Owens Supply Company provides a nationwide service to contractors by specializing in rebar pre-assembley. Our focus on innovating foundational reinforcement, helps us provide products such as caissons, drilled shafts, micropiles and continuous-flight-auger pile cages faster, cheaper and safer.
Welded Assembly of Reinforcement
A Review of Welded Assembly ASTM A706 Reinforcement and how It results in rapid on-site installation of reinforcement.
Paul R. Owens - Owens Supply Company LLC. Plainfield, II. 60585
There has always been pressure to reduce the time and cost of concrete construction. However prefabrication, a common way to Increase efficiency, has only recently been applied to reinforcement bars for concrete in the U.S.. In 1961 the American Welding Society published its first reinforcing steel welding standard. Over the years It has revised practices for welding rebar In the U.S. AWS Dl.4/Dl.4M:200S describes, In particular, the acceptability of welding ASTM A706/A706M low alloy steel. Material with a carbon equivalent of less than 0.55 can be welded. (AWS 01.4) American Concrete Institute's ACI 318-08, Building Code Requirements for Structural Concrete and Commentary. Section 3.5.2 of AC1318..Q8 states that welding of reinforcing bars shall conform to AWS 01.4 and that type and location of welded splices and other required welding shall be indicated on the design drawings or In the project specs.
Metallurgists typically define the weld ability of steel based on Its carbon content or C.E. The lower the carbon equivalent, the more weld able the steel. Steels with carbon contents less than 0.35% are considered to be readily weld able. According to table 5.2 in AWS 01.4, the C.E. for #7 (22) bars and larger should be less than 0.45% and for 86 (19) and smaller bars, C.E. should be less than 0.55% in order to weld them. If the C.E. is not less than the value Indicated, then the bars must be preheated as per AWS 01.4. The higher the strength and the carbon equivalent of the steel, the more susceptible it is to cold cracking (cracking that occurs after the metal has solidified) when welded. Brittle tack welds on cold .. worked steel have caused rebar failures.
The following is a review of prefabricated ASTM A706 reinforcement and how it results In rapid on-site installation of reinforcement. The main reason for specifying prefabricated ASTM A706 reinforcement is the shorter construction time. However, prefabrication requires commitment at the design stage If the benefits of faster construction and earlier completion are to be fully exploited. Prefabrication can lead to simplified reinforcement drawings, which are cheaper to produce, simpler to check and less likely to be misinterpreted on site. It also results In more uniform work load for setting crews, and less congestion at the jobsite, allowing better access and shorter setting times. For loose bar reinforcement, the setting price varies according to bar size and bar length, plus additional charges for degree of difficulty and reinforcement congestion. Difficult access slows productivity and Increases setting cost. The variation In setting costs Is considerably reduced with prefabricated reinforcement. Extra cost Is also Incurred with loose bars by the need to locate and clean them on a muddy site and to arrange their delivery to suit the construction sequence.
Welded ASTM A705 reinforcement assemblies can be used for all types of structural elements including caissons, footings, floors, columns, beams and walls. They offer benefits to the contractor, designer and client, resulting In:
1. Lower labor requirement
2. Faster setting rate
3. Less waste
4. Simplified detailing and easier setting
5. Improved site planning and organization
6. Improved quality from factory controlled assembly
When using ASTM A706 prefabricated reinforcement, the following points should be taken Into account. 1. Specifying prefabricated reinforcement at the design stage enables contractors to bid more competitively, allowing the consequent savings to be passed on to the client. 2. Repetition Is essential for economy when designing prefabricated reinforcement; for economic production a design should be used at least 20 times. 3. The choice between prefabricated and loose bar assemblies, depends on the availability of cranes, the amount of reinforcement, the project size and the need for greater speed of construction. The development of factory assembly of ASTM A706 reinforcement has created major opportunities for savings in project costs and construction times.
• Improved onsite productivity-eliminates time consuming jobsite assembly.
• Greater Dimensional Stability-welded rebar cages hold their dimensions throughout handling and setting.
• Fast-away from the construction site under controlled conditions using the MIG welding process. Take rebar assembly of the critical path.
The results of speed trials provide compelling evidence of the need for major change In the specification and detailing of ASTM A706 reinforcement for structural concrete
American Welding Society, 550 N.W. Le Jeune Road, Miami, FLo33126
American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428
American Concrete Institute 38800 Country Club Dr. Farmington Hills, M14833l-3439 USA
Concrete Reinforcing Steel Institute 933 N Plum Grove Rd Schaumburg, Il60173 External Links Concrete Reinforcing Steel Institute (http://www.crsl.org)
Quality Assurance Procedures
Owens Supply Company (OSC) strives to ensure a safe work place. Our production facility meets or exceeds the safety requirements of OSHA construction industry standard (29 CFR 1926).
Owens Supply Company (OSC) as required by AWS 01.4 (WPS) uses Visual Inspection (VT) of all welds on a daily schedule as follows.
1. Material-Ali materials that are to be fabricated will indicate producer, heat number, grade, type, & size. In addition the material will be inspected for cleanliness and freedom from defects.
2. Process-During welding (OSC) will indicate welding machine, wire size, speed & amperage settings. Verification that we are compliant with specified (WPS).
3. Inspection-Upon completion of each weld using appropriate lighting the size, appearance, bead profile and surface quality will be visually inspected. Upon completion of each assembly a supervisor will conduct an overall Inspection for fitness of purpose.
Environmental responsibility Is an Integral part of our business, not an obligatory side Issue.
Our primary 80alls to find solutions that make sense, both economically and ecologically, and to use resources efficiently while minimizing environmental impact. Reusable packaging and containers for parts shipping are used where possible.
Owens Supply Company LLC
10052 Clow Creek Rd
Plainfield, Il. 60585