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# Strong column, weak beam - Ductility condition - EN 1998-1

June , 15th 2024 | Via: Prontubeam | Seen: 407 times
This image shows the need to design columns to resist more than beams. It is based on EN 1998-1:2004 - 4.4.2.3 Global and local ductility condition, where the goal is for the moment resistance of the columns to be 1.3 times the moment resistance of the beams: ∑M_RC ≥ 1.3∑M_RB (4.29).

This is known as the "Strong Column, Weak Beam" principle.
EN 1998-1:2004 - 4.4.2.3 Global and local ductility condition:

(3)P In multi-storey buildings formation of a soft storey plastic mechanism shall be prevented, as such a mechanism might entail excessive local ductility demands in the columns of the soft storey.

(4) Unless otherwise specified in Sections 5 to 8, to satisfy the requirement of (3)P, in frame buildings, including frame-equivalent ones as defined in 5.1.2(1), with two or more storeys, the following condition should be satisfied at all joints of primary or secondary seismic beams with primary seismic columns:

∑M_RC ≥ 1.3∑M_RB (4.29)

where:

- ∑M_RC is the sum of the design values of the moments of resistance of the columns framing the joint. The minimum value of column moments of resistance within the range of column axial forces produced by the seismic design situation should be used in expression (4.29); and

- ∑M_RB is the sum of the design values of the moments of resistance of the beams framing the joint. When partial strength connections are used, the moments of resistance of these connections are taken into account in the calculation of ∑M_RB.

NOTE: A rigorous interpretation of expression (4.29) requires calculation of the moments at the centre of the joint. These moments correspond to development of the design values of the moments of resistance of the columns or beams at the outside faces of the joint, plus a suitable allowance for moments due to shears at the joint faces. However, the loss in accuracy is minor and the simplification achieved is considerable if the shear allowance is neglected. This approximation is then deemed to be acceptable.

[1] EN 1998-1:2004;

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