Seismic Response of Low-Rise Masonry Buildings with Flexible Roof Diaphragms

The study described in this paper compares the responses from shaking-table testing and analytical predictions, evaluated in the context of geometric scaling, to provide a coherent description of the seismic response of low-rise masonry buildings with flexible roof diaphragms.

Two, half-scale, low-rise, reinforced masonry buildings with flexible roof diaphragms are subjected to carefully selected earthquake ground motions on the Tri-axial Earthquake and Shock Simulator (TESS) at the US Army Construction Engineering Research Laboratory (USA CERL). Damage to the half-scale specimens is assessed using published protocols. Geometric scaling analysis relates response and damage of the half-scale specimens to those of the full-scale prototype structures.

In contrast to what is usually assumed in design, the half-scale specimens do not behave as systems with a single degree of freedom associated with the in-plane response of the shear walls. Calculated responses from linear elastic finite element (FEM) models are compared to measured responses. Robustness of the FEM models is assessed using parametric studies.

Linear elastic modeling is simplified to a generalized 2-DOF idealization. Response-spectrum analysis of such an idealization is accurate and justified for prediction of dynamic response of the half-scale specimens and the corresponding full-scale prototype.

It is shown that low-rise masonry buildings with flexible roof diaphragms can be designed for seismic loads as single-degree-of-freedom systems, using the degree of freedom associated with the in-plane response of the diaphragm in the building’s transverse direction, rather than the degree of freedom associated with the in-plane responses of the shear walls.