A wide range of commercial software is available to aid designers with the efficient and economic design of steel framed buildings and bridges. In addition, the steel sector has developed a number of free software packages and spreadsheet tools to aid designers, which are presented here.
BIM image of a large steel-framed building,(Image courtesy of Graitec UK Ltd.)
- 2Member design tools
- 3Connection design tools
[top]Interactive 'Blue Book'
CsJoint connection design software can be run as a stand-alone application and proved to be an efficient tool for structural connection design. Download structural design software csJoint 13.0 developed by ConSteel Solutions.
The “Blue Book”, SCI P363, is the essential aid for the design of steelwork. Comprehensive section property data is provided as well as tables of member resistances, which are given for grades S275 and S355. This enables rapid selection of steel members in compression, bending and tension. Tables are also provided for combined bending and compression, web resistance and shear resistance. It also provides:
- Section property data for: hot rolled open sections such as beams, columns, channels and angles; and hollow sections.
- Resistances for ordinary (non pre-loaded) bolts, pre-loaded bolts and welds.
An interactive version of the 'Blue Book' is also available that includes design information in accordance with the relevant parts of both the Eurocodes and BS 5950. Produced by the SCI on behalf of Steel for Life, this comprehensive web-hosted eBlue Book covers the full range of both open sections and hollow sections (both hot finished and cold formed), and will not require any software to be installed on the host computer.
Design data is available for:
- Universal beams, universal columns, bearing piles, and parallel flange channels to BS EN 10365[1]
- Structural tees (cut from either universal beams or universal columns) to BS 4-1[2]
- Equal and unequal angles to BS EN 10056[3]
- Hot-finished structural hollow sections to BS EN 10210-2[4]
- Cold-formed structural hollow sections to BS EN 10219-2[5]
Tables are provided for both S275 and S355 grades for open sections, S355 and S420 grades for hot-finished hollow sections, and S355 grade for cold-formed hollow sections. Comprehensive design data is also provided for bolts and welds, rolling tolerances are given, and there are comprehensive sets of explanatory notes for both the Eurocodes and BS 5950 data.
Click here to access the freely available Steel for Life Interactive “Blue Book”.
Note:
- Tables of member resistances for S460 and HISTAR® grades are available in ArcelorMittal's Orange Book
- Tables of member resistances for hollow sections are also available in Tata Steel’s (tubes only) Blue Book
[top]Member design tools
[top]Compression resistance
This design software calculates the design resistance of beams (UKB), columns (UKC) and hollow sections (both hot finished Celsius® and cold formed Hybox®), subject to axial compression. The design resistance is calculated in accordance with BS EN 1993-1-1[6] and the UK National Annex[7]. The user must select the steel grade, member type, section type and buckling length.
[top]Bending resistance
This design software calculates the design resistance of beams (UKB) and columns (UKC) in S275 and S355 subject to bending against the major axis. The design resistance is calculated in accordance with BS EN 1993-1-1[6] and the UK National Annex[7]. The lateral torsional buckling resistance is calculated using the lateral torsional buckling curves for rolled sections. The user must select the steel grade, member type, section type, buckling length and choose the shape of the bending moment diagram by selecting an appropriate C1 factor.
Bending Resistance - UKB and UKC
[top]Columns in simple construction
This design software may be used to verify columns in “simple construction” – subject to axial loads and nominal moments from eccentric beam reactions assumed to be 100 mm from the face of the column. The tool covers beams (UKB) and columns (UKC) in S275 and S355 steel. The verification follows the guidance in NCCI: SN048b-EN-GB Verification of columns in simple construction - a simplified interaction criterion.. The scope excludes the verification of class 4 sections. The user must select the steel grade, member type, section size and column length. The tool provides the opportunity to input an axial force (from above), and the design values of the reactions on each face of the column at both ends of the column - these reactions are used to calculate the bending moments in the major and minor axis.
[top]Combined axial compression and bending resistance
This design software provides verification for beams (UKB) and columns (UKC) in S275 and S355 subject to combined bending and axial compression. The calculated interaction between bending and axial compression is verified against BS EN 1993-1-1[6] Expression 6.61 and 6.62 in accordance with the UK National Annex[7]. The interaction factors are determined using Annex B of BS EN 1993-1-1[6]. Identical lengths for major axis buckling, minor axis buckling and lateral torsional buckling are taken. The scope of this tool excludes the verification of class 4 sections. The user must select the steel grade, member type, section type, buckling length and provide the axial compression as well as the maximum and minimum values of major and minor bending moments
[top]Resistance of beams at elevated temperature
This design software calculates the critical temperature of a beam (UKB) exposed to fire. The software also calculates the time to failure when the beam is unprotected. This software is valid only for restrained beams carrying non-composite precast planks or shallow steel deck floors. The design resistance is calculated in accordance with BS EN 1993-1-1[6] and BS EN 1993-1-2[8], and the UK National Annex[7][9]. The user must select the steel grade, the beam, the loading, the imposed load category and the protection applied. The software assumes that the load on the beam is uniformly distributed.
Resistance of Beams at Elevated Temperature
[top]Resistance of columns at elevated temperature
This design software calculates the critical temperature of a column (UKC) exposed to fire. The software also calculates the time to failure when the column is unprotected. This software only covers columns in braced frames. The design resistance is calculated in accordance with BS EN 1993-1-1[6] and BS EN 1993-1-2[8], and the UK National Annex[7][9]. The user must select the steel grade, the column, the loading and the imposed load category. The user must also select whether the column is at the top storey or an intermediate storey.
Resistance of Columns at Elevated Temperature
[top]Composite Beam Checking Tool
This design software carries out the design of simply supported composite beams to the Eurocodes. It is applicable to secondary beams subject to uniformly distributed loading, or primary beams loaded at midspan or third points. Steel sections may be selected from the range of Beams (UKB) in grade S355. The slab is constructed with metal deck, which may be selected from the ComFlor range, or specified for other metal decks.
Structural steel design is carried out to BS EN 1993-1-1[6], concrete design to BS EN 1992-1-1[10] and composite design to BS EN 1994-1-1[11]. All standards are as implemented by the UK National Annexes[7][12][13]. ULS and SLS checks are carried out for the execution and normal stages. At the execution stage the secondary beam compression flange is assumed to be fully restrained by the metal deck, and the primary beam compression flange is assumed to be restrained at load application points. The design shear connection at the normal stage follows the recommendations of NCCI PN001a-GB and SCI P405, when applicable.
Verification of the beam at elevated temperature is carried out to BS EN 1994-1-2[14]. and its National Annex[15], together with NCCIPN005c-GB which is used to determine temperatures within a concrete slab. The beam may be unprotected or protected; a range of protection types and thicknesses may be selected. If the beam is unprotected, the software reports the time to failure, which may be compared to the required period of fire resistance. If the beam is protected, two results are provided:
- the critical temperature, which may be used to specify the required performance from any protection system.
- the time to failure, which can be compared to the required period of fire resistance.
Composite Beam Checking Tool
[top]Elastic Critical Moment for Lateral Torsional Buckling
This design software calculates the elastic critical buckling moment for lateral-torsional buckling (Mcr), and the elastic critical load for buckling (Ncr). The scope of the tool includes standard UB and UC sections. Sections may also be defined by dimension, or by property, so the tool can be used to assess fabricated members. The cross section height can also vary linearly along the beam.
A wide range of supports, restraints and loading conditions can be specified. Supports and restraints can be specified at any location along the beam and at a distance from the shear centre, with variable stiffness values. Point, moment and trapezoidal distributed loads can be specified at any location along the beam, and at a distance from the shear centre, to assess destabilising and stabilising loading conditions. Files may be saved and subsequently uploaded from local storage. Reports (summary or detailed) may be printed or exported as XLS and PDF files.
Although the software uses the term ‘Beam’ to refer to the design member, the application of the software is not limited to beams, and it can be used to analyse steel members subjected to bending and axial loading.
A comprehensive help ‘tab’ is provided and it is recommended that first time users refer to this before commencing an analysis.
Mcr - Elastic Critical Moment for Lateral Torsional Buckling
[top]Frame stability
This design software evaluates the frame stability of multi-storey braced frames, in accordance with BS EN 1993-1-1[6]. The parameter αcr is determined using the combination of the Equivalent Horizontal Forces (EHF) and wind loads on the frame, in conjunction with the vertical loads. The calculations are performed for a single vertical bracing system, which is assumed to be a vertical Pratt truss. Beam and column members may be selected from the full range of UKB and UKC’s respectively, and bracing members may be circular or square hollow sections.
From the user-defined characteristic permanent and variable actions, and the floor area associated with the bracing system at each level, the software calculates the EHF. Factors αh and αm are set to 1.0. The characteristic wind load per bracing system is assumed to be uniform over the full height of the bracing system; it is converted to point loads at floor levels in proportion to the storey heights.
Two cases are verified, firstly with imposed load as the leading variable action and secondly with the wind as the leading variable action.
Frame Stability Tool
[top]Connection design tools
[top]Base plate designer
This design software calculates the axial resistance of a nominally pinned base plate. The column may be a beam (UKB), column (UKC) or hollow section (both hot finished Celsius® and cold formed Hybox®). The design resistance is calculated in accordance with BS EN 1993-1-1[6] and the UK National Annex[7]. In addition to selecting the column and the grade of concrete, the user must select the size, thickness and steel grade of the base plate.
[top]End plate designer
This design software calculates the vertical shear resistance and tying resistance of partial depth and full depth end plate connections on beams (UKB). The design resistances are calculated in accordance with BS EN 1993-1-8[16] and the UK National Annex[17], following the procedures in the ‘Green Book’ (P358). Selecting the steel grade and beam size generates a set of parameters for a typical standard end plate connection. These parameters (number of bolt rows, pitch, offset, edge distances, gauge, plate width and thickness) may subsequently be changed and the resistances re-calculated. At any stage, re-selecting the beam will generate the typical connection.
[top]Fin plate designer
This design software calculates the vertical shear resistance and tying resistance of fin plate connections on beams (UKB). The design resistances are calculated in accordance with BS EN 1993-1-8[16] and the UK National Annex[17], following the procedures in the ‘Green Book’ (P358). Selecting the steel grade and beam size generates a set of parameters for a typical standard fin plate connection. These parameters (number of bolt rows, pitch, offset, edge distances, gauge, and plate thickness) may subsequently be changed and the resistances re-calculated. At any stage, re-selecting the beam will generate the typical connection.
[top]Gusset plate designer
This design software may be used to verify the resistance of lapped gusset plate connections subject to compression, typically used where diagonal bracing connects to other members. The gusset plate may be supported on one edge only (sometimes used for lightly loaded roof bracing) or on two edges, which is the common case where vertical bracing intersects at a beam-to-column connection. The design model assumes that the unsupported end of the connection is free to displace laterally, as the bracing member buckles. The eccentricity between the two lapped plates is accounted for in the design model. The resistance of the connection is based on a yield line analysis, with the moment due to eccentricity distributed to the two plates in proportion to their stiffness.
The design model has been validated against tests and Finite Element Analysis for orthodox connections with maximum 20 mm plates, M20 grade 8.8 bolts in square or rectangular patterns and a bracing angle of between 20 ° and 70°. Full details may be found in the ‘Green Book’ (P358), section 8.5.
Gusset Plate Designer
[top]Floor response calculator
This design software allows designers to make an immediate assessment of the dynamic response of a floor solution. The results from this software provide an improved prediction of the dynamic response compared to the ‘manual method’ in SCI P354. The software may be used to examine complete floor plans or part floor plans, comparing alternative beam arrangements.
The software reports the results of approximately 19,000 arrangements of floor grid, loading and bay size, which have been investigated using finite element analysis. The designer must select between a variable action of 2.5 kN/m2 and 5 kN/m2, being typical imposed loads on floors. 0.8 kN/m2 is added to allow for partitions. The designer must also select the arrangement of secondary and primary beams, with typical spans, which depend on the arrangement of the beams. Secondary beams may be placed at mid-span or third points. The pre-set damping ratio of 3% is recommended for furnished floors in normal use.
When a decking profile is selected from the ComFlor range, an appropriate range of slab depths are then available to be selected. Generally, thicker slabs will produce a lower response factor. When selecting the slab depth, solutions which result in a response factor higher than 8 (the limit for a typical office) are highlighted.
The primary and secondary beams are selected automatically from the range of Beams (UKB) in grade S355 as the lightest sections which satisfy strength and deflection requirements; these cannot be changed by the user. The selection of the lightest sections is made to produce the most conservative dynamic response, as stiffer beams will reduce the response.
A visual plot of the response is also provided for both the steady state and transient response. Hovering over the plot shows the response factor. Generally the higher response will be in an end bay, where there is no continuity. The fundamental frequency of the floor is presented on the output screen.
If the actual design differs from the pre-set solutions in the tool, users should note the following:
- Using stiffer beams will reduce the response
- Using thicker slabs, and stiffer beams, will reduce the response
- The gauge of the metal decking has no significant impact on the response factor
- Voids that break the continuity of beam lines will lead to higher response factors
Floor response calculator
[top]Carbon footprint tool for buildings
This web tool enables designers of multi-storey buildings to easily estimate the embodied carbon footprint of the superstructure.
There are two ways to use the tool. In ‘Auto generate’ mode, the basic building geometry, structural grid and chosen floor system are used to estimate structural material quantities using algorithms developed by the Steel Construction Institute (SCI) for common structural steel solutions. Alternatively, a user may use the ‘Manual input’ mode to enter the actual material quantities for their building.
Whichever mode is used, appropriate carbon emission factors are then applied to the material quantities to estimate the overall carbon footprint of the building. The results are presented as a single CO2e figure for the building, a CO2e figure per m2 of floor area, and a bar chart illustrating the contributions to the total made by the various elements of the building, i.e. frame, concrete cores, floors, roof, fire protection and void walls.
BREEAM Excellent - Eliot Park Innovation Centre, Nuneaton
[top]Wind loading calculator
This design software calculates the unfactored design wind loading on walls and roofs of buildings with a rectangular shape in plan. The loading is calculated in accordance with BS EN 1991-1-4[18], the UK National Annex[19], and PD 6688-1-4[20]. Roofs may be flat, monopitch or duopitch. Orography is assumed to be not significant. The user must define the dimensions of the building and provide sufficient geographic data for the evaluation of peak velocity pressure.
[top]FireSoft - concrete filled, hot finished structural hollow section columns in fire and ambient conditions
An exposed, reinforced concrete filled hollow section
The UK National Annex to BS EN 1994-1-2[15] prohibits the use of Annex H in determining the capacity of a composite column subject to compression and bending at elevated temperature and makes reference to non-contradictory complementary information (NCCI) in lieu of this.
That NCCI is published as NCCI: PN006a-GB Design guide for concrete filled hot finished structural hollow section columns. This guidance document is consistent with the requirements of BS EN 1994-1-1[11] and BS EN 1994-1-2 [14], including the provisions of each standards' UK National Annex.
Tata Steel and University of Manchester have developed an excel plugin software package called FireSoft that will design a concrete filled hollow section column according to these provisions for fire periods up to 2 hours. It is also suitable for ambient temperature design
The guidance, and therefore FireSoft, is applicable to hot finished structural hollow sections of fine grain steel (BS EN 10210[21][4]) and does not apply to cold formed hollow sections. The guidance and software is applicable to simple construction only.
[top]Acoustic prediction tool
The acoustic prediction tool has been developed to provide designers and architects with a rapid indication of the likely level of acoustic performance for a form of construction selected by the user. The tool will estimate the acoustic insulation provided by different combinations of elements and materials used in the construction of steel wall and floor systems allowing users to carry out a ‘what if’ analysis before embarking on detailed design.
Flooring choices include shallow floors, downstand composite and light steel systems and users can select from a range of floor treatments above and ceiling options below the structural elements. Wall forms involving single or twin studs, with or without acoustic quilting and a range of different boarding options can be selected for analysis.
The values predicted by this tool are only intended to be used for preliminary design purposes because there are many other factors besides specification of the wall or floor format that will affect acoustic performance e.g. junction details, exact specification of products, adjoining construction form and workmanship during construction. The tool is based on empirical interpretation of test data from structures in the residential, health and school sectors to predict the acoustic performance of the user’s chosen arrangement so although these additional factors are not specifically included, their effect is built in to the underlying data allowing a realistic assessment to be made.
[top]Preliminary bridge design charts
Typical medium span composite highway bridge
A1, Appleyhead
A1, Appleyhead
This easy to use spreadsheet tool created by Atkins for the BCSA and Tata Steel provides initial estimates of flange areas and web thicknesses for typical steel composite bridge cross sections. It is consistent with the latest SCI guidance on composite highway bridge design, and the plate sizes were derived using the Eurocodes and relevant UK National Annexes.
The scope includes simply supported and continuous plate girders for both multi-girder and ladder decks. The spreadsheet tool accounts for the differences between inner and outer girders, and provides both elastic and plastic designs. It is accompanied by a helpful User Manual explaining exactly what the tool is, and how to use it. A series of design charts are also available to facilitate manual calculation if desired.
[top]Bridges carbon calculator
This easy to use spreadsheet tool created by Atkins for the BCSA and Tata Steel calculates the carbon footprint of typical steel composite bridges. It requires a minimum of data and preliminary design quantities to generate an initial result, which can be further refined as more information becomes available. It is accompanied by a helpful User Guide explaining exactly what the tool is, and how to use it.
The results are displayed graphically showing the relative proportions due to construction, maintenance, and traffic delays. The construction element is further sub-divided to show the proportions for the deck, substructures and foundations. This allows a bridge designer to see where the major CO2 burdens are, allowing the focus of design development to be on the big issues in terms of reducing carbon emissions.
The current version (September 2013) addresses a number of issues identified when the tool was recently used for HS2, and corrects a few other assumptions and errors that were noted during a thorough review by Atkins. The main changes include:
- Correcting an error in calculating all reinforced concrete CO2 values
- Correcting formwork tonnage assumptions
- Correcting the calculation of backfill volume
- Improving the algorithms to estimate the split of concrete volumes between abutment, pier and wingwalls, which now accounts for bridge length
- Improved algorithm for estimating the volume of backfill based on assumed abutment heights, estimated from abutment concrete volumes
- Corrected CO2 values from traffic delay using road closures and full diversions
[top]References
- ↑BS EN 10365:2017 Hot rolled steel channels, I and H sections. Dimensions and masses. BSI
- ↑BS 4-1:2005 Structural steel sections. Specification for hot-rolled sections, BSI.
- ↑BS EN 10056-1:2017 Structural steel equal and unequal leg angles. Dimensions, BSI.
- ↑ 4.04.1BS EN 10210-2:2019 Hot finished steel structural hollow sections. Tolerances, dimensions and sectional properties, BSI.
- ↑ BS EN 10219-2:2019 Cold formed welded steel structural hollow sections. Tolerances, dimensions and sectional properties, BSI.
- ↑ 6.06.16.26.36.46.56.66.76.8BS EN 1993-1-1:2005+A1:2014, Eurocode 3: Design of steel structures. General rules and rules for buildings, BSI
- ↑ 7.07.17.27.37.47.57.6NA+A1:2014 to BS EN 1993-1-1:2005+A1:2014, UK National Annex to Eurocode 3: Design of steel structures General rules and rules for buildings, BSI
- ↑ 8.08.1BS EN 1993-1-2: 2005, Design of steel structures. General rules - structural fire design. BSI
- ↑ 9.09.1NA to BS EN 1993-1-2: 2005, UK National Annex to Eurocode 3: Design of steel structures. General rules - structural fire design. BSI
- ↑BS EN 1992-1-1:2004+A1:2014 Design of concrete structures. General rules and rules for buildings. BSI
- ↑ 11.011.1BS EN 1994-1-1:2004 Eurocode 4. Design of composite steel and concrete structures. General rules and rules for buildings. BSI
- ↑NA+A1:2014 to BS EN 1992-1-1:2004+A1:2014, UK National Annex to Eurocode 2. Design of concrete structures. General rules and rules for buildings. BSI
- ↑NA to BS EN 1994-1-1:2004 UK National Annex to Eurocode 4. Design of composite steel and concrete structures. General rules and rules for buildings. BSI
- ↑ 14.014.1 BS EN 1994-1-2:2005+A1:2014, Eurocode 4. Design of composite steel and concrete structures. General rules. Structural fire design. BSI
- ↑ 15.015.1NA to BS EN 1994-1-2:2005 UK National Annex to Eurocode 4. Design of composite steel and concrete structures. General rules. Structural fire design. BSI
- ↑ 16.016.1BS EN 1993-1-8:2005. Eurocode 3: Design of steel structures. Design of joints, BSI
- ↑ 17.017.1NA to BS EN 1993-1-8:2005. UK National Annex to Eurocode 3: Design of steel structures. Design of joints, BSI
- ↑BS EN 1991-1-4:2005+A1:2010 Eurocode 1. Actions on structures. General actions. Wind actions, BSI
- ↑NA to BS EN 1991-1-4:2005+A1:2010 UK National Annex to Eurocode 1. Actions on structures. General actions. Wind actions, BSI
- ↑PD 6688-1-4:2015 Background information to the National Annex to BS EN 1991-1-4 and additional guidance, BSI
- ↑BS EN 10210-1:2006. Hot finished structural hollow sections of non-alloy and fine grain steels: Technical delivery requirements. BSI
Retrieved from ‘https://www.steelconstruction.info/index.php?title=Design_software_and_tools&oldid=10146’
Passive fire protection materials insulate steel structures from the effects of the high temperatures that may be generated in fire. They can be divided into two types, non-reactive, of which the most common types are boards and sprays, and reactive, of which thin film intumescent coatings are the most common example. Thin film intumescent coatings can be either on-site or off-site applied.
The UK is fortunate in having an efficient and competitive structural fire protection industry which delivers excellent quality at low cost.
Thin film intumescent coatings
(Image courtesy of Sherwin-Williams Protective and Marine Coatings)
(Image courtesy of Sherwin-Williams Protective and Marine Coatings)
- 1Intumescent Coatings
- 6Partial protection
[top]Intumescent Coatings
Intumescent coatings are paint like materials which are inert at low temperatures but which provide insulation as a result of a complex chemical reaction at temperatures typically of about 200-250°C. At these temperatures the properties of steel will not be affected. As a result of this reaction they swell and provide an expanded layer of low conductivity char.
Intumescent coatings can be divided into two broad families: thin film and thick film. Thin film materials are either solvent based or water based and are mainly used for building fires. Thick film intumescent coatings were originally developed for the off-shore and hydrocarbon industries but have been modified for use in buildings.
[top]Thin film intumescent coatings
Thin film intumescent coating systems generally have three components, a primer, a basecoat (the part which reacts in the fire) and a sealer coat. The basecoat usually comprises the following ingredients:
- A catalyst which decomposes to produce a mineral acid such as phosphoric acid.
- A carbonific such as starch which combines with the mineral acid to form a carbonaceous char.
- A binder or resin which softens at a predetermined temperature.
- A spumific agent which decomposes together with the melting of the binder, to liberate large volumes of non-flammable gases. These gases include carbon dioxide, ammonia and water vapour. The production of these gases causes the carbonaceous char to swell or foam and expand to provide an insulating layer many times the original coating thickness.
They are mainly used in buildings where the fire resistance requirements are 30, 60 and 90 minutes. In recent years, a number of products have been developed which can provide 120 minutes fire resistance . They can be applied either on-site or off-site. In general, most on-site application is carried out using water based materials. However, where the structure to which the material is applied is not to have an end use in a dry, heated (C1) environment, solvent based materials are commonly used. Solvent based materials also tend to be able to cover a wider range of section factors than water based materials and can be used on-site to protect smaller sections requiring high thicknesses.
Both solvent based and water based coatings can be used to achieve attractive surface finishes. If a decorative or bespoke finish is required, this should be included in the specification. Thin film intumescents have the added advantages that they can easily cover complex shapes and post-protection service installation is relatively simple.
Typical expansion ratios are about 50:1, i.e. a 1mm thick coating will expand to about 50mm when affected by fire.
Detailed guidance on the specification and installation of site applied, thin film intumescent coatings is available from the Association for Specialist Fire Protection[1].
- Examples of thin film intumescent coating
- (Images courtesy of Sherwin-Williams Protective and Marine Coatings)
[top]Off site applied intumescent coatings
The development of an industry to apply thin film intumescent coatings off-site has been a UK success story which is now being exported across the world. The process usually involves application in a large, well ventilated and heated facility remote from the construction site. It has a number of distinct advantages:
- Quicker construction
- Improved quality control
- Reduction in site disruption
- Cleaner sites
- Improved site safety
- Easier servicing installation
Specifiers should be aware that off-site applied thin film intumescent coatings are used mainly for non-aesthetic end uses. Aesthetic finishes are possible, and have been achieved, using off-site application but it requires an additional level of care and attention. This is because some damage in transit is inevitable, even though applicators work to minimise it. It is difficult (but not of course impossible) to repair damage to match the appearance of the rest of the coating but this adds a layer of complexity to the work.
Applying thin film intumescent coatings off-site is a specialised task. The Association for Specialist Fire Protection publishes a guidance document[2] to assist specifiers. This includes a model specification from which clauses can be taken to put in the specifier’s own contract documents.
Off-site application is more expensive than its on-site equivalent in terms of up-front costs but the value of the advantages can make it more cost effective overall. This is widely recognised and market surveys show that this process has a significant market share in the UK.
- Application of thin film intumescent coatings offsite
[top]Thick film intumescent coatings
- The New York Times HQ with thick film epoxy fire protection to the exterior steel
(Image courtesy of International Paint) - Preformed casings using thick film epoxy intumescent
(Image courtesy of Nuvia)
Thick film intumescent coatings are usually epoxy based and typically have a much higher dry film thickness than thin film alternatives. These materials are tough and durable and were originally developed for use with hydrocarbon fires, where the test heating regime is much more severe than that used for most industrial and commercial applications.A number of manufacturers have modified their materials for use in cellulosic fires. These modified materials are usually used in situations where the benefits of intumescent coatings in terms of appearance, weight and thickness are required but where circumstances are too severe, or maintenance too difficult, to allow the use of thin film materials. Typical recent examples have occurred in external steel in high rise buildings and exposed marine environments.
Expansion ratios for thick film intumescents are much lower than for thin film materials, typically about 5:1. Aesthetic finishes are possible and it can also be supplied in the form of preformed casings. Thick film intumescent coatings can also be applied off-site.
[top]Boards
Interfacing between boards and thin film intumescent coatings is quite common
(Image courtesy of Promat Ltd.)
(Image courtesy of Promat Ltd.)
Boards are widely used for structural fire protection in the UK. They are used both where the protection system is in full view and where it is hidden. They offer the specifier a clean, boxed appearance and have the additional advantages that application is a dry trade and may not have significant impacts on other activities. Also, boards are factory manufactured and thicknesses can be guaranteed. Furthermore, boards can be applied on unpainted steelwork.
There are broadly two families of board protection, lightweight and heavyweight. Lightweight boards are typically 150-250kg/m³ and are not usually suitable for decorative finishes. They are typically used where aesthetics are not important and are cheaper than heavyweight equivalents. Heavyweight boards are usually in the range 700-950kg/m³ and will generally accept decorative finishes. They are typically used where aesthetics are important.
Both types of board may be used in limited external conditions but the advice of the manufacturer should be sought. Detailed guidance on the installation of board protection systems is available from the Association for Specialist Fire Protection[3].
- Board protection systems
- Boards can be formed around complex shapes
(Image courtesy of Promat Ltd.) - Aesthetic and non-aesthetic boards together
(Image courtesy of Promat Ltd.)
[top]Sprays
Cementitious spray on beams
(Image courtesy of Promat Ltd.)
(Image courtesy of Promat Ltd.)
Spray protection is extensively used in the United States but is less common in the United Kingdom. It has the advantage that it can be used to cover complex shapes and details and also that costs do not increase significantly with increases in protection thickness. This is because much of the cost of application is in the labour and equipment and a minority is in the cost of the material. Some materials can also be used in external and hydrocarbon fire applications.
Sprays are not suitable for aesthetic purposes. Also, application is a wet trade and this may have impacts on other site operations. Allowance may have to be made in costing for the possible requirement for prevention of overspray. Detailed guidance on the installation of spray protection systems is available from the Association for Specialist Fire Protection[4].
[top]Flexible blanket systems
Flexible blanket system
(Image courtesy of Thermal Ceramics Ltd.)
(Image courtesy of Thermal Ceramics Ltd.)
Flexible fire protection systems have been developed as a response to the need for an easily applied fire protection material which can be used on complex shapes and details but where application is a dry trade. There are a limited number of manufacturers of these products. Fixing of a blanket is shown in the accompanying photograph.
[top]Concrete encasement
Until the late 1970s, concrete was by far the most common form of fire protection for structural steelwork. However the introduction of lightweight, proprietary systems such as boards, sprays and thin film intumescent coatings has seen a dramatic reduction in its use. Nevertheless, concrete encasement has its place and it continues to have a small percentage of the fire protection market with other traditional methods such as blockwork encasement also used occasionally.The principal advantage of concrete is durability. It tends to be used where resistance to impact damage, abrasion and weather exposure are important e.g. warehouses, underground car parks and external structures.The principal disadvantages are:
- Cost - compared to lightweight systems;
- Space utilisation (large protection thicknesses take up valuable space around columns)
- Weight.
Information on thickness of concrete encasement for specific periods of fire resistance is published by the Building Research Establishment[5]. It can also be found in BS EN 1994-1-2[6].
[top]Partial protection
Standard fire tests have shown that structural members which are designed to not be fully exposed to fire can exhibit substantial levels of fire resistance without applied protection. Methods have been developed using this effect to achieve 30 and 60 minutes fire resistance. Where higher periods of fire resistance are called for, reduced fire protection thicknesses can be applied to the exposed steelwork since the heated perimeter, and therefore the section factor, is less than that for the fully exposed case. See here for more details.
There are five ways in which partial protection can be used:
[top]Block infilled columns
30 minutes fire resistance can be achieved by the use of autoclaved, aerated concrete blocks cemented between the flanges and tied to the web of rolled sections. Longer fire resistance periods are possible by protecting only the exposed flanges. Guidance is available from the Building Research Establishment[7].
- Block filled columns
- BRE guidance on block filled columns
[top]Shelf angle floor beams
Shelf angle floor beams are beams with angles welded or bolted to the web to support the floor slab. This protects the top part of the beam from the fire while the bottom part remains exposed. Fire resistance increases as the position of the supporting angle is moved further down the beam and 60 minutes fire resistance is achievable in some instances. Shelf angle floor beams are more commonly bolted rather than welded as shown in the accompanying photograph.
Guidance is available in SCI P126.
[top]Slim floor beams
Protected 'Slim floor' beam with precast concrete planks
There are a number of shallow floor solutions using ‘integrated’ beams. The beams may either be rolled or fabricated, and a number of alternatives are available. One such fabricated beam consists of an H section (usually UC) with a welded bottom plate – this is often called a ‘Slim floor beam’. Others include Ultra Shallow Floor Beams (USFB) from Kloeckner Westok, and ArcelorMittal's Slim floor beams. The common theme is that the beams are asymmetric with a wider bottom flange than top flange to carry the deck slab, which may be either precast concrete (pc) units, or a deep deck composite slab.
A key feature of such shallow floor systems is that almost the whole steel section is protected from the fire by the floor slab and up to 60 minutes fire resistance is achievable without protection to the exposed bottom plate.
Where periods of fire resistance greater than 60 minutes are required, only the exposed bottom flange or plate or the beam requires protection. The section factor is calculated on the basis of the heated perimeter of the bottom flange or plate.
[top]Web infilled columns
Sixty minutes fire resistance can be achieved for columns when normal weight, poured concrete is fixed between the flanges by shear connectors attached to the web. The concrete is retained by a web stiffener fixed at the bottom of the connection zone.
The load carrying capacity of the concrete is ignored in the design of the columns but in fire, as the exposed steel weakens at high temperatures, the load carried by the flanges is progressively transferred to the concrete. This provides stability for periods of fire resistance up to 60 minutes . The connection zone is fire protected along with the beam. Guidance is available in the Steel Construction Institute publication SCI P124.
- Web infilled columns
[top]Composite beams and columns with full and partial concrete encasement
This is a form of construction which has been introduced to the UK by the publication of BS EN 1994-1-2[6], which describes the systems and also includes tabulated design guidance. It consists of steel beams and columns in which fire resistance is achieved by the inclusion of reinforcement between the flanges, held in position by concrete. Fire resistance periods up to 120 minutes is achievable on columns using this approach and 180 minutes on beams. Guidance is also given on enhancement to full concrete encasement by the inclusion of rebar and up to 240 minutes fire resistance can be achieved. However, this requirement is rare in the UK.
[top]Protecting cellular beams
A common scene in UK construction. A cellular beam protected using a thin film intumescent coating
For many years, beams with multiple web openings manufactured by splitting and welding hot rolled beams and columns (castellated and cellular beams), were fire protected on the basis of the section factor of the parent section plus 20%. This was based on the results of a number of tests on castellated beams which showed a small increase in heating rate compared to hot rolled sections. When a process of manufacturing cellular beams from plates was developed, the 20% rule was retained. The default limiting temperature for cellular beams was taken as being the same as for hot rolled beams carrying concrete slabs, i.e. 620°C for thin film intumescent coatings and 550°C for sprays and boards.
However, over time, additional testing showed that cellular beams can display complex failure mechanisms in fire. A much improved understanding of these mechanisms has now been developed and, from this, it has become clear that the assumption that the limiting temperature of such beams is the same as for unperforated sections is not correct. Instead it has been shown that the geometry of the beam defines the limiting temperature and that every cellular beams needed to be assessed on its own merits. Generalised (or universal) solutions are not appropriate.
The great majority of cellular beams are fire protected using thin film intumescent coatings. The Association for Specialist Fire Protection (ASFP) and the Steel Construction Institute (SCI) have developed structural models for beams with circular and rectangular web openings. These models enable the calculation of the limiting temperature as a function of beam geometry and load. This can then be used to determine the correct intumescent coating thickness for the required fire resistance period, based on a section factor calculated using the formula:
Section factor = 1400/t
where t is the web thickness in mm.[Note: in situations where the web thickness varies, this is the bottom web thickness]
Some cellular beam manufacturers will also supply limiting temperatures for their products. The ASFP publishes details of the test protocol that thin film intumescent coating manufacturers must follow if their material is to be used on cellular beams[8]. This has separate parts for testing on beams with circular and rectangular openings. Thin film intumescent coatings which are to be used on beams with circular web openings must be tested to that part of the protocol but thin film intumescent coatings which are to be used on beams with rectangular openings must be tested to both parts.
Only thin film intumescent coatings which have been tested to the ASFP protocol can be used to fire protect cellular beams. The exception to this is where it can be shown that a beam and/or thin film intumescent coating manufacturer have developed their own structural model and design software which specifies particular thin film intumescent coatings tested by them and independently third party certified.
Specifiers should always request confirmation that the performance of thin film intumescent coatings intended for use on their project has been tested and assessed for use on beams with web openings as required.
In rare instances, cellular beams are protected by sprays or boards. Advice on specification of fire protection in this instance is given in the ASFP guidance[8].
Consideration should also be given to filling of voids for cellular beams.
[top]Trends in structural fire protection
The most obvious trend in structural fire protection for steel over the past two decades has been the rise in popularity of thin film intumescent coatings. This has been driven by an intensely competitive industry which has in turn driven R&D. This has created an impetus behind better, cheaper, thinner materials to the point where, in real terms, costs are a fraction of what they were in the 1990s. This has also been helped by the development of off-site applied intumescent coatings which has given manufacturers a new market.
- Trends in structural fire protection
[top]Case studies
[top]References
- ↑ASFP Technical Guidance Document – TGD 11. Code of practice for the specification & on-site installation of intumescent coatings for fire protection of structural steelwork
- ↑ASFP Technical Guidance Document - TGD 16. Code of Practice for Off-site Applied Thin Film Intumescent Coatings
- ↑ASFP Technical Guidance Document - TGD 14. Code of practice for the installation and inspection of board systems for the fire protection of structural steel work
- ↑ASFP Technical Guidance Document – TGD 15. Code of practice for the installation & inspection of sprayed non-reactive coatings for the fire protection of structural steelwork
- ↑Guidelines for the Construction of Fire Resisting Structural Elements. Building Research Establishment.
- ↑ 6.06.1BS EN 1994-1-2: 2005+A1:2014, Eurocode 4. Design of composite steel and concrete structures. General rules. Structural fire design. BSI
- ↑BRE Digest 317. Fire resistant steel structures: free-standing blockwork-filled columns and stanchions. Building Research Establishment
- ↑ 8.08.18.2Fire protection for structural steel in buildings (5th ed). The Association for Specialist Fire Protection.
[top]Further reading
- Passive & reactive fire protection to structural steel. Lennon, T. & Hopkin, D. Building Research Establishment
[top]Resources
[top]See also
[top]External links
[top]CPD
Retrieved from ‘https://www.steelconstruction.info/index.php?title=Fire_protecting_structural_steelwork&oldid=887’