Specification for

Structural Joints
Using High-
Strength Bolts
June 11, 2020
Supersedes the August 1, 2014
Specification for Structural Joints Using High-Strength Bolts

Prepared by RCSC Committee A.1—Specifications and

approved by the Research Council on Structural Connections
16.2-6 SPECIFICATION FOR STRUCTURAL JOINTS USING HIGH-STRENGTH BOLTS

SECTION 2. BOLTING COMPONENTS AND ASSEMBLIES

2.1. Group Designations

This Specification addresses three tensile strength levels of bolts and categorizes
the bolting component or bolting assembly by Group, as shown in Table 2.1.

Table 2.1
Group Designations for Bolts and
Matched Bolting Assemblies
Tensile Matched
Group Bolts
Strength Bolting Assemblies
ASTM F3125 ASTM F3125
Group 120 120 ksi
Grade A325 Grade F1852
ASTM F3148
Group 144 144 ksi —
Grade 144
ASTM F3125 ASTM F3125
Group 150 150 ksi
Grade A490 Grade F2280

Commentary:
This Specification deals principally with high-strength bolts in three tensile
strengths—120, 144, and 150 ksi; their design, installation, inspection, and
performance in structural steel joints, and those few aspects of the connected
material that affect performance. Many other aspects of connection design
and fabrication are of equal importance and must not be overlooked. For more
general information on design and issues related to high-strength bolting and
the connected material, refer to current steel design textbooks and the Guide to
Design Criteria for Bolted and Riveted Joints, 2nd Edition (Kulak et al., 1987).
For convenience, this specification identifies these tensile strength levels as
Groups and categorizes the bolt or bolting assembly as shown in Table 2.1.
ASTM structural bolt standards currently provide for two types of high-strength
bolts, according to metallurgical classification. Type 1 bolts may be manufac-
tured from medium carbon steel, carbon boron steel, alloy steel, or alloy steel
with added boron. Type 3 bolts have improved atmospheric corrosion resistance
and weathering characteristics. When the bolt type is not specified, either Type
1 or Type 3 may be supplied at the Manufacturer’s option.
Structural bolts addressed in this Specification are supplied in diameters from
2 in. through 12 in. Not all styles are available in all diameters.
Structural bolts, nuts, and washers are required by ASTM standards to be
distinctively marked. In addition to mandatory marks, the Manufacturer may
apply additional distinguishing marks. The mandatory marks are illustrated in
Figure C-2.1.

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION 2. BOLTING COMPONENTS AND ASSEMBLIES 16.2-7

This Specification contains provisions for approval by the Engineer of Record of

alternative-design bolts and bolting assemblies. See the requirements in Section
2.12.

Bolt/Nut/Washer/Matched
Type 1 Type 3
Bolt Assembly

 ASTM F3125
Grade A325 bolt

 ASTM F3125
Grade F1852 bolt

 ASTM F3125
Grade A490 bolt

 ASTM F3125
Grade F2280 bolt

 ASTM F3148
Grade 144 bolt

Arcs indicate Grade C Arcs with “3” indicate

Grade C3

ASTM A563 nut

Grade D

Grade DH Grade DH3

Figure C-2.1. Required marks for acceptable bolt and nut components. (cont’d.)

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION 5. LIMIT STATES IN BOLTED JOINTS 16.2-39

(1) Fn from Table 5.1 shall be multiplied by the factor [1 - 0.4(t9 - 0.25)], which
shall not be taken as greater than 1.00 nor smaller than 0.85, where t9 is the
total thickness of fillers or shims, in.; or
(2) The fillers or shims shall be extended beyond the joint and the filler or shim
extension shall be secured with enough bolts to uniformly distribute the total
force in the connected element over the combined cross-section of the con-
nected element and the fillers or shims; or
(3) The size of the joint shall be increased to accommodate a number of bolts that
is equivalent to the total number required in (2) above; or
(4) The joint shall be designed as a slip-critical joint using Class A faying surfaces
with the turn-of-nut method; or
(5) The joint shall be designed as a slip-critical joint using Class B faying surfaces.

Table 5.1
Nominal Strengths per
Unit Area of Bolts
Applied Load Condition Nominal Strength per Unit Area, Fn , ksi
Group 120 Group 144 Group 150
Static 90 108 113
Tensiona
Fatigue See Section 5.5

Ls ≤ 38 in. 54 65 68
Threads included
in shear plane
Ls > 38 in. 45 54 56
Shear a,b
Ls ≤ 38 in. 68 81 84
Threads excluded
from shear plane
Ls > 38 in. 56 68 70
a Except as required in Section 5.2.
b Reduction for values for Ls > 38 in. applies only when the joint is axially end loaded, such as splice plates on a
beam or column flange, but it does not apply for web connections in shear.

Commentary:
The nominal shear and tensile strengths of ASTM F3125 Grades A325, F1852,
A490, and F2280 high-strength bolts as well as ASTM F3148 Grade 144
matched bolting assemblies are given in Table 5.1. These values are based upon
the work of a large number of researchers throughout the world, as reported in
the Guide and by others (Kulak et al., 1987; Tide, 2010; Roenker et al., 2017).

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION 5. LIMIT STATES IN BOLTED JOINTS 16.2-41

If pretensioned bolts are used in a joint that loads the bolts in tension, the ques-
tion arises as to whether the pretension and the applied tension are additive.
Because the compressed parts are being unloaded during the application of the
external tensile force, the increase in bolt tension is minimal until the parts sepa-
rate (Kulak et al., 1987). Thus, there will be little increase in bolt force above
the pretension load under service loads. After the parts separate, the bolt acts as
a tension member, as expected.
Pretensioned bolts have torsion present during the installation process. Once the
installation is completed, any residual torsion is quite small and will disappear
entirely when the bolt is loaded to the point of plate separation. Hence, there is
no question of torsion-tension interaction when considering the ultimate tensile
strength of a high-strength bolt (Kulak et al., 1987).
When required, pretension is induced in a bolt by imposing a small axial elonga-
tion during installation. When the joint is subsequently loaded in shear, tension,
or combined shear and tension, the bolts will undergo significant deformations
prior to failure that have the effect of overriding the small axial elongation
that was introduced during installation, thereby removing the pretension.
Measurements taken in laboratory tests confirm that the pretension that would
be sustained if the applied load were removed is essentially zero before the bolt
fails in shear (Kulak et al., 1987). Thus, the shear and tensile strengths of a bolt
are not affected by the presence of an initial pretension in the bolt.
See also the Commentary to Section 5.5.
Tests of connections with 24 18-in.-diameter A490 bolts indicated the reduc-
tion factor for bolt shear strength in connections with fillers as required in
Section 5.1 (1) is limited to a minimum of 85 percent. (Borello et al., 2009).

5.2. Combined Shear and Tension

When combined shear and tension loads are transmitted by a Group 120, 144, or
150 bolt, the factored limit-state interaction shall be:
2 2
 Tu   Vu 
  +  ≤1 (Equation 5.2a)
 (fRn )t   (fRn )v 
where
Tu = required strength in tension (factored tensile load) per bolt, kips
Vu = required strength in shear (factored shear load) per bolt, kips
(fRn)t = design strength in tension determined in accordance with Section 5.1,
kips
(fRn)v = design strength in shear determined in accordance with Section 5.1, kips

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-42 SPECIFICATION FOR STRUCTURAL JOINTS USING HIGH-STRENGTH BOLTS

When combined shear and tension loads are transmitted by a Group 120, 144, or
150 bolt, the allowable limit-state interaction shall be:
2 2
 Ta   Va 
  +  ≤1 (Equation 5.2b)
 ( Rn Ω )t   ( Rn Ω )v 
where
Ta = required strength in tension (service tensile load) per bolt, kips
Va = required strength in shear (service shear load) per bolt, kips
(Rn /W)t = allowable strength in tension determined in accordance with Section
5.1, kips
(Rn /W)v = allowable strength in shear determined in accordance with Section
5.1, kips

Commentary:
When both shear forces and tensile forces act on a bolt, the interaction can
be conveniently expressed as an elliptical solution (Chesson et al., 1965) that
includes the elements of the bolt acting in shear alone and the bolt acting in
tension alone. Although the elliptical solution provides the best estimate of
the strength of bolts subject to combined shear and tension and is thus used
in this Specification, the nature of the elliptical solution is such that it can be
approximated conveniently using three straight lines (Carter et al., 1997). Earlier
editions of this Specification have used such linear representations for the conve-
nience of design calculations. The elliptical interaction equation in effect shows
that, for design purposes, significant interaction does not occur until either force
component exceeds 20 percent of the limiting strength for that component.

5.3. Nominal Bearing Strength at Bolt Holes

For joints, the nominal bearing strength shall be taken as the sum of the strengths
of the connected material at the individual bolt holes.
The design bearing strength is fRn, where f = 0.75 and the allowable bearing
strength is Rn /W, where W = 2.00 of the connected material at a standard bolt hole,
oversized bolt hole, short-slotted bolt hole independent of the direction of loading,
or long-slotted bolt hole with the slot parallel to the direction of the bearing load and:
(1) When deformation of the bolt hole at service load is a design consideration,
Rn = 1.2 LctFu ≤ 2.4 dbtFu (Equation 5.3)
(2) When deformation of the bolt hole at service load is not a design consideration,
Rn = 1.5LctFu ≤ 3dbtFu (Equation 5.4)
The design bearing strength is fRn, where f = 0.75 and the allowable bearing
strength is Rn/W, where W = 2.00 of the connected material at a long-slotted bolt
hole with the slot perpendicular to the direction of the bearing load and:
Rn = LctFu ≤ 2 dbtFu (Equation 5.5)

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-44 SPECIFICATION FOR STRUCTURAL JOINTS USING HIGH-STRENGTH BOLTS

(a) Dimensions (b) Strength formulation

(per bolt)

Figure. C-5.1. Bearing strength formulation.

5.4. Design Slip Resistance

Slip-critical joints shall be designed to prevent slip and for the limit states of
bearing-type connections in accordance with Sections 5.1, 5.2, and 5.3. When bolts
in slip-critical joints pass through fillers, all faying surfaces subject to slip shall be
prepared to achieve design slip resistance.
At LRFD load levels the design slip resistance is fRn, and at ASD load levels the
allowable slip resistance is Rn /Ω where Rn, f, and Ω are defined below.
The nominal slip resistance per bolt for the limit state of slip shall be determined
as follows:
Rn = mDu hf Tmns ksc (Equation 5.6)
For standard size and short-slotted holes perpendicular to the direction of the load:
f = 1.00 (LRFD)    Ω = 1.50 (ASD)
For oversized and short-slotted holes parallel to the direction of the load:
f = 0.85 (LRFD)    Ω = 1.76 (ASD)
For long-slotted holes:
f = 0.70 (LRFD)    Ω = 2.14 (ASD)

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION 5. LIMIT STATES IN BOLTED JOINTS 16.2-45

where
m = mean slip coefficient for Class A or B surfaces, as applicable, and deter-
mined as follows, or as established by tests:
(1) For Class A surfaces (unpainted clean mill scale steel surfaces or
surfaces with Class A coatings on blast-cleaned steel or hot-dipped
galvanized)
m = 0.30
(2) For Class B surfaces (unpainted blast-cleaned steel surfaces or surfaces
with Class B coatings on blast-cleaned steel)
m = 0.50
Du = 1.13 for building structures, 1.00 for bridge structures. Other values may
be used with the approval by the Engineer of Record or by a Specification
body
Tm = minimum bolt pretension given in Table 5.2, kips
hf = factor for fillers, determined as follows:
(1) Where there are no fillers or bolts have been added to distribute loads
in the filler
hf = 1.0
(2) Where bolts have not been added to distribute the load in the filler:
(i) For one filler between connected parts
hf = 1.0
(ii) For two or more fillers between connected parts
hf = 0.85
ns = number of slip planes required to permit the connection to slip
Tu
ksc = 1 − ≥0 (LRFD) (Equation 5.7a)
DuTm nb

1.5Ta
ksc = 1 − ≥ 0 (ASD) (Equation 5.7b)
DuTm nb
where
Ta = required tension force using ASD load combinations, kips
Tu = required tension force using LRFD load combinations, kips
nb = number of bolts carrying the applied tension

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-46 SPECIFICATION FOR STRUCTURAL JOINTS USING HIGH-STRENGTH BOLTS

Table 5.2
Minimum Bolt Pretension,
Pretensioned and Slip-Critical Joints
Specified Minimum Bolt
Pretension, Tm , kips
Nominal Bolt Diameter,
d b, in.
Group 120 Group 144 and Group 150

/
12 12 15
/
58 19 24
/
34 28 35
/
78 39 49
1 51 64
11/8 64 80
1/14 81 102
1 3/8 97 121
1/12 118 148

Commentary:
The slip resistance of a joint is a function of the coefficient of friction, the bolt
pretension (clamping force), the number of faying surfaces, and the number of
bolts. In the equation for the nominal slip resistance per bolt (Equation 5.6), the
clamping force is calculated as the product of the specified minimum preten-
sion, Tm , and of a coefficient Du. The specified minimum pretensions shown in
Table 5.2 are based on 70 percent of the tensile strength of Group 120 or 150
fasteners computed as the product of their tensile strengths and tensile stress
areas, rounded to the nearest kip. For the sake of simplicity, Group 144 bolts are
required to be installed to the same minimum pretensions as Group 150 bolts.
The multiplier Du in Equation 5.6 accounts for the statistical relationship
between mean historical measured installed bolt pretension and the specified
minimum bolt pretension, Tm . For the design of building structures, the value
of Du = 1.13 is used for installation by the calibrated wrench method (Kulak et
al., 1987; Grondin et al., 2007). In the absence of other field test data, this value
is used for all installation methods. Turn-of-nut pretensioning results in mean
pretensions that are about 1.35 times the specified minimum pretension for
ASTM F3125 Grade A325 bolts, and about 1.26 for Grade A490 bolts (Kulak
et al., 1987; Grondin et al., 2007). Twist-off tension control- and direct ten-
sion indicator-installed pretensions are similar to those of a calibrated wrench
(Grondin et al., 2007). The combined method of installation results in a Du value
of 1.37 for F3148 bolts (Roenker et al., 2017). The bolt clamping force data
indicate that bolt pretensions are distributed normally for each pretensioning

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION 7. PRE-INSTALLATION VERIFICATION 16.2-55

(3) For Twist-Off Tension Control Bolt Method installation in accordance with

Section 8.2.3, pre-installation verification testing shall be in accordance with
Section 7.2.3,
(4) For Direct Tension Indicator Method installation in accordance with Section
8.2.4, pre-installation verification testing shall be in accordance with Section
7.2.4, and
(5) For Combined Method installation in accordance with Section 8.2.5, pre-instal-
lation verification testing shall be in accordance with Section 7.2.5.
7.2.1. Turn-of-Nut Method
Step 1: Snug-Tightening
The bolting assembly shall be installed to the snug-tight condition in the bolt
tension measurement device using the tools, bolting components, assembly con-
figuration, and installation methods to be used in the work.
Step 2: Matchmarking
If matchmarking is to be used in the work, the bolting assembly shall be match-
marked.
Step 3: Pretensioning
The rotation specified in Table 8.1 shall be applied to the bolting assembly.
Step 4: Final Verification
If the actual pretension developed in the bolting assembly is less than that speci-
fied in Table 7.1, the cause(s) shall be determined and resolved before the bolting
assemblies are used in the work. Cleaning, lubrication, and retesting of these bolt-
ing assemblies is permitted provided that all assemblies are treated in the same
manner.
7.2.2. Calibrated Wrench Method
Step 1: Snug-Tightening
The bolting assembly shall be installed to the snug-tight condition in the bolt
tension measurement device using the tools, bolting components, assembly con-
figuration, and installation methods to be used in the work.
Step 2: Pretensioning
The torque required for the installation tool to develop a pretension in the bolting
assembly equal to or greater than that specified in Table 7.1 shall be determined.
The installation torque shall be applied to the nut. The highest torque measured
from the three assemblies tested shall be the minimum installation torque to be
used in the work.
7.2.3. Twist-Off Tension Control Bolt Method
Step 1: Snug-Tightening
The bolting assembly shall be installed to the snug-tight condition using the tools,
bolting components, assembly configuration, and installation methods to be used
in the work.
Step 2: Intermediate Verification
It shall be verified that the splined end is not severed.

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-56 SPECIFICATION FOR STRUCTURAL JOINTS USING HIGH-STRENGTH BOLTS

Step 3: Pretensioning
The twist-off tension control bolt installation wrench shall be used to sever the
splined end from the bolt.
Step 4: Final Verification
It shall be verified that the splined end is severed. If the actual pretension developed
in the bolting assembly is less than that specified in Table 7.1, the cause(s) shall
be determined and resolved before the bolting assemblies are used in the work.
Cleaning, lubrication, and retesting of these bolting assemblies is not permitted,
except as allowed in Section 2.10, provided that all assemblies are treated in the
same manner.
7.2.4. Direct Tension Indicator Method
Step 1: Snug-Tightening
The bolting assembly shall be installed to the snug-tight condition using the tools,
bolting components, assembly configuration, and installation methods to be used
in the work. Snug tightening shall not exceed the pretension specified in Table 7.1.
Step 2: Intermediate Verification
The bolting assembly shall be further tightened to a pretension that is equal to that
required in Table 7.1. It shall then be verified that the job inspection gap has not
closed prematurely. To prove acceptability, the feeler gage used to verify the job
inspection gap shall be able to be inserted in half or more of the spaces between
the protrusions of the direct tension indicator. Verification with the feeler gage in
this step satisfies verification for both Step 1 and Step 2.
Step 3: Pretensioning
The bolting assembly shall be further tightened, as needed, until the feeler gage is
refused (i.e., cannot be inserted) in more than half of the spaces between the protru-
sions of the direct tension indicator.
Step 4: Final Verification
It shall be verified that the pretension achieved is at least that specified in Table
7.1. If the actual pretension developed in the bolting assembly is less than that
specified in Table 7.1, the cause(s) shall be determined and resolved before the
bolting assemblies are used in the work. Cleaning, lubrication, and retesting of
these bolting assemblies is permitted provided that all assemblies are treated in the
same manner.
7.2.5. Combined Method
Step 1: Initial Tensioning
The bolting assembly shall be installed in the bolt tension measurement device
using the tools, bolting components, assembly configuration, and installation meth-
ods to be used in the work. The initial torque shall be applied to the nut. If the
initial torque has not been provided by the Supplier, then the torque in Table 7.3
shall be used. Tools used shall demonstrate or have certified output that does not
vary by more than ±10 percent during use.

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
SECTION A3. SHORT-TERM COMPRESSION SLIP TESTS 16.2-85

A3.4. Slip Load

Typical load-slip response is shown in Figure A-4. Three types of curves are usu-
ally observed and the slip load associated with each type is defined as follows:
Curve (a) Slip load is the maximum load, provided this maximum occurs before a
slip of 0.02 in. is recorded.
Curve (b) Slip load is the load at which the slip rate increases suddenly.
Curve (c) Slip load is the load corresponding to a deformation of 0.02 in. This defi-
nition applies when the load versus slip curves show a gradual change in response.

A3.5. Slip Coefficient

The slip coefficient for an individual specimen ks shall be calculated as follows:

Slip load
ks = (Equation A3.1)
2 × Clamping force
The mean slip coefficient, m, for one set of five specimens shall be calculated as the
average of the five samples. Alternatively, in case the result of one of the samples
is substantially lower than the average of the other four, the mean slip coefficient
may be calculated as the average of four samples provided the lowest attained value
passes the following criteria:
µ - ksmin .
≥ 1.71 (Equation A3.2)
s

Figure A-4. Definition of slip load.

Specification for Structural Joints Using High-Strength Bolts, June 11, 2020
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS