# Numerical Study on the Bending Resistance of Lightweight Built-Up Steel-Concrete Composite Beams
## 5 Conclusions  
This paper summarizes the analytical approaches for calculating the bending resistance of the analyzed CFS-concrete composite beam with built-up CFS profiles connected by spot welds. It compares the characteristic analytical results with the maximum values of numerically obtained bending capacities based on FE analyses. Furthermore, the influence of the steel beam height, the type and degree of the shear connection, the connection between the steel elements, and the CW thickness on the bending capacity of the composite system is analyzed. In accordance with the presented parametric numerical and analytical models, the following conclusions are obtained:  
* The degree of shear connection has a significant influence on the bending capacity of the composite CFS-concrete system. After changing the shear connection type from a staggered arrangement to a tie connection, the bending capacity increased to approximately 30-50%, depending on the analyzed height of the composite beam. * The CW thickness has a negligible influence on the bending capacity, which increased by 11% in models with CW thicknesses of 0.8 mm and 1.5 mm. * Models with tied steel elements showed higher bending capacities (6-16%) than when steel elements were connected with spot welds. * The number of spot welds between the C profile and other steel elements had a small influence on the bending capacity of the system (3-6%). * The steel beam height greatly influenced the bending capacity in all models, regardless of which type of connection between steel elements was used, or the degree of shear connection that was achieved (i.e., by increasing the steel beam height from 400 mm to 600 mm, the bending resistance will increase by approximately 30%). * When comparing the numerical and analytical results for the full degree of shear connection, it was found that the FE calculated bending capacities exceeded the characteristic bending resistance for all analyzed steel beam heights. * Analytically calculated characteristic bending resistances for partial shear connections without the reduction factor, \(\mathrm{k_{t}}\), for steel beam heights of 400 mm (shear connectors in pairs and in staggered arrangements) and for steel beam heights of 600 mm (staggered arrangement), were reached using the bending capacities from FE models. For models with a steel beam height of 500 mm (arrangement in pairs) and a height of 600 mm (arrangement in pairs), the analytically calculated values were not reached. Analytically calculated characteristic bending resistances for partial shear connections with the reduction factor, \(\mathrm{k_{t}}\), and characteristic non-linear bending resistances, were reached for all analyzed FE models. All conclusions will be verified in future planned experimental research concerning CFS-concrete composite beams with built-up CFS profiles connected by spot welds; this research will comprise planned activities related to the LWT-FLOOR project. Furthermore, as it was not possible to take into account the CW thickness and arrangement, or the number of spot welds at the cross section of the analytical models, this topic will also be investigated in future research. **Author Contributions:** Conceptualization, A.R. and I.L. ; methodology, A.R. and I.L. ; software, A.R. and I.L. ; validation, I.L., D.S. and I.C. ; formal analysis, A.R. ; investigation, A.R. and I.L. ; resources, A.R., I.L. and I.C. ; data curation, A.R. and I.L. ; writing--original draft preparation, A.R. and I.L. ; writing--review and editing, A.R., I.L., I.C. and D.S. ; visualization, A.R. ; supervision, I.L., D.S. and I.C. ; project administration, A.R., I.L. and I.C. ; funding acquisition, A.R., I.L., I.C. and D.S. All authors have read and agreed to the published version of the manuscript. This research was partially funded by the Croatian Science Foundation, grant number UIP-2020-02-2964 (LWT-FLOOR project--Innovative lightweight cold-formed steel-concrete composite floor system), project leader: [PERSON]. Not applicable.