Application of Double‑End Studs in Bridges

Bridge‑used equal‑length double‑end studs comply with GB/T 901, featuring intermediate plain shank and threads at both ends, fastened with nuts on both sides. Most are grade 8.8 / 10.9 alloy steel (35CrMoA, 42CrMoA). Surface protection includes hot‑dip galvanizing, Dacromet and zinc‑aluminum flake coating. Subject to vibration and alternating load, spring lock washers shall not be adopted. Pre‑tension by torque control and double‑nut locking are applied.

Four Main Application Locations on Bridges

1. Connection of Bridge Bearings (Most Widely Used)For pot bearings and spherical bearings, double‑end studs pass through the base plate of bearing and embedded steel plates. Gaskets are fitted and nuts are tightened at both ends to clamp the bearing between pier top and beam bottom. Hex‑head bolts cannot be installed due to limited inner space of bearings, so double‑end studs are preferred.

2. Splicing of Steel Box Girder / Steel Cap Beam Flange SegmentsSteel box girders are prefabricated in workshops and assembled on‑site at flange joints. Double‑end studs penetrate two flange plates, with nuts tightened on both ends to transfer tension, bending moment and shear force. Custom extra‑long studs can be supplied for thick flanges where standard hex‑bolt length is insufficient.

3. Prefabricated Assembled Piers with Flange ConnectionFlange plates of upper and lower precast pier segments are connected by vertical double‑end studs running through both flanges and locked by nuts on two sides. Easy for installation and maintenance. Widely adopted in high‑speed railway and urban viaducts.

4. Steel Appurtenances: Crash‑proof Guardrails, Access Platforms, Embedded Parts for BearingsFor steel base of guardrails and access ladders, double‑end studs go through pre‑drilled holes of embedded base plates and are clamped by nuts from two sides.

Simplified Schematic Drawings (Cross‑Section)

① Double‑End Stud for Bearing Connection (Vertical Installation)

                            Bridge Beam Concrete
        ┌─────────────────────────────────────┐
        │        Embedded Steel Plate at Beam Bottom
        ├─────────────────────────────────────┤
        │        Upper Shim Plate
┌───────┴─────────────────────────────────────┴───────┐
│                Pot / Spherical Bearing Assembly
├─────────────────────────────────────┬────────────────┤
│        Lower Shim Plate             │
├─────────────────────────────────────┘
│        Embedded Steel Plate on Pier Top
└───────────────┬──────────────────────────────────────┘
                │
        【Upper Nut｜Washer】
                │
        ◄───────● Double‑End Stud (Plain Intermediate Shank) ●───────►
                │
        【Washer｜Lower Nut】
                │
        ┌───────┴───────┐
        │Pier Cap Concrete
        └───────────────┘

Construction Notes

1. The vertical double‑end stud fully penetrates embedded plate at beam bottom, bearing and pier‑top embedded plate. Threads extend out on both ends and nuts are tightened bi‑directionally to clamp the bearing. No bolt head is required to fit confined bearing inner space.

2. Hole diameter of steel plates: 1.1 times nominal stud diameter.

3. Spring lock washers are prohibited. Tighten in two stages (pre‑tightening & final‑tightening) with torque wrench. Double‑nut locking is required for certain designs.

4. Material: Grade 8.8 /10.9, 35CrMoA. Coating: Zinc‑aluminum flake coating / Dacromet.

② Horizontal Double‑End Stud for Steel Box Girder Flange Splicing

  Steel Box Girder Flange A        Steel Box Girder Flange B
┌───────────────┐              ┌───────────────┐
│               │              │               │
│               │◄────────────►│               │
│               │              │               │
└───────┬───────┘              └───────┬───────┘
        │                              │
【Washer｜Nut】    ●Double‑End Stud(Plain Shank)●    【Nut｜Washer】
        │                              │

Key Construction Points‑ Stud horizontally passes through two mating flange plates, nuts at both ends are pre‑tightened to compress joint gap and transfer bending moment and shear force. ‑ Reduced‑diameter intermediate plain shank is recommended for better fatigue resistance. ‑ On‑site assembly: Insert all studs first, perform pre‑tightening, then final‑tightening.

③ Prefabricated Pier with Flange Connection (Vertical Double‑End Stud)

        Upper Precast Pier Segment
┌─────────────────────┐
│ Upper Flange Steel Plate
└──────────┬──────────┘
           │
    【Upper Washer‑Upper Nut】
           │
           ● Double‑End Stud (Plain Intermediate Shank)
           │
    【Lower Nut‑Lower Washer】
           │
┌──────────┴──────────┐
│ Lower Flange Steel Plate
└─────────────────────┘
        Lower Precast Pier Segment

Upper and lower precast pier segments are assembled with flanges face‑to‑face. Vertical double‑end studs pass through flanges and are locked by nuts on both ends. Widely used for high‑speed railways and urban viaducts.

On‑Site Construction Procedure for Bearing Double‑End Studs

1. Complete pier cap construction and place pier‑top embedded steel plate.

2. Install bearing assembly and leveling shims.

3. Lift and position beam member, align holes of beam‑bottom embedded plate.

4. Insert complete double‑end stud to penetrate all steel components vertically.

5. Fit high‑strength thick washers at both ends.

6. Perform staged tightening: pre‑tightening → final‑tightening with torque wrench.

7. Repair coating for corrosion protection and implement sealing measures.

Difference: Bridge‑Used vs General‑Mechanical Double‑End Studs

‑ ✅ Bridge application: Equal‑length through‑type stud, threads exposed on both ends, clamped by nuts on two sides. All mating components are through‑holes; no internal threaded holes in connected parts. ‑ ❌ Traditional mechanical studs: One end is screwed into internal threaded hole of component, nut fitted only on the other end. This configuration is not adopted for bridge bearings or steel box girders.

CAD Annotation Text for Detail Drawings

Double‑end Stud GB/T 901 M36×L‑10.9, Material:35CrMoA Surface Treatment: Zinc‑aluminum flake coating Matching Parts: Grade‑10 high‑strength nuts, thickened flat washers Construction: Final tightening by torque method; spring lock washers shall not be used.