ASSEMBLY OF STRUCTURAL CONNECTIONS USING HIGH-STRENGTH BOLTS

BRIDGE CONSTRUCTION

INSPECTION TRAINING

2004/2013

HIGH STRENGTH BOLTS

GENERAL CONCEPTS

SPECIFICATIONS

FIELD ROTATIONAL-CAPACITY TEST

INSTALLATION

INSPECTION

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GENERAL CONCEPTSTYPES OF CONNECTIONS TYPES OF BOLTS

FABRICATION ERECTION

SPECIFICATIONS ROTATIONAL CAPACITY TEST

INSTALLATION INSPECTION

TYPES OF CONNECTIONSBEARING TYPE CONNECTION:

BEARING OF THE SHANK OF THE BOLT AGAINST THE SIDE OF

THE HOLE - PLATE MATERIAL.

(ADEQUATE FOR STATIC LOADING)

SLIP-CRITICAL CONNECTION

(SINGLE SHEAR)

SLIP-CRITICAL CONNETIONS:

TENSION FORCE IN THE BOLT GENERATES

A CLAMPING FORCE BETWEEN PIECES OF

MATERIAL BEING SPLICED TOGETHER.

(WHEN NO SLIP AT SERVICE LOAD IS DESIRED)(RESISTS FATIGUE LOADING -

STRESS REVERSALS)

What type of connections, for bolted

girder splices, do we (VDOT) use?

A) Full penetration field welds

B) Bolted bearing connections

C) Bolted slip-critical connections

C) Bolted slip-critical connections

AASHTO - VDOT Design Specification:

10.18 SPLICES

Bolted splices shall be designed as slip-

critical connections...

SPECIFICATIONSSEC 407.06

SEC 407.06(b)

SEC 226.02

SEC 226.02

What type of bolts do we (VDOT) typically

require for making structural field

connections in bridges?

A) 7/8” Diameter ASTM A307 bolts

B) 7/8” Diameter ASTM A325 bolts

C) 7/8” Diameter ASTM A490 bolts

B) 7/8” Diameter ASTM A325 bolts

SEC 407.06(b)

Field connections shall be made with high-

strength 7/8 inch diameter bolts fabricated in

accordance with ASTM A325,unless

otherwise specified.

http://www.youtube.com/watch?v=O

96AUlIBkU8

Torque vs. Tension

SPECIFICATIONS

407.06 (3)

Required minimum Tension (lb) for a 7/8” ASTM

A 325 bolt = 39,000 lbs.

39,000 lbs = 39 kips

Snug tight condition is best defined as?

A) Snug tight is defined as the tightness

attained such that the complete area of the

connecting surfaces are brought into firm

contact with each other.

B) Snug tight is defined as tightness attained

when installing high strength bolts using turn-

of-nut method.

C) Snug tight is defined as tightness attained

when all bolts in a connection have been

torqued to 569 FT-LB.

SPECIFICATIONSSEC 407.06(c)

2. Bolted parts:

Bolted parts shall fit solidly together when assembled and shall not be

separated by gaskets or any other interposed compressible material.

SPECIFICATIONS

407.06 (b)

3. Installation:

An approved tension-indicating device (SKIDMORE-WHILHELM

CALIBRATOR) shall be at all job sites where high-strength fasteners

are being installed and tightened. Bolt tensioning devices and complete

bolt assemblies shall be tested with this device at the start of

construction and as required for the installation procedure. The

calibrating device shall be capable of indicating actual bolt tension within

a tolerance of 2 percent. The manufacturer or an approved testing

agency shall have checked the device for the accuracy specified herein

within the previous 12 months. When turn-of-nut or direct tension

indicators are used, a representative sample of at least three complete

bolt assemblies of each diameter, length, and grade shall be tested.

Calibration

INSTALLATIONTIPS:

COORDINATE WITH CONTRACTOR AND STEEL ERECTOR PRIOR TO

DELIVERY OF STRUCTURAL STEEL

(METHODS OF ERECTION)

(PROCEDURES OF ERECTION AND BOLT INSTALLATION -TURN-OF-NUT METHOD OR DIRECT TENSION INDICATOR)

FIELD ROTATIONAL CAPACITY TEST REQUIRED FOR ALL METHODS OF

INSTALLATION

(RECOMMEND PERFORMING TESTS PRIOR TO STARTING STEEL ERECTION)

INSPECTIONSEC 407.06 (b)

3. Inspection:

When the inspection wrench is a torque wrench, each calibration test

bolt shall be tightened in the calibration device to the minimum tension

specified for its size in Table IV - 3. (7/8” Dia. ASTM A325 – 39,000 lbs)

The inspection wrench shall then be applied to the tightened bolt, and

the torque necessary to turn the nut or bolt head 5-degrees

(approximately 1 inch at 12 inches radius) in the tightening direction shall

be determined.

The average torque measured in the tests of three bolts shall be taken

as the job-inspection torque.

INSPECTIONSEC 407.06 (b)

3. Inspection:

Bolts that have been tightened in the structure shall be inspected in the

presence of the Engineer by applying, in the tightening direction, the

inspection wrench and its job-inspection torque to 10-percent of the

bolts, but not fewer than two bolts, selected at random in each

connection.

If no nut or bolt head is turned by this application of the job-inspection

torque, the connection will be accepted as properly tightened.

If any nut or bolt head is turned by the application of the job-inspection

torque, this torque shall be applied to all bolts in the connection. Bolts

whose nut or head is turned by the job-inspection torque shall be

tightened and re-inspected, or all the bolts in the connection may be

retightened and the connection resubmitted for the specified inspection.

SPECIFICATIONSSEC 407.06 (b)

3. Installation:

Fasteners shall be tightened to provide, when all fasteners in the connection

are tight, at least the minimum bolt tensions shown in Table IV-3 for the size

of fastener used. Minimum bolt tension is also known as the Proof Load .

For a 7/8” diameter ASTM A325 bolt the required minimum bolt tension (Proof

Load) is 39,000 lbs.

SPECIFICATIONSSEC 407.06 (b)

3. Installation:

MAJOR CHANGE IN VDOT SPECIFICATIONS

Tightening shall be performed by the turn-of-nut method,

or by the use of a direct tension indicator using a load

indicator washer.

Power wrenches, if used, shall be of adequate capacity and sufficiently

supplied with air to perform the required tightening of each bolt in

approximately 10 seconds.

A CALIBRATED WRENCH IS NO LONGER ALLOWED!

(POWER WRENCH CAN BE USED TO PERFORM TURN-OF-NUT)

SPECIFICATIONSSEC 407.06 (b)

3. Installation:

Snug tightening shall progress systematically from the most rigid part of the

connection to the free edges, and then the bolts of the connection shall be

retightened in a similar systematic manner as necessary until all bolts are

simultaneously snug tight and the connection is fully compacted.

a.Turn-of-nut tightening:

When the turn-of-nut method for tightening high-strength bolts is used, bolts

shall be installed in all holes and tightened to a snug tight condition to ensure

that all parts of the joint are brought into contact with each other.

All bolts shall be given a suitable match-mark and tightened additionally by

the applicable amount of nut rotation specified in Table IV-4, progressing

systematically from the most rigid part of the joint to its free edges.

SPECIFICATIONSSEC 407.06 (b)

3. Installation:

a.Turn-of-nut tightening:

TABLE IV – 4

BOTH FACES

BOLT LENGTH NORMALTO BOLT AXIS

Up to and including 4 diameters 1/3 turn

More than 4 but not more than 8 diameters 1/2 turn

More than 8 but not more than 12 diameters 2/3 turn

Match marking for turn of the nut method

Close up of match marking for turn of the

nut method

Close up of the best match marking for

turn of the nut method (don’t forget to

mark the bolt to make sure it does not

turn when the nut is tightened.

Is there a problem here?

ROTATIONAL-CAPACITY TEST

PURPOSE:

VERIFY THAT THE FASTENER ASSEMBLY PROVIDED WILL FUNCTION

PROPERLY AS A UNIT

THE ROTATIONAL-CAPACITY TEST ALSO CHECKS THE FOLLOWING

QUALITIES OF THE ASSEMBLY:

Efficiency of lubrication

Installation ductility

Stripping

Determine 10% of the specified proof load

for a 7/8 inch Diameter ASTM A325 Bolt?

(answer in a value of Tension)

A) 4,100 LB

B) 569 FT-LB

C) 3,900 LB

C) 3,900 LB

TABLE IV-3 BOLT TENSION

7/8 inch Diameter ASTM A325 Bolt

Required Min. Bolt Tension = 39,000 LB (Proof Load)

10% of Proof Load = 0.10 x 39,000 LB = 3,900 LB

ROTATIONAL-CAPACITY TEST

PERFORMING THE TEST:

UPON COMPLETION OF THE REQUIRED ROTATION, THE ASSEMBLY MUST

SHOW NO SIGNS OF FAILURE DEFINED AS FOLLOWS:

INABILITY TO ROTATE THE ASSEMBLY TO THE NUMBER OF TURNS AS

SPECIFIED IN SEC 226.02 (h) 3. a.

INABILITY TO REMOVE THE NUT FOLLOWING THE TEST

(NUT SHOULD SPIN “FREELY”)

SHEAR FAILURE OF THE THREADS DETERMINED BY VISUAL INSPECTION

(BOLT AND NUT THREADS)

TORSIONAL FAILURE OF BOLT (TWISTING)

ROTATIONAL-CAPACITY TEST

SEC 407.06(b)

1.Bolts, nuts, and washers:

Prior to installation, the Contractor shall perform a field rotational-capacity

test on two nut, bolt, and washer assemblies for each diameter and length in

accordance with Section 226.02(h)3.

SPECIFICATIONSSEC 407.06 (c)

3. Installation:

Bolts shall be installed with a hardened washer under the nut or bolt head,

whichever is the element turned in tightening.

The length of bolts shall be such that the point of the bolt will be flush with or

outside the face of the nut when completely installed without over-tensioning

the bolt.

(Contractor shall also perform field rotational-capacity test)

ROTATIONAL-CAPACITY TEST

PERFORMING THE TEST:

ELONGATION OF BOLT, IN THREADS BETWEEN THE NUT AND BOLT HEAD,

IS TO BE EXPECTED AT THE REQUIRED ROTATION AND IS NOT TO BE

CLASSIFIED AS A FAILURE.

ROTATIONAL-CAPACITY TEST

DOCUMENTATION:

SPECIFICATION AND CONSTRUCTION MANUAL DO NOT ADDRESS

DOCUMENTATION SHOULD BE KEEP IN PROJECT RECORDS (Diary)

RECORD: (TWO ASSEMBLIES TESTED PER LENGTH PER RCT LOT)

CALIBRATOR SERIAL NO. CALIBRATION DATE TYPE/GRADE BOLT

BOLT DIAMETER BOLT LENGTH RCT LOT NO.

NO. TURNS MEASURED TENSION MEASURED TORQUE

NOTE CONDITION OF BOLT AFTER COMPLETING TEST

CONTACT BRIDGE SECTION IF BOLTS DO NOT PASS RCT (DO NOT USE)

ROTATIONAL-CAPACITY TESTProject No. Date:

Rotational Capacity Test Results Grade A325,Galvanized Bolt Diameter 7/8"

Skidmore - Wilhelm Bolt Tension Calibrator Serial No. 5031 Calibration Date - 09/09/99

4 3/4" Length Lot # 508064 A 2 3/4" Length Lot # 508039 C

@ 1 turn @ 2/3 turn

Measured Tension # 1 53,000LB # 1 56,000 LB

# 2 50,000LB # 2 51,000 LB

Measured Torque # 1 760 FT-LB # 1 540 FT-LB

# 2 760 FT-LB # 2 610 FT-LB

4" Length Lot # 505364 A 2 1/2" Length Lot # 95094 A

@ 1 turn @ 2/3 turn

Measured Tension # 1 60,000 LB Length insufficient for tension

# 2 60,000 LB measurement

Measured Torque # 1 700 FT-LB # 1 700 FT-LB

# 2 800 FT-LB # 2 800 FT-LB

No failures noted - all threads OK after tensioning

ROTATIONAL-CAPACITY TEST

INSPECTIONSEC 407.06 (b)

3. Inspection:

(TORQUE WRENCH)

The Engineer will observe the installation and tightening of

bolts to determine that the selected tightening procedure is properly

used and will determine that all bolts are tightened.

The Contractor in the presence of the Engineer shall use an inspection

wrench to inspect the tightening of bolts.

There shall be a washer under the part turned in tightening each bolt if

washers are so used on the structure.

Bolts shall be inspected to ensure that the

proper _________ is achieved.

A) torque

B) tension

C) number of turns

B) tension

TABLE IV-3 BOLT TENSION

We want to ensure that the proof load (required

minimum bolt tension) for a given bolt is achieved.

(Proof load-7/8” Diameter ASTM A325 bolt = 39,000 LB)

INSPECTIONTIPS:

WHEN INSTALLING HIGH STENGTH BOLTS A MINIMUM BOLT TENSION IS

REQUIRED (SLIP-CRITICAL CONNECTION)

TORQUE CAN BE DIRECTLY RELATED TO TENSION UNDER IDEAL

CONDITIONS:

(PROPER STORAGE OF BOLTS, NUTS, WASHERS) (PROPER LUBRICATION OF BOLTS, NUTS)

(RUST FREE BOLTS AND NUTS)

ASTM A325 3/4 INCH DIAMETER BOLT (REQD MIN. TENSION = 28,000 LB)

CONDITION TENSION TORQUE FAILURE

NEW 28,000 LB 300 FT-LB NA

DRY 7,500 LB 300 FT-LB NA

RUSTED 10,000 LB 300 FT-LB NA

24,000 LB 750 FT-LB BOLT- SHEAR

SPECIFICATIONSSEC 407.06 (3b)

3 Installation:

b. Direct tension indicators:

http://www.appliedbolting.com/video-

squirter-dti-calibration.html

http://www.appliedbolting.com/content/boltin

g-resources/pop-videos.php?video=10

WHAT DOES THE FUTURE HOLD FOR BOLTS!