<p>In truss topology optimization, local buckling of compressed members is a critical design constraint. A particular challenge arises when collinear elements form a chain, interpreted as a single bar, requiring a corrected buckling length. Discontinuous updates of this length during gradient-based optimization—the so-called jumping of the buckling length phenomenon—pose significant difficulties. To address this, the novel density-based buckling length (DBL) method is proposed. Two subsets of design variables are introduced: artificial densities, governing bar presence or absence, and cross-sectional areas, sizing the existing bars. The densities continuously modulate the equivalent buckling length as the topology evolves, naturally handling chain effects. By setting a strictly positive area lower bound, excessively slender members are prevented, inherently mitigating the singularity phenomenon of buckling constraints. Mass and compliance minimization formulations, both subject to local buckling constraints, are explored. A novel geometric admissibility constraint is proposed to prevent spurious members that artificially reduce the buckling length in the mass formulation. Both Euler and Euler–Johnson buckling predictions are considered, the latter rarely if ever employed in truss topology optimization. The results demonstrate the correctness of the buckling length evaluation for chains in optimal layouts. The mass and compliance-based formulations may lead to different optimal topologies. The Euler–Johnson formula proves advantageous, as a priori the designer hardly knows the optimal member slenderness and, in case it comes low enough, safer designs are obtained. Finally, incorporating multiple-load cases in the compliance minimization problem provides kinematically stable design solutions.</p>