CONCRETE CONNECTIONS

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Questions and Answers

What is weldable rebar?

When welding of steel concrete reinforcement or rebar is needed the most common type of rebar used for these applications meets the requirements of ASTM A706 (A706).

Is all rebar weldable?

Under the right circumstances standard rebar or ASTM A615 rebar can also be welded, but this process can be difficult and expensive.

Where weldable A706 rebar is applicable? 1. Bridge and building construction. In any steel, concrete, or composite structure where steel reinforcement connections are

needed. 2. Precast concrete; railroad grade crossing boxes, structural precast, embedment anchors, etc. 3. Seismic Applications, reinforcement in high stress regions of a structure or any concrete connection where anchor ductility

is required. 4. Threaded, Bent and Straight Bar Stud Applications.

Why choose stud weldable A706?

1. Automatic machine controlled welds. Consistent weld quality. 2. Full Penetration weld vs. fillet. 3. Much faster production than using traditional welding methods. 4. Built in quality monitoring when using the Nelware software. 5. Cost savings over hand welded rebar.

What are difficulties in hand welding rebar? What are some selling points to stud welding vs. hand welding rebar?

Traditional rebar welding includes but is not limited to; costs of using an AWS certified welder, preparation of written welding procedure specifications, preheat when required, cutting bars to correct lengths in the field and welding consumables required.

It can be difficult for the welder to hand weld around the base of a #4 or #5 weldable rebar because of the size of rebar compared to the required bead of weld.

What is the required fillet weld (bead) size? o AWS D1.1 Table 7.2 has minimum fillet weld sizes per stud diameter, #4 requires 1/4” and #5 and #6 require 5/16”

minimum. Weld sizes should be designed or verified by the engineer of record and dependent on the application and loading requirements.

See Stud Welding vs. Hand Welding ROI below. Why choose D6L over D2L?

In seismically active areas or applications were ductility is key, this material will stretch and elongate before failure resulting in “ductile failure”. D2Ls have very little differentiation between yield and tensile resulting in “brittle failures” with very little elongation making them undesirable for use in the same application.

The D6L also has raised ribs similar to standard concrete reinforcing as opposed to the indented deformations of the D2L.

The ICC evaluation report for D2L acceptance includes language that leads to misunderstandings with inspectors and engineers.

When will you have an ICC report for the D6L?

Answer this question with another question. “Do you have an ICC report for any of the other welded rebar on your project?” ICC evaluation reports are used for proprietary products which do not have other building code acceptance. Nelson D6Ls are fully compliant with the codes listed above.

What is available, what is the lead time and how much does it cost?

#4 #5 and #6 in various configurations are available upon request. Any stud length required is available. What is our current threading capability?

Standard UNC threads.

Tapered thread (Lenton/Dayton Superior Terminator and Coupler compatible).*Note lead times and cost is TBD.

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Rebar Stud Anchors

Tensile Requirements

Grade 60 (420)

Tensile strength, min, psi (MPa) 80 000 (550*)

Yield strength, min, psi (MPa) 60 000 (420)

Yield strength, max, psi (MPa) 78 000 (540)

Elongation in 8 in. (200mm), min % - Bar Designation #’s 3, 4, 5, 6, (10, 13, 16, 19) 14

*Tensile strength shall not be less than 1.25 times the actual yield strength

D Stud Dia.

L Length

Part No.

1/2 6 3/16 102-065-013

1/2 12 3/16 102-065-004

1/2 18 3/16 102-065-003

1/2 24 3/16 102-065-002

1/2 36 3/16 102-065-001

1/2 42 3/16 102-065-019

1/2 48 3/16 102-065-014

1/2 52 3/16 102-065-020

1/2 56 3/16 102-065-018

5/8 12 3/16 102-065-016

5/8 18 3/16 102-065-007

5/8 24 3/16 102-065-006

5/8 30 3/16 102-065-005

5/8 48 3/16 102-065-017

3/4 12 3/16 102-065-015

3/4 18 3/16 102-065-011

3/4 30 1/4 102-065-009

3/4 36 1/4 102-065-008

3/4 48 3/16 102-065-021

A706 / A706M - 15

Deformed Bar Designation Numbers, Nominal Weights (Masses), and Nominal Dimensions

Nominal Dimensionsª

Bar Designation Nominal Weight, lb/ft

(Nominal Mass, kg/m) Diameter, in. (mm)

Cross-Sectional Area

in. 2 (mm

2)

Perimeter

in. (mm)

4 (13) 0.668 (0.994) 0.500 (12.7) .020 (129) 1.571 (39.9)

5 (16) 1.043 (1.552) 0.625 (15.9) 0.31 (199) 1.963 (49.9)

6 (19) 1.502 (2.235) 0.750 (19.1) 0.44 (284) 2.356 (59.8)

ª The nominal dimensions of a deformed bar are equivalent to those of a plain round bar having the same weight (mass) for foot (meter) as the deformed bar

D6L Rebar D6L Rebar studs are fully stud-weldable deformed bar concrete anchors

without the need for pre-heat treatment or specialized welding equipment &

accessories.

D6L Rebar Applications

Precast concrete grade crossings

Concrete connections where ductility is key

Thread, bent and straight bar stud uses

Seismic management

Bridge & building construction

The D6L Rebar Studs Meets all the Requirements of: ASTM A706 – Standard Specification for Deformed and Plain Low-

Alloy Steel Bars for Concrete Reinforcement

o Grade 60 Bars

ACI 318 – Building Code Requirements for Structural Concrete

o Chapter 18 (318-14) – Earthquake Resistant Structures

AWS D1.1 Structural Welding Code – Steel

o Certified Stud-weldable in accordance with the

requirements Clause 7 Stud Welding.

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Physical Properties of D6L Anchors

Dia. AS

Nominal Area

ASTM Designation

AS fy Yield fy

Lbs. (min.)

AS fu Tensile

Lbs. (min.)

fu - Ultimate strength (tensile) 80,000 psi min. fy - Yield strength 60,000 psi min. AS - Area of stud shank

Cold finished low carbon steel, ASTM A706: C – 0.33% max Mn – 1.56% max P – 0.043% max S – 0.053% max

Short Form Specification

To insure that certified Nelson products are used, the following specification is suggested: "(Welded Concrete Reinforcement / Deformed Bar Anchors / Concrete anchors) shall be Nelson, rebar anchors, type D6L, full penetration, automatic machine welded, as shown on the drawings. Studs shall be made from cold-worked, deformed wire per ASTM A-706 and shall be welded pursuant to the manufacturer’s commendations.”

3/8 0.11 3 6,600 8,800

1/2 0.2 4 12,000 16,000

5/8 0.31 5 18,600 24,800

3/4 0.44 6 26,400 35,200

Embedment Properties of D6L Anchors D6L Tensile Capacity in Concrete – Pull Out Strength

Deformed rebar anchors embedded in concrete have tensile capacities which may be conservatively calculated according to the formulas of Table 25.4.2.2 for development length in ACI 318-14. Following are embedment length requirements to develop the full bar strength capacity. Appropriate spacing with regard to free edges and adequate distance between anchors should be maintained to reach full capacity. Good engineering practice dictates that safety factors appropriate to the connection usage should always be used. Embedment length can be reduced using factors representing bar placement within concrete, transverse reinforcement across failure planes and excessive reinforcement provided over reinforcement required.

Minimum Embedment Length for D2L Anchors in Tension

D6L Tensile Capacity in Concrete – Pull Out Strength

Normal Weight Concrete Compressive Strength, f'c (psi)

Minimum Embedment Length for Full Anchor Capacity Development, After Welding (inches)

Bar Diameter, db

0.375 0.500 0.625 0.750

2500 18.00 24.00 30.00 36.00

3000 16.43 21.91 27.39 32.86

3500 15.21 20.28 25.35 30.43

4000 14.23 18.97 23.72 28.46

4500 13.42 17.89 22.36 26.83

5000 12.73 16.97 21.21 25.46 Note: Embedment lengths are calculated from ACI Standard ACI 318, Section 25. ACI minimum embedment length requirement is 12".

Light Weight Concrete Compressive Strength, f'c (psi)

Minimum Embedment Length for Full Anchor Capacity Development, After Welding (inches)

Bar Diameter, db

0.375 0.500 0.625 0.750

2500 24.00 32.00 40.00 48.00

3000 21.91 29.21 36.51 43.82

3500 20.28 27.04 33.81 40.57

4000 18.97 25.30 31.62 37.95

4500 17.89 23.85 29.81 35.78

5000 16.97 22.63 28.28 33.94 Note: Embedment lengths are calculated from ACI Standard ACI 318, Section 25. ACI minimum embedment length requirement is 12".

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ROI: D6L Rebar Stud vs. ASTM A706 Rebar COST COMPARISON CALCULATOR

Stud Type 1/2 x 18 3/16 Rebar Stud #4 Rebar 18" Long

Weld Type Full Penetration Stud Weld 1/4" Fillet Weld

Production Speed 200 - 250 Studs / day 50 - 60 Bars / day

Fabrication Time

Rebar Prep - Cutting* 0 seconds 0 seconds

Preparation - Preheat 0 seconds 30 seconds

Welding 15 seconds 180 seconds

Total 15 seconds 210 seconds Labor Costs

Actual Labor Cost $25.000 $/hr $55.000 $/hr

$0.007 $/sec $0.015 $/sec

Fabrication - Welding $0.10 /weld $3.21 /weld Material Cost

Raw Material - Type #4 x 18 D6L 12" long #4 Rebar Cost $2.21 $0.51 Welding Consumables N / A 0.03 lbs E7018 Electrode Cost $0.00 $0.11

Total $2.21 $0.62 Stud Welded Hand Welded

Fully Burdened Costs $2.31 $3.83

Annual Volume 1 units - welds 1 units - welds

Annualized Cost $2.31 $3.83

Cost Advantage $1.51

*Preparation of rebar (measuring, cutting, cleaning, etc.) for welding, this work is typically performed by someone with a different labor rate than the welder.

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Stud Welding Setup Parameters:

Full strength stud welding results can be obtained by understanding the following settings or adjustments, and how they relate to weld quality.

Plunge is the amount of stud that protrudes beyond the ferrule. This portion of the stud length is available to be “burned off”, or melted, to develop the weld flash. Long or excessive plunge may cause excessive splatter and high or uneven fillet formation. Plunge is a physical measurement set and measured with the stud and ceramic ferrule in place on the stud gun.

Lift is the distance the gun pulls the stud away from the base material. Lift is essential to the stud weld process since is creates an air gap which the current must bridge. The current flow across the resistance of this gap creates the heat to melt the stud and base material. If no gap exists, the current will not create sufficient heat to melt the metal. Short lift may allow molten metal to bridge the arc-gap, resulting in cold welds. Excessively long lift increases the chance of having arc blow and welds that are bonded on only one side of the stud base. Lift is set on the stud gun and is measured physically when the weld cycle is initiated. Note that this should be set and measured by placing the stud and ferrule on a non-conductive surface and initiating the weld cycle so that an actual molten weld is not made while lift is being measured.

Time is the normal duration of the weld. On thin base material, shorter than normal time and higher amperage can be used to achieve sufficient heat, and still prevent melting through the base material. On some base materials, longer times and reduced amperage improves the ductility of the weld zone.

Amperage is the current from the power source that flows through the weld arc. Increasing the amperage increases the weld heat. As with the time setting, a higher amperage setting is needed for larger stud sizes. Amperage is set on the stud welding control system current setting indicator.

Alignment is centering the stud in the ceramic ferrule so that the stud does not contact the ceramic ferrule during the lift and plunge, which may cause friction or binding between the stud and ferrule. Binding can slow the stud plunge so that there is less than full penetration of the stud into the molten weld pool resulting in less than full weld strength.

Electric Arc Stud Welding Parameter / Setup for D6L Rebar Studs

ASTM Designation

Diameter Area (in

2)

Downhand Welding Vertical Welding Overhead Welding

(in) (mm) Amp Sec Lift Plunge Amp Sec Lift Plunge Amp Sec Lift Plunge

#4 1/2 12.7 0.20 975 0.525 0.093 0.187

#5 5/8 15.9 0.31 1333 0.860 0.093 0.187

#6 3/4 19.1 0.44 1700 1.03 0.125 0.250 1800 0.800 0.125 0.250 1650 0.800 0.125 0.250

> These welding setup parameters produce satisfactory results, in our welding laboratory here in Elyria, Ohio. They should not be considered so restrictive, however, that they prevent modification by authorized personnel to meet specific application or jobsite conditions. Refer to American Welding Society's (AWS) requirements regarding production control, application qualification and manufacturer's stud base qualification for further clarification. > The settings shown are for welding directly to the base metal, in the downhand position. For welding through metal deck or welding in other positions consult your Nelson representative. > Stud welding, as with any welding process, should be done safely with properly maintained equipment and according to recommended practices. For additional information contact your Nelson Representative or see: ANSI/AWS C5.4 "Recommended Practices for Stud Welding", ANSI/ASC z49.1 "Safety in Welding and Cutting." Both available from American Welding Society... > Plunge is the distance from the face of ferrule to end of stud, not including the flux load. Lift is the distance the stud retreats when the gun is triggered. Compress the stud against a non-conductive surface to make the lift measurement. > Using a set of drill bits is a convenient way to properly gage the necessary lift and plunge during set up, note 1/16" = 0.0625", 1/8" = 0.125", 3/32" = 0.09375. > For detailed installation and maintenance data refer to the Operation and Service Manuals for the stud welding system and gun being used. > Special ferrules are required for vertical welding, overhead welding and specialized welding application, e.g. welding into the corner of a steel angle.

Welding Accessories for D6L Rebar Studs

ASTM Downhand Welding Vertical Welding Overhead Welding

Ferrule Chuck Grip Foot Ferrule Chuck Grip Foot Ferrule Chuck Grip Foot

#4 100101039 500011544 501006027 502002042 100101224 500011544 501006027 502002042 500011544 501006027 502002042

#5 100101152 500011545 501006027 502002042 100101226 500011545 501006027 502002042 500011545 501006027 502002042

#6 100101140 500011546 501006028 502002042 100109035 500011546 501006028 502002042 100101140 500011546 501006028 502002042

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Notes: