure determined at piping elevation h

Dn = Diameter of pipe

Reference ASCE 7-1993 V - 145 km / hr 50 year mean recurrence, I = 1.1, Exposure C

Height Zone Above Grade (m)

Z Velocity Pressure in Kg/m2

qz Gust Response Factors

Gh and Gz

0-6 107 1.29

6-9 114 1.26

9-12 125 1.25

12-15 134 1.22

15-18 142 1.21

18-24 151 1.18

24-30 164 1.17

30-36 173 1.15

36-45 183 1.14

45-60 198 1.12

60-90 219 1.10

90-120 241 1.08

Increase factors may be used to modify the projected areas of vertical and horizontal vessels (including insulation if any) to allow for attachments such as manholes, nozzles, piping, ladders and platforms.

The ‘shape increase factors’ may be used to modify the projected areas of vertical and horizontal vessels (including insulation if any) to allow for attachments such as manholes, nozzles, piping, ladders and platforms. Use Cf = 0.8.

Wind loads shall be separately computed for all supported equipment, ladders, and stairs except for vessels where ‘projected area increase factors’ have already been accounted for these items. Gust response factors G for main wind resisting systems of flexible buildings, structures and vertical vessels having a height exceeding five times the least horizontal dimension or a fundamental natural frequency less than 1.0 hertz shall be calculated. Calculations shall be based on a rational analysis that incorporates the dynamic properties of the main wind force resisting system. One such procedure for determining gust response factor is described in ASCE

No reduction shall be made for the shielding effect of vessels or structures adjacent to the structure being designed.

For main wind force resisting systems and walls, use Gh evaluated at the height h (top) of the structure. An exception is in the various structural specifications for equipment, the variable gust response factor Gz is used. For components and cladding, use Gz evaluated at centroid height z above ground.

Earthquake Load (Live Load)

Earthquake load shall be applicable according to project Location & in conformance to Uniform Building Code (U.B.C.) 1997-Division III-Seimic zone Tabulation Section 1653.

Crane / Impact Load (Live Load)

For structures carrying live loads that induce impact, the live load shall be increased sufficiently. If not otherwise specified, the live load increase shall be following:


Vertical Load Horizontal Load

For supports of elevators (dead and live load) 100%

Cab operated traveling crane support girders & and their connections

25% 20% 1 10%2

Pendant operated traveling crane support girders & and their connections 10%

Monorails, trolley beams, davits 50%

Light machinery, shaft or motor driven 20%

Reciprocating machinery or power driven units 50%

Hangers supporting floors and balconies 33%

1. Increase the sum of the weights of the rated capacity of hoist, crane trolley, cab and hooks.

Apply one-half of the load at the top of each rail acting in either direction normal to the runway rails.

2. The longitudinal force shall if not otherwise specified be taken as 10% of the maximum wheel loads of the crane applied at the top of the rail.

3. Live load on crane support girders shall be taken as the maximum wheel loads.

Dynamic Loads (Live Load)

Each structure shall be designed to withstand the effects of vibration and impact to which it may be subjected. Each structure and foundation supporting a compressor, turbine, pump or other machinery having significant dynamic unbalance shall be designed to resist the peak loads specified by the manufacturer. Vibration amplitudes of the supporting structure or foundation shall

be kept within acceptable limits for dynamic forces that occur during normal machine operation. In the case of a tall and slender structure, there may be a need to investigate the dynamic effects of wind gusts.

Centrifugal pump foundations for pumps less than 750 kW do not require a dynamic analysis. However, the foundation to pump assembly weight ratio shall not be less than 3 to 1.

Foundations for reciprocating machinery, centrifugal machinery and centrifugal pumps over 750 kW require a three dimensional dynamic analysis.
Thermal Load (Live Load)

ASCE 7 mentions thermal loads however, the ASCE thermal comments are not geared to heavy industrial work. Thermal loads shall be defined as forces caused by changes in temperature. The primary source of thermal loads in an industrial plant is the expansion or contraction of vessels and piping. Another source of thermal loads in a redundant structure is the expansion or contraction of the entire structure or individual structural components. Provisions shall be made for thermal forces arising from assumed differential settlements of foundations and from restrained dimensional changes due to temperature changes. Thermal loads and displacements caused by operating conditions shall be based on the design temperature of the item of equipment rather than the operating temperature. Design atmospheric temperature ranges from a minimum of 5 deg C to a maximum of 58 deg C. Low friction slide plates (Fluorogold, Teflon / PTFE or an approved equal) shall be used if the vessel operating condition weight is greater than 45 kN at the sliding end. For preliminary design, the temperature drop of 1.9 deg C / mm from the bottom of shell to bottom of saddle may be assumed. The following friction coefficients shall be used for calculating frictional restraint due to temperature change or lateral loading on sliding surfaces:

Surface Friction Coefficient

Steel-to-steel (corroded) 0.35

Steel-to-concrete 0.50


A straight line variation of 0.17 to 0.08 for bearing Stresses from 0.0 N/mm2 to 0.7 N/mm2, respectively Bearing stress greater than 0.7 N/mm2 0.17 to 0.08


Graphite-to-graphite 0.15

For computing friction loads due to the effects of pipe expansion in pipe racks, use the following friction coefficients:

Number of Lines on Support

Friction Coefficient

1 – 3 0.3

4 - 6 0.2

7 or more 0.1

For a given support, if considering only larger lines and ignoring smaller lines results in greater loads. These forces and associated friction coefficients shall be used instead of considering all the lines.

A concrete pipe rack beam shall be designed for an arbitrary horizontal pipe anchor force of 15 kN acting at midspan unless design calculations dictate a higher force and more locations. The pipe anchor force shall not be distributed to the foundations.
For pipe anchor forces transferred by longitudinal girders to structural anchors (bracing) an arbitrary force of 5% of the total pipe load per layer shall be taken into account unless design calculations dictate a higher force. These forces shall be distributed to the foundations.

Foundations and structures which are subject to temperature effects shall be designed for the various loading conditions and also for any temperature difference which may occur in parts of structural members.

a. Anchor and guide forces shall be obtained from the Designers Piping Engineering Department.

b. Structural Steel Pipe Supports shall be designed in accordance with Industry

Standard Structural Design Methods.

Erection Dead Load

The erection dead load is the weight of the equipment at time of erection plus the weight of the foundation. The foundation weight is the combined weight of the footing, pedestal, and overburden soil.
All possible loading conditions during erection shall be considered and for any member of a structure, the most unfavorable be considered.
Heavy equipment lowered onto a supporting structure can introduce extreme point loads on structural members exceeding any operating or test load. After placing of equipment, the exact positioning (lining out and leveling) can also introduce extreme point loads. The above should be interpreted on the basis of contractor’s practical experience, manufacturer’s information and allowed for in the design calculations accordingly.
Beams and floor slabs in multistory structures e.g. fire decks shall be designed to carry the full construction loads imposed by the props supporting the structure immediately above. A note shall be added on the relevant construction drawings to inform the field engineer of the adopted design philosophy.

Maintenance Loads (Live Load)

Maintenance loads are temporary forces caused by the dismantling, repair or painting of equipment.

The force required to remove the tube bundle from a shell and tube heat exchanger shall be assumed to act along the horizontal centerline of the exchanger with a value of 2 times the weight of the bundle but not less than 10 kN.

Miscellaneous Loads (Live Load)

Miscellaneous loads shall be defined as loads that do not fit into the categories listed in this section.

Earth / Hydrostatic Load and Buoyancy (Live Load)

Earth and hydrostatic water pressures on retaining walls and underground structures shall be determined. Outward pressures on liquid retaining structures shall also be considered. The buoyancy load is equal to the weight of the volume of displaced water.

Blast Load (Live Load)

Negligible Blast

Buildings located more than 610 m away from the potential explosive sources do not require special provisions with regard to explosion resistance.

Blast Resilient

Buildings within the 200 m to 610 m distance from potential explosive sources shall be designed to the same loading conditions as specified for buildings beyond the 610 m zone and in accordance with the following design concepts:

The building structural frame, roof, walls, bracing and connections shall be designed in such a manner that large plastic deformations of the major frame members as well as external wall panels will be allowed to occur without causing partial or total building collapse. Blast resilient buildings shall be designed and detailed in accordance with ACI 318, Chapter 21, “Special Provisions for Seismic Design”.

The building frame shall comprise of reinforced concrete or structural steel.

The building walls shall be constructed as reinforced concrete, reinforced masonry with concrete filled cells or properly designed carbon steel cladding system. Walls for these buildings shall not be used as mainframe members or to provide structural stability and / or structural strength.

The building roofs shall be constructed of monolithic reinforced concrete or a properly designed carbon steel roofing system. Loose lightweight concrete roof slabs or asbestos cement sheeting shall not be used. Gravel as a protection of roofing finish or loose tiles for walkways on top of the roof finish shall not be used.
For steel structures, structural steel bracing in roof and walls shall be provided.

Materials with a brittle behavior such as masonry shall not be used in such a way that provides strength.

For additional architectural construction requirements, refer to Specification for Architectural Design Basis (Not included)

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