GBS Platform Evaluation Using Field Instrumentation

A case history of the foundation behaviour of an offshore gravity base structure (GBS) is presented. The platform rests on an overconsolidated fissured clay, bounded, top and bottom, by pervious sand layers. Sixteen piezometers have been placed within this 30 m layer. Based on one-dimensional consolidation theory, independent analyses using both settlement and pore pressure measurements indicated a high degree of consolidation had occurred much sooner than was estimated in the initial design phase. These analyses indicated that laboratory oedometer tests underpredicted the coefficient of consolidation by one to two orders of magnitude. Updated settlements and stability analyses yielded 50% of the initially anticipated settlement and a 20% increase in the available safety factor. In addition, the certainty that the theory relating pore pressure to settlements was appropriate, led to confidence in the piezometer performance, and in turn the procedure used to install them

Age-Dependence of Femoral Strength in White Women and Men

Although age-related variations in areal bone mineral density (aBMD) and the prevalence of osteoporosis have been well characterized, there is a paucity of data on femoral strength in the population. Addressing this issue, we used finite-element analysis of quantitative computed tomographic scans to assess femoral strength in an age-stratified cohort of 362 women and 317 men, aged 21 to 89 years, randomly sampled from the population of Rochester, MN, and compared femoral strength with femoral neck aBMD. Percent reductions over adulthood were much greater for femoral strength (55% in women, 39% in men) than for femoral neck aBMD (26% in women, 21% in men), an effect that was accentuated in women. Notable declines in strength started in the mid-40s for women and one decade later for men. At advanced age, most of the strength deficit for women compared with men was a result of this decade-earlier onset of strength loss for women, this factor being more important than sex-related differences in peak bone strength and annual rates of bone loss. For both sexes, the prevalence of “low femoral strength” (<3000 N) was much higher than the prevalence of osteoporosis (femoral neck aBMD T-score of −2.5 or less). We conclude that age-related declines in femoral strength are much greater than suggested by age-related declines in femoral neck aBMD. Further, far more of the elderly may be at high risk of hip fracture because of low femoral strength than previously assumed based on the traditional classification of osteoporosis. © 2010 American Society for Bone and Mineral Research

Femoral Volumetric Bone Density, Geometry, and Strength in Relation to 25‐Hydroxy Vitamin D in Older Men

Low serum 25-hydroxy vitamin D (25(OH)D) concentrations are associated with increased hip fracture risk and decreased femoral areal bone mineral density (BMD) among elderly men. Structural dimensions of the proximal femur and volumetric BMD in cortical and trabecular compartments are also associated with hip fracture risk. However, associations of volumetric BMD or structural dimensions with serum 25(OH)D concentrations among older men remain unclear. In a random sample of 1608 men aged ≥65 years from the Osteoporotic Fractures in Men Study (MrOS), baseline serum 25(OH)D concentrations were measured by liquid chromatography/mass spectrometry assays. Femoral neck geometry and volumetric BMD derived from quantitative computed tomography included integral, cortical, and trabecular volumetric BMD; cross-sectional area; integral and cortical volume; and cortical volume as a percent of integral volume. We studied 888 men with vitamin D, parathyroid hormone (PTH), femoral neck geometry, and BMD measures. Whole-bone femoral strength and load-strength ratio from finite element (FE) analysis were also available for 356 men from this sample. Multivariable linear regression was used to estimate least square means of each femoral measure within quartiles of 25(OH)D adjusted for age, race, body mass index, height, latitude, and season of blood draw. Tests of linear trend in the means were performed across increasing quartile of serum 25(OH)D levels. Mean cortical volume (p trend = 0.006) and cortical volume as a percent of integral volume (p trend &lt; 0.001) increased across increasing quartile of 25(OH)D level. However, overall femoral neck size (area and integral volume) did not vary by 25(OH)D level. Femoral neck volumetric BMD measures increased in a graded manner with higher 25(OH)D levels (p trend &lt; 0.001). Femoral strength, but not load-strength ratio, increased with increasing 25(OH)D. Adjustment for PTH did not materially change these associations. We conclude that in older men, higher levels of endogenous 25(OH)D may increase whole-bone strength by increasing femoral volumetric BMD and cortical volume