March 12, 2026
Composite construction — in which a concrete deck slab and steel girders are connected to act as a single structural unit — is one of the most efficient and economical forms of bridge construction available. By exploiting the complementary strengths of the two materials (concrete in compression, steel in tension), composite bridges achieve higher load capacity and stiffness with less material than either material could achieve alone. The key to composite action is the shear connector, and the dominant form of shear connector in modern bridge construction is the headed shear stud.
In a non-composite bridge, the concrete deck and the steel girders act independently. Each carries load in proportion to its own stiffness, and there is relative slip at the interface between them. In a composite bridge, the shear connectors prevent this slip, forcing the deck and girders to act as a single section. The result is a dramatic increase in the effective section modulus — the composite section is typically 2 to 3 times stiffer than the steel girder alone — which translates directly into reduced deflections, reduced steel weight, and increased load capacity.
Stud welding of headed shear connectors to the top flange of a steel bridge girder. The stud welding process uses a drawn arc to create a full-fusion weld in less than one second, achieving a connection strength that exceeds the tensile strength of the stud shank.
A headed shear stud is a cylindrical steel pin with a circular head, typically 19 mm or 22 mm in diameter and 100–200 mm in height. It is welded to the top flange of the steel girder using a stud welding gun, which uses a drawn arc process to create a full-fusion weld in less than one second. Once the concrete deck is cast around the studs, they are embedded in the concrete and act as mechanical connectors, transferring horizontal shear forces at the steel-concrete interface.
The shear resistance of a single stud is governed by either the shear strength of the stud shank or the bearing/crushing strength of the surrounding concrete, whichever is lower. For a 19 mm diameter stud in C30/37 concrete, the design shear resistance per stud is approximately 73 kN (Eurocode 4). The required number of studs is determined by dividing the total horizontal shear force at the interface (equal to the lesser of the axial capacity of the steel section and the compressive capacity of the concrete slab) by the design resistance per stud.
Cross-section of a composite steel-concrete bridge deck showing the headed shear studs embedded in the concrete slab. The studs transfer horizontal shear forces at the steel-concrete interface, forcing the two materials to act as a single composite section.
| Parameter | AASHTO LRFD | Eurocode 4 (EN 1994-2) |
|---|---|---|
| Stud diameter (typical) | 22 mm (7/8 in) | 19 mm or 22 mm |
| Min. stud height/diameter ratio | 4.0 | 3.0 |
| Max. longitudinal spacing | 600 mm or 8×slab thickness | 800 mm or 4×slab thickness |
| Min. transverse edge distance | 25 mm | 20 mm |
| Fatigue design | Required (ADTT-based) | Required (damage equivalent) |
A significant proportion of the existing steel bridge stock was built as non-composite structures — either because composite design was not standard practice at the time of construction, or because the original design was conservative. These bridges can often be cost-effectively upgraded by adding shear connectors through the existing concrete deck using a technique known as post-installed shear connectors.
The process involves drilling holes through the concrete deck from above, inserting headed studs, and grouting them in place with a high-strength cementitious or epoxy grout. While the shear resistance of post-installed connectors is somewhat lower than welded connectors (due to the reliance on grout bond rather than direct weld), the technique can still provide a significant increase in composite action and load rating. Finite element analysis is used to determine the optimal stud layout and to quantify the improvement in structural performance.
Bridgent supplies headed shear studs in standard diameters of 13 mm, 16 mm, 19 mm, and 22 mm, manufactured from low-carbon steel to EN ISO 13918 and AWS D1.1 standards. We also supply stud welding guns, controllers, and ferrules for on-site installation. Technical support including stud layout design and weld procedure qualification is available.
Bridgent is your specialist partner for bridge construction and maintenance materials. From CFRP and post-tensioning systems to hydraulic jacks and noise barriers, we supply the complete range with full engineering support.
Tags:Bridge ConstructionComposite BridgeShear ConnectorsBridge RehabilitationBridgent Products
Westcoast New Area, Qingdao City ,Shandong Province ,China
