Project Overview

A heat exchanger was mounted on the roof of a Client’s ammonia condenser building in 1999. The original condenser fans caused vibration issues throughout the building’s structure; a subsequent upgrade to larger fan blades increased the amplitude of the vibrations.

Rally performed a structural analysis of the building, and recommended remedial actions to address the vibration issues. The dynamic response of the building was tuned to offset from the fans’ operating frequency by increasing the building stiffness in the lateral direction. This was achieved by adding and/or replacing vertical bracing in the east and west walls, in addition to stiffening the condenser supports.

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Scope Definition

Rally investigated the vibration characteristics of the building, when subjected to condenser dynamic loads, by carrying out a time history analysis in FEM software. Mechanical vendor data was analyzed and compared to the actual field installation to quantify the dynamic loads being imparted on the building. Potential building modifications were explored using the FEM model.

Detailed Deliverables

A structural analysis was completed of the entire building to allow tuning of the building’s dynamic response and determine the required stiffening.

A construction work package was engineered and issued with the recommended modifications to the building’s structural bracing. Rally’s scope included the design of member connections.

Field engineering support was provided during construction, including a walk-down at completion and drawing “as-built” services. The additional bracing reduced the vibration amplitude by more than 80%.

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