17630684 Design of Steel Shelter Final

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Design & Detailing of Steel Shelters

By Abir Mallick

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IntroductionIntroduction

This presentation is This presentation is developed as to provide developed as to provide a basic guideline of Oil & a basic guideline of Oil & Gas Plant Shelters. Gas Plant Shelters.

Its objective is to Its objective is to provide technical provide technical knowledge and knowledge and information for design of information for design of Steel Shelters/ Buildings.Steel Shelters/ Buildings.

The information The information provided is based on provided is based on common design and common design and construction practices construction practices for steel structures.for steel structures.

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What Will You Gain From This What Will You Gain From This Presentation?Presentation?

Basic idea of different types of shelters normally Basic idea of different types of shelters normally encountered in oil & Gas Plantsencountered in oil & Gas Plants

An understanding of different types of structural steel An understanding of different types of structural steel frames used in sheltersframes used in shelters

Different types of loading for which the structure has to be Different types of loading for which the structure has to be designeddesigned

Basic idea of analysis of Portal frameBasic idea of analysis of Portal frame Understanding of detailing work of steel Portal frames and Understanding of detailing work of steel Portal frames and

other necessary elements of sheltersother necessary elements of shelters Different types of foundation used for sheltersDifferent types of foundation used for shelters

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Different types of SheltersDifferent types of Shelters

Almost all Oil & Gas Plants will have Shelters to cater to Almost all Oil & Gas Plants will have Shelters to cater to the need of equipment, personnel or as an enclosure for the need of equipment, personnel or as an enclosure for production, storage. production, storage.

Shelters can be open/ partially closed or fully closed. Shelters can be open/ partially closed or fully closed. Choice of whether to provide closed or open shelter Choice of whether to provide closed or open shelter depends upon requirement of equipment, outside depends upon requirement of equipment, outside environment, personnel and client requirements. Closed environment, personnel and client requirements. Closed shelters are also termed as Building.shelters are also termed as Building.

Shelters can be made of Steel Structures or Concrete Shelters can be made of Steel Structures or Concrete Structures or even composite structures as well.Structures or even composite structures as well.

From operation point of view, Shelters can be From operation point of view, Shelters can be categorised into two:categorised into two:

Plant SheltersPlant Shelters related to direct operation of plant related to direct operation of plant equipment e.g. Compressor House, Substation etc.equipment e.g. Compressor House, Substation etc.

Utility buildingsUtility buildings like Workshop, Warehouse, Admin like Workshop, Warehouse, Admin Building, Guard house etc.Building, Guard house etc.

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Different Types of Steel SheltersDifferent Types of Steel Shelters

Open Shelter:Open Shelter: Only roofing, no side cladding.Only roofing, no side cladding.

Partially closed Partially closed SheltersShelters

Roofing and partially closed side Roofing and partially closed side claddingcladding

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Fully closed Shelters/ BuildingsFully closed Shelters/ Buildings Roofing and full side cladding to provide controlled environment inside the Roofing and full side cladding to provide controlled environment inside the

Shelter. Normally proper HVAC systems are installed to provide controlled Shelter. Normally proper HVAC systems are installed to provide controlled environment. Claddings are also made insulated to keep HVAC system environment. Claddings are also made insulated to keep HVAC system effective.effective.

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Truss type shelterTruss type shelter - - This type of structures are used This type of structures are used

when width of the shelter is quite when width of the shelter is quite high and at roof level, space for high and at roof level, space for HVAC ducting, Electrical/ HVAC ducting, Electrical/ Instrumentation equipments Instrumentation equipments installation are not required. Truss installation are not required. Truss type sometimes found out to be type sometimes found out to be quite economical if designed quite economical if designed properlyproperly

Portal frame type sheltersPortal frame type shelters - Because of their clean lines, good - Because of their clean lines, good

overhead clearance and relatively overhead clearance and relatively low cost, portal- frame shelters low cost, portal- frame shelters have become very popular and have become very popular and widely used in oil & Gas Plants. widely used in oil & Gas Plants. They make up a large percentage They make up a large percentage of the small to medium size single-of the small to medium size single-storey industrial buildings in storey industrial buildings in current usecurrent use

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Portal Frame SheltersPortal Frame Shelters

Depending upon the requirements, Portal framed Depending upon the requirements, Portal framed shelters can be varied in shapes, sizes, arrangements shelters can be varied in shapes, sizes, arrangements etc.etc.

• Shelters with mono pitch roofShelters with mono pitch roof• Shelters with duo pitch roofShelters with duo pitch roof• Shelters with multi pitch roofShelters with multi pitch roof• Shelters with flat roofShelters with flat roof• Shelters with Multi baysShelters with Multi bays• Shelters with Multi storyShelters with Multi story

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Portal frame SheltersPortal frame Shelters Portal framed steel clad structures Portal framed steel clad structures

are the most common types of are the most common types of industrial Buildings. industrial Buildings.

Major components of a portal Major components of a portal frame building are a series of frame building are a series of parallel portal shaped frames as parallel portal shaped frames as the major framing elements. Each the major framing elements. Each frame is rigid, and resists frame is rigid, and resists horizontal wind forces and gravity horizontal wind forces and gravity loads in the plane of the frame by loads in the plane of the frame by flexural action.flexural action.

Longitudinal wind forces that are Longitudinal wind forces that are perpendicular to the frames are perpendicular to the frames are resisted by triangulated bracing resisted by triangulated bracing systems (in braced bays) in the systems (in braced bays) in the roof and walls which prevent the roof and walls which prevent the frames from failing over.frames from failing over.

Depending upon the length of the Depending upon the length of the structure, one or more braced structure, one or more braced bays can be provided in a shelter.bays can be provided in a shelter.

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Major parts of Portal framed ShelterMajor parts of Portal framed Shelter

Main frame (column & Main frame (column & Rafter):Rafter): carry bending, carry bending, compression, tension and compression, tension and transverse shear forcestransverse shear forces

Longitudinal Tie BeamsLongitudinal Tie Beams : : carry axial loadscarry axial loads

Vertical Bracings at Braced Vertical Bracings at Braced Bays:Bays: carry longitudinal horizontal carry longitudinal horizontal forces and provide overall stabilityforces and provide overall stability

Horizontal Bracings:Horizontal Bracings: carry carry horizontal forces and provide lateral horizontal forces and provide lateral stabilitystability

Purlin, Horizontal Girts:Purlin, Horizontal Girts: beam beam members carrying roof and wall members carrying roof and wall cladding respectivelycladding respectively

Crane/ Monorail Supports:Crane/ Monorail Supports: carry vertical, transverse and carry vertical, transverse and longitudinal forces due to longitudinal forces due to movement of crane and monorailmovement of crane and monorail

Cladding :Cladding : provide proper provide proper enclosure to shelter from adverse enclosure to shelter from adverse environmental conditionenvironmental condition

Sag Rods :Sag Rods : provide lateral provide lateral stability to purlinsstability to purlins

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Structural elements of a Structural elements of a sheltershelter

Portal Framed Shelter with all Portal Framed Shelter with all the major elementsthe major elements

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Portal frame Structural ElementsPortal frame Structural Elements

Large clear spans of Large clear spans of abut 40m can be abut 40m can be achieved economically achieved economically using I sections column using I sections column and Beam Rafters. The and Beam Rafters. The columns are generally columns are generally larger than the rafter larger than the rafter because the rafters are because the rafters are haunched near the haunched near the columns to cater for the columns to cater for the peak bending moments peak bending moments at the columns.at the columns.

Length wise building can Length wise building can vary 30m to 100m or vary 30m to 100m or more. more.

Sometimes expansion Sometimes expansion joints in building joints in building becomes necessary if becomes necessary if building length is more building length is more to avoid undue to avoid undue temperature stress.temperature stress.

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Design of Portal Frame SheltersDesign of Portal Frame Shelters

Building design nowadays usually carried out by a Building design nowadays usually carried out by a multi-discipline design team. An architect draws up multi-discipline design team. An architect draws up plans for a building to meet the client’s requirements. plans for a building to meet the client’s requirements. The structural engineer examines various alternative The structural engineer examines various alternative framing arrangements and may carry out preliminary framing arrangements and may carry out preliminary designs to determine which is the most economical. designs to determine which is the most economical. This is termed the ‘conceptual design stage’. For a This is termed the ‘conceptual design stage’. For a given framing arrangement, the problem in structural given framing arrangement, the problem in structural design consists of:design consists of:

a)a) Estimation of loading;Estimation of loading;b)b) Analysis of main frames, trusses or lattice girders, floor Analysis of main frames, trusses or lattice girders, floor

systems, bracing and connections to determine axial systems, bracing and connections to determine axial loads, shears and moments at critical points in all loads, shears and moments at critical points in all members;members;

c)c) Design of the elements and connections using design Design of the elements and connections using design data from step (b);data from step (b);

d)d) Production of arrangement and detail drawings from Production of arrangement and detail drawings from the designer’s sketches.the designer’s sketches.

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Structural Framing SchemeStructural Framing Scheme Size of the ShelterSize of the Shelter depends on several aspects like space required depends on several aspects like space required

for equipment, lay-down area, space for maintenance, for equipment, lay-down area, space for maintenance, requirement for different utility/ service rooms, control area, crane requirement for different utility/ service rooms, control area, crane excess etc.excess etc.

Generally size requirement comes from other disciplines with close Generally size requirement comes from other disciplines with close co-ordination with structural engineers.co-ordination with structural engineers.

After finalization of size, After finalization of size, spacing of framesspacing of frames (position of columns) (position of columns) are decided keeping all the above requirements in mind. Keeping are decided keeping all the above requirements in mind. Keeping spacing around 7.5m found out to be a good industrial practice.spacing around 7.5m found out to be a good industrial practice.

Slope of the roofSlope of the roof also depends upon various aspects like roof also depends upon various aspects like roof access, protection against extreme weathers etc. The standard access, protection against extreme weathers etc. The standard practice is to keep slope around 6 to 15 degree (depending upon practice is to keep slope around 6 to 15 degree (depending upon the cladding type). This cambering also helps the Portal frame to the cladding type). This cambering also helps the Portal frame to counter deflection against vertical loads.counter deflection against vertical loads.

Depending upon length of the building, Depending upon length of the building, number of braced baysnumber of braced bays are are chosen. Up to 50-60m length one braced bay found out to be chosen. Up to 50-60m length one braced bay found out to be sufficient. The positioning of braced bay should be such a way to sufficient. The positioning of braced bay should be such a way to avoid any undue deflection and stress concentration.avoid any undue deflection and stress concentration.

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Different types of Loads on Different types of Loads on SheltersShelters

The loading of a building structure can take on a wide variety of forms. In The loading of a building structure can take on a wide variety of forms. In many cases the exact loading will not fit neatly into a specific category. Yet, many cases the exact loading will not fit neatly into a specific category. Yet, loads can usually be considered to be:loads can usually be considered to be:

1. 1. Primary LoadsPrimary Loads – Main loads which are normally used for design like – Main loads which are normally used for design like

• Dead LoadDead Load• Live LoadLive Load• Snow/ Sand LoadSnow/ Sand Load• Wind loadWind load• Seismic LoadSeismic Load• Crane load etc. Crane load etc.

2. 2. Secondary LoadsSecondary Loads - Loads are those due to - Loads are those due to

• Temperature loadTemperature load• Test load Test load • Construction EccentricitiesConstruction Eccentricities• Shrinkage of structural materialsShrinkage of structural materials• Settlement of foundation etc.Settlement of foundation etc.

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Dead Load on SheltersDead Load on Shelters Dead Load:Dead Load:

Dead Loads are those loads which are considered to act permanently; Dead Loads are those loads which are considered to act permanently; they are "dead," stationary, and unable to be removed. The dead loads they are "dead," stationary, and unable to be removed. The dead loads acting on a portal-framed industrial building arise from the following acting on a portal-framed industrial building arise from the following items:items:

• Self WeightSelf Weight• FireproofingFireproofing• Masonry Walls (Brick and Block Walls)Masonry Walls (Brick and Block Walls)• Concrete Walls and FloorConcrete Walls and Floor• Wall CladdingWall Cladding• Roof CladdingRoof Cladding• FinishingFinishing• Other permanent loads (Equipment and Piping Empty Weight, Cable Tray Other permanent loads (Equipment and Piping Empty Weight, Cable Tray

load, etc)load, etc)

These loads should be estimated as per unit weight of materials used in These loads should be estimated as per unit weight of materials used in the construction. Weight of equipment, piping and cables should be the construction. Weight of equipment, piping and cables should be furnished by respective disciplines. furnished by respective disciplines.

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Live Load on SheltersLive Load on Shelters Live Load:Live Load:

Live Loads are not permanent and can change in magnitude. They Live Loads are not permanent and can change in magnitude. They include items found within a shelter such as human weight, machinery, include items found within a shelter such as human weight, machinery, or stored materials.or stored materials.

Different types of live load normally considered in Shelter are:Different types of live load normally considered in Shelter are: Floor Live LoadFloor Live Load Roof Live LoadRoof Live Load Operating Load (Product , Content of Pipe , etc)Operating Load (Product , Content of Pipe , etc) Maintenance LoadMaintenance Load Storage LoadStorage Load Other Temporary LoadsOther Temporary Loads

These loads should be estimated as per human occupancy loads, Operating These loads should be estimated as per human occupancy loads, Operating weight of equipment, piping and cables tray loads which should be furnished by weight of equipment, piping and cables tray loads which should be furnished by respective disciplines. respective disciplines.

Following codes are usually used to estimate common dead/ live loads:Following codes are usually used to estimate common dead/ live loads: 1-UBC 1997 Chapter 161-UBC 1997 Chapter 16 2-IBC 2006 Chapter 162-IBC 2006 Chapter 16 3-ASCE 7-05 Chapters 3,4 and C3,C43-ASCE 7-05 Chapters 3,4 and C3,C4 4-BS 6399 Part 1 & 34-BS 6399 Part 1 & 3 Note that civil/structural specification of client is the main reference for Note that civil/structural specification of client is the main reference for

calculation of dead/ live load along with above mentioned codes and standards.calculation of dead/ live load along with above mentioned codes and standards.

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Snow/ Sand Load on SheltersSnow/ Sand Load on Shelters Snow/ Sand Load:Snow/ Sand Load:

Snow load in nature is a live load but because of great importance Snow load in nature is a live load but because of great importance of this load which is responsible for collapse of roofs of industrial of this load which is responsible for collapse of roofs of industrial buildings in cold areas, its effect is taken separately. buildings in cold areas, its effect is taken separately.

Similarly in desert areas accumulated weight of sand on roof can Similarly in desert areas accumulated weight of sand on roof can cause same problem as that due to snow load. cause same problem as that due to snow load.

Snow load on the roof of industrial buildings depends on geometry Snow load on the roof of industrial buildings depends on geometry of roof and location of buildings. All international codes define this of roof and location of buildings. All international codes define this load based on these two parameters. load based on these two parameters.

Following codes are frequently used Following codes are frequently used to estimate snow loads: to estimate snow loads:

1-ASCE 7-05 Chapters 7 and C71-ASCE 7-05 Chapters 7 and C7 2-UBC 1997 Chapter 162-UBC 1997 Chapter 16 3-IBC 2006 Chapter 163-IBC 2006 Chapter 16 4-BS 6399 Part 34-BS 6399 Part 3

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Snow/ Sand Load on SheltersSnow/ Sand Load on Shelters This sketch shows how Snow This sketch shows how Snow

load is taken for calculation load is taken for calculation purpose on gable roofs as per purpose on gable roofs as per ASCE 7-05.ASCE 7-05.

Note that civil/structural Note that civil/structural specification of client is the specification of client is the main reference for minimum main reference for minimum snow load in the location of snow load in the location of project as per available project as per available meteorological data and local meteorological data and local codes. codes.

It is also advisable to check It is also advisable to check the chance of snow the chance of snow accumulation on one side of accumulation on one side of roof because of wind effect roof because of wind effect which can result to which can result to unbalanced loading on roof. unbalanced loading on roof. Both ASCE 7 and BS 6399 are Both ASCE 7 and BS 6399 are addressing this matter.addressing this matter.

Ice load in very cold areas is also a concern and should be calculated as Ice load in very cold areas is also a concern and should be calculated as per requirements of codes (e.g. ASCE 7-05 Chapters 10 and C10).per requirements of codes (e.g. ASCE 7-05 Chapters 10 and C10).

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Crane Load on SheltersCrane Load on Shelters Crane/ Monorail Load:Crane/ Monorail Load:

Cranes, including runway beams, brackets, bracing, and connections, Cranes, including runway beams, brackets, bracing, and connections, shall be designed to support the maximum wheel load of the crane and shall be designed to support the maximum wheel load of the crane and the vertical impact, lateral, and longitudinal forces induced by the moving the vertical impact, lateral, and longitudinal forces induced by the moving crane. Also, the runway beams shall be designed for crane stop forces. crane. Also, the runway beams shall be designed for crane stop forces. The methods for determining these loads vary depending on the type of The methods for determining these loads vary depending on the type of crane system and support.crane system and support.

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Crane Load on SheltersCrane Load on Shelters Crane loads on industrial Crane loads on industrial

Buildings falls in to three Buildings falls in to three

categories:categories: 1.1. Vertical load plus impact Vertical load plus impact

(Static + Dynamic (Static + Dynamic Effect):Effect):

Vertical Dynamic effect of Vertical Dynamic effect of crane in most of building crane in most of building codes has been defined as codes has been defined as an increasing factor to static an increasing factor to static load of wheels called impact load of wheels called impact factor. Normally for factor. Normally for Electrically operated Cranes Electrically operated Cranes (EOT) this factor is taken as (EOT) this factor is taken as 25%. For manually operated 25%. For manually operated monorail this factor is taken monorail this factor is taken as 10%.as 10%.

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Crane Load on SheltersCrane Load on Shelters

2.2. Lateral Force (Surge load):Lateral Force (Surge load): This This is due to lateral movement of crane is due to lateral movement of crane wheels. The lateral force shall be wheels. The lateral force shall be assumed to act horizontally at the assumed to act horizontally at the traction surface of a runway beam, in traction surface of a runway beam, in either direction perpendicular to the either direction perpendicular to the beam. Normally the force is calculated beam. Normally the force is calculated as 10% of the sum of rated capacity of as 10% of the sum of rated capacity of the crane and the weight of the hoist the crane and the weight of the hoist and trolley.and trolley.

3.3. Longitudinal Load (Braking Longitudinal Load (Braking load):load): This is due to movement of This is due to movement of crane along the length of building. crane along the length of building. Longitudinal forces shall be assumed Longitudinal forces shall be assumed to act horizontally at the top of the to act horizontally at the top of the rails and in each direction parallel to rails and in each direction parallel to each runway beam. Normally this each runway beam. Normally this force is taken as 5% of maximum force is taken as 5% of maximum wheel load excluding impact.wheel load excluding impact.

In case of In case of monorailmonorail, because of , because of unidirectional nature of movement, unidirectional nature of movement, horizontal force will be only along horizontal force will be only along one direction.one direction.

Typical Crane Girder Typical Crane Girder SectionSection

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Crane Load on SheltersCrane Load on Shelters

At each end of gantry girder crane stop At each end of gantry girder crane stop is provided to stop the movement of is provided to stop the movement of crane and avoid any damage to the crane and avoid any damage to the building structure due to impactbuilding structure due to impact

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Wind Load on SheltersWind Load on Shelters Wind Load:Wind Load: Wind load generally is the major Wind load generally is the major

influence in the design of Industrial influence in the design of Industrial structure.structure.

As per aerodynamics, wind tunnel As per aerodynamics, wind tunnel test and other experiments, all test and other experiments, all international codes furnish similar international codes furnish similar methods to calculate wind load on methods to calculate wind load on low-rise and rectangular shaped low-rise and rectangular shaped buildings.buildings.

All these methods can be All these methods can be summarized as below:summarized as below:

Get Basic Wind Speed at site as Get Basic Wind Speed at site as per meteorological data.per meteorological data.

Basic Wind Pressure calculated Basic Wind Pressure calculated from Wind Basic Speed and type from Wind Basic Speed and type of terrain.of terrain.

Calculate Wind Pressure at the Calculate Wind Pressure at the required height. Calculate effect required height. Calculate effect of Geometry of Structure of Geometry of Structure defined as shape factors. This defined as shape factors. This effect can be pressure or effect can be pressure or suction.suction.

Wind flow around a low-rise buildingWind flow around a low-rise building

Instantaneous external pressure distributions on the Instantaneous external pressure distributions on the frame of a low-rise building and simplified code frame of a low-rise building and simplified code distributionsdistributions

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Wind Load on SheltersWind Load on Shelters

Following International codes are usually used to estimate common Following International codes are usually used to estimate common wind loads:wind loads: 1-UBC 1997 Chapter 161-UBC 1997 Chapter 16 2-IBC 2006 Chapter 162-IBC 2006 Chapter 16 3-ASCE 7-05 Chapters 6 and C63-ASCE 7-05 Chapters 6 and C6 4-BS 6399 Part 2 4-BS 6399 Part 2 Two basic types of forces due to windTwo basic types of forces due to wind• External Pressure (Cpe) External Pressure (Cpe) • Internal Pressure (Cpi)Internal Pressure (Cpi)

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Wind loads are well codified, Wind loads are well codified, and are function of local and are function of local climate condition, building climate condition, building height, building geometry and height, building geometry and exposure as determined by exposure as determined by the surrounding environment the surrounding environment & terrain.& terrain.

Depending upon the Depending upon the direction of wind and severity direction of wind and severity of magnitude, total building of magnitude, total building structure is divided into structure is divided into different zones ( A, B, C, D, E different zones ( A, B, C, D, E etc…) and accordingly etc…) and accordingly pressures are found out.pressures are found out.

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Both sketches shows how wind Both sketches shows how wind in Transverse direction is in Transverse direction is taken in roof and wall of taken in roof and wall of Building. Forces due to Building. Forces due to transverse wind aretransverse wind are

• Transverse pressure forceTransverse pressure force• Longitudinal suction forceLongitudinal suction force

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Wind in Longitudinal directionWind in Longitudinal direction• Longitudinal pressure forceLongitudinal pressure force• Transverse suctionTransverse suction Wind Longitudinal drag forceWind Longitudinal drag force

Suction due to Longitudinal windSuction due to Longitudinal wind

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Seismic Load on SheltersSeismic Load on Shelters

Seismic/ Earthquake Loads:Seismic/ Earthquake Loads: The main cause of damage to structures during an earthquake is their The main cause of damage to structures during an earthquake is their

response to ground motions which are input at the base. In order to response to ground motions which are input at the base. In order to evaluate the behavior of the structure under this type of loading condition, evaluate the behavior of the structure under this type of loading condition, the principles of structural dynamics must be applied to determine the the principles of structural dynamics must be applied to determine the stresses and deflections, which are developed in the structure.stresses and deflections, which are developed in the structure.

When considering the analysis of structures for dynamic motions, the term When considering the analysis of structures for dynamic motions, the term dynamic simply means “time-varying”. Hence the loading and all aspects of dynamic simply means “time-varying”. Hence the loading and all aspects of

the response vary with time.the response vary with time. Seismic loads are established by building codes and are based on:Seismic loads are established by building codes and are based on:• Degree of seismic risksDegree of seismic risks• The degree of potential damageThe degree of potential damage• The possibility of total collapseThe possibility of total collapse• The feasibility of meeting a given level of protectionThe feasibility of meeting a given level of protection

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Seismic Load on SheltersSeismic Load on Shelters Seismic loads are generally a function of:Seismic loads are generally a function of:• Geographic and geological location of buildingGeographic and geological location of building• The use of the buildingThe use of the building• The nature of the building structural systemThe nature of the building structural system• The dynamic property of the siteThe dynamic property of the site• The weight of the building and the distribution of the weightThe weight of the building and the distribution of the weight Following International codes are commonly usually used to Following International codes are commonly usually used to

estimate seismic loads:estimate seismic loads: 1-UBC 1997 Chapter 161-UBC 1997 Chapter 16 2-IBC 2006 Chapter 162-IBC 2006 Chapter 16 3-ASCE 7-05 Chapters 11 to 23 and C11 to C233-ASCE 7-05 Chapters 11 to 23 and C11 to C23 There are two commonly used procedures for specifying seismic There are two commonly used procedures for specifying seismic

design forces: design forces: • Equivalent Static Force Equivalent Static Force • Dynamic AnalysisDynamic Analysis

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Seismic Load on SheltersSeismic Load on Shelters In the In the equivalent static force procedureequivalent static force procedure, the inertial forces are , the inertial forces are

specified as static forces using empirical formulas. The empirical specified as static forces using empirical formulas. The empirical formulas do not explicitly account for the "dynamic formulas do not explicitly account for the "dynamic characteristics" of the particular structure being designed or characteristics" of the particular structure being designed or analyzed. The formulas were, however, developed to adequately analyzed. The formulas were, however, developed to adequately represent the dynamic behavior of what are called "regular" represent the dynamic behavior of what are called "regular" structures, which have a reasonably uniform distribution of mass structures, which have a reasonably uniform distribution of mass and stiffness. For such structures, the equivalent static force and stiffness. For such structures, the equivalent static force procedure is most often adequate.procedure is most often adequate.

A A dynamic analysisdynamic analysis can take a number of forms, but should can take a number of forms, but should account for the irregularities of the structure by modeling its account for the irregularities of the structure by modeling its "dynamic characteristics" including natural frequencies, mode "dynamic characteristics" including natural frequencies, mode shapes and damping.shapes and damping.

Two method commonly used for dynamic analysis:Two method commonly used for dynamic analysis:• Time History MethodTime History Method• Response Spectrum MethodResponse Spectrum Method Unless specified by Client, equivalent static method is normally Unless specified by Client, equivalent static method is normally

followed to calculate seismic loading on single storey portal followed to calculate seismic loading on single storey portal framed shelters.framed shelters.

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Other Loads for SheltersOther Loads for Shelters

There are other types of load also which sometimes required to be There are other types of load also which sometimes required to be calculated while designing the Shelter structures:calculated while designing the Shelter structures:

Blast LoadBlast Load : :For ballast and effects of blast overpressure refer to For ballast and effects of blast overpressure refer to (ASCE Document: Design of Blast Resistant Buildings in (ASCE Document: Design of Blast Resistant Buildings in Petrochemical Facilities).Petrochemical Facilities).

• Note that the concept of design of buildings against blast in general Note that the concept of design of buildings against blast in general is to reduce damages and losses as per project specification and is to reduce damages and losses as per project specification and ASCE document.ASCE document.

Soil/Hydrostatic LoadSoil/Hydrostatic Load Erection LoadErection Load Test LoadTest Load Temperature / Thermal Load: Temperature / Thermal Load: Only thermal loads resulted from Only thermal loads resulted from

expansion or contraction of structure should be considered under expansion or contraction of structure should be considered under this load.this load.

Thermal loads magnitude in structural elements basically depends Thermal loads magnitude in structural elements basically depends on the rigidity of structure.on the rigidity of structure.

To reduce the effect of load, avoid using more than one braced bay To reduce the effect of load, avoid using more than one braced bay in structure and as a good practice of engineering, in every 45-60 m in structure and as a good practice of engineering, in every 45-60 m consider an expansion joint in the structure.consider an expansion joint in the structure.

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Temperature LoadTemperature Load

The best bracing system for structures under severe temperature variation is The best bracing system for structures under severe temperature variation is Chevron (inverted V), K and V bracings. The outcome of using X bracing will be Chevron (inverted V), K and V bracings. The outcome of using X bracing will be a severe axial load in the braced bay elements. Braced bays are also kept a severe axial load in the braced bay elements. Braced bays are also kept approx. at the middle of the structure to avoid excessive deflection and tie force approx. at the middle of the structure to avoid excessive deflection and tie force at the longitudinal beams.at the longitudinal beams.

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Load combinationsLoad combinations Load combinations are formed by adding the effects of loads from each of Load combinations are formed by adding the effects of loads from each of

the load sources cited above.the load sources cited above. Codes or industry standards often give specific load combinations which Codes or industry standards often give specific load combinations which

must be satisfied. It is not always necessary to consider all the loads at full must be satisfied. It is not always necessary to consider all the loads at full intensity. Also, certain loads are not required to be combined at all.intensity. Also, certain loads are not required to be combined at all.

Fr example : Wind load is not considered acting simultaneously with Seismic Fr example : Wind load is not considered acting simultaneously with Seismic load.load.

In some cases only a portion of a load must be combined with other loads.In some cases only a portion of a load must be combined with other loads. When a combination does not include loads at full intensity, it represents a When a combination does not include loads at full intensity, it represents a

judgment as to the probability of simultaneous occurrence with regard to the judgment as to the probability of simultaneous occurrence with regard to the time and intensity.time and intensity.

Following International codes are usually used to estimate combinations of Following International codes are usually used to estimate combinations of different loads:different loads:

1-UBC 1997 1-UBC 1997 2-IBC 2006 2-IBC 2006 3-ASCE 7-05 Chapters 3 and C33-ASCE 7-05 Chapters 3 and C3 Dead + Live load, which is usually the load combination that dictates the Dead + Live load, which is usually the load combination that dictates the

choice of column and rafter sizes from a strength point of view. choice of column and rafter sizes from a strength point of view. Dead + Wind load, however, is often the combination that governs from a Dead + Wind load, however, is often the combination that governs from a

deflection point of viewdeflection point of view

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Load CombinationLoad Combination

A typical strength design A typical strength design load combination is given as load combination is given as per UBC 97.per UBC 97.

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Design MethodsDesign Methods Analysis and Design of Building is based on three design Analysis and Design of Building is based on three design

theories:theories: (1) Elastic design;(1) Elastic design; (2) Plastic design;(2) Plastic design; (3) Limit state design.(3) Limit state design. The aim of structural design is to produce a safe and The aim of structural design is to produce a safe and

economical structure that fulfills its required purpose. economical structure that fulfills its required purpose. Elastic designElastic design is the traditional method and is still commonly is the traditional method and is still commonly

used. Steel is almost perfectly elastic up to the yield point and used. Steel is almost perfectly elastic up to the yield point and elastic theory follows this methodology. Structures are elastic theory follows this methodology. Structures are analyzed by elastic theory and sections are sized so that the analyzed by elastic theory and sections are sized so that the permissible stresses are not exceed.permissible stresses are not exceed.

Plastic theoryPlastic theory developed to take account of behaviour past the developed to take account of behaviour past the yield point is based on finding the load that causes the yield point is based on finding the load that causes the structure to collapse and formation of plastic hinges at structure to collapse and formation of plastic hinges at different portions of the member. different portions of the member.

Finally, Finally, limit state designlimit state design has been developed to take account has been developed to take account of all conditions that can make the structure become unfit for of all conditions that can make the structure become unfit for use. The design is based on the actual behaviour of materials use. The design is based on the actual behaviour of materials and structures in use.and structures in use.

3737

Design MethodsDesign Methods Normally elastic analysis is carried out Normally elastic analysis is carried out

for building structures followed by limit for building structures followed by limit state design. However, plastic analysis state design. However, plastic analysis may in some cases lead to more may in some cases lead to more economical structures.economical structures.

Sometimes if required, second order Sometimes if required, second order analysis (P-Delta analysis) is also done analysis (P-Delta analysis) is also done to cater the additional forces induced to cater the additional forces induced in the frame due to the axial forces in the frame due to the axial forces acting eccentrically to the assumed acting eccentrically to the assumed member centroids as the frame member centroids as the frame deflects under load.deflects under load.

Two types of checks are done to Two types of checks are done to ensure the stability of structure:ensure the stability of structure:

• Strength check:Strength check: this takes care the this takes care the most severe load combinations most severe load combinations

• Serviceability check :Serviceability check : It is to make sure It is to make sure the structures behave satisfactory and the structures behave satisfactory and can perform its intended function at can perform its intended function at service load. It also limit excessive service load. It also limit excessive deflection of structure and some cases deflection of structure and some cases prevent excessive vibration.prevent excessive vibration.

• Normally Building specification will Normally Building specification will provide proper deflection limits to be provide proper deflection limits to be considered for each elements of the considered for each elements of the structure.structure.

Potential problems to excessive deflection Potential problems to excessive deflection are:are:

• Damage in claddingDamage in cladding

•Objectionable sag in rafter and suspended Objectionable sag in rafter and suspended ceiling etc.ceiling etc.

•Damage to external/ internal masonry walls, Damage to external/ internal masonry walls, mezzanine floor concrete slabs and other mezzanine floor concrete slabs and other architectural finishes.architectural finishes.

•Excessive deflection of column at crane Excessive deflection of column at crane gantry level may cause damage to the gantry level may cause damage to the alignment of crane bridge.alignment of crane bridge.

3838

Structural Analysis & DesignStructural Analysis & Design Analysis and Design can be done as per any of the following Analysis and Design can be done as per any of the following

widely popular software:widely popular software: STAAD-Pro STAAD-Pro Sap 2000Sap 2000 GTSTRUDLGTSTRUDL

3939

Analysis of BuildingAnalysis of Building

Analysis of shelter is done by modeling the structure in 3D space frame Analysis of shelter is done by modeling the structure in 3D space frame with proper support conditions, member releases etc.with proper support conditions, member releases etc.

Above sketch shows one 3D Model of closed Shelter generated in StaadproAbove sketch shows one 3D Model of closed Shelter generated in Staadpro

4040

Bending Moment PatternsBending Moment Patterns

Loading and BMD for Transverse Loading and BMD for Transverse WindWind

Loading and BMD for WL (Suction Loading and BMD for WL (Suction force due to long. wind)force due to long. wind)

4141

Bending Moment PatternsBending Moment Patterns

Typical Output from Staadpro AnalysisTypical Output from Staadpro Analysis

Loading and BMD for DL/LL/SL etc.Loading and BMD for DL/LL/SL etc. Loading and BMD for Crane LoadLoading and BMD for Crane Load

4242

Building DetailingBuilding Detailing

Roof Plan bracing PatternRoof Plan bracing Pattern

Transverse ElevationTransverse Elevation

Longitudinal ElevationLongitudinal Elevation

Basic details of different sections/ plans which are normally used in shelters are shown here

4343

Base Plate & Gable FrameBase Plate & Gable Frame Column Base:Column Base: The great majority of portal frames are The great majority of portal frames are

designed with nominally pinned bases. designed with nominally pinned bases. This is for reasons of economy and This is for reasons of economy and simple design. Not only are fixed bases simple design. Not only are fixed bases more expensive because of the need more expensive because of the need for thicker and larger base plates and for thicker and larger base plates and the stiffening that is necessary, but the stiffening that is necessary, but the foundations require to be much the foundations require to be much larger to resist the base moments.larger to resist the base moments.

Only in cases of large lateral Only in cases of large lateral deflection, or possibly where brick deflection, or possibly where brick walls are built into the columns, is it walls are built into the columns, is it necessary to resort to fixed bases. necessary to resort to fixed bases. These should be kept as simple as These should be kept as simple as possiblepossible

Gable Frame:Gable Frame: Where buildings are not designed Where buildings are not designed

for future lengthwise extension, for future lengthwise extension, there is no need for portal frames there is no need for portal frames to be provided at the ends. A to be provided at the ends. A more economical alternative is to more economical alternative is to supply a light I- or channel section supply a light I- or channel section rafter spanning across the tops of rafter spanning across the tops of the gable posts and tied laterally the gable posts and tied laterally into the rafter bracing system.into the rafter bracing system.

Both the rafter and the corner Both the rafter and the corner columns can be much lighter than columns can be much lighter than that of a portal, but more that of a portal, but more importantly the high cost of the importantly the high cost of the portal eaves and apex haunches portal eaves and apex haunches can be saved. It is necessary, can be saved. It is necessary, though, to provide lateral support though, to provide lateral support and this can be done by means of and this can be done by means of a simple bracing systema simple bracing system

4444

Steel ConnectionsSteel Connections

Holding Down Bolts (Anchor Holding Down Bolts (Anchor Bolts): Bolts): Anchorage of the holding-Anchorage of the holding-down bolts into the concrete down bolts into the concrete foundation should be sufficient to foundation should be sufficient to cater for any uplift forces and to cater for any uplift forces and to provide for any shears applied to provide for any shears applied to the bolts. The most commonly the bolts. The most commonly used anchor bolts are of grade 4.6/ used anchor bolts are of grade 4.6/ 5.6.5.6.

Connection Bolts:Connection Bolts: The most The most frequently used bolts in steel frequently used bolts in steel connections are non preloaded connections are non preloaded bolts of strength grade 4.6 and 8.8 bolts of strength grade 4.6 and 8.8 (high strength) used in 2mm (high strength) used in 2mm clearance holes. There may be a clearance holes. There may be a situation where engineer may situation where engineer may encounter large load reversal in encounter large load reversal in the joint (in high seismic zone, the joint (in high seismic zone, supporting vibrating equipment), supporting vibrating equipment), in those cases high strength in those cases high strength friction grip bolts are used to avoid friction grip bolts are used to avoid any failure due to fatigue.any failure due to fatigue.

4545

Steel ConnectionsSteel Connections

The most important aspect of The most important aspect of structural steelwork for buildings is the structural steelwork for buildings is the design of the connections between design of the connections between individual frame components.individual frame components.

Basically there are three types of Basically there are three types of connection, each defined by its connection, each defined by its structural behaviour.structural behaviour.

• Simple connection-Simple connection- It transmit It transmit negligible bending moment across the negligible bending moment across the joint. The connection is detailed to joint. The connection is detailed to allow the beam to rotate. The beam allow the beam to rotate. The beam behaves as simply supported beam.behaves as simply supported beam.

• Continuous connection-Continuous connection- The The connection is designed to transmit connection is designed to transmit shear force and bending moment shear force and bending moment across the joint. This connection will across the joint. This connection will have sufficient stiffness to take have sufficient stiffness to take moment.moment.

• Semi-continuous connection-Semi-continuous connection- It is in It is in between the first two connections between the first two connections where it can take some amount of where it can take some amount of moment along with shear.moment along with shear.

4646

Eaves & Ridge ConnectionsEaves & Ridge Connections The types of eaves and apex The types of eaves and apex

haunches shown in Figure are the haunches shown in Figure are the ones almost universally used because ones almost universally used because of their relative simplicity and the of their relative simplicity and the ease with which the frame can be ease with which the frame can be erected. The critical design condition erected. The critical design condition is usually gravity loading with the is usually gravity loading with the rafter-to-column connection having to rafter-to-column connection having to sustain a high negative moment and sustain a high negative moment and the apex connection a smaller positive the apex connection a smaller positive moment. moment.

The moment at the eaves produces a The moment at the eaves produces a high tensile force in the upper flange high tensile force in the upper flange of the rafter that is transmitted of the rafter that is transmitted through the upper tension bolts and through the upper tension bolts and the end plate to the inner flange of the the end plate to the inner flange of the column. The compressive force in the column. The compressive force in the lower flange of the haunch is lower flange of the haunch is transferred in bearing through the end transferred in bearing through the end plate onto the column flange and into plate onto the column flange and into the web.the web.

The transfer of moment at the apex is The transfer of moment at the apex is similar, except that here the moment similar, except that here the moment is positive so the forces are reversed. is positive so the forces are reversed. The haunch and apex regions are The haunch and apex regions are vitally important parts of the frame vitally important parts of the frame and must be carefully proportioned.and must be carefully proportioned.

4747

Connection Details of Portal FrameConnection Details of Portal Frame

Another type of rafter-to-column Another type of rafter-to-column connection (shown in this Figure) is connection (shown in this Figure) is widely used for portal frames. Here widely used for portal frames. Here normally the rafter and column normally the rafter and column have the same section size and are have the same section size and are shop-welded with their flanges shop-welded with their flanges beveled to receive complete beveled to receive complete penetration groove welds. This is a penetration groove welds. This is a simple connection and is simple connection and is supplemented by a site-bolted supplemented by a site-bolted splice some way up the rafter, at a splice some way up the rafter, at a point of reduced bending moment. point of reduced bending moment. The location of the splice should be The location of the splice should be such that the length of the column-such that the length of the column-rafter component, as appropriate, is rafter component, as appropriate, is within transport limitations. within transport limitations.

The apex joint is also shop-welded. The apex joint is also shop-welded. The length of the rafter to the The length of the rafter to the opposite splice should meet opposite splice should meet transport requirements.transport requirements.

In these type of connections, proper In these type of connections, proper protection need to be observed to protection need to be observed to avoid drilling holes at the location of avoid drilling holes at the location of weld for connection for ridge/ Eaves weld for connection for ridge/ Eaves beams.beams.

4848

Bracing Details of Portal FrameBracing Details of Portal Frame

Bracings:Bracings: These structural These structural system are used to resist lateral system are used to resist lateral loads. These can be continuous or loads. These can be continuous or wind-moment frames or braced- wind-moment frames or braced- bay or combinations of bothbay or combinations of both

Braced Bay:Braced Bay: These are positioned These are positioned in such a way to provide minimal in such a way to provide minimal impact in upon planning of the impact in upon planning of the building. Braced bay act as building. Braced bay act as vertical trusses which resist the vertical trusses which resist the wind loads by cantilever action.wind loads by cantilever action.

The bracing member can be The bracing member can be arranged in various fashion arranged in various fashion designed to carry solely tension designed to carry solely tension or alternatively tension & or alternatively tension & compression.compression.

““X” is the most common form of X” is the most common form of tension bracing and “K” is the tension bracing and “K” is the most common type of most common type of compression bracings.compression bracings.

4949

Connections of different Connections of different elementselements

Bracing connection for heavy compressive Bracing connection for heavy compressive loadingloading

Beam splice connectionBeam splice connection Beam to column simple shear Beam to column simple shear connectionconnection

5050

Connections of different Connections of different elementselements

Gable end middle column Gable end middle column connectionconnection

• Sometimes sliding connection is Sometimes sliding connection is provided to ensure that provided to ensure that vertical load from gable rafter vertical load from gable rafter should not transfer to mid column.should not transfer to mid column. Crane Gantry bracket connectionCrane Gantry bracket connection

5151

Detailing of Crane GirderDetailing of Crane Girder

Side sway due to crane Side sway due to crane loadload

Different arrangements to absorb crane surge forceDifferent arrangements to absorb crane surge force

Gantry Girder showing bumper locationGantry Girder showing bumper location Stiffeners to avoid local Stiffeners to avoid local failurefailure

5252

Purlins & GirtsPurlins & Girts Purlins & Girts are immediate Purlins & Girts are immediate

supporting members of roof and supporting members of roof and wall sheeting respectively. wall sheeting respectively.

They act principally as beams, but They act principally as beams, but also performs as struts and as also performs as struts and as compression braces in resisting compression braces in resisting rafters and columns laterally rafters and columns laterally against torsional buckling.against torsional buckling.

In some buildings purlins and girts In some buildings purlins and girts act as axial members to transfer act as axial members to transfer end wall wind loads to the braced end wall wind loads to the braced bays, while in some small shelters bays, while in some small shelters they may even act as the struts of they may even act as the struts of the triangulated roof bracing the triangulated roof bracing system.system.

Depending upon the load it is Depending upon the load it is carrying, purlins and girts can be carrying, purlins and girts can be hot rolled channel/ I sections or hot rolled channel/ I sections or cold rolled Z or C section.cold rolled Z or C section.

As Purlins are inclined members, As Purlins are inclined members, these are designed to withstand these are designed to withstand bi-axial forces.bi-axial forces.

5353

Purlins & GirtsPurlins & Girts

Strength is not the only criteria when Strength is not the only criteria when designing purlins. Purlin spacing designing purlins. Purlin spacing must be chosen to suit the type of must be chosen to suit the type of roof sheeting and ceiling system.roof sheeting and ceiling system.

Purlin deflection aspect also need to Purlin deflection aspect also need to be taken into consideration while be taken into consideration while deciding the spacing.deciding the spacing.

Purlin spacing can vary from 1.2m to Purlin spacing can vary from 1.2m to 2.5m.2.5m.

Fly bracingFly bracing helps to reduce purlin span helps to reduce purlin span and also it helps to provide lateral and also it helps to provide lateral restraint to compression flange of rafterrestraint to compression flange of rafter

5454

Sag RodsSag Rods

Sag rods are generally provided to give Sag rods are generally provided to give sufficient lateral restraint and stability to sufficient lateral restraint and stability to Purlins.Purlins.

It is a standard practice to provide sag rods It is a standard practice to provide sag rods at roof-purlin level when purlin span is high.at roof-purlin level when purlin span is high.

Sag rods are designed for axial tension force Sag rods are designed for axial tension force only.only.

For duo-pitch roof, at the ridge portion For duo-pitch roof, at the ridge portion sometimes plate/ angle (diaphragm plate) is sometimes plate/ angle (diaphragm plate) is provided to take compression and to provide provided to take compression and to provide proper stability to roof sag rod system.proper stability to roof sag rod system.

5555

Architectural Details of Architectural Details of SheltersShelters

Cladding: Cladding is required to be Cladding: Cladding is required to be weather tight, to provide insulation, to weather tight, to provide insulation, to have penetration for daylight and have penetration for daylight and access, to be aesthetically pleasing access, to be aesthetically pleasing and last the maximum time with a and last the maximum time with a minimum maintenance consistent with minimum maintenance consistent with the budget.the budget.

Two types of cladding are broadly used Two types of cladding are broadly used for both roofing and wall sheeting for both roofing and wall sheeting purpose.purpose.

• Single skin steel sheetingSingle skin steel sheeting• Double skin insulated sandwich steel Double skin insulated sandwich steel

panelspanels

5656

Architectural Details of Architectural Details of SheltersShelters

Roof/ wall sheeting spanning is the Roof/ wall sheeting spanning is the most important data to have before most important data to have before structural detailing work.structural detailing work.

Sheeting can span horizontally as well Sheeting can span horizontally as well as vertically.as vertically.

Accordingly purlin spacing, Accordingly purlin spacing, requirement of girts and their spacing requirement of girts and their spacing are worked out.are worked out.

Generally cladding manufacturer Generally cladding manufacturer provides data for minimum roof pitch, provides data for minimum roof pitch, maximum allowable spanning, maximum allowable spanning, support requirements etc.support requirements etc.

Other details like fixing door, window, Other details like fixing door, window, gutter, rain water down-comer etc. gutter, rain water down-comer etc. can be finalized and details as per can be finalized and details as per respective manufacturer’s data and respective manufacturer’s data and catalogues.catalogues.

Accordingly finish schedule, door-Accordingly finish schedule, door-window schedule, secondary wall window schedule, secondary wall (masonry) detail drawings need to be (masonry) detail drawings need to be prepared.prepared.

5757

Miscellaneous Structures inside Miscellaneous Structures inside SheltersShelters

Maintenance Platforms Maintenance Platforms surrounding Equipment surrounding Equipment Foundations (e.g. Compressor)Foundations (e.g. Compressor)

Mezzanine floor supporting Mezzanine floor supporting Equipments (e.g. AHU)Equipments (e.g. AHU)

Fan supports outside buildingFan supports outside building

5858

Miscellaneous Structures inside Miscellaneous Structures inside SheltersShelters

HAVC ducts hanging from HAVC ducts hanging from Roof ties and purlins.Roof ties and purlins.

Other equipment supports Other equipment supports and access Platforms and access Platforms attached to Sheltersattached to Shelters

Pipes and cable trays Pipes and cable trays supported from Building supported from Building structure.structure.

5959

Shelter FoundationShelter Foundation

Foundation Design:Foundation Design: Depending upon the soil property Depending upon the soil property

shelter foundations can beshelter foundations can be• Shallow footings (isolated, Shallow footings (isolated,

combined, strip etc.) orcombined, strip etc.) or• Piled foundationPiled foundation Different checks to be performed Different checks to be performed

for shallow foundations arefor shallow foundations are• Bearing pressure checkBearing pressure check• Sliding checkSliding check• Overturning checkOverturning check• Buoyancy checkBuoyancy check For pile foundation design, normally For pile foundation design, normally

individual pile capacities are given individual pile capacities are given by Client/ Soil investigation reports by Client/ Soil investigation reports and accordingly rigid pile and accordingly rigid pile foundations are designed as per foundations are designed as per standard codal provisions.standard codal provisions.

Piled Foundation (3 & 5 piled Pile caps)Piled Foundation (3 & 5 piled Pile caps)

6060


Foundation layout drawing Foundation layout drawing showing isolated footings with showing isolated footings with tie beamstie beams

Plan & Sectional Plan & Sectional views of isolated views of isolated footingsfootings

Plan & Sectional Plan & Sectional views of combined views of combined footingsfootings

6161


Inside shelter grade slab model and 2D Inside shelter grade slab model and 2D drawing showing position of different drawing showing position of different equipments, supports, trenches etc.equipments, supports, trenches etc.

6262


Slab on Grade-Slab on Grade- Design of grade slab is an important aspect of Building design as the Design of grade slab is an important aspect of Building design as the actual loading for design is unknown. Normally UDL is assumed for design of slab and actual loading for design is unknown. Normally UDL is assumed for design of slab and nominal reinforcement is provided for crack control as bending moment will not develop nominal reinforcement is provided for crack control as bending moment will not develop due to UDL.due to UDL.

Sometimes, loads due to forklift movement, maintenance work, pipe or other platform Sometimes, loads due to forklift movement, maintenance work, pipe or other platform supports need to be considered for slab design as those are non-uniform and supports need to be considered for slab design as those are non-uniform and concentrated in nature.concentrated in nature.

Extra precautions need to taken to cater those concentrated loads on slab. Generally Extra precautions need to taken to cater those concentrated loads on slab. Generally local thickening of slab with extra reinforcement surrounding those supports/ areas are local thickening of slab with extra reinforcement surrounding those supports/ areas are done to avoid punching failure. done to avoid punching failure.

6363

ENDEND

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17630684 Design of Steel Shelter Final