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EXPERIMENTAL AND

ANALYTICAL STUDY OF COLDFORMED STEEL SECTIONS

SUBMITTED BY

AMITKUMAR ASHOK SONAWANE

M TECH STRUCTURES

GUIDED BY

PROF K.K.SANGALE

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`Hot rolled steel

`Cold formed steel

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` Hot Rolled steel1.Yielding starts at actual yield

value as the original material.2. Unit weight is comparatively

huge

3. More ductile innature.

4.Most of the time, we consider

only the global buckling of themember.

5. Applicationin Load bearing

structures, usually heavy load

bearing structures and where

ductility is more important (

Example Seismic prone areas)

6. Research is in advanced stages

` Cold Rolled steel1.The yield value is increased by15%-30% due to prework.

2. It is much smaller.

3. Less ductile

4. Local buckling, DistortionalBuckling, Global Buckling have to

be considered.5.Applicationin many variety ofloading cases.This includesbuilding frames, automobile,aircraft, home appliances, etc. Uselimited in cases where high

ductility requirements.

6.More possibilities as the conceptis relatively new and material findswide variety of applications.

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` Change in the mechanical properties of the

material by virtue of the cold working.

` Yield strength, and to a lesser extent the ultimatestrength, is increased as a result of this cold

working particularly in the bends of the section.

` Strength increase could reach 20% to 50%.

` The ductility of the steel is reduced as result .

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` The use of cold-formed steel members in buildingconstruction beganin the 1850s.

` first edition of the Specification for the Design of LightGage Steel Structural Members was published by AISI

in1946.( Allowable stress design(ASD) Specification)

` It was revised subsequently in1956, 1960, 1962, 1968,1980, and 1986 to reflect the technical developments.

` In1991, AISI published the first edition of the load

and resistance factor design Specification.` Both ASD and LRFD Specifications were combined

into a single specificationin1996

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` In2001, the first edition of the North American

Specification for the Design of Cold-Formed Steel

Structural Members was developed.

` It was revised and expanded in2007.` This updated specificationincludes new and revised

design provisions with the additions of the Direct

Strength Method inAppendix 1 and the Second-Order

Analysis of structural systems inAppendix 2.

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` Design standards and recommendations are now

available in Australia, Austria , Canada,

Czechoslovakia , Finland , France , Germany ,

India , Japan , The Netherlands, New Zealand ,The Peoples Republic of China , The Republic of

South Africa , Sweden , Romania , U.K. , U.S. ,

USSR.

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` Applications in residential and other low-rise

buildings.

` Factory assembly ofprefabricated units.

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Author:Mahmood Md Tahir and Tan Cher Siang along with Shek Poi

Ngian

Proceedings of the 6th Asia-Pacific Structural Engineering and

Construction Conference (APSEC 2006), 5 6 September2006, Kuala

Lumpur, Malaysia

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` The Steel Technology Centre (STC), Universiti

Teknologi Malaysia has carried a ser ies of analytical

and exper imental research on cold-formed steelstructures. A series of research studies carried out in

UTM.

` Member capacities for lipped C-section and hat-

section.

` A full-scale test for roof truss system.

` Cold-formed steel tek-screw connection capacities.

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` Capacities of the proposed sections were ratio from

1.09- 2.21 compared to the design strength.

` The full-scale experimental test on roof truss alsoachieved two times of the estimated design capacities

` The tek-screw connection capacities in resistance to

shear force and pull-out force ranged 76%- 141%

higher than the design requirements.

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Author: DungM. Lue1, Ping-Tsung Chung, Jui-Ling Liu, and Chi-Ling

Pan

International Journal of Steel Structures

September2009, Vol 9, No 3, 231-240

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` The effective sectional area concept was adopted to

conduct the analysis.

` Study tested a total of21 channel specimens including

c-shaped cross-sections with and without web openings` Comparisons were made between the test results and

the predictions based on both the AISI standard and the

ANSYS analysis.

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1.Test specimen(65X45X10X1 mm & 92X45X10X1 mm)

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Setup of test

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Test results

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` The shell element (shell 93) of 3D, 8-node, and

homogenous materials was used for the structural

analysis.

` This element was used to simulate a 3-d entitystructure, which has the buckling analysis feature.

` Material property: the basis of the materials tension

test, its youngs modulus is 130,250 mpa.Moreover, its

yielding stress is 198 mpa and its poisson ratio isassumed to be 0.3.

` It is necessary to employ the nonlinear analysis.

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` The failure type of all specimens is observed and

identified as flexural-torsional buckling type.

` The experiment results indicated that the average

strength of specimen is slightly reduced caused bythe web openings.

` The average ratios of Ptest/PFEM prove that the FEM

is an efficient tool to predict the strength of

specimens.

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Author: B.W. Schafer*, T. Pekoz

Journal of Constructional Steel Research 47 (1998) 193210

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` Advanced computational modeling supplementsexperimental investigation.

` Accuracy of computational models relies significantlyon the characterization of selected inputs.

` No consensus exists on distributions or magnitudes tobe used for modelinggeometric imperfections and formodeling residual stresses of cold-formed steelmembers.

` Ideas are summarized in a preliminary set ofguidelinesfor computational modeling ofimperfections andresidual stresses.

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` Geometric imperfections refer to deviation of a

member from perfect geometry.

` Imperfections of a memberinclude bowing, warping,

and twisting as well as local deviations.` Local deviations are characterized by dents and regular

undulations in the plate.

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For type 2:

width/thickness

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` Computational modeling of residual stresses is

troublesome for analysts

` Residual stresses are often excluded altogether, or the

stressstrain behavior of the material is modified toapproximate the effect of residual stresses.

` Residual stresses are idealized as a summation of two

types: flexural and membrane.

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` Characterization of geometric imperfections and

residual stresses in cold-formed steel members is

possible.

`

Existing data on imperfections provides a limitedbut useful characterization of imperfection

magnitude

` Data on residual stresses provide insight into

appropriate selection of distribution andmagnitude.

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Author: B.W. Schafer

Fifth International Conference on Coupled Instabilities in Metal

Structures

Sydney, Australia, 23-25 June, 2008

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` Summarize Research and experiences with

computational modeling of cold-formed steel at Johns

Hopkins University.

`

Explains the importance ofimperfections, residualstresses, boundary conditions, element choice, element

discretizationin collapse modeling of cold-formed steel

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` Ultimate strength and post-buckling mechanisms are

both imperfection sensitive

` Imperfections are a modeling convenience (the most

common approach) then the distributionis typically thefirst buckling mode, and the magnitude is either a

function of the plate thickness (i.E., 0.1t) or the plate

slenderness.

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` In conventional models where residual stresses are ignoredThe vonMises yield criteria with isotropic hardeningisused universally.

Boundary Conditions:` Boundary conditions have an majorimpact on cold-formed

steel collapse modeling.` Boundary conditions in cold-formed steel systems are never

as clean as in the computational model, and are usually farmore complicated than would exist in laboratory testing aswell.

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The use of quadratic elements (e.g., S9R5) instead of linear elements gives more

accuracy in results.

Also number ofintegration points

through the thickness of the element needs to be taken care of.

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` Collapse modelinggenerally requires the use of

material and geometric nonlinear finite element

analysis.

`

Solution sensitivities depend on solvers, element choiceand discretization, boundary conditions, material

models, initial imperfections, initial residual stresses.

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` The objective of this project is to carry out

experimentation on cold formed steel sections and

verify experimental results with analytical

methods(computational modeling)

` Experimentation and analysis will be done for

slotted angle sections.

` Software's to be used for analysis ANSYS and

ABAQUS.

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