Owner: Blommer Chocolate Company
Client: Alfred Benesch & Company
Completion Date: 2014
Services: Existing Structures, Vibration Testing and Analysis

Summary:

J.R. Harris & Company (JRH) conducted a structural vibration study at the Blommer Chocolate Factory in Chicago, Illinois, to address excessive vibrations affecting three Buhler Classifiers located in the roaster room. These classifiers, used for separating cocoa bean shells, were mounted on a steel-framed floor, which exhibited noticeable vibration responses during operation. The structural flexibility of the steel-framed addition, combined with the dynamic forces generated by the classifiers, contributed to frequent equipment fatigue and cracking—issues not observed in similar machines installed on a slab on grade slab elsewhere in the facility.

To mitigate these vibrations, JRH performed detailed vibration measurements and finite element analyses to develop an effective modification strategy. The study confirmed that the floor's natural frequencies were close to the operational frequencies of the classifiers, amplifying the vibration effects. As a solution, two supplemental steel frames were designed to extend from the floor supporting the classifiers down to the precast concrete structure below. These modifications were calibrated through analytical modeling to improve damping characteristics and reduce vibration amplitudes.