Rigid Counterpart Research Articles

Seismic Ductility Demands Predicted by Alternate Models of Building Frames

Peak values of story ductility demands produced by earthquakes on several models of multistory rigid frames are evaluated by means of step-by-step nonlinear dynamic analysis of structural response to simulated ground motion time histories. The models studied include the basic rigid frame model with nonlinear behavior concentrated at plastic hinges eventually forming at the ends of beams and columns, as well as two approximations, the conventional shear-beam system and a shear-frame system constituted by ordinary reinforced concrete columns and infinitely stiff and strong beams. Two families of models were studied, including seven-story and fourteen-story systems, respectively. The contributions of soil-structure interaction, stiffness-degradation and P-delta effects were analyzed. The equivalent shear-beam model produced results clearly different from those of its rigid frame counterpart: while peak values of story ductility demands vary gradually along the height of rigid frames, they concentrate at the bottom story of shear-beam systems, where they are significantly greater than for the corresponding rigid frame. The responses of both, shear-beam and shear-frame systems, displayed a more pronounced sensitivity to variations in the lateral strengths of structural members than that observed in rigid frames.

Vibration of compressively loaded shear deformable flat panels exhibiting initial geometric imperfections

Numerical study results are presented which indicate that, in the prebuckling range, the natural frequency predicted by the shear-deformable plate theory is smaller than that associated with its transverse-shear rigid counterpart. The opposite behavior occurs in the postbuckling/postcritical range. With increasing transverse shear flexibility, greater differences between frequencies predicted by shear deformation and infinitely rigid transverse shear theories emerge. The character of in-plane boundary conditions is a determinant of both increasing/decreasing buckling loads and increasing/decreasing vibratory frequencies.

Office Flexible Cystoscopy

Since the development of the first purpose-built flexible cystoscope in 1984, flexible cystoscopy has become an accepted diagnostic and therapeutic modality. Indeed, it is estimated that more than 10 per cent of practicing urologists are already familiar with this technology. The flexible cystoscope has markedly extended the urologist’s ability to examine the bladder, and it has become a valuable adjunct to the rigid cystoscope. Although the operation of this instrument is vastly different from that of its rigid counterpart, with practice, the technique can be learned. After experience is obtained with diagnostic flexible cystoscopy, the urologist will likely prefer this new instrument for bladder inspection, as it provides for a more thorough yet less morbid and less expensive examination. In the future, the development of improved and smaller instrumentation will further extend the therapeutic indications for flexible cystoscopy. Indeed, advances in laser technology are already providing the urologist with 300- to 600-µm (0.9 to 1.8F) flexible probes capable of incision (KTP laser), fulguration (Nd:YAG laser), and stone disintegration (tunable dye laser). Lastly, the skills obtained in using the flexible cystoscope are all readily applicable to the development of dexterity with the already available flexible nephroscope and the more recently developed flexible ureteroscope.

The Generalized Transmission Error of Spiral Bevel Gears

The traditional definition of the transmission error of parallel-axis gear pairs is reviewed and shown to be unsuitable for characterizing the deviation from conjugate action of bevel gear pairs for vibration excitation characterization purposes. This situation is rectified by generalizing the concept of the transmission error of parallel-axis gears to a three-component transmission error for spiral bevel gears of nominal spherical involute design. A general relationship is derived which expresses the contributions to the three-component transmission error from each gear of a meshing spiral bevel pair as a linear transformation of the six coordinates that describe the deviation of the shaft centerline position of each gear of the pair from the position of its rigid perfect involute counterpart.

Office Flexible Cystoscopy

Since the development of the first purpose-built flexible cystoscope in 1984, flexible cystoscopy has become an accepted diagnostic and therapeutic modality. Indeed, it is estimated that more than 10 per cent of practicing urologists are already familiar with this technology. The flexible cystoscope has markedly extended the urologist's ability to examine the bladder, and it has become a valuable adjunct to the rigid cystoscope. Although the operation of this instrument is vastly different from that of its rigid counterpart, with practice, the technique can be learned. After experience is obtained with diagnostic flexible cystoscopy, the urologist will likely prefer this new instrument for bladder inspection, as it provides for a more thorough yet less morbid and less expensive examination. In the future, the development of improved and smaller instrumentation will further extend the therapeutic indications for flexible cystoscopy. Indeed, advances in laser technology are already providing the urologist with 300- to 600-micron (0.9 to 1.8F) flexible probes capable of incision (KTP laser), fulguration (Nd:YAG laser), and stone disintegration (tunable dye laser). Lastly, the skills obtained in using the flexible cystoscope are all readily applicable to the development of dexterity with the already available flexible nephroscope and the more recently developed flexible ureteroscope.

Flexible Nephroscope in Calculous Surgery

In difficult operations for multiple, staghorn or recurrent calculi after previous surgical intervention and in cases of chronic nephrostomy intrarenal inspection is facilitated by the use of a new flexible nephroscope. This flexible nephroscope, with its 16F tip, permits localization and removal of stone fragments without trauma.This instrument was used in 30 patients by 9 surgeons. An open surgical procedure was done in 27 patients and nephrostomy was done in 3. In 7 cases intraoperative radiography failed to localize calculi that were identified subsequently by nephroscopy. In all instances the surgeons rated the flexible nephroscope superior to its rigid counterpart. No complications resulted from its use.The flexible nephroscope offers several advantages over the rigid scope: 1) it is atraumatic, 2) it is easily inserted, 3) it offers superior optics, 4) it provides superior visualization and 5) it permits complete intrarenal inspection. Because it allows total intrarenal inspection without trauma or bleeding it should be used before forceps exploration of the kidney.