## 5 Design Suggestions of the Slab Width of Composite Joint Specimens
### Recommend Slab Width for Composite Joint Specimens  
Since researchers have not reached a consensus on the effective slab width for the composite joint, it was best to design a model following the current design specifications. As researchers, they are interested in the proportional relationship between the effective width and the actual width of the slab so that they can quickly design composite joint specimens based on the prototype structure. Thus, this paper also gives \(b_{e}/S_{0}\) for different specifications under different \(S_{0}/L\) values. The ratios of the positive and negative bending moment regions appear in Figures 7 and 8, respectively. It can be seen in Figures 7 and 8 that EN 1994-1-1, specifically GB50017, have calculated ratios greater than 1.0 under certain conditions. Under the condition that beams are continuous and have equal spacing, the ratio calculated by EN 1994-1-1 and GB50017 is always greater than AISC360 when \(S_{0}/L\) is less than \(1/3\). When \(S_{0}/L\) is greater than \(1/2\), almost all the calculating values of \(b_{\rm e}/S_{0}\) of three specifications are less than 0.5. The aim of our research was to avoid the brittle fracture of the bottom beam flange in the joint zone. The effective slab width under the sagging bending state is the most critical factor. However, most researchers mainly focus on seismic performance for composite joints, and cyclic or repeated loadings are commonly used in tests. So, the specimen slab width may be designed according to the effective width of the slab in the composite beam sagging and hogging bending region of the prototype frame. To facilitate the researchers' quick and safe designs of composite joint specimens, the recommended value \(b_{s}\), which is the width of the solid concrete slab used in the composite joint, is given based on the numerical calculation results mentioned above. \[b_{s}=aS_{0} \tag{7}\]  
where \(S_{0}\) is the actual width of the solid concrete slab and equals the distance to the centerline of the adjacent beam in the prototype frame; \(L\) is the beam span, center to center of the supports in the prototype frame, and where \(\alpha=1\), if \(S_{0}/L\leq 0.25\); \(\alpha=0.5\), if \(S_{0}/L\geq 0.5\); if \(0.25<S_{0}/L\leq 0.5\), then \(\alpha\) is obtained by linear interpolation. Figure 8: Comparison of effective flange width ratios (\(\rm b_{e}/S_{0}\)) in the negative bending moment region. (a) \(L1=L3=L2=L\); (b) \(L1=L3=1.5L2=1.5L\). Figure 7: Comparison of effective flange width ratios (\(\rm b_{e}/S_{0}\)) in the positive bending moment region. (a) At mid-span; (b) at end support. Like this article's research purpose, [PERSON] and [PERSON] recommend Equation (8) to calculate a composite steel beam at the ultimate state [21]. \[b_{\rm e}=[1-0.25(b_{\rm s}/L)]b_{\rm s}\ {\rm for}\ b_{\rm s}/L>0.25 \tag{8}\]  
where \(b_{\rm e}\) is the effective width of the concrete flange of a composite beam; \(b_{\rm s}\) is the width of the concrete flange of the composite beam and is the same as \(S_{0}\) in this paper, \(L\) is the same as the definition in this paper, and where \(b_{\rm e}=b_{\rm s}\) for \(b_{\rm s}/L\leq\ 0.25\) is the same as in this paper. Moreover, it is found through a calculation that when \(b_{\rm s}/L\geq\ 0.286\), calculation values of Equation (8) are always greater than Equation (7), and when \(0.25<b_{\rm s}/L<0.286\), calculation values of Equation (8) are always less than Equation (7). In this paper, the aim of proposing a recommended equation is to give the upper limit of the effective width corresponding to the ratio \(S_{0}/L\) (or \(b_{\rm s}/L\) in Equation (8)). It can help researchers to design composite joint specimens that meet design specifications quickly. Therefore, the reliability of Equations (7) and (8) had to be verified. Equation (7) is proposed based on conservative and safe design principles because the effective width of the slab in SMRFs is always smaller than its actual width.