A famous structure in any industrial project is the pipe rack that carries the piping and the cable tray. At the beginning of the design process, the actual piping load and that of the cable tray will not be precisely defined. The structural engineer will have the precise actual load data at the end of the project and the first activity on-site is the civil and structure work. Instead, we will use the following estimate loads for the piping and cable tray to begin the design. These nearly match the actual loads and, in the final phase, will be checked against the actual load.
• Piping loads
1. Dead loads for the piping carried on pipe racks shall be estimated using the following measurements, unless the actual load information is available and requires otherwise.
(a) Operating dead load (Do ): a uniformly distributed load of 40 psf (1.9 kPa) for piping, product, and insulation. This value is equivalent to schedule 40 pipes, 8 in. (203 mm) in diameter, full of water, at 15-in. (381-mm) spacing.
(b) Empty dead load (De): for checking uplift and components controlled by minimum loading, 60% of the estimated piping operating loads shall be used if combined with a wind or earthquake load, unless the actual conditions require a different percentage.
(c) Test dead load (Dt): the empty weight of the pipe plus the weight of a test medium contained in a set of simultaneously tested piping systems. Unless otherwise specified in the contract documents or by the owner, a minimum specific gravity of 1.0 shall be used for the test medium.
2. For any pipe larger than 12 in. (304 mm) in nominal diameter, a concentrated load, including the weight of piping, product, valves, fittings, and insulation, shall be used instead of the 40-psf (1.9-kPa) load used for 8-in. pipes. This load shall be uniformly distributed over the pipe’s associated area.
3. Pipe racks and their foundations shall be designed to support loads associated with full utilization of the available rack space and any specified future expansions. Among all the disciplines represented on an industrial project, structural engineers have the hardest luck. Unlike other disciplines, they must perform activities before the actual load data can be obtained. Therefore, it is necessary to use load values obtained from past experiences and projects. They will have the actual data about the load after procurement and before running the final simulation of the piping stress analysis. The guidelines below are derived from the experience of engineering offices and shall be used in conjunction with the structural engineer’s judgment, good industrial practice, and owner specifications.
• Pipe rack cable tray loads
Dead loads for cable trays on pipe racks shall be estimated as follows (unless actual load information is available and requires otherwise):
1. Operating dead load (Do ): a uniformly distributed dead load of 20 psf (1.0 kPa) for a single level of cable trays and 40 psf (1.9 kPa) for a double level of cable trays. These values estimate the full (maximum) level of cables in the trays.
2. Empty dead load (De ): to check uplift and components controlled by minimum loading, a reduced level of cable tray load (i. e., the actual configuration) shall be considered the empty dead load. The engineer’s judgment shall be exercised in defining the dead load for uplift conditions.