Torque vs. Tension

February 21, 2011

John O’Brien – Skidmore Wilhelm

Overview - Tension vs. Torque Bolt Tension Calibrator (Skidmore) 4 Methods of Pre-Installation Verification

◦ Each method can be compromised without proper diligence

Best Practices (how to keep the inspector happy)

Outline

What’s the difference between tension & torque?

Is it a big deal? 90% of torque overcomes friction (not tightening) Conditions outside control

of bolt manufacturer affects performance

Overview Tension vs. Torque

What does a Skidmore do?◦ Simulates bolted joint◦ Measures Force in Lbs

How does a Skidmore work?◦ Hydraulic Load cell

Why is it used?◦ Test Bolts◦ Verify bolt tensioning

Bolt Tension Calibrator (Skidmore)

Are bolts so different? Live Demonstration – Effect of Lubrication

Calibrator (continued)

Photo courtesy of Robert Shaw, President, Steel Structures Technology Center Inc.

Photo courtesy of Chris Curven, Vice President, Applied Bolting Technology

Rusty bolts okay? Can’t I just lube them?

Calibrator (continued)

Photo courtesy of Chris Curven, Vice President,

Applied Bolting Technology

.

Photo courtesy of Chris Curven, Vice President,

Applied Bolting Technology

Rusty bolts okay? Can’t I just lube them?

Calibrator (continued)

Photo courtesy of Chris Curven, Vice President,

Applied Bolting Technology

.

Which bolts maintain lubricity?

Calibrator (continued)

Photo courtesy of Robert Shaw, President, Steel Structures Technology Center Inc.

Photo courtesy of Chris Curven, Vice President, Applied Bolting Technology

Wrenches Compatible with Skidmore Units◦ Hand Torque Wrenches◦ Impact Guns◦ Electric Wrenches◦ Hydraulic Wrenches

Calibrator (continued)

Turn of the Nut Calibrated Torque Wrench Direct Tension Indicators (DTI’s or “squirter

washers”) Tension Control Bolts

4 Methods of Pre-Installation Verification

Turn of the Nut◦ Snug bolt◦ Mark bolt/nut/plate◦ Turn nut required amount– make sure

tension is at least 5% over required amount (see table)

◦ In structure bolt head must be prevented from turning

Turn of the Nut

Turn of the Nut?

Calibrated Wrench◦ Snug bolt◦ Tighten to tension plus 5%◦ Measure torque to move additional 5

degrees◦ Average 3 bolts assemblies

Calibrated Wrench

Calibrated Wrench

DTI◦ Snug bolt – Verify gaps with feeler gage◦ Tighten to tension plus 5%◦ Verify gaps with feeler gage◦ Squirter washers

Direct Tension Indicator

Tension Control (TC) Bolt◦ Snug bolt◦ Tighten to spline break◦ Verify tension is correct

Tension Control Bolts

Tension Control Bolts

Proper setup of Skidmore◦ Seat parts◦ Proper Clamping◦ Oil Leaks (small leak okay…get fixed

when able) Spacers – Don’t stack washers!! Torque reaction arms? Spacer Bushings

Best practices (how to keep the inspector off your back!)

Frequently Asked Questions◦ Temperature Effect◦ Calibrate the Skidmore? How often?◦ Is there a source for information on proper

bolting? www.boltcouncil.org Research Council Structural

Connections (RCSC) Structural Bolting Handbook – by SSTC

Questions?

Summary