Experiment and Modelling on Effective Width of Single and Twin I-beam Composite Girders

Zongyi Wen, Xing Wei*, Weiwei Lin, Junmin Zhao, Lin Xiao

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review


Effective width (b eff) has been widely used by designers, and several specifications can be selected. However, insufficient research has been conducted on the b eff of single and twin I-beam composite girders. Thus, finite element (FE) models, calibrated by the experiment, were used to study the effects of slab thickness, web position, interaction degree (ID) of shear studs, width-to-span ratio, and their coupling effects on b eff. Different loading types and two definitions of b eff were elaborated. The FE results were compared with specifications in Eurocode 4 (EC4) and AASHTO LRFD bridge design specifications (AASHTO). The following results were obtained. The modeling agrees with the experiment. The critical steel height-to-slab thickness ratio is around 4. When the ratio deviates from the critical value, b eff is reduced with the increase of slab thickness. ID has a slight influence on b eff. b eff changes within 10% when ID changes within 10%. The maximum b eff can be obtained when the web spacing-to-physical width ratio is 1/2. The decrease of web spacing brings a maximum reduction of 14% on b eff, whereas increasing web spacing results in a maximum reduction of 70% for twin I-beam. The coupled effect of web position and slab thickness is limited. The maximum difference is 25%. Recommended equations were proposed to evaluate b eff for single I-beam and twin I-beam composite girders based on the specifications in EC4 and AASHTO, which can ensure that the negative error is within 10%.

Original languageEnglish
Pages (from-to)2559-2569
Number of pages11
JournalKSCE Journal of Civil Engineering
Issue number6
Early online date29 Apr 2023
Publication statusPublished - Jun 2023
MoE publication typeA1 Journal article-refereed


  • Composite girder
  • Coupling effect
  • Effective width
  • Finite element
  • Width-to-span ratio


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