A numerical investigation into the behaviour of flexible uplifting structures with slip-friction connectors under earthquake loading
While there has been significant research into the behavior of uplifting (or rocking) rigid structures under seismic loading, far less attention has been paid to the behavior of flex- ible structures allowed to uplift. Recently, however, Acikgoz and DeJong (1) have shown that these types of structures have unique dynamic characteristics that arise from the interaction of rocking motion with elastic vibration. An understanding of the behavior of uplifting flexible structures is required in order to fully benefit from the damage avoidance potential of allow- ing uplift. This is because building structures are invariably flexible with a finite fundamental frequency, and it is the desire of the structural designer that the structures themselves remain elastic, even while displaying non-linear behavior in a global sense. This paper is concerned with the behavior of flexible uplifting structures adapted with slip-friction devices. These de- vices act as hold-down connectors resisting overturning moment. They have a definite force threshold at which sliding will occur, and exhibit close to perfect elasto-plastic behavior. The ability of shear walls to avoid damage through the use of slip-friction connectors has been previously demonstrated by Loo et al. (2). The modeling of the slip-friction connectors, using a combination of elements commonly available in finite element software packages, and their verification is discussed. Both single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) flexible structures were modeled with a single plastic deformable hinge at their ba- ses, and their behavior under various earthquake simulations investigated. These flexible structures (both SDOF and MDOF) were then affixed at their bases to a rigid platform, with slip-friction connectors implemented at the ends of the platform, and then subjected to the same earthquake simulations. It was found that the maximum drifts of structures with slip- friction connectors compared favorably with their equivalent structures with a single plastic deformable hinge. With a small amount of vertical load, residual drifts were also found to be small. The performance of MDOF structures with slip-friction connectors was somewhat su- perior to that of the SDOF structures, with maximum drifts and residual drifts smaller than that of comparable SDOF structures.
DUCTILE CONCENTRICALLY BRACED FRAMES USING SLOTTED BOLTED JOINTS
Summary The use of passive energy dissipating devices to protect structures from seismic damage is starting to receive more attention. This paper explores the use of such a device, the slotted bolted joint, as a means of providing concentrically braced frames (CBFs) with similar levels of ductility to moment-resisting frames whilst avoiding the associated plastic hinge damage. The benefits of this approach include the ability to consider CBFs as potential candidates for stiff, lightweight seismic-resisting systems, with the promise of lower repair costs after a damaging seismic event. In this preliminary study, sample joints are described and some results based on time-history analyses of a trial 6 storey structure subjected to a range of 'inelastic demand level' earthquake records presented. Structure ductility factors ranging from 6.7 to 18.6 were observed with maximum drift levels well within code limits.
Fortune and Responsibility in Calderón's La gran Cenobia
La gran Cenobia deals with the war between Queen Zenobia of Palmyra and the Emperor Aurelian. Calderón de la Barca draws most of his information from historical sources; the dramatist, however, changes history and adapts it to his own dramatic purpose. The theme of Fortune gives unity to the play. Aureliano is portrayed as a tyrant who, to prove his independence from Fortune, behaves tyrannically, causing his eventual downfall. Cenobia believes that Fortune controls her life, but does not acknowledge that her own actions contribute to her misfortune. The analysis concludes that Fortune, as depicted in this play, is not an omnipotent and blind force, but what one has forged with his or her own actions coupled with the actions of others and circumstance.