Moderately Ductile Concentrically Braced Frame

9.7. CONCENTRICALLY BRACED FRAME WITH MODERATE DUCTILITY LEVEL

The rules to be applied in the dimensioning of these concentrically braced frames with moderate ductility level are given below:

9.7.1. General Conditions

9.7.1.1 - The width-to-thickness ratios of elements should not exceed the limiting width-to-thickness ratios, λ_md, from Table 9.3, for members designed as moderately ductile members.

9.7.2. Structural System Analysis

The strength required to dimension the columns, beams and connections of the concentrically braced frame system with moderate ductility level shall be determined by taking into account the load combinations including earthquake effects with overstrength factor D as defined in 9.2.6.

9.7.3. Braces

Braces with moderate ductility level shall comply with the following requirements:

9.7.3.1 - The slenderness ratio ( effective buckling length / radius of gyration) in brace members must comply with condition KL / i ≤ 200. However, if V-braced or inverted V-braced systems are used, the requirement for slenderness ratio will be defined as:

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9.7.3.2 - Concentrically braced frames with moderate ductility level are permitted to use built-up members provided that the parts assembled the cross-section of the brace behave as one single element. This requirement should be met by tie plates placed equally in built-up members with a distance between the elements equal to the thickness of the connecting plate and in other cases by truss connection. Section 8.4 of the "Regulation on Design, Calculation and Construction Principles of Steel Structures" shall be based on the design of the connector elements of built-up braces.

9.7.3.3 - Braces shall be dimensioned by taking into account the load combinations including earthquake effect given in 9.2.5.