OCTOBER 2009 » book review

The Practice of Preservation Engineering

Structural Investigation of Historic Buildings: A Case Study Guide to Preservation Technology for Buildings, Bridges, Towers, and Mills
by David C. Fischetti, PE
John Wiley & Sons, Inc. Hoboken, NJ; 2009
288 pp.; hardcover; numerous color & b&w photos; $95
ISBN 978-0-470-18967-2

Reviewed by Judy L. Hayward

Do you ever find yourself asking, "Should I be documenting my own work in order to share lessons learned with my colleagues or to leave a record for posterity?" An example has now been set for practitioners of traditional building. Part memoir, part textbook, David Fischetti has delivered a book that documents his work, the 20th-century preservation movement, and the relationship between engineering, traditional craft practice, and modern building materials science.

Fischetti is a skilled storyteller and historian and arguably one of the nation's finest engineers specializing in historic properties. His book is a readable blend of case studies, technical details and frank discussion of what works and what needs to be improved in the practice of preservation engineering. The book is a humble reflection on Fischetti's dedicated work on some of America's beloved vernacular and high-style buildings, bridges, mills and towers.

The author sets forth a comprehensive approach that applies whether the subject is James Madison's Montpelier, the Cape Hatteras Lighthouse or the Yates Mill: Consider safety first; Comply with the Secretary of the Interior's Standards and use it as a guide to practicing sound preservation philosophy; Test according to accepted engineering standards; Study the strengths and weaknesses of traditional and modern materials in order to be able to interpret test results accurately; and assemble the right team for the work.

Fischetti is well aware of the controversy that can erupt on preservation projects, and he offers a methodical approach to gathering data that is beyond reproach and tempered with a deep understanding of building craft practice and in-situ building material performance. He offers practical insight into the complex process of structural evaluation, conditions assessment and repair. He graciously shares credit for successful projects with architects, fellow engineers, contractors, trades people and the building stewards with whom he has worked for nearly 40 years. He extols the virtues of teamwork in word and deed.

Fischetti then moves on to detailed case studies of projects that he has worked on throughout his career. Let's examine two: Relocating Cape Hatteras lighthouse and The Cornish-Windsor Covered Bridge. Construction of the Cape Hatteras lighthouse began in November 1868 at a distance of 1,600 feet from the shoreline. It served an area off the Outer Banks that has become known as the "graveyard of the Atlantic." More than 1,200 shipwrecks have been recorded there since 1526. The nature of the barrier islands is not only to erode with time but to also "migrate," by changing shape due to waves, tide and wind. Fischetti notes that average erosion at Cape Hatteras has been 11 feet per year. By 1932, the shoreline was only 100 feet away from the lighthouse.

It took a grass roots preservation movement and a lot of engineering analysis to arrive at the decision to relocate the lighthouse approximately 1,000 yards inland. Fischetti details the use of 150 tons of structural steel and 22 150-ton hydraulic jacks to move the lighthouse in one piece. He writes, "The physics involved in the horizontal moving of any object is rather simple." A system of steel, timber and jacks rested on dense, moist compacted sand beneath a layer of shifting sands. The 60-ft. tall structure was gently moved in a slow "leap-frogging" march accomplished in four to five foot increments.

Another example is the preservation of the Cornish-Windsor Covered Bridge. I first met David Fischetti amid the controversy over the best method to repair this bridge in the 1980s. This iconic structure has joined Cornish, NH, and Windsor, VT, since 1866. It is the only extant, notched Town lattice truss bridge and the longest two-span covered bridge in the world. By 1908, noticeable sag had occurred in the structure, and by 1980, its fourth chord was in failure. The mighty bridge was still supporting traffic due to its inherent redundancy but if it collapsed, lives would surely be lost. Something had to be done.

A very well-founded debate about the best method of repairing and strengthening the bridge ensued for eight years. A traditional means to strengthen the bridge would have involved adding arches that would have sprung from the piers and abutments four feet beneath the bridge. Local preservationists, and I was among them, feared that the bridge would be subjected to greater potential to loss from ice flows. I had personally observed ice hitting the base of the existing bridge.

Fischetti arrived at a proposed solution in 1988: to replace the original chords with glued laminated timber replacement chords. This respected the engineering system but achieved a greater strength to meet modern highway requirements He developed a modeling system on a personal computer – this was 1989, after all – that analyzed 1,600 members in 13 hours of running time on the computer. He devised a cable-stay support system that allowed work on the bridge during the frigid winter months when the Connecticut River was "iced over." Fischetti recounts that the use of the stays allowed 30 inches of camber to be introduced into the bridge, thereby correcting sags that began shortly after the bridge had been built.

The book is organized into 19 chapters, plus an index. Other case histories include St. Helena's church in Beaufort, SC; the Montague Building in Raleigh, NC; Watauga Hall at North Carolina State University; Market Hall in Charleston, SC; St. Philip's Moravian Church at Old Salem, NC; Montpelier, and the Tohickon Aqueduct in Pennsylvania. Each chapter concludes with references and/or a bibliography for additional reading.

Color photos are positioned in the center of the book while black-and-white photos are used throughout the chapters. The photos are not high quality, but nevertheless they convey quite a bit of information.

David Fischetti concludes his Cornish-Windsor Covered Bridge case study by stating that "Only through rigorous structural analysis, which recognizes the special conditions inherent in historic timber structures, does sufficient information on which to base sensitive preservation decisions become available." That message is the most important point made in the entire book and it defines this remarkable preservationist's career. Whether you're a seasoned preservation professional or engineering student with big dreams, read this book. TB

Judy L. Hayward is the education director for Restore Media, LLC, producers of the Traditional Building Exhibition and Conference, and the executive director of Historic Windsor, Inc., and the Preservation Education Institute in Windsor, VT. She can be reached at jhayward@restoremedia.com.

«BACK TO OCTOBER 2009 TABLE OF CONTENTS

Have something to say about this article? Feel free to comment!

Comments feed