L3 Materials Topic 6 Steel Construction

SUBJECT : MATERIALS LEVEL 3 TOPIC: 6 ITEMOHELENG CAMPUS DISTANCE LEARNING 2020-MAY LECTURER: KHOSI MOHAPELOA ) Downloaded from hlayiso.com

TOPIC 6: STEEL CONSTRUCTION LEARNING OUTCOMES: • BEHAVIOUR OF MILD STEEL AND HIGH-TENSILE STEELS • DESIGN OF STEEL STRUCTURES IN PREFABRICATED SECTIONS AND ITS ASSEMBLY ON SITE • INDICATE THE DIFFERENCES BETWEEN COLD FORMED AND HOT ROLLED STEEL SECTIONS • EXAMPLES OF HOT ROLLED AND COLD FORMED STEEL SECTIONS AND WHICH TYPE OF LOADS AND APPLICATIONS ARE BEST MATCHED WITH EACH TYPE • STRUCTURAL STEELWORK TOLERANCES WITH PERMISSIBLE DEVIATIONS • BEHAVIOUR OF STEEL STRUCTURES IN FIRE • METHODS OF FIREPROOFING STRUCTURAL STEEL • TRANSPORTING, HANDLING AND STACKING OF STRUCTURAL STEEL COMPONENTS TO AVOID DAMAGE Downloaded from hlayiso.com

TOPIC 6 :STEEL CONSTRUCTION LEARNING OUTCOMES: • REASONS FOR STARTING AT A BRACED BAY WHEN ERECTING STEEL STRUCTURES • THE ROLE AND TECHNIQUES OF TOLERANCE OF HOLDING DOWN (HD) BOLTS IN SUCCESSFULLY ERECTING AND COMPLETING STEEL FRAMED STRUCTURES • HOW BASE PLATES ARE LEVELLED OR ADJUSTED ACCURATELY USING STEEL SHIMS • THE FUNCTION OF GROUT FILLING BETWEEN THE CONCRETE FOUNDATION AND THE BASE PLATE. • ACCEPTANCE TOLERANCES FOR ERECTED BUILDINGS ACCORDING TO PRESCRIBED NATIONAL STANDARDS. • EXPLAIN AND PERFORM A FINAL INSPECTION AND THE Downloaded ROLE OF A HAND OVER from hlayiso.com

STEEL CONSTRUCTION Steel structure is a metal structure which is made of structural steel* components connect with each other to carry loads and provide full rigidity. Because of the high strength grade of steel, this structure is reliable and requires less raw materials than other types of structure like concrete structure and timber structure. In modern construction, steel structures is used for almost every type of structure including heavy industrial building, high-rise building, equipment support system, infrastructure, bridge, tower, airport terminal, heavy industrial plant, pipe rack, etc. Downloaded from hlayiso.com

BEHAVIOUR OF MILD STEEL AND HIGH-TENSILE STEELS Behaviour of steel is how it reacts when it has different types of loads applied to it, or how it will respond to temperature changes. Bellow figure is the stress strain diagram for mild steel, its components will be outlined in a form of tables on the next slide. Downloaded from hlayiso.com

BEHAVIOUR OF MILD STEEL AND HIGH-TENSILE STEELS Downloaded from hlayiso.com

BEHAVIOUR OF MILD STEEL AND HIGH-TENSILE STEELS Downloaded from hlayiso.com

DESIGN OF STEEL STRUCTURES IN PREFABRICATED SECTIONS AND ITS ASSEMBLY ON SITE Prefabricated steel sections are structural steel components that are made in a factory according to the design specifications of the building plan. Structural steel is designed to be made in sections that can be delivered to construction sites. There are several reasons for this: • Smaller sections of a larger structure, such as a warehouse, are easier to transport • Prefabrication saves time , its quicker to put sections together that are already made • The workshop that produces the sections can make sure that the sections are of high quality • Construction teams don’t need to employ people who know about manufacturing steel, they simply order what they need and use their own labour. • One does not need to worry about the storage onsite, you ask delivery ofDownloaded from sections as you need, hlayiso.com this saves space and material wont be damaged.

INDICATE THE DIFFERENCES BETWEEN COLD FORMED AND HOT ROLLED STEEL SECTIONS Downloaded from hlayiso.com

EXAMPLES OF HOT ROLLED AND COLD FORMED STEEL SECTIONS AND WHICH TYPE OF LOADS AND APPLICATIONS ARE BEST MATCHED WITH EACH TYPE HOT ROLLED STEEL COLD ROLLED STEEL These are hot-rolled long profiles Cold formed steel sheeting is used to used for structural steel that needs lightly loaded applications, such as: to bear heavy loads, such as: • Channel iron • Metal roofs • Joists • Lightly loaded beams • Angle iron • Architectural applications • Steel Bars • Vehicle body parts • Girders • Steel cans and containers • Steel supports • Roofing columns • All rails • Other Heavy structural components Downloaded from hlayiso.com

STRUCTURAL STEELWORK TOLERANCES WITH PERMISSIBLE DEVIATIONS Throughout the hot-rolling process, the steel is checked to make sure that it conforms to standards. These standards specify tolerances that define the permissible size and shape of steel sections. This is important, because it ensures that the load bearing capabilities of the different steel sections are uniform and that they all fit into place when they are put together onsite. The table bellow expresses these tolerances with permissible deviations. Downloaded from hlayiso.com

STRUCTURAL STEELWORK TOLERANCES WITH PERMISSIBLE DEVIATIONS Downloaded from hlayiso.com

STRUCTURAL STEELWORK TOLERANCES WITH PERMISSIBLE DEVIATIONS Downloaded from hlayiso.com

BEHAVIOUR OF STEEL STRUCTURES IN FIRE Structural steel behaves in the following way in a fire: • It loses strength and stiffness until it buckles. • It is not combustible, which means it does not catch fire itself. But it conducts heat very well, so it gets extremely hot. • By the time it reaches 600 ºC, it has already lost half of its strength. • When structural steel deform due to fire, they can no longer bear loads they were designed to bear, and the structure will eventually collapse. Downloaded from hlayiso.com

METHODS OF FIREPROOFING STRUCTURAL STEEL Fireproofing: Is ensuring that structural steelwork cannot catch fire or get damaged due to heat of fire. Downloaded from hlayiso.com

TRANSPORTING, HANDLING AND STACKING OF STRUCTURAL STEEL COMPONENTS TO AVOID DAMAGE Suitable ways for transporting, handling and stacking structural steel components: • Steel must be stored and transported in such manner that it stays dry • It must be stacked above ground on wooden blocks called dunnage. • Large, heavy steel sections should be stored separately from the smaller light sections, so that the lighter sections are not damaged or distorted by the heavier sections • Reinforcing bars can stored onsite or delivered to meet the placing schedules. • The storage area should be easily accessible by truck and cranes for delivery of the components, and for rehandling the bars for fixing. • Store components by size and lengths, in some logical manner and keep the tags at uniform ends for easy identification. Downloaded from hlayiso.com

REASONS FOR STARTING AT A BRACED BAY WHEN ERECTING STEEL STRUCTURES Its critical to commence at braced bay, because a braced bay is a secured part of the structure. So when you use a braced bay, you can not trust the bay to remain anchored firmly to the foundation and square and plumb. If you do not start at a braced bay, you need to use temporary bracing to secure the columns or frames. This prolongs times and is also relatively expensive. Downloaded from hlayiso.com

THE ROLE AND TECHNIQUES OF TOLERANCE OF HOLDING DOWN (HD) BOLTS IN SUCCESSFULLY ERECTING AND COMPLETING STEEL FRAMED STRUCTURES When erecting and completing steel framed structures, ensure each column has four holding down bolts to anchor it to the foundations. The bolts should be placed symmetrically on the foundation and into the column. The typical tolerance for HD bolts in steel structures is 15 mm to 20 mm. When you start erecting a steel structure, you cannot tighten the bolts completely at the braced bay, because you need to allow some play for when you make the columns plumb. Holding down (HD) bolts to be built into the foundations with 25mm play all around to allow for adjustment to plumb and line during erection of steelwork. Downloaded from hlayiso.com

HOW BASE PLATES ARE LEVELLED OR ADJUSTED ACCURATELY USING STEEL SHIMS Make sure the base plates are level. If they are not level, some bolts may experience shear forces for which they were not designed. The base plate could buckle if it is not level and if the column is not plumb (Perpendicular to the ground). Lower the base plate and place shims (very thin metal plates and washers) underneath it. This makes a space for the grout to be placed between the base plate and the concrete. Downloaded from hlayiso.com Base Plate

THE FUNCTION OF GROUT FILLING BETWEEN THE CONCRETE FOUNDATION AND THE BASE PLATE The purpose of the grout is to provide an even contact between the level base plate and the uneven concrete slab. Grout also protects the base plate, shims, nuts and bolts from corrosion. You can also level a base plate by placing nuts above and bellow it. The bottom nuts, levels the plate, and the top nuts hold it down. Downloaded from hlayiso.com

ACCEPTANCE TOLERANCES FOR ERECTED BUILDINGS ACCORDING TO PRESCRIBED NATIONAL STANDARDS Downloaded from hlayiso.com

ACCEPTANCE TOLERANCES FOR ERECTED BUILDINGS ACCORDING TO PRESCRIBED NATIONAL STANDARDS Aspect Permissible deviation Downloaded from hlayiso.com

EXPLAIN AND PERFORM A FINAL INSPECTION AND THE ROLE OF A HAND OVER Once a structural steel building has been completed, it needs to be inspected to make sure that it has been done properly. To inspect a steel structure, you need to make sure that the following has been done properly: • The national standards and architect or designer’s specifications have been adhered to. • The structural steel materials have been handled properly. • The steel structure has been fabricated properly, with the correct tolerances. • The welding and welding materials used in the structure have been used correctly. • The structure has been bolted correctly and tightened. • The steel surfaces that have been coated were prepared and painted correctly. When the inspector is certain that these things have been done properly, a handover certificate will be issued. This certificate tells the contractor that the steel structure has been properly erected according to the national standards. Downloaded from hlayiso.com

HOME ACTIVITY 1. What is a base plate ? (2) 2. Explain the following terms: • Elastic Behaviour • Yield Plateau • Ultimate strength • Stress strain curve (8) 3. Draw a stress-strain diagram (5) 4. List 4 methods of preventing steel from catching fire (4) 5. Tabulate the difference between hot rolled and cold formed steel sections (6) 6. What is the purpose of grouting in steel erection ? (3) 7. Tabulate 5 structural steelwork tolerance aspects, with permissible deviations (10) 8. Name 3 aspects to consider when doings final inspection and handover for of completed structural steel, use sketches where necessary ? (6) Downloaded from hlayiso.com Total: 44

HASTA LA VICTORIA SIEMPRE, VENCERENOS “Victory is certain if we all work together as a unit and a team” Downloaded from hlayiso.com

THANK YOU THANKS YOU Downloaded from hlayiso.com