Understanding the different types of metal deck attachments for your next project can help you get the best end result. In this article, we will review five different types of metal deck attachments and best practices for each:
- Fastening and Installing Deck
- Mechanical Fastening
- Shear Studs
- Side Lap Connections
This article is also available as a PDF download if you would like to print it or save it for easier reference later.
Types of Metal Deck Attachments
Depending upon the type of metal deck that you end up using on your project, whether it’s floor deck, roof deck, form deck, or composite metal decking, the recommended attachment method for your application will vary.
The Engineer of Record will ultimately determine the required fastening type and pattern. This is typically noted on the structural drawings or specifications of the scope of the project.
Fastening and Installing Deck
Metal deck is always installed in accordance with the “Approved for Construction” drawings presented by the designer of the project. At CSM Products & Solutions, we reinforce that deck must be installed by qualified and experienced workers.
The beginning point of the installation should be carefully selected for proper deck orientation and the edge of roof or floor slab location. At the same time, it’s important to maintain the rib or flute alignment across the whole structure while also keeping in mind that panel cover widths must be maintained in order to achieve long straight runs of deck.
We recommend using a snap chalk line at reasonable intervals to assure proper alignment of deck panels before starting any installation. On-site experience has shown that the frequency of snapping a chalk line determines the accuracy of rib and flute alignment. This minor effort at the time of deck placement eliminates the need for field corrections.
In order to have your deck perform its design functions and serve as a working platform, it must be properly attached. Often the deck is used as part of the horizontal bracing system and the fastening method and pattern have been selected to provide a certain strength and stiffness in the plane of the deck.
Roof deck is usually left exposed on the bottom and the rib alignment has to be parallel to the girders at all girder lines to prevent unsightly conditions.
Floor deck flutes should, if permitted, maintain alignment to achieve continuous concrete ribs across abutting sheet ends, to minimize concrete leakage. Flutes that do not align can create closure problems that may interrupt the slab design. Proper alignment can only be achieved by proper adjustment of each deck panel while it is being placed because cover width errors across the bay cannot be corrected with the last sheets in the run.
Important: No substitution of fastener type or pattern should be made without the approval of the designer.
Deck fastening to the structural frame can be accomplished with self-drilling screws, welds, powder-driven or air-driven fasteners. A minimum of 1 ½” of end bearing should be provided for deck unless noted otherwise on the deck installation drawings. In the unusual case there is less than 1 ½” of bearing, additional fastening should be provided and the deck web crippling capacity should be inspected. For deck that is intended to end lap, usually seen on roof deck, the end lap location should be adjusted so the center of the lapped portion occurs over the support or, when supported by bar joists, over a top chord member.
We strongly advise that only qualified operators use powder-actuated tools while working on-site. In accordance with ANSI/ASSE A10.3-2013, operators must be trained by the tool manufacturer or other authorized party.
Electric screw-guns specially made for this type of project are used to drive self-drilling screws to attach deck to the structural frame. These screw guns are equipped with a clutch and depth limiting nosepiece to prevent over-torquing. Screws are typically #12’s or ¼” diameter with a special drill point selected according to the total thickness of metal (deck plus frame) being joined.
Power-Actuated Fasteners (Powder Cartridge Actuated)
Powder-actuated tools are designed to drive fasteners, specifically designed for deck attachment, through the sheet metal decking and into the base steel. A powder cartridge (blank cartridge) is used as the energy source to drive the fastener into the steel. Low-velocity tools utilize a captive piston which has much greater mass than the fastener.
The energy from the powder cartridge acts on the piston which in turn drives the fastener. Only low-velocity tools, designed specifically for the decking application, should be used to fasten the metal deck. OSHA requires that users of these tools are qualified to operate the specific tool they are using.
Powder-actuated fasteners are made from hardened steel, with a ballistic point to penetrate the sheet steel and base steel. The fasteners typically have a knurling pattern which improves the hold of the fastener in the steel. Powder-actuated fasteners used for decking attachment should have one or more integrated washers which serve to clamp the deck sheet metal to the base steel, thereby improving the shear resistance capacity of the connection as well as the uplift capacity.
Power-Actuated Fasteners (Compressed Gas/Air Actuated)
Air-driven tools are operated at a pre-set pressure level consistent with the fastening requirements of the deck attachment. Air is supplied by a compressor or equipped with a regulator that prevents overdriving or underdriving the fastener. The fasteners have a flat head at the drive end and a ballistic point at the penetrating end.
Welding should be done in accordance with the Structural Welding Code, AWS D1.1 or D1.3. Any type of welding must be done by a qualified welder during proper weather conditions. Top-quality deck welding requires experience and the selection of proper amperage and electrodes. A weld quality control test procedure is shown in this image.
While weld washers are required for metal thicknesses less than 0.028 inches, they are not recommended for deck thicknesses of 0.028 inches (minimum 22 gage) and greater. Proper welding requires good metal-to-metal contact, hence, lapping composite deck sheets with embossments is not recommended. At the same time, built-in hanger tabs (for floor deck) that bear on structural steel should be flattened or removed.
In accordance with AWS D1.1, shear studs are welded in place with special equipment that can serve as welding to hold the deck to the frame when installed as shown in this image. These studs tend to be installed after the deck has been spread to act as a working platform. Because of this, it is necessary that the platform be adequately attached to the structure before the studs are installed.
Shear studs can be welded through the double metal thickness of cellular deck. However, if the deck is heavier than 16 gage the stud manufacturer should be consulted for installation procedures.
Since most construction work is done in open air, ventilation for welding is usually adequate. However, for closed-in areas, ventilation must be provided. Adequate ventilation is extremely important when welding galvanized deck. All workers involved in the welding operation must wear eye protection to avoid weld flash.
Sheet-to-sheet connections may be required at the side laps of deck, which are frequently referred to as stitch connections. Self-drilling screws, welds, clinching or button punches are the usual stitch connections when using sidelap connections. The installer must be sure that the underlying sheet is drawn tightly against the top sheet. When screws are used as the frame attachment, the special screw driving guns are used to prevent over-torquing.
A button punch tool is an economical, efficient option for attaching metal deck, which is faster than welding, does not require a large amount of experience to use, and is very versatile. If you are looking for weather tightness, the button punch side lap connection method would be your best choice. You’ll also want to take into consideration the type of metal decking you’re using and whether it’s interlocking or not.
Contact CSM’s Team for Additional Guidance
At CSM Products & Solutions, our sales and manufacturing teams have the necessary knowledge and tools to create a metal deck that meets your construction project’s needs. Don’t hesitate to contact us if you need guidance or recommendations on which metal decking or attachment is best for your particular project. We have more than 50 years of experience and are happy to help.