Conceptual and Preliminary Structural Design for Buildings

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Conceptual and Preliminary Structural Design for
Buildings
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BACKGROUNDWhat is Structural Design?

• What are the loads and how do they get to the
  ground?
• Where are the loads?
• How do they get from one place to another?
• What are the required
• Members?
• Floors/roof, columns, walls, beams, girders, etc.
• Connections?

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BACKGROUNDStructural Design

• Safely and economically carry the loads that are
  likely to be imposed
• Maintain psychological comfort (deflections)
• Some level of risk because we cant predict with
  100 confidence the loads over the life of the
  structure.
• Nor do we really know what a members capacity
  is!
• Requires engineering judgment and experience.

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Structural Design

• Structural design is the art of using materials
  we do not fully understand to create geometry we
  cannot accurately analyze to withstand forces we
  cannot confidently predict in such a way that the
  general public has no reason to suspect our
  ignorance.
• Anonymous

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BACKGROUNDStructural Design Specifications

• International Building Code
• Material codes such as Steel Construction
  Manual, Timber Construction Manual, Building Code
  Requirements for Structural Concrete, Steel Deck
  Composite Slab Systems, Precast/Prestressed
  Concrete Institute (PCI), etc.
• ASCE7
• Most available in the Parks library or Town.

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OVERVIEWStages of Design

• Conceptual design
• Preliminary design
• Final design

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OVERVIEW-Conceptual Designs

• Functional spaces and requirements
• Geometry of spaces and enclosure
• Approx. overall size
• Basic sense of the expected loadings
• Structural design options to consider
• Superstructure type(s) and arrangement(s).
• Material type(s).
• Type and number of supporting elements.
• Supporting element shapes.
• Connections
• Foundation requirements

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OVERVIEWConceptual Design

• Structure types
• Slabs, walls, beams, girders, columns, trusses,
  cables, braced frames, rigid frames ...
• Materials
• Timber, engineered wood, steel, reinforced
  concrete, prestressed concrete, post-tensioned
  concrete, masonry, composite materials, .what
  about combinations?

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OVERVIEW EXAMPLEConceptual Designs

• Should be able to be summarized in a few simple
  sketches.gives you and your colleagues a sense
  of what it is.

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OVERVIEW EXAMPLEHow Do We Get Started?

• TSL - Type, Size, and Location
• Where is it? How big is it? And what does it
  generally look like?

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OVERVIEW EXAMPLEConceptual Designs

• Often summarized in one to several simple
  sketches - gives you and your colleagues and/or
  clients a sense of what it is.

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OVERVIEWPreliminary Design

• Based upon your experience and frequent feedback
  from others (in particular, the client owner?
  architect?), develop one to several conceptual
  alternatives or combinations of alternatives.

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OVERVIEWWhat is a Preliminary Design?

• Configuration of the primary structure
• Column and bearing/shear wall locations
• Floor depths and elevations
• Overhangs, cantilevers, long spans, etc.
• Main/principal member sizes
• Number of individual elements
• Beams, girders, floor, columns, footings, etc.
• Likely connectivities between elements including
  typical connections

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OVERVIEWThe Preliminary Design Product

• Structural design drawings for each floor or
  typical floor
• Cover sheet.
• Plan of each level or typical floor, including
  foundation
• Elevation/section views needed to clarify the
  concept
• Sheets detailing atypical or unusual members
• Sheets detailing atypical or unusual connections
• Preliminary quantities.
• Preliminary notes
• Preliminary specifications.
• Project notebook the meat behind the design
  report follow strict engineering process and
  procedure for completing the design.

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OVERVIEWFinal Design

• Using some sort of decision making tool, select
  the best of the preliminary designs (unless the
  client dictates which one they want used).
• Complete all analysis, design, and detailing of
  the final design
• All foundation locations, sizes, and details
• All member locations, sizes, reinforcing details,
  bracing, standards followed, etc.
• All connection details.
• The client should understand what they are
  getting and the contractor must be able to build
  it.

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OVERVIEWWhat is the Final Design Product

• Structural design drawings for each floor or
  typical floor
• Cover sheet.
• Plan of each level or typical floor, including
  foundation
• Elevation/section views needed to clarify the
  configuration and all details of the final design
• Sheets detailing all main members
• Sheets detailing all connections
• Quantities.
• Notes.
• Schedules columns, beams, slabs, reinforcing,
  etc.
• Final specifications (materials, material
  requirements and specifications, testing
  requirements, etc.)
• Project notebook that traces the design process
  and decisions made in detail

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How to Complete a CE486 Conceptual Structural
Design

• You need to determine
• What are the needs of the client.
• What are they really after if they know!
• What are all possible solutions to the problem.
• Realistic.
• Unrealistic.
• Previously tried.
• Previously untried.

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Conceptual Design Steps

• Step 1 Define the needs of the client.
• What do they want the product to do?
• What are the size requirements (volume, plan
  dimensions, height, spans, etc.)?
• What are other constraints (aesthetics, ease of
  modification, thermal mass, etc.).
• Do they have a preference for certain attributes?
  If so, what are they?

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Conceptual Design Steps

• Step 2 Define the principal geometry.
• Overall and individual interior volumes
• Plan dimensions of primary spaces
• Height of primary spaces
• Size relationships to adjacent primary spaces
• Functional needs
• Circulation (hallways, stairs, elevators, etc.)
• HVAC, utilities, lighting, etc.
• Openings (in floors and walls)
• Geometric constraints from the client, colleagues.

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Conceptual Design Steps

• Step 3 Determine and estimate the loads
• Dead loads.
• Live loads.
• Wind loads.
• Earthquake loads.
• Snow loads.
• Hydrostatic loads.
• Other.

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Conceptual Design Steps

• Step 4 brainstorm, brainstorm, brainstorm.
• Structure types bearing walls, shear walls,
  braced frames, rigid frames, columns, trusses,
  beams, girders, arches, suspension cables, short
  span, long span, big, small,
• Material types concrete, steel, timber, masonry,
  composites, ...

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Conceptual Design Steps

• Step 5 Ask yourself Do any of these meet the
  needs of the client?
• If yes, sketch em out. For each
• Show general configuration and appearance.
• Show the big picture
• List the major pluses (and minuses?)

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Conceptual Design Steps

• Step 6 - Prepare the products
• Sketches.
• Report with documentation of process.

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Keys to Economical Structures

• Repetition and regularity as much as possible
• Exposed framing if and when possible
• Consistent orientation (decking, beams, girders)
• Shallow floor systems (economy sections often
  do not result in overall economy)
• Working with contractors and subcontractors

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Comments on Lateral Loads

• Lateral loads on buildings are induced by wind,
  earthquake, and soil pressure
• Lateral loads increase as a structural design
  issue as buildings become taller
• Systems for resisting lateral loads include
• Bracing (diagonal, X, K, knee, etc.)
• Shear walls (reinforced concrete or masonry)
• Rigid connections (reinforced concrete, steel)
• Combinations of these three (common)

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Lateral load resistance bracing

• X-Bracing
• one of several bracing systems possible
• located in exterior and/or interior bays
• not necessarily in same location at all levels
• those shown for N-S resistance only
• floor diaphragms integral part of the lateral
  load resisting system.

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Lateral load resistance shear walls

• Shear walls
• usually reinforced concrete or masonry
• located in exterior and/or interior bays
• not necessarily in same location at all levels
• often double as elevator shaft and/or stairwell
  enclosures
• those shown for N-S resistance only
• floor diaphragms integral part of the lateral
  load resisting system.

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Lateral load resistance rigid joints

• Rigid joints
• inherent in site-cast reinforced concrete
• easy to obtain in steel construction
• member stiffnesses, especially of columns,
  important

• for frame shown (reinforced concrete),
  resistance provided in all directions
• floor diaphragms integral part of the lateral
  load resisting system.

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CE486 Preliminary Structural Design for a
Building

• Step 1 Pick the 2 (or 1? Or 3? Or 4?) most
  promising conceptual designs.
• Work with the client.
• Setup a decision making process.
• Get input.
• Get input.
• Get input.
• Apply and evaluate the decision making process.
• Ask Do these REALLY meet the needs of the
  client?

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CE486 Preliminary Structural Design for a
Building

• Step 2 More precisely determine the loads on
  the structure.
• Dead loads.
• Live loads.
• Wind loads.
• Earthquake loads.
• Snow loads.
• Hydrostatic loads.
• Other.

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CE486 Preliminary Structural Design for a
Building

• Step 3 Perform a structural analysis.
• Make good assumptions about likely connectivity.
• Use basic engineering principles OR possibly
  available structural analysis/design software OR
  possibly load/design tables.

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CE486 Preliminary Structural Design for a
Building

• Step 4 Size the main members based upon the
  analysis results.
• What material?
• What size?
• Standard designations possible?
• Custom sections likely needed?

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CE486 Preliminary Structural Design for a
Building

• Step 5 - Step back and assess the realism of the
  design.
• Does it make sense?
• Are the members sizes realistic?
• Can you do basic calculations that give you
  confidence in the design sizes?
• Do em.
• Ask a colleague to critique.

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CE48 Preliminary Structural Design for a Building

• Step 6 - Prepare the preliminary design documents
• Drawings
• Specifications
• Schedules
• Project notebook

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Plan Sheets

• Coversheet.
• Plan views.
• Elevation view(s)
• Cross-section(s)
• Summary of primary members.
• Preliminary quantities.
• Preliminary notes.

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Questions?