Structural types and behaviour factors 1
Ehe same upper limits of the reference behaviour factors specified for steel framed structures (Section 6 of EN 1998-1) are also employed in Section 7 of EN 1998-1 for composite structures. Ehis applies to composite moment resisting frames, composite concentrically braced frames and composite eccentrically braced frames. However, whilst in composite moment frames the dissipative beam and/or column zones may be steel or composite, the dissipative zones in braced frames are in most cases only allowed to be in steel. In other words, the diagonal braces in concentrically braced frames, and the bending/shear links in eccentrically braced frames, should in most cases be designed and detailed such that they behave as steel dissipative zones. Ehis limitation is adopted in the code as a consequence of the uncertainty associated with determining the actual capacity and ductility properties of composite steel/concrete elements in these configurations. As a result, the design of composite braced frames follows very closely those specified for steel, and are therefore not discussed in detail herein. n the other hand, several specific criteria related to the dissipative behaviour of composite moment frames are addressed in subsequent sections of this chapter.
A number of additional composite structural systems are also referred to in Section 7 of EN 1998-1, as indicated in Eable 7.1, including:
• Steel or composite frame with connected infill concrete panels (Type 1), or reinforced concrete walls with embedded vertical steel members acting as boundary/edge elements (Type 2).
• Steel or composite coupling beams in conjunction with reinforced concrete or composite steel/concrete walls (Type 3).
• Composite steel plate shear walls consisting of vertical continuous steel plates with concrete encasement on one or both sides of the plates and steel/composite boundary elements.
Ehe upper limits of reference q for the above-listed systems are shown in able 7.1 for and . s noted in previous chapters, these reference values should be reduced by 20 per cent if the building is irregular in elevation. Also, an estimate for the multiplier a /a may be determined from conventional nonlinear 'pushover' analysis, but should not exceed 1.6. In the absence of detailed calculations, the default value of a /a ay be assumed as 1.1 for Types 1-3. For composite steel plate shear walls, the default value may be assumed as 1.2. It should be noted that for buildings that are irregular in plan, the default values of a /a should be assumed as 1.05
Table 7.1 Structural types and behaviour factors (additional to those in Section 6 of EN 1998-1)
Structural Type
Type 1
Structural Type
Type 1
Type 2
Type 2
Type 3
a/ all q-factor
Post a comment