A deformation-based criterion for redistribution of seismic forces in masonry buildings after linear analysis

Abstract

The redistribution of internal forces after linear analysis is a well-established practice in structural codes since several decades for different structural typologies, extending beyond seismic design. A typical example is the redistribution of bending moments in reinforced concrete continuous beams under gravity loading. The limitations of linear analysis in representing the nonlinear response of masonry buildings, acknowledged since the late 1970s, motivate the development of simplified yet physically sound approaches, such as the redistribution of seismic forces among walls following linear analysis. Although the possibility of redistributing internal forces in the seismic design and assessment of masonry buildings has been introduced in several design codes and recommendations since the mid-1980s, no systematic study has defined rational limits for its application. In this context, this paper proposes a possible rational approach based on wall deformation capacities to define limits for force redistribution in the seismic design and assessment of masonry buildings with rigid floor diaphragms. The methodology is first detailed for single-storey buildings without torsional response, and subsequently extended to include cases involving torsional effects, considering torsionally restrained buildings. Validated through incremental nonlinear time-history analyses, the proposed method defines maximum redistributable forces based on a conservative configuration of in-plane wall displacements representative of building ultimate conditions, thereby eliminating the need for predefined overstrength ratios. The extension to low-rise multi-storey buildings is also discussed, addressing the complexities arising from the presence of multiple storeys. The proposed criterion is illustrated through three worked examples, demonstrating its advantages. The outcomes of this research provide a background for the provisions included in the new version of prEN1998-1–2 (Eurocode 8, Design of structures for earthquake resistance, Part 1–2, Rules for new buildings).