Steel Structures and Materials Engr & EnP Richard J. AQUINO Associate Professor V Department of Civil Engineering College of Engineering Central Mindanao University University Town, Musuan, Bukidnon 13 January 2025 Contents Steel Structures Structural Steel Elements Warehouse Steel Elements Roof Trusses Bridge Trusses Truss Parts Truss Comparison: Howe, Pratt and Warren Typical Truss Joints Typical Beam-Column Joint Structural Design of Buildings Loads and Load Path Typical Truss/Frame Structural Members Contents A very short history Structural Steel Tensile Properties f − −ϵ diagram Metal Properties 101: Ductility, Ductile vs Brittle Materials, Toughness High vs Medium vs Low Carbon Steel Idealized f − −ϵ Diagram Comparison of Young’s Modulus 0.2% Offset Method Yield Stress Most Common Steel Shapes Available Steel Grades Pre-Engineered Steel Building and Structure Steel Structures Figure: 2016 Prize Bridge Awards msc.aisc.org Figure: Truss Bridge French River at Ontario Figure: Chaotianmen Bridge at Yangtze River, Chongqing, China Figure: Tappan Zee Bridge at New York Figure: Artic Train Station at Anaheim, California Figure: Denver Union Station, Colorado Figure: Liège-Guillemins Railway Station at Belgium Figure: Bird’s Nest (National Stadium at Beijing, China Figure: ING House at Amsterdam, The Netherlands Structural Steel Elements Warehouse Building Elements Warehouse Building Elements Roof Trusses Bridge Trusses Truss Parts Truss Comparison: Howe, Pratt and Warren Typical Truss Joints Typical Beam-Column Joint Structural Design of Buildings Structural design requires determination of the overall proportions and dimensions of the supporting framework and the selection of the cross sections of individual members. Ideally, the engineer and architect will collaborate throughout the design process to complete the project in an efficient manner, i.e. the architect decides how the building should look; the engineer must make sure that it doesn’t fall down. Structural engineer’s priority: safety, serviceability (structure performance in appearance and deflection), and economy. Loads and Load Path Dead, Live, Earthquake, Wind, etc. Structural Members Note: These are typical truss/frame for a building. Trusses carry only tensile and compressive forces. Beams such as AB and BC carry bending moments. Column BD carry only axial loads while Beam-Columns AE and CF carry both axial load and bending moment. A very short history wrought iron (approx. 4000 B.C.): produced by heating ore in a charcoal fire cast iron (late 18th century): used in bridges steel, an alloy of iron and carbon (less carbon than cast iron) (19th century), due to Bessemer converter in 1855. Steels used in construction are generally carbon steels, alloys of iron and carbon. In US, the first structural steel railroad bridge was the Eads bridge, constructed in 1874 In 1884, the first building with a steel frame was completed in Chicago. First (Cast) Iron Bridge in the World at England - 1779 Source: https://www.ricksteves.com/europe/england/ironbridge-gorge Fiamous wrought iron structure - 1889 Source: https://abbyirondoors.com/our-favorite-famous-wrought-iron-structures/ Eads Bridge at St. Louis, Missouri - 1874 Note: This is the first important use of steel in any major construction project and is still-existing. Home Insurance Company Building in Chicago - 1884 Note: First high-rise steel-framed building (10-story, later, 12-story). Source: Structural Steel Definition Steel is an alloy (composed of two or more metals). main component is iron smaller component is carbon (contributes to strength but reduces ductility) other components include copper, manganese, nickel, chromium, molybdenum, silicon Structural Steel according to composition Plain carbon steels: mostly iron and < 1% carbon Low-alloy steels: iron and carbon + < 5% other components High-alloy or specialty steels: same composition with low-alloy steels but with higher %-age of the components added to iron and carbon, with specialty quality, e.g. resistance to corrosion Structural Steel Tensile Properties different grades using ASTM designation ASTM A36 or A36 (mild steel) - one of the most commonly used structural steels yield stress, Fy = 248 MPa (36 ksi) tensile strength, Fu = 400 to 552 MPa (58 to 80 ksi) A992 - Grade 50 steel yield stress, Fy = 345 MPa (50 ksi) tensile strength, Fu = 448 MPa (65 ksi) f − ϵ Diagram The characteristics of steel can be examined by plotting the results of a tensile test. If a test specimen is subjected to an axial load P, the stress and strain can be computed as follows: f = where f = axial tensile stress A = cross-sectional area ϵ = axial strain L = length of specimen ∆L = change in length P A and ϵ= ∆L L typical diagram for ductile, or mild steel engineering stress: original x-area is used engineering strain: original length is used Metal Properties 101 Strength, Toughness and Hardness The terms hardness, strength and toughness are often used interchangeably. But in reality, they have three distinct definitions – at least, when it comes to metals. For example, a tough substance doesn’t have to be hard or strong. Here are the key differences. Metal Properties 101 Strength, Toughness and Hardness Metal Properties 101 Venn Diagram Ductility ability to undergo large deformations before fracturing and measured by the elongation e= Lf − L0 × 100 L0 where e = elongation (expressed as a percent) Lf = length of the specimen at fracture L0 = original length (1) Ductile vs Brittle materials Brittle materials fracture at low strains and absorb little energy. Conversely, ductile materials fail after significant plastic strain (deformation) and absorb more energy.1 1 Note that in this idealised example, the yield and ultimate tensile stresses are the same for both materials; brittle or ductile behaviour are not necessarily related to strength. Toughness as defined in NDE-Ed.org The ability of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness. Recall that ductility is a measure of how much something deforms plastically before fracture, but just because a material is ductile does not make it tough. The key to toughness is a good combination of strength and ductility. A material with high strength and high ductility will have more toughness than a material with low strength and high ductility. Therefore, one way to measure toughness is by calculating the area under the stress strain curve from a tensile test. High vs Medium vs Low Carbon Steel Idealized f − ϵ Diagram proportional limit, elastic limit, upper and lower yield points is yield point, Fy maximum stress is ultimate tensile strength, Fu Modulus of Elasticity, E Hooke’s Law stress = E × strain σ = Eϵ Definition Young’s Modulus, E is the ratio of stress to strain within the elastic range E = 200,000 MPa (29,000 ksi) (2) (3) Comparison of Young’s Modulus 0.2% offset method High-strength steels less ductile (than mild steel) and no well-defined yield point or yield plateau Yield stress Yield point - mild steel Yield strength - high-strength steel Fu and Fy are the two properties usually needed in structural steel design a generic term yield stress is used to mean either yield point or yield strength Most Common Steel Shapes Available Steel Grades A36 steel is readily available in the Philippines Grade 36 (A36) or higher steel grades (A992) can be ordered in Vietnam, South Korea or China PEB Steel (Vietnam) - Catalogue link https://qrco.de/bdtk9Z Pre-Engineered Steel Building and Structure Source: https://pebsteel.com/en/solutions/ End of Presentation.
