scholarly journals An Investigation of the Duration of Load of Structural Timber and the Clear Wood

Forests ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1148
Author(s):  
Qiongyao Wu ◽  
Liangliang Huo ◽  
Enchun Zhu ◽  
Shuang Niu ◽  
Huajie Wang
Keyword(s):  
Modulus Of Elasticity ◽  
Structural Timber ◽  
Bending Test ◽  
Term Strength ◽  
Short Term ◽  
Loading Test ◽  
Clear Wood ◽  
Dimension Lumber ◽  
Short Term Strength

In this study, DOL of structural timber and the clear wood and DOL of modulus of elasticity of wood were investigated. The dimension lumber of Spruce-Pine-Fir of Grade No. 2 and Grade No. 3 and the small clear specimens of the same species of the dimension lumber were used to conduct the short-term and the long-term bending test. The short-term strength distributions of the dimension lumber and the small clear specimens were obtained. The long-term tests were conducted under constant environmental conditions for 18 months. The sample matching technique was used to estimate the short-term strength of the specimens that underwent long-term tests. It was found out that there is virtually no difference in DOL between different grades or quality of lumber and no difference between structural timber and clear wood, and DOL obtained from the test of this study is more in agreement with Wood’s curve. A threshold stress ratio of about 0.55, loaded above which the wood began to experience strength loss, was revealed from the test. Making use of the threshold ratio concept, the DOL of wood can be obtained not only from failed specimens under load in the process of the long-term loading, but also from the ramp loading test of the specimens that survived the long-term test. Sustained load also poses DOL on the modulus of elasticity of wood, though to less degree than DOL of strength of wood.

Duration of load tests for shear strength

1986 ◽  
Vol 13 (2) ◽  
pp. 188-195 ◽  
Author(s):  
R. A. Spencer ◽  
Borg Madsen
Keyword(s):  
Shear Strength ◽  
Stress Ratio ◽  
Control Sample ◽  
Term Strength ◽  
Short Term ◽  
Current Design ◽  
Short Term Strength ◽  
Load Effects ◽  
Duration Of Load

The strength of wood falls with time under load, and in current design codes the short-term strength of wood is reduced by about 40% to account for duration of load effects. This figure is based on tests made on small bending specimens. In this paper are described tests made on wooden torque tubes to investigate the effect of duration of load on shear strength. A control sample was tested to establish a curve for short-term strength, and four groups of 80 specimens each were then tested under various levels of constant long-term load. Stress ratio at failure was estimated by assuming that the short-term strength of each group could be represented by the control curve, and that under long-term loading specimens would fail in the order of their short-term strength. In each group the stress ratio at failure fell with time under load, and this reduction appears to be related to that predicted by a viscoelastic plastic model. It is concluded that the Madison curve presently used to predict duration of load effects may be conservative at normal levels of applied stress. Key words: wood, shear, long-term loading, duration of load.

scholarly journals ESTIMATION OF STRENGTH OF GLULAM BEAMS DEPENDING ON DEFECTS OF LAYERS/MEDINIŲ KLIJUOTŲ LENKIAMŲJŲ ELEMENTŲ STIPRUMO VERTINIMAS PAGAL SLUOKSNIŲ DEFEKTUS

1999 ◽  
Vol 5 (4) ◽  
pp. 245-249
Author(s):  
Algirdas Baltrušaitis
Keyword(s):  
Testing Machine ◽  
Solid Wood ◽  
Time To Failure ◽  
Term Strength ◽  
Normal Stresses ◽  
Short Term ◽  
Theoretical Investigations ◽  
Short Term Strength ◽  
Factors Of Influence

Timber, as structural material, has various defects, especially knots. They influence the strength of timber members. The influence of knots is lower for glulam members when comparing with solid wood. The article is the theoretical and experimental investigation of influence of knots on the strength of glulam beams. Theoretical investigation deals with probability of coinciding of knots in the same cross-section of member. The factors of influence of knots on glulam beam strength are the results of theoretical investigations. The short-term tests on 12 model beams with measurements 2140×120×152(h) mm were carried out in a testing machine. Results of these tests are in line with the conclusions of theoretical investigations and show the higher strength of glulam beams when comparing with solid members of the same quality. The long-term tests were carried out on model beams when temperature and moisture were cyclically changed. Wetting cycle—14 days long, drying cycle—7 days. Two series, 12 model beams each, were tested. The moisture of outer layer 20 mm depth changed from 6–8% to 20–22%, while the moisture in the rest area changed from 9% to 13%. The load of the first group of beams was 40% of short-term strength, and duration of tests 147 days. For the second group the normal stresses were σ = 18.2 MPa for each beam, and the duration of tests—210 days. Deflection of beams was observed and moments of beams rupture were registered. The relationships between long-term strength and logarithm of time to failure for two types of model beams were the results of long-term tests. Long-term tests show the dependence upon the size of knots and long-term strength of glulam beams.

scholarly journals CRITERIAL METHOD OF CALCULATIONS OF LONG-TERM STABILITY OF THE BOREHOLE

2018 ◽  
pp. 79-84
Author(s):  
O. A. Shipilova ◽  
S. V. Shafieva
Keyword(s):  
Strength Criterion ◽  
Oil Wells ◽  
Term Strength ◽  
Short Term ◽  
Term Stability ◽  
Long Term Stability ◽  
Short Term Strength

The article examines the possibility of applying the Mohr - Coulomb short-term strength criterion to the calculations of long-term stability of open oil wells. The results of calculation of long-term and short-term strength on the basis of the polygon of stability are analyzed.

Static fatigue of sand particles

2018 ◽  
Vol 55 (11) ◽  
pp. 1682-1687
Author(s):  
Su Liu ◽  
Jianfeng Wang
Keyword(s):  
Fatigue Test ◽  
Compressive Load ◽  
Fatigue Tests ◽  
Time Dependent ◽  
Static Fatigue ◽  
Term Strength ◽  
Short Term ◽  
Short Term Strength ◽  
Sand Particles

Static fatigue is of particular concern when studying the time-dependent mechanical behavior of brittle geomaterials. In this regard, the time-dependent strength behavior of individual particles is essential for understanding the creep behavior of sand. In this study, short-term strength tests and static fatigue tests of individual sand particles subjected to a uniaxial compressive load were carried out using a mini-loading apparatus and modified oedometer frames, respectively. The sand particles in the static fatigue test were loaded in an incremental manner, and the load at each stress level was maintained for a fixed period of time. Scatter of the strength of sand particles was described using the Weibull distribution. Long-term strength from the static fatigue test of individual sand particles is found to be less than the short-term strength.

Effects of latex modification on fresh state consistency, short term strength and long term transport properties of cement mortars

2017 ◽  
Vol 133 ◽  
pp. 226-233 ◽  
Author(s):  
Faruk Eren ◽  
Eren Gödek ◽  
Muhammer Keskinateş ◽  
Kamile Tosun-Felekoğlu ◽  
Burak Felekoğlu
Keyword(s):  
Transport Properties ◽  
Term Strength ◽  
Short Term ◽  
Cement Mortars ◽  
Fresh State ◽  
Short Term Strength

Effects of Training Loads on Short-term Strength Adaptations in Older Adults

2011 ◽  
Vol 43 (Suppl 1) ◽  
pp. 516
Author(s):  
Sandor Dorgo ◽  
Rebecca J. Reed-Jones ◽  
Chantal A. Vella ◽  
Christina Samples ◽  
Chandrasekhar Bulusu
Keyword(s):  
Older Adults ◽  
Term Strength ◽  
Short Term ◽  
Short Term Strength

SUBSTANTIATION OF THE SPECIFIC CRITERION FOR THE CORROSIVE EFFECT OF FORMATION MEDIA ON THE CYCLIC STRENGTH OF STEEL OF DOWNHOLE EQUIPMENT

2020 ◽  
pp. 60-64
Author(s):  
E.S. Yushin
Keyword(s):  
Approximate Calculation ◽  
Oil And Gas ◽  
Endurance Limit ◽  
Cyclic Strength ◽  
Cyclic Loads ◽  
Term Strength ◽  
Short Term ◽  
Specific Criterion ◽  
Corrosive Effect ◽  
Short Term Strength

The article provides the substantiation of the specific coefficient of corrosion influence, considered per unit of the limit of short-term strength of the metal, with the help of which it is possible to simplify the most approximate calculation of the limited endurance limit of steels of oil and gas equipment operating under cyclic loads, as well as perform subsequent resource calculations.

scholarly journals Strength exercise reduces hepatic pyruvate carboxylase and gluconeogenesis in DIO mice

2020 ◽  
Vol 247 (2) ◽  
pp. 127-138
Author(s):  
Rodrigo Martins Pereira ◽  
Kellen Cristina da Cruz Rodrigues ◽  
Marcella Ramos Sant’Ana ◽  
Guilherme Francisco Peruca ◽  
Ana Paula Morelli ◽  
...  
Keyword(s):  
Strength Training ◽  
Pyruvate Carboxylase ◽  
Hepatic Glucose Production ◽  
Glucose Production ◽  
Mrna Levels ◽  
Strength Exercise ◽  
Term Strength ◽  
Short Term ◽  
Hepatic Glucose ◽  
Short Term Strength

Obesity is linked to a reduction in the control of hepatic glucose production, which is the primary mechanism related to fasting hyperglycemia and the development of type 2 diabetes mellitus (T2DM). The main system involved in hepatic gluconeogenesis synthesis is controlled by pyruvate carboxylase (PC), which increases in obesity conditions. Recently, we showed that short-term strength training is an important tool against obesity-induced hyperglycemia. As aerobic exercise can reduce the hepatic PC content of obese animals, we hypothesized that strength exercise can also decrease this gluconeogenic enzyme. Therefore, this study investigated whether the metabolic benefits promoted by short-term strength training are related to changes in hepatic PC content. Swiss mice were divided into three groups: lean control (Ctl), obese sedentary (ObS), and obese short-term strength training (STST). The STST protocol was performed through one session/day for 15 days. The obese exercised animals had reduced hyperglycemia and insulin resistance. These results were related to better control of hepatic glucose production and hepatic insulin sensitivity. Our bioinformatics analysis showed that hepatic PC mRNA levels have positive correlations with glucose levels and adiposity, and negative correlations with locomotor activity and muscle mass. We also found that hepatic mRNA levels are related to lipogenic markers in the liver. Finally, we observed that the obese animals had an increased hepatic PC level; however, STST was efficient in reducing its amount. In conclusion, we provide insights into new biomolecular mechanisms by showing how STST is an efficient tool against obesity-related hyperglycemia and T2DM, even without body weight changes.

scholarly journals Short-term strength training reduces gluconeogenesis and NAFLD in obese mice

2019 ◽  
Vol 241 (1) ◽  
pp. 59-70 ◽  
Author(s):  
Rodrigo Martins Pereira ◽  
Kellen Cristina da Cruz Rodrigues ◽  
Chadi Pellegrini Anaruma ◽  
Marcella Ramos Sant’Ana ◽  
Thaís Dantis Pereira de Campos ◽  
...  
Keyword(s):  
Weight Loss ◽  
Insulin Sensitivity ◽  
Strength Training ◽  
Term Strength ◽  
Obese Mice ◽  
Short Term ◽  
Fat Accumulation ◽  
Hepatic Insulin Sensitivity ◽  
Short Term Strength ◽  
Hepatic Fat

Non-alcoholic fatty liver disease (NAFLD) has a positive correlation with obesity, insulin resistance and type 2 diabetes mellitus (T2D). The aerobic training is an important tool in combating NAFLD. However, no studies have demonstrated the molecular effects of short-term strength training on the accumulation of hepatic fat in obese mice. This study aimed to investigate the effects of short-term strength training on the mechanisms of oxidation and lipid synthesis in the liver of obese mice. The short duration protocol was used to avoid changing the amount of adipose tissue. Swiss mice were separated into three groups: lean control (CTL), sedentary obese (OB) and strength training obese (STO). The obese groups were fed a high-fat diet (HFD) and the STO group performed the strength training protocol 1 session/day for 15 days. The short-term strength training reduced hepatic fat accumulation, increasing hepatic insulin sensitivity and controlling hepatic glucose production. The obese animals increased the mRNA of lipogenic genes Fasn and Scd1 and reduced the oxidative genes Cpt1a and Ppara. On the other hand, the STO group presented the opposite results. Finally, the obese animals presented higher levels of lipogenic proteins (ACC and FAS) and proinflammatory cytokines (TNF-α and IL-1β), but the short-term strength training was efficient in reducing this condition, regardless of body weight loss. In conclusion, there was a reduction of obesity-related hepatic lipogenesis and inflammation after short-term strength training, independent of weight loss, leading to improvements in hepatic insulin sensitivity and glycemic homeostasis in obese mice. Key points: (1) Short-term strength training (STST) reduced fat accumulation and inflammation in the liver; (2) Hepatic insulin sensitivity and HPG control were increased with STST; (3) The content and activity of ACC and content of FAS were reduced with STST; (4) STST improved hepatic fat accumulation and glycemic homeostasis; (5) STST effects were observed independently of body weight change.

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