Steel strucure lec # (17)

Prof. Dr. Zahid Ahmad Siddiqi
CONNECTIONS
• Connections are the devices used to join elements
of a structure together at a point such that forces
can be transferred between them safely.
• Connection design is more critical than the design
of members.
• The failure of connection usually means collapse
of a greater part or whole of the structure.
• In general, relatively more factor of safety is
provided in the design of connections.

• The rigid connection should provide
sufficient strength and ductility.
• The ductility is very useful for redistribution
of stresses and dissipation of extra energy in
case of earthquakes, etc.

TYPES OF CONNECTIONS
Based On Means Of Connection
A. Welded connections
B. Riveted connections
C. Bolted connections

Based On Forces To Be Transferred
A. Truss connections
B. Moment connections
– i) Fully rigid connections
– ii) Semi-rigid connections
C. Simple/shear connections
D. Splices
E. Brackets

Moment Connections
• Moment connections are also referred to as rigid,
continuous frame or FR connections.
• Knee joints are the typical example.
• They are assumed to be sufficiently rigid keeping
the original angles between members practically
unchanged after application of loads.
• Greater than 90 percent moment may be
transferred with respect to ideally rigid connection
besides the full transfer of shear and other forces.

• These connections are particularly useful
when continuity between the members of
the building frame is required to provide
more flexural resistance and to reduce
lateral deflection due to wind loads.
• Both the flanges and web of the member are
to be connected for this type of connection.
• End connections of restrained beams
girders, and trusses shall be designed for the
combined effect of forces resulting from
moment and shear induced by the rigidity of
the connections.

Semi-Rigid / Partially
Restrained Connections
• Type PR connections have rigidity less than 90
percent compared with ideally rigid connections.
• Although the relative rotation between the
joining members is not freely allowed, the
original angles between members may change
within certain limits.
• They transfer some percentage of moment less
than 90 percent and full shear between the
members.

• Semi-rigid connections provide rigidity in-
between fully restrained and simple
connections.
• Approximately 20 to 90 percent moment
compared with ideal rigid joint may be
transferred.
• End moments may develop in the beams and
the maximum beam moment may be
significantly reduced.
• Usually no advantage is taken of this
reduction and beams are designed as simply
supported because of various reasons.

• One of the reasons is the difficulty of structural
frame analysis for varying degrees of restraints at
the joints and unpredicted rotations.
• Further, LRFD Specification states that a
connection can only be considered as semi-rigid if
proper evidence is presented to prove that it is
capable of providing a certain end restraint.
• These are the commonly used types of
connections in practice because their performance
is exceptionally well under cyclic loads and
earthquake loadings.

Shear Connections
• Simple or shear connections have less than
20 percent rigidity.
• They are considerably flexible and the
beams become simply supported due to the
possibility of the large available rotation.
• Moment may not be transferred in larger
magnitudes with the requirement that the
shear force is fully transferred.

• In these connections, primarily the web is to
be connected because most of the shear
stresses are concentrated in it.
• Connections of beams, girders, or trusses
shall be designed as flexible joints to resist
only the reaction shears except otherwise
required.
• Flexible beam connections shall
accommodate end rotations of unrestrained
beams.

Bearing Joints
• There shall be sufficient connectors to hold
all parts of the section securely in place
when columns rest on bearing plates.
• All compression joints shall be designed to
provide resistance against uplift and tension
developed during the uplift load
combination.

SPLICES
These are used to extend the length of a
particular member.
The two sides of the member may have same or
different cross-sections.
Splice joint is a connection between two parts of
the same member whereas a regular joint is the
connection of more than one members of the
structure.

BRACKETS
Brackets are the connections used to transfer
torque besides other types of forces.
The term bracket is generally used for an extra
plate projecting out of the column and acting
like a seat for the beam.

Types of Joints Based On Placement
Of Parts To Be Joined
The types of joint depends on factors such as the
size and shape of the members coming into the
joint, the type of loading, the amount of joint area
available for welding, and the relative costs for
various types of welds.
Butt joints
The butt joint is used mainly to join the ends of flat
plates of the same or nearly the same thickness.
A gap or groove is left between abutting members,
which is later on filled with weld (Figure 8.1).

The principal advantage of this type of joint is to
eliminate the eccentricity developed in single lap
joints.
Groove filled with
weld
Bolted Butt
Joint
Welded Butt
Joint

Lap joints
The members are either overlapped with each
other or with some connecting plates like gusset
plates, splice plates, etc, as shown in Figure 8.2.
Eccentricity of load and hence moment may be
produced in these joints.
In welded lap joints, the minimum amount of lap is
to be five times the thickness of the thinner part
joined, but not less than 25 mm.

Welded Lap Joint Bolted Lap Joint
Advantages of Lap Joints
a. The plates of different thickness can easily
be joined such as in a truss connection (Figures
8.3 and 8.4).
b. Ease of Filling: Pieces being joined do not
require the preciseness in fabrication, as do the
other types of joints.

Lapped plate Lapped plate
Beam
bracket
Splice joint
Truss Connection

The pieces can be slightly shifted to accommodate
minor errors in fabrication or to make adjustments
in length.
c. Ease of Joining: The edges of the pieces
being joined do not need special preparation and
are usually sheared or flame cut.
Occasionally the pieces are positioned by a small
number of erection bolts, which may be either left
in place or removed after the welding is
completed.

Tee joint
In a tee joint, one member
meets the other member at
right angles, as shown in
Figure 8.4.
Corner joint
A typical example of corner
joint is shown in Figure 8.5.
Edge joint
The parts to be joined come
parallel to each other from one
side and are joined at their edge.

WELDING
Welding is a process in which metallic parts are
connected together by heating their surfaces to a
fluid state and allowing the parts to flow together
and join with or without the addition of other
molten metal.
General Types Of Welding
Gas welding
In gas welding a mixture of oxygen and
acetylene is burned at the tip of a torch or
blowpipe held in the welder’s hand.

Additional metal is introduced by a metal rod
known as filler or welding rod.
Gas welding is a rather slow process as
compared to other means of welding and is
normally used for repair and maintenance work
and not for the fabrication and erection of large
steel structures.
Electric arc welding
In arc welding an electric arc is formed between
the pieces being welded connected to negative
terminal of battery and an electrode held in the
operator’s hand with some type of holder
connected to positive terminal of battery.

The arc is a continuous spark which upon contact
brings the electrode and the piece being welded to
the melting point.
The resistance of the air or gas between the
electrode and the piece being welded changes the
electrical energy into heat.
A temperature of somewhere between 3100 and
5500 oC is produced in the arc.
In electric-arc welding the metallic rod, which is
used as the electrode, melts off in to the joint as it
is being made.

Hence, the type of welding electrode is very
important as it decidedly affects the weld properties
such as strength, ductility, and corrosion resistance.
Electrode covering (+)
Metal and slag
droplets
Penetration depth
Base material (-)
Molten weld pool
Weld
Slag
Shielding
atmosphere
Weld filler
material

Advantages Of Welding
1- Welded structures allow the elimination
of a large percentage of the gusset and
splice plates necessary for riveted or bolted
structures along with the elimination of rivet
or bolt heads.
In some bridge trusses it may be
possible to save up to 15% or more of the
steel weight by using welding making the
structure economical.

2- Welding requires appreciably less labor
than does riveting because one welder can
replace the standard four person riveting crew.
However, skilled and experienced welders are
needed for better quality.
3- Welding has a much wide range of
application than riveting or bolting. Consider a
steel pipe column and the difficulties of
connecting it to other steel members by riveting
or bolting.
4- Welded structures are more rigid because
the members are often welded directly to each
other.

The connections for riveted or bolted structures
are often made through connection angles or
plates which deflect due to load transfer, making
the entire structure more flexible.
On the other hand, greater rigidity can be a
disadvantage where simple end connections with
little moment resistance are desired. For such
cases designers must be careful as to the type of
joint they specify.
5- Welding changes and repairs are quick and
easy.
6- Welding has relative silence of operation.

7- Fewer pieces are used and as a result time
is saved in detailing, fabrication and field
erection.
8- Welded connections are not recommended
for temporary connections, where bolts are
preferred.
9- Welding gives truly continuous structures
with smooth and clean surfaces.
Types Of Welds Depending Upon
Weld Shape
The welds may be groove or fillet welds.

Groove welds
This type of weld is used in approximately 15% of
construction. A groove of one of the shapes
shown in Figure 8.8 is formed between the
adjoining surfaces, which is then filled with weld.

t2t1
weld
Name Symbol Use
1. Square t £ 10mm
2. Single - V t £ 12mm
3. Double - V t > 12mm
4. Single - bevel t £ 12mm
5. Double - bevel t > 12mm
6. Single - U t £ 12mm
7. Double - U t > 12mm
8. Single - J t £ 12mm
9. Double - J t > 12mm

Fillet Welds
Fillet welds owing to their overall economy, ease
of fabricating and adaptability are the most widely
used (in approximately 80% of construction).
It is actually triangular filling of weld around the
overlapping edges.
Slot and Plug Welds
In this type of welding, the pieces to be joined are
placed one above the other and a hole or slot is
drilled in the top plate.
This hole or slot is then filled with the weld
material (Figure 8.9).

AA
Slot weld
(Called plug weld
if circular)
Symbol :
Section AA

Intermittent Welds
The effective length of any segment of
intermittent fillet welding shall be not less than 4
times the weld size, with a minimum of 38mm.
Minimum effective length of one weld segment
should be 4 tw, but not less than 38 mm. In lap
joints, the minimum amount of lap shall be five
times the thickness of the thinner part joined,
but not less than 25 mm.
1 3 5 7
2 4 6 8
1 3 5 7
2 4 6

Other Welding Symbols
Some other common symbols are shown in Figure.
= weld all around
= field weld
= flush contour
= convex contour
= concave contour

Standard Welding Symbol
A standard weld symbol is used on the
drawings and it gives complete information
about the referenced weld.
A typical standard weld symbol is shown in
Figure 8.11 and the terms used in it are
explained below:

T
S(E) D
G
L - P
or L@P
F
A
This line is
contour symbol
(Weld specification for side opposite to arrow)
Field weld symbol
Weld all around symbol
Arrow connects to
arrow side of joint
Reference line
(Weld specification for arrow side)
Figure 8.11. Standard Weld Symbol.

T = Specification reference. Tail is omitted
when reference is not used.
S = Depth of preparation or size (mm).
E = Effective throat (mm).
F = Finish symbol.
A = Groove angle or included angle of
countersink for plug welds.
D = Apposite-to-arrow side weld shape
symbol.
G = Arrow-side weld shape symbol.
L = Length of weld (mm).
P = Pitch (center-to-center spacing) of
welds (mm).

1506
The symbol indicates fillet weld on near or
arrow side. Size of weld is 6 mm and length
of weld is 150 mm.
50@150 or
50 - 15012
The symbol shows 12 mm thick fillet weld on far
or opposite-to-arrow side. The weld is
intermittent with length of each segment equal to
50 mm and pitch equal to 150 mm.

1506
6mm fillet weld, 150mm long is present on both
sides. As indicated, if weld dimensions are same
on both sides, write only once. Further, it is field
weld.
50 - 15010
A staggered, intermittent, 10mm fillet weld,
50mm long, 150 on centers, is provided on
both sides.

Minimum Weld Size For Fillet Welds
The minimum fillet weld sizes for
various thicknesses of thinner
parts joined are given by AWS
D1.1 (American Welding Society)
and are reproduced in Table 8.1.
tp2
tp1
Table 8.1. Minimum Fillet Weld Sizes.
Base metal thickness of thinner
part joined (tp2)
mm
Minimum leg size of fillet weld
(tw)min.
mm
0 < tp1 £ 6
6 < tp1 £ 13
13 < tp1 £ 19
19 < tp1
3
5
6
8

Maximum Fillet Weld Size
1- Along edges of material less than 6
mm thick,
(tw)max. = tp1 where tp1 =
thickness of thinner plate joined.
2- Along edges of material 6 mm or
more in thickness,
(tw1)max. = tp1 - 2

Practical Weld Size
The smallest practical weld size is about
3mm and the most economical size is probably
about 8mm giving the best efficiency of welder.
This 8mm weld is the largest size that can be
made in one pass with the shielded arc welding
process.
Optimum weld size (tw)opt = 8mm

Minimum Length Of Fillet Weld
There is always a slight tapering off in the
region where the fillet weld is started and where
it ends.
Therefore, if the length is very small, large
percentage difference is created between actual
and expected strengths.
Hence, the minimum effective length of a fillet
weld is specified as four times its nominal size.
(lw)min. = 4 tw

If this requirement is not met, the size of the weld
for calculating strength should be considered to
be one-fourth of the effective length provided.
The effective length of any segment of
intermittent fillet weld shall be not less than 4tw,
with a minimum of 38 mm.
Recommended Maximum Weld Length
lmax. = 30 tw
If the weld length is greater than this limit, it is
better to use intermittent weld at a clear
spacing of 100 - 150mm.

Strength Of Weld
Strength of weld depends upon the following factors:
1- Size of weld (tw).
2- Length of weld (l1, l2).
3- Type of electrode.
4- Type of weld.
5- Type of base metal.
6- Thickness of plates.

Table 8.3. Shielded Metal Arc Welding (SMAW) Electrodes.
Electrode Type Minimum Tensile Strength (FE)
MPa
E60 425
E70 495
E80 550
E100 690
E110 760

STRESSES IN FILLET WELDS
Fillet welds are subjected to shear stresses in
case of connection of tension and compression
members.
For the cases where fillet weld is subjected to
direct tension or compression, the failure is still
expected at the maximum shear stress plane
due to the ductile nature of the weld material.

Tests have shown that fillet welds are stronger in
direct tension and compression than they are in
shear, so the controlling fillet weld stresses given
by the various specifications are shearing
stresses.
Further, when practical, it is desirable to arrange
welded connections so that they will be subjected
to shear stresses only and not to a combination of
shear and tension or shear and compression.
Effective Throat Of Fillet Welds

Weld Face
Theoretical
Face
Effective Throat
Leg of WeldRoot of Weld
Leg of
Weld
Effective Throat
Weld Face
(a) Convex Surface (b) Concave Surface
Theoretical
Face
The theoretical throat of a weld is the shortest
distance from the root of the weld to its theoretical
face.

tw
45°
45°
tw
Throat
b
a
te
(a) a not equal to b
te =
(b) a = b = tw
te = 0.707 tw
22
ba
ab
+

Area of weld = te ´ length of weld = 0.707´ tw ´lw
The effective throat of the weld (te) is the shortest
distance from the root of the weld to its theoretical
face.
For the 45° or equal leg fillet, the throat
dimension is 0.707 times the leg of the weld (tw),
but it has a different value for fillet weld with
unequal legs, as shown in Figure 8.16.

Adopted Or Selected Weld Size (tw)
Three limiting weld sizes, (tw)min, (tw)max and
(tw)opt are found as explained earlier and are
arranged in ascending or descending order.
The middle value is then selected and is
rounded to the nearest whole number millimeter.
Selected Weld Length
Selected weld length at any face of the member
(l1, l2, and l3) should be greater than or equal to
the calculated value but should be within (lw)min
and (lw)max.

Weld Value (Rw)
It is the strength or load carrying capacity in kN of a unit
length of the weld (usually 1mm) depending on weld or
member strength, whichever is lesser.
Rw = lesser of the following two:
1) fRnw = f ´ effective throat (te) ´ unit length ´ weld
shear strength
= 0.75 ´ 0.707 ´ tw ´ 1 ´ 0.6 FE / 1000
2) fRBM = 0.75 ´ 0.6 Fu ´ Ans / 1000
= 0.75 ´ 0.6 Fu ´ t ´ 1 / 1000
where t = thickness of base metal

REQUIRED LENGTH OF WELD
The total weld length required is calculated by
dividing the design force with the weld value.
This weld length is then divided into weld on three
sides of the member namely l1, l2 and l3, as
shown in Figure 8.17.
These calculations are made depending on the
basic requirement that no moment should be
generated at the connection.
lw = = l1 + l2 + l3
w
u
R
F

Fu
l1
l2
l3
l1
l2
l2
l1

Fu
A
B
y
d - y
P1
P3
P2
Gravity axis
l1
l3
l1 + l2 + l3 = lw =
w
u
R
F
P1 = Rw l1
P2 = Rw l2
P3 = Rw l3
Fu = Rw lw

Taking moments about point A and equating it to
zero, following expression is obtained:
P2(d) + P3(d/2) – P ´ y = 0
l2 d + l3 d/2 - lw y = 0
l2 =
2d
y 3w ll
-
Similarly taking moments about the point B,
length l1 may be calculated as follows:
l1 =
( )
2d
yd 3w ll
-
-
Length of weld on that side of the member will be
greater which is closer to centroidal axis, like
towards the projecting leg of the member, etc.

If l1 is greater than l2 and l3 is first selected
equal to zero, the following procedure may be
used to check the lengths for the minimum
and the maximum limits.
If l1 £ (lw)max and l1 ³ (lw)min Use l1 without any change
If l1 < (lw)min Increase l1 to (lw)min
If l1 > (lw)max a) Provide l3 equal to length of end face of
the member and revise l1 and l2 (most
common solution)
b)Increase tw, if it is lesser than (tw)max and
revise calculations
c) Provide intermittent weld
Check l1:

PROCEDURE FOR DESIGN OF
WELDED TRUSS CONNECTIONS
1. Write all the known data including selected
member sections, factored member forces, etc.
2. In case of lap joints, the amount of lap shall
be five times the thickness of the thinner part
joined, but not less than 25mm.
3- Decide gusset plate thickness such that it
should be:
a) same throughout the truss,

b) comparable to greatest thickness of
members joining with it,
c) not less than 6mm, and
d) preferably kept at a minimum of 10mm.
This thickness is most commonly used.
e) Size and shape of the gusset plate are
decided during drawing as explained in
Reference-1 (in instructions to make
working drawing for a truss).
4- In case of members with reversal of forces,
only design for the greater magnitude force and
use the corresponding section capacity.

5- Find out load carrying capacity of the
member, ftTn or fcPn, if not known.
6. The design factored force (Fu) for a member
discontinued at the joint is taken as the greater of
applied load and 50% (any value may be specified
for effective use of the member strength up to
100%) of the section capacity.
7. If the member is double angle section,
consider Fu as half of the above force for one angle.
The weld will be designed for one angle and the
same will be provided on the other side.
8. Find d and y for the section from the table.

9. Select size of weld (tw) considering (tw)min,
(tw)max and (tw)opt.
10. Decide the type of electrode to be used.
11. Find weld value (Rw) as smaller of f Rnw and
f RBM.
fRnw = f ´ te´1´0.6 FE / 1000
where te = 0.707 tw : f = 0.75
fRBM = f ´ tp1´1´0.6 Fu / 1000
for base plate subjected to shear, f =0.75

12. Calculate total weld length required (lw) as
follows:
lw =
w
u
R
F
13. Calculate (lw)min and (lw)max.
14. Divide total weld length (lw) into l1 and l2,
which are weld lengths at top and bottom of the
member, considering l3 = 0 in the start.
l1 = lw ´ y / d and l1 = lw ´
d
yd -
Greater value is provided on that face of the
member which is closer to the centroidal axis.

15- Check lengths l1 and l2 for minimum and
maximum limits and decide the side weld length l3.
a- Assuming that l1 is the greater length, first
check it against the limiting values as follows:
If l1 ³ (lw)min and l1 £ (lw)max Þ OK
If l1 < (lw)min Þ use l1 = (lw)min
If l1 > (lw)max Þ
i) Take l3 = d, l1 and l2 will be previous values
minus d / 2.
ii) If l1 is still bigger than (lw)max., we can
increase tw or use intermittent weld.

b- Similar check is made for the smaller length
out of l1 and l2.
The minimum length of one segment of
intermittent weld should be larger of 4tw and
38mm.
16- The connection length for a tension member
must be such that a better shear lag factor may be
achieved. The preferred connection length may
be calculated as under:
U = 1 -
l
x
For U = 0.9 1 - = 0.9
pref
x
l

= 0.1
pref
x
l
lpref = 10 x
where = distance between centroid of the
element and the plane of load tranfer
x
17- Check block shear strength, for tension
members only.
The nominal strength for block shear is the lesser
of the following two cases because only that will
cause the final separation of the block from the
member.
Rn = lesser of 0.6 Fu Anv + Ubs Fu Ant
and 0.6 Fy Agv + Ubs Fu Ant

Nominal tension rupture strength = Ubs Fu Ant
Nominal shear rupture strength = 0.6 Fu Anv
Shear yielding strength = 0.6 Fy Agv
0.6Fy @ yield shear strength = ty
0.6Fu @ ultimate shear strength = tu
f = 0.75 (LRFD) and W = 2.00 (ASD)
Agv = gross area subjected to shear
Anv = net area in shear
Ant = net area in tension
Ubs = tensile rupture strength reduction factor
(subscript ‘bs’ stands for block shear)
= 1.0 when tensile stress is uniform

Splice Plate
Figure 8.6. Spliced Top And Bottom Chord Joints.
18. If more than one member is meeting at a
joint, consider free body diagram of each member
separately, to design the weld. For example, each
member of Figure 8.6 is to be designed separately
for its force.

19. If the top or bottom chord member is
discontinued at a joint (Figure 8.6), splice plate
should be used with the projected leg of the
member, perpendicular to the gusset plate.
Thickness of this splice plate must be
approximately equal to thickness of the member.
This type of joint is called a Spliced Joint.
Splicing is done at some distance away from the
point of intersection of members to avoid stress
concentration on gusset plate.

Force transferred to splice plate may be taken as
50 percent of lesser member force out of the
forces on both sides.
This force may be used to check the size of the
plate for the required strength.
20. In case of un-spliced and unloaded top or
bottom chord joint (as in Figure 8.20), the top or
bottom chord weld is designed for the difference
of forces on the two sides, which is greater of:
a) ½F1 – F2½, greater of F1 and F2 may be
replaced with 50 percent of member capacity
for the corresponding member, if it is larger in
magnitude.

b) ½F3 cosq3 – F4 cosq4½
c) 25 percent capacity of larger member.
F2 F1
F4 F3
F5
q4 q3
Figure 8.20. Un-Spliced Top And
Bottom Chord Joints.

21. In case of loaded un-spliced joint, design is
carried out as in step 20 but an additional check as
under is performed at the end.
This is required because the weld should provide
extra strength to transfer perpendicular load (V)
from the member to the gusset plate.
In Figure 8.21, P = 1.2 PD + 1.6 PL
and V = P cosq
Calculate
( ) ( )
2
provw
2
provw
u'
w
VF
R
÷
÷
ø
ö
ç
ç
è
æ
+
÷
÷
ø
ö
ç
ç
è
æ
=
ll

F1
F2
V
P
Gravity Load
q
F3
F4
F5
Figure 8.21. Loaded Un-Spliced Top And Bottom Chord Joints.

If OK
Otherwise:
i) Increase the weld length in steps and check
ii) Increase the weld size if it is lesser than (tw)max
22- Show results of weld design on a neat
sketch using standard weld symbol.
ww RR £¢
Example 8.1: Design weld for the tension-
member shown in Figure 8.22 using E 70 electrode.
The thickness of gusset plate is 10 mm and the
factored tensile force is 300 kN.

Tu = 300 kN
l1
l2
L89 ´ 76 ´ 9.5
d – y
y

Solution:
From tables (Reference – 1), y = 27.4 mm,
d – y = 61.6 mm and A = 1480 mm2.
ft Tn = 0.9 ´ 250 ´ 1480/1000 = 333.0 kN
ft Tn = 0.75 ´ 400 ´ 1.0 ´ 1480/1000
= 444.0 kN
ft Tn / 2 = 166.5 kN
Design force for the connection,
Fu = greater of 166.5 kN and 300 kN
= 300 kN

tp1 = 9.5 mm ; tp2 = 10 mm
(tw)max = tp – 2 = 7.5 mm
(tw)min = 5 mm
topt = 8 mm
(tw)adopted = 7.5 mm » 8 mm
fRnw = 0.75 ´ 0.707 ´ 8 ´ 1 ´ 0.6 ´ 495 / 1000
= 1.26 kN/m
fRBM = 0.75 ´ 0.6 ´ 400 ´ 9.5 ´ 1 / 1000
= 1.71 kN/m
Rw = 1.26 kN/m

Length of weld lw = 300 / 1.26
= 238 mm
l2 = =
= 73 mm (say 75 mm)
l1 = lw – l2 = 165 mm
d
yw ´l ( )
89
4.27238
For efficiency factor (U) of 0.85,
preferred length of connection = 6.7 ( )x
= 6.7 (21.1)
@ 145 mm
l1 = 165 mm

(lw)min = 4 tw = 32 mm
(lw)min = 30 tw = 240mm
32 mm £ l1, l2 £ 240 mm OK
Block Shear Strength
Perform the check as done in tension
member design
The results are
shown in Figure
8.23.
8
8
75
165

Example 8.2: Design welded connection for the
truss compression member shown in Figure 8.26
using E70 electrode. The weld length on any face
should not exceed 150 mm.
Pu = 600 kN
2Ls 102´102´9.5
A = 1850 mm2
L = 1.5 m
l1
l3
l2
y
10mm Thick Gusset Plate

Solution:
A = 1850 mm2 for one angle
y = 29 mm
rx = 31.2 mm
Iy = 2(181 ´ 104 + 1850 ´ 342)
= 790 ´ 104 mm4
ry = = 46.2 mm
18502
10790 4
´
´
R = = @ 48 :
fFcr = 199.13 MPa
minr
K l
2.31
15001´

½ fcPn = ½ ´ 199.13 ´ 2 ´ 1850 / 1000
@ 368.4 kN
Fu for 2 angles = larger of 600 and 368.4
= 680 kN
and Fu for one angle = 300kN
tp1 = 9.5 mm ; tp2 = 10 mm
(tw)max = tp – 2 = 7.5 mm
(tw)min = 5 mm
topt = 8 mm
(tw)adopted = 7.5 mm » 8 mm
fRnw = 0.75 ´ 0.707 ´ 8 ´ 1 ´ 0.6 ´ 495 /
1000 = 1.26 kN/m

fRBM = 0.75 ´ 0.6 ´ 400 ´ 9.5 ´ 1 / 1000
= 1.71 kN/m
Rw = 1.26 kN/m
lw = = 238 mm
26.1
300
l1 = = 170 mm( ) ( )
102
29102238 -
=
-
d
ydwl
l2 = 238 – 170 = 68 mm
The joint efficiency and block shear checks are not
required here because it is a compression member.

As l1 > 150 mm, let l3 = 102 mm
l1 = 170 – = 119 mm (say 120 mm)
2
102
l2 = 68 – = 17 mm
2
102
(lw)min = 4tw = 32
(lw)max = 30 tw = 240 mm
l1 is between (lw)min and (lw)max OK
l2 < (lw)min l2 = 32 mm (say 35 mm)

Final Result
l1= 120 mm
l2= 35 mm
l3= 102 mm
To show the results on a neat sketch are left as exercise
for the reader.

Steel strucure lec # (17)

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