steel design Flashcards
shape factors of sections
hollow circle - 1.27
circular plate - 1.7
diamond section- 2
triangular section- 2.34
Center of gravity of semi circles
semi circular line = 2R /pi
semi circular plate =4R/3pi
hemisphere = 3R/8
ultimate plastic load for propped cantiliver
11.656 Mp / L^2
hinge at x= 0.414 L
maximum permissible deflection in SSB
table 6 is 800:2007
elements succeptible to cracking = L/300
not succeptible to cracking = L /240
for cantiliver = L/150 and L/120
limiting grip length in lap joint
Lg < 5d
effect of bending stress can be ignored in above condition
8d >Lg > 5d , reduction factor required
Lg > 8d , redesign required
minimum pitch, guage , end distance
pitch/guage = 2.5 bolt
end = 1.5 hole
= 1.7 hole (for hand cut element)
maximum edge , pitch distance in welds and bolts
end distance = 12 t.e , e = sqrt(250/fy)
comp pitch distance = 12t or 200 mm
tension pitch distance = 16t or 200 mm
in case of staggered = 1.5* distances
maximum pitch of tack bolt
for plates, flats = 32 t or 300 mm
if exposed to weather 16t or 200 mm
for compression = 600mm or λ1 <40 , 0.6λ
for tension member = 1000 mm
bolt and bolt hole
dia = 6.06 sqrt(t) Unwins formula nominal dia : hole clearence 12 ~ 14 mm : 1mm 16 ~ 24 mm : 2mm > 24 mm : 3mm
slot welding size limitation
width of slot > 25mm or 3.t
long joints, weld and bolt unbuttening effects
L > 150 throat
L > 15 bolt
slenderness ratio limits of steel members
λ < 180 , compression member
λ < 180 , tension member, but stress reverse due to
live load
λ < 250 , for wind earthquake loads
λ < 350 Tension member but reversal of stress due to wind load
λ < 400 , for tension members
net tearing area of staggered bolting
[ B -n.D +(S^2) /4g ] * t
lug angle design
minimum bolts at lug > 2 bolt number of bolts at locations n1 = Fconnect /Rv n2= 1.4* Fout /Rv n3= 1.2* Fout /Rv n2 interconnecting bolt must start in advance
design of bolted connection
- find dia of bolt = 6.04 *sqrt(t)
- find rivit value
- find no of bolts required
- arrangement of bolts
- width and thickness of plates
- efficiency of joint (if asked)
design of lacing
1. spacing of lacing
C /r.min <50 or 0.7*λ
2. dimension of lacing
t > L1 /40, or L1 /60
λl = K.L1 /r < 145 (K=0.7 for double lacing or welded )
3. Forces in Lacing
V= 2.5% of Pu
F = V/ N*sin()
4. Forces < strength compressive and tensile
T= 0.9fu Anet /1.25
T= Ag * fy /1.2
C= fcd* Ag (fcd depends on λl)
5. tie plate or batten plate
Dend > 2.B
> centroidal distance between main memberswidth of lacing bars
bolt dia mm - width of lacing bar 16 - 50 18 - 55 20- 60 22- 65
to prevent web crippling
A = a +2.5*h2
to prevent web buckling
find K.l /r =2.45d / tw
fcd *Ag > R
A= a + d (1:1 dispersion)
condition of plastic , compact and semi compact rolled I-section
b/tf < 9.4 e
d /tw < 84e
compact
b/tf < 10.5 e
d /tw < 105e
semi compact
b/tf < 15.7 e
d /tw < 126e
bolt grade 4.6
400 mpa strength
Kb in bearing of bolt
Kb =min [e/3d , p/3d -0.25, fub/fu, 1]
rivit hole size
d' = d+ 1.5 for d<25 d' = d + 2 for d>25
carbon content in mild steel
0.23%
characterstics of steel used as plasstic steel
fy < 450 Mpa
fu/fy > 1.2
εplastic > 1.15*εelastic
what is stainless steel made of
iron and chromium
minimum size of weld based on size of thicker plate
thicker plate min size of weld
<10 mm 3mm
11 ~ 20 mm 5mm
21~32 mm 6mm
>32mm 8mmmaximum size of weld
T - 1.5mm
0.75 T
reasons of flange buckling, web buckling, web crippling
Flange buckling - Bending compression
Web buckling - Diagonal compression
web crippling - Bearing stress
permissible deflections in gantry girder
span/500 manual operated
span/750 electrically operated
span/1000 capacity > 50t
use criteria of stiffners in Plate girders
d1/tw >90, verticle stiffners for web buckling
d1/tw > 200, horizontal stiffners at 0.2d from flange
d1/tw > 250, horizontal at N.A
d1/tw > 400, section redesign
end bearing stiffners Leff, area
Leff = 0.7L1
A = 4Aoutstand + 40twtw
designed as columns
so tight bearing
outstand Area of outstand leg
A2e= kA2
k = 3A1 /(3A1+A2)
Ae = A1 + k*A2 ,
0.875A in case of symmetric angle
for field rivets , permissible stresses are reduced by what percentage?
10%
The critical slope of a roof truss above which snow load need not be considered.
50 degree
slenderness ratio of bracing for hangers
160
if beams arent restrained by cleats at ends for torsion
Length increased by 20%
design wind speed factors k1, k2, k3
k1 = risk cofficient k2 = terrain, height , size factor k3 = topography factor
The depth of web of a plate girder usually varies between
1/8 to 1/12 of the span.
From serviceability requirement the web is considered to be unstiffened if the spacing of transverse stiffeners is greater than
3 times the web depth.
batten design properties
Column is divided into a minimum of three bays (i.e. minimum 4 number of battens required).
- Thickness of batten plate shall not be less than 1/50th the distance between outer most connecting line of rivets of welds.
- (i) Effective depth of intermediate battens
> 0.75 α
> 2 *b*g
{b = width of column component
α= spacing of C.G. of column}
(ii) Effective depth of end battens
> α
> 2*b
approximate are of web and flange contributing in strength of plate girder
Aeff = Aflange + (1/6)*Aweb
maximum spacing of purlins in asbestos roofing
1.4 m
Max Moment in continuous members like purlin
w.L^2 /10
Effective length of compression flanges depending on end conditions
Effective length of compression flanges depending on end conditions
ends of compression flange unrestrained = L
ends of compression flange partially restrained = 0.85L
ends of compression flange fully restrained = 0.7 L
cantilevers
-built in support, free at end = 0.85L
-built in support, restrained against torsion at end by continuous construction = 0.75L
-built in support, restrained against torsion at end by cross members over several beams = 0.5L
- continuous and unrestrained against torsion at support and free at end = 3L
- continuous and partially restrained against torsion at support and free at end = 2L
continuous and restrained against torsion at support and free at end = L
