6. structure (connectors, forces, beams, etc)

• The structural system of a building is designed and constructed to support and transmit the applied gravity and lateral loads safely to the ground without exceeding the allowable stresses in its members. It is a configuration of components that are dependent on one another and act together in a framework.
• The superstructure is the vertical extension of a building above the ground. It includes all columns and beams and load-bearing walls supporting the floor and roof structures. The substructure is the underlying structure forming the foundation of a building.
• No matter whether the carcass is masonry, a timber or a steel frame, all structural elements and their interaction form the structural framework of the building. No single element alone is responsible for the supporting structure, but the combination of members together with the configuration of joints.
• Vertical members


  wall<|>pillar<|>column<|>post<|>stud<|>pier
• Horizontal members


  slab<|>beam<|>truss<|>girder<|>joist<|>lintel<|>cantilever
• Statics is a branch of mechanics concerned with the analysis of forces acting on a system. Each system has to be designed in such a way that it can withstand the forces. This state is called equilibrium.
• Loads


  • static
  • dynamic
  • permanent load or dead load
  • imposed load or live load
  • concentrated load
  • uniformly distributed load
• Compression


  A pressing force that causes a structural member to shorten
• Tension


  A pulling force, which causes a member to stretch
• Shear


  The force acting parallel to the surface or axis of the material
• Torsion


  The force that causes a member to twist
• Modulus of elasticity


  A measure that indicates how a material will deform under stress
• The modulus of elasticity defines the relationship between tensile stress and tensile strain.
• The behaviour of steel is best explained in a stress-strain graph. At first, when stress is increased, the object obeys Hooke's law and the stress-strain relationship is linear and elastic. Just before the plastic region is reached the proportional limit is met. The behaviour beyond this point is no longer linear, but the stretching is still elastic. After the yield point, the steel enters the plastic deformation region, which means that the deformation is permanent. At the fracture point the steel snaps.
• The modulus of elasticity for softwood is 10,000 N/mm²; that of steel is 210,000 N/mm².
• Buckling


  Slender posts, pillars and walls are subject to buckling
• The following diagram is an example of a structural system. It is a simple supported beam with a uniformly distributed load and a cantilever with a concentrated load imposed on the end.
• All parts of a building can be categorised according to their function. From a constructional point of view, there are horizontal elements, such as beams, lintels and floor slabs, and vertical elements, such as walls, pillars, and posts.
• Structural frameworks


  • one-dimensional
  • two-dimensional
  • three-dimensional
• Free bearings


  Allow rotation, longitudinal and transverse movement
• Fixed bearings or hinged supports

  Only allow rotation, vertical and horizontal movements are prevented
• Fixed-end bearings


  Do not allow any movement
• Beams are horizontal structural elements designed to carry and transfer loads across a space to the supporting elements. Beams are subject to bending; the internal strength of the material has to resist the forces. Deflection is the deformation of the beam under load.
• Structural design


  • Focuses on the load-bearing elements and their structural effectiveness
  • Can be subdivided into one-dimensional, two-dimensional and three-dimensional frameworks
• Supports


  Prevent movement of structural members
• Types of supports


  • Free bearings (allow rotation, longitudinal and transverse movement)
  • Fixed bearings or hinged supports (allow rotation, prevent vertical and horizontal movements)
  • Fixed-end bearings (do not allow any movement)
• Beams


  • Horizontal structural elements designed to carry and transfer loads across a space to the supporting elements
  • Subject to bending, internal strength of material has to resist the forces
  • Deflection increases with load and span, decreases with increase of moment of inertia
• Types of beams


  • Simply supported beam
  • Beam on two supports with cantilevers
  • Fixed-end beam
  • Continuous girder
  • Cantilever
  • Continuous articulated beam (Gerber beam)
• Truss


  A structure comprising one or more triangular units constructed with straight slender members, with external forces acting only on the nodes resulting in tensile or compressive forces in the members
• Rigid frame


  A beam simply supported by two columns that is capable of resisting lateral forces, with joints connecting the columns and beam capable of resisting both forces and moments
• Types of frames


  • Rigid frame (statically indeterminate structure)
  • Two-hinged frame (statically indeterminate structure)
  • Three-hinged frame (statically determinate structure)
• Foundations


  • Transfer building loads to the ground, which has to be able to bear the load
  • Footing is extended laterally to distribute the load over a greater area of soil to meet the bearing capacity
  • Placed below the depth of frost penetration to minimise frost heaving
• Deep foundations


  Extend down through unsuitable soil strata to transfer building loads to a more appropriate bearing stratum
• Differential settlement


  Can cause the building to shift or cracks to appear, may require underpinning
• Diaphragm wall construction


  Excavate trench in short lengths, fill with bentonite and water slurry, install reinforcement, place concrete using tremie to displace slurry