۱- Introduction

۲- Designing and modeling diagrid archetype models

۳- Equipping the diagrid structural models with BRBs

۴- Nonlinear static analyses

۵- Nonlinear dynamic analyses

۶- Conclusion

References

Abstract

The seismic performance of diagrids equipped with buckling restrained braces (BRBs) is investigated. In that regard, the effects of BRBs on the seismic performance characteristics of diagrids such as response modification factor, R, overstrength factor, Ω۰, ductility ratio, μ, and median collapse capacity, ^ SCT, are evaluated. To this end, 6 three dimensional diagrid structures with various heights and diagonal angles are modeled using OpenSees program and are equipped with BRBs in a novel arrangement. Utilizing nonlinear static analysis, the seismic performance factors of models are evaluated. Subsequently, the median collapse capacity (^ SCT) of the models are determined by performing nonlinear dynamic analyses. The results indicate that using BRBs improve the seismic performance of the considered models due to accumulation of plastic damages in BRBs and a better distribution of plastic hinges over those models. The nonlinear static analyses indicate that for the original diagrid models, the response modification factor, R, ranges from 1.7–۲٫۵, while the ductility ratio, μ, varies between 1.2 and 2.5, depending on the diagonal angles. Also, the results show that the Ω۰ remains fairly constant. However, in BRB equipped diagrids, the range of R increases to 2.4–۳٫۳, while the ductility ratio μ varies in the range 2.1–۳٫۱٫ Similar to regular diagrids, Ω۰ remains constant for BRB equipped models. Furthermore, the output of the dynamic analyses indicates that the ^ SCT, which is a function of diagonal angles and generally increases by growing the diagonal angles, could rise up to 60% for diagrids equipped with BRB.

Introduction

After a long period of ignoring aesthetic aspects of brace elements in building constructions, now, the engineering societies are convinced to benefit from the appearance of these components as a symbol of concinnity in urban construction. One of the manifest examples of this trend is the diagrid system which has emerged as an innovative and adoptable approach to create not only the building structures but also constructions with various functionalities. Over time people learnt how to increase the resistance of the building structures against lateral forces such as wind, soil pressure, water pressure, and earthquakes, by “use of oblique elements” [۱]. Nonetheless, utilizing only pure triangulate modules to build a structure commenced in 20th century by Vladimir Shukhov in designing a radio tower (opened 1922). After that, triangulation concept assisted Walther Bauersfeld to construct the first geodesic dome, for a planetarium (opened 1926). Some years later, in 1953, Goldsmith [2], who majored civil engineering at the Illinois Institute of Technology, probably was the first person that academically investigated the diagrids. He proposed three different diagrid shapes that did not receive much attention, until one of them was utilized by Fazlur Khan [1] in designing the John Hancock Center in Chicago. In 1963, IBM building in Pittsburgh was constructed which can be considered as the most prominent example of shifting to diagrid structures. Fig. 1 shows some important diagrid structures built around the world [1].