AEC_204_Chapter_19_Spring_2025_Instructor_Notes

Evolution of Steel Construction

• Prefabricated Structural Frame: Refers to the construction of a steel building's structural frame by assembling prefabricated steel components on-site.

• Comparison with Other Structures:

  • In contrast to steel buildings, load-bearing masonry or cast-in-place reinforced concrete structures are constructed almost entirely on-site without prefabrication.

  • Key focus areas in steel structures involve component fabrication, erection, and assembly.

Framing Layout Considerations

• Role of Preliminary Layout:

  • Preparing the preliminary framing layout of steel (and other material) buildings is integral, involving structural and non-structural factors such as HVAC, aesthetics, fire resistance, and budget.

  • This stage is crucial and showcases an architect’s expertise during the design development phase.

• Framing Plans:

  • Typically created in plan view, referred to as framing plans.

  • Roof and floor framing plans differ due to varying load requirements.

  • Establishing a structural grid is essential, as it determines column locations (grid lines also act as column lines).

• Component Characteristics:

  • Steel building floor/roof components function as one-way elements, spanning in one direction. This contrasts with cast-in-place concrete slabs, which can be either one-way or two-way.

Use of W-Sections in Framing

• Types of Structural Elements:

  • Structural elements include primary (girders) and secondary (beams) components, utilizing W-sections or steel joists:

    • Both primary and secondary elements made of W-sections.

    • W-sections for primary elements, steel joists for secondary.

    • Steel joist girders/trusses for primary and steel joists for secondary components.

  • For certain buildings with load-bearing walls, secondary elements may be omitted, supporting the roof deck directly on primary elements.

Detailing and Fabrication Processes

• Prefabricated Components:

  • Unlike masonry or cast-in-place concrete, structural steel components arrive prefabricated and ready for assembly at the site, minimizing on-site modifications.

  • Detailing by fabricators based on provided framing plans ensures both efficiency in erection and adherence to architectural aesthetics.

• Ordering Materials:

  • Post completion of shop drawings, materials are ordered based on reviews, allowing for continued progress while awaiting approvals.

• Fabrication Environment:

  • Large fabrication shops utilize semi-automated systems for precision and efficiency, manually executing most welding operations except for repetitive tasks.

  • Computer-aided machines cut and drill components with high precision, reducing manual labor.

Erection Process of Steel Frame

• Erection Responsibility:

  • Erection can be handled by either the fabricator or a separate company. Contracts can be awarded based on competitive bids from fabricators who also take on the erection job.

  • Ideally, fabrication and erection would be performed by the same entity for better coordination.

• Erection Steps:

  • Starting with Columns: Erection initiates with column placement, utilizing shop-welded base plates secured to foundation bolts.

  • Cranes and Equipment: Various cranes facilitate the lifting and positioning of steel members, ensuring precise assembly.

  • Alignment Processes:

    • Making connections often requires members to align, using tools like drift pins for accurate positioning.

Connection Design and Types

• Connection Types:

  • Common connections include:

    • Column-to-beam

    • Beam-to-beam

    • Column splices

  • The AISC categorizes connections into:

    • Rigid connections: Moment connections (Type I)

    • Simple connections: Shear connections (Type II)

• Column Splices:

  • Splicing is essential for multi-story buildings due to the limitations on the length of steel members; typically placed every two stories.

  • Smoothly milled column ends are used for proper load transfer.

Advantages and Disadvantages of Welds vs. Bolts

• Welding:

  • Advantages: Greater applicability, continuity between members, potential steel savings.

  • Disadvantages: Requires skilled labor, environmental conditions can impact quality (hence preferred in controlled settings).

• Bolting:

  • Advantages: Rapid assembly, requires less skilled labor, unimpacted by weather conditions, easier surface preparation.

Types of Frames and Stability Considerations

• Rigid vs. Braced Frames:

  • Rigid frames resist load through bending across all members, which is often less economical than braced frames, which are simpler and often more efficient in material use.

• Bracing Options: K-braces and variations help stabilize the structure against lateral loads.

  • Rigid frames can achieve interior design flexibility due to fewer structural elements.

• Building Core Support Varieties:

  • High-rise structures often utilize reinforced concrete cores paired with braced steel frames to enhance stability and space management.

Evolution of Steel Construction

Prefabricated Structural Frame

• Refers to the construction of a steel building's structural frame by assembling prefabricated steel components on-site. This method allows for rapid assembly and reduces the time needed for construction as elements are often manufactured off-site in a controlled environment.

Comparison with Other Structures:

• In contrast to steel buildings, load-bearing masonry or cast-in-place reinforced concrete structures are constructed almost entirely on-site without prefabrication. Steel construction offers advantages such as lighter weight, high strength-to-weight ratios, and greater design flexibility, enabling architects to achieve complex and open layouts.

• Key focus areas in steel structures involve component fabrication, erection, and assembly, which differentiate them from traditional construction methods utilizing concrete or masonry.

Framing Layout Considerations

Role of Preliminary Layout:

• Preparing the preliminary framing layout of steel (and other material) buildings is integral, involving both structural and non-structural factors such as HVAC systems, aesthetics, fire resistance protocols, and budget constraints. This stage is crucial and showcases an architect’s expertise during the design development phase, ensuring that all necessary systems are adequately incorporated into the final structure.

Framing Plans:

• Typically created in plan view, referred to as framing plans, which detail the layout of beams, columns, and other structural components.

• Roof and floor framing plans differ due to varying load requirements. Roof framing must account for snow load, wind load, and potential water pooling, while floor framing caters to live loads and dead loads.

• Establishing a structural grid is essential, as it determines column locations; grid lines also act as column lines, influencing the distribution of loads throughout the structure.

Component Characteristics:

• Steel building floor/roof components function as one-way elements, spanning in one direction to efficiently transfer loads to supports. This contrasts with cast-in-place concrete slabs, which can be either one-way or two-way depending on the design and load distribution intended.