Withdrawal strength and stiffness of screw fastenings in cross-laminated timber

Introduction – Cross-laminated timber (CLT) is a product that is becoming increasingly common in the construction industry. CLT is categorized as homogeneous or combined, where homogeneous has the same strength classes throughout the entire cross-section and combined has varying strength classes across the cross-section. The strength and stiffness are compensated in the combined material by placing the highest strength class furthest out in the cross-section. When it comes to stiffness in timber structures, however, joints often represent the weakest link. This is particularly relevant in the construction of taller buildings where stiffness becomes a crucial variable for stability. To broaden the knowledge of screw connections in CLT this study aims to investigate the comparison of homogeneous and combined CLT with regards to strength and stiffness in axially loaded screw connections in CLT. Method – A literature review was conducted to design a test setup for measuring the strength and stiffness of axially loaded screw connections in CLT. Relevant studies and standards were examined to develop a suitable setup for the study. Tensile tests were conducted to determine the difference in strength and stiffness between homogenous and combined CLT as well as between strength class C24 and C35, providing numerical values for comparison. Result – The literature study resulted in empirical data presenting various test setups for measuring axially loaded screws connections in CLT. The experiment, conducted in the form of tensile tests, resulted in data in the form of measured force in relation to displacement, which could be used to calculate strength and stiffness.  Analysis – The test setup which was designed to measure the strength and stiffness of axially loaded screw connections in CLT was based on guidelines from SS-EN 1382 (SIS, 2016) and ISO 6891 (ISO, 1983), as well as inspiration from previous studies with similar test setups. The tensile tests showed that no significant difference in strength and stiffness could be observed between the combined and homogeneous CLT elements that were tested. Discussion – The results show no significant percentage differences in relation to the coefficient of variation between combined CLT and homogeneous CLT. However, the results do show a significant difference when only strength class C35 and C24 are tested separately. Additionally, the experiments show that displacement measurements should be made locally due to deformations in the tensile testing machine and equipment. Due to deformations in the screw, it also turns out to matter where in relation to the test specimen and screw the local measurements are made

Withdrawal strength and stiffness of screw fastenings in cross-laminated timber

Introduction – Cross-laminated timber (CLT) is a product that is becoming increasingly common in the construction industry. CLT is categorized as homogeneous or combined, where homogeneous has the same strength classes throughout the entire cross-section and combined has varying strength classes across the cross-section. The strength and stiffness are compensated in the combined material by placing the highest strength class furthest out in the cross-section. When it comes to stiffness in timber structures, however, joints often represent the weakest link. This is particularly relevant in the construction of taller buildings where stiffness becomes a crucial variable for stability. To broaden the knowledge of screw connections in CLT this study aims to investigate the comparison of homogeneous and combined CLT with regards to strength and stiffness in axially loaded screw connections in CLT. Method – A literature review was conducted to design a test setup for measuring the strength and stiffness of axially loaded screw connections in CLT. Relevant studies and standards were examined to develop a suitable setup for the study. Tensile tests were conducted to determine the difference in strength and stiffness between homogenous and combined CLT as well as between strength class C24 and C35, providing numerical values for comparison. Result – The literature study resulted in empirical data presenting various test setups for measuring axially loaded screws connections in CLT. The experiment, conducted in the form of tensile tests, resulted in data in the form of measured force in relation to displacement, which could be used to calculate strength and stiffness.  Analysis – The test setup which was designed to measure the strength and stiffness of axially loaded screw connections in CLT was based on guidelines from SS-EN 1382 (SIS, 2016) and ISO 6891 (ISO, 1983), as well as inspiration from previous studies with similar test setups. The tensile tests showed that no significant difference in strength and stiffness could be observed between the combined and homogeneous CLT elements that were tested. Discussion – The results show no significant percentage differences in relation to the coefficient of variation between combined CLT and homogeneous CLT. However, the results do show a significant difference when only strength class C35 and C24 are tested separately. Additionally, the experiments show that displacement measurements should be made locally due to deformations in the tensile testing machine and equipment. Due to deformations in the screw, it also turns out to matter where in relation to the test specimen and screw the local measurements are made

Multi-proxy analyses of a peat bog on Isla de los Estados, easternmost Tierra del Fuego: a unique record of the variable Southern Hemisphere Westerlies since the last deglaciation

We have analyzed an almost 14,000 year old peat sequence on the island of Isla de los Estados (55 degrees S. 64 degrees W), east of Tierra del Fuego, in the core of the Southern Hemisphere Westerlies. A multitude of methods have been used: high resolution C-14 dating; detailed lithologic descriptions including humification degree; loss on ignition; magnetic susceptibility; bulk density; pollen and spore analysis and determination of Aeolian sand influx. By combining proxies for wind and precipitation we have been able to reconstruct how the westerlies have varied over time in the Atlantic sector of the Southern Ocean. It shows that this westerly wind belt was most intense at the onset of the record, 13,600-13,200 cal BP, coinciding with the mid to late part of the Antarctic Cold Reversal, followed by a gradual decline. At 12,200 cal BP the westerlies seem to have shifted to a position south of Tierra del Fuego and this phase, the calmest and driest period on the island throughout the sequence, ended at 10,000 cal BP when the westerlies moved equatorward again. Since then the westerlies have been present but with a variable impact on the 55 degrees S latitude of the Atlantic. Mostly conditions have been fairly similar to today, but occasionally with a wider or narrower and/or weaker or stronger wind belt. At 7200 cal BP wind intensity began to increase and between 4500 and 3500 cal BP these southern latitudes experienced a distinct wind and precipitation maximum, both in terms of perseverance and intensity. Our results show a both wide and strong wind belt, with possible niveo-aeolian activity in Tierra del Fuego in winter, and possibly creating milder summers around the Antarctic Peninsula. In the later part of the Holocene, expansion contraction phases of the wind belt, especially in winter, seem to have been a common phenomenon. (C) 2012 Elsevier Ltd. All rights reserved

Results of surgery for sporadic primary hyperparathyroidism in patients with preoperatively negative sestamibi scintigraphy and ultrasound.

PURPOSE: The purpose of this study is to investigate the results of first-time surgery for sporadic primary hyperparathyroidism (pHPT) in patients with preoperatively negative sestamibi scintigraphy and ultrasound. METHODS: Data were gathered prospectively in a multicenter database for quality control in parathyroid surgery. Between 2004 and 2008, 3,158 patients underwent first-time surgery for sporadic pHPT. A total of 984 patients were subjected to preoperative localization with ultrasound and sestamibi scintigraphy, and in 173 patients, both investigations were negative. Intraoperative findings and early outcome are reported. RESULTS: One hundred and fifty-five of 173 patients underwent bilateral neck exploration. The median weight of excised parathyroid tissue was 350 mg. In 23 patients (13.3%), the exploration was negative. A total of 112 patients (64.7%) had a histological diagnosis of parathyroid adenoma and 38 patients (22%) had multiglandular disease. Six weeks after operation, 164 patients were available for analysis, and 30 patients (18%) had persistent pHPT. The risk for persistent pHPT increased for patients with few intraoperatively identified (p = 0.001) and excised (p = 0.024) parathyroid glands. Patients operated with intraoperative parathyroid hormone (iOPTH) had lower risk for persistent pHPT 7/79 (9%) compared with 23/85 patients (27%) operated without iOPTH (p = 0.003). CONCLUSIONS: Negative localization with sestamibi and ultrasound in pHPT infers a highly selected patient population with small parathyroid adenomas, an alarmingly high rate of negative exploration, and an increased risk for persistent disease. The use of iOPTH influences cure rate favorably

Impact of modern techniques on short-term outcome after surgery for primary hyperparathyroidism: a multicenter study comprising 2,708 patients.

PURPOSE: Preoperative localization procedures and the use of intraoperative parathyroidism (iOPTH) have led to a shift of paradigm from bilateral neck exploration to focused parathyroidectomy in primary hyperparathyroidism (pHPT). However, only a small number of randomized trials from specialized centers have been published. The main purpose of the study was to analyze the impact of localization procedures and iOPTH on short-term outcome after pHPT surgery in a multi-institutional setting. METHODS: An audit for quality assurance in pHPT surgery was performed in 23 Scandinavian departments in 2004-2008. Data were gathered prospectively in a database. Two thousand seven hundred and eight patients were registered and 78% were females. The median serum calcium level was 2.79 mmol/l. RESULTS: Localization procedures were performed in 1,831 patients (68%), (sestamibi in 54% and ultrasound in 41%) and iOPTH in 792 operations (29%). Bilateral exploration was performed in 61%, focused parathyroidectomy in 17%, and unilateral exploration in 22%. Histology showed parathyroid adenoma in 82%, with the median weight of 0.6 g. The alleviation of hypercalcemia at the first follow-up was 93% (94% for primary operation). In the multivariate logistic regression analysis, iOPTH increased cure rate (OR 1.70, 95% CI 1.14-2.53, p = 0.0092). The risk for postoperative medically treated hypocalcemia decreased with the use of localization procedures (OR 0.56, 95% CI 0.43-0.78, p = 0.0004) and iOPTH (OR 0.56, 95% CI 0.39-0.90, p = 0.0015). CONCLUSIONS: Localization procedures and iOPTH decreased the risk for hypocalcemia after pHPT surgery. Additionally, iOPTH influenced short-term cure rate favorably

Incidence of hyperthyroidism in Sweden

Introduction: The incidence of hyperthyroidism has been reported in various countries to be 23-93/100000 inhabitants per year. This extended study has evaluated the incidence for similar to 40% of the Swedish population of 9 million inhabitants. Sweden is considered to be iodine sufficient country. Methods:All patients including children, who were newly diagnosed with overt hyperthyroidism in the years 2003-2005, were prospectively registered in a multicenter study. The inclusion criteria are as follows:clinical symptoms and/or signs of hyperthyroidism with plasma TSH concentration below 0.2 mIE/l and increased plasma levels of free/total triiodothyronine and/or free/total thyroxine. Patients with relapse of hyperthyroidism or thyroiditis were not included. The diagnosis of Graves' disease (GD), toxic multinodular goiter (TMNG) and solitary toxic adenoma (STA), smoking, initial treatment, occurrence of thyroid-associated eye symptoms/signs, and demographic data were registered. Results:A total of 2916 patients were diagnosed with de novo hyperthyroidism showing the total incidence of 27.6/100 000 inhabitants per year. The incidence of GD was 21.0/100 000 and toxic nodular goiter (TNG=STA+TMNG) occurred in 692 patients, corresponding to an annual incidence of 6.5/100 000. The incidence was higher in women compared with men (4.2:1). Seventy-five percent of the patients were diagnosed with GD, in whom thyroid-associated eye symptoms/signs occurred during diagnosis in every fifth patient. Geographical differences were observed. Conclusion:The incidence of hyperthyroidism in Sweden is in a lower range compared with international reports. Seventy-five percent of patients with hyperthyroidism had GD and 20% of them had thyroid-associated eye symptoms/signs during diagnosis. The observed geographical differences require further studies

Scandinavian quality register for thyroid and parathyroid surgery: audit of surgery for primary hyperparathyroidism.

Background and aim Scandinavian Quality Register for Thyroid and Parathyroid Surgery is an on-line web-based database with the aim to improve the quality of thyroid and parathyroid surgery. Preliminary data from surgery for primary hyperparathyroidism are reported here. Materials and methods Fifteen departments registered 806 operations, with 639 women (79.7%) and 167 men. The median age of the patients was 62 years. Results Approximately 95.4% of the patients had sporadic disease and first time operation was performed in 93.8% of the patients. Localization examinations were performed in 524 patients (65%); sestamibi scintigraphy in 413 patients, with a true positive adenoma localization in 64.4% and ultrasound in 293 patients with adenoma localization in 61.1%. Bilateral neck exploration was performed in 66.8%, unilateral exploration in 16.1%, and focused minimal invasive surgery in 17.1%. In 301 patients planned for limited parathyroid exploration, conversion to bilateral neck surgery occurred in 11%. The cure rate, based on short follow-up, was 91.9%. Postoperative hypocalcemia occurred in 11.4% of the patients, and was associated with reoperation, concomitant thyroid operation, and the weight of excised parathyroid tissue. Conclusion Localization examinations are performed in 2/3 of the patients, but limited neck exploration was performed in only approximately 1/3 of the operations. The cure rate was lower and postoperative hypocalcemia was more frequent than expected