COLD FORMED STEEL STRUCTURES

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COLD FORMED STEEL STRUCTURES

Transcript of COLD FORMED STEEL STRUCTURES

  • COLD FORMED STEEL STRUCTURES

    LECTURES PREPARED BY:PROF. DR. Abdelrahim Khalil Dessouki

    Lecture 1

  • Cold-Formed Steel Structures

    Introduction. Stability of plates & thin elements under different

    stresses. Post buckling behavior of plates. Effect of local buckling on the overall stability of

    the member. Design of cold formed members to resist Axial

    tension, Axial compression, Simple bending and Combined Action of Axial Force and Bending Moment.

    Course outline:

  • Cold-formed steel

    Formerly the use of cold-formed thin-walled steel sections was mainly confined to products where weight saving was of prime importance, e.g. in the aircraft, railway and motor industries. Simple types of cold-formed profiles (mainly similar to hot-rolled shapes), as well as profiled sheeting, have also been used as non-structural elements in building for about one hundred years.

    Introduction

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • Cold-formed steel

    Systematic research work, carried out over the past four decades, as well as improved manufacturing technology, protection against corrosion, increased material strength and the availability of codes of practice for design, have led to wider use of cold-formed sections within the building industry. In many countries cold-formed steel construction is the fastest growing branch of the structural steel market.

    Introduction continued

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • Typical Products and Uses

    Cold-formed sections are prismatic elements, of constant sheet thickness, formed by a sequence of plane sub-elements and folds in order to perform specific load bearing functions for members and also sometimes a space-covering function (see Figures).

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • More Typical Products and Uses

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • Historical Review

    The research for utilizing stainless steel in building structureswas due to the advancement of cold-formed steel, especiallyin the USA, by G. Winter and his followers, which resulted in adesign manual "Design of Cold Formed Stainless SteelStructural Members -Proposed Allowable Stress DesignSpecification with Commentary". On the other hand, researchon structural stainless steel for building use dates back only tothe late 1980's growth of economy, when the researchers andengineers intended to use stainless steel in heavy steelconstructions. This led to the Establishment of specification ofdesign and construction of heavy stainless steel structures.

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • AdvantagesThe use of cold-formed structural members offers many advantages over construction using more standard steel elements:

    the shape of the section can be optimized to make the best use of the material.

    there is much scope for innovation (in practice this has proved to be very significant).

    cold-formed members combined with sheeting offer economic and reliable solutions which provide a space-covering function and lateral restraint against buckling. Light-weight industrial buildings constructed form cold-formed members and sheeting are an example of the combination of these two effects (Figure 4).

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • Applications

    Aerospace Metal BuildingSpar-webs in Aircraft Wing Main Frame Elements

    Lecture Notes By: Prof. Dr. Nabil El-Atrouzy

  • Cold-formed steelapplications in the construction industry.

  • Linear Method for Computing Propertiesof Formed Sections

    If the thickness of the formed section is uniform, thecomputation of properties of such sections can be simplified by using a linear or midline method. In this method the material of the section is considered to be concentrated along the centerline or midline of the steel sheet and the area elements are replaced by straight or curved line elements. The thickness dimension t is introduced after the linear computations have been completed. Thus the total area A = L t and the moment of inertia of the section I = I t, where L is the total length of all line elements and I is the moment of inertia of the centerline of the steel sheet. The properties of typical line elements are shown in Fig. below:

  • Example 1.1 Determine the full section modulus Sx of the channel section shown in Fig. below. Use the linear method.

    1. Flat width of flanges (element 1):Lf = 1.5 0.292 = 1.208 in.

    2. Distance from xx axis to centerline of flange:3.0 0.105/2 = 2.948 in.

    3. Computation of properties of 90 corner (element 2)R = 0.1875 +0.105/2 = 0.240 in.Lc = 1.57 (0.240) = 0.377 in. C = 0.637 (0.240) = 0.153 in.

    4. Flat width of web (element 3):Lw = 6.0 2(0.292) = 5.416 in.

    5. Distance from xx axis to centerof gravity (c.g.) of corner:y = 5.416/2 + 0.153 = 2.861 in.

  • 6. Linear Ix , moment of inertia of midlines of steel sheets:Flanges: 2(1.208)(2.948)2 = 21.00Corners: 2(0.377)(2.861)2 = 6.17Web: 1/12 (5.416)3 = 13.24

    Total: 40.41 in.37. Actual Ix:

    Ix = Ix t = 40.41(0.105) = 4.24 in.4 8. Section modulus:

    Sx =Ix/(d/2) =4.24/3.0 = 1.41 in.3

    The accuracy of the linear method for computing the properties of a given section depends on the thickness of the steel sheet to be used and the configuration of the section. For the thicknesses of steel sheets generally used in cold-formed steel construction, the error in the moment of inertia determined by the linear method is usually negligible. The expected errors is less than 1% if the material is 1/4 in. or thinner.

    COLD FORMED STEEL STRUCTURESCold-Formed Steel Structures Cold-formed steelCold-formed steelTypical Products and Uses More Typical Products and Uses Historical Review Advantages Applications Cold-formed steelapplications in the construction industry.