Force-based design of a novel self-centring concentrically braced steel frame validated by nonlinear time-history analysis

Self-centring concentrically braced frames (SC-CBFs) are intended to limit residual deformation after strong earthquakes, but practical code-oriented procedures for their design remain limited. This study presents a force-based design (FBD) procedure for a horizontally post-tensioned SC-CBF consistent with Eurocode 8 and Eurocode 3. The procedure defines the seismic base shear, brace sizing, allocation of shear resistance between the concentrically braced frame and post-tensioning system, and capacity checks for beams, columns, braces, and strands. A regular four-storey archetype was designed using q = 4 as a case-study assumption and evaluated using nonlinear time-history analyses in OpenSees under 12 spectrum-matched earthquake records. The first-mode period obtained numerically (0.356 s) was close to the Eurocode estimate (0.34 s). Record-specific peak responses and the suite mean were examined; mean peak floor displacements and inter-storey drifts remained within the FBD design profiles, residual drifts were substantially below the adopted tolerance, and post-tensioning forces remained below the specified design capacity. Within the scope of this single archetype, these findings support the proposed FBD procedure as a practical basis for preliminary design of the investigated SC-CBF configuration. The adopted q value and the final 60:40 CBF-to-PT shear allocation are case-study-specific and require further evaluation across other structural and seismic conditions.