Structural elements and behaviour under load

• Selection of appropriate general form

  1st step
• Developed into a detailed construction form

  2nd step
• Prime determinant of the construction

  Related to space
• Users demands


  The space and size suggest the scale and shape
• Design and resource conditions

  Lead to a dominant economic detailed solution
• Three general groups of structural form

  • Load bearing walls
  • Skeletal frames
  • Long span roofs
• Load bearing walls


  • Used in domestic homes due to the semi permeable (hollow cavity) construction
  • Provides a stable, dry box
  • Due to the trussed roofs, internal load bearing walls do not need to extend to the roof level
• Beams


  • Great strength
  • Small deflections
  • Small section size
  • Low weight
  • Good looks
  • Low cost
  • Fast erection
• Portal frame in a long span roof

  • Typically steel, but a building with the correct use, scale, and size, could be made from reinforced concrete or even timber in a laminated form
• Slab floors


  • More economical in flats due to the sound and fire resistance
  • Prefabricated walls have the advantage of repetition and gain a production advantage
• If developed into multi storey blocks

  The alternative structural form of the skeletal frames will become an economical alternative
• The most cost-effective way to limit heat loss during the cold months is insulation between the walls
• Strut


  Loaded and goes into compression. Commonly identified as a column. Pushing down on a pole etc.
• Tie


  Loaded and goes into tension, indicated by lengthening. Pulling a pole etc.
• Pushing down on a triangle, the two sides in the air are struts, the tie is on the floor being pulled apart
• Beam


  Spanning member, loads cause it to bend
• All bending members have a second pair of tension and compression forces. Shear
• Walls can be in compression when taking loads through the building but may be in bending if resisting horizontal forces such as wind, or ground pressure as part of a basement structure. Shear loading is created when the wall is used to stabilise the racking effect of wind
• Suspended slabs will be in bending
• Ground supported slabs are in compression
• Slabs under columns or walls as foundations, the forces they experience depend on the ratio of the depth to the width of the foundation. If wide foundation – bending, if too narrow – punching shear
• If bending or known to bend, (bad in tension) a material that's great with tension can be added to the underneath
• Slenderness


  Function of the height (or length) to width ratio, but it is also dependant on the way in which it is connected to the structure
• Lateral distortions


  Known as buckling
• Eccentric loads


  Acts on a structural member at any point other than the member's centroid. A measure of how far the load acts away from the axis. These loads may cause the member to overturn if the dimensions and/ or connections are not sufficient for it to remain stable. If the member Is not disturbed in this way, it can cause bending. If the ends are restrained – torsion. These distortions do not replace other distortion effects caused by loads
• Strain


  A measure of the tendency of an element to suffer deformation under load
• The relationship between stress and strain (subject to loading limits) is directly proportional and is a measure of the material stiffness. The ratio of the stress/strain is known as the modulus of elasticity
• Beams without shear support (rebar) are more susceptible to a shear failure. Linear relationship between applied load and the vertical displacement at midspan until the brittle shear failure
• Moments


  The result of a force applied perpendicular to an element at a distance from a point of rotation
• Moments must be in equilibrium to remain stable
• Modulus of elasticity


  Measures stiffness, the ratio between a structural element's original length and its actual length under load
• Load bearing structures rely on the use of continuous walls with uniform loading and minimal openings. As multiple storeys are added, the walls at lower levels need to be made stronger or thicker to deal with compressive forces. Thus, building height and spans of interior spaces for these structures tend to be smaller than those of framed structures which rely on a variety of more concentrated point loads carried by columns. This type of structure allows for a more varied approach to external walls and for larger spaces and taller, bigger building forms