What is dynamics? Why have a course in it?

A few reasons:

• Natural dynamic loads, such as wind and earthquake, are major sources of human and economic loss in buildings.

• The organization of structural systems to resist such loadings typically has a major influence on the overall planning and configuration of a building.

• Wind and seismic loads are a major consideration in curtain wall and cladding systems, and providing for them can significantly influence the architectural impact of a building.

• Building vibration can be a significant cause of human dissatisfaction with a building, but it is not addressed in American building codes.

• Ask Norman Foster....

  • BBC: Troubled Bridge over Water (10 June 2000)
  • BBC: In Depth (2000)
  • Arup: Millenium Bridge

   

Dynamic Phenomena in Action

Seismic testing of a full-scale house.

The Tacoma Narrows Bridge

Translational vibration.

Torsional vibration.

Hurricane Hugo

Topics

• Physics
  Dynamics involves additional aspects of physics to explain the behavior of structures in motion.

• Geology
  Geology has a strong influence on the type of earthquake that can be expected at a given site, and can be an important factor in choosing a structural system.

• Weather
  Criteria for wind loading are based on meterological measurements, and it is important to understand how the measurements are made and what them mean. Whenever you see a reported wind speed, the first questions to ask are: measured at what height and for what duration?

• Probability
  Hurricanes and earthquakes are highly unlikely events, and design must consider the acceptable levels of risk and appropriate events to design for; this requires an understanding of some basic probablilty concepts.

  For example: What is the probabilty that a "100 year storm" will occur during a 100-year period? (63%).

• Human perception
  Many design criteria for dynamic loading are based on human comfort and acceptable levels of vibration and acceleration in a given setting. This requires an understanding of human perception of motion.

• Structures, construction, and architecture
  These are key factors in making appropriate design decsions, and are the emphasis of the course.

Computer analysis

• Understanding global behavior of structures.
  

  

  

• Building blocks

  Node
  Nodes are infinitely small points; the state of the nodes (e.g. forces, displacements, temperatures, boundary conditions) determines the state of the rest of the model.

  Element
  Elements represent the material of the structure. The geometry of an element is determined by the nodes it connects to. In linear elastic analysis (most common in practice), elements can be viewed as springs connecting the nodes.

  Boundary Condition
  A boundary condition is a restraint on the state of a node. The most common boundary condition is to prevent movement of a node along one or more degree of freedom, modelling the effect of a support where the model is attached to something such as a foundation that restricts its movement.

  Action
  An action changes the state of the structure in terms of its displacements, reactions, and internal forces; this change in state is called the response of the structure to the action. Common types of action include nodal loads, element loads, displacements imposed on nodes, or temperature changes specified at nodes or in elements.

• Acounting for three dimensions