STRUCTURESYear 1 – Term 2

Danae Polyviou

Rob Knight

Role of Structural Engineer:

• Imagine the likely behaviour of a structure that does not yet exist

• Bring experience from other projects (an engineer will work on many more projects

than an architect)

• Suggest appropriate structural forms

• Think both qualitatively and quantitatively about loads, materials and structures and

switch between both modes of thought

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Rob Knight

Ove Arup

The term ‘Total Architecture’ implies that all relevant

design decisions have been considered together and

have been integrated into a whole by a well organised

team empowered to fix priorities.

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Rob Knight

Pier Luigi Nervi

Architecture, for Nervi, was "a synthesis of technology

and art." To find the logical solution to a limiting set of

factors within a highly competitive situation was, for him,

"to build correctly."

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Rob Knight

Frei Otto

To build means to make architecture

real on the borders of knowledge.

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Rob Knight

Gaudi

Do you want to know where I found my model? An

upright tree; it bears its branches and these, in turn, their

twigs, and these, in turn, the leaves

While designing the Sagrada Familia, in order to evolve a

structure in equilibrium, Gaudi designed catenary cord

models with weights that transformed the hanging curves

into funicular polygonal elements from which the masons

took measurements.

Danae Polyviou

Rob Knight

What is a structure?

• A structure is something that can support an object or a load.

Danae Polyviou

Rob Knight

What does a structure consist of?

1. A structural element i.e beam, column, arch, strut, tie, wall, slab

2. Combination of structural elements/ systems i.e truss, frame, gridshell

Key parameters affecting element’s behaviour?

- Material

- Span

- Structural system (i.e simply supported, continuous, cantilever , moment frame etc)

- Geometry of section (i.e I-beam, RHS, CHS etc)

- Support conditions (i.e pinned, fixed, slider)

- Connection between elements

- Load type (i.e point load, uniformly distributed load etc)

- Geometry

Danae Polyviou

Rob Knight

Structure must be designed to satisfy:

• Strength to support its own weight and whatever load is applied to it without breaking

• Stiffness to prevent excessive deflections

• Stability to prevent collapse

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Rob Knight

Strength: How much load can it take before breaking?

Depends on

- the material and its capacity

- Size of profile

- the combination of the elements

- The structural system

- Support conditions

- Span

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Rob Knight

Stiffness:

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Stiffness:

E – Young’s Modulus – Elasticity – depends on the material

I – Second moment of Inertia – depends on the size/ geometry of the section

EI – Stiffness

E= Stress, σ/ Strain, ε

Stress: amount of internal forces acting on an element

Strain: deformation of a solid due to stress

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Rob Knight

Stiffness:

I = Second moment of Inertia

I= bd3 / 12 + A d2

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Rob Knight

Self-weight

Dead

Imposed

Cladding

Snow

Vehicles

Braking

Blast / impact

Seismic

Thermal

Shrinkage

Pre-stress

Wind

Notional

Soil pressure

Hydrostatic

Heave

Cleaning

Elevators

Plant

Services

Typical Loads On A Building

Danae Polyviou

Rob Knight

Static and Dynamic Analysis

Static: Is the branch of mechanics that deals with forces and force systems that

act on bodies in equilibrium as described in the following.

Dynamics: Is the branch of mechanics that deals with the motion of a system of

material particles under the influence of forces. Dynamic equilibrium , also known

as kinetic equilibrium, is the condition of a mechanical system when the kinetic

reaction of all forces acting on it are in dynamic equilibrium.

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Equilibrium

• Externally applied loads cause internal forces and deflections and external reactions

• Key concept of equilibrium – resultants of all forces sum to zero

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Rob Knight

Structural behaviour under action of loads:

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Rob Knight

Structural behaviour under action of loads:

Compression Shorten Tension Elongate Bending Bends

Locally :Top: Compression

Bottom: Tension

Shear Slide

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Rob Knight

Shear Diagram

Moment Diagram

Deflection

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Rob Knight

Buckling:

Failure mode of compression elements.

Parameters affecting it: - Load

- Span of element

- Stiffness of section ( geometry + size)

Elements in compression are noticeable fatter than elements in tension because

they have to be designed against buckling.

Danae Polyviou

Rob Knight

Load Vectors

Vertical : Dead Load , Live Load, Snow Load, Wind Load, Seismic etc

Horizontal: Wind Load, Seismic, Human Impact etc

Require a structural system for each direction. Either the same or a different structural system.

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Rob Knight

Frame

Lateral Stability

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Rob Knight

Frame

Lateral Stability

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Rob Knight

Supports

Roller

Pin

Fixed

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Rob Knight

The Elements

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1. Spanning structures

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Beam

It bends in order to carry the load

It carries the load in : - Bending

Locally: - Tension on bottom

- Compression on top

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Rob Knight

Atrium Roof Beams - The Angel Building, Islington EC1V 4AB

Beams

Bridge of Aspiration, Wilkinson Eyre Architects – Floral Street, Covent Garden

Beams

Cantilever

They have to be fixed at one end . They work in bending

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Rob Knight

Diving Boards, London Aquatic Centre - Olympic Park, Stratford, London E20

Cantilevers

Vauxhall Bondway Bus Station Canopy – Vauxhall, London SE11

Cantilevers

Truss

Trusses are an efficient way to carry loads with minimal material.

They support load much like beams, but for longer spans. They bent in order to carry the load as :

- Tension on bottom

- Compression on top

Danae Polyviou

Rob Knight

Borough High Street rail bridge – London Bridge SE1

Trusses

St Pancras Station

Trusses

Slabs / Plates/Decks

Work in bending

Transfer vertical loads. If stiff enough can also contribute

to the lateral stability.

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Rob Knight

National Theatre – Southbank, London SE1

Slabs

Queen Elizabeth Hall foyer – Southbank, London SE1

Slabs

2. Vertical load bearing structures

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Column

Carry vertical loads to the ground

In Compression Prone to buckling

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Rob Knight

Barbican Centre

Columns

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02 Arena -Greenwich Peninsula, London SE10

Columns

Walls

Vertical Load Path

Can act as shear walls for lateral stability

Barcelona Pavilion

Thermal Baths Vals

Walls

3. Arching structures

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Arch

It is in compression throughout.

Arches transmit large horizontal thrust into their supports.

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Dome

An arch but in 3D. It is in compression throughout.

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St Paul’s Cathedral – London EC4M

Dome

St Martin in the Fields Crypt – Trafalgar Square, London WC2N

Dome / Vault

4. Lateral stability systems

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Moment or Braced Frames

Combination of beams and columns

Lateral Stability

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Neo Bankside - Bankside London SE1

Braced Frame

Murray Grove Flats – Murray Grove, London N1

Braced Frame

gerkin

Swiss Re (“The Gherkin”) - 30 St Mary Axe, City of London EC3A

Tower Stability

The Shard - Joiner Street, Southwark,London SE1

Tower Stability

Core/ Braced cores or Shear Walls

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5. Tensile systems

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Cable

Only in Tension

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Millennium Bridge – London

Suspension Span

Albert Bridge, Battersea, London

Golden Jubilee Footbridges - Hungerford Bridge, London

Suspension Span

6. Form active structures

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Rob Knight

Gridshells

Grid of slender elements that transfer axial loads. They are form-active structures as they acquire

their strength and stiffness through their form and shape. They are most efficient when doubly

curved.

Danae Polyviou

Rob Knight

Westfield Shopping Mall – Shepherd Bush

Gridshells

Cutty Sark - Greenwich

Gridshells

Fabric Structures

Only in Tension

Danae Polyviou

Rob Knight

Fabric Structure – Spitafield Markets

Fabric Structures

Serpentine Slacker Gallery

Fabric Structures

Structural design – Load path diagrams

1. Loads : which loads are acting on our structure and in which form/ direction?

2. Which parameters do we have to fulfill? – Strength + Stability: to avoid collapse

- Stiffness: to avoid excessive deflections

3. Sketch a load path or alternative load paths on our structure in order to identify the best structural

system or systems:

a) Begin by drawing the load vectors

b) “Walk” along the structure with your pen following the path of the load from their point of

application towards the ground / supports

c) Sketch structural elements/ combined elements for transferring the loads

d) Make sure we have a structural system for transferring the loads from their point of application

to the ground

Danae Polyviou

Rob Knight

Action

Re-Action

Load Path

Re-Action

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Structural system and deflected shape

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Rob Knight