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GUEST ARTICLE
Isolating Building Joints
August 2009

How will International Building Code (IBC) regulations impact your next building design?

By Mark A. Capriotti

The International Building Code (IBC) requires architects, engineers and building owners to adapt to new building requirements related to seismic regulations. Building movement must be detailed at all building joints for specific movement in X, Y and Z axis’s plus rotation. Design analysis for greater movements must be considered when we assess the complexity and height of a given structure. All buildings must address seismic movement under Section 1614.1 (Scope) of the IBC states “Every structure and portion thereof, shall as a minimum be designed and constructed to resist the effects of earthquake motions and assigned a Seismic Design category as set forth in Section 1616.3.” Under the IBCode, the criteria to establish building displacement are equal to load definitions under the Structural Design Section 1613.

Section 1613 of the IBC includes earthquake load definitions relative to building structures. The structural engineer will design the structure to comply with this section of the code. Design displacement; the design earthquake lateral displacement, excluding additional displacement due to actual and accidental torsion, required for design of the isolation system (building joints). Total design displacement; the design earthquake lateral displacement, including additional displacement due to actual and accidental torsion, required for design of the isolation system (building joints). Total Maximum Displacement; the maximum considered earthquake lateral displacement, including additional displacement due to actual and accidental torsion, required for verification of the stability of the isolation system (building joints) or elements thereof, design of building separation, and vertical load testing of isolator unit prototype. Mechanical engineers must be aware of building displacement and consider the displacement as designed for the building by the structural engineer when designing the mechanical system. Design displacement information from the structural engineer then needs to get to the mechanical engineer so they may properly design and detail the mechanical piping and support system in relation to the building/seismic joint locations to insures proper specification of components within the system.

Section 1621 of the IBC specifically addresses piping systems in section 1621.3.10; “Piping systems shall be designed to meet the force and displacement requirements of Section 1621.1.5. Where piping systems could displace relative to one another where the piping system crosses the seismic isolation interface (building joint), the piping system shall be designed to accommodate the seismic relative displacements specified in Section 1621.1.5.”

Flexible pipe loops are an effective way to address the displacement requirements in piping systems as defined by Section 1613 of the IBC. Flexible loops that have three flexible sections allow it to compensate movement in six degrees of freedom (three coordinates axes, plus rotation about those axes simultaneously from random seismic shifts) will be the only devices that meet the stringent requirements of this section of the IBC. Other “V” or “U” shaped devices or loops fail to meet the stringent requirements set forth in Section 1613 of the IBC. Other “V” or “U” loop systems state or claim movements in all planes but may require pipe alignment guides on their installations. The recommendation and need to apply pipe alignment guides limits the motion to a longitudinal axis movement. “V” or “U” loop manufacturers design considerations and recommendations cautions against and do not recommend torsional movement and as a result fail to meet the movements as defined in Section 1613 of the IBC for total design displacement or total maximum displacement.

Design professionals must also consider a system to effectively hang and support a piping system and its components to protect essential equipment within a structure. Section 1621.3.4 of the IBC details requirements for component supports; “Mechanical and electrical component supports and the means by which they are attached to the component shall be designed for the forces determined in Section 1621.1.4 and in conformance with the requirements of this code applying to the materials comprising the means of attachment. If standard or proprietary supports are used, they shall be designed by either load rating (i.e. testing) or for the calculated seismic forces. The stiffness of the support shall be designed such that the seismic load path for the component performs its intended function.” This section of the IBC also addresses supports and attachments for other piping in systems under section 1621.3.10.2.1 “Supports and attachments for other piping. In addition to meeting the force, displacement and other requirements of this section, attachments and supports for piping shall be subject to the following other requirements and limitations: Seismic supports are not required for: Section 1621.3.10.2.21. Piping supported by rod hangers provided that hangers in the pipe run are 12 inches (305mm) or less in length from the top of the pipe to the supporting structure and the pipe can accommodate the expected deflections. Rod hangers shall not be constructed in a manner that would subject the rod to bending moments.” Hanging or support systems for flexible” or “U” shaped loops systems typically will require a support (hangar rod) to prevent the device from drooping or torqueing. Some requirements will ask for a specific “minimum” length of the hangar rod to allow the “U” or “V” to move as the loop flexes. By design the movement of “V” or “U” shaped flexible loops will subject a hangar rod 12” or longer to a bending moment at its connection point. This type of support hanging system is not compliant with IBC Sections 1621.3.4 and 1621.3.10.2.1. System design considerations should include cable hanger assembly kits that meet the requirements of Sections 1621.3.4 and 1621.3.10.2.1 of the International Building code for component supports in that they are to be designed for load rating and be third party tested. Design should include third party tested seismic wire rope/cable that conform to the requirements of the American Society of Civil Engineers (ASCE) guidelines for structural application of wire rope in that the cable is prestretched and permanent end fittings maintain the breakstrength of the cable with a safety factor of two.

Coordinating and the sharing of design information as defined in Section 1621.1.5 of the IBC between the structural and mechanical engineers is critical in the specification and selection of devices to properly address building seismic joints. Flexible pipe loops are an effective solution for isolating building joints. Design considerations must always consider a complete piping and mechanical system and that will address and comply with all applicable sections of the IBC. Failure to comply with the IBC will compromise the structure, essential building equipment, piping and mechanical systems and its components.

About the Author

Mark Capriotti, Vice President of Commerical sales at Flex-Hose Company, Inc., has been in HVAC, Contracting and Industrial sales for over twenty five years. After attending Syracuse University, Mr. Capriotti’s career has covered a wide range of positions including an industrial sales engineer specializing in corrosion resistant products, a field superintendent for a mechanical contracting firm, sales management for an HVAC manufactures’ representative, and his current position as Vice President of Commercial Sales. A member of ASHRAE (Past President; Central New York Chapter), ASPE, ASME, the US Green Building Council, TACNY, and USA Hockey, Mr. Capriotti is involved with and sits on the board of various organizations in Central New York. He can be reached at 315.437.1611 or at flexhose@flexhose.com.


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