دانلود رایگان مقاله انگلیسی کمانش پویای مهاربندی ها در قاب های مهاربندی شده متمرکز - وایلی 2017

Abstract

Axially loaded members might experience compressive forces above their static buckling capacity because of dynamic buckling under rapid shortening. Although the subject is studied in the context of engineering mechanics, it has not been thoroughly investigated in the field of earthquake engineering. Such dynamic overshoots in the compressive capacity can also be observed for braces of concentrically braced frames (CBFs) during earthquakes. Consequently, a comprehensive investigation is conducted in this study regarding the effects of dynamic buckling of braces on the seismic behavior of steel CBFs. After providing a theoretical background, recent dynamic experiments on braces and CBFs are simulated and discussed to investigate the occurrence of dynamic overshoot during these tests. Eight archetype CBFs are then designed, modeled, and subjected to a large set of ground motions to provide a quantified insight on the frequency and anticipated level of dynamic overshoot in the compressive capacity of braces during earthquakes. Results of a total of 1600 nonlinear time history analyses revealed that dynamic overshoots occur frequently in braces and affect the behavior of CBFs notably. Considerable increases are recorded in forces transmitted to other members of CBFs as a consequence of such dynamic overshoots. Importance of incorporating these dynamic overshoots in the capacity design procedure of columns, beams, and gusset plates is highlighted. Furthermore, results of a parametric study are presented and summarized in the form of a simple formula that can be used as a guide for estimating the level of dynamic overshoot.

6 | CONCLUSIONS

The dynamic buckling behavior of brace members during strong earthquakes and its effect on the seismic behavior of CBF systems and their members have been thoroughly studied in this paper. The following can be concluded from the study:

• Investigation of the recent dynamic experiments demonstrated that dynamic overshoot in brace forces has been reported, though not discussed thoroughly, in some studies. Furthermore, simulation results revealed that the dynamic overshoot would have been readily observed in other tests provided that the experiment was conducted with slight modifications such as increasing the applied loading rate or altering the utilized displacement history.

• Detailed FE analyses indicated that dynamic buckling of a steel brace is a rather complex phenomenon, which is highly dependent upon many factors such as the brace slenderness, imposed displacement history, magnitude and variation of the loading rate, imperfection of the brace, and the change in its residual out‐of‐plane deformation.

• Results of a comprehensive study on archetype CBFs revealed that dynamic overshoots can frequently be observed in brace forces during strong earthquakes. Overshoots of the order of 10% to very high values in excess of 200% were recorded in the FE analyses. The brace slenderness as well as the experienced loading rate are the effective factors in the observed level of overshoot, with the former being the most dominant parameter.

• As a consequence of dynamic buckling of braces, notable changes were recorded in forces transmitted to other members of the studied CBF systems. Increases as high as 20% to 150% were recorded in column axial forces for different cases. In general, the percentage of increase is expected to be larger in low‐rise CBFs and upper columns of mid‐ and high‐rise CBFs, and more particularly, when slender braces are used in the system. Similarly, considerable increases as high as 25% to 50% were recorded in beam axial forces of the studied archetypes.

• Dynamic buckling of braces was found to be less influential on altering the deformation demands. Changes in brace ductility demands and the maximum interstory drift ratios were mostly bounded by ±25% and ±10%, respectively, with a higher tendency toward reduction due to overshoots.