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8/14/2019 CW1 - Struct,Steel n Concrete Comp
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Adeel Ahmad
11268158
Word Count 1,402
Adeel Ahmad
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Structural Steel / Concrete
Comparison
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CONTENTS
Structural Steel / Concrete comparison..............................................................................4
References
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STRUCTURAL STEEL / CONCRETE COMPARISON
INTRODUCTION
Steel and reinforced concrete are commonly used for the structure of framed buildings.
This coursework explores the suitability of these materials for this purpose.
Prestressed concrete is a method for overcoming the concretes natural weakness in
tension. It can be used to produce beams, floors or bridges with a longer span than is
practical with ordinary reinforced concrete. Prestressing tendons (generally of high
tensile steel cable or rods) are used to provide a clamping load which produces a
compressive that offsets the tensile stress that the concrete compression member would
otherwise experience due to a bending load. Traditional reinforced concrete is based onthe use of steel reinforcement bars, rebars, inside poured concrete.
Reinforced concrete is concrete in which steel reinforcement bars (Rebars") or fibers
have been incorporated to strengthen a material that would otherwise be brittle.
STEEL
BACKGROUND
Steel has many significant advantages, of which it is able to comply with the demands of
sustainable developments. In the construction industry where regulations on
environmental issues are becoming more rigorous it can be one of the main reasons why
steel is the most commonly use material for fabrication. Steel is a sustainable material, it
is produced from iron one of the most abundant and recycled elements on our planet
therefore production and processing is environmentally friendly.
Steel are used widely in the construction of roads, railways, infrastructure, and buildings.
Most large modern structures, such as stadiums and skyscrapers, bridges, and airports,
are supported by a steel skeleton. Even those with a concrete structure will employ steelfor reinforcing.
Structural steel is steel construction material, a profile, formed with a specific shape or
cross section and certain standards of chemical composition and strength. Structural
steel shape, size, composition, strength, storage, etc, is regulated in most industrialized
countries.
Structural steel members, such as I-beams, have high second moments of area, which
allow them to be very stiff in respect to their cross-sectional area.
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http://en.wikipedia.org/wiki/Skyscraperhttp://en.wikipedia.org/wiki/Bridgehttp://en.wikipedia.org/wiki/Airportshttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Profile_(engineering)http://en.wikipedia.org/wiki/Shapehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Second_moment_of_areahttp://en.wikipedia.org/wiki/Skyscraperhttp://en.wikipedia.org/wiki/Bridgehttp://en.wikipedia.org/wiki/Airportshttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Materialhttp://en.wikipedia.org/wiki/Profile_(engineering)http://en.wikipedia.org/wiki/Shapehttp://en.wikipedia.org/wiki/Cross_section_(geometry)http://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Second_moment_of_area8/14/2019 CW1 - Struct,Steel n Concrete Comp
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EXCHANGE HOUSE (1990)
LOCATION
Broadgate Exchange House is one of the unique structures that blend and express
architecture with structural engineering. This structure uses four-tied arches to clear an
entire office building 78m over a congested railroad track. The Exchange House provided
a rare design and innovative prospect for merging a bridge with an office building, it is a
10-storey office building spanning over Liverpool Street Station.
FRAME
Several frame types were considered, 10-storey X-braced system 10-storey centenary
suspension system, and a parabolic arch system. In each case the building had to
span 78m distance across the rail tracks.
The parabolic arch produces the most direct load path by axial compression when
subjected to uniform loading. The building frame functions on a modular basis, with
uniformly spaced gridwork of columns and beams. The load carrying abilities of the
parabolic arch, when subject to point loads, the slope of each segment if proportional to
the vertical load carried. The centre segment of the arch is flat because the shear is zero
at the centerline of the span and the segment carries only the horizontal thrust of the
arch. The segment next to the centre has the vertical load of one column/hangar and
hence has to have a slope. As the following segment pick up additional vertical load, the
slope increases proportionately.
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BEHAVIOUR
The primary gravity loads are uniform and the system responds as intended, with the
arch segments in compression with correspondingly high vertical stiffness. Non-uniformlive loads fall into two categories: symmetrical and unsymmetrical. These live loads
cause horizontal kick forces at the node joints.
Unsymmetrical loads produce an undesirable side way deformation mode in arch system,
with consequent high bending moment in the arch segments.
Since the arch is a compression element, its overall in-plane buckling strength is of
concern. Tied arches with hangers are fundamentally very stable systems.
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Arch
Node
Hang
Colum Arc
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Other major and steel and iron components of Exchange House are:
Arch Segments
Primary & Secondary ties
Arch diagonal
Hangers/columns
The parabolic arch produces the most direct load path by axial compression when
subject to uniform
loading.
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Primary and
SecondaryBase
Pier
Forces
resisted
Hanging
cables in
Arch always
in
The arch nodes are
where the hangers
and columns meet
and attach to the
arch.
Angles
change in
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The forces above the arch are in tension whereas, in contrast to, below the arch they are
in compression.
CONCRETE
BACKGROUND
STRENGTH
The compressive strength of concrete is very high, but its tensile strength is relatively
low. As a result concrete must be reinforced with steel in order to resist stretching,
bending or twisting, such as; in beams, girders, walls, columns, etc. But concrete that is
designed to only resist compression may not require any reinforcement. The most
important factor of controlling the strength on concrete is the water-cement ratio, or in
other terms the proportion of water to cement in the mix.
DURABILITY
The durability on concrete refers to the extent to which the material is capable of
resisting deterioration caused by exposure to service conditions. Concrete is also strong
and fireproof. Concrete that is subject to wear, such as floor slabs must be capable of
resisting abrasion.
The major factor that controls the durability of concrete is its strength. The stronger the
concrete, the more durable it is.
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HARLEQUIN BUILDING, WATFORD
LOCATION
The shopping centre is situated within the ring road and the high street.
FRAME
The frame is mostly of in-site concrete, with precast concrete floor soffit slabs acting
compositely for car park phases and was preferable to steel for a number of reasons.
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The beam and slab construction was chosen for malls and for the retail units. Reinforced
concrete transfer beams and slabs provide for the changes in the column grid at the
basement level.
The ground floor, constructed as a beam and slab, acts as a huge transition zonebetween the different column layouts of the wide traffic ways below and the shopsabove. In terms of structural steels, it would have been required to create deepersections, resulting in more excavation.
Simply by changing the amount of concrete cover to the reinforcement, the fireresistance requirements of four hours in the basement were immediately satisfied. Anyadditional fire-cladding or spraying was not necessary, as it would have been with asteelwork frame.
Connections between in-situ walls and adjacent slabs and staircases were generallymade using reinforcement continuity strips cast into the walls. Reinforcement hidden inthe continuity strips was bent out to form starter bars after formwork was struck.
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COMPARISON
Steel is the best structural system for residential, high-rise office buildings, span
distances, design flexibility and also easy to inspect because it is exposed. Design
flexibility of long spans is possible with steel; this is also an important factor in
remodeling.
The greater number of support columns needed in concrete construction often limits the
moving of walls and partitions. Cantilevering with concrete is expensive, demanding form
set-up and carpentry to hold the concrete until it cures. Cantilevering with steel means
only specifying an extended end.
The intended use for a building will also influence whether steel or concrete is the bestchoice. In general steel buildings work very well for storage buildings, indoor sports
facilities, workshops, and aircraft hangers, but they are less suited for higher-trafficked
buildings.
Comparatively speaking, steel walls are less durable than concrete walls. This holds true
in the face of natural forces (hurricanes, earthquakes) as well as for truck or forklift
accidents. For owners who want to build a warehouse or other facility where trucks or
forklifts will be used, this can be a very important point of concern.
While steel is reasonably durable, concrete remains the material of choice for buildings
that require less upkeep and maintenance over the years. Concrete is less pervious to
corrosion than its steel competitor.
When factoring in potential repairs and ongoing maintenance, the added fire safety and
durability of a concrete building will usually be reflected in lower insurance premiums.
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REFERENCES
http://www.tpub.com/content/construction/14043/css/14043_149.htm
http://www.civl.port.ac.uk/rcc2000/pdfs/harleq.pdf
http://www.concretecentre.com/main.asp?page=1285
Broadgate Exchange House: Structural Systems
The Structural Engineer/Volume 71/No 9/May 93
OTUA - Office Technique pour l'Utilisation de l'Acier
http://www.materialsengineer.com/E-Steel%20Properties%20Overview.htm
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http://www.tpub.com/content/construction/14043/css/14043_149.htmhttp://www.civl.port.ac.uk/rcc2000/pdfs/harleq.pdfhttp://www.concretecentre.com/main.asp?page=1285http://www.materialsengineer.com/E-Steel%20Properties%20Overview.htmhttp://www.tpub.com/content/construction/14043/css/14043_149.htmhttp://www.civl.port.ac.uk/rcc2000/pdfs/harleq.pdfhttp://www.concretecentre.com/main.asp?page=1285http://www.materialsengineer.com/E-Steel%20Properties%20Overview.htm