Because conventional seismic force resisting systems rely on yielding of key structural members to limit seismic forces, structural damage is expected after a design-level earthquake. Repairing this damage can be very expensive, if it is possible at all. Researchers have been developing a new family of self-centring systems that avoid structural damage. One such system is a controlled rocking steel frame, which is the subject of this thesis. In a controlled rocking steel frame, the columns of a frame are permitted to uplift from the foundation, and the response is controlled by using a combination of post-tensioning and energy dissipation. Although previous studies have confirmed the viability of this system, they have also shown that rocking does not fully limit the peak seismic forces because of higher mode effects. If a structure is designed to account for these effects, it may be uneconomical, but if it is not designed to account for them, it may be unsafe. The purpose of this thesis is to develop recommendations for the design of controlled rocking steel frames, particularly with regard to higher mode effects. A theoretical framework for understanding higher mode effects is developed, and large-scale shake table testing is used to study the behaviour of a controlled rocking steel frame. Two mechanisms are proposed to mitigate the increase in structural forces due to higher mode effects, and these mechanisms are validated by shake table testing. Numerical modelling of controlled rocking steel frames is shown to become more reliable when higher mode mitigation mechanisms are used to limit the seismic response. In the final chapters, the thesis proposes and validates a new methodology for the limit states design of controlled rocking steel frames.

Because conventional seismic force resisting systems rely on yielding of key structural members to limit seismic forces, structural damage is expected after a design-level earthquake. Repairing this damage can be very expensive, if it is possible at all. Researchers have been developing a new family of self-centring systems that avoid structural damage. One such system is a controlled rocking steel frame, which is the subject of this thesis. In a controlled rocking steel frame, the columns of a frame are permitted to uplift from the foundation, and the response is controlled by using a combination of post-tensioning and energy dissipation. Although previous studies have confirmed the viability of this system, they have also shown that rocking does not fully limit the peak seismic forces because of higher mode effects. If a structure is designed to account for these effects, it may be uneconomical, but if it is not designed to account for them, it may be unsafe. The purpose of this thesis is to develop recommendations for the design of controlled rocking steel frames, particularly with regard to higher mode effects. A theoretical framework for understanding higher mode effects is developed, and large-scale shake table testing is used to study the behaviour of a controlled rocking steel frame. Two mechanisms are proposed to mitigate the increase in structural forces due to higher mode effects, and these mechanisms are validated by shake table testing. Numerical modelling of controlled rocking steel frames is shown to become more reliable when higher mode mitigation mechanisms are used to limit the seismic response. In the final chapters, the thesis proposes and validates a new methodology for the limit states design of controlled rocking steel frames.

Controlled Rocking Steel Braced Frames (CRSBFs) have been developed as a high-performance structural solution to resist seismic forces, due to their ability to minimize structural damage and self-centre the structure back to its original position after an earthquake. A CRSBF is intentionally allowed to uplift and rock on its foundation, which acts as the nonlinear mechanism for the system rather than member yielding and buckling. While the CRSBF is in the rocking phase, the response of the system is controlled by prestressing which anchors the frame to the foundation and energy dissipation devices which are engaged by uplift. Although CRSBFs have shown promising structural performance, an assessment of the overall effectiveness of this system must also consider the performance of nonstructural components which have a significant impact on the safety and economic performance of the system. The purpose of this thesis is to compare the performance of nonstructural components in buildings with CRSBFs to their performance in a conventional codified system such as a buckling restrained braced frame (BRBF), while also investigating which design parameters influence nonstructural component demands in CRSBFs. The responses of various types of nonstructural components, including anchored components, stocky unanchored components that slide, and slender unanchored components that rock, are determined using a cascading analysis approach where absolute floor accelerations generated from nonlinear time-history analyses of each structural system are used as input for computing the responses of nonstructural components. The results show that the trade-off of maintaining elastic behaviour of the CRSBF members is, in general, larger demands on nonstructural components compared to the BRBF system. The results also show that the stiffness of the frame and vibration of the frame in its elastic higher modes are the main influencers for nonstructural component demands in buildings with CRSBFs, while energy dissipation has a minimal impact. / Thesis / Master of Applied Science (MASc) / Controlled Rocking Steel Braced Frames (CRSBFs) have been proposed as a high-performance structural system that resists earthquake forces on buildings. This system has the ability to minimize damage to structural members and self-centre the building back to its original position after an earthquake, two characteristics that are typically not achieved by current conventional systems. However, an assessment of the CRSBF’s overall effectiveness cannot be limited to the consideration of only the structural skeleton, as the performance of nonstructural components (e.g. architectural elements, mechanical and electrical equipment, furnishings, and building contents) that are not part of the structural skeleton can have a significant impact on the safety and economic performance of earthquake resisting systems. This thesis compares the demands on nonstructural components in buildings with CRSBFs to their demands in a more conventional system during earthquake motions. The results show that the trade-off for avoiding damage to structural members in the CRSBFs is often higher demands on the nonstructural components.