Algor FEA Helps to Save National Art Treasure
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In April of 1976, Alexander Calder's design of Mountains and Clouds was accepted by a panel of curators to be installed in the towering, asymmetrical 90-foot-high atrium of the Hart Senate Office Building, then under construction just across from the United States Capitol in Washington, D.C. Despite early setbacks, Calder's vision of the massive sculpture was realized in 1986.
As the name implies, the sculpture consists of both mountains and clouds. The mountains are made up of four flat, angular steel plates with five mountain peaks among them and two arch-like legs, one branching from the other. The clouds, the mobile part of the sculpture, consist of four uniquely shaped hollow objects made of an aluminum skin painted black, formed around a center beam span, which is the primary load-carrying component that allows predecessor or successor clouds to be suspended . Designed to be turned by a computer-controlled motor that generates random patterns as perceived by typical viewers, the clouds ceased to move in 1992 when a mechanical problem was discovered that forced the immediate shutdown of the motion. After an exhaustive inspection of the bearing system, the Architect of the Capitol (AOC) awarded a contract in 2001 to Architrave, P.C. Architects to determine the cause of the failure and propose a solution. Architrave hired Integra Engineering, a company of T&T Engineering Services, Inc., of Houston, Texas and ALGOR, Inc. as subcontractors to diagnose the malfunction and provide recommendations for renovation and restoration of the clouds' mechanical system.
The main cloud assembly consisted of a motor supported at the roof of the atrium, a shaft that extended through the roof to the inside of the atrium and a swivel assembly that connected the main cloud to the shaft, allowing for partial rotation of the cloud system. The main swivel assembly was comprised of two ringed hangers joined by a connecting shoulder-bolt pin with four springs attached to the bottom hanger and four stops mounted on the top hanger to constrain and redirect the rotation. Visual inspection by engineers verified that one of the springs from the main swivel assembly had broken off during operation.
T&T Senior Engineer Keith Orgeron, P.E., and ALGOR Manager of Application Engineering Jeff Wanko used ALGOR's Mechanical Event Simulation (MES) software to model the swivel assembly and simulate the malfunction event as one aspect of a root-cause failure analysis. MES combines large-scale motion and stress analysis and includes linear and nonlinear material models. The combination of motion and stress analysis considering full inertial effects allows engineers to see motion and its results, such as impact, buckling and permanent deformation. Since only one pair of springs was in use during each reversing action and one spring was found to be missing, the swivel assembly was modeled with only the one remaining spring.
The simulation results indicated that the missing spring created a wider gap between the stop and the hanger. This, in turn, produced a greater spring reaction force on the other side as it collided with the rotating hanger. The remaining, active spring quickly compressed, yielding a "solid" hard-stop, transferring a great deal of eccentric force into the hanger-hanger connection, producing dynamic excitation, unforeseen 3-D motions, misalignment and load amplification. The swivel's shoulder-bolt pin was noted to experience higher loading and stress than previous manual calculations had shown, and thus correlated better with an inspection report describing the failed components.
After both engineers evaluated the results of the MES analysis, Orgeron concluded that correcting the root causes of failure would require replacement of the problematic design features, especially the hanger connection spring stops, the hanger connection shoulder-bolt pins (the heart of the swivel assembly) and the drive motor controls-with a new, main hanger connection design, modern motor controls and a back-up mechanical torque-limit. A novel, fixed hanger-hanger connection design with the reversing motions controlled by the motor was proposed as the preferred solution. This new connection design was accepted by the customer and then detailed and verified by Wanko using ALGOR FEA software.
Based on the on-site inspection and the results of the analyses, the original work scope was expanded. The additional tasks included redesigning and replacing the rooftop components, development of motion control curves, installation of an appropriate torque-limiting coupling, field-verifying the lower clouds' swivel assembly designs to determine whether they can be left in place or whether some or all need to be replaced and possibly performing additional MES analyses on a detailed model of the clouds. Field inspection results would help determine the need, if any, for simulating the accidental "drop" that occurred during the time when the failed swivel assembly was being removed.
In their final report to the AOC, T&T Engineering and ALGOR submitted specifications for repairing the structure to ensure safe and continuous future operation. The AOC has secured a contractor to perform the necessary repairs. When the repair and reconstruction are complete, Alexander Calder's Mountains and Clouds will once again be reanimated-bringing closure to the mechanical problems that stalled it over a decade ago.
"I rely upon ALGOR's MES software to quickly model nonlinear and dynamic events for our mechanical engineering solutions," said Orgeron. "ALGOR FEMPRO allows us to thoroughly evaluate the FEA results, interface with other software, manage the FEA projects and provide first-class, professional documentation of our work."
Julie Halapchuk
Marketing Communications
ALGOR, INC.
150 Beta Drive
Pittsburgh,
PA 15238-2932
USA
Phone: 1-412-967-2700
Fax: 1-412-967-2781
E-mail: info@ALGOR.com
URL: www.ALGOR.com
