# Research on the Equivalent Span of Hybrid Girder Bridges

## TL;DR

This paper introduces a new method to calculate the spanning capacity of hybrid girder bridges using simplified models and introduces a new coefficient for design purposes.

## Contribution

The paper introduces the equivalent span increase coefficient, κ, and a simplified formula for its calculation based on hybrid ratio and load ratio.

## Key findings

- The Leq method was developed using classical beam theory to compare hybrid girder components.
- The equivalent span increase coefficient, κ, is solely related to the hybrid ratio, μ, and the linear load ratio, γ.

## Abstract

Hybrid girder bridges achieve significant improvements in spanning capacity by utilizing lightweight and high-strength materials in the midspan beam segments. To quantitatively describe the enhancement in spanning capacity, this study introduces a simplified analytical model for hybrid girder components, avoiding complex factors, such as span ratio and boundary conditions, typically encountered in previous system-level analyses. The Leq method is proposed based on this new model, utilizing classical beam theory model to calculate and compare hybrid girder components with both uniform and variable cross-sections. The equivalent span increase coefficient, κ, is introduced for the first time, and a simplified formula for its calculation is derived. The calculation errors are kept within 8%, which meets the requirements for preliminary design. Validated through engineering practice, the formula is concise and reveals that κ is solely related to the hybrid ratio, μ, and the linear load ratio, γ. This method provides valuable guidance for the conceptual design and ultimate span prediction of hybrid girder bridges.