A Study of the Progressive Degradation of Masonry Shear Walls Subjected to Harmonic Loading

This masonry research investigated the differences in the static and dynamic stiffness for the seismic range of loads and frequencies for a pressed clay masonry wythe. The effective stiffness has been defined in Newtonian physics and Damage Mechanics. This research used the concept of measured stiffness defined as the measured stress field divided by the measured strain field. A two-part test rig was constructed to apply the loading to the wythe. The first loading mechanism was a compression frame that supplied in plane bi-axial nonproportional compression stress to reflect the loading on a shear wall from the dead load of a structure. The second loading mechanism was a shear yoke designed to apply a harmonic shear stress to the edge of the panels. A finite element analysis of two masonry structures concluded that the forcing function applied to the shear yoke could be represented as a harmonic function of single frequencies. The experimental study was based on a systematically varied harmonic loading pattern. The measured stiffness was shown to approach the effective stiffness as the frequency of the loading function approaches zero. A relationship has been established between the static or effective stiffness and dynamic or measured stiffness based on Newton’s second law and shown to be experimentally valid. The damage parameter was encapsulated from the effective stiffness data and tri-linear curve recommended for engineering design purposes. The degrading stiffness can now be used in the further development of codes such as FEMA 273. Progressive Degradation of Masonry Shear Walls 23 Chapter