###### Abstract  
Interfacial slip effects and the unbonded phenomenon of external tendons are the key mechanical features of the externally prestressed steel-concrete composite beams (EPCBs). In this paper, an 8-node fiber beam element is built for the nonlinear analysis of the composite beam with interfacial slip effects. A multi-node slipping cable element is proposed for the simulation of external tendons. The derived formulations are programmed in OpenSees as newly developed element classes to be conveniently used for the flexural analysis of EPCBs. The effectiveness of the proposed model is fully verified against the experimental tests of simply supported and continuous beams and then applied to the parametric study. The results show that the increasing deviator spacing will significantly decrease the tendon effective depth at ultimate states and further decrease the flexural capacity. The larger effective depth is beneficial to the tendon stress increments and further improves the flexural capacity. The enhancement of interfacial shear connection degree will increase the structural capacity but the effects on the tendon stress increments and second-order effects were not monotonic. external tendon; composite beam; interfacial slip; nonlinear behavior; flexural analysis Article  
Flexural Analysis Model of Externally Prestressed Steel-Concrete Composite Beam with Vertical-Concrete Composite Beam with  
[PERSON] et al. [11; 12], [PERSON] et al. [13] and [PERSON] et al. [14] tested the effects of external prestressing in continuous EPCBs and revealed that both the tendon stress increments and interfacial slip effects affected the structural deformation and load-carrying capacity. Recently, more concerns were paid to EPCB designed with a partial shear connection [17; 18] or existing structures with degraded interfacial shear resistance in particular [19]. The tests by [PERSON] et al. [15] and [PERSON] et al. [16] showed that an increase in shear connection degree from 0.4 to 1.0 led to a 46% load capacity increment of an EPCB. The simultaneous effects of interfacial slip and the unbonded phenomenon of external tendons lead to more difficulties for flexural response predictions of EPCB. The numerical model was usually taken as the optional solution. A reliable numerical model for EPCB should include the following considerations: the material and geometrical nonlinearities, the nonlinear interfacial connection, and the free-slip behaviors of external tendons at deviators. To date, there are mainly two kinds of numerical models presented in the references, the refined solid model and the beam-tendon model. In the refined solid models, the steel beam, concrete slab, and even the shear connectors were all modeled by the shell or solid elements concerning actual geometrical shapes [20; 21; 22; 23; 24; 25; 26]. These models were usually directly modeled in common FE software. The interfacial shear-slip behaviors between the steel beams and concrete slabs were modeled by the contact element with cohesive or friction properties. But there were still no available element types in current 3D FE software for external tendons with free-slip behaviors at deviators. The conventional truss element [23; 24; 25] cannot satisfy the strain-compatible relation between the adjacent tendon segments. Meanwhile, the complex modeling process and enormous computational costs were usually needed in these models, reducing the analysis efficiency for large-scale structures. In beam-tendon models, the composite beam and external tendons were all modeled by the one-dimensional structural element types, such as beam and link/truss elements. (1) For composite beam, [PERSON] et al. [27; 28; 29; 30] and [PERSON] et al. [31] adopted the conventional fiber beam element to model the flexural behaviors. The interfacial slip effect was not considered as there was no interfacial slip defined for the conventional fiber beam element. To address this issue, [PERSON] et al.