week 6

• Basement


  A storey which is below ground and is therefore constructed below ground

  
• Retaining walls


  • Vertical structures designed to retain soil on one side, preventing it from collapsing
  • The principal characteristic is being able to withstand the pressure exerted by the retained soil
  • Lateral earth pressures increase proportionally to a maximum value at the lowest depth
  • Groundwater behind the wall that is not dissipated by a drainage system causes hydrostatic pressure on the wall
• Retaining wall stability


  1. Weight of the wall and reinforcement bars in the wall

  2. Cables anchored in the rock or soil behind it

  3. Wall connected to a foundation slab, the weight of the back-fill stabilises the wall against overturning

  4. Pile acts as a temporary wall that has been driven or drilled into an excavation

  
• Backfilling


  • Gravity and cantilever retaining walls are required to be backfilled
  • Backfill material should be a free draining, well graded gravel
• Drainage


  • Agricultural drain or propriety system placed behind wall and at base of footing
  • Drainage system usually covered with a geofabric to prevent clogging the system
• Waterproofing retaining walls


  • External walls must be constructed to prevent rain or dampness penetrating to the inner parts of a building
  • Basement walls need to be waterproofed to prevent water ingress, particularly if the basement is a habitable area
• Untanked basement walls


  • Masonry has low water resistance - not recommended
  • Concrete has higher water resistance and water tightness is reliant on high quality dense concrete and waterstops installed in joints
  • Waterstops provide an integral sealing system for movement and construction joints
• Types of waterstop


  • Hydrofoil - made from PVC, impervious to moisture
  • Hydrophilic - made from foam, expand with moisture
• Bituminous tanking


  • Sheet of polyethylene with a layer of rubberised asphalt
  • Application: either self adhesive or heat
  • Forms one of the best forms on impervious barrier to moisture ingress
• Bituminous tanking application


  1. Receiving surface is to be free from voids, spalled areas, loose aggregate, protrusions

  2. Tears and damages to be repaired and patched

  3. Joints to be lapped

  4. Horizontal applications should be flood tested

  5. Tanking to be protected from damages during backfilling
• Alternative to untanked and tanked basements
• Waterproofing resistant renders and coatings

  Surface of retaining wall is treated with water resistant renders and coatings
• Weep holes and drains

  • Weep holes (pipe) placed through wall to allow excess water to drain from behind wall
  • Spoon drain necessary to carry water to discharge point
• Concrete code


  AS 3600: 2018 specifies minimum requirements for the design and construction of concrete building structures and members that contain reinforcing steel or tendons, or both
• Trades involved in cast-in-situ concrete construction

  • Formwork
  • Services
  • Reinforcement
  • Concrete
• Sequence of cast-in-situ concrete construction

  1. Install formwork and falsework

  2. Rough-in services

  3. Fix reinforcement place and finish concrete

  4. Strip formwork

  
• Formwork and falsework


  • Needs to be strong, stiff, accurate, watertight, robust, easy to strip, standardised, and safe
• Formwork materials


  • Solid sawn timber sections
  • Manufactured timber sections
  • Steel pans
  • Aluminum beams
• Falsework


  Temporary structure used to support a permanent structure, material, plant, equipment and people until the construction of the permanent structure has advanced to the stage where it is self-supporting
• Formwork safety


  • Avoid falling from heights when erecting formwork
  • Formwork/false-work must be inspected prior to placing reinforcement and concrete
  • Strip formwork safely
• Reinforcing


  Hot-rolled and/or tensile steel used for its good tensile and shear properties
• Reinforcing buildability


  • Congested reinforcing will not permit concrete to be placed and compacted correctly
• Post-tensioning


  • A method of reinforcing concrete with high-strength steel strands typically referred to as tendons
  • High-strength steel tendons are covered with duct to prevent them from bonding with the concrete
  • After the concrete has cured, the tendons are clamped on one end and jacked against the concrete on the other end until the required force is developed
• Benefits of post-tensioning


  • Allow longer clear spans, thinner slabs, fewer beams
  • Thinner slabs mean less concrete is required
  • Significant reduction in building weight versus a conventional concrete building with the same number of floors
• Concrete buildability considerations


  • Safe site access
  • Pump placement and accessibility
  • Rate of concrete placement
• Post-tensioning


  • Injecting grout into the spaces around the sheathed strands
  • Allows longer clear spans, thinner slabs, fewer beams
  • Thinner slabs mean less concrete is required (i.e. slabs-on-ground 0% to 20% less concrete)
  • Can allow a significant reduction in building weight versus a conventional concrete building with the same number of floors (e.g. slabs-on-ground 70% to 90% less reinforcement bar)
• Installing the jacking machine

  1. Duct

  2. Tendon
• Alternative reinforcing for concrete structures

  
• Strongforce Slab Post Tensioning System - Bing video
• Concrete buildability considerations


  • Safe site access. This includes consideration of the size of the delivery truck and traffic management planning to ensure there are no delays on the day of the pour
  • Pump placement and accessibility needs to be considered
  • Rate of concrete placement should be specified so the supplier can plan production and schedule deliveries to match
  • Method that will be used to place the concrete, such as a chute, pump (type, size and length of the line), crane (kibble)
• Concrete placing methods


  • Chute
  • Pump
  • Kibble
• Concrete placing


  • Be careful not to damage or move the formwork and reinforcement
  • Place concrete as near to its final position as possible
  • Start placing from the corners of the formwork or, in the case of a sloping site, from the lowest level

  
• Concrete segregation


  • When the coarse and fine aggregate, and cement paste, become separated
  • Makes the concrete: weaker, less durable, and will leave a poor surface finish
• Avoiding concrete segregation


  1. Check the concrete is not 'too wet' or 'too dry'

  2. Make sure the concrete is properly mixed. It is important that the concrete is mixed at the correct speed in a transit mixer for at least two minutes immediately prior to discharge

  3. The concrete should be placed as soon as possible. When transporting the mix, load carefully

  4. If placing concrete straight from a truck, place vertically and never let the concrete fall more than one-and-a-half metres
• Concrete compaction


  • Shaking or vibrating of the concrete to liquify it and expel any trapped air
  • The concrete settles, filling all the space in the forms
  • Properly compacted concrete is more dense, strong and durable. Off-form finishes will also be better
  • For concrete of average workability (i.e. slump of 80 mm) with a poker size between 25–75 mm, concrete should usually be vibrated for between 5 and 15 seconds
  • It is worse to UNDER-VIBRATE than to OVER-VIBRATE concrete
• Stripping and back-propping


  1. Instructions regarding proper timing, sequence and method in form stripping for back-propping and for form removal must be specific and clearly stated, referencing the expected concrete strength, curing time and temperature, design load and other specifications

  2. Where back=propping is required, proper drawings and specific instructions must be provided instead of using such loose specifications as 50% or 70% back-propping, in note form. Back-propping plans should be submitted to the consulting Structural Engineer for consideration and approval
• Cross laminated timber (CLT)


  An engineered wood product, similar in construction to an extremely large plywood panel, used for pre-fabricated structural applications
• Glue Laminated Timber (Glulam)


  Made with multiple layers of solid wood lumber bonded together with high-strength adhesive to form a single structural unit
• If the construction team is used to building with precast concrete panels products then the process of using GluLam beams and CLT panels is much the same. The difference is that the erection will be quicker because the structure can be built using one trade instead of three.
• Precast concrete


  • Poured into a reusable mould or 'form', cured in a controlled environment, then lifted into place
  • Common production methods include tilt-up (poured on site) and precast (poured off site and transported to site). Each method has advantages and disadvantages and choice is determined by site access, availability of local precasting facilities, required finishes, and design demands
  • Can provide a fast building process. However, careful design and planning is needed to ensure the openings and other details meet the design needs
  • Costs can range in the upper end of high-mass solutions. Reduced construction times and need for on-site trades can offset this to some extent
  • Economies of scale and repetition can further reduce costs