Micro-Meter Crack Response Book
This web site presents cases studies that have been developed since the writing of the book ceased. It is an attempt to keep the book alive by providing new data as it becomes available in the form of additional appendices and additions to an expanded form of the Grand Summary Table (GST). These new cases are presented in the same Appendix and GST format as in the book to provide a consistent link between the book and this new information. From time to time this web site will be supplemented with yet more cases histories. Reports and theses upon which the appendices are based can be downloaded from the ITI – ACM -- web site of the ISEE web page for this book. If more interpretative information is needed, readers are encouraged to purchase the book.
Each case history is summarized in the “Grand Summary Table (GST)”. The new case studies are summarized at the top of the GST in the green band entitled – Additional Case Study Summaries. Below the green band are the cases in the book. Each line summarizes a single crack. They are presented in a nearly historical sequence by excitation mechanism that produces the ground motions. Since the greatest interest in vibratory response is generated by mine and quarry blasting, it should not be surprising that the first cases involve coal and aggregate mining. The major exception to this organizational scheme is the group labeled “Without Vibration.” Even though these case studies occurred early in the development of Autonomous Crack Monitoring (ACM), they were placed last because of the lack of externally driven vibratory crack response.
The GST information is expanded in an appendix for each case history, which often involves response of several cracks in a single house. The Appendix is identified by a two letter abbreviation as shown in the GS T in column one; eg Evansville, IN is entitled “(EV).” Cases that involve two homes in the same city/quarry and are presented in a single case history for each pair. Each appendix begins with a photograph of the house or structure and a one to one and a half page summary. This summary is then followed by plan or elevation views showing the crack locations, close up photographs of the cracks, time histories of ground motions and dynamic crack response(s) of typical events, and time histories of long-term crack response to climatological change. Each appendix begins with the photograph and background summary, which is followed by the figures. All figures and tables are labeled with the two capital letters of the appendix title.
Data for this Appendix, as is the case for the majority of this book, was extracted from reports, articles and theses written to document measurements made on projects with which I have been associated. Without the excellent summaries provided by the student researchers and co authors, this work would not be possible. Data employed by the students to write their theses was made possible through the work of the ITI staff, whose unsung assistance was critical to the consistent gathering of the data through the ACM concept. Writing a thesis involves several to a few drafts of both text and figures, review of which normally requires heavy editing. Normally upon completion of the thesis, a co authored paper is written to condense the major findings. Most of the resulting documents are provided to the public on the Infrastructure Technology Institute (ITI) web site.
While the writing in this book is mine, the figures, which were often mutually created, have been electronically extracted from pdf or word files available at the ITI web site, publications that I have co authored, or reports written as part of the ACM development . In some cases the figures have been modified slightly. In most cases they have not been modified. Rather than tediously reference each figure, in the appendix copying of the figures from specific reference materials is explicitly stated in the first paragraph of the case history.
Below is the link to the expanded table with additional case study summaries added after the book placed above the original table data for comparison.
Guide to the Original Grand Summary Table
As shown in the “Location” or far left column of the Grand Summary Table, crack responses were recorded in 12 states from Connecticut to Nevada and from Minnesota to Florida. Thus all potential climates are represented: from the desert to the tropics; from the West to the East Coast.
Some 22 different structures were instrumented. As shown in the structural description columns “Frame - Crack Location,” the majority were of one story. Only 7 or 33% were two or more stories. While almost all were constructed with a wooden frame, three were constructed with a cementicious block exterior frame. Periods of surveillance varied considerably as shown in the “Obs. time” column from several days (0.2 weeks) to over a year (> 52).
Behavior of cracks in many materials has been measured. Of the interior cracks or joints, 13 were in gypsum dry wall, 6 were in plaster and lath, 2 were in brick or block, 1 was in wood and 1 was at a wood-brick joint. Of the exterior cracks, 8 were in stucco, 4 were in block, and 1 in adobe. Cracks were fitted with either Kaman eddy current or Macrosensor LVDT micrometer displacement sensors as shown in the “sensor type” column. Instrumented cracks are much wider than their micrometer response. Compare their estimated micrometer width in the “crack width” column with the measured seasonal or maximum responses in columns under the headline “max crack response.”
Long-term response of the cracks is described in three ways: “season,” max,” or “daily.” Magnitude depends upon whether the results were recorded as a zero to peak (0-p) or peak to peak (p-p) manner, as shown in the next to the last column. For any one case this distinction is unimportant because the ratio of dynamic to long-term response in the far right column would be the same whether the results were recorded as 0-p or p-p. It is only important when absolute micrometer (μm) values are compared between cases. Any issues that arise from this difference can be resolved by referring to time histories of long-term and dynamic crack responses in each case history.
Dynamic responses in the “vibration” column are reported in the same manner as the long-term responses, 0-p or p-p with the same definition as for the maximum responses. The dynamic environment is described in the “max ppv” and “max air pressure” columns by the peak particle velocity and (in some cases) the air over-pressure to which the structure was subjected during observation. The ratio of vibratory to weather induced response for each crack is then presented in the far right column.
These appendices summarize the full reports in which data in the Grand Summary Table can be found. These full reports can be found in the publications section of the ACM website: http://www.iti.northwestern.edu/acm/publications.html