Lifting Systems for Precast Concrete Products - MC ...
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| |Lifting Systems for Precast Concrete Products | |
| |Safe, effective, economical lifting and handling of precast concrete products is essential for| |
| |producers and users of these products. Precast concrete products need to be lifted and handled| |
| |a number times during production and installation, particularly when removing from the casting| |
| |bed or form, transporting from the casting bed to storage or from storage to point of use, | |
| |lifting into installed position or anchoring to a structural frame or other concrete members | |
| |(where required). | |
| |Precasters use a variety of methods and equipment, including commercially manufactured | |
| |inserts, home-made devices, lifting clamps and grooves for slings. There are a number of | |
| |considerations that precasters use when selecting lifting systems. These include safety,, ease| |
| |of use by the producer and the installer, and the impact on finished concrete product. | |
| |Safety | |
| |Concern about the safety of employees and other personnel involved in the production and | |
| |installation of precast concrete products is paramount. There are many reasons for this, but | |
| |most importantly, prioritizing safety is just the right thing to do. There are also good | |
| |business reasons for establishing excellent safety practices. When accidents and injuries to | |
| |workers occur, potential costs include: | |
| |Damage to products | |
| |Worker's compensation (actual costs and future policy increases) | |
| |Absence of worker | |
| |Morale | |
| |Adverse publicity | |
| |Liability | |
| |Product Integrity. Precast concrete products should not be moved until the concrete has gained| |
| |sufficient compressive strength. In some cases, the form and the product are moved at the same| |
| |time with the lifting hook connected directly to the form. Some forms are made to remain in | |
| |place while inserts, hooks, or slings are used to remove the product. | |
| |Liability. In legal cases where accidents have occurred, companies not complying with the | |
| |applicable codes and standards can be found liable or incompetent. Attorneys rely on codes | |
| |being state of the art. | |
| |Compliance with Safety Requirements. In general, the capacity of lifting inserts should be | |
| |four times the actual load. Lifting hardware should be five times the actual load. When wire | |
| |rope is used in a lifting system, the U.S. Occupational Safety and Health Administration | |
| |(OSHA) recommends a minimum safety factor (FS) of five. The American National Standards | |
| |Institute (ANSI), however, recommends a minimum safety factor of seven. Because of the | |
| |differing standards, the designer needs to evaluate the situation and choose an appropriate | |
| |safety factor. If the wire rope will experience mild "wear and tear," then an FS of five might| |
| |be satisfactory. At the other extreme, severe "wear and tear" conditions will warrant an FS of| |
| |seven. | |
| |Several organizations have related regulations or standards. OSHA is entrusted with | |
| |enforcement and can levy penalties (usually financial) on organizations not complying with the| |
| |requirements of CFR Title 29. Two organizations, ANSI and the American Society for Testing and| |
| |Materials (ASTM), create and update codes and standards. Various U.S. and Canadian agencies | |
| |and local governments may have additional requirements. | |
| |Types of Lifting Inserts | |
| |Precast concrete producers use various types of inserts. When choosing lifting inserts, | |
| |precasters are concerned with many factors, including safety, compliance with OSHA and other | |
| |requirements, ease of installation, ease of use by rigger, angle of lift/pull, vacuum and | |
| |water testing, patching, quality, liability, and cost. | |
| |Commercially Manufactured Inserts. A variety of manufactured lifting inserts are currently | |
| |available. These products are manufactured from several different materials, including | |
| |hot-forged high quality steel, wire coil, carbon steel roping, grade 60 rebar, plastics | |
| |(bonded impact polystyrene, thermoplastic, Hytrel¨ polyester, polypropylene, etc.), and | |
| |ductile iron. | |
| |Generally, electo-galvanizing (per ASTM A 633) or hot-dipped galvanizing (per ASTM A 123 or A | |
| |153) is available to protect the inserts from external corrosion. Plastic tips or stainless | |
| |tips are also often available. Most manufacturers recommend against any welding modification | |
| |to their products. | |
| |Full-service suppliers will provide comprehensive engineering and design information with | |
| |their products. Product catalogs often provide comprehensive information on selection, | |
| |installation, rigging, and handling. | |
| |Detailed engineering data is essential for the precast concrete producer to properly use and | |
| |install lifting inserts. | |
| |Precasters should use the appropriate hardware and inserts for lifting their products. | |
| |Occasionally, hardware and inserts are used in situations beyond their design capacity or in | |
| |applications for which they were not designed. They may function adequately for long periods | |
| |of time, but eventually they most likely will fail. The end result may not only be a product | |
| |dropped in the yard, but a lifting insert failure that could lead to serious accidents and | |
| |injuries. | |
| |Manufacturers design inserts based on static loads, proper installation and specific concrete | |
| |design strength. If a product is moved prior to reaching the design strength of the concrete | |
| |or subjected to a dynamic load (such as being transported at a high rate of speed or bumped | |
| |when driving over a ditch), the insert may fail. Lifting a concrete product frozen to the | |
| |ground will also exert additional forces on the lifting system and the lift truck. | |
| |When the inserts are stressed due to forces and loadings beyond the design capacity, the | |
| |inserts may not fail, but be permanently damaged. This is very dangerous, because the system | |
| |will appear to be intact, but may later fail at loads below the rated capacities. | |
| |Some manufactured inserts are not engineered. It can be very difficult to evaluate the | |
| |strength and capacity of such products. Additionally, liability for failures can be complex. | |
| |Types: | |
| |plastic inserts (special attachment required) | |
| |recessed pockets with loops | |
| |split anchors | |
| |ring clutches | |
| |lifting eye bolts | |
| |coil inserts | |
| |plates | |
| |pulling irons | |
| |lift pins (remain in product; special forklift attachment required) | |
| |Advantages of commercially manufactured inserts: Load tested and designed to meet OSHA | |
| |requirements. Does not have to be removed at the jobsite, generally no mortar patching | |
| |required. May be more economical than other inserts. Special reinforcing may be added to | |
| |increase a load capacity of an insert. Reduces spalling at insert location. Manufacturers may | |
| |be able to provide extensive technical support to precasters using their products. | |
| |Disadvantages: Often appear to be more expensive than "home-made" devices. May need special | |
| |handling attachments or equipment that can be costly. These items must be installed as | |
| |designed by the manufacturer, otherwise failures and pullouts may occur. Any change in use | |
| |from designed purpose should be verified by the manufacturer's technical services department. | |
| |"Home-made" devices. These devices usually are not engineered or load tested. Several types of| |
| |home-made devices are routinely used, including bent reinforcing steel bar, prestressed strand| |
| |as loops and recessed bars (countersunk with temporary blockouts). | |
| |Bent bars or loops must be carefully placed within the formwork and rebar cage to ensure | |
| |adequate concrete cover. If rebar is placed close to the finished concrete surface, corrosion | |
| |of the rebar may occur. The rebar will expand due to this corrosion and spall the concrete | |
| |surface. Deformed bars work best, since smooth bars require longer development lengths. | |
| |Loops are cut off after the precast concrete product is installed to reduce corrosion. | |
| |Sometimes a recessed pocket is created with a neoprene blockout for the bent bars or loops. | |
| |After the precast product is installed the recessed pockets can be filled with grout or other | |
| |concrete patching material. The recessed pocket should be designed such that a chain or sling | |
| |will not damage the surrounding concrete. | |
| |Advantages of home-made devices: Inexpensive, simple to use, no need for special lifting | |
| |hardware or attachments, quick connect/disconnect. | |
| |Disadvantages: Expensive and/or inconvenient to load test or design to meet OSHA documentation| |
| |requirements. Often mortar patching is required at the jobsite. Installers can be sloppy about| |
| |positioning of loops and bars, which can affect performance. | |
| |Lifting clamps/grapples. These products work with cranes and forklifts. They are specialized | |
| |lifting devices designed for specific types of precast products, such as grapples for | |
| |transportation barriers, pipe handlers (clamps) for manhole sections, box culvert handlers and| |
| |lift clamps for precast concrete steps. | |
| |Advantages of lifting clamps/grapples: Fork truck/crane operators can accomplish all handling | |
| |operations without leaving the truck. When properly operated, there is reduced damage to | |
| |products. Lower labor costs as fewer workers can move more product. | |
| |Disadvantages: No option for others to install the product unless inserts are also installed. | |
| |Specialized, sometimes expensive equipment required. Operators need training to avoid | |
| |overloading the equipment (similar to lift truck training). | |
| |Grooves for slings. Some precasters design their forms to create a horizontal groove in end | |
| |walls of box-shaped products, such as utility vaults and septic tanks. Lifting cables are | |
| |placed in the grooves on each side of the product. | |
| |Advantages of grooves for slings: Inexpensive, easy to install in precast products. Handling | |
| |equipment (slings) is standard, readily available and uncomplicated. No problems with | |
| |spalling, no holes made through the product. | |
| |Disadvantages: Crane/fork lift operator must have substantial experience. Slings can fray and | |
| |need to be regularly inspected. Can only be used for rectangular shapes, such as septic tanks | |
| |and small utility vaults. | |
| |Selection Tips | |
| |Selection of proper anchors for lifting precast concrete products requires consideration of a | |
| |number of factors including the type of load, type of lift, concrete thickness, reinforcement,| |
| |ease of attachment to product, compliance with safety requirements, ease of use by rigger | |
| |during final installation and cost. Precasters should consider the following factors when | |
| |determining the load per insert: | |
| |Weight of the concrete shape. | |
| |Weight of form, if product will be lifted before concrete product is stripped. | |
| |Adhesion to the form surface. | |
| |Type of concrete (normal, light weight, etc.). | |
| |Dynamic loads (impact due to handling, transport or erecting conditions). | |
| |Concrete compressive strength at time of initial lift. | |
| |Number of lifting points and type of rigging to be used. | |
| |Direction of pull (cable or sling angle). | |
| |Flexural stresses of thin concrete shapes. | |
| |Panel or product thickness. | |
| |Edge distance (thin wall, free edge or shear loading conditions). | |
| |Removing a precast concrete product from its form can create additional loads that effectively| |
| |increase the dead load of the item. Forces due to adhesion will vary with different form | |
| |release agents. One insert manufacturer recommends using the following loads when determining | |
| |adhesion forces (additional dead load) for a precast item: | |
| |Concrete Forms 20 lbs./sq. ft. | |
| |Steel Forms 25 lbs./sq. ft. | |
| |Plywood Forms 50 lbs./sq. ft. (Flat Surface) | |
| |Plywood Forms 75 lbs./sq. ft. (Ribbed Surface) | |
| |Detailed calculations should be made by an engineer to determine the loads for each insert. | |
| |Ease of Use by Precast Concrete Producer | |
| |Lifting inserts should be simple and straightforward for the precast concrete worker to | |
| |install into a product. Secure attachment to the steel reinforcement or to the formwork is | |
| |essential. Inserts must not shift or move during concrete placement. Welding of manufactured | |
| |precast concrete accessories is not recommended. Detailed knowledge of materials, heat | |
| |treatment and welding procedures is required for structural welding. Simple tack welding can | |
| |damage iron castings, cause carbides and extreme brittleness near the weld point, and may | |
| |destroy most of a casting's load value. | |
| |Recessed anchors can be advantageous because they are easily grouted in after the concrete | |
| |product is installed. Recessing products provide several functions. They can fasten the | |
| |anchors to the formwork, protect the anchor head from seeping concrete, and form a void that | |
| |is shaped to receive the rigging attachment (hook, ring clutch, etc.). Recessing products are | |
| |available in steel/iron, flexible/reusable foams, disposable plastic and reusable plastic. | |
| |Recessing products can be attached to formwork with a holding rod or bayonet assembly, a | |
| |holding plate, screws/wingnuts or nails. They also can be suspended from temporary cross | |
| |supports or tied to reinforcing steel. | |
| |Some commercial precast concrete lifting systems use special lifting hooks, ring clutches or | |
| |other devices. These products may add to the convenience and safety of the system. | |
| |Unfortunately, these special handling devices may be expensive. It can be a nuisance and an | |
| |additional expense if workers misplace or abuse these items. | |
| |Impact on Finished Concrete Product | |
| |Once safety concerns are resolved, product quality is a top priority. Lifting inserts and | |
| |anchors should not create spalling problems and should have minimal patching requirements. If | |
| |watertightness or vacuum testing is required of a precast concrete product, lifting inserts | |
| |should not adversely compromise the manhole, septic tank or other product. | |
| |Aesthetics are a primary concern for many precast products, especially architectural wall | |
| |panels. Anchors and inserts should be installed in discrete locations and patching should be | |
| |minimal. Anchors are generally inserted into the ends of these panels. | |
| |Cost is always a priority in the competitive business world. Calculating the costs of lifting | |
| |inserts, anchors and systems is not simple. Some of the many factors influencing cost include | |
| |design of the anchor and lifting system, initial cost of the anchor, labor costs to install, | |
| |costs to handle product after casting, handling costs for final installation of the product, | |
| |losses due to damage, and patching and repair costs. | |
| |Review Your Lifting Systems | |
| |Most lifting inserts, anchors and lifting systems have been tried and true for years. | |
| |Nevertheless, it may be worthwhile to review the systems at your facility to make certain, for| |
| |example, that inserts comply with OSHA, ANSI, ASTM or equivalent Canadian requirements or to | |
| |find ways to reduce damage during handling of precast products by revamping your lifting | |
| |inserts. | |
| |Call NPCA at (800) 366-7731 for the following resources: | |
| |A list of manufacturers who produce lifting inserts. | |
| |Detailed information on designing lifting inserts. | |
| |Safety videos relating to material handling and cranes. | |
| |[pic] | |
| |OSHA: U.S. Department of Labor (Occupational Safety and Health Administration) | |
| |Code of Federal Regulations (CFR) Title 29 (1990 Revision) Section 1926.704 C states: | |
| |(c) Lifting inserts which are embedded or otherwise attached to precast concrete members, | |
| |other than the tilt-up members, shall be capable of supporting at least four times the maximum| |
| |intended load applied or transmitted to them. | |
| |(d) Lifting hardware shall be capable of supporting at least five times the maximum intended | |
| |load applied or transmitted to the lifting hardware. | |
| |(e) No employee shall be permitted under precast concrete members being lifted or tilted into | |
| |position except those employees required for the erection of those members. | |
| |Code of Federal Regulations (CFR) Title 29 (1990 Revision) Section 1926.704 C states: (a)(4) | |
| |Special custom design grabs, hooks, clamps, or other lifting accessories, for such units as | |
| |modular panels, prefabricated structures and similar materials, shall be marked to indicate | |
| |the safe working loads and shall be proof-tested prior to use to 125 percent of their rated | |
| |load. | |
| |Code of Federal Regulations (CFR) Title 29 (1990 Revision) Section 1926.251C states : | |
| |(c)(1) Tables H-3 through H-14 shall be used to determine the safe working loads of various | |
| |sizes and classifications of improved plow steel wire rope and wire rope slings with various | |
| |types of terminals. For sizes, classifications, and grades not included in these tables, the | |
| |safe working load recommended by the manufacturer for specific, identifiable products shall be| |
| |followed, provided that a safety factor of not less than 5 is maintained. | |
| |[pic] | |
| |ANSI: American National Standards Institute | |
| |Standard A10.9-1983: Concrete and Masonry Work - Safety Requirements | |
| |9. Precast Concrete | |
| |9.3 Handling and Erection | |
| |9.3.3 Lifting hardware shall be designed to provide sufficient strength to withstand the | |
| |imposed loads with a factor of safety of at least 5. | |
| |Embedded inserts used in precast concrete elements or precast, prestressed concrete shall have| |
| |a minimum safety factor of 4 and shall be used in the manner described in manufacturers' | |
| |bulletins. | |
| |Standard A10.5-1992: Safety Requirements for Material Hoists | |
| |14 MATERIAL-HOIST WIRE ROPE AND SHEAVES | |
| |14.1 Breaking Strength. All hoisting rope shall be of such a breaking strength as to provide a| |
| |minimum factor of safety of 7. | |
| |[pic] | |
| |ASTM: American Society for Testing and Materials | |
| |ASTM C 1227-97 - Standard Practice for Precast Concrete Septic Tanks | |
| |6.1.5 Inserts embedded in the concrete shall be designed for an ultimate load that is four | |
| |times the working load (Factor of Safety = 4). | |
| |6.5 Lift equipment shall be designed for an ultimate load that is five times the working load | |
| |(Factor of Safety = 5). | |
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