Collapse risk and residual drift performance of steel buildings using post-tensioned MRFs and viscous dampers in near-fault regions

The potential of post-tensioned self-centering moment-resisting frames (SC-MRFs) and viscous dampers to reduce the collapse risk and improve the residual drift performance of steel buildings in near-fault regions is evaluated. For this purpose, a prototype steel building is designed using different seismic-resistant frames, i.e.: moment-resisting frames (MRFs); MRFs with viscous dampers; SC-MRFs; and SC-MRFs with viscous dampers. The frames are modeled in OpenSees where material and geometrical nonlinearities are taken into account as well as stiffness and strength deterioration. A database of 91 near-fault, pulse-like ground motions with varying pulse periods is used to conduct incremental dynamic analysis (IDA), in which each ground motion is scaled until collapse occurs. The probability of collapse and the probability of exceeding different residual story drift threshold values are calculated as a function of the ground motion intensity and the period of the velocity pulse. The results of IDA are then combined with probabilistic seismic hazard analysis models that account for near-fault directivity to assess and compare the collapse risk and the residual drift performance of the frames. The paper highlights the benefit of combining the post-tensioning and supplemental viscous damping technologies in the near-source. In particular, the SC-MRF with viscous dampers is found to achieve significant reductions in collapse risk and probability of exceedance of residual story drift threshold values compared to the MRF. © 2016 Springer Science+Business Media Dordrech

Oral bisphosphonate compliance and persistence: a matter of choice?

Compliance to oral bisphosphonates is suboptimal, with negative consequences of increased healthcare utilization and less effective fracture risk reduction. Extending dose interval increased adherence only moderately. We used literature derived from multiple chronic conditions to examine the problem of noncompliance with osteoporosis medication. We reviewed the literature on adherence to osteoporosis medication as well as that across multiple chronic conditions to understand what is known about the cause of the poor adherence. Poor compliance to oral medications is due mostly, not to forgetfulness, but to deliberate choice. Gender differences and style of healthcare management also play a role. Preliminary data suggest psychobehavioral interventions may help to improve motivation. We need to understand better reasons for poor compliance before effective interventions can be developed. Forgetfulness is only a small part of poor compliance. Patient preferences must be considered in medication decision making

Low free 25-hydroxyvitamin D and high vitamin D binding protein and parathyroid hormone in obese Caucasians. A complex association with bone?

Background Studies have shown altered vitamin D metabolism in obesity. We assessed differences between obese and normal-weight subjects in total, free, and bioavailable 25-hydroxyvitamin D (25(OH) D, 25(OH) D-Free, and 25(OH) D-Bio, respectively), vitamin D binding protein (DBP), parathyroid hormone (PTH) and bone traits. Methods 595 37-47-year-old healthy Finnish men and women stratified by BMI were examined in this cross-sectional study. Background characteristic and intakes of vitamin D and calcium were collected. The concentrations of 25(OH) D, PTH, DBP, albumin and bone turnover markers were determined from blood. 25(OH) D-Free and 25(OH) D-Bio were calculated. pQCT was performed at radius and tibia. Results Mean +/- SE (ANCOVA) 25(OH) D-Free (10.8 +/- 0.6 vs 12.9 +/- 0.4 nmol/L; P = 0.008) and 25(OH) DBio (4.1 +/- 0.3 vs 5.1 +/- 0.1 nmol/L; P = 0.003) were lower in obese than in normal-weight women. In men, 25(OH) D (48.0 +/- 2.4 vs 56.4 +/- 2.0 nmol/L, P = 0.003), 25(OH) D-Free (10.3 +/- 0.7 vs 12.5 +/- 0.6 pmol/L; P = 0.044) and 25(OH) D-Bio (4.2 +/- 0.3 vs 5.1 +/- 0.2 nmol/L; P = 0.032) were lower in obese. Similarly in all subjects, 25(OH) D, 25(OH) D-Free and 25(OH) D-Bio were lower in obese (P Conclusions The associations between BMI and 25(OH) D, 25(OH) D-Free, and 25(OH) D-Bio, DBP, and PTH suggest that obese subjects may differ from normal-weight subjects in vitamin D metabolism. BMI associated positively with trabecular bone traits and CSI in our study, and slightly negatively with cortical bone traits. Surprisingly, there was a negative association of free and bioavailable 25(OH) D and some of the bone traits in obese women.Peer reviewe

Seismic assessment of a heavy-timber frame structure with ring-doweled moment-resisting connections

The performance of heavy-timber structures in earthquakes depends strongly on the inelastic behavior of the mechanical connections. Nevertheless, the nonlinear behavior of timber structures is only considered in the design phase indirectly through the use of an R-factor or a q-factor, which reduces the seismic elastic response spectrum. To improve the estimation of this, the seismic performance of a three-story building designed with ring-doweled moment resisting connections is analyzed here. Connections and members were designed to fulfill the seismic detailing requirements present in Eurocode 5 and Eurocode 8 for high ductility class structures. The performance of the structure is evaluated through a probabilistic approach, which accounts for uncertainties in mechanical properties of members and connections. Nonlinear static analyses and multi-record incremental dynamic analyses were performed to characterize the q-factor and develop fragility curves for different damage levels. The results indicate that the detailing requirements of Eurocode 5 and Eurocode 8 are sufficient to achieve the required performance, even though they also indicate that these requirements may be optimized to achieve more cost-effective connections and members. From the obtained fragility curves, it was verified that neglecting modeling uncertainties may lead to overestimation of the collapse capacity

Centrifuge modeling of mitigation-soil-foundation-structure interaction on liquefiable ground

Significant progress has been made in recent years toward a better understanding of the liquefaction phenomena. Yet, the combined effects of excess pore pressure generation, permanent soil deformation, and ground shaking, with and without mitigation, on the performance of the soil-foundation-structure system remain poorly understood. Moreover, there is a lack of physical model studies incorporating these important effects for a range of conditions to validate numerical models. This paper presents an experimental study of the performance of 3-story structures with shallow foundations on a saturated soil profile including a thin liquefiable layer. The influence of three different mitigation techniques was evaluated: 1) ground densification; 2) enhanced drainage with prefabricated vertical drains (PVDs); and 3) reinforcement with in-ground structural walls. Densification was observed to slightly reduce excess pore pressures and permanent foundation settlement and tilt, but amplified the demand transferred to the superstructure. Use of PVDs reduced permanent foundation settlement and rotation by reducing the duration of large excess pore pressures, but amplified roof accelerations and flexural drift. The performance of the stiff structural wall depended on the properties of the earthquake motion. During more intense, longer-duration motions, confining the soil and inhibiting flow inside the structural wall led to liquefaction, larger settlements, and larger translational and rotational accelerations on the foundation. In this case, the dissipation of seismic energy through additional foundation movements reduced the moment-rotation demand on the columns. These experimental results emphasize the importance of evaluating the potential tradeoffs of liquefaction mitigation, which may reduce settlement and sometimes tilt, but result in larger transient drifts and damage to the superstructure