The Effect of the Hanger Type and Cable Slack on the Seismic Performance of Cable Bracing for Sprinkler Piping

Cable brace assemblies used for seismic protection of sprinkler systems consist of a hanger and two high-strength “aircraft” cables. These cables follow a defined manufacturing process, and their minimum breaking strength is defined by ASTM A1023. In 36 shake table tests with 12 different test setups, however, it is demonstrated that the seismic performance of cable brace assemblies does not only depend on the cable properties, but also on the hanger and the quality of the installation. Unrestricted pipe movement due to cable slack can lead to impact loads on the cables which may exceed their design strength. This does not get addressed by ASCE 19 and ASCE 7. The impact loads are particularly critical if the pipe can swing upwards and gain potential energy which is then released in a high shock load on the stiff and brittle cables when the pipe drops. Both numerical simulations and shake table tests showed that impact loads increase with larger cable slack and larger allowable pipe upswing.