projects and documents terÄshallin suunnitelmia · lecture 14.1.1 : single - storey buildings:...

RAKENNUSTEKNIIKKA Olli Ilveskoski 30.08.2006 rev2 10.01.2007

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PROJECTS AND DOCUMENTS

TERÄSHALLIN SUUNNITELMIA:

Tasopiirustus

Kokoonpanopiirustuksia


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Leikkauspiirustus

Leikkauspiirustus


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Kokoonpanokuva

Kuva mallikehistä


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MALLIPROJEKTEJA:

Kuva: TRY ry:n / Risto Liljan Oppimisympäristö

http://www.tamk.fi/terasrakenteet/suunnittelu/piirustukset/try/RAK/piirustusluettelo_tryrak.htm

Esimerkit

Kuva: TRY ry:n / Risto Liljan Oppimisympäristö

http://www.tamk.fi/terasrakenteet/suunnittelu/esimerkit/parveke/Parvekkeen%20ripustus.pdfhttp://www.tamk.fi/terasrakenteet/suunnittelu/esimerkit/Mainostorni/main_torn_diag_mit.pdf


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Opiskelija perehtyy teräsrakennuksiin..ks ESDEP – oppimisympäristö: http://www.terasrakenneyhdistys.fisuomenkielinen versio

Course Contents

WG 14 : STRUCTURAL SYSTEMS: BUILDINGS

Lecture 14.1.1 : Single- Storey Buildings: Introduction and Primary Structure

Lecture 14.1.2 : Single Storey Buildings: Envelope and Secondary Structure

Lecture 14.2 : Analysis of Portal Frames: Introduction and Elastic Analysis

Lecture 14.3 : Analysis of Portal Frames: Plastic Analysis

Lecture 14.4 : Crane Runway Girders

Lecture 14.5 : Space Structure Systems

Lecture 14.6 : Special Single Storey Structures

Lecture 14.7 : Anatomy of Multi-Storey Buildings

Lecture 14.8 : Classification of Multi-Storey Frames

Lecture 14.9 : Methods of Analysis for Multi-Storey Frames

Lecture 14.10 : Simple Braced Non-Sway Multi-Storey Buildings

Lecture 14.11 : Influence of Connections on Behaviour of Frames

Lecture 14.12 : Simplified Method of Design for Low-Rise Frames

Lecture 14.13 : Design of Multi-Storey Frames with Partial Strength and Semi-Rigid Connections

Lecture 14.14 : Methods of Analysis of Rigid Jointed Frames

Lecture 14.15 : Tall Building Design


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Workgroup Contents

Lecture 14.1.1 : Single- Storey Buildings: Introduction and Primary Structure

Top

1. INTRODUCTION

2. ANATOMY AND CONCEPTION OF THE STRUCTURE

2.1 Cladding

2.2 Secondary Elements

2.3 The Main Frame of the Structure

2.3.1 Simplest Frames

2.3.2 Portal frames

2.3.3 Lattice Trusses

3. LOADING

3.1 External Gravity Loads

3.2 Wind Loads

3.3 Internal Gravity Loads

3.4 Cranes

3.5 Other Actions

4. FABRICATION

5. TRANSPORTATION

6. ERECTION

7. CONCLUDING SUMMARY

8. REFERENCES


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9. WIDER READING

Previous | Next | Contents

ESDEP WG 14

STRUCTURAL SYSTEMS: BUILDINGS

Lecture 14.1.1: Single- Storey Buildings: Introduction and Primary Structure

OBJECTIVE/SCOPE

• To describe the anatomy of single-storey buildings, cladding, secondary elements and main frame structures.

• To clarify how the loads are supported.• To present the basic principles of design and analysis of a single storey

building.• To give a design example.

PREREQUISITES

Lecture 1B.1: Process of Design

Lecture 1B.3: Background to Loadings

Lecture 1B.5.1: Introduction to Design of Industrial Buildings

Lecture 9.1: Thin-walled Members and Sheeting

RELATED LECTURES

Lecture 14.1.2: Single-Storey Buildings: Envelope and Secondary Structure

Lecture 14.2: Analysis of Portal Frames: Introduction and Elastic Analysis

Lecture 14.3: Analysis of Portal Frames: Plastic Analysis

Lecture 14.4: Crane Runway Girders

Lecture 14.5: Space Structure Systems

Lecture 14.6: Special Single-Storey Structures


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SUMMARY

Single-storey steel buildings are used to accommodate many functions such as factories, leisure facilities, and supermarkets. The structure consists of several elements. The lecture examines the function of each element, gives general indications of the cost as a proportion of the total cost of the building.

The lecture also gives information on loading, on the different factors affecting the concept of the main frame, and on considerations relating to the construction process of the structure.

1. INTRODUCTION

Steel construction is used for the majority of non-domestic single-storey buildings, the proportion is as high as 90% in the UK and 70% in France. This large proportion is due to the ability to design relatively light, long span, durable structures in steel which are easy to erect safely and quickly. The developments in steel cladding and light-gauge purlin and rail systems in recent years have enabled architects and engineers to create economical, attractive designs for a wide range of applications and budgets.

The rate of change of any activity is very rapid as technology develops. Clients expect therefore their buildings to have a lifetime several times longer than the initial layout. A primary requirement is therefore flexibility of planning which results in a demand for as few columns as possible. The ability to provide spans up to 60m, but more commonly around 30m, using steel has proved very popular for commercial and leisure buildings. The lightness and flexibility of this kind of steel structure reduces the sizes and the costs of foundations and makes them less sensitive to the geotechnical characteristics of the soil.

The brief for the design of the majority of single storey industrial buildings is essentially to provide a structure which is without, or has a limited number of, internal columns. In principle the requirement is for the construction of four walls and a roof for a single or multi-bay structure. The walls can be formed of steel columns with cladding which may be of profiled or plain sheet, precast concrete, or masonry. The designer considers a system of beams or frameworks (latticed or traditional) in structural steel to support the cladding for the roof. Use is made of hot rolled hollow sections (circular, rectangular) and traditional sections (I sections, angles, etc.) and also cold formed sections.

Light latticed frameworks for the roof of an industrial building provide a neat, efficient, structure which is simple to design, economic to execute and frequently satisfies architectural requirements. Whilst the structural envelope and the design are 'basically' simple, it is essential to ascertain correctly the loads applied to the structure and to predict the load paths from the sheeting to the purlins and side rails, through the roof girder to the column and finally to the foundation and supporting soil.


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2. ANATOMY AND CONCEPTION OF THE STRUCTURE

The skeleton of a typical single-storey building is shown in the diagram (Figure 1). It consists of three major elements: cladding for both roof and walls; secondary steel to support the cladding and form framing for doors, windows and the like; and the main frame of the structure, including all necessary bracing. In addition, the building requires foundations which have to be designed and built to transmit all the loads to the soil.

2.1 Cladding

The primary functions of the cladding are to provide shade, shelter, and an attractive appearance. The cladding is therefore arguably the most important element of the structure. It is likely to be some 50% of the total cost even if a fairly basic specification is used. The frame members, both primary and secondary are there to support the cladding and services.

The requirements for walls and roof are somewhat different although both need to be weather tight, durable and provide insulation.

The weathertightness of the roof is clearly paramount, particularly for lower pitches.

In the case of walls the appearance will be the highest priority in making the selection. Cladding formed from metal sheets has emerged as the most popular choice since its introduction in the 1970's. Steel is the most usual substrate with aluminium as a more expensive second choice. The higher coefficient of expansion of aluminium can lead to difficulties in some circumstances.


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2.2 Secondary Elements

In the normal single-storey building the cladding is supported on secondary members, which transmit the loads back to main structural steel frames.

An economic solution is provided by the use of cold-formed light gauge sections [1]. These sections are of proprietary shape and are produced to order on "computer numerically controlled" rolling machines. These processes are extremely efficient since the components are delivered to site pre-engineered to the exact requirements. As a result fabrication and erection times are minimised and material wastage is eliminated. With high volume rolling the material content of purlins and rails is a very significant part of the cost and manufacturers have developed shapes which are extremely material efficient. The most common are zeds, modified Zeds and sigma shapes as shown in Figure 2. Spans are commonly 5-8m but longer spans up to 12m can be achieved.

It is also traditional to use hot-rolled sections as I or C shapes, not so sensitive to the effect of local instability. The centre to centre distance of the portal frames is then reduced, in general, to 5 or 6m.

Generally, the cost breakdown of various elements will be cladding 50%; purlins and rails 10%; mainframe 30%; and foundations 10%. These figures are indicative, as clearly there is considerable variation in specification and cost of the cladding which is the largest single element. Cladding can vary from 10 ecu/m2 to over 150 ecu/m2.

The remainder of this lecture discusses the main frame of the structure. Cladding and secondary elements are considered in Lecture 14.1.2.

2.3 The Main Frame of the Structure

The loads are transferred from the sheeting onto the purlins and rails, which in turn are supported by a primary (or main) structure. These loads can be obtained from the relevant codes. They will include:


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• the self weight of the cladding, of the secondary elements (purlins and rails) and of the frame itself,

• the applied loads from services, etc,• the vertical and horizontal loads from cranes,• the snow loads,• the wind loads,• the earthquake effects, in some areas.

When the length of the structure is not too great, say 50 to 100m depending on temperature range, it is normal practice not to consider the effects produced by changes of temperature. It is usual practice, also, not to consider differential settlement of foundations if they are below 2cm.

Wind can of course cause pressure, suction and drag loads on the cladding. Figure 3 illustrates the various components of load to consider in the design.

The primary structural frames will normally be spaced from 5 to 8m centres. Although larger spacings are growing in popularity, an analysis of a purlin manufacturers' sales shows that about 6m remains the most popular spacing. The most straight forward single-storey structural form consists of a pair of vertical columns supporting a spanning beam. To be practical, there is a need for a fall in the roof finish to provide adequate drainage. For the small spans for which this arrangement is suitable, the fall can be achieved in the finishes or by a nominal slope in the beam. This form of construction, is shown in Figure 4. Stability against wind loading can be provided by the cladding which is fixed from frame to frame. This simple form of structure is used for small workshops. It is only suitable for spans up to approximately 12m.


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For longer spans this simple solution becomes, in general, uneconomic. Then portal frames and lattice trusses are more competitive solutions.

Figure 5 shows some options commonly used for portal frames. The more popular solutions are pinned bases if there is no crane to be supported and the fully rigid version when it is necessary to support crane loads and to obtain smaller horizontal displacements. Less weight of steel results, in any case, from fixed based frames, but the additional cost of the foundations of the supports can be higher than the saving of steel.

Figure 6 shows an example of solid column with a typical lattice girder.


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Whichever solution is chosen, all loads have to be transferred to the ground in a coherent fashion in even the simplest of buildings. The provision of bracing is covered in Lecture 14.1.2.

Restraints to the main structure against out-of-plane buckling can be provided by the purlins connected to the top flange of the rafter and by the rails connected to the outer column flange. Figure 7 shows three typical ways of providing adequate restraint.


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Plastic design of portal frames brings limitations on the spacing of restraints of about 1,8 to 2m. At plastic hinge locations, it is necessary to provide stays from the rail to the inner flange in order to avoid the lateral buckling of the compressed flange. The cladding spans between the purlins and commercially available profiles are economic in this range of spacing to meet the requirements for walkability, strength (corrugation depths), and drainage.

Where lattice structures are used, secondary bending in the top boom is avoided if the purlins are supported at the node points. Spacings of about 1,8m are often found convenient and economic.

It is also possible to use the cladding as a stressed skin in order to transmit the horizontal forces generated in the roof by the wind and the tendency of the frame to out-of-plane buckling.

2.3.1 Simplest Frames

The cross-section shown in Figure 4 is undoubtedly the simplest framing solution which can be used to provide structural integrity to single-storey buildings. Used predominately in spans of up to 10m, where flat roof construction is acceptable, the


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frame comprises standard hot-rolled sections having simple or moment-resisting joints.

Flat roofs are notoriously difficult to weatherproof, since deflections of the horizontal cross-beams induce ponding of rainwater on the roof which tends to penetrate the laps of the traditional cladding profiles and, indeed, any weakness of the exterior roofing fabric. To counteract this, either the cross-member is cambered to provide the required fall across the roof, or the cladding itself is laid to a predetermined fall, again facilitating drainage of surface water off the roof.

Due to the need to control excessive deflections, the sections tend to be somewhat heavier than those required for strength purposes alone, particularly if the cross-beam is designed as simply supported. In its simplest form, the cross-beam is designed as spanning between columns. For gravity loadings the latter are in direct compression apart from a small bending moment at the top of the column due to the eccentricity of the beam connection. The cross-beam acts in bending due to the applied gravity loads, the compression flange being restrained either by purlins, which support the roof sheet, or by a proprietary roof deck which may span between the main frames and which must be adequately fastened.

Resistance to lateral loads is achieved by the use of a longitudinal wind girder, usually situated within the depth of the cross-beam. This transmits load from the top of the columns to bracing in the vertical plane, and thence to the foundation. The bracing is generally designed as a pin-jointed frame, in keeping with the simple joints used in the main frame.

Buildings which employ the use of beam-and-column construction often have brickwork cladding in the vertical plane. With careful detailing, the brickwork can be designed to provide the vertical sway bracing, acting in a similar manner to the shear walls of a multi-storey building.

Resistance to lateral loading can also be achieved either by the use of rigid connections at the column/beam joint or by designing the columns as fixed-base cantilevers.

Rigid connections and rigid column/foundation joints reduce also the deflection of the beam and need less weight of structural steel for the frame.

2.3.2 Portal frames

As explained above, the two most popular arrangements are the portal frame with pinned bases, if there is no crane to be supported, and the fully rigid portal frame, which is often used if there is a crane. These forms are both functional and economic. In- plane stability is derived from the provision of moment-resisting connections at the top and at the beam-to-column connections for the first situation and also at the base in the second one [2].

The falls required to the roof are naturally provided by the cladding carried on purlins which, in turn, are supported by the main frame members. Architectural pressures


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lead to the use of the flattest slopes compatible with weathertightness. The most common slope is about 6°, but slopes as low as 1° have been used.

The frames are constructed from I-section rafters and columns with haunches at the connections at the eaves as illustrated in Figure 1. The haunch length is approximately 10% of the span and can be formed from welded plate or more commonly a cutting from a rolled section. The depth at the column face is typically slightly deeper than the rafter section. The design of these frames is dealt with in Lecture 14.2 and Lecture 14.3. Portal frames can be also built with tapered rather than haunched sections. Frames of this type are common in the USA and are being used more frequently in Europe. The sections are fabricated from plate on automated welding machines. The ability to vary web thickness, flange dimensions and section depth results in high material efficiency. Deep slender sections are used to maximise economy. Suitable design methods are described in Lecture 14.3. In addition to material economies there are benefits in reduced deflections resulting from the high in-plane stiffness of the deep sections.

Portal frames are particularly economic up to 40m spans and, where the internal planning permits, multi-bay configurations of 20-30m spans are effective. They have been used for frames up to 75m span.

2.3.3 Lattice Trusses

Figure 8 shows a typical frame built with lattice trusses. Lattice structures are lighter than the portal alternatives for spans greater than 25m but the additional workmanship increases fabrication costs [3]. Figure 9 gives an indication of the relative material weights. It is not possible to be definitive but based on structural requirements, lattice systems are likely to be cost effective for spans over 50 m.


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Because lattice girders have a much larger second moment of area and section modulus than a corresponding I section of a similar weight, they have greater stiffness and resistance to load. These enhanced properties are however accompanied by higher fabrication and erection costs due to the required effort for the connections. Spans up to 80m have been realised in that way.

When deciding the size of different elements of the lattice girder, the engineer should be aware that stress reversals are likely due to wind effects.

Frames are normally positioned at 6,0m to 8m centres. These spacings generally provide economic solutions for the cold-formed purlin and side rail arrangements.

Generally a decision is taken early during the process of conceptual design on the type(s) of member(s) to be used for the latticed frame. There are many alternatives:

a. Hollow sections - circular or rectangular.

b. Traditional sections - angles, tees, channels, I sections.

c. Combination of (a) and (b).

The selected truss should reflect not only the design aim to produce the lightest frame but also fabrication and erection requirements.

Examples of composite form are shown in Figure 10 where the booms are I sections and the internal members are RHS. The I sections enable easy connection of services


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to the truss and easy connection to columns. Bracing in the plane of the roof can be provided using simple in-plane members and simple connections, or by using the relative stiffness of an I or H section.

The specific advantages of hollow sections (and tubes) when compared with traditional sections (I sections, channels, angles, etc.) are the high strength to weight ratio, maximum efficiency in tension, efficiency as struts, good torsional properties, appearance and maintenance. In considering use of CHS or RHS the designer should remember that some fabricators are not fully equipped to fabricate circular hollow sections. (Connection costs are considerably reduced if RHS beams are selected, with CHS or RHS web members). The main disadvantages of CHS and RHS are the higher cost of connections at some nodes and the relative difficulties of making on-site connections for services (electrical, etc.). In addition basic costs are higher than traditional sections on a tonnage basis (overall however frames of lighter weight are produced).

The relative slopes of the internal members should be considered in relation to the detailing and fabrication process. If they are parallel to each other then the angle of cut at each end is identical for all members.

The final decision on the type(s) of member(s) to be used may be influenced by aesthetics and not cost.

Early industrial buildings were built with saw tooth truss layouts illustrated in Figure 11. The vertical (or nearly vertical) elements were glazed and north facing to allow the maximum daylight with minimum direct sun light. In modern times the need for natural lighting has diminished with modern lighting systems and while 10% of area of roof lighting through translucent panes is common, many take advantage of the more reliable and controllable conditions with no natural lighting at all.


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Generally, the columns to the frame are I or H sections (Figure 12a). The latter have a greater transverse stiffness than the former and are preferred in cases of biaxial bending. When the building incorporates an overhead travelling crane of high capacity, a built-up load or battened column may be used (Figure 12b). In some cases the built-up columns are continued by I sections over the level of the crane supporting structure in order to reduce the costs (Figure 12c).


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3. LOADING3.1 External Gravity Loads

The dominant gravity load is from snow. The general case is the application of a basic uniform load, but with sloping roofs having multiple spans and parapets, the action of drifting snow has to be considered. The basic loading is variable according to location. Design information is currently given in national load codes and will be addressed in Eurocode 1, in due course. The main frame design for portals can be carried out using the uniform load case but the variable loads caused by drifting are to be applied to cladding and purlins. The effects of drifting are idealized into triangular loadings with formulae given for the various effects of valleys, parapets, upstands, etc. Early tests carried out in the UK established that equivalent uniformly distributed loads can be used for the purlins design. In the areas of high local load, consideration has to be given as to whether to reduce purlin spacing or to increase the gauge. Where practicable the reduction of spacing is preferable as it prevents the


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dangers and disruption involved with identification and production of different thicknesses of purlin supplied to one job.

For portal frames the frame strength will usually be determined by the snow load case, unless the eaves height is large in relation to span.

3.2 Wind Loads

With lightweight cladding and purlins and rails, wind loads are important. Cladding and its fasteners are designed for the local pressure coefficient, for example as given in BS6399: Part 3 and other national codes. Purlins and main frames are designed using the relevant statistical factors, but not additional local coefficients. Care must be taken to include the total effect of both internal and external pressure coefficients.

3.3 Internal Gravity Loads

Service loads for lighting, etc., are reasonably assumed to be globally 0,6kN/m2. As service requirements have increased, it has become necessary to consider carefully the provision to be made.

Most purlin manufacturers can provide proprietary clips for hanging limited point loads to give flexibility of layout. Where services and sprinklers are required, it is normal to design the purlins for a global service load of 0,1 - 0,2kN/m2 with a reduced value for the main frames to take account of likely spread. Particular items of plant must be treated individually. The specifying engineer should make a realistic assessment of the need as the elements are sensitive and, while the loads may seem low, they represent a significant percentage of the total and affect design economy accordingly.

3.4 Cranes

Where moving loads such as cranes and conveyors are present (Figure 13), in addition to the gravity loads, the effects of acceleration and deceleration have to be taken into account in the design. A quasi-static approach is generally used in which the moving loads are enhanced and treated as static loads in the design. The enhancement factors to be used depend on the particular plant and its acceleration and braking capacity. Manufacturers must be consulted where heavy, high speed or multiple cranes are being used.


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To take into account dynamic effects due to cranes, the maximum vertical loads and the horizontal forces are increased by specific factors which can be found in national guidance.

The repeated movement of a crane gives rise to fatigue conditions. Fatigue effects are restricted to the local areas of support, the crane beam itself, support bracket and the connection to main columns. It is not normal to design the whole frame for fatigue as the stress levels due to crane travel are relatively low.

3.5 Other Actions

In certain areas, the effects of earthquakes should be considered. In those countries affected, there are maps which identify the seismic level of each zone and standards to evaluate structural behaviour. Eurocode 8 [5] deals specifically with this problem.

In common practice, it is not necessary to take into account differential settlement of less than 2,5cm. If differential settlement exceeds 2,5cm, its effects must be examined, both from the structural and functional points of view. In less ductile structures, such as those constructed with sections not in Class 1 or 2, it is always important to evaluate the sensitivity of the structure in relation to possible differential settlement.

It is also general practice not to take into account the effects of temperature when the maximum dimension of the building is less than 40 to 50m, or when expansion joints have been used which separate the structure into zones which do not exceed this dimension. Elsewhere, it is important to evaluate the effects of variations in temperature. It is also necessary to ensure that the characteristics of the finished structure, both the systems of fastening and the seals in the envelope, are compatible with the inevitable deformations due to change in climate.


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4. FABRICATION

Important factors which must be considered at the conceptual and detailing stages are the questions of workshop facilities and space and of transport between workshop and site. Whilst large girders and/or large sections may appear to be desirable in order to reduce the number of site connections, the use of large members can often reduce the number of fabricators who can tender for a given project.

The lengths of members available from stockists or direct from the mill can vary. When long lengths are deemed desirable it is necessary to check their availability. Generally standard sections can be obtained in a reasonable time but there are likely to be delays and additional cost if non-standard sections are required. The use of slightly heavier sections and standardisation of section size may lead to a cheaper fabricated structure. When large prefabricated trusses are used it may be necessary to provide lifting points (eyes) which are located to minimise stresses induced during lifting. All parts which are shop painted need to be handled carefully to avoid damaging the coating.

Latticed girders are made up of long, basically slender members, and may therefore be subject to severe distortion due to welding unless care is taken during the fabrication process.

It is essential that the design engineer notes that:

i. bulk orders of minimum size variation are cheaper than small orders of many different sizes.ii. the number of pieces to be handled should be kept to a minimum.iii. weld distortion and tolerances should be allowed for.iv. automated fabrication is generally cheaper.v. careful design can minimise transportation costs.vi. specifications need to be realistic to reduce costs.vii. good quality control is essential.

5. TRANSPORTATION

In each country there are specific lengths and widths of structures that may be transported without any problems, e.g. widths up to approximately 3 m, lengths up to 15m. For larger dimensions a police notification or special permission is required.

It should be noted that the various police authorities specify different periods when abnormal loads are allowed to move through their districts. If neighbouring "times" are significantly out of phase and general traffic hold-ups cause disruption to the movement of abnormal loads, it is possible for loads to be delayed by up to 24 hours. If one or more cranes and associated erection staff are unable to work because of these enforced delays, the additional costs can be very significant. Some towns and cities place length restrictions on materials which can be moved by road.

Girders can be fabricated and despatched lying flat. The overall height allowed for the load is dependent upon the route travelled and the clear height of any bridges


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likely to be encountered. Rail transport can accommodate long pieces, but width and height are more restricted.

To limit the length of units being transported, trusses may be divided into welded parts (2, 3 or more parts) which may be bolted together on site. The complete rafter can be then craned into position.

For export where shipment is involved, pieces up to the same dimensions as for road transport may be accommodated. It should be appreciated, however, that shipping charges are often based on volume rather than weight. There are often relatively severe restrictions on the length of a piece that can be carried in the hold of a ship. The ship's engineer may refuse to carry steelwork as deck cargo. It may be found more economical to despatch the steel in pieces for subsequent assembly on site.

6. ERECTION

In considering the erection of a framework, the designer seeks an economic but safe process. The cost of erection can be a significant proportion of the cost of a steelwork contract. It is often useful for a designer with little or no experience of steel erection to discuss possible solutions with a contractor. The latter will know how to build and avoid the possibility of collapse and how to satisfy the insurer. Potentially steelwork erection is hazardous and good control is required to ensure safety of the erectors.

Latticed girders can conveniently be assembled on the ground and lifted into place. However, since cranes are likely to be used, the effect of dynamic lifting loads or stress reversals should not be ignored. All steel structures are likely to require temporary bracing, which may be part of the permanent system. The temporary systems need to be carefully designed. The following points summarise the process:

a. Structural steelwork erection is an operation requiring meticulous planning from conception to completion.

b. The operation involves many disciplines and requires co-operation and communication between all those involved.

c. It is an operation which is dependent upon the personal competencies of all those involved to ensure the contract is completed without accident, on time and within the budget.


• At the most basic level single-storey structures have to provide shade and shelter for designated activity in the building.

• Steel provides the means to obtain economical buildings with large column-free spaces. The structural systems are discussed.

• The structural system is clad to resist the weather. The cladding is supported on secondary cold-formed sections which, in turn are supported on the main frame.


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• The span range is from 6m to 100m. To cover this range, structural systems are available ranging from simple beams and columns through portal frames to lattice trusses.

• Lateral stability can be achieved either by bracing systems or moment resisting joints in the frames.

• The proportions of costs for a simple shed are approximately: 50% cladding, 10% rails, 30% main frame 10% foundations.

8. REFERENCES

[1] Davis, J. M. and Raven, G. K., 'Design of Cold Formed Steel Purlins', IABSE Thin Walled Metal Structures in Buildings Colloquium, Stockholm 1986.

[2] Dowling, P. J. et al, 'A Development in the Automated Design and Fabrication of Portal Framed Industrial Buildings', Institution of Structural Engineers, London, October 1982.

[3] Horridge, J. F. and Morris, L. J., 'Comparative Costs of Single Storey Steel-Framed Structures', Institution of Structural Engineers, London, July 1986.

9. WIDER READING

[1] Ballio, G. and Mazzolani, F. M., 'Theory and Design of Steel Structures', Chapman and Hall, 1983.

[2] Eurocode 3: "Design of Steel Structures": ENV 1993-1-1: Part 1, General rules and rules for buildings, CEN 1992.

[3] Dowling, P. J., Knowles, P. R., and Owen, S. G. W., "Structural Steel Design", Butterworths, 1988.

[4] Steel Designers' Manual, fifth edition. The Steel Construction Institute, 1992.

[5] Eurocode 8: "Structures in Seismic Regions - Design", CEN (in preparation).



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Workgroup Contents

Lecture 14.1.2A : Single Storey Buildings: Envelope and Secondary Structure

Top

1. INTRODUCTION

2. CLADDING SYSTEMS

2.1 Roof Cladding

2.2 Wall Cladding

3. RESISTANCE OF CLADDING TO LOADS

4. SHAPES OF PURLINS AND RAILS

4.1 Cold-Formed Shapes

4.2 Hot-Rolled Shapes

5. RESISTANCE OF PURLINS AND RAILS TO LOADS

6. MAIN FRAME BRACING


8. REFERENCES


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ESDEP WG 14

STRUCTURAL SYSTEMS: BUILDINGS

Lecture 14.1.2: Single Storey Buildings: Envelope and Secondary Structure

OBJECTIVE/SCOPE

To describe further the functions and characteristics of the cladding and the elements of the secondary structure in single-storey buildings and to give guidance of purlin/wind designs.

PREREQUISITES

None.

RELATED LECTURES

Lecture 1B.5.1: Introduction to Design of Simple Industrial Buildings

Lectures 9: Thin-Walled Construction

Lecture 14.2: Analysis of Portal Frames: Introduction and Elastic Analysis

Lecture 14.3: Analysis of Portal Frames: Plastic Analysis

Lecture 14.4: Crane Runway Girders

SUMMARY

The functions and characteristics of the elements of the envelope and secondary structure of single storey buildings are described. The derivation of the load-carrying resistance of cladding using manufacturers' tables is presented and the design of purlins using manufacturers information is outlined.

Finally the requirements for main frame bracing are discussed.

1. INTRODUCTION

Lecture 14.1.1 provided a brief outline of the functions of the various elements of single-storey buildings. Design methods for frames of the various configurations are presented in other lectures and are also described in conventional text books. The derivation of design and selection of commercially available cladding, purlin and rail systems are not generally covered elsewhere.


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The lecture reviews the available systems and selection criteria. It concludes with a description of bracing systems used in single-storey buildings.

2. CLADDING SYSTEMS

Steel-based cladding sheets are formed from a substrate with layers of galvanising, primer and colour coating as indicated in Figure 1. For the weather face the coating will normally be polyvinyl chloride (PVC), polyvinyl fluoride (PVF2) or, where price is a constraint, the less durable acrylic coatings. PVC and PVF2 can be expected to have a life to first maintenance of 10 to 25 years depending on environmental conditions. Light colours should be used on roofs to minimise heat absorption and thermal movement. PVC should not be used in latitudes less than 49° [1].

There are four main categories of cladding system:

• single skin trapezoidal (Figure 2a)• double skin trapezoidal (Figure 3)• standing seam/secret fix (Figure 4)• composite panels (Figure 2b).


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Where double skin systems are used the liner sheet, normally as thin as 0,4mm, has a similar coating build-up but with a light coloured polyester paint to the inner face. In addition to providing weather protection the cladding provides insulation to the building. The thickness varies according to the insulation required with typical values of 0,45 w/m2° C being obtained from 80mm of fibreglass or mineral wool. The equivalent in composite panels would normally be obtained from 50mm thickness. Manufacturer's literature should be considered for particular cases.

2.1 Roof Cladding

The characteristics of the various roof systems are:

Single Skin Trapezoidal Roofing

This is the most basic form of cladding construction. The main problem is to prevent condensation since it is difficult to exclude damp air from the underside of the sheeting. The internal appearance is utilitarian since the insulation usually takes the form of unrolled thermal quilting supported on wire mesh or rigid boards supported on T Bars.


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Double Trapezoidal Shell Roof Construction

This is the most common form of cladding both for walls and roofs, with pitches down to approximately 5°. It consists of a steel liner sheet fastened to the purlins or rails with an outer weather sheet held apart by Zed spacers. The gap created contains insulation normally of fibreglass or mineral fibre. Sealing of the liner skin or addition of a vapour barrier and breather membrane can be employed to improve performance in situations where there is a higher condensation risk. Manufacturers normally supply a co-ordinated range of accessories and rooflights to match their particular profiles.

A typical construction is shown in Figure 3.

Standing Seam and Concealed Fix Roofs

As steel has replaced asbestos cement in sheeting, lower roof slopes have become possible and the appearance of buildings has greatly improved, both in form and colour treatment.

It is feasible to disguise the sloping roofs and provide the rectangular appearance recently favoured by planners, engineers and architects who have become increasingly involved in this type of building. The problems associated with drifted snow and internal gutters, together with the wasted heated in the space in a sloping roof encouraged the development of systems which remain weathertight at slopes down to 1°. These developments have been achieved by minimising laps and through fasteners. The current range of standing seam and concealed fastener systems are provided in long lengths, up to 32m with special transport arrangements, and use of clips to hold the sheeting down to the purlins. Typical construction is shown in Figure 4.

The outer sheeting is used to provide the weather skin in both single and double construction, as previously described.

Composite or Sandwich Panels

This is the most recently developed form of cladding and consists of panels where the insulating foam is integral with the two metal skins [2]. The foam, which during manufacture is pumped into the space between the skins, expands to totally fill the void and adheres to both liner and outer sheet (Figure 2b). This composite action gives robust stiff panels, with the further benefit of rapid erection since the whole skin is fastened in one operation.

Composite panels are available with traditional type trapezoidal outer skins and through fasteners, while more recent developments include standing seam variations allowing slopes down to 1°.

2.2 Wall Cladding

The systems used for walls are similar in construction to those for roofing. Since the sheets will normally be vertical the weatherproofing requirements are less rigorous.


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Another important difference compared to roofs is the lower angle of incidence of the sun allowing the full range of colours to be used without excessive surface temperatures, so giving the architect the widest possible scope for creative use of colour.

Given appropriate attention to joint detailing, wall cladding can be fixed horizontally, diagonally or in combinations.

The range of construction includes, as for roofs, single skin, double skin and composite systems, with both conventional and secret fastenings. Appearance is a major consideration in the selection of the particular type to be used.

All reputable manufacturers supply brochures giving details of the systems offered. General advice can be obtained from literature.

3. RESISTANCE OF CLADDING TO LOADS

Non-composite Systems

Since the sheets are rolled formed, the designer has to select the profiles from the various manufacturers pre-determined shapes. The sheets must be strong enough to resist the various loads which will be applied in construction and during service without damage or excessive deflection. For simple profiles, calculation methods are available in some national codes and European recommendations. Most manufacturers carry out full scale tests to determine the strength of their various profiles.

The test regimes for steel sheeting are designed to take account of the various limiting criteria. The criteria relate to shear of the webs combined with bending at internal supports for shorter spans and mid-span bending for longer, simple spans. Sheets are therefore tested with jacking loads and spreader beams, air bags or vacuum boxes with spans representative of the shortest and longest support spans anticipated in practice. The maximum allowable shears and moments are derived together with deflection behaviour and load tables for service conditions drawn up for pressure and suction conditions.

One important facet of a roof sheet is its ability to withstand local point loads both to sustain personnel walking on it during construction and also in service for maintenance purposes. It is this aspect which governs the minimum thickness acceptable for a roof sheet. This thickness is between 0,6 and 0,7mm. Current approval regimes include a point load test. Sheeting which passes this test will be suitably robust for construction loads but care needs to be taken with walking on PVF2 and painted finishes.

Wall cladding is often 0,5mm thick. To allow selection of the appropriate profile and thickness the majority of profilers (manufacturers) publish catalogues containing suggested fixing and sealing details together with allowable loads for the range of span conditions for both pressure and suction actions.


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In addition to resisting externally applied loads, conventional cladding with screw fasteners can provide lateral restraint to the purlins and side rails supporting it. In this application care should be taken in the specification of the fasteners concerning prevention of corrosion around the connections. Standing seam or concealed fastener systems have clips which hold the sheets down but allow expansion and contraction of the sheets and so provide a lower restraint value to the rails. Where these systems are used it is necessary to provide supplementary restraints to the purlins. At present there is no generally accepted guidance on the amount of restraint provided by these newer forms of cladding. Advice on the necessary inclusion of additional restraint in the form of sag bars is available from rail manufacturers relating to their particular products.

Where a metal liner tray is used in conjunction with a cladding system fixed by clips, adequate rail restraint is normally provided if the tray is fastened in the conventional manner.

Composite Systems

The use of foam filled panels has become more common over the past few years. They are more complicated to evaluate in design since the properties of the foam and its adhesion to the two metal skins are fundamental to the performance of the panels. In addition to the normal applied loads, the inherent insulating qualities of the panels leads to significant temperature gradients which have to be taken into account in the panel design.

Calculation methods for analysis are available but the shapes of practical panels are outside of their current scope. It is normal therefore for extensive testing to be carried out by manufacturers in order to obtain type approval from the appropriate national authorities. The tests, in addition to normal load tests, include thermal cycling on full scale panels and foam evaluation to ensure the essential adhesion to the skins is obtained. Quality assurance regimes are an essential part of the manufacturing process. The results of the tests are collated and simplified to produce load carrying tables.

4. SHAPES OF PURLINS AND RAILS

Although some long-span cladding systems are available which will span up to 6m, most portal frame structures are designed with purlins and rails supporting the cladding and spanning between the main frames.

The spans between frames are between 4,5 and 10m with 6 to 7,5m being most popular. Roof decks of larger span are used primarily in flat roof systems and are supported directly on the trusses.

The purlins can be designed as continuous beams supported by three or more portal frames. Because of the difference in the value of the support reactions, it is necessary to stagger the joints to obtain equal loads on the main frames.


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4.1 Cold-Formed Shapes

The purlins and rails are commonly supplied by specialist manufacturers who deliver pre-cut and punched cold-rolled items together with the necessary sag bars, cleats or rafter stays. Material economy is vitally important to the manufacturers whose output is often in excess of 80km/week. They have therefore developed and refined by testing a variety of shapes. The more common ones are Zeds, modified Zeds and Sigma shapes illustrated in Figure 7.

Depending on the slope, anti-sag bars may be necessary to provide one or two intermediate supports in the direction of the weak axis of the beam (Figure 8). Generally, the anti-sag bars are connected using diagonal ties to the portal frames to avoid an increase of the load in the purlins at the top.

Zeds

The Zed section was the first shape to be introduced. It is material efficient but its major disadvantage is that the principal axes are inclined to the web and so out-of-plane forces are generated. When asbestos covered roofs with slopes of the order of 10° were normal these forces were advantageous and opposed to the down slope forces.

Modified Zeds


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As lower roof pitches have been introduced, modified Zeds have been developed with the inclination of the principal axis considerably reduced, so enhancing overall performance. Stiffening has also been introduced, improving material efficiency.

These more complicated shapes have to be produced by rolling rather than by press braking.

Sigma Shape

The first shapes to be employed were the simple Zed and Channel since they could be formed by press brakes. As described above the Zed shape has been modified to overcome its major disadvantage. The Channel has not achieved much use, since, although its principal axes are parallel to the major elements, the shear centre lies well outside of the section. Undue twisting under load results which can be reduced by shaping the web and creating a sigma shape such that the shear centre is approximately coincident with the load application line. One manufacturer now produces an economical second generation product of this configuration using rolling techniques.

4.2 Hot-Rolled Shapes

Classical I-beams such as IPE I CDN or HE can also be used as purlins. I-beams and channel shapes can be used as rails. These shapes are less sensitive than the previous ones to the effect of local instabilities and there is preferences to use them in some countries. However, cold-formed sections are generally the most economical solution.

5. RESISTANCE OF PURLINS AND RAILS TO LOADS

Cold-formed sections manufactured from thin gauge material are particularly prone to twisting and buckling due to factors which are directly related to the section's shape. The torsional constant of all thin gauge sections is low due to it being a function of the cube of the thickness; in the case of lipped channels the shear centre is eccentric to the point of application of load thus inducing a twist on the section; in the case of zeds the principal axes are inclined to the plane of the web thus inducing bi-axial bending effects. Clearly the above secondary effects, induced by the primary load application, affect the load-carrying resistance of the section.

When used in service the support system is subject to downward loading due to dead and live loads arising from the weight of the cladding, snow, services, etc., and uplift if the design wind pressure is greater than the dead load of the system. Therefore, for a typical double span system as shown in Figure 9, most of the compression flange is directly restrained laterally and against rotation by the cladding for downward loading, but it is not so restrained in the case of load reversal.


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In supporting the external fabric of the building, the purlins and side rails gain some degree of restraint against twisting and rotation from the cladding and the method of its fastening to the supporting members. In addition, the connection of the support members to the main frame also has a significant effect on the load-carrying resistance of the section. Economical design, therefore, must take account of the above effects.

Several approaches are used for the design of purlin and rail systems.

a. Design by calculation based on an elastic analysis as detailed in the relevant codes of practice. This approach neglects any beneficial effect of cladding restraint for the uplift case and in the compression zone adjacent to the central support in double span arrangements. It is normally confined to "one-off" situations where material savings do not justify more rigorous solutions.

b. Design by calculation based on a rational analysis which accounts for the stabilising influence of the cladding, plasticity in the purlin as the ultimate load is approached and the behaviour of the cleat at the internal support. The effects, however, are difficult to quantify. Although understanding of the restraint of purlins by cladding is improving and methods for including the cladding/purlin interaction are available, the methods are necessarily conservative. They are included in Eurocode 3: Part 1.3 [4] but are likely to be used in the short term only by small to medium volume users where potential material savings do not justify a major test programme.

In some countries, despite the almost traditional nature of these forms of construction, it is not permitted to take account of cladding restraint to the purlins in the section design if the cladding is to be supplied and fixed by differing suppliers. This restriction is due more to the apportionment of responsibility should there be failures than due to lack of technical knowledge. This situation is unusual since a great deal of construction depends on the interaction of elements supplied and fixed by different contractors.

c. Design on the basis of full-scale testing


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Manufacturers differ in the design methods they use. The methods are based on the observed behaviour of the system under test.

For volume production, design by testing is the approach which is normally used. Although this approach is expensive, maximum economy of material can be achieved and the cost of the testing can be spread over several years of production.

Design by testing involves the "fine-tuning" of theoretical expressions for the collapse load of the system.

For example, although the sections involved are inevitably slender, the collapse mechanism which occurs with a well developed two-span system is essentially as represented in Figure 10. The published paper [3] on one manufacturer's system shows that the collapse load will be:

Wc = f (M1, M2, x, L)

with

x = f (M1, M2, L)

and

θp = f (Wc, M1, L)


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The performance of a two-span system is considerably enhanced if some redistribution of bending moment from the internal support is taken into account. The moment-rotation characteristic at the support depends very much on the cleat detail and the section shape. The characteristics of the central support can be found by testing a simply supported beam subject to a central point load applied through a cleat so as to simulate the behaviour of the central support of a double span system.

From this test, the load-deflection characteristics can be plotted well beyond the deflection at which first yield occurs. A lower bound empirical expression can then be found for the support moment, M1, based on an upper limit of rotational capacity. A similar expression can be found for M2, the internal span moment, again on the basis of a test on a simply supported beam subject to a uniformly distributed load, applied by the use of a vacuum rig, or perhaps sand bags.

The design expressions can then be confirmed by the execution of numerous full-scale tests.

The results of the full-scale tests are then condensed into easy to use load span tables which are detailed in the purlin manufacturers' design and detail literature.

The tabular format is typical of that contained in purlin manufacturers' technical literature. The table is generally prefaced by explanatory notes regarding fixing condition and lateral restraint requirements, the latter being particularly relevant where load reversal occurs. Conditions which arise in practice, and which are not covered in the technical literature are best dealt with by the manufacturer's Technical Service Department, which should be consulted for all non-standard cases. Anti-sag bars are used on longer spans to assist erection and improve performance under wind suction.

Side rail design is essentially identical to that for purlins, and load resistances are again arrived at via test procedures.

The practical construction problem of levelling side rails in the field, to remove self weight deflection about the weak axis of the section, is overcome by the use of a tensioned wire system incorporating the use of tube struts, typically at mid-span for spans of 6 - 7m, and third-points of the span for spans of 7 - 8m and above. Typical methods are shown in Figure 12.


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6. MAIN FRAME BRACING

Returning to the requirements for the main frame which were discussed in Lecture 14.1.1, most frame configurations for larger spans have moment resisting joints at the column/roof member connections. In addition to assisting with deflection control and reducing member sizes, this arrangement provides inherent resistance to lateral in-plane loads such as those from side winds and crane movements.

Bracing, both horizontal and vertical, must be provided to transfer to the foundations the horizontal loads due to wind possibly earthquake and out-of-plane loads.

It is possible to use the cladding and wall panels instead of braces for this purpose.In that case stressed skin design should be used (Lecture 9.5).

When masonry is used as all or part of the vertical cladding, it is feasible to use that element as part of the bracing system.

The bracing can be single diagonals or cross members. If the former system is adopted, the members are designed to support compressive and tensile loads. When cross members are used only the members in tension are assumed to be effective, those in compression being designed to satisfy the slenderness criteria.

Bracing may be located either at mid-length of the building (Figures 13a, 14a, and 14c) or at its ends (Figures 13b, and 14b). Bracing at the ends helps for erection purposes, since it provides a stable structure at one end of the building when the


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erection starts. Its disadvantage is that it prohibits the free movement of the building due to temperature so that stresses in the members, sometimes of considerable amount, may result. By putting the braces at the mid-length this disadvantage disappears since the building is able to expand freely. However additional temporary braces should be provided during the erection stage to stabilise the first part of the building. The horizontal forces have to "travel" from their point of application in the gable to the brace thus causing compression in the purlins.


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• A variety of cladding systems is available manufactured from pre-coated steel.

• These systems are normally supported by light gauge purlins and rails but hot-rolled profiles are also used.

• The theoretical design procedures for these systems are improving although large volume manufacturers still carry out full-scale testing as a basis for design in order to achieve material economy.

• Many single-storey frame arrangements have inherent in-plane resistance to side loads but bracing systems have to be provided to transfer longitudinal loads to the foundations.

8. REFERENCES

[1] Colourcoat in Building, British Steel Strip Products, Newport, Wales.

[2] ECCS Recommendations for Sandwich Panels: Part 1 Design, Part 2 Good Practice.

[3] Davies, J. M. and Raven G. K., 'Design of Cold Formed Steel Purlins', IABSE "Thin Walled Metal Structures in Buildings" Colloquium, Stockholm 1986.

[4] Eurocode 3: "Design of Steel Structures" Part 1.3, Cold Formed Thin Gauge Members and Sheeting, CEN (in preparation).

PANELS

Wind loads in kN/m2 WIND

Span 'L' (in metres)Deflection limit

Span condition

Thickness of profile

(mm)1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0

0,5 3,00 2,30 1,66 1,24 0,94 0,73 0,58 0,46

0,55 3,47 2,60 1,88 1,40 1,07 0,83 0,66 0,52

0,6 3,96 2,91 2,11 1,57 1,20 0,93 0,73 0,59

0,7 4,98 3,61 2,61 1,95 1,49 1,16 0,91 0,73

0,8 6,02 4,21 3,05 2,27 1,73 1,35 1,06 0,85

0,5 2,70 2,19 1,81 1,52 1,30 1,12 0,97 0,85

0,55 2,94 2,41 2,01 1,71 1,46 1,27 1,11 0,97

L/90

0,6 3,61 2,93 2,43 2,04 1,74 1,50 1,30 1,14


370

0,7 4,55 3,68 3,05 2,56 2,17 1,87 1,62 1,42

0,8 5,14 4,20 3,49 2,95 2,51 2,17 1,90 1,66

0,5 3,28 2,67 2,22 1,87 1,60 1,39 1,14 0,91

0,55 3,54 2,92 2,45 2,09 1,80 1,56 1,29 1,04

0,6 4,41 3,58 2,97 2,51 2,14 1,81 1,44 1,16

0,7 5,56 4,52 3,74 3,15 2,68 2,25 1,79 1,44

0,8 6,24 5,11 4,26 3,61 3,08 2,62 2,08 1,68

0,5 1,96 1,36 0,98 0,73 0,55 0,42 0,33 0,26

0,55 2,22 1,54 1,11 0,82 0,62 0,48 0,37 0,29

0,6 2,48 1,73 1,24 0,92 0,70 0,54 0,42 0,33

0,7 3,07 2,14 1,54 1,14 0,87 0,67 0,52 0,41

0,8 3,58 2,49 1,80 1,33 1,01 0,78 0,61 0,48

0,5 2,70 2,18 1,81 1,52 1,30 1,08 0,86 0,69

0,55 2,94 2,41 2,01 1,71 1,46 1,22 0,97 0,78

0,6 3,61 2,94 2,42 2,04 1,74 1,37 1,08 0,87

0,7 4,55 3,68 3,05 2,56 2,18 1,70 1,35 1,08

0,8 5,14 4,20 3,49 2,95 2,51 1,98 1,57 1,26

0,5 3,28 2,62 1,90 1,42 1,08 0,84 0,66 0,53

0,55 3,54 2,92 2,15 1,60 1,22 0,95 0,75 0,60

0,6 4,41 3,32 2,40 1,79 1,37 1,06 0,84 0,67

0,7 5,56 4,11 2,98 2,22 1,70 1,32 1,05 0,84

L/150

0,8 6,24 4,79 3,47 2,59 1,98 1,54 1,22 0,98

Figures shown in bolder type are limited by deflection. All other loads are limited by stress.


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ROOF PANELS

Maximum loads in kN/m2 deflection limit L/100

FACING DETAILS

THICKNESS (mm)

SPAN 'L'(m)PANEL THICKNESS (mm)

SPAN CONDITION

MATERIAL

Outer Inner 1,6 1,8 2,0 2,5 3,0

0,5 0,4 + 2,54

- 3,02

2,16

2,59

1,85

2,25

1,28

1,63

0,76

1,22

STEEL

0,6 0,4 + 2,80

- 3,30

2,39

2,85

2,06

2,48

1,42

1,82

0,82

1,36

ALUMINIUM 0,7 0,5 + 2,32

- 2,70

1,66

2,26

1,21

1,74

-

-

-

-

0,5 0,4 + 2,54

-3,02

2,16

2,56

1,85

2,21

1,30

1,63

0,94

1,22

STEEL

0,6 0,4 + 2,80

- 3,30

2,39

2,85

2,06

2,48

1,46

1,82

1,06

1,36

ALUMINIUM 0,7 0,5 + 2,34

- 2,64

1,93

2,25

1,62

1,91

1,08

1,32

0,76

0,96

0,5 0,4 + 2,54

- 3,02

2,16

2,59

1,85

2,25

1,30

1,63

0,94

1,22

37

STEEL

0,6 0,4 + 2,80

- 3,30

2,39

2,85

2,06

2,48

1,46

1,82

1,06

1,36


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ALUMINIUM 0,7 0,5 + 2,34

- 2,70

1,93

2,26

1,62

1,91

1,08

1,32

0,76

0,96

0,5 0,4 + 3,91

- 4,55

3,40

3,97

2,98

3,52

2,17

2,63

1,59

1,99

STEEL

0,6 0,4 + 4,01

- 4,65

3,48

4,05

3,07

3,58

2,38

2,79

1,69

2,23

ALUMINIUM 0,7 0,5 + 3,85

- 4,33

3,23

3,75

2,51

3,20

1,38

2,00

0,78

1,20

0,5 0,4 + 3,20

- 3,37

2,68

2,86

2,29

2,49

1,65

1,86

1,24

1,47

STEEL

0,6 0,4 + 3,70

- 3,88

3,10

3,30

2,65

2,86

1,90

2,13

1,44

1,68

ALUMINIUM 0,7 0,5 + 2,91

- 3,00

2,44

2,56

2,08

2,23

1,48

1,68

1,11

1,34

0,5 0,4 + 3,62

- 3,90

3,07

3,35

2,64

2,93

1,93

2,23

1,47

1,78

STEEL

0,6 0,4 + 4,01

- 4,47

3,48

3,84

3,04

3,35

2,22

2,54

1,70

2,02

60

ALUMINIUM 0,7 0,5 + 3,42

- 3,68

2,89

3,17

2,49

2,78

1,81

2,11

1,36

1,68

WALL PANELS

Maximum loads in kN/m2 deflection limit L/100 L/100

FACING DETAILS

THICKNESS (mm)

SPAN 'L'(m)PANEL THICKNESS (mm)

SPAN CONDITION

MATERIAL

Outer Inner 1,5 2,0 2,5 3,0 3,5

STEEL 0,5 0,4 + 2,78

- 2,78

1,69

1,97

0,96

1,06

-

-

-

-

37

STEEL 0,5 0,4 + 2,78

- 2,78

2,09

2,09

1,67

1,67

1,26

1,39

0,90

1,08


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STEEL 0,5 0,4 + 2,78

- 2,78

2,09

2,09

1,66

1,67

1,11

1,38

0,78

0,94

STEEL 0,5 0,4 + 3,40

-3,40

2,55

2,55

1,81

2,04

1,18

1,39

0,79

0,91

STEEL 0,5 0,4 + 3,40

- 3,40

2,55

2,55

2,04

2,04

1,70

1,70

1,33

1,33

60

STEEL 0,5 0,4 + 3,40

- 3,40

2,55

2,55

2,04

2,04

1,70

1,70

1,33

1,33

Notes to Load Tables

1. + reload indicate pressure or snow loading - ve load indicates suction loading.2. Indicates values too low for normal applications.3. The permissible loads take account of dead and imposed loading, including their long term effects, and differential

thermal loading.4. Values for loads at intermediate spans can be obtained by linear interpolation.5. The concealed fixing system can be used for all + ve loading conditions. Under suction loading the clip capacity is

limited to 4kN wall and 6kN roof. Where the clip capacity is exceeded, additional through fasteners or reduced purlin rail spacings may be required. If in doubt contact WBC Technical Department. For concealed fix aluminium panels contact WBC in every case.

6. The roof loadings are based on the standard colour range. For variations to this range consult the Technical Department.

7. When designing roofs with pitches between 1

° and 4° a deflection limit of span/200 should be used to prevent ponding.

8. CW 1200 values are for all four wall panels.

ULTIMATE LOAD TABLES

INTRODUCTION

The following load tables have been prepared to assist the designer in specifying cold formed sections.

The tabulated values are only valid for use with the fixing details and recommendations proposed by the manufacturer.

This information has been prepared as a supplement to the main handbook for ease of reference in the design office.

USE OF TABLES

1. The load tables show the ultimate load for double span sections in terms of a UDL per span.


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2. Section self weight has not been subtracted in the loads shown.3. Loadings have also been tabulated that will produce the noted deflection ratio.4. Loads shown assume lateral restraint to the top flange of the section and that the beams

are fixed in accordance with manufacturers instructions.5. Ultimate reversal loads may be obtained by multiplying the loads shown by a factor of

0,8.6. Interpolation of the ultimate loads shown is permissible on a linear basis.

Note: These values are typical and should not be used in design.

LOAD FACTORS

The following load tables have been prepared to assist the designer in specifying cold formed sections.

The tabulated values are only valid for use with the fixing details and recommendations proposed by the manufacturer.

This information has been prepared as a supplement to the main handbook for ease of reference in the design office.

USE OF TABLES

1. The load tables show the ultimate load for double span sections in terms of a UDL per span.

2. Section self weight has not been subtracted in the loads shown.3. Loadings have also been tabulated that will produce the noted deflection ratio.4. Loads shown assume lateral restraint to the top flange of the section and that the beams

are fixed in accordance with manufacturers instructions.5. Ultimate reversal loads may be obtained by multiplying the loads shown by a factor of

0,8.6. Interpolation of the ultimate loads shown is permissible on a linear basis.

Note: These values are typical and should not be used in design.

LOAD FACTORS

Loading Factor

Dead load 1,4

Dead load restraining uplift or overturning 1,0

Dead load acting with wind and imposed loads combined 1,2

Imposed load 1,6

Imposed load acting with wind load 1,2

Wind load 1,4

Wind load acting with imposed load 1,2

Forces due to temperature 1,2


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PURLINS

Span

(m)

Section UDL Deflection

L/200

B120/150 11,89 7,77

A140/155 15,35 13,67

A140/165 17,16 14,56

*A140/180 19,85 15,89

A170/160 20,40 20,40

4,5

A170/170 22,70 22,70


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*A170/180 24,97 24,97

B120/150 10,79 6,29

A140/155 13,99 11,07

A140/165 15,62 11,79

*A140/180 18,04 12,87

A170/160 18,63 18,02

A170/170 20,71 19,16

5,0

*A170/180 22,76 20,30

A140/155 12,84 9,15

A140/165 14,33 9,75

*A140/180 16,54 10,64

A170/160 17,14 14,89

A170/170 19,03 15,84

*A170/180 20,90 16,78

A200/160 21,27 21,27

A200/180 23,88 23,88

5,5

*A200/200 28,10 27,43

A140/155 11,87 7,69

A140/165 13,23 8,19

*A140/180 15,26 8,94

A170/160 15,87 12,51

A170/170 17,60 13,30

*A170/180 19,32 14,10

A200/160 19,81 18,38

A200/180 22,11 20,72

6,0

*A200/200 25,98 23,05


377

A230/180 26,44 28,92

A230/200 31,11 32,18

*A230/240 40,14 38,68

A170/160 14,77 10,66

A170/170 16,37 11,34

*A170/180 17,95 12,01

A200/160 18,43 15,66

A200/180 20,58 17,65

6,5

*A200/200 24,15 19,64

Figure 11. Ultimate load tables for purlins


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