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Steel buildings have become increasingly popular in recent years due to their durability, versatility, and cost-effectiveness. In , structural steel framing was fabricated and erected for more than 18,000 buildings, bridges, and industrial facilities. (Mordor)
After a 2.6% decline in , US steel use bounced back by 1.3% in and is expected to grow again by 2.5% through .
So, whether you&#;re planning to construct a warehouse, garage, or even a residential property, this step-by-step guide will provide you with all the information you need to successfully build a steel building from start to finish.
Table of Contents:
Before diving into the construction process, it&#;s essential to have a solid understanding of the basics of steel buildings. These structures are made primarily of steel, and offer numerous advantages over traditional building materials such as wood or concrete.
Steel is a versatile and durable material that has been increasingly popular in construction due to its strength and sustainability. They are known for their structural integrity and ability to withstand harsh environmental conditions.
The use of steel in construction provides a high strength-to-weight ratio, making it an ideal choice for facilities that require large open spaces and minimal support columns.
Additionally, steel facilities are highly customizable, allowing for unique architectural designs and efficient use of space.
They come in a variety of types, each designed to suit specific needs and requirements. The most common types include:
There are several notable benefits to choosing steel as the primary material for your building:
Furthermore, steel buildings are known for their energy efficiency, as steel is a good conductor of heat, allowing for better temperature regulation within the structure. This can lead to lower energy costs over time and a more comfortable indoor environment for occupants.
The versatility of steel also allows for faster construction times, reducing labor costs and overall project timelines.
Check out: Exploring The Versatility Of Prefabricated Steel Buildings For Investors
Once you have a clear understanding of steel buildings and their benefits, it&#;s time to gather the necessary materials and tools for the construction process. Planning and ensuring you have all the required items will streamline the building process and help you avoid unnecessary delays.
Before diving into the construction of a steel building, it&#;s essential to consider the foundation requirements. Depending on the size and design of the structure, you may need to gather materials such as concrete, rebar, and formwork to create a stable and durable foundation.
Properly preparing the foundation is crucial for the structural integrity and longevity.
To ensure a smooth building process, it&#;s crucial to have all the necessary materials on hand. Some essential materials include:
Additionally, considering factors such as weather resistance and energy efficiency, selecting the right type of insulation material is key. Options range from traditional fiberglass insulation to newer, more advanced materials like spray foam insulation, offering improved thermal performance and moisture control.
Equipping yourself with the right tools will make the building process more efficient and effective. Here are some must-have tools:
When it comes to welding equipment, having a reliable welding machine suitable for working with steel is essential. Whether it&#;s stick welding for structural connections or MIG welding for attaching metal panels, investing in quality welding equipment will ensure strong and durable bonds in your steel facility construction.
With the materials and tools ready, it&#;s time to prepare the construction site for building your steel structure.
Before diving into the construction process, it is essential to understand the significance of proper site preparation.
A well-prepared construction site sets the stage for a successful project, ensuring the structural integrity and longevity of your steel building.
Choosing the right location for your steel building is crucial for its long-term stability and functionality. Consider factors such as accessibility, drainage, and utility connections when evaluating potential sites.
Accessibility is key not only for construction purposes but also for the future use of the building. Adequate drainage is essential to prevent water accumulation, which can compromise the integrity of the structure over time.
Additionally, evaluating utility connections such as electricity, water, and sewage ensures that your steel building can efficiently meet its operational needs.
Prepare the ground by removing any obstacles, leveling the surface, and compacting the soil. This will provide a stable foundation for your steel building.
Obstacles such as rocks, debris, and vegetation must be cleared to create a smooth and even surface for construction. Properly leveling the ground not only aids in the structural stability of the building but also facilitates construction processes such as laying the foundation and erecting the steel framework.
Compacting the soil is crucial to prevent settling and shifting of the structure over time, ensuring a durable and secure foundation for your steel building.
Pro tip:
Successful ground preparation is essential for any construction project, and soil stabilization plays a key role in this process. When dealing with sandy soils, it&#;s common to use additives such as lime or cement to enhance their strength. Granular soils may necessitate mechanical compaction techniques.
The foundation is the backbone of any construction project, and building a strong foundation for your steel structure is essential. Before embarking on the construction of a steel building, it is crucial to understand the significance of a well-built foundation.
A solid foundation not only supports the weight of the structure but also ensures its longevity and stability over time.
When it comes to steel structures, the foundation plays a critical role in distributing the load of the building evenly to the ground below. This distribution of weight helps prevent settlement and ensures that the structure remains structurally sound for years to come.
A strong foundation provides stability and ensures that your steel building can withstand various loads and environmental conditions. In addition to supporting the structural integrity of the building, a well-designed foundation can also help mitigate potential issues such as settling, shifting, or structural failure.
Properly constructed foundations are especially crucial for steel buildings, as they are typically lightweight structures that rely on the foundation to anchor them securely to the ground.
Without a strong foundation, a steel building may be susceptible to movement or even collapse under certain conditions.
Pouring a concrete foundation involves several steps:
Each step in the process is crucial to ensuring the strength and durability of the foundation. Excavating the area and setting up formwork provide the necessary structure for the concrete to be poured into while placing reinforcement bars helps reinforce the concrete and prevent cracking.
Pouring and leveling the concrete must be done with precision to ensure a smooth and even foundation surface, and curing and protecting the concrete is essential for allowing it to reach its full strength and durability.
Now it&#;s time to begin assembling and erecting the steel frame of your building. This crucial step forms the skeleton of your structure, providing the support and framework for the entire building.
Before diving into the assembly process, it&#;s essential to understand the intricacies of steel frame construction. Steel frames offer durability, strength, and versatility, making them a popular choice for various construction projects, from warehouses to commercial facilities.
Prioritize safety during the frame erection process by wearing appropriate safety gear, following safety guidelines, and ensuring a safe working environment.
Remember, safety should always be the top priority on any construction site to prevent accidents and ensure a smooth building process.
Additionally, conducting a thorough safety briefing with all workers involved in the steel frame assembly can help address potential hazards and promote a culture of safety awareness.
Assembling the steel frame involves several steps that require precision and attention to detail to ensure a sturdy and reliable structure:
Each step in the assembly process plays a crucial role in ensuring the structural integrity and longevity of your building. Attention to detail and adherence to manufacturer guidelines are key to a successful construction project.
Building a steel structure demands meticulous planning, quality materials, and skilled execution. By following this comprehensive guide and seeking assistance from professionals when needed, you can embark on your construction project with confidence. Remember, safety is paramount throughout every stage of the process to create a secure and reliable building.
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When constructing new buildings, approximately 20% of the total cost is allocated to framing and trusses. Despite the common belief that it would be significantly more expensive, steel framing costs only about 5% more than wood trusses.
The installation of steel structures or metal buildings typically results in labor cost reductions of up to 50% compared to wood construction, thanks to the faster and easier installation process of metal trusses.
The most affordable foundation option is typically a floating slab, also known as a slab on grade. This type of foundation involves a simple concrete slab that is poured directly onto the ground.
The construction timeline depends on various factors such as the size, complexity, and location of the project. In general, simple projects can be completed from quote to installation/construction in as little as 8-10 weeks, and 16-18 weeks for more complex projects.
Generally, you can expect to pay between $6 and $10 per square foot to erect a steel building and approximately $110 to $150 per sq ft for the full construction cost (including materials, interior build-out, and construction) for &#;small&#; projects under 100,000 square feet. For 200,000 SF projects and up, cost per square foot can start to reduce significantly.
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The design process encompasses the architectural design, the development of the structural concept , the analysis of the steel structure and the verification of members. Steel solutions are lighter than their concrete equivalents, with the opportunity to provide more column-free flexible floor space, less foundations and a fast, safe construction programme.
For the designer, a steel solution means reliable materials, assured material and section properties, precise off-site manufacture and extensive support including software, design guides and easy to use resistance tables.
Design process
Main articles: Concept design, Steel material properties
The fundamental process of structural design commences with the preparation of a structural concept, which is itself based on an architectural design for the structure. For simple, common forms of structure, it will be possible to prepare a concept design directly from the architectural design - typical solutions are well understood.
For more complex structures, or innovative designs, best practice is to develop the structural concept in conjunction with the architectural scheme, so that an efficient, appropriate solution can be developed.
Once the concept design has been established, the structural design can be completed, involving determination of loads, frame analysis and member verification.
Steel design
Steel is ideally suited for design. Material properties are known and member properties are accurate, meaning that analysis is precise. Design rules are clear and mature, without undue conservatism, having been developed over many decades. There is a wealth of support resources, including software, to facilitate efficient design.
Concept design
Main articles: Concept design, Steel material properties, Multi-storey office buildings, The case for steel, Service integration
The choice and design of the primary structure is a fundament part of the concept design of buildings, and ideally should be integrated with the development of the architectural design. Meeting client, planning and Building Regulation requirements are paramount, but there will be a range of structural forms that meet these requirements, each with its own advantages. The merits of different structural forms should be reviewed against the requirements for the structure. Key considerations include:
Principal structural elements of a multi-storey building
Minimising embodied and operational carbon is an important driver in construction. Structural solutions to minimise carbon include (where appropriate):
The principal structural elements of a typical multi-storey building comprise floors, beams and columns. A wide variety of alternative forms and arrangements can be used in multi-storey steel framed structures to deliver the benefits of:
Efficient, low-carbon design
Main articles: Sustainability, Multi-storey office buildings, The case for steel
Efficient steelwork design is fundamental to reducing embodied carbon emissions of buildings. Before low-carbon products and materials are specified, the structural engineer should strive to design structures as efficiently as possible to reduce material use. The is the approach enshrined in the IStructE hierarchy of net zero design.
SCI has published SCI P449 which gives guidance to structural engineers to help them design steel structures more efficiently to reduce demand for steel without compromising safety and creativity and, by doing so, reduce embodied carbon emissions. The guidance will help to deliver Lever 1 in the BCSA decarbonisation roadmap.
The following summary presents the designer&#;s responsibility to prepare a design which is as efficient as possible:
Factors affecting choice of structural system
Main articles: Long-span beams, Floor systems, Service integration, Braced frames, Continuous frames, Simple connections, Moment resisting connections, Steel construction products, Composite construction, Facades and interfaces
Floor grids define the spacing of the columns in orthogonal directions, which are influenced by:
The British Council for Offices (BCO) Guide to Specification[1] provides extensive guidance on the preparation of scheme designs.
For naturally ventilated offices, a building width of 12 m to 15 m is typically used, which can be achieved by two spans of 6 m to 7.5 m, with a column placed adjacent to a central corridor. Natural lighting also plays a role in choice of the width of floor plate. In larger buildings, a long-span solution provides a considerable enhancement in flexibility of layout. For air conditioned offices, a clear span of 15 m to 18 m is often used.
Floor-to-floor height will be an important consideration at the concept design stage. The table below gives typical floor to floor heights for buildings of different use.
Typical floor-to-floor heights Prestige office 4 - 4.2 m Speculative office 3.6 - 4.0 m Renovation project 3.5 - 3.9 m
If planning restrictions limit overall building height, shallow floor solutions may be adopted, or solutions that involve integrating the services within the structural depth. Typical structural depths for different types of construction are given in the table below.
Stability systems
Typical bracing in a multi-storey frame
The structural system required for stability is primarily influenced by the building height. For buildings up to eight storeys height, the steel structure alone may be designed to provide stability, but for taller buildings, concrete or braced steel cores are more efficient structurally. The following structural systems may be considered for stability.
For buildings up to eight storeys high, braced steel frames are commonly used with bracing members generally located within a cavity in the facade, or around stairs or other serviced zones.
A steel braced frame has three key advantages:
For buildings up to four storeys high, continuous frames may be used in which the multiple beam to column connections provide bending resistance and stiffness to resist horizontal loads. This is generally only possible where the beams are relatively deep (400 mm to 500 mm) and where the column size is increased to resist the applied moments. The connections between members are likely to be more expensive than those in braced frames.
Concrete or steel cores
Concrete cores are the most practical system for buildings of up to 40 storeys high, with the concrete core generally constructed in advance of the steel framework. In this form of construction, the beams often span directly between the columns on the perimeter of the building and the concrete core. Special structural design considerations are required for:
Typical beam layout around a concrete core
A braced steel core
SCI-P416
Braced steel cores may be used as an economic alternative where speed of construction is critical. Such cores are installed with the rest of the steelwork package. An example of a braced steel core is shown in the figure above middle.
Guidance for the design of cast-in steel plates for connecting structural steel beams to concrete core walls is available in SCI-P416. This publication provides a model for the design of simple connections that transfer shear force due to permanent and variable loads and a non-coincident axial tie force resulting from an accidental load case. It points out additional issues which must be considered where coincident shear forces and axial forces are to be dealt with. A sample design of a simple connection for a 610 serial size UB is presented, and the design of punching shear reinforcement for the wall is included. The guide discusses the responsibilities of the building structural engineer and the steelwork contractor and suggests where the responsibilities are best divided. It also considers the impact of deviations between the theoretical positions of the parts of the connection and their as-erected positions.
Columns
Columns in multi-storey steel frames are generally H sections , predominantly carrying axial load. When the stability of the structure is provided by cores, or discreet vertical bracing, the beams are generally designed as simply supported. The generally accepted design model is that nominally pinned connections produce nominal moments in the column, calculated by assuming that the beam reaction is 100 mm from the face of the column.
For ease of construction, columns are usually erected in two, or sometimes three storey sections, i.e. approximately 8 m to 12 m in length. Column sections are joined with splices , typically 300 mm to 600 mm above the floor level.
S460 column sections are available, which should be considered for multi-storey buildings. The higher strength and more advantageous buckling curve for S460 sections mean that smaller, lighter sections may be selected compared to lower strength alternatives.
A wide range of floor solutions is available. Although steel solutions are appropriate for short spans (typically 6 m to 9 m), steel has an important advantage over other materials in that long-span solutions (between 12 m and 18 m) can be easily provided. This has the key advantage of column-free space, allowing future adaptability, and fewer foundations.
Floors spanning onto the steel beams will normally be either precast concrete units, or composite floors. The supporting beams may be below the floor, with the floor bearing on the top flange (often known as "downstand" beams), or the beams may share the same zone with the floor construction, to reduce the overall depth of the zone. The available construction zone is often the determining factor when choosing a floor solution.
Typical floor solutions Form of construction Typical solution Low rise, modest spans, no restriction on construction depth Downstand beams precast units or composite floors Modest spans (less than 9 m), restricted construction depth Integrated solutions &#; precast or composite floors Low rise, long span (e.g. 15 m) Downstand beams in the façade. Composite floors with secondary steel beams spanning 15 m Medium and high rise, modest spans, no restriction on construction depth Downstand beams, composite construction Medium and high rise, long spans (to 18 m) restricted construction depth Composite floors with cellular long span secondary steel beams
The span range of various structural options in both steel and concrete are shown in the table. Long-span steel options generally provide for service integration for spans of over 12 m. Cellular beams and composite trusses are more efficient for long-span secondary beams, whereas fabricated beams are often used for long-span primary beams.
Typical spans for various floor systems
Long-span beams have gained in popularity in the commercial building sector because they offer the following benefits in design and construction:
Foundations
In inner city and on difficult or brownfield sites, the time and cost of constructing the foundations has a major effect on the viability of a project. Although the weight of the frame is relatively small compared with the floors and walls, a steel frame can be significantly lighter than a comparable reinforced concrete frame. Further reductions in weight can be achieved by using light floor construction such as composite metal deck floors and lightweight concrete.
Difficult ground conditions may dictate the column grid. Long spans may be required to bridge obstructions in the ground. More generally, widely spaced columns reduce the number of foundations, simplifying the substructure construction and reducing cost.
Integration of building services
Services integrated with a cellular floor beam
Service runs can be integrated within the depth of the structure or separated by fixing them at a lower level.
Separation of zones usually requires confining the ducts, pipes and cables to a horizontal plane below the structure, which will increase the overall floor construction. However, the services remain readily accessible for maintenance and future refitting.
Integration of services and structure reduces the construction depth but requires a perforated structure; installation and subsequent refitting of services may be more difficult.
External envelope
Cladding systems that are used in multi-storey buildings depend on the building height and the degree of fenestration. Fully glazed facades are widely used, although provision for solar shading generally has to be made. Cladding systems include:
Brickwork
Ground supported up to 3 storeys. Supported by stainless steel angles attached to edge beams for taller buildings.
Glazing systems
Generally triple glazing or double layer facades supported on aluminium posts or glass fins.
Curtain walling
Aluminium or other lightweight facade that is attached to the perimeter steelwork.
Insulated render or tiles
Cladding system supported on light steel infill walls, mainly used in public sector buildings and residential buildings.
The external skin of a multi-storey building is usually supported off the structural frame. In most high quality commercial buildings, the cost of external cladding systems greatly exceeds the cost of the primary structure. This influences the design and construction of the structural system in the following ways:
Structural principles
Main articles: Modelling and analysis, Design codes and standards, Portal frames, Allowing for the effects of deformed frame geometry
Once the structural concept has been fixed, the structural design may be completed. The structural design process involves the following steps:
Variable actions
Characteristic variable actions include:
Characteristic variable actions should be determined from the appropriate parts of BS EN -1[2] and the relevant UK National Annexes[3].
Analysis
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Model of a building constructed with cellular beams
For 'simple construction', frame analysis will not be necessary at the Ultimate Limit State (ULS), as the members can be designed in isolation. It may be necessary (or convenient) to use analysis software to determine the lateral deflections at the Serviceability Limit State (SLS) and when assessing frame stability. Analysis will be required for continuous frames.
Generally, elastic analysis is used. Plastic analysis (and elastic-plastic analysis) is generally only used for the design of portal frames .
Although manual methods of analysis may be used, most designers find it convenient to use readily available software .
Modelling members
Most software contains libraries of all the standard steel sections, with the associated member properties used in the analysis. Non-standard members may be modelled with equivalent section properties. Tapered or haunched members may be modelled with a number of short elements, each with different section properties. Curved members may be modelled with a series of straight members.
Modelling Joints
Common UK practice is to assume joints are either nominally pinned (and modelled as perfectly pinned) or nominally rigid (and modelled as perfectly rigid). It is then important to ensure that the physical details correspond to the design assumptions.
Sensitivity to second-order effects
All frames experience second-order effects, typically because under lateral loads (or simply due to frame imperfections), the vertical loads are no longer concentric with the bases. The effect of this displacement is not accounted for in a first-order analysis. Some frames are sufficiently stiff such that second-order effects are small enough to be ignored. When second-order effects must be accounted for, this can be achieved by using second-order analysis, or by a simple amplifier of the lateral loads.
All frames must be assessed for sensitivity to second-order effects, and these effects allowed for if necessary.
Design Standards
Main articles: Design codes and standards
The over-arching requirement for design in the UK is to satisfy the Building Regulations. Practically, design of steel structures will generally be in accordance with BS [4] or the Eurocodes .
Building Regulations
Building Regulations require that a safe structure be constructed. Although a series of design Standards are cited in the Regulations, there is no absolute requirement that the listed Standards are used for design.
BS
Although BS [4] was withdrawn in March , it is likely to be used for steel building design for a number of years. The advantages of design to BS include:
Eurocodes
The Eurocodes are a set of unified structural design standards for use across Europe, developed by CEN (European Committee for Standardisation), to cover the design of all types of structures in steel, concrete, timber, masonry and aluminium.
In the UK, the Eurocodes are published by BSI under the designations BS EN to BS EN ; each of these ten Eurocodes is published in several Parts and each Part is accompanied by a UK National Annex (which must be used for construction in the UK) that adds certain UK-specific provisions.
In addition to the Eurocodes and the National Annex, non-contradictory complementary information (NCCI) is provided, to provide further guidance on the application of the Eurocodes.
National Annexes
The National Annex (NA) is an essential document when using any Eurocode Part; the relevant NA covers the country where the construction will take place. Where the opportunity is given in the text of the Eurocode, the National Annex will:
The National Annex may give references to publications and other guidance containing non contradictory complementary information (NCCI) that will assist the designer when designing a structure to the Eurocodes.
The Eurocodes omit some design guidance where it is considered to be readily available in text books or other established sources. Publications that contain such design guidance may be referenced in the National Annex as NCCI.
Several 'Published Documents' (PDs) are available, published by BSI . These NCCI documents are informative, without the status of a Standard, but are generally helpful reference documents for designers.
Basis of structural design
BS EN [5] can be considered as the 'core' document of the structural Eurocode system as it establishes the principles and requirements for the reliability, serviceability and durability of structures. It also describes the basis for structural design and verification. The main sections of BS EN [5] include:
Designers will refer to BS EN [5] (and its National Annex[6]) for load factors and combination factors, used when determining design combinations of actions (ULS loads).
BS EN -1 (Eurocode 3)
BS EN -1 Eurocode 3: Design of steel structures comprises a set of general rules in twelve parts (BS EN -1-1[7] to BS EN -1-12[8]) for all types of steel buildings. The commonly used Parts include:
Additional rules are provided in separate Parts for other structures, e.g. BS EN -2[11] provides design rules for bridges.
A comprehensive range of design guidance is available for use in the UK, all incorporating the influence of the UK National Annexes.
BS EN (Eurocode 4)
BS EN [12] covers the design of composite structures and elements .
Guidance is available covering the design of composite floors in accordance with Eurocode 4 in SCI publication Composite design of steel framed buildings (P359).
Common structural systems
Main articles: Braced frames, Continuous frames, Composite construction, Floor systems, Steel construction products, Long-span beams
Building frames may be broadly classified by their stability system, as braced or continuous frames . A portal frame is a particular type of a continuous frame. For multi-storey frames, a braced frame is likely to be most economical, because the fabrication effort for the joints in braced frames is generally much less than for joints in continuous frames. Continuous frames must be used when bracing cannot be provided within the structure.
Within both types of frame, a wide range of floor systems is available. Several floor systems utilise the benefits of composite construction , which will be the de facto solution for many structures. The floor systems in common use are briefly described in the following sections
Trapezoidal decking on downstand steel beams
Composite construction is the dominant form of construction for the multi-storey building sector. Its success is due to the strength and stiffness that can be achieved, with minimum use of materials, utilising the compressive strength of concrete and the tensile strength of steel. Composite floors offer significant advantages related to speed of construction and reduced overall construction depth.
Composite floor slabs generally use either relatively shallow profiled steel decking , typically spanning up to 3.75 m, or deep deck systems, spanning up to 9 m (if propped during construction). Composite floor slabs may also be constructed using pre-cast planks as the permanent formwork.
Floor slabs may be formed from pre-cast planks, but still allow the supporting beam to be designed as a composite member.
Composite beams involve the transfer of force between the steel section and the concrete which it supports, preventing slip and thus ensuring the two elements perform as a composite whole. For beams located wholly under the slab (known as "downstand" beams) the transfer of force is commonly achieved using headed shear studs, which are attached to the upper flange of the steel beam. Studs are usually welded on site, through the decking, to the (unpainted) top flange of the beam. Alternatively, smaller shear connectors may be shot-fired to the steel beam. In some forms of construction, the shear bond between the steel member and the encasing concrete is sufficient to provide composite action without additional shear connectors.
Different types of composite beam are available:
Conventional "downstand" beam
Integrated beam with deep decking
Precast concrete units
Precast concrete units may be used in conjunction with steel beams. The units may be solid or hollow-core, and with tapered or bluff ends. They are normally prestressed. The steel beams and precast units may be designed as a composite member, provided specific detailing rules are satisfied to ensure the necessary composite behaviour.
Precast concrete floor slabs on a steel frame
(Image courtesy of Severfield (Design & Build) Ltd.)
Integrated floor solutions
Integrated (or 'shallow') floors offer a range of benefits, including a reduced construction depth (compared to an orthodox "downstand" solution) and, in some solutions, a virtually flat soffit, allowing easy location of services.
A number of integrated floor solutions are available, including a range of rolled and fabricated options providing shallow depth members with wide bottom flanges, so that precast planks or steel decking can be placed on the bottom flange.
Long spans result in flexible, column-free internal spaces, reduced substructure costs, and reduced erection times. This broad range of benefits means that they are commonly used in a wide range of building types.
Long-span beam options include:
The design of long-span steel and (steel-concrete) composite beams is generally carried out in accordance with BS [4], BS EN [13] or BS EN [12]. For some types of beam this codified guidance is complemented by specific design guidance, such as that on the design of beams with large web openings, or manufacturers' software.
Long-span roof trusses, The Emirates Stadium, Arsenal Football Club, London
(Image courtesy of Severfield (UK) Ltd.)
Main article: Trusses
A truss is essentially a triangulated system of straight interconnected structural elements. The most common use of trusses is in buildings, where support to roofs, the floors and internal loading such as services and suspended ceilings, is readily provided. Trusses are commonly used in a range of buildings including airport terminals, aircraft hangers, sports stadia roofs, auditoriums and other leisure buildings . Trusses are also used to provide large column-free spaces in commercial buildings. The main reasons for using trusses are:
Trusses may be exposed within the structure and be fabricated from hollow sections for aesthetic appeal. Large loads may require the use of open sections (UKC, typically) or sections built up from plate. In all cases, the additional fabrication costs make trusses more expensive than conventional beam and column structures.
Main articles: Portal frames, Moment resisting connections, Single storey industrial buildings
Portal frames are low-rise structures, comprising columns and rafters, connected by moment-resisting connections. The resistance to lateral and vertical actions is provided by the rigidity of the connections and the bending stiffness of the members, which is increased by a substantial haunch to reinforce the rafter sections where the bending moments are highest. This form of continuous frame is stable in its plane and provides a clear span that is unobstructed by bracing. Bracing is provided in the longitudinal direction, between frames.
Portal frames are structurally efficient and lightweight, accounting for over 90% of the single-storey market in the UK. Portal frames are used for industrial, storage , retail and commercial applications.
Steel framed, steel clad single storey distribution warehouse building
Principal components of a portal framed building
In addition to a primary steel structure, portal framed buildings also commonly include:
Main article: Member design
Steel member design is based on the requirements given in BS EN -1-1[7] . The overall process in member design involves:
Member design is often completed using software, of by reference to the resistance tables in the 'Blue Book'.
Connections
Main articles: Cost planning through design stages, Braced frames, Continuous frames, Simple connections, Moment-resisting connections
The cost of connections is a significant proportion of the overall cost of the structure and the use of standardised, simple details is recommended wherever possible. Moment resisting connections will undoubtedly be more expensive than the nominally pinned connections used in braced construction .
Although standardised semi-continuous connections are designed to transfer moment, they are partial strength. The standardised connections may require more expensive fabrication than standardised nominally pinned connections, but due to their partial strength are significantly cheaper than nominally rigid connections.
Design of joints in steel structures in the UK is covered by BS EN -1-8[10] and its UK National Annex[14]
BS EN -1-1[7] requires that connection behaviour be accounted for in frame analysis, if it is significant. Nominally pinned connections and continuous connections may be modelled as pinned and rigid (respectively) in the analysis, but semi-continuous joint behaviour should be taken into account.
BS EN -1-8[10] provides numerical methods to classify a joint, but offers the option that joints may be classified on the basis of previous satisfactory performance. The UK National Annex[14] specifies that joints designed in accordance with the industry standard guides (on nominally pinned and moment-resisting connections) are nominally pinned and rigid respectively. Classification in accordance the guidance in the UK NA is recommended.
Simple connections are nominally pinned connections that transmit end shear only and do not transfer significant moments. This assumption underpins the design of multi-storey braced frames in the UK, in which the beams are designed as simply-supported and the columns are designed for axial load and the small nominal bending moments induced by the end reactions from the beams.
End plate connections
Fin plate connection
Simple connections include:
Moment-resisting connections
Moment resisting connections are used in continuous frames . Connections in multi-storey frames are most likely to be full depth end plate connections and extended end plate connections.
Connections in portal frames will be haunched at the eaves, often with stiffeners in the column member. The apex connection may have a small haunch or a simple extended end plate.
Moment-resisting connections may also be provided by providing a welded connection between members.
Eaves connection
Apex connection
Main articles: Structural robustness
Building Regulations require that all buildings should be designed to avoid disproportionate collapse. Commonly, this is achieved by designing the joints in a steel frame (the beam-to-column connections and the column splices) for tying forces. Guidance on the design values of tying forces is given in BS EN -1-7[15] Annex A, and its UK National Annex[16] .
Two generic types of strategy for designing robust structures for accidental actions are provided in BS EN -1-7[15] :
The robustness requirements relate to the building Class (the type, size and use of a building) and establish required levels of robustness for different building Classes.
Detailed guidance on robustness strategies for steel framed buildings designed in accordance with the Eurocode is available.
Specification of structural steelwork
Main articles: Steelwork specification, Fabrication, Construction
The purpose of a structural steelwork specification is to state what materials and products should be used and how work (fabrication and erection ) should be carried out, in order to ensure that the completed structure meets the designer's assumptions and the client's needs.
Under the Eurocode system, fabrication and erection should comply with the execution standard BS EN [17] which covers material specification, component specification, workmanship and tolerances.
In the UK, the National Structural Steelwork Specification (NSSS) is recommended for use with steel building structures which are identified by the designer as Execution Class 2 (EXC2). The NSSS complements BS EN [17], by providing additional requirements on transfer of information, weld inspection etc, and other requirement which are not addressed in BS EN [17].
BS EN Execution of steel structures
BS EN Execution of steel structures and aluminium structures consists of three parts:
BS EN -2[19] specifies general requirements for the execution of structural steelwork as structures or as manufactured components, depending on the Execution Class of the structure. Four Execution Classes are identified and more onerous fabrication and erection requirements are demanded for the higher numbered Execution Classes.
BS EN -2[19] also gives guidance for the steelwork of steel and concrete composite structures designed in accordance with BS EN [12].
The 7th Edition of the NSSS covers structures designed in accordance with either BS or Eurocode 3 and is for Class 2 structures to be executed in accordance with BS EN [17].
The principal topics covered in the NSSS are as follows:
These topics present, in a concise manner, the requirements in BS EN [17] for orthodox building (Execution Class 2) structures.
Provision is included for modifications to suit any unorthodox construction.
The 7th Edition of the NSSS also contains an Annex of the requirements for Execution Class 3 for static structures and an Annex giving general guidance on Execution Class 3 for buildings subject to fatigue, such as crane supporting structures.
To ensure that the constructional steelwork industry is ready to meet the new challenges presented by the Building Safety Act [21], BCSA has revised the 7th edition of the National Structural Steelwork Specification for Building Construction. Published on 3rd April , it will come into force on 2nd October . The NSSS Corrigenda () is freely available here
NSSS Annex J - Sustainability Specification
The 1st edition of the Sustainability Specification for structural steelwork for building construction was published by BCSA in January , and is freely available here. This document came into force on 1st June and will constitute a new Annex J to the National Structural Steelwork Specification for Building Construction (NSSS) when revised in its 8th edition.
Given demands to promote more sustainable construction, and particularly in the context of the climate emergency, this document specifies general requirements and practices for achieving environmentally sustainable steel building construction. Prepared under the guidance of a steering committee comprised of structural steel suppliers, steelwork contractors, designers, and individual sustainability experts from BCSA, SCI, and IStructE, it supplements the requirements of Clauses 1 to 11 of the NSSS and includes guidance on both the sustainable design of structural steelwork and the specification for sustainable fabrication of structural steelwork.
BCSA also published a Model specification is for the purchase of reclaimed steel sections in March , to be used in conjunction with NSSS Annex J &#; Sustainability Specification. This model specification applies to the contract between the stockholder (the supplier) and the steelwork contractor (the purchaser) for steel products placed on the market as reclaimed structural steel sections for the fabrication of structural steelwork. It covers the selection and acceptance criteria for reclaimed steelwork, the technical specification for those steel products including tolerances on dimensions and shape and material performance requirements, product testing and quality management requirements and documentation.
References
Guide to Specification, British Council for Offices,
BS EN -1 Eurocode 1. Actions on structures. General actions. (Various Parts). BSI
NA to BS EN -1 UK National Annex to Eurocode 1. Actions on structures. General actions. (Various Parts). BSI
BS Structural use of steelwork in building (Various Parts). BSI
BS EN :+A1:. Eurocode: Basis of structural design. BSI
NA to BS EN :+A1:. UK National Annex for Eurocode: Basis of structural design. BSI
BS EN -1-1:+A1:, Eurocode 3: Design of steel structures. General rules and rules for buildings, BSI
BS EN -1-12: Eurocode 3. Design of steel structures. Additional rules for the extension of EN up to steel grades S 700, BSI.
BS EN -1-5:+A2:. Eurocode 3: Design of steel structures Plated structural elements. BSI
BS EN -1-8:. Eurocode 3: Design of steel structures. Design of joints, BSI
BS EN -2: Eurocode 3. Design of steel structures. Steel bridges. BSI
BS EN Eurocode 4: Design of composite steel and concrete structures. (Various Parts). BSI
BS EN Eurocode 3: Design of steel structures. (Various Parts) BSI
NA to BS EN -1-8: UK National Annex to Eurocode 3: Design of steel structures. Design of joints, BSI
BS EN -1-7:+A1:. Eurocode 1: Actions on structures. General actions. Accidental actions. BSI
NA+A1: to BS EN -1-7:+A1:. UK National Annex to Eurocode 1: Actions on structures. Accidental actions, BSI
BS EN Execution of steel structures and aluminium structures (Various Parts), BSI.
BS EN -1:+A1: Execution of steel structures and aluminium structures. Requirements for conformity assessment of structural components BSI.
BS EN -2: Execution of steel structures and aluminium structures. Technical requirements for steel structures. BSI.
BS EN -3: Execution of steel structures and aluminium structures. Technical requirements for aluminium structures. BSI.
Further reading
Resources
Member design tools:
Connection design tools:
Other design tools:
See also
CPD
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