Abstract

Determining whether an earthquake, blasting, or pile driving caused non-structural “cosmetic” wall cracks or extended pre-existing fractures is often based on judgment: The structure presumably vibrated; therefore, new cracks formed, and existing fractures were extended. The proposed two-part, primarily post-event, fracture mapping and analysis of intensity data are designed to test the static, as opposed to vibratory, cause of wall fractures, assuming: (1) tension fractures form perpendicular to the principal tensile stress (σ3) direction; (2) during structure vibrations, the local stress field rotates relative to the static stress field; (3) stress reversals, common during earthquakes, can cause tension fractures at all corners of rectangular doors and windows; (4) progressively younger en echelon tension fractures, originating at the corner of a rectangular wall opening, trend toward horizontal due to the transient rotation of the principal stresses, whereas fractures from non-vibrational causes trend toward vertical; (5) crack extension occurs when two fractures are linked by hook-shaped fractures; and (6) site-specific intensity observations and local intensity data provide qualitative data regarding the timing and amplitude of wall strains and the potential for co-seismic damage. Co-seismic tension fractures can therefore be differentiated from pre-existing cracks, suggesting pre-blasting and pile-driving crack mapping, building condition surveys, and co-seismic ground and structure motion recordings may not be required: (1) if the building has no prior exposure to potentially damaging vibrations; and (2) a reconnaissance inspection indicates there are no pre-existing horizontal or sub-horizontal wall fractures.

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