![Structural-steel-icons](https://upload.wikimedia.org/wikipedia/commons/b/bb/Structural-steel-icons.jpg)
Structural steel is a category of
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
used for making
construction material
This is a list of building materials. Many types of building materials are used in the construction industry to create buildings and structures.
These categories of materials and products are used by architects and construction project managers t ...
s in a variety of shapes. Many structural steel
shape
A shape or figure is a graphics, graphical representation of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other properties such as color, Surface texture, texture, or material type.
A pl ...
s take the form of an elongated beam having a
profile
Profile or profiles may refer to:
Art, entertainment and media Music
* ''Profile'' (Jan Akkerman album), 1973
* ''Profile'' (Githead album), 2005
* ''Profile'' (Pat Donohue album), 2005
* ''Profile'' (Duke Pearson album), 1959
* '' ''Profi ...
of a specific
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
. Structural steel shapes, sizes,
chemical composition
A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound.
Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...
, mechanical properties such as strengths, storage practices, etc., are regulated by
standards Standard may refer to:
Symbols
* Colours, standards and guidons, kinds of military signs
* Standard (emblem), a type of a large symbol or emblem used for identification
Norms, conventions or requirements
* Standard (metrology), an object th ...
in most industrialized countries.
Most structural steel shapes, such as
-beams, have high
second moments of area, which means they are very stiff in respect to their cross-sectional area and thus can support a high
load without excessive
sagging.
Common structural shapes
The shapes available are described in many published standards worldwide, and a number of specialist and proprietary cross sections are also available.
![I-Beam 002](https://upload.wikimedia.org/wikipedia/commons/4/40/I-Beam_002.JPG)
*
-beam (-shaped cross-section – in Britain these include Universal Beams (UB) and Universal Columns (UC); in Europe it includes the IPE, HE, HL, HD and other sections; in the US it includes Wide
Flange
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
(WF or W-Shape) and sections)
*Z-Shape (half a flange in opposite directions)
*HSS-Shape (
Hollow structural section
A hollow structural section (HSS) is a type of metal profile with a hollow cross section. The term is used predominantly in the United States, or other countries which follow US construction or engineering terminology.
HSS members can be circu ...
also known as SHS (structural hollow section) and including square, rectangular, circular (
pipe
Pipe(s), PIPE(S) or piping may refer to:
Objects
* Pipe (fluid conveyance), a hollow cylinder following certain dimension rules
** Piping, the use of pipes in industry
* Smoking pipe
** Tobacco pipe
* Half-pipe and quarter pipe, semi-circular ...
) and elliptical cross sections)
*Angle (-shaped cross-section)
*
Structural channel
The structural channel, also known as a C-channel or Parallel Flange Channel (PFC), is a type of (usually structural steel) beam, used primarily in building construction and civil engineering. Its cross section consists of a wide "web", usually ...
, or -beam, or cross-section
*Tee (-shaped cross-section)
*
Rail profile (asymmetrical -beam)
**
Railway rail
**
Vignoles rail
**
Flanged rail
**
Grooved rail
*Bar, a long piece with a rectangular cross section, but not so wide so as to be called a
sheet.
*Rod, a round or square section long compared to its width; see also
rebar
Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a Tension (physics), tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concr ...
and
dowel
A dowel is a cylindrical rod, usually made of wood, plastic, or metal. In its original manufactured form, a dowel is called a ''dowel rod''. Dowel rods are often cut into short lengths called dowel pins. Dowels are commonly used as structural ...
.
*Plate, metal sheets thicker than 6 mm or in.
*Open web steel
joist
A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the s ...
While many sections are made by
hot
Hot or the acronym HOT may refer to:
Food and drink
*Pungency, in food, a spicy or hot quality
*Hot, a wine tasting descriptor
Places
* Hot district, a district of Chiang Mai province, Thailand
**Hot subdistrict, a sub-district of Hot Distric ...
or
cold
Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
rolling
Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...
, others are made by
welding
Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing Fusion welding, fusion. Welding is distinct from lower ...
together flat or bent plates (for example, the largest circular hollow sections are made from flat plate bent into a circle and seam-welded).
The terms ''angle iron'', ''channel iron'', and ''sheet iron'' have been in common use since before
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag Inclusion (mineral), inclusions (up to 2% by weight), which give it a ...
was replaced by steel for commercial purposes. They have lived on after the era of commercial wrought iron and are still sometimes heard today, informally, in reference to steel angle stock, channel stock, and sheet, despite that they are
misnomer
A misnomer is a name that is incorrectly or unsuitably applied. Misnomers often arise because something was named long before its correct nature was known, or because an earlier form of something has been replaced by a later form to which the name ...
s (compare "tin foil", still sometimes used informally for aluminum foil). In formal writing for metalworking contexts, accurate terms like ''angle stock'', ''channel stock'', and ''sheet'' are used.
Standards
Standard structural steels (Europe)
Most steels used throughout Europe are specified to comply with the
European standard
European Standards (abbreviated EN, from the German name ("European Norm")) are technical standards which have been ratified by one of the three European standards organizations: European Committee for Standardization (CEN), European Committee for ...
EN 10025. However, many national standards also remain in force.
Typical grades are described as 'S275J2' or 'S355K2W'. In these examples, 'S' denotes structural rather than engineering steel; 275 or 355 denotes the
yield strength
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...
in newtons per square millimetre or the equivalent
megapascal
The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is define ...
s; J2 or K2 denotes the materials
toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.[Charpy impact test
In materials science, the Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain rate test which determines the amount of energy absorbed by a material during fracture. Absorbed energy is a measure of the mate ...]
values; and the 'W' denotes
weathering steel
Weathering steel, often referred to by the genericised trademark COR-TEN steel and sometimes written without the hyphen as corten steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rus ...
. Further letters can be used to designate fine grain steel ('N' or 'NL');
quenched and tempered steel ('Q' or 'QL'); and thermomechanically rolled steel ('M' or 'ML').
1. S275JOH Specification
S275JOH is steel grade in EN 10219 specification, EN 10210 standard. And the most widely used specification is EN10219 standard, which is Cold formed welded structural hollow sections of non-alloy and fine grain steels.
EN10219-1 specifies the technical delivery conditions for cold formed welded structural hollow sections of circular, square or rectangular forms and applies to structural hollow sections formed cold without subsequent heat treatment.
Requirements for S275JOH pipe tolerances, dimensions and sectional s275 pipe properties are contained in EN 10219-2.
2. S275JOH Steel Pipes manufacture Process
The steel manufacturing process shall be at the discretion of the steel producer. S275JOH carbon steel pipes can be made in ERW, SAW or seamless process. All S275JOH steel material and S275JOH pipes should conform to EN10219 standards.
The normal yield strength grades available are 195, 235, 275, 355, 420, and 460, although some grades are more commonly used than others e.g. in the UK, almost all structural steel is grades S275 and S355. Higher grades are available in quenched and tempered material (500, 550, 620, 690, 890 and 960 – although grades above 690 receive little if any use in construction at present).
A set of
Euronorm
Euronorm (also referred to as the European Standard) is an international technical standard for a wide variety of commercial and industrial activities that has been recognized as applicable in the European Union. It has been prepared by CEN membe ...
s define the shape of a set of standard structural profiles:
* European I-beam: IPE –
Euronorm 19-57
Euronorm (also referred to as the European Standard) is an international technical standard for a wide variety of commercial and industrial activities that has been recognized as applicable in the European Union. It has been prepared by CEN membe ...
* European I-beam: IPN –
DIN 1025-1
DIN or Din or din may refer to:
People and language
* Din (name), people with the name
* Dīn, an Arabic word with three general senses: judgment, custom, and religion from which the name originates
* Dinka language (ISO 639 code: din), spoken by ...
* European flange beams: HE –
Euronorm 53-62
* European channels: UPN – DIN 1026-1
* European cold formed IS
IS 800-1
In linguistics, a copula (plural: copulas or copulae; abbreviated ) is a word or phrase that links the subject of a sentence to a subject complement, such as the word ''is'' in the sentence "The sky is blue" or the phrase ''was not being'' i ...
Standard structural steels (US)
Steels used for building construction in the US use standard alloys identified and specified by
ASTM International
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
. These steels have an alloy identification beginning with A and then two, three, or four numbers. The four-number
AISI steel grades
The SAE steel grades system is a standard alloy numbering system (SAE J1086 - Numbering Metals and Alloys) for steel grades maintained by SAE International.
In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were both ...
commonly used for mechanical engineering, machines, and vehicles are a completely different specification series.
The standard commonly used structural steels are:
Carbon steels
*
A36 – structural shapes and plate.
*
A53 – structural pipe and tubing.
*
A500 – structural pipe and tubing.
*
A501 – structural pipe and tubing.
*
A529 – structural shapes and plate.
*
A1085 – structural pipe and tubing.
High strength low alloy steels
*
A441
List of A roads in zone 4 in Great Britain
Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European isla ...
– structural shapes and plates (Superseded by A572)
*
A572 – structural shapes and plates.
*
A618 – structural pipe and tubing.
*
A992 – Possible applications are W or S I-Beams.
*
A913 – Quenched and Self Tempered (QST) W shapes.
*
A270 – structural shapes and plates.
Corrosion resistant high strength low alloy steels
*
A243
A, or a, is the first letter and the first vowel of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''a'' (pronounced ), plural ''aes'' ...
– structural shapes and plates.
*
A588 – structural shapes and plates.
Quenched and tempered alloy steels
*
A514 – structural shapes and plates.
*
A517 – boilers and pressure vessels.
*
Eglin steel Eglin steel (ES-1) is a high- strength, high-performance, low-alloy, low-cost steel, developed for a new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It ...
– Inexpensive aerospace and weaponry items.
Forged steel
*
A668 – Steel Forgings
CE marking
The concept of
CE marking
On commercial products, the letters CE (as the logo ) mean that the manufacturer or importer affirms the good's conformity with European health, safety, and environmental protection standards. It is not a quality indicator or a certificatio ...
for all construction products and steel products is introduced by the
Construction Products Directive (CPD). The CPD is a
European Directive
A directive is a legal act of the European Union that requires member states to achieve a particular result without dictating the means of achieving that result. Directives first have to be enacted into national law by member states before thei ...
that ensures the free movement of all construction products within the European Union.
Because steel components are "safety critical", CE Marking is not allowed unless the
Factory Production Control (FPC) system under which they are produced has been assessed by a suitable certification body that has been approved to the European Commission.
In the case of
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
products such as sections, bolts and fabricated steelwork the CE Marking demonstrates that the product complies with the relevant harmonized standard.
For steel structures the main harmonized standards are:
* Steel sections and plate – EN 10025-1
* Hollow sections – EN 10219-1 and EN 10210-1
* Pre-loadable bolts – EN 14399-1
* Non-preloadable bolts – EN 15048-1
* Fabricated steel –
EN 1090 −1
The standard that covers CE Marking of structural steelwork is
EN 1090-1. The standard has come into force in late 2010. After a transition period of two years, CE Marking will become mandatory in most European Countries sometime early in 2012. The official end date of the transition period is July 1, 2014.
Steel vs. concrete
Choosing the ideal structural material
Most construction projects require the use of hundreds of different materials. These range from the concrete of all different specifications, structural steel of different specifications, clay, mortar, ceramics, wood, etc. In terms of a load bearing structural frame, they will generally consist of structural steel,
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
,
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
, and/or wood, using a suitable combination of each to produce an efficient structure. Most commercial and industrial structures are primarily constructed using either structural steel or
reinforced concrete
Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
. When designing a structure, an engineer must decide which, if not both, material is most suitable for the design. There are many factors considered when choosing a construction material. Cost is commonly the controlling element; however, other considerations such as weight, strength, constructability, availability, sustainability, and fire resistance will be taken into account before a final decision is made.
*Cost – The cost of these construction materials will depend entirely on the geographical location of the project and the availability of the materials. Just as the price of gasoline fluctuates, so do the prices of cement, aggregate, steel, etc. Reinforced concrete derives about half of its construction costs from the required form-work. This refers to the lumber necessary to build the "box" or container in which the concrete is poured and held until it cures. The expense of the forms makes
precast concrete
Precast concrete is a construction product produced by casting concrete in a reusable molding (process), mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples i ...
a popular option for designers due to the reduced costs and time.
Steel being sold by weight, the structural designer must specify the lightest members possible while maintaining a safe structural design. Using many identical steel members rather than many unique ones also reduces cost.
*Strength/weight ratio – Construction materials are commonly categorized by their strength to weight ratio—or
specific strength
The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile applic ...
, which is the strength of a material divided by its density. These ratios indicate how useful the material is for its weight, which in turn indicates its cost and ease of construction. Concrete is typically ten times stronger in compression than in tension, giving it a higher strength to weight ratio in compression.
*Sustainability - Many construction companies and material vendors are becoming more environmentally friendly.
Sustainability
Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livi ...
has become an entirely new consideration for materials that will be in the environment for generations. A sustainable material minimally affects the environment upon installation and throughout its life cycle. Reinforced concrete and structural steel can be sustainable if used properly. Over 80% of structural steel members are fabricated from recycled metals, called A992 steel. This member material is cheaper and has a higher strength to weight ratio than previously used steel members (A36 grade). Concrete's material components are naturally occurring materials that are not harmful to the environment, and concrete can now be poured to be permeable, letting water flow through a paved surface to reduce the need for drainage or runoff infrastructure. Concrete can also be crushed and used as aggregate in future concrete applications, avoiding the land fill.
*Fire resistance - One of the most dangerous hazards to a building is a fire hazard. This is especially true in dry, windy climates and for structures constructed using wood. Special considerations must be taken into account with structural steel to ensure it is not under a dangerous fire hazard condition. Reinforced concrete characteristically does not pose a threat in the event of a fire and even resists the spreading of fire, as well as temperature changes. This makes concrete excellent insulation, improving the sustainability of the building it surrounds by reducing the required energy to maintain climate.
*Corrosion – Some structural materials are susceptible to corrosion from such surrounding elements as water, heat, humidity, or salt. Special precautions must be taken when installing a structural material to prevent it, and the occupants of the building must know of any accompanying maintenance requirements. For example, structural steel cannot be exposed to the environment because any moisture, or another contact with water, will cause it to rust, compromising the structural integrity of the building and endangering occupants and neighbors.
Reinforced concrete
*Characteristics – Generally consisting of
portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
, water,
construction aggregate
Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates ...
(coarse and fine), and steel reinforcing bars (
rebar
Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a Tension (physics), tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concr ...
), concrete is cheaper in comparison to structural steel.
*Strength – Concrete is a composite material with relatively high compressive strength properties, but lacking in
tensile
In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as t ...
strength/ductility. This inherently makes concrete a useful material for carrying the weight of a structure. Concrete reinforced with steel rebar give the structure a stronger tensile capacity, as well as an increase in
ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
and
elasticity
Elasticity often refers to:
*Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress
Elasticity may also refer to:
Information technology
* Elasticity (data store), the flexibility of the data model and the cl ...
.
*Constructability – Reinforced concrete must be poured and left to set, or harden. After setting (typically 1–2 days), a concrete must cure, the process in which concrete experiences a chemical reaction between the cementitious particles and the water. The curing process is complete after 28 days; however, construction may continue after 1–2 weeks, depending on the nature of the structure. Concrete can be constructed into nearly any shape and size. Approximately half of the cost of using reinforced concrete in a structural project is attributed to the construction of the form-work. In order to save time, and therefore costs, structural concrete members may be pre-cast. This refers to a reinforced concrete beam, girder, or column being poured off site and left to cure. After the curing process, the concrete member may be delivered to the construction site and installed as soon as it is needed. Since the concrete member was cured off location beforehand, construction may continue immediately after erection.
*Fire resistance – Concrete has excellent fire resistance properties, requiring no additional construction costs to adhere to the
International Building Code
The International Building Code (IBC) is a model building code developed by the International Code Council (ICC). It has been adopted for use as a base code standard by most jurisdictions in the United States. The IBC addresses both health and saf ...
(IBC)
fire protection
Fire protection is the study and practice of mitigating the unwanted effects of potentially destructive fires. It involves the study of the behaviour, compartmentalisation, suppression and investigation of fire and its related emergencies, as we ...
standards. However, concrete buildings will still likely use other materials that are not fire resistant. Therefore, a designer must still take into account the use of the concrete and where it will require fire hazardous materials in order to prevent future complications in the overall design.
*Corrosion – Reinforced concrete, when constructed properly, has excellent corrosion resistance properties. Concrete is not only resistant to water, but needs it to cure and develop its strength over time. However, the steel reinforcement in the concrete must not be exposed in order to prevent its corrosion as this could significantly reduce the ultimate strength of the structure. The
American Concrete Institute
The American Concrete Institute (ACI, formerly National Association of Cement Users or NACU) is a non-profit technical society and standards developing organization. ACI was founded in January 1905 during a convention in Indianapolis. The Institu ...
provides the necessary design specifications for an engineer to ensure there is enough concrete covering any steel reinforcement to prevent exposure to water. This cover distance must be specified because concrete will inevitable crack at locations carrying tension, or locations containing reinforcing bars for the purpose of carrying said tension. If the concrete cracks, it provides a path for water to travel directly to the reinforcing bars.
Some reinforcing bars are coated in epoxy as a second order measure of preventing corrosion due to water contact. This method induces higher costs on the overall project, however, due to the higher cost of the epoxy coated bars. Also, when using epoxy coated bars, reinforced concrete members must be designed larger, as well as stronger, in order to balance the loss of friction between the reinforcing bars and concrete. This friction is referred to as bond strength, and it is vital to the structural integrity of a concrete member.
Structural steel
*Characteristics – Structural steel differs from concrete in its attributed compressive strength as well as tensile strength.
*Strength – Having high strength, stiffness, toughness, and ductile properties, structural steel is one of the most commonly used materials in commercial and industrial building construction.
*Constructability - Structural steel can be developed into nearly any shape, which are either bolted or welded together in construction. Structural steel can be erected as soon as the materials are delivered on site, whereas concrete must be cured at least 1–2 weeks after pouring before construction can continue, making steel a schedule-friendly construction material.
*Fire resistance – Steel is inherently a noncombustible material. However, when heated to temperatures seen in a fire scenario, the strength and stiffness of the material is significantly reduced. The International Building Code requires steel be enveloped in sufficient fire-resistant materials, increasing overall cost of steel structure buildings.
*Corrosion – Steel, when in contact with water, can corrode, creating a potentially dangerous structure. Measures must be taken in structural steel construction to prevent any lifetime corrosion. The steel can be painted, providing water resistance. Also, the fire resistance material used to envelope steel is commonly water resistant.
*Mold – Steel provides a less suitable surface environment for mold to grow than wood.
The tallest structures today (commonly called "
skyscrapers
A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ris ...
" or
high-rise) are constructed using structural steel due to its constructability, as well as its high strength-to-weight ratio. In comparison, concrete, while being less dense than steel, has a much lower strength-to-weight ratio. This is due to the much larger volume required for a structural concrete member to support the same load; steel, though denser, does not require as much material to carry a load. However, this advantage becomes insignificant for
low-rise
A low-rise is a building that is only a few stories tall or any building that is shorter than a high-rise, though others include the classification of mid-rise.
Definition
Emporis defines a low-rise as "an enclosed structure below 35 metres 15 ...
buildings, or those with several stories or less. Low-rise buildings distribute much smaller loads than
high-rise structures, making concrete the economical choice. This is especially true for simple structures, such as parking garages, or any building that is a simple, rectilinear shape.
Structural steel and reinforced concrete are not always chosen solely because they are the most ideal material for the structure. Companies rely on the ability to turn a profit for any construction project, as do the designers. The price of raw materials (steel, cement, coarse aggregate, fine aggregate, lumber for form-work, etc.) is constantly changing. If a structure could be constructed using either material, the cheapest of the two will likely control. Another significant variable is the location of the project. The closest steel fabrication facility may be much further from the construction site than the nearest concrete supplier. The high cost of energy and transportation will control the selection of the material as well. All of these costs will be taken into consideration before the conceptual design of a construction project is begun.
Combining steel and reinforced concrete
Structures consisting of both materials utilize the benefits of structural steel and reinforced concrete. This is already common practice in reinforced concrete in that the steel reinforcement is used to provide steel's tensile strength capacity to a structural concrete member. A commonly seen example would be parking garages. Some parking garages are constructed using structural steel columns and reinforced concrete slabs. The concrete will be poured for the foundational footings, giving the parking garage a surface to be built on. The steel columns will be connected to the slab by bolting and/or welding them to steel studs extruding from the surface of the poured concrete slab. Pre-cast concrete beams may be delivered on site to be installed for the second floor, after which a concrete slab may be poured for the pavement area. This can be done for multiple stories.
A parking garage of this type is just one possible example of many structures that may use both reinforced concrete and structural steel.
A structural engineer understands that there are an infinite number of designs that will produce an efficient, safe, and affordable building. It is the engineer's job to work alongside the owners, contractors, and all other parties involved to produce an ideal product that suits everyone's needs.
When choosing the structural materials for their structure, the engineer has many variables to consider, such as the cost, strength/weight ratio, sustainability of the material, constructability, etc.
Thermal properties
The properties of steel vary widely, depending on its alloying elements.
The austenizing temperature, the temperature where a steel transforms to an
austenite
Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K ...
crystal structure, for steel starts at for pure iron, then, as more carbon is added, the temperature falls to a minimum for
eutectic steel (steel with only .83% by weight of carbon in it). As 2.1% carbon (by
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
) is approached, the austenizing temperature climbs back up, to . Similarly, the melting point of steel changes based on the alloy.
The lowest temperature at which a plain carbon steel can begin to melt, its
solidus
Solidus (Latin for "solid") may refer to:
* Solidus (coin), a Roman coin of nearly solid gold
* Solidus (punctuation), or slash, a punctuation mark
* Solidus (chemistry), the line on a phase diagram below which a substance is completely solid
* S ...
, is . Steel never turns into a liquid below this temperature. Pure Iron ('Steel' with 0% Carbon) starts to melt at , and is completely liquid upon reaching . Steel with 2.1% Carbon by weight begins melting at , and is completely molten upon reaching . 'Steel' with more than 2.1% Carbon is no longer Steel, but is known as
Cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
.
Fire resistance
![Owsj deck fireproofing](https://upload.wikimedia.org/wikipedia/commons/e/ef/Owsj_deck_fireproofing.jpg)
Steel loses strength when heated sufficiently. The ''critical temperature'' of a steel member is the temperature at which it cannot safely support its load. Building codes and structural engineering standard practice defines different critical temperatures depending on the structural element type, configuration, orientation, and loading characteristics. The critical temperature is often considered the temperature at which its
yield stress
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...
has been reduced to 60% of the room temperature yield stress.
[Industrial fire protection engineering, Robert G. Zalosh, copyright 2003 pg.58] In order to determine the fire resistance rating of a steel member, accepted calculations practice can be used, or a
fire test can be performed, the critical temperature of which is set by the standard accepted to the Authority Having Jurisdiction, such as a building code. In Japan, this is below 400 °C. In China, Europe and North America (e.g., ASTM E-119), this is approximately 1000–1300 °F
[Zalosh, Table 3.3] (530–810 °C). The time it takes for the steel element that is being tested to reach the temperature set by the test standard determines the duration of the
fire-resistance rating
A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail other criteria, involving eviden ...
.
Heat transfer to the steel can be slowed by the use of
fireproofing materials, thus limiting steel temperature. Common fireproofing methods for structural steel include
intumescent
An intumescent is a substance that swells as a result of heat exposure, leading to an increase in volume and decrease in density. Intumescent materials are typically used in passive fire protection and require listing, approval, and compliance in ...
, endothermic, and plaster coatings as well as drywall, calcium silicate cladding, and mineral wool insulating blankets.
[Best Practice Guidelines for Structural Fire Resistance Design of Concrete and Steel Buildings, NIST Technical Note 1681, L. T. Phan, J. L. Gross, and T. P. McAllister, 2010]
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Concrete building structures often meet code required fire-resistance ratings, as the concrete thickness over the steel rebar provides sufficient fire resistance. However, concrete can be subject to spalling
Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...
, particularly if it has an elevated moisture content. Although additional fireproofing is not often applied to concrete building structures, it is sometimes used in traffic tunnels and locations where a hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
fuel fire is more likely, as flammable liquid fires provides more heat to the structural element as compared to a fire involving ordinary combustibles during the same fire period. Structural steel fireproofing materials include intumescent, endothermic
In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. p. ...
and plaster coatings as well as drywall
Drywall (also called plasterboard, dry lining, wallboard, sheet rock, gypsum board, buster board, custard board, and gypsum panel) is a panel made of calcium sulfate dihydrate (gypsum), with or without additives, typically extruded between thick ...
, calcium silicate
Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·SiO2. It is also referred to by the shortened trade name Cal-Sil or Calsil. It occurs naturally as the mineral larnite.
...
cladding, and mineral or high temperature insulation wool blankets. Attention is given to connections, as the thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
of structural elements can compromise fire-resistance rated assemblies.
Manufacturing
Cutting workpieces to length is usually done with a bandsaw
A bandsaw (also written band saw) is a power saw with a long, sharp blade consisting of a continuous band of toothed metal stretched between two or more wheels to cut material. They are used principally in woodworking, metalworking, and lumb ...
.
A beam drill line (drill line) has long been considered an indispensable way to drill holes and mill slots into beams, channels and HSS elements. CNC beam drill lines are typically equipped with feed conveyors and position sensors to move the element into position for drilling, plus probing capability to determine the precise location where the hole or slot is to be cut.
For cutting irregular openings or non-uniform ends on dimensional (non-plate) elements, a cutting torch is typically used. Oxy-fuel
Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures ...
torches are the most common technology and range from simple hand-held torches to automated CNC coping machines that move the torch head around the structural element in accordance with cutting instructions programmed into the machine.
Fabricating flat plate is performed on a plate processing center where the plate is laid flat on a stationary 'table' and different cutting heads traverse the plate from a gantry-style arm or "bridge". The cutting heads can include a punch, drill or torch.
See also
* Diamond plate
Tread plate, also known as checker plate and diamond plate, is a type of metal stock with a regular pattern or lines on one side for slip resistance. The most common alloy used for aluminum tread plate is 6061, although 5086-H34 and 3003-H231 are ...
* Dowel
A dowel is a cylindrical rod, usually made of wood, plastic, or metal. In its original manufactured form, a dowel is called a ''dowel rod''. Dowel rods are often cut into short lengths called dowel pins. Dowels are commonly used as structural ...
* Flame cleaning Flame cleaning, also known as flame gouging, is the process of cleaning a structural steel surface by passing an intensely hot oxyacetylene flame over it. Mill scale and rust are removed by the reducing effect of the flame and the action of the heat ...
* Flange
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
* Gusset plate
Gusset plate is a plate for connecting beams and girders to columns. A gusset plate can be fastened to a permanent member either by bolts, rivets or welding or a combination of the three. They are used in bridges and buildings, as well as oth ...
* Hollow structural section
A hollow structural section (HSS) is a type of metal profile with a hollow cross section. The term is used predominantly in the United States, or other countries which follow US construction or engineering terminology.
HSS members can be circu ...
* I-beam
An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish language, Polish, Bulgarian language, Bulgarian, Spanish language, Spanish ...
* I-joist
An engineered wood joist, more commonly known as an I-joist, is a product designed to eliminate problems that occur with conventional wood joists. Invented in 1969, the I-joist is an engineered wood product that has great strength in relation to ...
* Light steel structure
Steel frame is a building technique with a " skeleton frame" of vertical steel columns and horizontal I-beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all attached to the frame. The develo ...
* Open web steel joist
In structural engineering, the open web steel joist (OWSJ) is a lightweight steel truss consisting, in the standard form, of parallel chords and a triangulated web system, proportioned to span between bearing points.
The main function of an OWS ...
* Railway rail
* Steel design
Steel Design, or more specifically, Structural Steel Design, is an area of structural engineering used to design steel structures. These structures include schools, houses, bridges, commercial centers, tall buildings, warehouses, aircraft, ships ...
* Structural channel
The structural channel, also known as a C-channel or Parallel Flange Channel (PFC), is a type of (usually structural steel) beam, used primarily in building construction and civil engineering. Its cross section consists of a wide "web", usually ...
* Structural engineering
Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
* Structural shape rolling
Structural shape rolling, also known as shape rolling and profile rolling, is the rolling and roll forming of structural shapes by passing them through a rolling mill to bend or deform the workpiece to a desired shape while maintaining a constant ...
* T-beam
A T-beam (or tee beam), used in construction, is a load-bearing structure of reinforced concrete, wood or metal, with a -shaped cross section. The top of the -shaped cross section serves as a flange or compression member in resisting compress ...
References
External links
Guide to the CE Marking of Structural Steelwork, BCSA Publication No. 46/08.
Encyclopedia for steel construction information
Structural Steel Handbook
{{Authority control
Structural engineering
Steels