1.1 GENERAL
Steel products are extensively used in Buildings, Industries, Bridges, Transmission line towers, etc, because of its light weight and high strength to weight ratio, resulting in the reduction of dead weight.
The two main groups of structural steel members are hot rolled steel structural members & Cold formed steel members.
The use of hot rolled steel sections becomes uneconomical for the steel subjected to light and moderate loads and for the structural members of short span lengths (e.g purlins, roofs trusses, storage racks, complete framing of one and two storey residential commercial and industrial structures). So cold formed steel sections have gained considerable prominence over hot rolled sections.
1.2 LATTICED STEEL MEMBERS
Light weight steel constructions plays an important role in Industrial structures due to their economy and the ease and speed with which they can be fabricated and erected. One of the efficient ways of using structural steels in light weight construction in by means of latticed members. The latticed members have high strength – weight ratio, because they resist loads by truss action. The latticed steel members results in economic type of construction.
In these, as the chords are kept apart, the radius of gyration will be larger and hence the radius of gyration for unit weight of materials used is higher than that conventional section. As a circular bar is very stiff torsionally and flexurally and when they used as the system of web elements continuously bent and welded to main chords which are also continuous provide a high torsional and flexural stiffness at joints. Though the open web section result in economic type of construction, presently use of such member in construction is very limited because of the complexity involved in the analysis and lack of understanding of the behaviour of such section. Further in the case open section since shear centre does not coincide with the centre of gravity such sections are subjected to multiple modes-distortional, flexural and flexural torsional buckling. Long column fail in flexural or flexural torsional buckling and short column in distortional buckling.
1.4. Scope of the Investigation
This thesis attempts to study behaviour of latticed column under compression.
Past Experiments results & conclusions have been studied.
Ansys software and theoretical results have to be compared for different geometrical section and to present design methodology.
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3.2 MODULUS OF ELASTIC FOUNDATION
The modulus of the elastic foundation, equivalent to the elastic resistance of the web elements is calculated, by establishing the relation between the force or applied at the joints (Web elements and main chords) and the deflection that would be provide if the chord at the free end is removed.
δ = [RL13] / (3E1I1] ---------------
Where I1 = moment of inertia of the web elements
E1 = young’s modulus the web elements
L1 = length the web elements
δ = 1, R = 3E1I1 / l12 …………. (16)
and spring constant Rw = 2R since two diagonals meet at a joint.
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2. REVIEW OF LITERATURE
ENGESSER has done an investigations for the buckling of latticed column. The effect of shear on critical load of a solid section was investigated by engesser & is given.
Pcr = Pe / 1 + n(Pe/AG) (1)
Where pcr is the Euler critical load
N is a numerical factor depending on the shape of the cross section.
A is the total cross sectional area
G is the modulus of rigidity
A laced compression member considering the deflection due to shear of lacings also has been dealt by Engesser.
TIMOSHENKO and GERE have developed an interaction equation and presented a graph for torsional-flexural critical load for cross-sections with on axis of symmetry further they investigated for combined torsional and flexural buckling of a bar with continuous elastic supports and on torsional buckling under thrust and end moments. They have given a modified shear equation for the effect of shear on critical load of a solid section and presented a graph for critical compressive force. The critical web for a laced compression member considering the deflection due to shear of lacings also has been dealt by them.
CHAJES AND WINTER have presented a simple method to account for the torsional flexural buckling of thin-walled linear elastic compression with singly symmetric section subjected to axial loading. The solution of equilibrium equation to determine torsional flexural buckling load is presented in an interaction form.
PEKOZ AND WINTER have presented the behaviour of thin-walled singly symmetric open section under eccentric axial loading in the plane of symmetry.
GANAPATHY CHETTIAR has made an attempt to evolve a method of analysis for strength, deflection and stability of plane and spatial latticed members.
MULLER BRESLAU has made an assumption and analyzed that the flange are continuous and connected by pin joined diagonal members.
CONCLUSION: by this it is clear that the cold steel is economically
important than tne ordinary steel in heavy
constructions like bridge constructions..
..........THANK YOU...........
26th February 2008, 11:21 am