Internal stresses in the cross-grain direction in glulam induced by climate variations

Holzforschung ◽  
2004 ◽  
Vol 58 (2) ◽  
pp. 154-159 ◽  
Author(s):  
J. Jönsson
Keyword(s):  
Climate Change ◽  
Experimental Investigation ◽  
Cross Section ◽  
Moisture Gradient ◽  
Internal Stresses ◽  
Stress Distributions ◽  
Climate Variations ◽  
Before And After ◽  
Stress States ◽  
Natural Climate

Abstract Results are presented from an experimental investigation to determine internal stress states perpendicular to grain in glulam induced by moisture variations. The stresses are determined by measuring the released strains before and after cutting. Stress distributions are determined for specimens seasoned in constant humidity, specimens exposed to an artificial single climate change, specimens exposed to cyclic climate change and for specimens exposed to natural climate outdoors under shelter. Results for seasoned specimens show that internal stresses exist in glulam without the presence of moisture gradients. Stresses in specimens with an induced moisture gradient become larger when moistening from a specific climate A to another climate B than when drying from B to A. Tests in an outdoor sheltered climate show large variations in strains and stresses. The tensile stress level in the inner part of the glulam cross section exceeds the characteristic strength of 0.5 MPa during a period of approximately 80 days.

Climate Measurement and Modeling

1997 ◽  
Author(s):  
Douglas V. Hoyt ◽  
Kenneth H. Shatten
Keyword(s):  
Climate Change ◽  
Carbon Dioxide ◽  
Climate Variability ◽  
Atmospheric Carbon Dioxide ◽  
Climate Models ◽  
Climate Variations ◽  
Noise Sources ◽  
Earth’S Climate ◽  
Definition Of ◽  
Natural Climate

Having considered the sun and its variations, we now turn to Earth’s climate and climatic variations. We examine the definition of climate and the difficulties in measuring it. Awareness of these complexities is critical for an appreciation of how difficult it is to demonstrate changing climate. Separating trends from random variations is the first step in defining climate change. After reviewing the statistical properties of climate, we deal with theoretical climate models. This background is important for understanding how solar variations might affect climate. The following four chapters review specific sun/climate relationships, and the statistical and physical guidelines developed now will be used to select pertinent studies. As the heat source that drives Earth’s climate, the variable sun is important when studying climate change. With many, if not most, modern popular accounts focusing on how humanity is altering climate, it is important to realize that solar variations may play a significant role in the background natural variability. To understand anthropogenic (human-made) influences on climate change, we must be able to make distinctions among the contributions that arise from naturally occurring climate variability. Natural climate variations include a possible solar-irradiance component. Man-made climatic changes are not well known, and natural climate variations are uncertain too. For example, we do not know whether a man-made doubling of atmospheric carbon dioxide provides a 1.5 or a 4.5 °C increase in mean global temperature. This uncertainty arises, in part, because natural climate variability acts as “noise” to confuse our measures of man-made influences. To obtain accurate results, we must understand and remove these background noise sources. Although these temperature changes seem small, they can have tremendous global impact on the survivability of species and on many different aspects of life. In addition, the uncertainty factor of 3 is highly important because it tells us that the risk in emitting a quantity of carbon dioxide is uncertain by this same factor.

The Greenhouse Theory of Climate Change: A Test by an Inadvertent Global Experiment

Science ◽  
1988 ◽  
Vol 240 (4850) ◽  
pp. 293-299 ◽  
Author(s):  
V. RAMANATHAN
Keyword(s):  
Climate Change ◽  
Climate System ◽  
Radiative Heating ◽  
Climate Feedback ◽  
Interglacial Period ◽  
Climate Variations ◽  
Surface Warming ◽  
Historical Times ◽  
Natural Climate ◽  
Atmospheric Concentrations

Since the dawn of the industrial era, the atmospheric concentrations of several radiatively active gases have been increasing as a result of human activities. The radiative heating from this inadvertent experiment has driven the climate system out of equilibrium with the incoming solar energy. According to the greenhouse theory of climate change, the climate system will be restored to equilibrium by a warming of the surfacetroposphere system and a cooling of the stratosphere. The predicted changes, during the next few decades, could far exceed natural climate variations in historical times. Hence, the greenhouse theory of climate change has reached the crucial stage of verification. Surface warming as large as that predicted by models would be unprecedented during an interglacial period such as the present. The theory, its scope for verification, and the emerging complexities of the climate feedback mechanisms are discussed.

Absolute inner-shell cross section determination for EELS analysis

1988 ◽  
Vol 46 ◽  
pp. 534-535
Author(s):  
P.A. Crozier
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Absolute Cross Section ◽  
Specimen Thickness ◽  
Mass Thickness ◽  
Scattering Cross ◽  
Before And After ◽  
Estimated Error ◽  
Scattering Cross Sections ◽  
Electron Microscopist

Absolute inelastic scattering cross sections or mean free paths are often used in EELS analysis for determining elemental concentrations and specimen thickness. In most instances, theoretical values must be used because there have been few attempts to determine experimental scattering cross sections from solids under the conditions of interest to electron microscopist. In addition to providing data for spectral quantitation, absolute cross section measurements yields useful information on many of the approximations which are frequently involved in EELS analysis procedures. In this paper, experimental cross sections are presented for some inner-shell edges of Al, Cu, Ag and Au.Uniform thin films of the previously mentioned materials were prepared by vacuum evaporation onto microscope cover slips. The cover slips were weighed before and after evaporation to determine the mass thickness of the films. The estimated error in this method of determining mass thickness was ±7 x 107g/cm2. The films were floated off in water and mounted on Cu grids.

Research in the cross-section of community psychology and global climate change: A call for action

2009 ◽  
Author(s):  
Marci Culley ◽  
Holly Angelique ◽  
Courte Voorhees ◽  
Brian John Bishop ◽  
Peta Louise Dzidic ◽  
...  
Keyword(s):  
Climate Change ◽  
Cross Section ◽  
Global Climate Change ◽  
Community Psychology ◽  
Global Climate ◽  
The Cross

Experimental Investigation of Finger Dynamics Before and After Metacarpophalangeal Joint Arthroplasty

2006 ◽  
Vol 31 (2) ◽  
pp. 228-235 ◽  
Author(s):  
Bassem Elhassan ◽  
David Mcneal ◽  
Shawn Wynn ◽  
Mark Gonzalez ◽  
Farid Amirouch
Keyword(s):  
Experimental Investigation ◽  
Metacarpophalangeal Joint ◽  
Joint Arthroplasty ◽  
Before And After

Plane turbulent jets in a bounded fluid layer

1992 ◽  
Vol 241 ◽  
pp. 587-614 ◽  
Author(s):  
T. Dracos ◽  
M. Giger ◽  
G. H. Jirka
Keyword(s):  
Experimental Investigation ◽  
Cross Section ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Two Dimensional ◽  
Vortical Structures ◽  
Secondary Currents ◽  
Fluid Layers ◽  
Bounding Surfaces

An experimental investigation of plane turbulent jets in bounded fluid layers is presented. The development of the jet is regular up to a distance from the orifice of approximately twice the depth of the fluid layer. From there on to a distance of about ten times the depth, the flow is dominated by secondary currents. The velocity distribution over a cross-section of the jet becomes three-dimensional and the jet undergoes a constriction in the midplane and a widening near the bounding surfaces. Beyond a distance of approximately ten times the depth of the bounded fluid layer the secondary currents disappear and the jet starts to meander around its centreplane. Large vortical structures develop with axes perpendicular to the bounding surfaces of the fluid layer. With increasing distance the size of these structures increases by pairing. These features of the jet are associated with the development of quasi two-dimensional turbulence. It is shown that the secondary currents and the meandering do not significantly affect the spreading of the jet. The quasi-two-dimensional turbulence, however, developing in the meandering jet, significantly influences the mixing of entrained fluid.

The Analysis of Reinforcing the Bottom Chord around the Tapped Holes Based on the Thermosetting Resin Composite Materials

2012 ◽  
Vol 531 ◽  
pp. 609-612
Author(s):  
Xue Dong Han ◽  
Li Wei ◽  
Gang Luo ◽  
Li Ping Chang
Keyword(s):  
Composite Material ◽  
Resin Composite ◽  
Steel Bridge ◽  
Stress Distributions ◽  
Element Analysis ◽  
Steel Truss Bridge ◽  
The Finite Element Analysis ◽  
Before And After ◽  
Truss Bridge

The intensity of the joint in the bottom chord would affect the quality of the whole bridge because that the force of the bottom-through bridge is transferred mainly through the bottom chord, and the members of the truss connect each other by using the thread. In this paper, the bottom chord around the tapped holes is reinforced by composite material , and the stress on the bottom chord is analyzed before and after the reinforcement using the finite element analysis method, and the stress distributions in the directions of X,Y and Z on every layer of the composite material under the bilateral reinforcing condition are extracted and compared. The results show that: Reinforcing the bottom chord around the tapped holes using the composite material can change the stress level of the bottom chord effectively, helping to improve the quality of the construction of the steel bridge and the effect of the bilateral reinforcing is better than the unilateral reinforcing and providing certain reference for the security of the steel truss bridge

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