CE 8601/ DESIGN OF STEEL STRUCTURAL ELEMENTS UNIT I INTRODUCTION AND ALLOWABLE STRESS DESIGN Structural steel types – Mechanical Properties of structural steel- Indian structural steel products-Steps involved in the Deign Process -Steel Structural systems and their Elements- -Type of Loads on Structures and Load combinations- Code of practices, Loading standards and Specifications - Concept of Allowable Stress Method, and Limit State Design Methods for Steel structures-Relative advantages and Limitations-Strengths and Serviceability Limit states. Allowable stresses as per IS 800 section 11 -Concepts of Allowable stress design for bending and Shear –Check for Elastic deflection-Calculation of moment carrying capacity –Design of Laterally supported Solid Hot Rolled section beams-Allowable stress deign of Angle Tension and Compression Members and estimation of axial load carrying capacity. PART-A (2 marks) 1. What are the types of steel available? o wrought iron – Carbon content: not greater than 0.15% o Steel - Carbon content: 0.15% to 1.5% o Cast iron - Carbon content :2% to 4% Based on carbon content o Mild steel – 0.15 to 0.25% o Medium carbon steel - 0.25 to 0.6% ( rail wheels) o High carbon steel - 0.6 to 1.5% 2. What are the structural steel sections available? o Angle sections o Channel sections o I-sections o T-sections o Flat sections o Steel plates o Corrugated sheets o Round bars o Square bars 3. What is meant by structural system? 1 Bridges, buildings, dams, transportation facilities, liquid or gas storage facilities, industrial factories and plants, power generation and transmission units 4. What are the basic structural elements? o Axially Loaded Members in Tension o Columns – Axially Loaded Members in Compression o Beams – Shear and Bending Moment o Planar Trusses – All Members Axially Loaded o Planar Trusses – All Members Axially Loaded o Arches – Direct Compression o Cables – Flexible Members in Tension o Rigid Frames o Plates or Slabs o Thin Shells 5. What are the properties of structural steel? o Density. Density of a material is defined as mass per unit volume. o Elastic Modulus. o Poisson's Ratio. o Tensile Strength. o Yield Strength. o Melting Point. o Specific Heat. o Hardness. 6. Which type of steel is most commonly used in general construction? Why? Mild Steel is most commonly used in general construction because of its durability and malleability 7. Define permissible stresses and Working stresses. Permissible stresses Permissible stresses = factor of safety / yield stress Working stresses: The stresses used in practical design are working stresses and they should never exceed the permissible stresses specified by codes. 8. How the rolled steel beams are classified? Indian Standard junior beams (ISLB) 2 Indian Standard light beams (ISLB) Indian Standard medium weight beams (ISMB) Indian Standard wide flange beams (ISWB) 9. What are the load combinations for the design purposes? Dead load + Imposed Load (Live load) Dead Load + Imposed Load + Wind Load or earthquake load Dead Load + Wind Load or Earthquake load 10. Mention the advantages and disadvantages of steel structures? Advantages: Ability to resist high loads Due to its high density, steel is completely non-porous Durability Easy to disassembling or replacing some steel members of a structure Disadvantages: Corrosion At high temperature steel loses most of its strength, leading to deformation or failure 11. What is meant by tensile stress? When a structural member is subjected to direct axial tensile load, the stress is known as tensile stress (σst). The tensile stress is calculated on net cross- sectional area of the member. σst=Pt/An Where, Pt is the direct axial tensile load and An is the net cross-sectional area of the member. 12. What is meant by compressive stress? When a structural member is subjected to direct axial compressive load, the stress is known as compressive stress (σsc). The compressive stress is calculated on gross cross-sectional area of the member. σsc = Pc/Ag Where, Pc is the direct axial compressive load and Ag is the gross-sectional area of the member. 13. Define bearing stress. 3 When a load is exerted or transferred by the application of load through one surface for another surface in contact, the stress is known as bearing stress ( σ p). the bearing stress is calculated on net projected area of contact. σp = (P/A) Where, P = load placed on the bearing surface 14. What is working stress? The working stress is also termed as allowable stress or permissible stress. The working stress is evaluated by dividing yield stress by factor of safety. For the purpose of computing safe load carrying of a structural member, its strength is expressed in terms of working stress. The actual stresses resulting in a structural member from design loads should not exceed working stress. 15. Define factor of safety. The factor of safety is defined as the factor by which the yield stress of the material is divided to give the working stress (permission stress) in the material. 16. What are the methods employed for the design of the steel framework? Simple design Semi-rigid design Fully rigid design Plastic design. 17. What are the assumptions made in simple design? o The beams are simply supported o All connections of beams, girders, or truss are virtually flexible and are proportioned for the reaction shears applied at the appropriate eccentricity o The members in compression are subjected to forces applied at the appropriate eccentricities. o The members in tension are subjected to longitudinal forces applied over the net area of the sections 18. Define Modulus of Elasticity The modulus of elasticity is defined as the ratio of longitudinal stress to the longitudinal strain within the elastic region; it is denoted by ‗E‘. 19. Define Poisson‟s Ratio. The Poisson‘s ratio is defined as the ratio of transverse strain to the longitudinal strain under an axial load. It is denoted by ‗μ‘ or 1/m. the value of Poisson‘s ratio for steel within the elastic region ranges from 0.25 to 0.33. 4 20. What are the steps involved in structural design? o Forces or loads o Structural arrangement and material selection o Analyzing internal stresses o Proportioning of members 21. What is meant by Allowable Stress Design? Allowable Stress Design (ASD) is also referred to as the service load design or working stress design (WSD). The basic conception (or design philosophy) of this method is that the maximum stress in a structural member is always smaller than a certain allowable stress in bridge working or service conditions. The allowable stress of a material determined according to its nominal strength over the safety factor. 22. What are the advantages and disadvantages of allowable stress design? Advantages: Elastic analysis for loads becomes compatible for design. Old famous books are according to this method. Experienced engineers are used to this method. In past it was the only method for design purposes. This method is included in AISC-05 specifications as an alternate method. Disadvantages: Same factor of safety is used for different loads. Latest research and literature is very limited. Failure mode is not directly predicted. With some overloading, the material stresses increase but do not go to collapse. The failure mode cannot be observed. The warning before failure cannot be studied precisely. Results cannot be compared with experimental tests up to collapse. 5 24. What is meant by limit state design? (IS800:2007-Pg: 28) Limit state design method is technologically sound method which results in significant economy in design of structures. The design of a structure to satisfy all appropriate requirements derived from probability considerations is referred to as a limit state design. 25. State the different limit states. (IS800:2007-Pg: 28) The limit states are broadly grouped in to two major types, namely: o Limit state of strength o Limit state of serviceability. 26. What are the four types of serviceability limit states applicable to steel structures? (IS800:2007-Pg: 28) Deflection Durability Vibration Fire resistance 27. Define durability. (IS800:2007-Pg: 2) It is defined as ability of the structure to maintain its level of reliability and performing the desired function in the working environment under exposure conditions, without deterioration of cross sectional area and loss of strength due to corrosion during its life span. 28. How the loads are classified? (IS800:2007-Pg: 4) Dead load Live load Earthquake load Wind load Dynamic loads. 29. What is a partial safety factor? (IS800:2007-Pg: 4). The safety of the structure depends on each of the two principal design factors namely, load and material strength, which are not the functions of each other. Each of the two factors contributes partially to safety and they are termed as partial safety factors. 30. Define design load. The partial safety factor for loads is a load factor which is multiplied to characteristic load, gives the design load. 6 Design load = γf x Characteristic load UNIT II CONNECTIONS IN STEEL STRUCTURES Type of Fasteners- Bolts Pins and welds- Types of simple bolted and welded connections Relative advantages and Limitations-Modes of failure-the concept of Shear lag-efficiency of joints- Axially loaded bolted connections for Plates and Angle Members using bearing type bolts –Prying forces and Hanger connection– Design of Slip critical connections with High strength Friction Grip bolts.-Design of joints for combined shear and Tension- Eccentrically Loaded Bolted Bracket Connections- Welds-symbols and specifications- Effective area of welds-Fillet and but Welded connections-Axially Loaded connections for Plate and angle truss members and Eccentrically Loaded bracket connections. Types of sections – Net area – Net effective sections for angles and Tee in tension – Design of connections in tension members – Use of lug angles – Design of tension splice – Concept of shear lag PART-A (2 marks) 1.