AN INVESTIGATION OF DAMPING MODIFICATION FACTORS CORRESPONDING TO DIFFERENT DAMPING RATIOS FOR SDOF SYSTEMS

The damping ratio is an important parameter in dynamic analyses and plays a key role in the design of building structures. Elastic response spectra are widely used in this design to describe the earthquake action in specific site classes. 5% damped response spectra are generally used for most of the conventional structures. However, other types of structures may not have a damping ratio of 5% and can have much lower or much larger damping ratios. The damping ratio is recommended at about 5% for concrete structures whereas it is estimated at 2% for steel structures. Tall slender buildings may have much lower damping ratios and low-rise buildings may be designed using much larger damping ratios than 5%. For these types of buildings, elastic response spectra are modified to account for different levels of damping ratios. This study proposes the damping modification factors (DMFs) which are computed using 5% response spectra as the benchmark. A strong ground motion set has been selected for the stiff site class and the displacement, pseudo-velocity, and pseudo-acceleration response spectra have been computed for single-degree-of-freedom (SDOF) systems. DMFs have been obtained in terms of these spectra and 3%, 10%, 20%, and 30% damping ratios have been considered. Variations of DMFs with different damping ratios have been obtained graphically. It can be seen from the results that DMFs are sensitive to the vibration period of the SDOF system

Scheduling surgery after transarterial embolization: does timing make any difference to intraoperative blood loss for renal cell carcinoma bone metastases?

PURPOSEOur purpose is to clarify the optimal timing of surgery after transarterial embolization (TAE) for renal cell carcinoma (RCC) bone metastases.METHODSThis retrospective study included 41 patients with RCC bone metastases embolized between 2013 and 2019. Different-sized particulate and/or liquid embolic agents were used for TAE. Embolizations were categorized into groups 1–3 according to the interval between TAE and surgery (group 1: 3 days). Degree of embolization after TAE was graded visually based on angiographic images (90%). The relationship between the TAE–surgery interval and intraoperative blood loss (IBL) and the correlation between IBL and embolization grade were examined. Lesion sizes and the relationships among lesion localizations and contrast media usage, intervention time, and IBL were also analyzed.RESULTSForty-six pre-operative TAEs (single lesion at each session) were performed in this study (26 in group 1, 13 in group 2, 7 in group 3). Lesion sizes and distributions were similar between groups (p = 0.897); >75% devascularization was achieved in 40 (TAEs 86.96%), but the IBL showed no correlation with the embolization rate (r=0.032, p = 0.831). The TAE–surgery interval was 1–7 days. The median IBL in group 1 (750 mL; range, 150–3000 mL) was significantly lower than those in the other groups (p = 0.002). Contrast media usage (p = 0.482) and intervention times (p = 0.261) were similar for metastases at different localizations. IBL values after TAE were lower for extremity metastases (p = 0.003).CONCLUSIONBone metastases of RCC are well-vascularized, and to achieve lowest IBL values, surgery should preferably be performed <1 day after TAE

An energy-based approach to determine the yield force coefficient of RC frame structures

This paper proposes an energy-based approach for estimating the yield force coefficient of reinforced concrete (RC) frame structures. The procedure is mainly based on the energy balance concept and it considers the nonlinear behavior of structures. First, an energy modification factor is defined to consistently obtain the total energy of the equivalent elastic-plastic single-degree-of-freedom (SDOF) system. Then, plastic energy is formulated as functions of the several structural parameters such as the natural frequency, the strength reduction factor and the yield displacement. Consequently, the plastic energy formulation is derived for multi-degree-of-freedom (MDOF) systems and the yield force coefficient is determined by equating the plastic energy relation to the work needed to push the structure from the yield displacement up to the maximum displacement monotonically. The validity of the energy-based approach is assessed on several RC frame structures by means of nonlinear static pushover analysis considering both material and geometrical nonlinearity. A modification factor is proposed for the yield force coefficient to consider the strain-hardening effects in lateral forces. Moreover, the modified energy-based yield force coefficients are correlated to practical design by using the ductility ratios imposed by Turky Building Earthquake Code and a quite good agreement is observed

AN INVESTIGATION OF DAMPING RATIO EFFECT ON EARTHQUAKE ENERGY INPUT

Recent earthquakes show that the strength and displacement-based methods in many seismic design codes are not as reliable as the energy-based methods in seismic design and evaluation of structures. The determination of earthquake energy input to structures is the main concern for the energy-based structural design methods. The seismic energy input to structures mainly depends on the strong ground acceleration and the velocity time history of the structures. Current studies about the seismic energy input show that the bases of researches are established almost entirely for the single-degree-of-freedom (SDOF) systems. This study investigates the variation of earthquake input energy of SDOF systems which have different period and damping ratio values. Five real earthquake records are selected to perform nonlinear time history analyses. SDOF systems are assumed to be located on the same type of soil profile according to the shear wave velocity values of the first thirty meters of the soil. Bilinear hysteretic model is used and constant ductility is considered. Three different damping ratios as three, five and ten per cent are taken. Energy time-histories of bilinear SDOF systems are obtained graphically for selected earthquakes and for different damping ratios. The main objective of the research is to see to what extent the energy input has changed for different damping ratio values