Sutro Tower

In late 2017, Iconic Sutro Tower required structural evaluation as one of its three antennas needed replacement with new equipment.  This evaluation included the effects of combined gravity and lateral forces.

• Wind loading: recorded and scaled wind tunnel test data was used.

• Seismic (NLRHA) loading: three batches of 11-ground motions, carefully selected and scaled to represent various dynamic responses were used.  These 33 earthquake accelerations were applied at the base of the structure allowing realistic capture of the structure behavior.

Wind loading was found to be the controlling load case, and the two options proposed to the client and city were:

1. Keeping cladding on tower legs, and retrofit and strengthening of a large number of vulnerable elements and connections
2. Removing structures cladding to reduce wind caught, and retrofit of a much smaller number of elements and connections shown vulnerable from reduced wind loading and/or seismic loading