Size effects in timber explained by a modified weakest link theory

1986 ◽  
Vol 13 (2) ◽  
pp. 218-232 ◽  
Author(s):  
Borg Madsen ◽  
Andrew H. Buchanan
Keyword(s):  
Size Effects ◽  
Design Method ◽  
Bending Test ◽  
Test Results ◽  
New Approach ◽  
Weakest Link ◽  
Link Theory ◽  
Tension Members ◽  
Depth Effects ◽  
Good Agreement

This paper represents a new approach to size effects in timber. The design process in Canadian Standards Association code CAN3-086-M80 allows for size effects in shear and in tension but not in bending. A large number of bending test results arc analyzed in this paper to show that size effects in bending are very important. A modification is made to the traditional weakest link theory for size effects to reflect the anisotropic nature of timber. Good agreement is obtained between tests and theory. The theory enables us to compare tests with different spans and (or) load configurations with an understanding not previously possible. Results from several large testing programs are used to quantify the theory. For bending members, length effects and load configuration effects are found to be much more important than depth effects, and a simple design method is proposed. Information for tension members is less comprehensive; nevertheless, a tentative suggestion for the design of those members is included.

Pull-out capacity of single batter piles in sand

1986 ◽  
Vol 23 (3) ◽  
pp. 387-392 ◽  
Author(s):  
A. M. Hanna ◽  
A. Afram
Keyword(s):  
Design Method ◽  
Soil Mechanics ◽  
Earth Pressure ◽  
Axial Loading ◽  
Test Results ◽  
Passive Earth Pressure ◽  
Sand Soil ◽  
Pull Out ◽  
Batter Piles ◽  
Good Agreement

The pull-out capacity of single rigid vertical and batter piles in sand and subjected to axial loading has been investigated. Good agreement was found when test results on instrumented model piles were compared with theoretical estimates. The effect of pile inclination on the pull-out capacity has been explained by means of variable mobilized passive earth pressure on the pile's perimeter. A design method and charts are presented. Key words: pile foundation, pull-out capacity, vertical pile, batter pile, sand–soil mechanics.

Size effects in defect-free Douglas fir

1990 ◽  
Vol 17 (2) ◽  
pp. 238-242 ◽  
Author(s):  
Borg Madsen
Keyword(s):  
Size Effects ◽  
Volume Effect ◽  
Douglas Fir ◽  
Material Behavior ◽  
Empirical Methods ◽  
Clear Wood ◽  
Weakest Link ◽  
Link Theory ◽  
Structural Engineers ◽  
Free Material

This paper describes experimental work on size effects occurring in defect-free Douglas fir and suggests empirical methods for modelling these. It was found, contrary to present belief, that the size effects could best be described as a volume effect. It was also found that wet and dry materials behaved very differently with respect to size effects. Defect-free material represents the stronger and more expensive range of materials available to the structural engineers. It is, therefore, important that the material behavior be better understood in order to create structures that are both safe and economical. Key words: size effects, clear wood, defect-free wood, volume effect, length effects, load configuration effect, moisture content, weakest link theory.

Bearing Performance and Design Method of Aluminum Alloy Bolted Connections

2011 ◽  
Vol 71-78 ◽  
pp. 882-889 ◽  
Author(s):  
Yuan Qing Wang ◽  
Huan Xin Yuan ◽  
Yong Jiu Shi ◽  
Gui Xiang Zhang
Keyword(s):  
Aluminum Alloy ◽  
Design Method ◽  
Sheet Thickness ◽  
Test Results ◽  
Bolted Connections ◽  
Bolted Connection ◽  
End Distance ◽  
Screw Diameter ◽  
Primary Form ◽  
Good Agreement

Served as the primary form of joints in aluminum structures, the bolted connection is of great necessity to be investigated. The bearing performance of aluminum alloy bolted connections was evaluated by test and finite element (FE) analysis. A total of 20 bolted connections were tested and the varying parameters incorporated screw diameter and end distance. The test results included the ultimate bearing capacities and relationship between applied load and bolt hole deformation. Numerical simulation for the test process was implemented; thereupon reliability and accuracy of the FE models could be validated by good agreement with test results. By virtue of the verified numerical model, elaborated analysis of principle variables including inner and outer plies, end distance, screw diameter, sheet thickness and so on was carried out. Compared to the current overly conservative design rules, a new design method that could make full use of the bearing capacity was proposed. The corresponding design value of bearing strength was also presented with reference to the recommended constructional provisions.

A New Rationale for Scatter in Fracture Toughness Measurements

2008 ◽  
Author(s):  
Silvester J. Noronha
Keyword(s):  
Fracture Toughness ◽  
Size Distribution Function ◽  
Ferritic Steels ◽  
Crack Plane ◽  
Weibull Analysis ◽  
Weakest Link ◽  
Brittle Ductile Transition ◽  
Link Theory ◽  
Detailed Statistical Analysis ◽  
Good Agreement

The observed scatter in fracture toughness is investigated based on a dislocation simulation model that has been proposed to predict the brittle ductile transition in ferritic steels. We carried out a series of Monte-Carlo simulations using uniform distribution of microcracks on the crack plane of macrocrack. Detailed statistical analysis of the simulation results showed that the fracture is always initiated at one of the largest microcracks, whose size correspond to the tail of the size distribution function, and the inherent scatter arises from the distribution in the size of the critical microcrack that initiates the fracture and not from the variation of the location of the critical microcrack. Utilizing the weakest-link theory, Weibull analysis shows good agreement with the Weibull modulus values obtained from fracture toughness measurements.

Profile Shifted Conical Involute Gear With Deep Tooth Depth

2007 ◽  
Author(s):  
Tatsuya Ohmachi ◽  
Atsushi Uchino ◽  
Hidenori Komatsubara ◽  
Makoto Saito ◽  
Kohei Saiki ◽  
...  
Keyword(s):  
Design Method ◽  
Test Results ◽  
Hypoid Gear ◽  
Shift Coefficient ◽  
New Concepts ◽  
Tooth Surfaces ◽  
Involute Gears ◽  
Conical Gears ◽  
Conical Gear ◽  
Good Agreement

This paper proposes a new design method for profile shifted conical gear with deep tooth depth. This method has two new concepts. First, this method is based on the designed pitch point where the rack shift coefficient is not zero. Second, this method is based on the theory of nonintersecting bevel gear such as hypoid gear, to decide the mounting dimensions of the profile shifted conical involute gears with deep tooth depth. The profile shifted conical involute gears have the designed pitch point that is not the standard pitch point. Limits of the rack shift coefficient and the facewidth, for the undercut and the zero top land, are clarified. Next, the production system is shown, and several typical test gears are manufactured. Paths of contact between tooth surfaces of profile shifted conical gears are obtained by tooth bearing tests. As a result, the measured value of limits of the rack shift coefficient and the facewidth on the manufactured tested gears are in good agreement with the theoretical ones. Moreover, test results of tooth bearing are in good agreement with the theoretical ones.

Statistical Size Effects on Compressive Strength and Mechanical Behavior of Concrete

2017 ◽  
Vol 754 ◽  
pp. 317-320 ◽  
Author(s):  
Chi Cong Vu ◽  
Jérôme Weiss ◽  
Olivier Plé ◽  
David Amitrano
Keyword(s):  
Compressive Strength ◽  
Size Effects ◽  
Aggregate Size ◽  
Dissipated Energy ◽  
Compression Tests ◽  
Weakest Link ◽  
Link Theory ◽  
Long Time ◽  
Compressive Strength Of Concrete ◽  
Main Shortcoming

The size effect on strength of concrete has been studied for a long time from various approaches. In particular, the weakest-link theory remains nowadays the basic tool to interpret statistical size effects, i.e. how the probability of failure under a given stress depends on external size. The main shortcoming of Weibull’s theory is that the activation of fracture from the weakest flaw is assumed to set the final strength, i.e. possible interactions between microcracks and defects during progressive damage are implicitly neglected. The objective of this study is to determine experimentally the influence of “external” (sample) size and “internal” (microstructural) size on compressive strength of concrete. For this purpose, more than 250 uniaxial compression tests were conducted on concrete specimens with two different cylindrical sizes (110×220 mm and 160×320 mm) and prepared from three different compositions (mean aggregate size and proportion). The relationships between compressive strength, dissipated energy up to failure in one hand, and microstructural as well as specimen sizes on the other hand, were analyzed statistically. This demonstrated the failure of the weakest-link approach to describe size effects on compressive strength of concrete.

Investigation of the mechanical properties of lignin nanofibrous structures using statistical modeling

2017 ◽  
Vol 88 (17) ◽  
pp. 1943-1953 ◽  
Author(s):  
Seyed Abdolkarim Hosseini ◽  
Li-Ting Lin ◽  
Frank Ko
Keyword(s):  
Mechanical Properties ◽  
Industrial Applications ◽  
Fiber Bundles ◽  
Environmental Concerns ◽  
Weakest Link ◽  
Link Theory ◽  
Distribution Parameters ◽  
Fiber Fragmentation ◽  
Good Agreement

The growing use of nanomaterials, environmental concerns and related industrial applications have provided unique opportunities for the development of nanofibers from natural biopolymers such as lignin. The main purpose of this study was to develop a direct relationship between lignin single nanofiber, the aligned nanofiber mat and the twisted nanofiber yarn’s strength using the weakest link theory of strength and the statistical model proposed for parallel fiber bundles. Twisted yarn strength was obtained via in situ mechanical properties of yarn constituent nanofibers affected by the Weibull distribution parameters, fiber fragmentation phenomenon, and obliquity. The results showed that the estimated strength of the single nanofiber and the aligned nanofiber mat was in a good agreement with the experimental data. As it might be expected, the yarn’s estimated strength was found to be highly influenced by the fiber fragmentation phenomenon.

Theoretical Analysis on Radial Gate Vibration

2006 ◽  
Author(s):  
Kunihiro Ogihara
Keyword(s):  
Theoretical Analysis ◽  
Model Test ◽  
Pressure Change ◽  
Test Results ◽  
New Approach ◽  
Water Gate ◽  
Pipe Line ◽  
Gate System ◽  
Radial Gate ◽  
Good Agreement

The instability analysis on vibration of radial gate has been done in 1999 under the research project In JPGA (Japan penstock and water gate association) and also the model test of gate vibration has been preceded. The almost theoretical results have been satisfied of the model test results, but there is one point not to be able to explain the relation of natural frequency of gate support system. The instable condition is given by the forth power of frequency of gate system in model test, and the fact that the region of instable becomes smaller as the gate opening larger, is same as the results of theoretical analysis. In this paper, author develop the new approach which is considering the pressure change by stopping the water flow same as water hummer in pipe line. And the unstable analysis on vibration equation of radial gate motion has been done and gotten good agreement on model test results.

Length effects in 38 mm spruce–pine–fir dimension lumber

1990 ◽  
Vol 17 (2) ◽  
pp. 226-237 ◽  
Author(s):  
Borg Madsen
Keyword(s):  
Size Effect ◽  
Cross Sections ◽  
Design Method ◽  
Research Information ◽  
Weakest Link ◽  
Dimension Lumber ◽  
Tension And Compression ◽  
Original Strength ◽  
Tension Members ◽  
Length Effects

This paper deals with some of the problems arising when the strength of a structural member varies along its length such as occurs in timber members where knots and other natural growth characteristics create cross sections with varying strengths along the length of the member. Failure may then take place wherever a weak cross section happens to be subjected to high stresses. A different concept of strength must be introduced into the design codes in order to reflect the probability of such an occurrence. Strength becomes a function of length, depth, and load configuration, all of which must be considered in the design process if both economical and safe structures are to emerge. In this paper, which was directed toward establishing the length effects for 38 mm thick spruce–pine–fir in tension and compression as well as bending, the results of a testing program are described. It was, for instance, found that when the length of tension members is doubled from 3.0 to 6.0 m, the strength reduces to 86% of the previous strength, or if the length is quadrupled (as may occur in the bottom chords of trusses), the strength could reduce to 73% of the original strength. A review of the available research information is presented and evaluated in order to assess the adequacy of the available size effect information for design purposes. The present size effect requirements incorporated in some existing timber codes are also reviewed. Key words: timber, strength, size effects, length effect, weakest link theory, design method, load configuration, bending, compression, tension.

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