07-Strength of Bolted Connections (Steel Structural Design & Prof. Shehab Mourad)

1. 1 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
Strength of Bolted Connections
Type of bolts
- According to strength
SBC 306 TABLE 10.3-2: Design Strength of Fasteners
Tensile Strength Shear Strength in
Bearing-type Connections
Nominal Nominal
Description of Fasteners Resistance
Factor f
Strength,
MPa
Resistance
Factor f
Strength,
MPa
A307 bolts
0.75
310 [a]
0.75
165 [b,e]
A325 or A325M bolts, when
threads are not excluded from
shear planes
620 [d] 330 [e]
A325 or A325M bolts, when
threads are excluded from
shear
planes
620 [d] 414 [e]
A490 or A490M bolts, when
threads are not excluded from
shear planes
780 [d] 414 [e]
A490 or A490M bolts, when
threads are excluded from
shear planes
780 [d] 520 [e]
[a] Static loading only.
[b] Threads permitted in shear planes.
[c] The nominal tensile strength of the threaded portion of an upset rod, based upon the cross-sectional area at its
major thread diameter, AD shall be larger than the nominal body area of the rod before upsetting times Fy.
[d] For A325 or A325M and A490 or A490M bolts subject to tensile fatigue loading, see Section 11.3.
[e] When bearing-type connections used to splice tension members have a fastener pattern whose length,
measured parallel to the line of force, exceeds 1270 mm, tabulated values shall be reduced by 20 percent.
1- Ordinary bolts , A307 are made of carbon steel
similar of A36 steel
2- High strength bolts, A325 & A490, are made from
medium carbon heat-treated steel and have strength
two or more times those of A307.
For A325 bolts Fu = 620 MPa, Fv= 330 - 414 MPa
For A490 Bolts Fu = 780 MPa, Fv = 414 - 520 MPa

2. 2 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
- According to tightening method
SBC 306 TABLE 10.3-1:
Minimum Bolt Pretension, kN*
1- snug-tight bolts, used when all
surfaces are in firm contact and
tightened with the full effort of a
person using a spud wrench.
2- Pretension joints, bolts are
pretension to approximately 70%
of its minimum tensile stresses
using one of the tensioning
methods. Such joints are used in
tension applications when load
reversal can occur such in cases
of seismic and fatigue loading.
3- Slip-critical joints, are as
pretension joints and are
required for situations involving
shear combined with tension.
Shear is mainly resisted by
friction between the faying
surfaces
b. Fasteners loaded in shear
a. Fasteners loaded in tension c. Fasteners loaded in combined shear and tension

3. 3 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
Methods for Fully Tensioning High-Strength Bolts
Types of Connections
1-Slip-crtical connection:
Bolts need to be pretensioned, to provide sufficient friction
between plates to resist the applied shear and to prevent any
slippage at the connection.
2- Bearing type connection:
Bolts need to be snug-tight, so the applied shear force are
resisted by bearing and shearing of bolts
a- Turn-of-the Nut method :
The nut is turned from 1/3 to one
full turn depending on the bolt
length
b- Calibrated Wrench method:
An impact wrench is adjusted to
apply a certain torque that is
sufficient to tension the bolt with
certain diameter.
c- Direct Tension Indicator:
Consists of a hardened washer
which has protrusions on one
face in the form of small arches.
The arches are flattened as the
bolt is tightened

4. 4 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
Sizes and Types of Holes
Limitations on Bolt Spacing and Edge Distance
Hole spacing, Sh
Sh≥3d b
· Edge distance, SE
SE ≥ 1.5db or values from Table 10.3-4
SE ≤ Min(150 mm,12t)
SBC 306 TABLE 10.3-3
Nominal Hole Dimensions, mm
Hole Dimensions
Bolt Standard Oversize Short-slot Long-slot
Diameter (Dia.) (Dia.) (Width x Length) (Width x
Length)
M16 18 20 18 × 22 18 × 40
M20 22 24 22 × 26 22 × 50
M22 24 28 24 × 30 24 × 55
M24 27 [a] 30 27 × 32 27 × 60
M27 30 35 30 × 37 30 × 67
M30 33 38 33 × 40 33 × 75
≥M36 d + 3 d + 8 (d + 3) × (d + 10) (d + 3) × 2.5d
[a] clearance provided allows the use of a 25 mm, bolt, if desirable.
≥3d b
≥1.5d b or values from Table
10.3-4

5. 5 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
1- Slip-Critical Connection
Fig Shear planes in bolted connection
Ø =( 0.85 for over size holes) or (1.0 for standard holes)
µ =coefficient of friction.
i)µ= 0.33 for unpainted clean surface
ii)µ= 0.5 for unpainted blast-clean surface
Nb = Number of bolt
Fu b = Tensile strength of bolt
d b = Diameter of bolt
Ns = number of shear planes = 2 (for case of double shear)
1 (for case of single shear)
2- Bearing type connection
a) Shear failure of bolt.
Fvb= Shear Strength of bolt
Ab= Area of bolt = (π *d2
b/4 )
Nb = Number of bolt
Ns = number of shear planes = 2 (for case of double shear)
1 (for case of single shear)
b) Bearing failure of plate. For Le > 1.5*d
Fu = Tensile strength of steel
db = Diameter of bolt
tmin = min of thickness of (2tangle) or (tg)
Nb = Number of bolt
Ns = 2
double shear
Ns = 1
Single shear
Ø Rn = Ø * 1.13 * µ * 0.7 * (π*d2
b/4) * Fu b* Nb * Ns
Ø Rn = 0.75 * Fvb * Ab * Ns * Nb
ØRn = 0.75 * 2.4 * Fu * db * tmin * Nb

6. 6 Prepared by Prof. Shehab Mourad – Department of Civil Eng. - KSU
Example
Determine the factor resistance of the given bolted connection if it is a
slip- critical connection.
Given :
Fu = 620 Mpa
Fv = 400 Mpa
2L 89 x 76 x 6.4 mm
Le = 51 mm
s = 76 mm
dbolt = 19 mm
dhole = 19 + 3 = 22 mm
g = 51 mm
Fig Dimensions of bolted connection
for single angle
Ag = 1020 mm2
µ = 0.5 (for unpainted blast-clean surface)
Ø = 1.0 (for standard holes)
Solution:
1- Slip- critical connection.
Ø Rn = Ø* 1.13 * µ * 0.7 * (π*d2
b/4) * Fub * Nb * Ns
= 1 * 1.13 * 0.5 * 0.7 * {π*(19)2
/4}*620 * 3 * 2 /1000 = 416.9 kN
2- Shear failure of bolt.
Ø Rn = 0.75 * Fvb * Ab* Ns * Nb
= 0.75 * 400 *{π*(19)2
/4} * 3 * 2 / 1000 = 510 kN
3- Bearing failure of plate.
tmin = (tangle= 2*6.4 = 12.8 mm or tgusset= 12 mm)
tmin = 12 mm
Ø Rn = 0.75 * 2.4 * Fu * db * tmin* Nb
= 0.75 * 2.4 * 400 * 19 * 12 * 3 / 1000 = 492.5 kN
PuPu
SS Le2Le1 1
Le1 S Le2S
1
Ø Rn = 416.9 kN which is governed by slip-critical connection