Connection Design Details
Connection Detail: Clip, Bolt and the No-Weld Rule
FRP cannot be welded - there is no weld pool. Every connection is a mechanical bolted or clipped joint, and the detail that locates the panel also governs fatigue, corrosion and thermal movement. This chapter sets the clip selection, bearing design and the bolt schedule that replaces welded steel fixings.
Selecting the Right Clip
| Clip | Best for | Notes |
|---|---|---|
| G-clip (single / double) | General hold-down, molded edges | The default; double at joints / heavy load |
| M-clip | Dished molded bars | Hooks the molded profile |
| C-clip / saddle | Pultruded I/T bearing bars | Grips the bar flange |
| L-clip | Edge panels / perimeter | Locates against the edge |
| Expansion (slotted) clip | Long / hot panels | Locates without clamping thermal movement |
Bearing Stress, Washers and Hole Clearance
Over-tightening crushes the resin; an undersized washer concentrates load on a few square millimetres. Use SS316 (or SS304 in mild service) bolts, a washer of at least 25 mm OD, and a hole 1.5-2 mm over the bolt diameter so the panel can slide thermally. Edge distance from hole centre to cut edge >= 2.5x bolt diameter to prevent tear-out. Snug torque only - see the fastener torque standards article (M8: 8-12 N.m; M10: 15-22 N.m).
How FRP Substitutes for Welded Connections
In steel construction, panels are often welded to the substructure. FRP replaces this with: (a) bolted clips to a steel or FRP support frame (the common route), (b) bolted angle or plate cleats where a fixed end is needed, and (c) slotted holes / expansion clips where the panel must move. Neoprene or FRP washers isolate dissimilar metals in chloride service. See structural connections for failure modes and clips & accessories.
One Fixed, One Sliding
Fix clips firmly at one support; use slotted holes or expansion clips at the other so the panel can move. Fixing both ends traps thermal expansion and causes summer buckling. Insert a divider every 6-9 m on long runs. This is the same rule as thermal expansion - the connection detail and the expansion design are the same decision.
Fasten every intersection
Min. four clips per panel, spacing <=1200 mm; never rely on gravity or friction.
Snug, not tight
Hand torque only; over-torque crushes the bar and strips threads.
SS316 in chloride
Galvanized hardware fails in chloride where FRP does not.
Connection Types and Hardware
| Connection | Hardware | Function |
|---|---|---|
| G-clip / saddle clip | SS316 bolt + washer | Standard panel-to-support fixing at bearings |
| Hold-down clip | SS316 | Uplift resistance on windy or process decks |
| Bolted plate | SS316 bolt set | Heavy-duty connection; panel to structural steel |
| Bonded connection | Structural adhesive | Permanent joints where bolting is impractical |
Bearing Stress, Washers and Clearance
FRP is softer than steel under compression; a small bolt head without a washer crushes the laminate locally. Use washers sized to spread the clamping load, drill holes with clearance for the fastener (typically 1–2 mm over nominal), and torque to the recommended value — snug, not tight. The same rule applies to clips: the clip bears on the bar through a broad contact face, and the bolt is the load path, not the clamp. In chloride service use SS316 throughout; isolate dissimilar-metal contact with a non-metallic barrier where carbon steel supports meet stainless hardware.
FRP is softer than steel under compression; a small bolt head without a washer crushes the laminate locally. Use washers sized to spread the clamping load, drill holes with clearance for the fastener (typically 1–2 mm over nominal), and torque to the recommended value — snug, not tight. The same rule applies to clips: the clip bears on the bar through a broad contact face, and the bolt is the load path, not the clamp. In chloride service use SS316 throughout; isolate dissimilar-metal contact with a non-metallic barrier where carbon steel supports meet stainless hardware.Need a Connection Detail Drawing?
Send support type, panel style and environment - ZeAllgrate returns clip schedule, torque values and fixed/sliding support layout.
Source: ZeAllgrate (Fiberglass Grating Manufacturers Council / ACMA) design guidelines; ASTM International; ISO 14122; OSHA 29 CFR 1910. Indicative data for specification guidance only — final design verified by ZeAllgrate engineering against certified load/span charts.