The earliest known shaking table, driven by hand-power, was constructed in Japan at the end of the 19th century. At the beginning of the 20th century developments had moved to the Stanford University in the U.S. with the introduction of an electric motor to produce a more refined oscillatory motion in one direction, the response of the testpiece being recorded mechanically by pens on a rotating drum. Major earthquakes in the 1920s prompted renewed interest at Stanford resulting in a uni-directional table moving on rails, activated either by a pendulum striking at one end-the other being resisted by springs-or by a wheel with an eccentric-mass attached to the table. A valuable feature here was that the size of the eccentric mass could be varied as the harmonic motion continued, thereby providing a method of control. In the 1950s, a similar pendulum input was used on a table constructed at the University of California, but instead of rails, it was supported by a group of vertical bars flexible in one direction only, and the 1939-1945 war had resulted in the availability of electrical devices for measuring response. Also, in Italy at this time the use of pendulums was augmented by contra-rotating mass input devices giving better frequency control; arrays of several electrodynamic exciters were also used. In Japan, motion was induced by the release of compressed springs.The idea of producing input by an oil-filled piston was introduced at MIT after the 1933 Long Beach earthquake to a table suspended from above by wires. Two other innovations here were of the greatest significance. First was an analogue device for using an actual earthquake record as input, and the second was control of the motion by an error-driven electrically controlled feedback loop. The development of these ideas into the shaking tables, which we use today, had to wait upon the general development of control engineering during the 1939-1945 war, followed by progressively greater speeds in digital computation. This history ends (c.1985) after the continuation of these advances made possible full 6-DOF control using many oil-filled actuators, but before they became able to give us real-time control with the attendant abilities of multi-support input and the experimental study of inelastic behaviour. Figure 15. A diagram indicating the essential features of the 20×20 ft UCB shaking table.the central rib, and were positioned such that any yawing motion of the table could be resisted by the control system. The four vertical actuators, each of 25 kips, were attached to the table at the locations shown in Figure 15 by means of prestressing rods in 2 in diameter pipes running vertically through the table on a 3 ft square grid. The pipes also served as attachment points for the structure being tested. The actuators had a swivel joint at each end, of such a length that they made a significant contribution to de-coupling the vertical and the horizontal motions of the table, with further de-coupling provided by the electronic control system.Although these ve...

SUMMARYAmbient accelerations due to dynamic excitation by wind and traffic were measured on the deck, towers, cables and hangers of the Fatih suspension bridge. From these measurements it was possible to obtain natural frequencies, mode shapes and damping ratios for vertical, lateral, torsional and associated modes in the deck and tower up to a maximum of 2 Hz.

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Summary.Traffic and wind excitation has been used to obtain the dynamic characteristics of the fust Bosporus suspension bddge. Structural symmetry and the absence of suspended side-spans allowed attettion to be focused on the main span and the Asian tower. For the main spa4 18 vertical and 20 lateral modes were obtained, including to$ional modes. For the tower, 12 vertical plane and lateral plane modes were abstracted, again ircluding torsion. All these modes lie in the range G1.1 Hz.A detailed comparison is given between tbese modes and corresponding calculated on€s, obtained by use of a three-dimensional finite element model which includes a geometdc stiffness matrix. Of particular interest is the validity of the theoretical model used for tbe box dec\ because of its subsequent use in respotse studies under aysnchronous seismic input.Cornparison with a more limited study made in 1973 shows that the bridge continues to behave as it was designed to behave, partiolarly with regard to the deck-towe! interface. From ltatuml frequency measurements of two hangers, the load which they carry was assessed.Introduction.

SUMMARYTheoretical dynamic characteristics of the Fatih Bridge in terms of natural frequencies and mode shapes of free vibration were obtained using a range of finite element models. Based on this free-vibration data, separate analyses of the asynchronous response of the bridge to earthquake excitation in three orthogonal axes with different speeds of wave propagation, and of stochastic response to vertical excitation were used to estimate levels of dynamic response due to seismic loading.Fatih is the third of three modern European long-span box-girder suspension bridges that have been investigated and the relationship of the different design features and the dynamic responses of this type of bridge is reviewed.The main conclusion is that where seismic response is an important consideration, the effects of asynchronous excitation can be significant and must be considered.