ABSTRACT
The different criteria provided by the EC8 for the modeling of the two types of braced frames and for the evaluation of their lateral strength come from the different slenderness ratios expected for chevron and diagonal braces. If chevron braces and diagonal braces are inserted within frames having the same story height and span length, chevron braces are stockier than diagonal braces. Based on this consideration, it is expected that chevron braces, which are stockier, can sustain a significant axial force before their buckling. Therefore, the numerical model adopted for the estimation of the effect of seismic force on chevron braced frames has to include the braces in both tension and compression. Furthermore, the lateral strength provided by a pair of chevron braces is assumed as the horizontal reactions that they transmit when the axial force of the brace in compression is equal to the buckling resistance Nb:
VRd ( )Nb qN ( )fb b y qNA22 − cosθ θ (1) where Nq is the axial force of the brace due to gravity loads, θ is the angle of inclination of the brace with respect to the beam longitudinal axis, Ab is the area of the brace cross-section, fy is the steel yield stress, and χb is the ratio between the buckling and plastic strengths.
