Vibration Mitigation and Sound Testing in SUE Hall at the Field Museum in Chicago

ABR-Full Page APT ad-8.5x11-4C

Vibration Mitigation and Arne Johnson Sound Testing in SUE Hall Mohamed ElBatanouny William Simpson at the Field Museum n in Chicago

How to settle down your Tyrannosaurus rex before you take it out in public: vibration-mitigation design for a 67- million-year-old museum specimen.

Fig. 1. Completed SUE Hall, Field Museum, Chicago, Illinois, soon after public opening, with sound show and digital animations on glass screens in background. Photograph by John Weinstein, 2018. © Field Museum of Natural History GN92620_092B.

“SUE” is the most complete Tyrannosaurus rex specimen in the world, with approximately 90 percent (by volume) of its actual bones mounted for exhibit. The specimen was discovered in 1990 in western South Dakota from the Hell Creek Formation dated approximately 67 million years old. The Field Museum in Chicago, Illinois, acquired the specimen, catalog no. PR 2081, now one of the most valuable objects in the museum’s collection, in 1997 for $8.3 million. From the outset, the museum intended to mount the real bones, not facsimiles, and hired a spe- cialist to produce an intricate steel armature constructed in such a way that the bones could be removed for study. All mounts of real dinosaur bones are Fig. 2. SUE showing nearly fragile, and this one particularly so because of its complexity. The “Original” Waterless Cleaner. complete reassembly at its new second-floor location when The museum building had been constructed in 1915 with six light wells to ® ABR Waterless Cleaning Poultice is an efficient, ready-to-use, cleaner vibration concerns were first allow natural light and air into the building. Over the years, five of the six designed to remove grime, dirt, soot and years of environmental pollutants identified. Photograph by WJE, light wells were roofed over, and the floors filled in to add space for the 2018. from surfaces where a trouble free, waterless cleaning method is needed. museum’s ever-growing research collections. Powerful performance in an easy, three-step method— The museum intended to put SUE into its own gallery in the middle of the Paint on. Let dry. Peel the dirt away! fossil halls on the second floor, at the location of the one light well that had American Building Restoration Products, Inc. — 800.346.7532 • abrp.com 45 APT BULLETIN: THE JOURNAL OF PRESERVATION TECHNOLOGY / 51:4 2020

not yet been filled in. However, infill of that light well was not expected to occur until the mid-2000s. Therefore, SUE was temporarily installed at the north end of Stanley Field Hall, the large main exhibit hall on the first floor of the museum, and unveiled to the public in 2000. Though the remaining light well was filled in by 2005, it was not until 2018 that funding became available to finally move SUE into the gallery always meant to be its final home (Fig. 1). In February 2018, SUE was dismantled and moved into Hall 25A (SUE Hall). The steel post at the center of the armature was carefully positioned over an existing steel girder. During the remounting, it was noticed that the floor transmitted vibrations much more readily than the floor in Stanley Field Hall. The remounting was on display through a window in the adjacent fossil hall, which attracted crowds of visitors during spring break. On March 30, bone fragments were found on the floor below SUE. The area was carefully examined, and all fragments were collected. The distal section of one of the neck ribs had detached from the armature. It was suspected that vibrations originating from visitors at the viewing window caused the rib to fail. Though the rib was reassembled without any loss of bone, the museum concluded that the floor was too “lively” and needed remediation. Defining the Problem The authors’ firm was engaged by the museum to define and solve the vibration problem. The first step was to Vibration testing quickly confirmed the review the structure and perform in situ Fig. 3. Partial plan and section museum’s concerns. Floor vibrations through the new SUE Hall, with new testing. from human activities and hydraulic columns and footings shown in At SUE’s previous location in Stanley scissor-lift operations in SUE Hall were green. Drawing by WJE. Field Hall, the first-floor structure is three to six times greater than at SUE’s original to the building; it consists of previous location. Furthermore, the heavy concrete framing and terra-cotta natural frequency of the second floor arches. In contrast, the second-floor was only approximately 6 Hertz (Hz), structure in SUE Hall (the infill con- compared to approximately 13 Hz in structed in 2005) consists of a light- Stanley Field Hall. Brisk walking and weight concrete slab on a metal deck sharp movements with a scissor-lift in supported by 24-inch-deep steel girders, the vicinity of SUE produced distinctly which span the entire width of the gal- perceptible floor vibrations and notice- lery, approximately 39 feet, in between able dynamic response (resonant shaking) the original load-bearing masonry walls of individual bones in the mounted (Figs. 2 and 3). skeleton.

46 VIBRATION MITIGATION AND SOUND TESTING IN SUE HALL

Structural review determined that the Table 1. Vibration-Testing Results before and after Retrofit. structure, though sufficient to support the weight of SUE, was susceptible to Stanley Field Hall New SUE Hall New SUE Hall vibrations because of its long flexible before retrofit after retrofit span, relatively lightweight framing, Structure Heavy concrete 39-ft span, Columns added to lack of structural continuity, and framing with terra- lightweight steel reduce span by half lack of energy-absorbing (damping) cotta arches framing components like partition walls. With Natural frequency 13 Hz 6 Hz 12 Hz the floor’s natural frequency of approximately 6 Hz closer to the input Damping (% critical) 8% 4% 6% frequencies commonly associated with Walking, typical 0.02 in/sec 0.14 in/sec 0.01 to 0.03 in/sec human foot traffic, typically 1.5 to maximum response 2.2 Hz, the new location experienced Impacts (heel drops 0.07 to 0.11 in/sec 0.35 to 0.44 in/sec 0.06 to 0.19 in/sec greater dynamic amplification from and scissor-lifts), human activities than the stiffer floor typical maximum at the previous location. Moreover, response the floor vibrations at the new lo- Typical maximum 0.1% of g 1.0% of g 0.1% of g cation transmitted readily into the floor acceleration response due to armature base and support posts of footfalls SUE since the armature is stiff relative to the floor. Resonant shaking of 1 individual bones occurred where the 9 Hz. An office environment represents measurements. Using the “tuned” model, localized vibration characteristics hap- humans in a quiet, contemplative posi- the relative benefit of various vibration- pened to match or be multiples of the tion, which was judged to be consistent mitigation solutions was studied. with the gallery environment. frequency of the floor vibrations. Vibration-Mitigation Options With respect to protecting SUE, it was The Museum’s Goals The vibration-mitigation options that recognized that a safe vibration limit were studied, and the calculated benefits The museum’s goals were clear: to for such a one-of-a-kind object was and disadvantages of each, are detailed protect SUE by reducing the movement unknown. Generalized vibration limits in a previous article by the authors.4 In of the bones during normal gallery use have been used to protect “most mu- summary, the following approaches were and to install the vibration-mitigation seum objects in reasonably sound con- considered: solution before the new gallery opened dition” during numerous construction in six months. With the tight time frame projects.2 More specific to this case, it • stiffening the floor structure by retro- fitting (stiffening) the existing long- and the gallery debut already announced was recognized that SUE had subsisted span girders to the public, the solution had to work. without adverse effects for almost 18 At the time the vibration concern was years at its previous location in Stanley • stiffening the floor structure by adding identified, mounting of the specimen Field Hall. columns below the girders was nearing completion; disassembling Testing in Stanley Field Hall demonstrated • adding damping to the floor using or lifting the skeleton to install a vibra- that SUE had been subjected to frequent tuned mass dampers or direct-acting tion-mitigation scheme was not feasible. floor vibrations (e.g., from footfalls) of dampers Any vibration-mitigation solution needed approximately 0.02 in/sec peak particle • isolating the base of SUE by inserting to be hidden within the base of SUE or velocity (PPV) and infrequent floor isolation pads or springs between the in the ceiling of the first-floor gallery vibrations (e.g., from scissor-lift opera- concrete floor and the armature. below. tion) of up to 0.11 in/sec PPV. The latter Investigation showed that even the value is comparable to the limit of 0.1 thickest and softest arrangement of iso- Toward a Solution in/sec PPV that has been used by several lation pads (such as Sorbothane) would The target with respect to human an- institutions to protect museum objects have a natural frequency no lower than noyance (i.e., visitors being concerned from construction vibrations.3 It was about 9 Hz, well above the 2 to 4 Hz by noticeable floor vibrations) was to agreed that reducing vibrations in SUE needed to effectively isolate SUE. Other reduce floor vibrations to within the Hall to those measured in Stanley Field systems, such as air isolators, spring iso- recommendations of the American Insti- Hall was a sensible target for protection lators, or custom active isolators, could tute of Steel Construction’s Steel Design of SUE. provide frequencies in the desired range; Guide Series 11 for an office environ- For assessment relative to these targets, however, such an extremely soft support ment: that is, no more than a baseline a finite-element structural-analysis model could introduce other risks, including acceleration of 0.5 percent of gravity of the second-floor structure was devel- the propensity of the specimen to slowly (0.005 g) in the frequency range of 4 to oped and calibrated to match the field rock back and forth, since it has a high

47 APT BULLETIN: THE JOURNAL OF PRESERVATION TECHNOLOGY / 51:4 2020

center of gravity. Given the challenges the exhibit show, and especially the and associated costs, base isolation was low-frequency growling and roaring not pursued. noises, would cause detrimental vibra- Vibration-Mitigation Retrofit tion of the fossils, even after the retrofit. Similar questions are being raised by Analytical modeling showed that the museums worldwide regarding the vi- most effective vibration-mitigation op- bratory effects of sound and music on tions—in order of anticipated benefit— museum collections. Research into this would be stiffening the floor structure by topic by the present authors and others adding columns, stiffening the girders, is ongoing. A survey sponsored by sev- and adding tuned mass dampers. eral museum organizations was recently After weighing all the factors, the Field circulated in order to gather data on mu- Museum elected to install three columns seums’ current practices and experiences below the footprint of SUE, with the with respect to musical events.5 columns extending two floors to the Fig. 4. One of three supplemental columns The retrofitted SUE gallery presented ground (see Fig. 3). The multiple walls installed below the existing steel girders and exhibit cases in the Ancient Ameri- of SUE Hall, with hydraulic preloading an ideal opportunity to compare human cas gallery on the first floor allowed the underway to ensure initial tightness of the traffic–induced vibrations, to which columns to be positioned with limited system and preloading of the soil below museum objects are routinely exposed, disruption to gallery use. the new spread footings. Photograph by with vibrations of objects induced by WJE, 2018. sound systems. To this end, non-contact In the late 1800s, the Chicago lakefront laser vibrometer measurements were had been reclaimed using urban fill, so the response, if found to be necessary in taken directly on selected bones in the the soils below the new spread footings the future, could be accomplished mount of the skeleton during human in the basement of the museum could by locally stiffening the slab or adding activities in the gallery (previous mea- prove to be soft and variable. During isolation pads below the posts. construction, the exposed soils were surements were taken only on the floor SUE Hall opened to the public with tested, and the new columns and spread and armature base). The laser vibrometer great acclaim on December 21, 2018. footings were preloaded using hydraulic measurements were repeated during the To verify performance during public rams and digital instrumentation (Fig. exhibit sound show, without human occupancy, a vibration-monitoring sys- 4). This ensured initial tightness of the traffic. Under the museum’s supervision, tem was installed inside the base of SUE. system and pre-compression of the soils the soundtrack volume was increased, During the first month the gallery was as necessary for effective long-term per- especially the growling and roaring seg- open, 83 percent of the measured vibra- formance of the retrofit. ments, while the response of the fossils tion amplitudes were less than the target was monitored. A digital synthesizer and Verification Testing of 0.02 in/sec, and 98 percent of the music clips were also played through the The retrofitted gallery floor was tested amplitudes were less than 0.04 in/sec, sound system in the gallery. in the same manner and at the same lo- confirming the successful performance cations as before the retrofit. As shown of the retrofit. Six setups were completed, with three in Table 1, consistent with the analytical Vibrations Induced by setups on each side of the specimen. In predictions, the natural frequency of the the Sound System each setup, the floor vibrations, as well floor system increased from approxi- as the vibrations of selected presacral SUE Hall includes digital animations mately 6 to 12 Hz. ribs and gastralia (rib-like bones below with soundtracks that illustrate SUE the rib cage), were measured during the Typical peak response to walking around hunting for food and fighting other following activities: SUE ranged from 0.01 to 0.03 in/sec dinosaurs, complete with loud growling PPV—roughly 5 to 10 times less than and roaring noises. Six 9-foot-tall, • ambient conditions, no sound or hu- the approximately 0.14 in/sec measured ultra-high-definition screens are situated man traffic (ambient vibrations were essentially zero) before the retrofit. The typical response behind SUE, forming a panorama, that was near, although slightly above, the project a series of rotating five-minute • floor impact using a calibrated heel- drop plate target value of 0.02 in/sec, which was videos. The show employs six projectors, the maximum response measured due to audio amplifiers, 17 ceiling speakers, • random walking (three to four people) walking at SUE’s previous location. four wall-mounted cabinet speakers, around the specimen and six ceiling-mounted subwoofers. • roar segments excerpted from the Higher peak response was measured A narrated light show also points out soundtrack near the head post (up to 0.04 in/sec) key details on SUE’s bones. • single low-frequency synthesizer notes and near the mid-tail post (up to 0.05 • four genres of music (classical, jazz, in/sec) because these posts are located As part of the vibration assessment, rock, and R&B). between the supported girders. Reducing questions were raised about whether

48 VIBRATION MITIGATION AND SOUND TESTING IN SUE HALL

Maximum vibration of the fossils due place for SUE to “live” and a pleasant Museum Construction Projects,” webinar to random walking was measured to be space for visitors to gather without sponsored by Wiss, Janney, Elstner Associates, Inc., Association of Registrars and Collection approximately 0.2 to 0.5 in/sec, indi- bothersome vibrations. Specialists, and American Institute for cating an amplification of three to eight Conservation of Historic and Artistic Works, times the maximum vibrations of the Acknowledgment Oct. 10, 2018, accessed May 29, 2020, https:// floor from walking (this is a common The authors thank the Field Museum www.wje.com/knowledge/webinars/detail/ vibration-control-during-museum-construction- amplification range due to resonant-like of Natural History staff for their part- projects. W. (Bill) Wei, Siobhan Watts, Tracey behavior of geometric objects supported nership and assistance throughout this Seddon, and David Crombie, “Protecting on a floor). By comparison, the maxi- project. Museum Collections from Vibrations Due mum vibration of the same fossils due to to Construction: Vibration Statistics, Limits, Arne Johnson is a structural engineer Flexibility and Cooperation,” Studies in the roaring segments of the soundtrack and principal with over 30 years of Conservation 63, no. 1 (2018): S293–S300. was lower, from approximately 0.03 to Andrew Smyth, Patrick Brewick, Raphael experience at Wiss, Janney, Elstner 0.2 in/sec. Similar results were obtained Greenbaum, Manolis Chatzis, Anna Serotta, Associates, Inc., (WJE) in Chicago. and Isabel Stünkel, “Vibration Mitigation and for the synthesizer and music clips. His areas of practice include structur- Monitoring: A Case Study of Construction in a In short, vibrations of the fossils induced al testing, assessment, and repair and Museum,” Journal of the American Institute for Conservation 55, no. 1 (2016): 32–55. Kerstin by the sound system, though notewor- rehabilitation. He has served as vibra- Kracht and Thomas Kletschkowski, “From thy, were considerably less than the vi- tion-control expert for numerous muse- Art to Engineering: A Technical Review of the brations of the fossils caused by normal ums across the United States. He can be Problem of Vibrating Canvas, Part 1: Excitation reached at [email protected]. and Efforts of Vibration Reduction,” Facta walking in the gallery after installation Universitatis, Series: Mechanical Engineering 15, of the vibration-mitigation retrofit. As Mohamed ElBatanouny is a structural no. 1 (2017): 163–182. such, vibrations from the exhibit show engineer and senior associate at WJE in 3. Arne Johnson and Bob Hannen, “Vibration should not have any significant det- Limits for Historic Buildings, Art Collections Chicago. He has extensive experience rimental effects on SUE. It should be and Similar Environments,” APT Bulletin: in vibration testing and instrumenta- The Journal of Preservation Technology 46, noted that the sound system in the SUE tion, condition assessment, and repair nos. 2–3 (2015): 66–74. William Wei, Leila gallery is not designed to have a large design. He has served on numerous Sauvage, and Jenny Wölk, “Baseline Limits for bass response like that in a live band or Allowable Vibrations for Objects,” in ICOM-CC instrumentation and monitoring DJ setup; strong bass inputs may cause 17th Triennial Conference Preprints, ed. Janet projects for museums, buildings, and Bridgland (Melbourne: International Council more significant vibration of objects. highway bridges. He can be reached of Museums, 2014), 1–7, https://www.icom- cc-publications-online.org/PublicationDetail. Summary and Conclusion at [email protected]. aspx?cid=e1d9f03d-2fde-458b-a31e- The move and reassembly of SUE onto William Simpson is a vertebrate paleon- 93009c9acbef. the flexible floor of an infilled light well tologist with 40 years of experience at 4. Johnson and ElBatanouny, “Vibrations and Museum Collections, Part 1.” presented the museum with unforeseen the Field Museum of Natural History. 5. Catherine Higgitt, Arne Johnson, Mohamed problems that had to be solved in short As Head of Geological Collections and ElBatanouny, W. (Bill) Wei, Mark Ryan, J. P. order. Vibration testing and analysis as- McCarter Collections Manager of Fossil Brown, Tomasz Galikowski, and Peter Henson, sisted museum staff in understanding the Vertebrates, he is responsible for all “International Research Group Questionnaire: vertebrate fossils at the museum, both Vibratory Impacts of Music and Transport problem and selecting a solution (from a on Museum Collections, Current Practices variety of options) that best fit the muse- those on exhibit and those in the re- and Experiences,” issued April 16, 2020, um’s needs. Now that the museum staff search collection. He can be reached and still active, https://survey.vovici.com/ knows this may be a problem, testing at [email protected]. se/7052282A06D8EA8E. and study will precede exhibit construction for future projects involving fragile, Notes vibration-sensitive objects. 1. Thomas M. Murray, David E. Allen, and Eric E. Ungar, Floor Vibrations Due to Human SUE is one of the crown jewels of the Activity, Steel Design Guide Series 11 (Chicago: Field Museum’s collections, and SUE American Institute of Steel Construction, Inc., 1997), 1–69. Hall is a driver of attendance for the 2. Arne Johnson, Bob Hannen, and Frank The APT Bulletin is published by the institution, which stands at over 1.3 Zuccari, “Vibration Control during Museum Association for Preservation Technology. million visitors annually. Supporting the Construction Projects,” Journal of the American APT’s mission is to advance appropriate weight of the dinosaur and its mount Institute for Conservation 52, no. 1 (2013): 30– traditional and new technologies to care 47. Arne Johnson and Mohamed ElBatanouny, for, protect, and promote the longevity of was straightforward but getting the “Vibrations and Museum Collections, Part 1: gallery floor “tuned” properly to avoid The Effects of Vibrations from Human Traffic the built environment and to cultivate the vibratory response of this fragile object and Construction on Museum Collections,” exchange of knowledge throughout the was challenging and had to succeed. Journal of the International Association of international community. A subscription Museum Facility Administrators 20, no. 2 to the Bulletin and free online access to With the vibration-mitigation retrofit (2019): 4–9. Arne Johnson, Frank Zuccari, past articles are member benefits. For more installed, the gallery is now a safe and Mark Ryan, “Vibration Control during information, please visit www.apti.org.