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Structural SystemStructural S
ystem
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Factors Affecting Choice of StructuralSystems
The design should ensure a coordinated approach including
structure, envelope, services and finishes.
The principal decisions regarding structure relate to column
layout, foundation conditions, integration of building services,
and external wall construction.
The design of steel framed buildings encompasses not only the
structure, but also the building envelope, services and finishes.
ll these elements must be coordinated by a firm dimensional
discipline which recogni!es the modular nature of the
components to ensure maximum repetition and standardi!ations
in the predetermined grid layout.
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Types of Structural System"ollowings are the three types of Structural System#
Load-bearing wall construction
Skeleton framing
Combination of the two
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Factors Governing TypesFactors Governing Types
SelectionSelection
Economics $ not necessary the one that
requires the least structural materials
Architectural, Mechanical, Electrical
and other costs may be affected
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1. Load Bearing Walls
%oad &earing 'alls serves as#
Facades
Enclosures
Separators
Fire barriers
Carry oor ! roof loads
to the foundation
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Load-Bearing WoodLoad-Bearing Wood
Walls:Walls:
(ne to three storey buildings
)*ouses+
- x - or - x /- construction
Studs on 0/” to ” centers
Top 1 &ottom plates
*eaders
2ax. 'all ht. )3nsupported+ 4
05-
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Load-Bearing Masonry Walls:Load-Bearing Masonry Walls:
06 Storeys or 2ore
Thickness of 'alls vary depending on height
Trape!oidal cross section
%intels or arches at openings
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Load-BearingLoad-Bearing
reinforced concretereinforced concrete
Walls:Walls:
Thinner than 2asonry
Solid or 7avity
Load-Bearing WallsLoad-Bearing Walls
are used for:are used for:
8xterior
9nterior :artitions
'ind &racing
Service 7ore 8nclosure
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Load-Bearing Partitions:Load-Bearing Partitions:
Short inter"als
Carry Floor#Ceiling Loads
Load-Bearing walls:Load-Bearing walls:
Can ser"e as Shear $alls % &esists $ind !
Earth'uake (Seismic) Loads
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2. Skeleton Framing
Skeleton Framing serves
as:
7olumns carry "oundation
%ateral "orces resisted by
7olumns and ;iagonal &races, or
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Horizontal Structural Sla orHorizontal Structural Sla or
!eck:!eck:
"loor=7eiling=;ucts
"lat $ :late 7onstruction
"lat $ Slab reinforced concrete
Slab $ &and 7onstruction
Two 'ay Slabs
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Beam " #irder $onstruction:Beam " #irder $onstruction:
'ood >oist or
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Heavier Load % Longer S&ans:Heavier Load % Longer S&ans:
(ne $ 'ay
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Multi-Storey Medium
Span
Structures
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Multi-Storey Buildings W'y Multi-Storey Buildings are made(
%arge 3rban :opulation
8xpensive %and
o Multi-Storey Buildings make more e)cient use of land:
*igher the building )2ore Storeys + $ %arger the ratio of the building
"loor area to the used land area
o *ec'nological com&etition +very Hig' uildings,
o ntil t'e end of t'e ./t' century most uildings of
several storeys in t'e Western World were made of:
7ontinuous 'alls of brick or stone masonry supporting the roof
"loor from timber beams
o *'e same structural system used in t'e 0oman $ity of
Herculaneum
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Multi-Storey buildings beginningsMulti-Storey buildings beginnings Beginning of t'e .1t' century 2 forefront of
industrial revolution in 3ngland: ;emand for large factory buildings of several storeys and large clear
floor areas
7ast iron available in bulk 7ast iron columns used instead of bearing walls and cast iron beams in
stead of timber floor >oists.
3levator invented in S4 in ./567 enaling muc'
taller o)ce and a&artment uildings to e
constructed
Most multi-Storey uildings in S4 were still
making use of masonry walls instead of columns
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Forms of Multi-Storey Buildings"ollowings are the three "orms of 2ulti@Storey &uildings#
*+ on Continuous Columns with Continuous
.eams
/+ Continuous Multi-Storey Columns and
.eams
0+ Cross - $all Construction
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1. on !1. on ! "ontinuous"ontinuous "olumns and"olumns and
"ontinuous Beams#"ontinuous Beams#
Single Storey columns are >ointed at each floor level. :re@cast
edge beams or internal spine beams are erected over these
columns and are connected using high strength dowel bars in
grouted dowel tubes cast in the both the beams and columns.
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2. "ontinuous Multi-Storey "olumns
and Beams 2ulti@Storey 7olumns up to four storeys tall are commonly
used as perimeters columns with integrated corbel details.
"or buildings taller than four storeys, columns in two storey
lengths are used at higher levels with designed tie
connections at the column >oints. 7olumns can be
manufactured economically in the lengths of up to 0m.
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$. "ross ! Wall "onstruction 7ross $ 'alls 2ulti@Storey Structures consists of flooring and
%oad@&earing walls, where the walls support the floors and the
structure above. %ateral stability is provided transversely across
the building by the cross@wall system and longitudinally by stairs
and lift shaft cores, which are also formed by pre@cast wall
panels. This type of construction is ideal for buildings of cellular
structure, for example *otels, (ffice or partment &locks.
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Benefits 3naffected by the site weather conditions
7ompetitive :ricing
"actory :roduction to exacting quality standards
Speed of erection
8fficient and economic structure, based on earlier completion
period
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"ollowings are the Structural 8lements used in
2ulti@Storey &uilding# Columns
.eams
1lates
Arches
Shells
Catenaries
Structural Elements
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"olumns#
7olumns are elements that carry only axial force $ either
tension or compression $ or both axial force and bending
)which is technically called a beam@column but practically,
>ust a column+. The design of a column must check the axial
capacity of element and buckling capacity.
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Beams#A .eam may be2
7antilevered supported at one end only with a fixed connection
Simply supported )supported vertically at each end but able to rotate
at the supports+
7ontinuous )supported by three or more supports+
7ombination of the above )Supported at one end and in the middle+
&eams are elements which carry pure bending only. &ending
causes one section of a &eam )divided along its length+ to go into
compression and the other section into tension. The compression
section must be designed to resist buckling and crushing, while the
tension section must be able to adequately resist the tension.
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%lates# :lates carry bending in two directions. concrete flat slab is an
example of a plate. :lates are understood by using 7ontinuum
2echanics, but due to the complexity involved they are most
often designed using a codified empirical approach, or
computer analysis.
They can also be designed with yield line theory, where an
assumed collapse mechanism is analy!ed to give an upper
bound on the collapse load. This is rarely used in practice.
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S&ells# Shells derive their strength from their form and carry forces in
compression in two directions. dome is an example of Shell.
They can be designed by making a hanging@chain model, which
will act as a catenaryBs in pure tension and inverting the form to
achieve pure compression.
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Arches: rches carry forces in compression in one direction only
which is why, it is appropriate to build arches out of masonry.
They are designed by ensuring that the line of thrust of the
force remains within the depth of the arch.
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"atenaries# Catenaries derive their strength from their form and
carry transverse forces in pure tension by deflecting (just
as a tightrope will sag when someone walks on it). Theyare almost always cable or fabric structure. A fabric
structure acts as catenaries in two directions.
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Large Span StructureLarge Span Structure
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Structural Forms"ollowings are the structural "orms used for large
span structure#
.eam Structures
1ortals and Arches
Masted Structures
Space Frames
3mbrella Structures
Cable Structures
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Beam StructuresBeam Structures Structures consisting of beams supported on columns are simpleStructures consisting of beams supported on columns are simple
and commonly used, especially where the minimum internaland commonly used, especially where the minimum internal
volume is required.volume is required.
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%ortal and 'rc&es%ortal and 'rc&es
rches, which can take a variety of forms, are efficientstructures for long span roofs.
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Masted StructuresMasted Structures The concept of 2asted Structures is not new, but they have only
recently become popular as a means of providing lightweight
structures for general use.
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(mbrella Structures(mbrella Structures The final option for consideration is the umbrella or tree structures
in which the roof cantilevers from a central column and can be
repeated and >oined to other similar assemblies at each or any side
to form a continuous structures
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"able Structures"able Structures 7ables $ Aood resistance in tension, but no strength in compression
Tent# cable structure consisting of waterproofing membrane supported
by ropes or cables and posts
7able must be maintained in tension by pre@stressing in order to
avoid large vibrations under wind forces and avoid collapse
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"ables # )oof Structures"ables # )oof Structures 7ables in a cable $ supported roof
must be maintained in tension
easily achieved if the roof issaddle@shaped
Example:Example: *yperbolic paraboloid
with curvatures in opposite sense
in directions at right angleso 7ables hung in direction &;
o second set of cables placed
over them, parallel to direction
7 and put to tensiono 7ables from the second set press
down on those from the first one.
:utting them into tension as well #
"ully$tensioned network
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Example: (ne of the first doubly
curved saddle@shaped cable
supported roof was the ;orton
rena in
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"ables# Suspension Bridge"ables# Suspension Bridge Suspension &ridges#The simple design of early bridges#
7ables ) catenaries+
%ight deck
*angers suspending the deck on catenaries
%ack of stability in high winds
Gery flexible under concentrated loads, as the form of the cablewill adapt to loading form
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Example: 7apilano Suspension &ridge, 7anada.
7 ti
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7ontinue#
9mproved behavior under traffic and wind loads#
Stiffening trusses at the level of the deck that distributes
concentrated loads over greater lengths
lternatively# restrain vertical movement of the catenaries by
inclined cables attached to the top of the towers or below the deck
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Example:Example: The kashi@Haikyo &ridge, ?apan# 0DD0m spanThe kashi@Haikyo &ridge, ?apan# 0DD0m span
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Example: Aolden Aate &ridge, 7alifornia, 3S# 0I6m span
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Example: &rooklyn &ridge, 3S ) The largest from 0IIF until0D6F+# I/m span
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Famous Collapse:
Tacoma Carrows &ridge, 3S, collapsed on Covember E, 0D6due to wind@induced vibrations. 9t had been open for traffic for a
few months only before collapsing.
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"ables-Stayed Bridge"ables-Stayed Bridge cables@stayed &ridge consists of one or more piers, with cables
supporting the bridge deck
&asic idea# reduce the span of the beam )deck+ several times
compared to the clear span between the piers
Steel cable@stayed &ridges are regarded as the most economical
bridge design for the spans ranging between 66m and 66m
Shorter span# truss or box girder bridges
%arger spans# suspension bridges
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Example:
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Example: The 2illau Giaduct, "rance. %ongest span# Fm. Totallength# /6m.