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Steel and Composite Structures
  Volume 38, Number 4, February25 2021, pages 415-430

Effective width of steel-concrete composite beams under negative moments in service stages
Li Zhu, Qi Ma, Wu-Tong Yan, Bing Han and Wei Liu

    The effective flange width was usually introduced into elementary beam theory to consider the shear lag effect in steel-concrete composite beams. Previous studies have primarily focused on the effective width under positive moments and elastic loading, whereas it is still not clear for negative moment cases in the normal service stages. To account for this problem, this paper proposed simplified formulas for the effective flange width and reinforcement stress of composite beams under negative moments in service stages. First, a 10-degree-of-freedom (DOF) fiber beam element considering the shear lag effect and interfacial slip effect was proposed, and a computational procedure was developed in the OpenSees software. The accuracy and applicability of the proposed model were verified through comparisons with experimental results. Second, a method was proposed for determining the effective width of composite beams under negative moments based on reinforcement stress. Employing the proposed model, the simplified formulas were proposed via numerical fitting for cases under uniform loading and centralized loading at the mid-span. Finally, based on the proposed formulas, a simplified calculation method for the reinforcement stress in service stages was established. Comparisons were made between the proposed formulas and design code. The results showed that the design code method greatly underestimated the contribution of concrete under negative moments, leading to notable overestimations in the reinforcement stress and crack width.
Key Words
    effective flange width; composite beams; negative moments; fiber beam element
Li Zhu, Bing Han and Wei Liu: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, PR China
Qi Ma: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, PR China
Wu-Tong Yan: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, PR China;
China Railway Economic and Planning Research Institute, Beijing 100038, PR China

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