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NEES earthquake engineers monitoring structural soundness of the historic Watts Towers

 


Taciroglu climbing central tower

Project PI Ertugrul Taciroglu climbed the central tower to install acceleration and tilt sensors.


Test pipeline

Displacement sensors monitor crack movements.

A mini weather station collects wind speed data.

 

RAPID: Wind, Thermal, and Earthquake Monitoring of the Watts Towers, award 1331299
Principal investigator: Ertugrul Taciroglu, UCLA

In Los Angeles, civil engineers from the University of California, Los Angeles (UCLA) are helping to preserve the iconic Watts Towers monument. Experts in structural monitoring, the engineers are working with conservators from the Los Angeles County Museum of Art (LACMA), who want to repair and prevent persistent cracks in the structures.

The Watts Towers, comprised of 17 artistic steel towers built by folk artist Simon Rodia, have long been a symbol of strength and beauty in South Los Angeles.

Rodia, an Italian immigrant, spent 32 years building the towers in his backyard. Some are nearly 100 feet tall. After spending his evenings and weekends working on them, he finally finished construction in 1954.

Engineering expertise

The research is funded by the Hazard Mitigation and Structural Engineering Program of the National Science Foundation, and utilizes monitoring equipment and technical support from the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), an NSF-sponsored network of experimental facilities and cyber infrastructure aimed at reducing losses from earthquakes. Data gleaned from the monitors will all be available on the NEEShub, the network’s data sharing infrastructure.

Principal investigator on the monitoring project is associate professor of engineering Ertugrul Taciroglu. Also working on the job is research engineer Bob Nigbor. Both are with the UCLA’s Department of Civil and Environmental Engineering and NEES research engineers.

Last year, seeking ways to quantify and analyze the environment’s impact on the Watts Towers, LACMA conservators sought advice from UCLA’s civil engineers. Said Taciroglu, “Our measurements, and our analysis of those data, will provide answers to a multitude of questions about the nature of the problem.”

Cracks in the towers

The steel towers are layered with cement, which is inlaid with glass, ceramic pieces and other colorful objects Rodia found. Over the years, the towers have developed persistent cracks and many of the original inlaid items are missing. The most serious cracks are at the base of the towers, although degradation is evident throughout the structures.

This spring the UCLA engineering team installed a series of sensors to on the central tower to measure acceleration, tilt, and crack displacements. Accelerometers will be used to estimate the magnitudes of external forces due to wind and earthquakes. They also installed a weather station to discover how environmental factors like temperature and wind speed correlate with the crack movements. High-resolution digital data are recorded continuously on site, and data can be viewed and queried remotely through the Internet. The team will monitor the structures for a year.

Environmental problems

The local environment is surprisingly fierce. Taciroglu explained that every day, as the sun rises and begins to heat the structure, the materials expand, and the towers lean away from the sun. In the spring the structures are buffeted by the Santa Ana winds, uni-directional airstreams that can reach 60 MPH. In addition to these forces, the Watts Towers are also subjected to relatively frequent small earthquakes centered typically 15-20 miles away.

“As civil engineers, we would like to quantify how much dynamic characteristics of structures vary with respect to the severity of the excitations and environmental factors, such as temperature,” Taciroglu said.

The flexibility of the steel towers has helped them remain standing during hailstorms and earthquakes, but ironically the elasticity of the towers is what repairing them difficult.

Taciroglu said that that the measurements and analysis his team provides will help LACMA conservators develop a suitable mortar mixture for repairing the cracks. “They want a recipe for a mortar that won’t damage original elements of the towers, will adequately seal the cracks, and yet be flexible enough to accommodate the towers’ movements,” Taciroglu explained.

Seeking lasting solutions for outdoor art

Ultimately the LACMA team will use UCLA’s engineering data to prepare a formal conservation strategy for the Watts Towers—a handbook that will include repair and preservation solutions that will endure for at least a decade.

“Our measurements and conclusions will be part of that document,” said Taciroglu. “And we hope that it will have an impact on conservation efforts on other outdoor monuments and heritage sites worldwide, such as the Magic Gardens in Philadelphia and the Nek Chand Rock Garden in India.”

Images courtesy of Ertugrul Taciroglu, UCLA

by Marti LaChance