An Inherent Technology for Steel Braced Structures
Seminar | February 21 | 10-11 a.m. | 542 Davis Hall
Steel braced frames constitute the main earthquake-resistant mechanism in steel structures but exhibit two main drawbacks. Steel braces provide with a limited post-yielding stiffness that may result in a soft-story failure mechanism and exhibit severe mid-length local buckling that leads to unstable energy dissipation and finally fracture. Conventional steel braces, therefore, can satisfy with difficulty many performance objectives beyond their yielding.
The present study proposes a novel design for steel braces. An intentional eccentricity is introduced along the brace length, which changes the brace behavior in a natural way. Strength and stiffness can be assigned independently in the preliminary design. Beyond yielding in tension, the brace provides with large post-yielding stiffness, which is beneficial in residual story drift reduction. The brace bends in compression, and stresses and strains are distributed more uniformly along its length. Local buckling delays and fracture ductility increases. Suitable gusset plate connections are designed to accommodate the new brace deformation mechanism.
To enhance further the seismic behavior of proposed brace, the brace is designed to be a steel tube with strength variation in its cross-section. One-half of the section has a several times larger yield stress than the other half, which yields earlier and dissipates energy. The stronger part of the section remains elastic until large deformations and post-yielding stiffness increases. The effectiveness of eccentricity to magnify the contrast of material benefits provides the braces with the advantage of satisfying multiple strength and deformation performance objectives. The brace displays a controllable multiphase response.