Lecture 5 s.s.iii Design of Steel Structures - Faculty of Civil Engineering Iaşi

COLUMNS FOR THE INDUSTRIAL BUILDINGS
C.Teleman_S.S.III_Lecture5
1
STEEL INDUSTRIAL BUILDINGS

• SPECIFIC FEATURES
 The cross section of the columns
• - constant or variable;
• - build-up or compound from different elements interconnected (battened or laced);
• - with constant section on the height of the column or variable on the height of the
column (tappered) or in steps of variation (stepped columns).
 Steel elements (profiles)
• - build-up cross sections: thick plate welded (web and flanges) or hot-rolled profiles
or build-up sections welded together to increase the stiffness of the cross section;
• -laced cross sections: hot-rolled profiles or build-up cross sections and the lace
system is obtained from angles welded or bolted at the joints;
- battened cross sections.
 Stiffening elements
- ribs and stiffening diaphragms: longitudinal and transversal stiffening ribs and
diaphragms welded to the hot-rolled sections
COLUMNSFORTHEINDUSTRIALBUILDINGS
2

Fig.1.Columnsforindustrialbuildingswithconstantcrosssectionsonthe
height:
1),2)-builduporcompoundfromhot-rolledsectionsformarginaland
centralcolumns;3)-compoundsectionfromhot-rolledshapes,laced;
4)-compoundsection,battened,axiallyloaded;
5)-compoundsection,laced,axiallyloaded
Fig. 2. Columns for industrial buildings with variable sections on the height:
6)…9)-variation in two steps; 10)…13) continuous variation on the height
TYPES OF SECTIONS USED FOR COLUMNS WITH HEAVY LOADS
3

• capital of the column; lateral cross-pieces are welded to the profiles and
supplementary cross-piece should also be welded as intermediate web.
• brackets and the supports: the crane girder is connected to the column
transferring the forces in all exploitation conditions.
02111 M
yf
tbtL
N



a)- girder is continuous  the corrugated steel sheet of the platform must be welded to
the diaphragms of the column, important negative bending moments and sometimes
uneven negative reactions being expected.
b)- girder is simply supported  the corrugated steel sheet is not welded to the column
because at the top flange level the translations due to the rotation of the girder on
the support must be allowed.
Capital of the columns: transfer of loads through thick plates, welded to the capital and the bearing surface
4

SOLUTIONSFORTHE SUPPORTS OF CRANEGIRDER ON STEPPEDCOLUMN
•Details of supports for the continuous
crane girders
Details of simply supported crane girders
5

ELEMENTS FORTHE DESIGNOFCOLUMNS
Brackets on columns
a) The stress is transferred to the cross section of the rib from the flanges of the bracket.
b) M =Re - moment induced by the eccentricity of application of the reaction from the crane
girder
c) Fatigue checking is necessary for the joint considering that a single crane acts on the
girder.
d) horizontal diaphragm needs strengthening with vertical stiffeners
W
MA
H
AA
t
tt



)2(1
21
;
 
 
h
eR
h
heR
RNNN
h
eR
R
h
heR
RNNN
MR
MR








2
2
2
2
2
1
 2
01
3
4
Mwu
Myt
ww
f
fA
la





6

THEJOINTS BETWEENTHETOP ANDTHEBOTTOMPART OFTHECOLUMN
M
N M
h
a T
N M
h
tr
I
tr    ( ) ;
2 2
0
00
22
3
;
3
;
M
y
ech
M
y
trtr
tr
M
y
tr
tr
f
f
ht
Tf
W
M











N
N M
h
Rtr   
2
trtr lh  6,0...5,0min,
M R c T Rtr
II II
tr
II II
  ;
7

• THE TOP PART IS PERFORATED IN THE WEB
M
T h
N
M
h
N
0 0
02 2 2
   ;
00
32
;
0
00
M
y
iiM
y f
th
Tf
A
N
W
M








0
22
3
M
y
ech
f

 ,
8

STIFFENING ELEMENTS INTHE CROSSSECTIONANDINTHECAPITALAREA
Ribs and diaphragms for stiffening the columns
sections and prevent from torsion effects
Capital for the columns of industrial buildings
(central columns), details of supporting the
rafter (girder or truss)
9

BASEOFTHECOLUMNS WITHCOMPOUNDSECTIONS
22
3
;
3
21
Mw
u
str
Mw
u
str
f
AH
f
AH
 



20
3
;
2
4
4 Mw
u
s
M
y f
AZ
f
A
Z
 


00
3
;
M
y
trM
y
x
f
th
Zf
W
eZ










2
3
2
2
2
1max
Mw
uf




2
2
32
;
3
2
,
1
Mw
u
trs
Mw
u
sx
f
ha
Z
f
W
eZ












00 132
;;
M
ytr
M
ytr
tr
tr
f
A
Hf
AA
H
h
eZ
H



 




10
Gusseted base plates

11
COLUMN BASES
Hinged bases
The base plate is fixed to the foundation with two hold down bolts. Both shear and axial tension forces
(when present) are transferred to the bolts . Compression is transferred to the base plate.
Fixed bases
The moment resistant bases have hold down bolts also and the base plate may be stiffened with
outstanding gussets. The surface of the base plate is imposed by the necessity of limiting the pressure
on the foundation to the resistance of the concrete.
Generally, the hold down bolts take no horizontal forces, but only axial tension

12
Columns with gusseted base plates
Brittle fracture is avoided by using frames mounted on base plate in which holes are drilled
for the anchor bolts. The bolts have a long shank of minimum 15dia for a free deformation
being appropriate column bases subjected to seismic action.
COLUMN BASES

C.Teleman_S.S.III_Lecture 5 13
HOLD DOWN BOLTS
Tension in the shank is taken entirely by bond between the bolt and the concrete.
When there is not enough depth to insure the bonding, the shank is shortened
and processed in different shapes to enlarge friction forces or different steel
profiles or plates are welded at the bottom of the shank
Normal length of the shank Shorten shank with welded plate for distribution
of friction forces
Threaded
part
Threaded
part
Foundation
level
Foundation
level

14
DESIGN RESISTANCE OF THE HOLD DOWN BOLT
IN BENDING MOMENT RESISTANCE FOUNDATIONS
Bond capacity of the hold down bolt
- anchor length of the bolt from the inferior face of the base plate
- diameter of the bolt
- bond resistance of the concrete for profiled round bars
For round bars with diameter under 33 mm
For round bars with diameters of more than 33 mm
2.25 – coefficient that takes into account the fact that the bolt is not profiled
Design tension resistance of the hold down bolt

15
For minimum two bolts that take tension the force transmitted is:
and must comply with the condition of resistance of the bolts in tension:
2
N
th
M
F Ed
fcc
Ed
Ed,T 


)Fmax(F2 Ed,TRd,ancor,t 
2M
sub
Rd,ancor,t
Af9.0
F


For one single row of bolts (2, externally to the column flange) :
8.1
)Fmax(
F Ed,T
Rd,anc,t 
 
ub
Ed,T
f
Fmax
1.1d 
For two rows of bolts (2, externally and internally to the column flange) :
6.3
)Fmax(
F Ed,T
Rd,anc,t 
 
ub
Ed,T
f
Fmax
8.0d 
Length of the bolt in the shank:
bd
Ed
b
fd
F
l




16
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO SHEAR
1. Transmission of the shear force through friction between the base plate and
the grout or the in-filling concrete
cf,d - friction coefficient between the base plate and the grout (=0.20 for sand and
cement grout);
Nc,Ed – design value of compression in the column
2. Transmission of the shear force through shear in the shank of anchor bolts
and friction between the base plate and the grout
Bolts shear situation is provided in the design by SR EN 1993-1-8, considering a
limited lateral translation of the connection under horizontal forces. As the holes
for bolts in the base plate have big diameters, bearing of the whole row of bolts
does not govern. The verification addresses to small loading and cases when
compression only is under the base plate.
For post installed anchors the holes in the base plate are large; washers placed
under nuts are welded providing the adequate shear resistance of the bolts.
Cast-in place anchor bolts need normal sized holes in the base plate and the shank
must in this case be designed to shear.

17
Resistance to shear of the connection is then designed as the sum between the friction
resistance of the base plate and shear of the anchor bolts:
Ff,Rd – friction resistance of the base plate to the grout surface;
Fvb,Rd – shear resistance of the anchor bolt;
nb – number of bolts in shear
Resistance to shear of the bolt is:
- bearing resistance;
- shear resistance
Final verification to external loading

18
3. Transmission of the shear force through shear lug
Hot rolled I or H sections are used, also angles, in case of lower level of shear force.
Certain design conditions are imposed for the shear lug preventing it from pulling of
from foundation:
- height of the shear lug: hn0.4hc
- length of the shear lug: 60 mm  deff,n 1.5hn
Flanges of the I section are subjected to a small local bending and the slenderness is
thus limited for the flange: bfn/tfn 20. (Exceptions from verification: HEA 260, 280, 300.

19
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO
COMBINED AXIAL FORCE AND MOMENT
Design according to EN 1993-1-8 release the concept of method of verification to
failure of the individual components of the connection.
Strength verifications address to possible risk areas in exploitation due to the
development of the failure mechanisms of yield: cross section in the bottom part of
the column, base plate and anchor bolts.
Failure mechanism: a- plastic hinge in the column; b- plastic hinge in the base plate; c- plastic
hinge in the anchor bolt under the base plate; d- plastic hinge in the anchor bolt above the base
plate
a b
Yield length in
the bolt
Yieldlengthinthebolt

20
RESISTANCE OF THE WHOLE CONNECTION IN FOUNDATION TO
COMBINED AXIAL FORCE AND MOMENT
STAGES FOR DESIGN
I. Identify the components of the connection
II. Evaluate the resistance and stiffness characteristics for every component
III. Determine the global characteristics of strength and stiffness
I Components
The T stub in tension – bolts in tension, part of the base plate in bending and tensioned
flange of the column
The T stub in compression – grout and concrete in compression ,a part of the base plate in
compression and the compressed flange of the column
Note:
If bending moment is dominant at the base plate, the contribution of the web in compression
and the afferent base plate is not relevant. This may become important when the
compression is dominant
Components of the
foundations of columns:
hinged and fixed

22
DESIGN RESISTANCE OF THE CONNECTION
TO AXIAL FORCES AND BENDING MOMENTS
The capacity to resist to tension of the area in left side of the connection FT,l,Rd is
determined considering the following individual resistances of the components :
The capacity to resist to tension of the area in right side of the connection FT,r,Rd is
determined considering the following individual resistances of the components :
The capacity to resist to compression of the area in left side of the connection FC,l,Rd is
determined considering the following individual resistances of the components:
The capacity to resist to compression of the area in right side of the connection FC,r,Rd is
determined considering the following individual resistances of the components:
where:
resistance of the column web in tension under the left/right flange of the column
resistance of the base plate in bending under the left/right flange of the column
resistance of the left/right flange of the column, web in compression
resistance of the concrete in foundation under the left/right flange of the column

23
T STUB SUBJECTED TO TENSION
The effective length of a T-stub subjected to tension is determined on the basis of
the value of the resistance of the flange of this T- stub which must be at least equal
with the resistance of the basic components which are substituted by it.

24
Length of an equivalent T-stub in tension with one row of bolts
on the interior side and one on the exterior
The following must be analyzed:
- Failure mode of the T-stub;
- Failure mode of the base plate that is part of the tensioned T –stub connection;
- Distances between the anchor bolts axes.
Failure modes of an equivalent T-stub are:
a. mode 1: whole plastic mechanism - plastic bending of the base plate along the anchor
bolts line;
b. mode 2: partial plastic mechanism because of premature failure of a bolt which stops
the development of plastic stresses in the connection;
c. mode 3: braking of the bolts in tension , the connected plates acting rigid;
d. mode 4: plastic failure of the web of the T-stub in tension;
e. mode 1-2: plastic failure of the flange of the tensioned T-stub and important
deformation of the bolts that cancels the prying forces effects

25
T STUB SUBJECTED TO COMPRESSION
The components modeled by the T-stub in compression are:
-base plate in bending due to the pressure from the reaction in the foundation;
-concrete and/or grout;
The verification of the compressed part of the column (flange and web) is
covered by the verifications of the column in the cross section at the base part.
Simplifications in the verification stages of the compressed part of the column and foundation
The dimensions of the T-stub in compression depend on:
- Resistance to local crush;
- In plan dimensions of the column;
- Base plate dimensions;
- Resistance to bending of the base plate

26
Equivalent T-stub in compression: area in case of short projection; b- area in case of long projection
T STUB SUBJECTED TO COMPRESSION
T-stub in compression: 1-one row of anchor bolts; 2- surface in compression of the equivalent T-stub

27
Resistance to compression of a T stub FC,Rd is determined with:
-bef and lef are the effective width and effective length of the T stub;
- fjd – design resistance of the joint to pressure
-jd - coefficient of the material in the joint, equal with 2/3 if the characteristic
resistance is not exceeding 1/5 of the resistance of the concrete in the
foundation and the thickness of the layer is not exceeding 1/5 from the
minimum width of the base plate.
If the thickness of the grout is not exceeding 50 mm, the characteristic
resistance of the concrete must be at least equal to the resistance of the
concrete in the foundation;
-FRdu - design resistance of the concrete to point load (EN 1992)
and:

28
The thickness of the base plate is determined with the help of the I mode of failure
of a T stub (total plastic mechanism).
If one single row of anchor bolts are placed outside the flange of the column with
H section then:
If there are four bolts placed in two rows inside and outside the H section of the
column, then:
Resistance of the base plate Nj,Rd subjected to centric compression may be
determined by summarizing the individual resistance FC,Rd of the three T stubs,
which are not overlapping
The three T sub elements obtained from sizing the base plate to axial compression

29
a.- hinged connection; b,c – moment resistant connection
The anchor bolts may be placed in rigid framework of steel plate with a hole greater
than the diameter of the bolt. In this case the bolt and the framework must be placed
inside the reinforcement of the concrete

30
Cast in place anchor bolts:
1-nut; 2- washer or drilled steel
plate; 3-leveling nuts
Detail of base of column provided
with shear lug according to NP-
112-2004 (rev 20011):
1- column, 2-shear lug, 3- anchor
bolt, 4-washer, leveling nut, 6-
concrete filling about 50 mm thick,
7- plastic pipe

Lecture 5 s.s.iii Design of Steel Structures - Faculty of Civil Engineering Iaşi

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Lecture 5 s.s.iii Design of Steel Structures - Faculty of Civil Engineering Iaşi