LOGBOOK WEEK and 5 COLUMNS WALLS, GRIDS
COLUMNS
Columns considered slender members, and can be short or long. Short columns are shorter in length and thicker in cross section. Short columns have length to smallest cross section dimension ratio of less than 12:1. Long columns are longer in length and slimmer in cross section. Long columns have column length to smallest cross sectional dimension of greater than 12:1. Shorter columns fail due to crushing. Structurally adequate if load does not exceed compressive strength of column cross section. Longer columns fail by buckling, this is determined by length and type of joints.
Walls enclose, separate, moderate climate for occupants, insulate. Walls can be major structural components. MELB SCHOOL DESIGN has columns carrying loads down to foundations. Precast concrete walls hang externally to concrete slabs. Structural frames can be concrete, steel or timber. Concrete usually found in larger scale. Steel in industrial warehouses. Timber frames less common, can be used in sloping sites. Precast concrete in apartment complexes. Stud walls light gauge steel framing or timber framing. MSD has concrete structural frame, with reinforcement. Steel frames usually have a grid of columns connected to beams and girders. Frames stabilised through bracing and shear walls. Timber typically uses grid of timber posts connected to beams. Bracing of members between bays at corners of post and beam joints. Load bearing walls: concrete load bearing walls can be in situ or precast. Reinforced masonry can be core filled hollow concrete blocks or grout filled cavity masonry. Bond beams over openings can be created using special concrete blocks which are filled with concrete to bond units together. Temporary propping removed once concrete sets leaving only concrete wall. Used as alternative to steel or concrete lintels. Solid masonry walls can be created with single or multiple skins of bricks; joined together using brick (heading showing in face) or with metal wall ties. Cavity masonry typically two skins. Have damp proof course and weep halls to allow moisture out. Stud framing very common with metal and timber. Smaller sections of framing timber or light gauge steel. Consists of top plates, bottom plates, vertical studs, noggings, cross bracing and ply bracing. Brick veneer construction combinations of 1 skin or non-structural masonry and 1 skin of structural frame wall.
WOOD TIMBER
Early wood rapid growth thin large cells and lighter colour. Late wood slow growth limited by lack of water, thick small cells darker. Grain direction determines structural performance. Strong paralled and stiff parallel to grain. Weak perpendicular to grai. Wood is seasoned and dried, moisture is removed to increase strength. Air seasoning 6 months to 2 years for every 50mm thickness. Cheap. Kiln drying typically 20 – 40 hours to dry to 12% below what it is as living material. Solar kiln used to save energy – less expensive. Seasoned timber > 15% moisture content. Softwood and hardwoods have different properties. Softwoods – pine from plantations. Hardwoods – native (eucalyptus species: jarrah, brown box) Quarter sawing – across the rings. Advantages: Best grain shows on face, good wearing for floors and furniture, wide sections possible, few knots on edge. Disadvantages: slower seasoning nailing on surface causes splitting. Back sawing – rings parallel to long edge of piece. Advantages: seasons faster, less prone to splitting while nailing, wide sections possible, few knots on edge. Disadvantages: shrink more across width when dries, more likely to warp and cup, collapsed timber more difficult to recondition. Radial sawing – face is always a radial cut. Advantages: dimensional stability, less prone to warping and cupping, less wastage in milling. Disadvantages: wedge shaped cross section, more difficult to detail, more difficult to stack.
Timber properties and considerations
High permeability Extremely varied density Poor conductors, good insulators. Can be very durable. Very high. Low embodied energy Generally cost effective – labour dependent. Different sizes for different timber Suitable for different scenarios. Strength grading. Species varies performance and appearance. Insect repellents and treatment required. Not available everywhere. Knots – weakness. Don’t want knot in tension (on bottom) Water protection important, >20% can result in fungal problems.
Engineered Timber Products
Engineered and manufactured into larger sections – structural sections, curved forms, long spans. More effiecient use. Lvl – beams posts and frames. Glulam (glue laminated timber) – structural, beams posts and frames. CLT (cross laminated timber) – structural panels, horizontal and vertical. Alternate laminated direction. Plywood – gluing laminates into sheet – structural bracing, structural flooring, formworks, joinery MDF – broken down hardwood or softwood into wood fibres – non structural (joinery) Chipboard and strandboard – made by layering hardwood or softwood residuals with wax and resin – structural flooring. I beams – timber/lvl flanges, plywood OSB webs lightweight suitable for medium spans (floor joists/rafters) Box beams Timber flanged steel web joists.
Frank Gehrys own home
Materials – chain link fencing, metal sheet, cardboard, lightweight Wrappings – packaging old house in packaging materials. Collisions and fragments
ACTIVITY: EASTERN SKYLIGHT
By translating the A3 drawings of the pavilion, reading member dimensions and calculating the appropriate scale, the group was able to create a portion of the Melbourne University Sports Pavilion.
Stud: Nogging: Lintel: Axial load: Buckling: Seasoned timber: