دانلود رایگان مقاله انگلیسی رفتار چرخه ای از قابهای مهاربندی شده با مهاربندی مرکب بخش های مجزا - اشپرینگر 2018

Abstract

Concentrically braced frames are earthquake resistant systems commonly used in buildings. Seismic behavior of this type of structures is affected by their configurations, brace properties, and brace to gusset plate connections. In this paper, the results of three experiments conducted to investigate the cyclic behavior of concentrically braced frames with braces built-up of double channels are reported. Significant damage was observed in beam to column connections. Large out of plane deformation of braces caused some cracks in the connector welds; however they did not result in fracture. Although large drift was applied to the frames, no brace fracture was observed. Furthermore, experiments showed that the majority of compressive strength in post-buckling state and a noticeable portion of tensile strength originated from frame action. By choosing connector spacing as the main parameter and using finite element models, a parametric study was performed to investigate the effect of this parameter on this type of frames with two different details of brace to gusset plate connections. It is observed that reducing the connector spacing increases the inelastic strain demand in braces and decreases it in gusset plates. However, gusset plates, which accommodate 2t linear clearance, are less dependent on connector spacing, compared to those accommodating 6t elliptical clearance. It seems that the limitations of slenderness ratio of individual section, stipulated in current seismic provisions, need further study.

7. Summary and Conclusions

In this paper, the cyclic behavior of concentrically braced frames with braces built-up of channel sections was investigated. Based on the results of experimental and numerical studies, the following conclusions are drawn:

(1) In this type of frames, damage may be expected in beam to column connections, gusset plate corners and in connector welding along the braces during cyclic loading. However, in the reported experiments, although significant damage was observed in connection, minor cracks in gusset plate corners and connector welding occurred.

(2) Although quite a number of cycles with high drifts in last cycles (about 3% in each direction) were applied to the frames and the braces were fairly slender, no fracture was observed in braces. One reason can be the low width to thickness ratios of flange and web of the brace sections, which were about 3.7 and 8 respectively.

(3) Frame action plays an important role in compression strength of the whole frame especially in post-buckling state of brace. According to the test results, 88% of the compression strength belonged to the frame action in this state. On the other hand, this action is highly dependent on details of connection of beam to column. This phenomenon can dominate the damage sequence of frame. Although, AISC commentary (AISC 2010a) proposes some details to reduce frame action, for existing structures, further studies seem to be necessary.

(4) For the range of studied models, connector spacing does not affect the hysteretic curves of frames considerably. Frames with different connector spacing but the same brace and gusset-brace details have almost the same hysteretic curves from the stiffness and strength point of view