أسئلة حول الهياكل الفولاذية

Course Notes: Steel Structures for Architecture

• Course Title: Steel Structures
• Course Instructor: Dr. Hossein Parvin Sani
• Department: Architecture Engineering
• University: Razi University/Zanjan Branch

Chapter 1: Introduction to Steel and Steel Structures

• Advantages of Steel Structures:

  • High strength-to-weight ratios, suitable for large spans, high-rise buildings, and structures on unstable ground.
  • Predictable elastic behavior (following Hooke's Law).
  • Ductility, enabling the structure to withstand dynamic and impact loads.
  • Consistent Material Properties due to controlled manufacturing processes.
  • Durability; when maintained properly, steel structures can last for many decades.
  • Material Continuity; metallic components are typically homogenous and continuous, whereas concrete structures can suffer damage to reinforcement cover during earthquakes.
  • Low Weight
  • Space Efficiency
  • Ease of Modification and Expansion; strengthening can be done by adding components to a metal structure.
  • Ease of Construction & Installation; on-site installation, regardless of weather conditions.
  • Speed of Construction

• Disadvantages of Steel Structures:

  • Susceptible to degradation in high temperatures (above 600°C).
  • Corrosion in various environments; maintenance costs may be high.
  • Potential for buckling in compressive members.
  • Weld quality issues; skilled welding and specific quality control measures need consideration.
  • Higher initial cost compared to concrete structures.

• Types of Steel:

  • Simple Carbon Steels (Fe-C):
    • Low Carbon Steel (%C < 0.25-0.3)
    • Medium Carbon Steel (0.25-0.3%C < 0.65-0.7)
    • High Carbon Steel (%C > 0.65-0.7)
  • Alloy Steels (Fe-C + Alloy Elements)

• Effect of Alloying Elements: Carbon, Manganese, Silicon, Sulfur, Phosphorus, and others significantly impact the properties of steel, especially weldability. High carbon content can lead to brittle welds. Manganese improves strength, but high levels can reduce weldability. Silicon enhances strength, but excessive amounts with high-carbon can cause brittleness. Sulfur improves machinability, but should be kept low to prevent brittleness ( typically < 0.035%). Phosphorus is considered an impurity and should be minimized to prevent brittleness (typically < 0.04%).

• Stress-Strain Curve:

  • Hooke's Law: σ =Eε ( stress = modulus of elasticity × strain)
  • Yield Strength (F_y)
  • Ultimate Tensile Strength (F_u)
  • Elastic Range
  • Plastic Range
  • Fracture Point

• Steel Properties:

  • Modulus Of Elasticity (E), Poisson's Ratio, Density, Coefficient of Thermal Expansion

Chapter 2: Loading of Structures

• Dead Loads: The weight of all permanent structural elements (beams, columns, walls, floors, roofs etc, and permanently installed equipment). Use Appendix 1 of Iranian National Building Regulations (weights of different materials) for calculations.
• Live Loads: Non-permanent loads (e.g., people, furniture, snow, wind, earthquake). Live loads depend on the usage. See Iranian National Building Regulations, Chapter 6, for different types of live loads.
• Internal Partition Walls: Minimum live load of 1 kN/m² unless a lighter wall has a mass below 0.4 kN/m².
• Snow and Wind Loads: Calculated based on location and building geometry using Chapter 6 of the Iranian National Building Regulations.
• Earthquake Loads: Design parameters such as basic seismic acceleration (A), coefficient of reflection (B), and importance factor (I). Also includes building behavior factor (R_u)

Chapter 3: Common Roof Systems in Steel Structures

• Precast Concrete joist and block system: Common roof design technique. Advantages & Disadvantages of concrete joist systems and detailed specifications.

• Steel Joists (Kermite): Suitable for long spans and high loads. Advantages include speed of construction and reduction in dead load. Disadvantages include higher costs.

• Composite Roofs: Combining steel beams with concrete.Advantages include lighter construction. Note that the joists or beams may need additional bracing elements to prevent excessive movement or vibration issues.

• Prestressed/Post-Tensioned Roofs: -Advantages include reduced structural height and wider spans, and potentially reduced weight. -Types and details for prestressed and post-tensioned systems.

• Hollow Balloon Slabs: Engineered for light weighting and optimized design. Focuses on eliminating non-structural material and the impact of this design on structural elements like beams, columns, etc.

• Prefabricated/Prestressed Hollow Slabs System: Pre-fabricated concrete slabs with hollow spaces. Advantages include reduced weight, ease of installation. Specific considerations for connecting these slabs to the main structure.

• Roofix composite concrete slabs: Lightweight engineered composite slab designs that can lead to cost-effectiveness and faster construction.

• Double Tee System: Using paired 'T' shaped beams with concrete topping. Benefits include faster construction and potential for lighter-weight systems.

Chapter 4: Seismic Considerations in Structures

• Types of Structural Systems:
  • Bearing Wall Systems: Loads are primarily carried by walls, which act as shear walls.
  • Framed Systems: Loads are carried by framed structures and lateral resistance provided by shear walls or braced frames.
  • Framed-Moment Resisting: Similar to framed systems, but the entire structure is designed to resist lateral loads through bending moments in the frames.
  • Dual System: Combination of frame and shear wall systems, with each system contributing to load-bearing.
  • Cantilever Column Systems: Lateral forces are resisted by cantilever columns.
• Architectural and Structural Considerations: Details on how architectural decisions can impact seismic performance. Examples for considerations include the avoidance of severe irregularities in the building geometry.
• Regularity and Irregularity in Structures: Discusses symmetry, abrupt changes in plan shape, and variations in stiffness or mass, impacting structural performance. Significant variations in the plan's distribution of mass/stiffness in the plan will introduce complications with load-bearing.
• Soft Story and Weak Story: Structural weakness in certain floors or levels prone to collapse in stronger structural connections. The design needs to prevent localized soft-story or weak-story effects. (see the diagram notes on irregular structures in the document).
• Bracing Systems: Diagonal bracing (inclined/straight), and how they impact energy absorption.

Chapter 5: Introduction to Connections

• Welding and Welded Connections:

  • Definition of Welding
  • Types of Welding Processes (e.g., Shielded Metal Arc Welding [SMAW], Gas Metal Arc Welding [GMAW], Flux-Cored Arc Welding [FCAW].
  • Types of Welds (e.g., Fillet, Groove, Butt, Plug, Slot)
  • Weld Preparation

• Bolts and Bolted Connections:

  • Types of Bolted Connections (e.g., slip-critical, friction)
  • Bolt Grades
  • Pre-tensioning Forces
  • Hole Types (e.g., standard holes, oversized holes, slotted holes)
  • Minimum and Maximum Distances from edges of the plate.

• Types of Connections(simple joints): Details on different basic, or simple joint connection designs, including but not limited to: connections made with plates and angles.

• Types of Connections (rigid connections): Details on different forms of strong frame connections, including but not limited to: connections with welded joints and various plate and angle types.

Chapter 6: Design of Tensile Members

• Introduction: Design considerations for tensile members in structural systems.
• Gross Section Area: Total cross-sectional area without considering holes from the fasteners.
• Net Section Area: Reduced cross-sectional area after deducting holes from the gross area.
• Net Effective Section Area: Reduced area to account for stress concentrations, or distortions affecting the load-bearing capacity of the structural member.
• Slenderness Limits: Limits on the slenderness ratio (L/r) for tensile members to avoid or mitigate buckling.
• Design Criteria: The design must meet the criteria based on the critical limit states, or limit conditions.
• Design of Bracing Members and Pinned Members: Design considerations for bracing and pinned members and considerations for this type of metal part.

Chapter 7: Design of Compression Members

• Introduction: Design considerations for compression members.
• Buckling of Compression Members: Theoretical calculation of critical buckling load.
• Slenderness Limits: Limits on the slenderness ratio (KL/r) to avoid buckling. (Specific values based on conditions of the support -e.g., Fixed/pinned).
• Design Criteria: Criteria for designing compression members based limit states (e.g., initial yield, rupture etc.)

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