Industrial Const

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Transcript of Industrial Const

  • 8/16/2019 Industrial Const




  • 8/16/2019 Industrial Const




     Industrial construction consist of the buildings including terrace factories or worsho!s" detached factories" warehouse" factor# canteens" $arets" hawer centers" s!orts halls" industrial training centers" etc%arecharacteri&ed

     b# large clear o!en s!aces under light roof structures%


    The usual for$s of roof structures are triangulated truss frames, lattice

     girders and solid web portal frames and their choice de!ends considerabl#

    on the e'tent of clear floor s!ace%   Truss frames or lattice girders are usuall# $ore econo$ical in ter$s of

    $aterial re(uired%    Portal frames are chea!er to fabricate faster in construction and ha)e

    ad)antages in aesthetic" ease of $aintenance and added headroo$" unobstructed b# ties or bracing $e$bers%

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    Portal frames

     A portal frame is distinguised !" te rigid #onne#tion of te rafters to te $osts of te frame so tat under load moments are distri!uted troug te rafter and te $ost% 

    T"$es of $ortal frames:

    *  Reinforced concrete !ortal fra$es

    *  Steel !ortal fra$es

    *  Ti$ber !ortal fra$es

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     Steel $ortal frames:

     Short + $ediu$ s!an fra$es

      Long s!an fra$es

     Short and $ediu$ s!an fra$es the

    a!e' or ridge" where the rafters

    connect" is generall# $ade as an on,

    site" rigid bolted connection for

    con)enience in trans!orting half

     !ortal fra$es %

    Short,s!an !ortal fra$es $a# be fabricated off site as one fra$e% Mediu$,s!an

     !ortal fra$es are generall# fabricated in two hal)es for ease of trans!ort and are

    asse$bled on site with bolted connections of the rafters at the ridge" with high

    strength friction gri! bolts%

    Bolted conne


    Bolted connection

    Short,s!an !ortal fra$e

    Rafters & posts from same

    Section of steel beam 

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     In long s!an steel !ortal fra$es the

     !osts and lowest length of the rafters"

    towards the nee" $a# often be fab

      ricated fro$ cut and welded I,sections   so that the !ost section and !art of the

      rafter is wider at the nee than at the

      base and ridge of the rafter% 

    Long%s$an $ortal frames

     Long s!an steel !ortal fra$es ha)e

    the connection of the rafters to the !osts

    at the nee" haunched to $ae the

    connection dee!er than the $ain rafter section for additional stiffness%

      The haunched connection of the

    rafters to the !osts can be fabricated

    either b# welding a cut I,section to the

    underside of the rafter" as illustrated in

    gi)en -ig" or b# cutting and bending

    the botto$ flange of the rafter and

    welding in a steel gusset !late%

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    The .unction of the rafters at the

    ridge is often stiffened b# welding

    cut I,section to the underside of the

    rafters at the bolted site connection 

     Steel !ortal fra$es $a# be fi'ed to or  !inned to bases to foundations% -or short s!an !ortal fra$es" where there is co$!arati)el# little s!read at the nee or haunch" a fi'ed base is often used% It will be seen fro$ that the steel

     base !late" which is welded through gusset !lates to the !ost of the !ortal fra$e" is set le)el on a bed of ce$ent grout on the concrete !ad foundation and is secured b# four holding,down

     bolts set or cast into the concretefoundation%

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     A !inned base is $ade b# sitting the

     !ortal base !late on a s$all steel

     !acing on to a se!arate base !late

     bearing on the concrete foundation%

     /ortal fra$es with a s!an of u! to 01$

    are defined as short s!an" fra$es with a

    s!an of 02$ to 31$ as $ediu$ s!an and

    fra$es with a s!an of 32$ to 24$ as

    long s!an%

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    *Co$binations of slender ti$ber sections glued and nailed together" are used in

     !ortal fra$es for $ediu$, and long,s!an roofs for such buildings as churches"

    asse$bl# halls" s!orts halls and other single store# structures where the ti$ber

     !ortal fra$es are e'!osed for a!!earance sae%

      *The ad&antages of ti$ber as a structural $aterial in this for$ are its low self

    weight and the co$!arati)el# little $aintenance re(uired to !reser)e and $aintain its strength and a!!earance%

    *S"mmetri#al%$it# glued laminated tim!er $ortal : These !ortal fra$es are

    usuall# fabricated in two sections for ease of trans!ort and are bolted together at

    the ridge% These co$!arati)el# e'!ensi)e !ortal fra$es are s!aced fairl# widel# a!art to

    su!!ort ti$ber or steel !urlins which can be co)ered with an# of the sheet

    $aterials" slates or tiles% 


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    Light weight roof covering on

    225x50 timber purlins


    Cavity wall

    Span 14.5 m

    loor slab

    Shoes bolte! to concrete base

    Laminations taper 

    "0 !eg slope 20 !ia bolt

    oot of portal frame insi!e cast iron shoe

    *The la$inations of ti$ber

    fro$ which the !ortal is

    $ade are arranged to ta!er in

     both the rafter and the !ost so that the de!th is greatest at

    the nee" where the fra$e

    tends to s!read under load"

    and slender at the a!e' or

    ridge and the foot of the !ost"where least section is

    re(uired for strength and


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     /re,cast reinforced concrete !ortal fra$es was su!!lied for the econo$ic

     benefit of re!etiti)e casting in standard $oulds and close control of $i'ing"

     !lacing and co$!action of concrete that is !ossible in factor# conditions%

     -or con)enience in casting" trans!ort and erection on site" !re,cast concrete  !ortal fra$es are generall# cast in two or $ore sections which are bolted

    together on site either at the !oint of contra fle'ure in rafters or at the .unction

    of !ost and rafter" or both%

  • 8/16/2019 Industrial Const


  • 8/16/2019 Industrial Const


      The !oint of #ontrafle)ure is that !osition along the rafters

    where negati)e or u!ward bending changes to !ositi)e ordownward bending% At this !oint the $e$ber is !resu$ed to be

    suffering no bending stresses so that structurall# this is the

    soundest !oint to $ae a connection%

    Concrete !ortal fra$es are usuall# s!aced at fro$ 4.5 to

    6.0m a!art to su!!ort !re,cast reinforced concrete !urlins and

    sheeting rails" cast in lengths to s!an between fra$es and

    hooked or bolted   to the rafters and !osts% As an alternati)e

    cold,for$ed steel 5ed !urlins and sheeting rails $a# be used for the fi'ing of !rofiled steel sheeting% 

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      The bases of concrete portal frames are placed in

    mortices cast in concrete pad or strip foundations and

    routed in position!

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    #etails ot a two$bay

    symmetrical pitch concrete

    portal frame. 

    It will be seen that the

    rafter, which is cast as

    one unit, is bolted to the

     posts at the point of


     A single post supports

    the rafter of the frames

    below the valley in the

    roof and these posts

    are shaped to receive

    a pre-cast reinforced

    concrete valley

    gutter, bolted to the

    rafters, which is laid

    without fall to rainwater

     pipes and lined with felt.

  • 8/16/2019 Industrial Const


      The spacin of the internal columns belo" #alle$s ma$ be

    increased b$ the use of a pre%cast concrete #alle$ beam to

    support e#er$ other internal roof frame! The bul&$ #alle$ beam

    "ill obstruct clear head room and add considerabl$ to the

    cost of the structure! The disad#antae of this multiba$form of concrete portal frame is the number of comparati#el$

    bul&$ internal columns obstructin a free "or&in area!

      %he pre$cast reinforce! concrete purlins are usually of angle section with stiffening ribs an! cast in lengths to span between portal frames. %he purlins are fixe! by

    loops protru!ing from their en!s which fit over an! are bolte! to stu!s cast in the rafters& with the  'oint being complete! with in$situ$ cast cement an! san! mortar.

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    Corrugate! fibre cement sheeting is hoo( bolte! to

    the concrete purlins over an insulating lining lai!

    over the purlins. )s an alternative& profile! steel

    sheeting with a