An Integrated Method for Sustainable Performance-based Design Optimization of RC Buildings using Mini-haunch Beam–column Connections

This study develops an integrated computational workflow for sustainable performance-based seismic design (PBSD) of reinforced concrete moment frames detailed with mini-haunch beam–column connections. The design problem is cast as a multi-objective optimization that simultaneously minimizes initial construction cost and embodied CO₂, while enforcing member strength and PBSD drift limits at Immediate Occupancy, Life Safety, and Collapse Prevention levels. Nonlinear static pushover analysis is embedded in the loop, and candidate designs are searched using the Enhanced Colliding Bodies Optimization (ECBO) algorithm. Unlike conventional treatments that fix the detail, the haunch geometry is parameterized and varied explicitly so its influence on stiffness, hinge locations, and global mechanism can be quantified. A four-story frame case study shows that mini-haunches shift plastic hinges away from the beam–column joint region and promote a more desirable strong-joint response under lateral loading. In the optimal set, the mini-haunch solution reduces embodied emissions by about 8.3% relative to a prismatic baseline, with only a 3.5% increase in cost, indicating a practical trade-off between sustainability and seismic reliability, and provides a transferable template for designers using standard analysis tools.