Steel Structures - Building technology.pptx

Steel Structures

1. STEEL STRUCTURES

2. STEEL STRUCTURES Steel construction is most often used in High rise buildings because of its strength, low weight, and speed of construction. Long span Structures such as Sports Stadiums, airport terminal, Bridges and other Infrastructure. • Industrial buildings & warehouses because of its ability to create large span spaces at low cost Residential buildings in a technique called light gauge steel construction, also because of its speed of construction. Temporary Structures as these are quick to set up and remove

3. STEEL STRUCTURES

4. STEEL STRUCTURES

5. ADVANTAGES OF STEEL STRUCTURES Strength - Most steel construction is done with Mild steel . Mild steel is a material that is immensely strong. Speed of construction - They are super-quick to build at site, as a lot of work can be pre-fabricated at the factory. Flexible - which makes them very good at resisting dynamic (changing) forces such as wind or earthquake forces. Plasticity or ductility - This means that when subjected to great force, it will not suddenly crack like glass, but slowly bend out of shape or deform , thus giving warning to inhabitants to escape. Structural Stability - Failure in steel frames is not sudden - a steel structure rarely collapses Earthquake resistant - Steel in most cases performs far better in earthquake than most other materials because of these properties. Less Raw material - Because of the high strength grade of steel, this structure requires less raw materials than other types of structure like concrete structure and timber structure.

6. ADVANTAGES OF STEEL STRUCTURES They can be made to take any kind of shape , and clad with any type of material. Multiple joining methods - A wide range of joining methods is available, such as bolting, welding, and riveting. Light weight Construction – Consider a single storey building measuring 5 x 8m . Let us first construct this in concrete , with four columns at the corners, beams spanning between the columns, and a 150mm thick concrete slab at the top. Such a structure would weigh about 32 Tons (32,000 kg) in total . If we build this of steel instead , with a sloping roof covered with corrugated metal sheeting with insulation, this would weigh only about only 2.6 Tons (2,600 kg). So the concrete building is over 12 times heavier ! This is for single storey structures - in multi-storey structures, the difference will be less, as the floors in multi-storey steel buildings are built of concrete slabs for economy - but the difference is still significant.

7. DISADVANTAGES OF STEEL STRUCTURES They lose strength at high temperatures, and are susceptible to fire . At 500 degrees Celsius (930 degrees F), mild steel can lose almost half its strength. This is what happened at the collapse of t he World Trade Towers in 2001 They are prone to corrosion in humid or marine environments.

8. STEEL AS A MATERIAL Steels is an alloys of Iron in which iron is mixed with carbon and other elements. Steels are described as Low, medium- or high-carbon steels according to the percentage of carbon they contain, although this is never greater than about 1.5%. Around 3500 different grades of steel are available. Type of steel - Percentage of carbon Low Carbon Steel (Mild steel) - Up to 0.25% Medium carbon steel - 0.25% to 0.45% High carbon steel - 0.45% to 1.50% Based on Manufacturing Process steel sections are known as - Hot rolled sections Cold Rolled sections.

9. STEEL MANUFACTURING PROCESS

10. ROLLED STEEL SECTIONS The steel sections manufactured in rolling mills and are casted in continuous casting molds without any joints . Steel sections are named according to their cross sectional shapes. Regular steel sections - sections are readily available in the market and have frequent demand Special sections - sections which are rarely used and are produced on special requisition. ‘ISI Handbook for Structural Engineers’ gives nominal dimensions, weight and geometrical properties of various rolled structural steel sections. Different shapes or forms of rolled steel sections are explained below – Angle Sections (Equal Angles and Unequal Angles) Channel Section T section I Section Round bars Square bars Flat bars Hollow Sections Corrugated sheets Expanded metal Plates Ribbed bars (mild steel)

11. ROLLED STEEL SECTIONS ANGLE SECTION : Angle sections are widely used for roof truss constructions and for filler joist floors. Equal angle sections are available from 20 mm x 20 mm x 3 mm to 200 mm x 200mm x 25 mm with their corresponding weights as 9 N (0. 9 KG) and 736 N ( 73 . 6 KG) per meter length respectively.. Unequal angle sections are available from 30 mm x 20 mm x 3 mm to 200mm x 150mm x 18mm with 11 N and 469 N per meter length weight respectively.

12. ROLLED STEEL SECTIONS CHANNEL SECTION : The channel section or C- section consists two equal flanges connected to web at both ends. Channel sections are extensively used in steel framed structures. They are available in various sizes ranging from 100 mm x 45 mm to 400mm x 100 mm. Corresponding unit weights are 58 N and 494 N per meter length respectively. I SECTION : Also called as steel beams or rolled steel joist Used as beams, lintels, columns etc. It consists two flanges and a web. These are available in various sizes ranges from 75 mm x 50 mm at 61 N per meter length to 600 mm x 210 mm at 995 N per meter length.

13. ROLLED STEEL SECTIONS T SECTION : Used in steel roof trusses to form built up sections. Two angle sections can also be joined to get T section. Rolled T sections size varies from 20 mm x 20 mm x 3 mm to 150 mm x 150mm x 10 mm with 9 N and 228 N as their corresponding weights per meter length. ROLLED STEEL PLATES: They are used for connecting steel beams, tensional member in roof truss etc. They are designated with their thickness which is varying from 5 mm to 50 mm.

14. ROLLED STEEL SECTIONS ROLLED ROUND BARS : Used as reinforcement in concrete and steel grill work etc. Available in various diameters varies from 5 mm to 250 mm. ROLLED SQUARE BARS : Used for gates, windows, grill works etc. Sides of square cross section ranges from 5 mm to 250 mm. ROLLED FLAT BARS : Flat bars are also used for gates, windows, grill works etc. Width of the bar varies from 10 mm to 400 mm. thickness of flat bars will be from 3 mm to 40 mm.

15. Hollow sections- Rectangular hollow sections Square hollow sections Tube sections

16. ROLLED STEEL SECTIONS CORRGATED SHEETS: Plain steel sheets are passed through machines which produce bends by pressing them called corrugations. These sheets are used for roof coverings. EXPANDED METAL : Expanded metal sheets are made from mild steel sheets Which are cut through machine and expanded. Generally, Diamond shaped mesh is appeared in this type of sheets

17. COMPOUND AND BUILT UP SECTIONS Compound sections are formed by : 1. Strengthening a rolled section such as a universal beam by welding on cover plates. 2. Combining two separate rolled sections, as in the case of the crane girder: The two members carry loads from separate directions. Compound Beams Crane Girder Built Up sections: Built-up sections are made by welding plates together to form I, H or box members that are termed plate girders, built-up columns, box girders or columns, respectively. These members are used where heavy loads have to be carried and in the case of plate and box girders where long spans may be required.

18. COLD ROLLED OPEN SECTIONS Thin steel plates can be formed into a wide range of sections by cold rolling. The most important uses for cold-rolled open sections in steel structures are for purlins, side and sheeting rails. Three common sections – the zed, sigma and lipped channel are shown. Z Section Sigma Section Lipped Channel Section

19. CASTELLATED BEAMS Castellated comes from a Latin word that meant: to structurally fortify. Castellated beam has a regular pattern of holes (circular, hexagonal or octagonal) in its web and made from hot rolled section, which is first divided by a lengthwise cut into two halves following a special pattern, then welded together to increase its depth. Sometimes additional flats are used between two web cuts for even further deeper section.

20. ADVANTAGES OF CASTELLATED BEAMS Higher load bearing capacity at same beam weight. Light weight compared to conventional wide flange beam section. Typically longer spans with fewer columns MEPs can integrate. Can lower floor-to-floor height by integrating MEP runs. Faster construction. Less material is required, result on light weight foundations, hence economical.

21. METHODS OF CONNECTION IN STEEL WORK The various members of steel framed structure are to be suitably connected for transfer of load. Following are the methods adopted for connecting the members in steelwork Bolts Rivets Welding CONNECTIONS - BOLTS Bolting is common in field connections, since it is simple and economical to make. Bolting is also regarded as being more appropriate in field connections from considerations of safety. Bolts used in steel structures are of three types Black Bolts Turned and Fitted Bolts and High Strength Friction Grip (HSFG) Bolts.

22. CONNECTIONS - RIVETS Rivets generally are made of low carbon steel. Riveting is used To avoid after thermal effects, as in case of welding Used for metals which have poor weldability Used for heterogeneous materials like asbestos friction lining and steel. Types of Rivets Advantages of riveted joints : Cheaper fabrication cost Low maintenance cost Dissimilar metals can also be joined, even non-metallic joints are possible with riveted joints. Ease of riveting process. Disadvantages of riveted joints: Skilled workers required Leakage may be a problem for this type of joints, but this is overcome by special techniques.

23. Types of Riveting Hot Riveting Cold Riveting Hand Riveting Machine Riveting According to the position of plates connected riveted joints are classified into two types: Lap joint: In a lap joint the edges of plates are simply laid over each other and riveted. Butt joint: In Butt, joint plates lie in the same plane and joined through cover plates. CONNECTIONS - RIVETS

24. CONNECTIONS - WELDING There are five different types of welded joints Butt joint : In Butt welded type, the parts lie in the same plane and are joined at their edges. Corner joint : The parts in a corner joint form a right angle and are joined at the center of the angle. Lap joint : Lap joint consists of two overlapping parts. Tee-joint : In a Tee-joint, one joint is the right angle to the other joint in the approximate shape of the letter “T”. Edge joint: The parts in edge joint are parallel with at least one of their edges in common and the joint is made at the common edge(s).

25. CONNECTIONS - WELDING

26. STEEL CONNECTION Design of connections is an integral and important part of design of steel structures. They are also critical components of steel structures, since They have the potential for greater variability in behavior and strength. They are more complex to design than members They are usually the most vulnerable components, failure of which may lead to the failure of the whole structure. Many types based on function Column to Base Plates to foundation Column-to-Column Connections Column to Beam Beam-to-Beam Connections

27. STEEL CONNECTIONS – COLUMN TO BASE

28. STEEL CONNECTIONS – COLUMN TO COLUMN

29. CONNECTIONS – COLUMN TO BEAM

30. STEEL CONNECTIONS – BEAM TO BEAM

31. STEEL CONNECTIONS – BRACING Bracings are additional elements added to a frame in order to increase its ability to withstand lateral loads . It consists of diagonal braces located in the plane of the frame. Ends of the brace join at the end points of other framing members to form a truss, creating a stiff frame. Concentric bracing may be arranged in several different configurations – such as X, K or one- directional diagonal bracing – and the bracing members may be designed to act in tension or compression or both.

32. COMPOSITE SLABS OR METAL DECK FLOORING Compressive strength of Concrete and Tensile strengths of Metal deck are utilized efficiently to form composite slabs. Metal deck flooring is much stiffer and stronger than many other flooring systems, so the weight and size of the primary structure along with project cost can be reduced. Rapid speed of construction, reducing overall project time. Provides the tensile reinforcement requirements of the slab Integral ceiling and service fixing system The decking acts as permanent shuttering Can achieve up to 4hr fire rating for the slab

33. COMPOSITE SLABS OR METAL DECK FLOORING

34. WALLS – USING BUILDING BLOCKS / CONCRETE BLOCKS

35. FIRE SAFETY IN STEEL STRUCTURES

36. FIRE SAFETY IN STEEL STRUCTURES

37. PORTAL FRAMES They are commonly used to create wide-span enclosures. They tend to be lightweight. It can be fabricated off site, and then bolted a sub-structure. Material used for portal frame is steel or steel reinforced precast concrete. Portal frame is simplest form of structure which is characterized by a beam (or supported) at either end of column. Portal frames can be defined as rigid frames that have the basic character of a rigid joint between column and beam. Joints are made 'rigid' by adding a haunch, bracket, or by a deepening of the section at the joints. A secondary framework of purlins fixed to the rafters & rails fixed to the column provides support for cladding. Portal frame structures are often clad with prefabricated composite metal panels, incorporating insulation, masonry cladding may be provided at low level to give greater resilience & security.

38. PORTAL FRAMES ADVANTAGES OF PORTAL FRAME Less members & hence faster & easy erection at site. Less load at foundation due to pin joints and Economical. Site welding is almost eliminated. It is easy to fabricate at shop and transport. DISADVANTAGES OF PORTAL FRAME Large sectional members will physically & visually obstruct. Costlier for small spans. For erection heavier cranes are required. Not much flexibility in arrangements & heavier loads may not be suitable.

39. PORTAL FRAMES TYPES OF PORTAL FRAME Duo-pitch portal frame. Mono-pitched portal frame. Curved portal frame. Portal with crane. Portal frame with mezzanine. Two span portal frame. Tied portal frame.

40. PORTAL FRAMES