Structural Steel Design 2

8/16/2019 Structural Steel Design 2

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Prepared by: Eng. Chamil DumindaMahagamage

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Introduction to Eurocodes

The Eurocodes are a family of ten European codes of practice for the

design of building and civil engineering structures in concrete, steel,timber and masonry, amongst other materials

!tructural Eurocodes


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E" 1##0, the head Eurocode, is the $orld%s &rst material independentdesign code and provides guidance on determining the design value ofactions and combination of actions, including partial safety factors for

actions E" 1##1 provides characteristic values of actions needed fordesign'n order to produce documents $hich are (a) concise, (b) describe theoverall aims of design and (c) provide speci&c guidance as to ho$these aims can be achieved in practice, the material in the Eurocodesis divided into *rinciples% and +pplication rules%

*rinciples comprise general statements, de&nitions, reuirements andmodels for $hich no alternative is permitted *rinciples are indicatedby the letter * after the clause number The +pplication rules aregenerally recognised rules $hich follo$ the statements and satisfy thereuirements given in the principles The absence of the letter * afterthe clause number indicates an +pplication rule The use of alternative

application rules to those recommended in the Eurocode is permittedprovided it can be sho$n that the alternatives are at least euivalentand do not adversely a-ect other design reuirements 't is $orthnoting, ho$ever, that if an alternative +pplication rule is used theresulting design $ill not be deemed Eurocode compliant*ossible di-erences in construction material/products and design and

construction practices, and regional di-erences in climatic conditions,e $ind and sno$ loadin has meant that some arameters e


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.haracteristic +ctions(oads)

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Prepared by: Eng. Chamil Duminda Mahagamage B.Sc.Eng (Hons), C Eng,

*ermanent +ctions () 3ariable +ctions (4)

nclude sel" #eigh$, allarchi$ec$uralcomponen$s such ase%$erior cladding , par$i$ions and ceilings.E&uipmen$ and s$a$icmachinery and all permanen$ '%$ures.

eigh$s o"occupan$s, "urni$ure

or machinery. he pressure o" #ind,

$he #eigh$ o" sno#,and o" re$ained

ear$h or #a$er, and$he "orces caused by

$hermal e%pansionor shrin*age o" $he

concre$e.

efer ! E" 1##17 E.1


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8esign values ofactions

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'n general, the design value of an action is obtained by multiplying

the representative value by the appropriate partial safety factor foractions

The ma:imum values of partial safety factors for permanent andvariable actions recommended in E.1 are 15 and 15 respectively

The comparable values in ! ;110 are 19 and 16

't can also be seen that the partial safety factors for actions dependon a number of other aspects including the category of limit stateas $ell as the e-ect of the action on the design situation underconsideration


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5


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Design of steel structures


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Symbolsefer clause 16 of E.

Member axes ( Cl. 1.6.7, EC!

"aterally unrestrained beams


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#asis of designie ! 5#50, E. is based on the limit state method and for designpurposes principally considers t$o categories of limit statesA ultimate

and serviceability + separate (third) category of durability is alsomentioned in clause 9 of E. $hich covers the limit states ofcorrosion, mechanical $ear and fatigue

The ultimate limit states (>!) are those associated $ith collapse, or$ith other forms of structural failure $hich may endanger the safety ofpeople $hile serviceability limit states (!!) concern states beyond

$hich speci&ed service criteria, for e:ample the functioning of thestructure or member, the comfort of people and appearance of thestructure, are no longer met (clauses and 9 of E" 1##0)

$ominal strengt%s (Cl. .&! The Table belo$ sho$s the steel grades and associated nominal values

of yield strength and ultimate tensile strength for hot rolled steelsections


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10


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'artial factors, m (Cl 6.1, EC!

3alues of partial factor applied to characteristic values of resistancesare given in clause 61 of E. The factor m assumes di-erent values

depending on the type of resistance being veri&ed as indicated belo$

resistance of cross section BC0 D 100

resistance of member to instability BC1 D 100

resistance of cross7section to fracture BC2 D 125

Material coe)cients ( Cl. .&.*, EC!Codulus of elasticity (E) D 210 000 "/mm2

!hear modulus () D E/2(1F) G ;1 000

"/mm2

*oisson%s ratio in elastic stage (F) D 0coeHcient of linear thermal e:pansion D 12 : 1076 ? 71 (for TI

100 0.)8ensity (J) D @;50 g/m


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Classi+cation of crosssections (Cl *.*, EC!.lass 1 cross7sectionsA plastic% in ! 5#50.lass 2 cross7sectionsA compact% in ! 5#50

.lass cross7sectionsA semi7compact% in ! 5#50.lass 9 cross7sectionsA slender% in ! 5#50

.lassi&cation of a cross section depends upon the proportions of eachof its compression elements The highest (least favourable) classnumber should be uoted for particular section


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1


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19


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15


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16


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1@


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esistance of the $eb to transverse forces (.l 6, E.75)E. 75 distinguishes bet$een t$o types of forces applied through aKange to the $ebA

(1) Lorces resisted by shear in the $eb (loading types (a) and(c))(2) Lorces transferred through the $eb directly to other Kange

(loading type (b))

Lor loading types (a) and (c) the $eb is liely to fail as a result of(i) crushing of the $eb close to the Kange accompanied byyielding of the Kange, the combined e-ect sometimes referred to as $ebcrushing

(ii) localised bucling and crushing of the $eb beneath theKange, the combined e-ect sometimes referred to as $eb crippling


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Lor loading type (b) the $eb is liely to fail as a result of(i) $eb crushing(ii) bucling of the $eb over most of the depth of the member

*rovided that the compression Kange is adeuately restrained in thelateral direction, the design resistance of $ebs of rolled beams undertransverse forces can be determined in accordance to the clause 6 of E.

758esign resistance of $ebs to local bucling


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'n $hich D is the reduction factor due to local bucling calculated asdiscussed belo$

D is the e-ective loaded length, appropriate to the length ofsti- bearing !s +ccording to clause 6 of E. 75, !s should be taen as

the distance over $hich the applied load is e-ectively distributed at aslope of 1A1 , but !s I h$

+educ$ion "ac$or

+ccording to clause 69 ,

Lor $ebs $ithout longitudinal sti-eners L is obtained from Lig 61 E.75

and ly is obtained as follo$s


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Eec$i-e loaded leng$h+ccording to clause 65 for loading types (a) and (b) the e-ective loadedlength is given by

Lor loading type (c) ly is taen as the smallest value obtained from

follo$ing t$o euations


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n$erac$ion be$#een shear "orce and bending momen$ +ccording to clause @ of E.75, $here the $eb is also subMect to bendingthe combined e-ect should satisfy the follo$ing


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ateral Torsional ucling of eams (.l 62, E.)'n order to prevent the possibility of a beam failure due to lateraltorsional bucling, the designer needs to ensure that the bucling

resistance moment, Cb,d e:ceeds the design moment, CEd CEd/Cb,d I 10

Buc*ling ac$or / ! / ! is the reduction factor for lateral torsional bucling T$o methods of

calculating / ! are provided in E. as follo$s

(1)eneral case mentioned in clause 622 is applicable to all membersof constant cross7section

(2)The approach detailed in clause 62 is applicable to rolled sectionsonly


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(1)eneral case (cl 622 E.)


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(2) Lor rolled sections (cl 62 E.)

'n order to tae account of thebending moment curve bet$eenpoints of lateral restraint thereduction factor NT may be

modi&ed as,


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Prepared by: Eng. Chamil Duminda Mahagamage2;

Exam-le &

.hec the suitability of 56 : 1@1 : 51 g/m > section in !2@5 steelloaded by uniformly distributed loading g D ;"/m and D 6"/m as

sho$n belo$ +ssume that the beam is laterally and torsionally restrainedonly at the supports and that the beam sits on 100mm bearings at eachend 'gnore self $eight of beam

Exam-le epeat E:ample 02, but this time assume that the beam is laterally andtorsionally restrained at mid7span and at the supports

Exam-le 1 The &gure sho$s a simply supported beam and cantilever $ith uniformlydistributed loads applied to it >sing grade !2@5 steel and assuming fulllateral restraint, select and chec a suitable beam section

Structural Steel Design 2

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Transcript of Structural Steel Design 2