# Numerical Study on the Bending Resistance of Lightweight Built-Up Steel-Concrete Composite Beams
## 2 Materials and Methods  
### Analytical Approaches for the Bending Resistance of Composite Beams  
#### 2.1.1 Literature Overview  
In the available literature, different approaches for calculating the bending resistance of composite steel-concrete systems can be found, depending on which standards are used (e.g., American, Australian, European, or Chinese). The prediction of the flexural strength of the composite CFS section and the concrete slab, wherein the steel beam consists of two C-sections oriented 'toe-to-toe' to form a box section, is shown in [2]; the bending resistance is calculated using the elastoplastic theory, which is based on EN 1994-1-2004 [9]. The structural behavior of double CFS-lipped channel sections that are connected to a concrete slab as a composite beam was analyzed [11]; the channel sections were placed back-to-back and connected with bolts. The plastic theory was used to calculate the ultimate moment capacity of the full-scale composite beams. To compare the results, the experimental and theoretical load capacities (interpolation method, stress block method, and web crippling) were calculated in accordance with European [9] and British standards [17]. In addition to the interactions between steel and concrete, as presented in the aforementioned articles, the composite action between CFS beams and wood-based floorbounds is shown in [18]. The theoretical plastic bending resistance was calculated and the full shear connection and plastic stress distribution was estimated in accordance with EN 1994-1-1 [9]. In [19], a comparison of two different standards of composite beam, European (EN 1994-1-1 [9]) and Chinese (JGJ 138 [20]), were used for a bending experiment wherein a novel configuration of cold-formed U-shaped steel-concrete composite beams was tested. The flexural behavior of CFS composite beams was the subject of an article by [PERSON] et al. [21]. The researchers investigated the simplified the method for calculating the flexural elastic capacity. Another comparison between European and Chinese standards was analyzed; it concerned the flexural behavior of rebar truss stiffened cold-formed U-shaped steel-concrete composite beams [22]. The test results showed that the ultimate bending capacity could be calculated using EC4 and JGJ 138 with three modification factors to account for the effective slab width, depth, and steel web, as well as the actual compressive strength of the concrete. The calculated bending resistances align well with the experimental results. The same modification was used in [23] to investigate the flexural behavior of rebar truss stiffened cold-formed U-shaped steel-concrete composite beams. [PERSON] et al. [24] investigated a CFS floor truss with concrete-filled compression chords to show how external loading forces act on the trusses, and how they induce axial strain and bending strain on the chord elements. The total number of chord strains at the most critical cross-section can be calculated as the sum of the strains due to the two effects mentioned. [PERSON] et al. [25] analyzed the negative bending behavior of novel U-shaped composite steel and concrete beams. The whole procedure for calculating the negative bending capacity, which is the sum of the moments caused by the corresponding force of each part of the composite system, is explained. In addition, [PERSON] et al. [26] also analyzed the U-shaped steel-encased concrete composite beams. [PERSON] et al. [7] conducted an experimental study on the bending behavior of double channels and hollow light gauge steel sections. An approach from the Australian-New Zealand standard for CFS structures [27] was used to calculate the nominal beam bending moment capacity. [PERSON] [8] investigated the strength of a composite beam made of concrete and a thin-walled CFS stiffened channel section. In addition to the bending strength, the shear strength and the interactions between the shear and bending forces were also analyzed. [PERSON] et al.