BluSkyi·Engineering Insight Article
Hybrid Girder Bridges · Steel-Concrete Joints · Shear Connectors
Three-Path Load Sharing Makes a Hybrid Bridge Joint Simpler to Design
A finite element study of the steel-concrete joint in a 262 m hybrid girder bridge finds axial load carried by three paths, with bearing plate and shear connectors sharing it almost equally.
- Source Journal
- Applied Sciences
- Lead Institution
- Tongji University
- Published
- 24 June 2026
- Discipline
- Civil
- Focus Area
- Structural Engineering & Analysis
- Research Type
- Theoretical
- Licence
- CC BY 4.0
- Authors
- Lin et al.
The Bottom Line
Hybrid girder bridges that splice a steel-concrete composite segment into a prestressed concrete span address the pavement and fatigue problems of steel box decks, but the joint between the two has lacked a clear design basis. This modelling study shows axial force split almost evenly between bearing plate and shear connectors, identifies points of diminishing return for plate thickness and joint length, and isolates a single connector row that governs shear design.
Key Findings · At a Glance
- Axial force splits across three paths: top slab concrete 20.7%, bearing plate 40.1% and shear connectors 39.2%.
- Interface friction carries about 27.1% of vertical shear, but the authors advise ignoring it in design.
- Thickening the bearing plate from 20 mm to 100 mm cuts peak concrete stress by only about 1 MPa.
- Beyond a joint length of 1.0 times beam height, central connectors contribute little shear resistance.
- The first row of web connectors carries 34.8% to 47.2% of web shear, loaded almost uniformly across the row.
- Web connectors carry more than 90% of vertical shear regardless of connector stiffness or joint length.
- Softer connectors spread shear more evenly; web connectors show a non-uniformity coefficient above 2.3 against just under 2.0 elsewhere.
Opportunity
Long-span hybrid girder bridges have typically paired prestressed concrete box girders with steel box girders. The paper argues this carries a hidden cost: two deck types need two paving systems, which complicates construction, and steel box girders bring high pavement costs, pavement damage and poor fatigue durability of the steel deck.
An alternative places a steel-concrete composite girder in one segment of the main span and uses prestressed concrete girders everywhere else. Because the composite segment carries a concrete deck, the longitudinal integration is more rational. The weak point is the joint where the two girder types meet. Beyond the usual bearing plate, shear connectors, reinforcement and tendons, it must tie the concrete deck into the steel girder flange, producing what the authors call intricate interfacial stress states and ambiguous load paths. The method has been used in cable-stayed bridges, but its load transfer in girder bridges has been little studied.
The team, led from the Department of Bridge Engineering at Tongji University, modelled such a joint for a three-span continuous bridge of 60 m, 142 m and 60 m, with a 52 m composite section in the main span. The 2.5 m joint uses a 50 mm steel bearing plate, perforated-plate (PBL) connectors and welded studs embedded in transition concrete. A detailed finite element model examined the governing negative bending case, and a simplified parametric model then varied plate thickness, connector stiffness and joint length.
Results
Where the force goes
Under a bending moment of 7446 kN·m and a shear force of 4204 kN applied at the composite end, the joint shares axial force three ways: 20.7% through the top slab concrete, which is in tension under negative bending, 40.1% through the bearing plate and 39.2% through the shear connectors. Peak compressive stress in the concrete at the bearing surface reached 14.0 MPa, driven by local prestress anchorage, but the stress became nearly uniform 1 m from the bearing surface.
Friction helps, but is left out
Vertical shear behaves differently. With interface friction modelled, the bearing plate carries 27.1% of shear and the connectors 66.4%; without it, the connectors take 96.3%. Friction cut the peak vertical shear on the web PBL nearest the bearing plate from 90 kN to 60 kN. The authors still recommend ignoring it, because under positive bending part of the prestress pressure it relies on is diverted into the concrete top slab, and the mechanism is uncertain. Ignoring friction builds in a margin the model does not count on.
Diminishing returns
Increasing bearing plate thickness from 20 mm to 100 mm evened out concrete stress but cut the peak by only about 1 MPa and left peak connector forces almost unchanged. Thick plates also raise the risk of lamellar tearing and make welding harder, so the authors settle on 50 mm. Joint length shows a similar threshold. Stretching it from 0.5 to 1.5 times beam height raises the connector rows from 8 to 23, but beyond 1.0 times beam height the shear distribution forms an inverted N-shape and the central connectors do little.
One row governs
Conceptually, the model's clearest contribution is a map of where shear concentrates. Connector stiffness mainly redistributes load. Raising stiffness from 600 kN/mm to 2400 kN/mm lifted the connectors' share of axial force only from 30.0% to 32.7%, yet pushed the first row of web PBLs from 34.8% to 47.2% of web shear. That row, the authors conclude, "largely determines the overall shear resistance of the joint". Its non-uniformity coefficient stays near 1.05 to 1.06 across the stiffness and length ranges tested, which justifies treating it as uniformly loaded. Web PBLs carry more than 90% of vertical shear throughout.
What This Enables
Bridge design practice
The model supplies a first-principles basis for sizing this joint type: a 50 mm bearing plate, a joint length near one beam height, and shear design controlled by the first row of web connectors.
Bridge owners and fabricators
A clearer picture of the joint makes the composite-segment layout, which targets the pavement and fatigue problems of steel box girders, easier to assess, and argues against thick plates that add welding difficulty for little benefit.
Design guidance
Disregarding interface friction and treating the first connector row as uniformly loaded are conservative simplifications that could enter design procedures once tested.
Assessment
The authors are candid about the limits. Their models use linear elastic materials and ignore concrete cracking and steel yielding, and the findings have no experimental validation, so they caution against extrapolating the conclusions to other structural contexts. They call for nonlinear finite element analysis combined with physical testing to confirm the load-transfer mechanisms.
Everything rests on one bridge configuration and one governing load case, and connectors are represented as linear springs, so connector-level behaviour and fatigue are outside scope. The parametric model is a simplified half-structure, and its load shares differ from the full model: the concrete deck carries around 39.5% of axial load there against 20.7% in the detailed model, so its trends are best read as directional. The 2.3 against 2.0 non-uniformity contrast reported in the abstract reflects connector location, web against slab, more than stiffness. For owners weighing hybrid layouts, the study lowers the analytical barrier to this joint; the evidential barrier of physical testing remains.
About the Research
Conducted by Yiteng Lin and colleagues at the Department of Bridge Engineering, Tongji University, China, with researchers from Shanghai Urban Construction Design and Research Institute and Stanford University. Published open access in Applied Sciences under a Creative Commons Attribution 4.0 licence.
Citation
Lin, Y., Su, Q., Matanmi, F. O., Yan, X., & Gao, S. (2026). Mechanical behaviour and parametric analysis of the hybrid girder bridges joint between steel-concrete composite girder and prestressed concrete girder. Applied Sciences, 16(13), 6322.