## 4 Limit States Criteria  
SCBFs are designed as concentric truss members, and the frame bending and brace buckling effect are neglected. They are designed for higher inelastic capacity, which is introduced through the buckling and yielding of the brace. The compactness of the brace member should satisfy the criteria for the highly ductile member for the SCBF system. The slenderness limit of the brace member is restricted to 200 as it precludes the dynamic effect related to the extremely slender braces. In the design, it is expected that the brace should resist 30% to 70% of the total horizontal force in tension. The buckling of the brace is expected at the story drift of 0.3% to 0.5%. The braces in the SCBF system are designed to have axial deformation of 10 to 20 times the yield displacement of the brace. The capacity-based design methodology is used for the design of the beam, column, and connection of the SCBF system. The required resistance of the brace for tension and compression in the capacity design method is taken as \(P_{bt}=R_{y}F_{y}A_{g}\) and \(P_{bc}=(1/0.877)F_{cr}A_{g}\) respectively. The excepted post-buckling strength of the brace is taken 0.3 times the excepted compressive strength of the brace. In the expression, \(P_{bt}\) and \(P_{bc}\) are the excepted tensile strength and compressive strength of the brace, \(R_{y}\) is the ratio of the excepted yield strength to the minimum specified yield strength (\(F_{y}\)),\(A_{g}\) is the gross cross-sectional of the brace, and \(F_{cr}\) is the critical stress associated with the brace buckling. A factor equal to 1.1 was applied to calculate the expected buckling strength in the earlier edition of Seismic Provision AISC 341-10 [25] and was removed from the current edition of AISC 341-16 [26] to include the effect of the conservative column curve equation. The effective length coefficient (K) is taken as 1 to calculate the critical buckling stress as per AISC 341-16 [26]. The brace length used to calculate the effective length is the length from brace end to brace end. The columns are designed for the inelastic capacity of the brace based on the plastic mechanism discussed in AISC 341-16 [26]. The column splices are designed to develop at least 50% of the lesser connected member's plastic flexural strength (MP). The connection, which plays an important role in transferring the forces from the brace to the beam-column junction, is required to bear the high inelastic demand of the SCBF system. As discussed earlier, the inelasticity demand on the SCBF system is fulfilled by the hinges on the prescribed location. The various limit states design criteria for the IPB braced system are shown in Figure 2. In order to have the desired yield hierarchy and to avoid premature fracture, the connection of the IPB braced system has to satisfy all the design limit state criteria. The design of the IPB braced system has more limit states and requires a lot more calculation than the OOPB braced system. This is due to the extra element introduced to the IPB braced system called the knife plate. The seismic load path of both types of connections is explicitly different due to the inherited different detailing and yielding zone. The limit states for the IPB braced system were not explored much compared to the OOPB braced system, which led to the premature structure failure observed in the recent experimental studies [10; 27]. In the absence of that, the design of the IPB brace system is carried out based on the prescribed limit state of the OOPB braced system or not considered in the design. The yielding of the gusset plate and knife plate is measured using the Whitmore width [28] concept. The Whitmore effective width is defined as the projection of a 30\({}^{\circ}\) angle from the start to the end of the bolted or welded joint. The buckling capacity of the gusset plate is calculated using the Thornton method [12], which uses the effective length of the gusset plate based on the average centroidal length and the lengths at two ends of Whitmore's effective width.