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Structural analysis comprises the set of physical laws and mathematics required to study and predict the behavior of structures. The subjects of structural analysis are engineering artifacts whose integrity is judged largely based upon their ability to withstand loads; they commonly include buildings, bridges, aircraft, ships and cars. Structural analysis incorporates the fields of mechanics and dynamics as well as the many failure theories. From a theoretical perspective the primary goal of structural analysis is the computation of deformations, internal forces, and stresses. In practice, structural analysis can be viewed more abstractly as a method to drive the engineering design process or prove the soundness of a design without a dependence on directly testing it.
Structures and Loads
A structure refers to a system of connected parts used to support a load. Important examples related to Civil Engineering include buildings, bridges, and towers; and in other branches of engineering, ship and aircraft frames, tanks, pressure vessels, mechanical systems, and electrical supporting structures are important. In order to design a structure, one must serve a specified function for public use, the engineer must account for its safety, esthetics, and serviceability, while taking into consideration economic and environmental constraints.
Classification of Structures
It is important for a structural engineer to recognize the various types of elements composing a structure and to be able to classify structures as to their form and function. Some of the structural elements are tie rods, rod, bar, angle, channel, beams, and columns. Combination of structural elements and the materials from which they are composed is referred to as a structural system. Each system is constructed of one or more basic types of structures such as Trusses, Cables and Arches, Frames, and Surface Structures.
Once the dimensional requirement for a structure have been defined, it becomes necessary to determine the loads the structure must support. In order to design a structure, it is therefore necessary to first specify the loads that act on it. The design loading for a structure is often specified in codes. There are two types of codes: general building codes and design codes, engineer must satisfy all the codes requirements for a reliable structure. There are two types of loads that structure engineering must encounter in the design. First type of load is called Dead loads that consist of the weights of the various structural members and the weights of any objects that are permanently attached to the structure. For example, columns, beams, girders, the floor slab, roofing, walls, windows, plumbing, electrical fixtures, and other miscellaneous attachments. Second type of load is Live Loads which vary in their magnitude and location. There are many different types of live loads like building loads, highway bridge Loads, railroad bridge Loads, impact loads, wind loads, snow loads, earthquake loads, and other natural loads.
To perform an accurate analysis a structural engineer must determine such information as structural loads, geometry, support conditions, and materials properties. The results of such an analysis typically include support reactions, stresses and displacements. This information is then compared to criteria that indicate the conditions of failure. Advanced structural analysis may examine dynamic response, stability and non-linear behavior.
There are three approaches to the analysis: the mechanics of materials approach (also known as strength of materials), the elasticity theory approach (which is actually a special case of the more general field of continuum mechanics), and the finite element approach. The first two make use of analytical formulations which apply mostly to simple linear elastic models, lead to closed-form solutions, and can often be solved by hand. The finite element approach is actually a numerical method for solving differential equations generated by theories of mechanics such as elasticity theory and strength of materials. However, the finite-element method depends heavily on the processing power of computers and is more applicable to structures of arbitrary size and complexity.
Regardless of approach, the formulation is based on the same three fundamental relations: equilibrium, constitutive, and compatibility. The solutions are approximate when any of these relations are only approximately satisfied, or only an approximation of reality.
Each method has noteworthy limitations. The method of mechanics of materials is limited to very simple structural elements under relatively simple loading conditions. The structural elements and loading conditions allowed, however, are sufficient to solve many useful engineering problems. The theory of elasticity allows the solution of structural elements of general geometry under general loading conditions, in principle. Analytical solution, however, is limited to relatively simple cases. The solution of elasticity problems also requires the solution of a system of partial differential equations, which is considerably more mathematically demanding than the solution of mechanics of materials problems, which require at most the solution of an ordinary differential equation. The finite element method is perhaps the most restrictive and most useful at the same time. This method itself relies upon other structural theories (such as the other two discussed here) for equations to solve. It does, however, make it generally possible to solve these equations, even with highly complex geometry and loading conditions, with the restriction that there is always some numerical error. Effective and reliable use of this method requires a solid understanding of its limitations.
Strength of materials methods (classical methods)
The simplest of the three methods here discussed, the mechanics of materials method is available for simple structural members subject to specific loadings such as axially loaded bars, prismatic beams in a state of pure bending, and circular shafts subject to torsion. The solutions can under certain conditions be superimposed using the superposition principle to analyze a member undergoing combined loading. Solutions for special cases exist for common structures such as thin-walled pressure vessels.
For the analysis of entire
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Answers:There are several levels of structure in studying a leaf. A leaf attached to the tree at a node. The stalk that attaches the leaf to the tree is the petiole which extend into the midrib of the leaf called the rachis. There may be a pair of extensions from the base of the petiole called stiplules. Many veins branch off the rachis. The flat part of the leaf is called the blade. There are many shapes of leaves and different margins. If you take a section of the leaf, you would find the following tissue layers from top to the bottom of the leaf: upper epidermis covered with a waxy cuticle, palisade mesophyll and spongy mesophyll in which the photosynthesis occurs, a lower epidermis perforated with numerous holes called stomata. The stomata are surrounded by guard cells that can open and close. The stomata allow gas exchange (carbon dioxide in and oxygen and water vapor out). There will be cross sections of veins as well. In the vein, there will be xylem carrying water and minerals at the top of the vein with phloem on the bottom of the vein. The structure of the leaf allows for maximum absorption of sunlight for photosynthesis.
Answers:For more on the subject please click on the link below. Section 6.3 Basic Forms of Organizational Structure Informal Organization Key Terms Functional organization Divisional organization Divisions Matrix structure International organizational structure Informal organization Grapevine Intrapreneuring Section Outline I. Basic Forms of Organizational Structure A.Functional B.Divisional C.Matrix D.International E.Boundaryless, team, virtual, and learning organizations II. Informal Organization A.Informal groups and the use of grapevine communication B.Intrapreneuri http://wps.prenhall.com/bp_ebert_be_5/0,8774,1161250--1161317,00.html Kev, Liverpool, UK.
Answers:Guard cells are used to let gas exchange in a plant and helps water up the stem (cohesion and capillary action).They look like elongated curved cells connected at the tips. The guard cells line a hole in the leaf (stomata) To regulate gas exchange and water loss/retention, the guard cells must be able to open and close. That's why the cells are curved. When the cells are turgid - filled with water - the cells become curved and leave a hole in the leaf. This is because the plant is able to to lose some water for for gas exchange to keep photosynthesis/cell respiration running. However, when water is scarce, water leaves the guard cells, which then become limp and close the hole. This retains water, but the plant holds in waste gasses. In short, plants use their stomata to help regulate internal conditions. The plant also uses ions to make the guard cells turgid/limp. (water potential) Plants in the desert (ex. CAM plants) have different adaptations that deal with the plant's structure and when to open up the stomata.
Answers:Do both! External - flat & thin, absorb lot of light, rapid diffusion of gases. Internal - most chloroplasts in palisade cells, closer to light, palisade cells closely packed, shape of palisade cells transparent cell walls air spaces in spongy mesophyll.