Chevron brace

Kelvin model is used as the model of VE damper. The model parameters are sixteen times as great as the ones shown in Table 3. It is assumed that ten dampers are located on the frame. The chevron braces used are as the ones described in Example 1. 

Structural control should be based on economic principles. With this aim inexpensive control devices should be developed and number of such devices, required for obtaining optimal control, should be minimized. In most structural applications passive or active devices in are connected to diagonal or Chevron braces. When a damper is connected to Chevrone braces the interstoiy drift and drift velocity are transferred to the damper. If a damper is connected to diagonal braces, the displacement and velocity, transferred to the damper are lower, compared to the interstory drift and drift velocity, respectively. 

For evaluating the efiSciency of control systems with limited set of dampers, connected to Chevron braces, the following criteria were proposed (Ribakov, in press) ... 

Figure 1. Dampers configurations (a) Chevron brace, (b) toggle brace, (c) lever arm, (d) scissor jack...

At the next stage the earlier defined efficiency criteria (Equations 2, 3, 4, 5, 6, and 7) were calculated. Figure 4 demonstrates efficiency of control systems with various numbers of active floors in reduction of structural responses to the white noise ground motion compared to that obtained in the case when all floors are active. As it follows from the figure and from Table 1, when control devices are connected to Chevron braces, if half of the floors in the structure are active (23 devices are used), it is possible to achieve an affect of70- 85%, compared with that obtained by a control system with optimally distributed dampers located at all floors (37 devices). When the control devices are connected to lever arms, the same effect may be achieved using just 11 devices. 

Case 2 Structure with a control system including optimally distributed dampers, located at all floors and connected to Chevron braces ... 

It was assumed that in the frame of this study the number of active floors, m is equal to 8. This number ofactive floors allows an economical solution yielding according to the selected efficiency criteria about 70 - 85% of the effect that may be achieved by an optimal set of active controlled devices located at all floors (see Figure 4). Following Table 1, the optimal solution requires 21 devices connected to Chevron braces or 9 devices connected to lever arms. 

Peak floor displacements in the stmcture under the artificial and natural earthquake records for the four study cases specified above are shown in Figure 5. As it follows from this figure, reduction in peak values of floor displacements under the natural earthquakes were very significant. Using amplifiers allowed reduction of control devices number to 9 and resulted in an effect that was equivalent to that obtained by 21 devices connected to Chevron braces. 

It was demonstrated that using an optimal limited set of active controlled devices yields almost the same reduction in structural displacements and accelerations like an optimal set of devices located at all floors. It was further shown that connecting the control devices to lever arms allows getting the same improvement in structural behavior like by connecting them to Chevron braces, but the first configuration requires less devices and enables... 

FIP Industriale, Prof Rodolfo Antonucci and Francesco Balducci) detail of the damper (a) and installation with external chevron braces (b)... 

Four columns or legs supporting the Citicorp Center s frame are positioned at the middle of each side of the building. LeMessurier designed a unique system of V-shaped wind braces on each facade, arranged in a chevron pattern, to transfer loads to the column. Construction of the Citicorp Center was completed in 1977. 

Figure 7, for instance, shows an application of EVDs, in which the devices are mounted as part of chevron steel braces externally connected to the main structural frame. In this way, energy is dissipated through the shear deformations within each EVD (Fig. 7a), which in turn are caused by the relative movements of the stories. 

Low-yield steel plates with hourglass and triangular shapes have been proposed, and they are best known with the acronyms ADAS (added viscous and stiffness) and TADAS (triangular ADAS), respectively. Such devices are usually installed at the top of stiff chevron steel braces, so that the relative lateral movement of two consecutive stories induces bending about the weak... 

Braced frames can be constructed of single diagonal, X and k braces, chevron and split braces, and lattice or knee braces, and they can be used in interior cores - so connections could be easily made with wall panels, as well as in the exterior. Composite braced frames are also becoming popular where concrete bracings are supporting steel frames. 

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