## 3 Provisions for Effective Flange Width of the Composite Beam in Current Design Specifications
### EN 1994-1-1:2004  
EN 1994 is the Structural Eurocode that deals with composite steel and concrete structures. Among others, it replaced the following national standards: BS 5400-5, BS 5950-3.1, and BS 5950-4. EN 1994 also replaced the national standards in many other countries, not only in the United Kingdom. EN 1994 consists of three parts: Part 1-1, General rules and rules for buildings (EN 1994-1-1); Part 1-2, General rules--Structural fire design (EN 1994-1-2); Part 2, General laws and rules for bridges (EN 1994-2). EN 1994-1-1:2004 incorporated corrigendum in April 2009. It is the oldest version of the current specification, but it significantly impacts design specifications in many countries, including the United States, Australia, New Zealand, and China. According to EN 1994-1-1:2004 [12], \"Action effects may be calculated by global elastic analysis, even where the resistance of a cross-section is based on its plastic or non-linear resistance\", \"The effects of shear lag and local buckling shall be taken into account if these significantly influence the global analysis\", and \"Allowance shall be made for the flexibility of steel or concrete flanges affected by shear in their plane (shear lag) either by means of rigorous analysis or by using an effective width of the flange.\" The following provisions should determine the effective width of concrete flanges. 1. When the global elastic analysis is used, a constant effective width may be assumed over the whole of each span. This value may be taken as the value \(b_{\text{eff, 1}}\) at mid-span for a span supported at both ends, or the value \(b_{\text{eff, 2}}\) at the support for a cantilever. 2. At mid-span or internal support, the total effective width \(b_{\text{eff}}\), see Figure 4, may be determined by the following equation: \[b_{\text{eff}}=b_{0}+\sum b_{\text{ei}}\] (2) where \(b_{0}\) is the distance between the centers of the outstand shear connectors; \(b_{\text{ei}}\) is the value of the effective width of the concrete flange on each side of the web and taken as \(L_{\text{e}}/8\) but not greater than the geometric width \(b_{\text{i}}\). The value \(b_{\text{i}}\) should be taken as the distance from the outstand shear connector to a point mid-way between adjacent webs, measured at mid-depth of the concrete flange. Except at a free edge, \(b_{\text{i}}\) is the distance to the free edge. The length \(L_{\text{e}}\) should be taken as the approximate distance between points of zero bending moment. For typical continuous composite beams where a moment envelope from various load arrangements governs the design, and for cantilevers, \(L_{\text{e}}\) may be assumed to be as shown in Figure 4.  
Figure 4: Equivalent spans for the effective width of the concrete flange in EN 1994-1-1 [12]. 3. The effective width at end support may be determined by the following equation: \[b_{\rm eff}=b_{0}+\sum\beta_{\rm i}b_{\rm ei}\] (3) with \[\beta_{\rm i}=(0.55+0.025L_{\rm e}/b_{\rm ei})\leq 1.0\] (4) where \(b_{\rm ei}\) is the effective width (see (b)) of the end span at mid-span, and \(L_{\rm e}\) is the equivalent span of the end span, according to Figure 4. 4. The distribution of the effective width between supports and mid-span regions may be assumed to be as shown in Figure 4. 5. Where the bending moment distribution is influenced by the resistance or the rotational stiffness of a joint in buildings should be considered in the determination of the length \(L_{\rm e}\). 6. For analysis of building structures, \(b_{0}\) may be taken as zero and measured from the center of the web. In EN 1994-1-1:2004, for serviceability limit states, the elastic analysis should be used with appropriate corrections for non-linear effects such as the cracking of concrete.