A capacity-based design process for earthquake-resistant steel frames

Capacity-based design ensures that the structure collapses according to a desired scenario in the event of a large earthquake to minimise loss of life. This design approach has been widely researched and incorporated into some building codes. However, current methods still have limitations, leading to potential uncontrolled collapses in certain scenarios. Many researchers have worked to address these shortcomings, but existing procedures remain complex and challenging to apply in practice. This paper introduces a new design method that focuses on optimising structures beyond the elastic range. First, the frame is calculated for optimal plasticity according to the earthquake load to determine the plastic moments. These plastic moments are used to redesign the cross-sections of beams and columns. The beam cross-section is designed according to the calculated plastic moments. Meanwhile, the moment value for designing the column cross-section is equal to the calculated plastic moment value multiplied by a factor > 1. The results show that the steel frames designed using the proposed method attain a global collapse mechanism. Additionally, the ductile behaviour of the frames has been controlled. A 3-story, 1-span 2D frame and a 6-story, 3-span 2D frame are analysed using this capacity design approach to demonstrate the effectiveness and performance of the proposed procedure and compared with other methods.