Architectural Structural Systems

Introduction to Structural Systems

• Structural systems are key to architectural design, supporting other building systems and activities
• They define a building's shape and spaces, working similarly to how a skeleton supports a body
• A structural system must successfully balance design, space, and contextual elements with constructability

Fundamental Concepts in Architecture

• Architectural design involves more than sizing structural elements, with the system complementing form, space, and architectural vision
• The structure and building design have a crucial relationship, achieved through exposing, concealing, or celebrating the structure

Strategies of Structural Expression

• Structures can be exposed to show historic masonry or modern materials like timber, steel, or concrete
• Concealing structures involves hiding them under cladding for practical reasons like fire resistance or aesthetic reasons
• Celebrating structures makes them a focal point through material and form, like the Eiffel Tower or Sydney Opera House

Structure and Spatial Composition

• Structures and space correspond when the structural system dictates spatial layout, or vice versa
• Ideal designs balance structure and space to determine form and flow
• Lack of correspondence can allow layout flexibility, enabling different parts of the structure to support various spatial configurations

Role of Systems in Architecture

• Systems are assemblies of interrelated parts serving a unified purpose, such as structural, mechanical, and electrical systems working together in a building
• The structure must effectively transmit loads to the foundation while stabilizing the building

Substructure vs. Superstructure

• The substructure (foundation) supports and anchors the superstructure
• Substructures use shallow foundations on stable soil, including column footings, foundation walls, and mat foundations
• Deep foundations, like caissons and piles, are used when soil near the surface is unsuitable for bearing capacity
• The superstructure is the building above the foundation and includes the shell and interior structure
• A shell, including the roof, exterior walls, windows, and doors, provides shelter, security, and access to light and air
• Columns, beams, and load-bearing walls provide structural support

Types of Structural Systems

• Bulk-active structures use bulk and continuous material to redirect forces, such as beams and columns
• Vector-active structures use tension and compression members, like trusses, to redirect forces
• Surface-active structures redirect forces along the surface, like plate or shell structures
• Form-active structures redirect forces through material form, like arches or cable systems

Material Considerations

• Masonry walls are strong in compression but weak in bending, so they are thicker than reinforced concrete walls
• Steel columns are thinner than wooden posts for the same load-bearing capacity
• Reinforced concrete slabs can span greater distances than wood decking

Design Implications

• Structural Analysis affects overall design and later detailing of individual structural elements
• Contextual factors like site and environment impact structural and architectural choices
• Structural analysis determines a structure's ability to carry loads safely without distress or deformation, based on arrangement, shape, materials, and stresses

Structural Design

• Structural design arranges, interconnects, sizes, and proportions structural members to carry loads safely
• It must consider uncertainty, ambiguity, and approximation like other design activities
• Structural design looks for a system that meets load demands and addresses architectural, urban, and programmatic aspects
• The process is kickstarted by a building's design, site, context, and material availability
• Designs may be affected by code requirements, supply, labor, or costs

Joints and Connections

• Force transfer and system performance rely heavily on joint and connection types
• Structural elements are joined in three ways:
• Butt joints allow one element to be continuous, often with a mediating element
• Overlapping joints allow connected elements to bypass each other and be continuous
• Elements can also be molded/shaped for structural connections

Geometric Basis for Connections

• Structural connections are categorizable on a geometric basis, like points, lines, or planes

Fundamental Connection Types

• Pin or hinge joints allow rotation but resist translation
• Roller joints or supports allow rotation and translation perpendicular to its face
• Rigid or fixed joints maintain angular relationships, restrain rotation/translation, and provide force and moment resistance
• Cable supports or anchorages allow rotation but resist translation only in the cable's direction

Building Design Factors

• Design considerations include if an overarching form is needed or if articulation and hierarchical ordering are necessary
• Principals also need to assess whether elements need to be planar or linear

Building Program Factors

• Designers must balance program space scale/proportion with structural system spanning capabilities and support layout
• Important to assess spatial reasons for using one-way or two-way spanning systems

Systems Integration

• Important to understand how mechanical and other systems can be integrated with the structural systems
• Integrations must coordinate with building codes, scalability and construction materials

Code Requirements

• It is important to know the code requirements for use, occupancy, and building scale
• Type of construction/structural materials must align with regulations

Economic Feasibility

• Material availability, fabrication, transportation, labor, equipment, and construction time all influence structural system choice
• Designs may need to allow expansion either horizontally or vertically

Legal Constraints

• There exists a relationship between the size of built structures and their intended use
• Size is related to the required structural system and employed materials

Zoning and Building Codes

• Zoning constrains the bulk (height and area) and shape of buildings based on location by specifying its dimensions
• Codes control air, light, solar access, and privacy through minimum distances from property lines
• Building codes specify fire-resistance ratings depending on location, use, occupancy, height, and area
• International Building Code® (IBC) limits maximum height and area by construction type and occupancy, and expresses a relationship between fire resistance, size, and occupancy nature

Allowable Construction

• The larger the building, number of occupants, or risk of occupancy, the more fire-resistant the structure ought to be
• The goal is to protect from fire and give time to evacuate/respond
• IBC Table 503 determines allowable height/area by occupancy group and construction type; higher fire resistance (Type A) allows greater height/area

Occupancy Classification

• A is for assembly, like in auditoriums, theaters, and stadiums
• B is for business, like in offices, laboratories, and higher education
• E id for education, like in childcares, facilities and schools
• F is for factories and industrial, like fabricating, assembling, or manufacturing
• H is for hazards, like facilities handling dangerous/hazardous materials
• I is for institutional, like hospitals, nursing homes, and reformatories
• M is for mercantile, like stores
• R is for residential, like homes, hotels, and apartments
• S is for storage, like warehousing
• Heights are expressed as height above grade plane/fire-resistance and height in stories/occupancy.

Types of Construction

• IBC classifies based on material fire resistance
• Type I buildings feature noncombustible materials (concrete, masonry, steel), however, some combustible materials are allowed if they are ancillary
• Type II buildings are like Type I but reduce fire-resistance
• Type III buildings have noncombustible exterior walls and interior elements of approved materials
• Type IV (Heavy Timber, HT) buildings feature noncombustible exterior walls/major interior elements of solid/laminated wood of specified sizes and no concealed spaces
• Type V buildings have structural/exterior/interior elements of approved materials
• Protected construction requires major elements (except non-bearing walls/partitions) to have one-hour fire-resistance
• Unprotected construction has no requirements, but can need exterior wall protection based on property line proximity

Failure Prevention

• Normal elements experience elastic deformation (deflection/torsion) and return to their original shape, however extreme forces create plastic deformation and become unable to return to their original shape
• Ductility enables plastic deformation after elastic limits are breached and is an indicator of reserve strength, so it is desirable
• Factor of Safety is the ratio of maximum stress a member can endure vs what's allowed

Redundancy

• Redundancy and continuity build safety, durability, and proficiency into design
• Build redundancy to avoid failure, as well as include a factor of safety and use ductile materials
• It provide alternative force transfer paths during structural distress

Progressive Collapse and Load Paths

• Progressive collapse is the spread of local failure from member to the entire structure, which causes major damage/loss of life
• Continuity ensures a direct, uninterrupted pathway for loads down the structural system
• Continuous load paths ensures forces are delivered from application point to foundation
• Preventing collapse requires adequately tying elements together so forces/displacements can be transferred between them
• Continuity in structures supplies a pathway for loads through a building, from roof to foundation
• Continuous load path help to ensure forces are delivered from from application to the foundation
• Inadequate connections are weak load paths that create more damage/earthquake collapse
• Rigid, non-structural elements need to be properly isolated from main structure
• Disrupting vertical alignment of columns/bearing walls on floors diverts vertical loads horizontally and induces bending stresses to supporting areas