steel sections & metal truss system

7/23/2019 Steel Sections & Metal Truss System

1/8

SECTIONS &

METAL TRUSS

SYSTEM

Submitted By:-

Azhar

Ayyub


2/8

TRUSSESINTRO"UCTION

Trusses are triangular frame works in which the members are subjected toessentially axial forces due to externally applied load. They may be plane

trusses [Fig. 1(a)! wherein the external load and the members lie in thesame plane or space trusses [Fig. 1(b)! in which members are oriented inthree dimensions in space and loads may also act in any direction.

Trusses are fre"uently used to span long lengths in the place of solid webgirders and such trusses are also referred to as lattice girders.

Trusses are used in roofs of single storey industrial buildings! long span#oors and roofs of multistory buildings! to resist gra$ity loads [Figs. 1(a)and 1(b). Trusses are also used in multi%storey buildings and walls andhori&ontal planes of industrial buildings to resist lateral loads and gi$elateral stability [Figs. 1(c) and 1(d). Trusses are used in long span bridgesto carry gra$ity loads and lateral loads [Fig. 1(e).


3/8

TRUSS MEMBERSThe members of trusses are made of either rolled steel sections or built%upsectionsdepending upon the span length! intensity of loading! etc. 'olled steel

angles! tee sections! hollow circular and rectangular structural tubes areused in the case of roof trusses in industrial buildings [Fig. (a). n longspan roof trusses and short span bridges hea$ier rolled steel sections!such as channels! sections are used [Fig. (b). *embers built%up using sections! channels! angles and plates are used in the case of long spanbridge trusses [Fig. (c)


4/8

TY#ES O$ TRUSSES


5/8

CON$I%URATION O$ TRUSSES#ithed R' Tru((e(*ost common types of roof trusses are pitched roof trusseswherein the top chord is pro$ided with a slope in order to facilitate

natural drainage of rainwater and clearance of dust+snowaccumulation. These trusses ha$e a greater depth at the mid%span. ,ue to this e$en though the o$erall bending e-ect is largerat mid%span! the chord member and web member stresses aresmaller closer to the mid%span and larger closer to the supports.

The typical span to maximum depth ratios of pitched roof trussesare in the range of to /! the larger ratio being economical inlonger spans. 0itched roof trusses may ha$e di-erentcongurations. n 0ratt trusses [Fig. 2(a) web members arearranged in such a way that under gra$ity load the longerdiagonal members are under tension and the shorter $erticalmembers experience compression. This allows for e3cient design!since the short members are under compression. 4owe$er! thewind uplift may cause re$ersal of stresses in these members andnullify this benet. The con$erse of the 0ratt is the 4owe truss[Fig. 2(b). This is commonly used in light roong so that the

longer diagonals experience tension under re$ersal of stresses


6/8

CON$I%URATION O$ TRUSSES


7/8

CON$I%URATION O$ TRUSSESTra)ezida* Tru((e(n case of $ery long span length pitched roof! trusses ha$ing trape&oidalconguration! with depth at the ends are used [Fig. (a). Thisconguration reduces the axial forces in the chord members adjacent tothe supports. The secondary bending e-ects in these members are alsoreduced. The trape&oidal congurations [Fig. (b) ha$ing the slopingbottom chord can be economical in $ery long span trusses (spans 5 67m)! since they tend to reduce the web member length and the chord

members tend to ha$e nearly constant forces o$er the span length. t hasbeen found that bottom chord slope e"ual to nearly half as much as therafter slope tends to gi$e close to optimum design.


8/8

CONNECTIONS*embers of trusses can be joined by ri$eting! bolting or welding. ,ue toin$ol$edprocedure and highly skilled labour re"uirement! ri$eting is not common

these days!except in some railway bridges in ndia. n railway bridges ri$eting may beused due to fatigue considerations. 8$en in such bridges! due to recentde$elopments! high strength friction grip (49F:) bolting and welding ha$ebecome more common. 9horter span trusses are usually fabricated inshops and can be completely welded and transported to site as one unit.

;onger span trusses can be prefabricated in segments by welding in shop.These segments can be assembled by bolting or welding at site. Thisresults in a much better "uality of the fabricated structure. 4owe$er! thehigher cost of shop fabrication due to excise duty in contrast to lower eldlabour cost fre"uently fa$our eld fabrication in ndia.

steel sections & metal truss system

Documents