During full-scale dynamic testing on the NEES@UCSD shake table, safety restraining towers are necessary to avoid catastrophic failure and prevent damage to the shake table equipment if collapse of the test structure is imminent. Two main undesirable situations must be controlled:
To ensure the safety of the facility, four restraining towers were designed in-house at UCSD. These towers are 30 ft high trusses with floor platforms at 10 ft and 20 ft above the ground. The 4 column members are W16 rolled sections and the braces are made from HSS tubes.
The towers have an approximate footprint of 8 ft by 8 ft and have 8 anchor points. There is an anchor point at each corner and an additional anchor point midway between corners. These anchor points are spaced such that the tower can be located anywhere on the 2 ft by 2 ft anchor grid on the LHPOST platen and the surrounding reaction mass. The four corner anchor points have a 3 ft tube section which allows for adequate tensioning of the anchor bar for maximum shear resistance.
The towers were designed to take point loads on the outside flange of the vertical columns in the plane of the column web. The towers can resist a 50 kip point load anywhere on the column flanges or a combination of point loads totaling 50 kips over the entire frame. The load should be delivered directly to the column flange or by a bolt on system using a prescribed bolt pattern as specified by ESEC. The towers were not designed to support loads in their transverse directions. The towers were designed to have an estimated deflection of H/1000 minimum when subjected to the IBC design spectra with Sds of 2 g in either transverse or longitudinal direction. The tower frequency is about 15 Hz.
Design details of the towers are available here.