Many construction workers wonder how thread bars(Rock bolt) are firmly anchored inside concrete.
A single thread bar alone cannot achieve reliable tension locking and load-bearing capacity. Special supporting fittings are mandatory. Today we will introduce the core anchoring accessories for thread bars: nuts, bearing plates and couplers.
These three components each have distinct functions and are indispensable for all prestressed engineering projects. Keep this core mantra in mind:
Nuts lock tension, bearing plates disperse pressure, and couplers extend bar length.
1. Nuts: The Locking Switch for Thread Bars
As the core load-bearing component of the anchoring system, nuts fall into three mainstream types: flat nuts, conical nuts and spherical nuts. They are strictly designated for different working conditions and must never be mixed up.
Flat Nuts – For Fixed Ends
Used on thread bar ends that do not require jack tensioning. Tighten directly to fix and position the bars under static uniform loads, widely applied to embedded bridge components and anti-floating fixed ends of structures. Matched with flat bearing plates.
Spherical Nuts – For Tensioning Ends
Specially designed for jack tension operations. Its tapered surface fits perfectly with spherical bearing plates to ensure even force distribution during tensioning, preventing eccentric loading, plate cracking and wire slippage. Ideal for bridge beams and vertical prestress tension construction.
Dome Nuts – Dedicated to Slope Support
Customized for highway & railway slopes, tunnel surrounding rock reinforcement and foundation pit anchor bolts, paired with Dome type bearing plates.
Rock surfaces are uneven in slope construction, making it hard for anchor bolts to stay perfectly perpendicular to the slope. Ordinary flat or spherical nuts easily cause partial compression and stress deviation, leading to bolt shear failure and plate cracking under long-term loads.
The protruding Dome surface of dome nuts allows minor angle adjustment inside the dome plates. Even if anchor bolts are tilted, full-surface contact is maintained to centralize force distribution, disperse lateral rock pressure and greatly improve the durability and safety factor of slope anchorage.
Common materials include 45# and 40Cr. All three nut types are compatible with PSB500,PSB830,PSB930, PSB1080 and other high-strength thread bar.
Critical Safety Reminder
Nut strength grade must match the thread bar grade. Poor-quality nuts with insufficient strength may crack completely under high-tonnage tension, triggering severe safety accidents.
2. Bearing Plates: Protective Base for Concrete
Bearing plates are supplied as matched sets with corresponding nuts, classified into flat plates, spherical plates and dome plates. Mismatched combinations are prohibited.
Many people underestimate bearing plates as simple iron sheets, which is a serious misunderstanding.
Their core function is to disperse concentrated pressure. Nuts exert enormous pressure during tensioning. Without bearing plates, nuts will directly press against concrete or rock. The tiny contact area will instantly crush concrete or crack rock edges, resulting in complete anchorage failure.
• Flat bearing plates: Matched with flat nuts to disperse pressure at fixed ends
• Spherical bearing plates: Matched with spherical nuts to bear loads at tensioning ends
• Dome plates: Compatible with spherical nuts for adaptive pressure bearing on uneven slope rock surfaces, offering larger load-bearing area
3. Couplers: Extension Joints for thread Bars
Ordinary thread bars can be lengthened by welding or lapping, but welding threaded bar is strictly forbidden. Welding damages the prestress performance of thread bar, making them brittle and prone to fracture — a major construction taboo.
Couplers are used to extend bars when length is insufficient. Working like pipe connectors, they screw onto two thread bar at both ends to realize seamless extension, meeting construction demands for long-span structures, deep foundation pits and high-slope long anchor bolts.
These three compact supporting parts serve as the reliable perfect match ensuring stable load bearing and long-term safety for all prestressed projects including bridges, foundation pits and slopes.
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