cw1 - struct,steel n concrete comp

8/14/2019 CW1 - Struct,Steel n Concrete Comp

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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_area


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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

cw1 - struct,steel n concrete comp

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