Ductility classes and rules for cross sections

To achieve some consistency with other parts of the code, the most recent version of EC8 explicitly addresses three ductility classes namely DCL, DCM and DCH referring to low, medium and high dissipative structural behaviour, respectively. For DCL, global elastic analysis and the resistance of the members and connections may be evaluated according to EC3 without any additional requirements. The recommended reference q factor for DCL is 1.5-2.0. For buildings that are not seismically isolated or incorporating effective dissipation devices, design to DCL is only recommended for low seismicity situations. In contrast, structures in DCM and DCH need to satisfy specific requirements primarily related to ensuring sufficient ductility in the main dissipative zones. Some of these requirements are general rules that apply to most structural types whilst others are more relevant to specific configurations.

The application of a behaviour factor larger than 1.5-2.0 must be coupled with sufficient local ductility within the critical dissipative zones. For elements in compression or bending (under any seismic loading scenario), this requirement is ensured in EC 8 by restricting the width-to-thickness (b/t) ratios to avoid local buckling. An increase of b/t ratio results in lower element ductility due to the occurrence of local buckling (as illustrated in Figure 6.1) leading to a reduction in the energy dissipation capacity, which is expressed by a lower q factor. The classification used in EC3 is adopted but with restrictions related to the value of q factor as given in Table 6.2 (Section 6.5.3 and Table 6.3 of EN 1998-1). It is worth noting that the seismic cross-section requirements in US practice imply more strict limits for certain section types.

The cross-section requirements apply to all types of frame considered in EC8. These provisions implicitly account for the relationship between local buckling and rotational ductility of steel members that has been extensively

Table 6.2 Cross-section requirements based on ductility class and reference q-factor

Ductility Class

Reference q-factor

Cross-Section Class

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Responses

  • kris
    What is a ductility class?
    3 years ago
  • patrick
    How to classify ductility class?
    2 years ago
  • marcho burrowes
    What are the ductility classes?
    1 year ago
  • patricia hall
    What is crosssectional class of dissipative elements?
    5 months ago
  • mara
    What are ductlity class high, low and medium?
    5 months ago

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