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Advanced analysis for structural steel
building design
Ms. Priya Kumari
1, Mr. Abhishek Arya
21
M.Tech Student, Dept. of Civil Engg., M.R.I.E.M., Rohtak
1
Asst. Professor, Dept. of Civil Engg., M.R.I.E.M., Rohtak
ABSTRACT
The 2005 AISC LRFD provision for Structural Steel Buildings are to make it possible for designer to be acquainted with plainly the structural resistance provided within the elastic and inelastic ranges of behavior and up to the greatest load limit state. There is an escalating awareness of the need for practical second-order analysis approach for a direct determination of overall structural system comeback. This paper tries to present a easy, brief and logically widespread introduction to some of the theoretical and practical approaches which have been used in the conventional and contemporary processes of design of steel building structures.
Keywords: advanced structure analysis, structural steel building design, introduction.
INTRODUCTION
The principle of structural design is to produce a physical structure capable of withstanding the environmental conditions to which it may be subjected. Many factors affect the design process, from loading to foundation to dimension lay out to risk and cost, but basically the ultimate design is a reflection of the properties of the structural material and the geometrical imperfection of its structural members, and in particular its mechanical properties and the residual stresses induced in the structural members during manufacturing and fabrication, which define the characteristic response of the material and the member to the environmental forces.
At present, in engineering design perform, there is a essential two-stage technique in the design operation: firstly, the forces which acts on each structural member in the structure must be intended; secondly, the loads who carry capacity of each of these structural members to those forces acting on it must be determined. The firstStage involve an examination of the sharing of forces and all the moments which act on each of these structural members; the second stage involve familiarity of the load carrying capacity of these members to counteract all of these forces and moments acting on them. The extra widespread this awareness, the more literal will be the design and the more consistent will be the structure.
Since we know that the the load carrying capacity of structural a member depend on the type of load acting on the member, geo-metrical imperfection, property of material and residual stress, the knowledge of load-carrying capacity of all structural members has been determined mostly on the basis of full scale tests in the form of pin-ended column strength curves for axially loaded member, simply sup-ported beam strength curve for bending dominated member, and beam-column interaction curve for members under combined axial force and bending moment. These ingredient strength curves are formally implied as the member strength curves or equations for design put into practice.
After dividing all the structural members in a framed structure into three classes, namely column, beam, and beam-column, and after determination their respective strength by full scale tests with perfect end or frontier circumstances, the subsequently stage must be to significantly simplify the material behavior under stress in such a way as to readily support the engineer in analyze the stress division in the structure in order to size up the structural members in a frame structure. At present, the practicing engineer bases design primarily on the simple model of linear elasticity of the material for those early designs. All title and author details must be in single-column format and must be cantered.
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the structure is weighted down only in the working load level. The large safety factor is therefore used to adjust the design to take into account inelastic facial appearance in the material to avoid failure. Most structural analyses in engineering practice have been based on linear elastic analysis. First-order linear elastic analysis has been the characteristic of structural engineering in early years, at the same time as the second-order linear elastic analysis for a structural System has been developed and is increasingly being utilized in current years.
First-order elastic structural analysis with K-factors
The boundary conditions of a framed member in a frame structure are relatively different from that of an out-of-the-way member that is used as the basis for the development of column strength curves (pin-pin end conditions) or beam strength curves (simply supported end conditions). In order to size up the framed member, the framed member boundary conditions must be in the swing of things to the the same pin-pin end conditions for the case of column design, for example, so that the column strength curves can be properly used in determining the required size of the framed member under contemplation (see Fig. 1).
Fig. 1: Interaction between structural system and its component members
43 have any resemblance whatever to the elastic buckle mode of the structural system that is the basis for the determination of the effective length factor K.
The second, and perchance the most serious restriction, is probably the rationale of the current two-stage process in design: elastic analysis is used for the determination of allotment of forces acting on each member of a structural system, whereas the member’s ultimate strength curves are developed for design either on the basis of full scale tests or by inelastic analysis with each member treated as an isolated component [2,3]. There is no verification of the compatibility between the isolated member and the member as part of a frame. The individual mem-ber strength equations as specified in specifications are not concerned with system compatibility. As a result, there is no explicit guarantee that all members will sustain their design loads under the arithmetical arrangement imposed by the framework.
The second, and perchance the most serious restriction, is probably the rationale of the current two-stage process in design: elastic analysis is used for the determination of allotment of forces acting on each member of a struc-tural system, whereas the member’s ultimate strength curves are developed for design either on the basis of full scale tests or by inelastic analysis with each member treated as an isolated component [2,3]. There is no verification of the compatibility between the isolated member and the member as part of a frame. The individual mem-ber strength equations as specified in specifications are not concerned with system compatibility. As a result, there is no explicit guarantee that all members will sustain their design loads under the arithmetical arrangement imposed by the framework.
Second-order elastic structural analysis with K-factors
The taking up of elastic structural analysis with K-factors for steel design may be divided into two stages of progress. The simplest first stage of progress with K-factors in the design process is the first-order elastic analysis with strengthening factors to include the second-order effects as generally provided by the specifications [4]. This is described in the preceding section. Logically, the next stage of progress is a direct second-order elastic analysis without the use of strengthening factors for second-order effects [4]. Both methods are based on the arrangement of first plastic hinge defined as the failure of the system.
As mentioned previously, the effective length factor will generally yield good designs for framed structures, but it does have some drawbacks also must be numbered using uppercase Roman numerals. Table captions must be centred and in 8 pt Regular font with Small Caps. Every word in a table caption must be capitalized except for short minor words as listed in Section III-B. Captions with table numbers must be placed before their associated tables, as shown in Table 1.
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Elastic and Plastic Behavior of Structural Members
Introduction to Elastic-Plastic Behaviour Attempts to systematically utilize and quantify reserve strength to overcome the shortcoming of classical elastic analysis were made as early as 1914 (Hayman 1998). Significant advances were made after the 1930s. The fundamental theorems available in the late 1940s to early 1950s (Horne 1950, Greenberg and Prager 1952) eventually provided a foundation for the widespread acceptance of the theory of plasticity. Plastic Versus Elastic Design of Steel Structures - Sutat Leelataviwat, Subhash C. Goel, Shih-H Chao ©Encyclopedia of Life Support Systems (EOLSS) Central to the idea of all plastic analysis methods is an implicit assumption that the structure being analyzed is made from ductile materials. Most civil engineering materials possess ductility to a certain degree. However, in this article, the discussion will be limited to steel. Ductile nature of steel makes it one of the most suitable candidates for plastic analysis. Figure 1.
44 beyond the elastic limit and to redistribute the loads to other parts of the structure that are less stressed. The effect of inherent ductility on the response of a simple structure.
CONCLUSIONS
On the basis of the present study, following conclusions are made: The second order effects found to increase the storey displacements at all level of the structure. Compare to the structure subjected to other than second order effects. The concept of using Steel bracing is one of the advantageous concepts to strengthen or to retrofit the existing structure. From the results was found that storey displacement of the building are greatly reduced by the use of Concentric (X) bracing in comparison to Eccentric bracings. The interstorey drifts greatly reduced in presence of Continuous bracing system in comparison to Alternative bracing even the second order or PDelta effects are considered. The displacement value for P-delta analysis is increases from 70 to 75% for Continuous type bracing and 85 to 95% for Alternative type bracing has compared to static analysis. The Axial Force for Continuous type in P-delta analysis is increase 22% has compared to static analysis. The value of Axial Force increased twice more for other bracings in case of P-delta analysis. The value of Axial Force for Alternative type in P delta analysis is twice more has compared to static analysis.
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