Summary A performance‐based earthquake engineering approach is developed for the seismic risk assessment of fixed‐roof atmospheric steel liquid storage tanks. The proposed method is based on a surrogate single‐mass model that consists of elastic beam‐column elements and nonlinear springs. Appropriate component and system‐level damage states are defined, following the identification of commonly observed modes of failure that may occur during an earthquake. Incremental dynamic analysis and simplified cloud are offered as potential approaches to derive the distribution of response parameters given the seismic intensity. A parametric investigation that engages the aforementioned analysis methods is conducted on 3 tanks of varying geometry, considering both anchored and unanchored support conditions. Special attention is paid to the elephant's foot buckling formation, by offering extensive information on its capacity and demand representation within the seismic risk assessment process. Seismic fragility curves are initially extracted for the component‐level damage states, to compare the effect of each analysis approach on the estimated performance. The subsequent generation of system‐level fragility curves reveals the issue of nonsequential damage states, whereby significant damage may abruptly appear without precursory lighter damage states.
Abstract Endogenous Cushing's syndrome (CS) in children causes growth retardation, decreased bone mass, and increased total body fat. No prospective controlled studies have been performed in children to determine the long-term sequelae of CS on peak bone mass and body composition. A 15-year-old girl with Cushing disease (CD), and her healthy identical co-twin, were followed for 6 years after the CD was cured. At the 6-year follow-up both twins had areal bone mineral density (BMD) and body composition determined by dual-energy X-ray absorptiometry (DXA) and three-dimensional quantitative computed tomography (3DQCT). Z scores for height, weight, and body mass index (BMI) were −2.3, −0.8 and 0.2, and 1.2, 0.2, and −0.6, in the twin with CD and her co-twin, respectively. In the twin with CD, areal BMD and bone mineral apparent density (BMAD) at different sites varied from 0.7 to 3 SD below her co-twin. Volumetric lumbar spine bone density Z score was −0.75 and 1.0, and total body, abdominal visceral, and subcutaneous fat (%) was 42, 10, and 41 versus 26, 4, and 17 in the twin with CD and her co-twin, respectively. The relationship between total body fat and L2-L4 BMAD was inverse in the twin with CD (p < 0.05), which by contrast in her co-twin was opposite and direct (p < 0.001). In the twin with CD, despite cure, there was a persistent deficit in bone mass and increase in total and visceral body fat. These observations suggest that hypercortisolism (exogenous or endogenous) during adolescence may have persistent adverse effects on bone and fat mass.
Excess endogenous glucocorticoid production, whether corticotropin-dependent or -independent, results in the classic clinical and biochemical picture of Cushing's syndrome. The diagnosis requires demonstration of an increased cortisol secretion rate, but in mild cases, distinction from the hypercortisolism of pseudo-Cushing states may prove difficult. A dexamethasone or ovine corticotropin-releasing hormone test or close monitoring of the patient for a few months may be helpful. Most cases are diagnosed using: corticotropin-releasing hormone—stimulated plasma corticotropin level measurements and adrenal imaging procedures, A discrete pituitary lesion on imaging and a standard ovine corticotropin-releasing hormone test with results consistent with such a lesion are sufficient to proceed to transsphenoidal surgery. If no visible pituitary lesion is present, or if the ovine corticotropin-releasing hormone test is equivocal, bilateral simultaneous inferior petrosal sinus sampling with ovine corticotropin-releasing hormone administration is necessary to distinguish between a pituitary and an ectopic source. Surgical ablation is the treatment of choice for all types of Cushing's syndrome. In cases in which transsphenoidal surgery fails or in which the disease recurs, repeat transsphenoidal surgery and radiation therapy in association with mitotane treatment are reasonable alternatives. Bilateral adrenalectomy effectively cures hypercortisolism if resection of the corticotropin-secreting tumor is unsuccessful and radiation or medical therapy fails.