Cyclic Behavior of Double Angle Bracing Members with End Gusset Plates.

The performance of braced frames during earthquakes strongly depends on the behavior of bracing members and their connections. In some instances earthquakes have caused total or partial failure of double angle bracing members and their connections. This dissertation presents the results of an experimental investigation of the cyclic behavior of full-size bracing members and a study of philosophies and procedures currently employed for designing bracing members with end gusset plates. Seventeen full-size test specimens made of double angle sections connected to the end gusset plates by fillet welds or high strength bolts were tested under large amplitude cyclic loading. Members designed by current code procedures generally showed fracture during early cycles of loading. New design procedures which are proposed to improve ductility and energy dissipation capacity of the bracing members are shown to have successful results. Procedures are given for the design of end connections and stitches to survive large post-buckling deformations. While the existing building code design philosophies for bracing members connections consider only strength, it is recognized that a rational design philosophy must consider ductility of connections. Such criteria are included in proposed design procedures. Experimental full size bracing member hysteresis loops compare favorably with those calculated by means of a semi-empirical model proposed by Gugerli and Goel.Ph.D.Civil engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159130/1/8304436.pd

The response of tall buildings to far-field earthquakes and the case of a 49-storey steel building

This paper investigates the seismic response of an instrumented 49-storey steel structure in San Francisco to weak, far-field, and strong, near-field ground motions. The instrumentation records obtained during the 1989 Loma Prieta earthquake are used to verify the accuracy of the predictions of the time-history analysis of the model. The ChiChi-002 ground motion record from the 1992 Chi-Chi earthquake in Taiwan (PGA = 0.08 g), representing a 'weak, far-field' earthquake and the record from the 1994 Northridge-Newhall earthquake (PGA = 0.60 g) representing a 'strong, near-field' earthquake were used in the study. The results showed that the force, acceleration, and displacement responses of this long-period structure to the 'weak far-field' ground motion are much larger than its response to the 'strong, near-field' ground motion. Also, the response attenuates at a slower rate for the weak, far-field earthquake, indicating the possibility of greater damage, both to structural and non-structural elements, during the earthquake. Interim seismic design recommendations are formulated to address this issue in the design of tall buildings with long periods

Seismic behavior of concentrically braced frames designed to AISC341 and EC8 provisions

Steel concentrically braced frames (CBFs) are frequently used as efficient lateral load resisting systems to resist earthquake and wind loads. This paper focuses on high seismic applications where the brace members in CBFs dissipate energy through repeated cycles of buckling and yielding. Widely-used seismic provisions have somewhat different approaches for the seismic design of CBFs. The present study evaluates in detail the similarities and differences between the design philosophies and provisions used in the United States and Europe for these systems. The requirements of both provisions applied during a full design procedure are summarized and compared. Furthermore, X-braced, split X-Braced, and V-braced archetypes are designed accordingly and the differences in the design outcomes are investigated regarding section sizes and the weight of steel used in each design. Finally, inelastic structural models of the designed archetypes are developed and subjected to a large set of ground motions to study their seismic behaviors. The results of a total of 880 nonlinear time history analyses are then synthesized to investigate the way in which the requirements of these provisions affect the seismic behavior of the designed CBF. Notable differences are observed between the performances of the CBFs designed using American and European provisions. The similarities and differences as well as drawbacks of the provisions are thoroughly discussed. Recommendations and future research needs are suggested to enhance the seismic performance of steel CBFs designed according to these provisions