Key Â Terms Â Joist Â â€“ Â a Â length Â of Â timber, Â steel Â or Â concrete Â that Â supports Â the Â structure Â of Â the Â building Â Steel Â Decking Â â€“ Â A Â metal Â sheet Â used Â to Â construct Â the Â membrane Â of Â the Â roofing Â system. Â Span Â â€“ Â The Â distance Â measured Â between Â two Â structural Â supports. Â Girder Â â€“ Â They Â are Â the Â main Â beams Â of Â the Â floor Â system Â Concrete Â Plank Â â€“ Â A Â flat Â beam Â used Â for Â roofing Â and Â flooring. Â Spacing Â â€“ Â The Â repeating Â distance Â between Â a Â series Â of Â like Â or Â similar Â elements. Â Span Â and Â Spacing Â Span-Ââ€? Â the Â distance Â measured Â between Â two Â structural Â supports. Â It Â can Â be Â measured Â between Â vertical Â supports Â (for Â a Â horizontal Â member) Â or Â between Â horizontal Â supports Â (for Â vertical Â member). Â This Â is Â necessarily Â not Â the Â same Â as Â the Â length Â of Â a Â member. Â Â
Spacing Â â€“ Â The Â repeating Â distance Â between Â a Â series Â of Â like Â or Â similar Â elements. Â This Â is Â associated Â with Â supporting Â elements Â (such Â as Â beams, Â columns Â etc.) Â and Â can Â be Â measured Â horizontally Â or Â vertically. Â Spacing Â is Â measured Â centre-Ââ€?line Â to Â centre-Ââ€?line. Â
Slabs Â of Â various Â types Â are Â used Â to Â span Â between Â structural Â supports. Â These Â can Â be Â one-Ââ€?way Â or Â two-Ââ€?way Â spans Â slab Â thicker Â estimated Â to Â be Â around Â the Â span Â of Â the Â slab Â divided Â by Â thirty. Â Â đ?‘†đ?‘?đ?‘Žđ?‘› Â đ?‘œđ?‘“ Â đ?‘†đ?‘™đ?‘Žđ?‘? = đ?‘†đ?‘™đ?‘Žđ?‘? Â đ?‘‡â„Žđ?‘–đ?‘?đ?‘˜đ?‘›đ?‘’đ?‘ đ?‘ Â 30 Â To Â decide Â on Â what Â span Â to Â use Â (one-Ââ€?way Â or Â two-Ââ€?way) Â depends Â on Â the Â cost Â efficiency, Â workload Â and Â also Â the Â function Â of Â the Â building Â such Â as Â the Â columns Â placements. Â Â Steel Â Systems Â
Floor Â Systems Â Floor Â systems Â consist Â of Â concrete, Â timber Â and Â steel. Â Timber Â is Â span Â joist Â to Â joist. Â Timber Â floorboards Â need Â to Â be Â thicker. Â Open Â web Â trusses Â are Â lighter Â weight Â joist Â are Â slowly Â space. Â Concrete Â Systems Â
Steel Â framing Â systems Â take Â various Â forms, Â with Â some Â utilizing Â heavy Â gauge Â
structural Â steel Â members Â others Â uses Â light Â gauge Â steel Â framing. Â Many Â combinations Â of Â member Â types Â (heavy Â and Â lights) Â are Â used Â depending Â on Â the Â structural Â function. Â Â The Â open Â web Â joist Â is Â a Â quite Â efficient Â used Â of Â steel Â since Â it Â is Â an Â expensive Â material. Â Also Â the Â services Â such Â as Â water Â pipes Â can Â be Â carry Â by Â the Â joist. Â Sometimes Â steel Â framing Â systems Â combine Â with Â concrete Â slab Â systems Â to Â where Â the Â particular Â benefits Â of Â steel Â framing Â and Â shallow Â depth Â floor Â slab Â systems Â and Â desired. Â The Â spanning Â capabilities Â of Â the Â particular Â materials Â help Â to Â determine Â the Â spacing Â requirements Â of Â the Â supports. Â Concrete Â is Â applied Â on Â the Â steel Â decking Â to Â support Â the Â tensile Â strength. Â The Â description Â of Â steel Â or Â concrete Â depends Â on Â the Â factor Â of Â cost, Â fire Â rating Â of Â a Â building Â (larger Â building Â such Â as Â hospitals Â tend Â to Â be Â build Â in Â concrete Â which Â is Â able Â to Â cope Â with Â fire Â with Â a Â
longer Â period Â of Â time Â then Â most Â steel Â or Â timber). Â Timber Â System Â This Â is Â the Â most Â common Â system Â in Â Australia. Â Traditionally Â timber Â floor Â framing Â systems Â use Â a Â combination Â of Â bearers Â (primary Â beams) Â and Â joists Â (secondary Â beams). Â The Â span Â of Â the Â bearers Â determines Â the Â spacing Â of Â the Â piers Â or Â stumps Â and Â the Â spacing Â of Â the Â bearers Â equals Â the Â span Â of Â the Â joist. Â Joist Â supports Â floorboards, Â decking Â or Â ply Â panels. Â The Â joists Â are Â supported Â by Â bearers. Â Typically Â floorboards Â span Â 450-Ââ€?600mm. Â Bearers Â would Â be Â added Â to Â reduce Â the Â span Â by Â approx. Â 50%. Â Floors Â normally Â have Â a Â lot Â of Â joist. Â To Â keep Â their Â cross-Ââ€?sectional Â area Â small, Â the Â joist Â is Â tend Â not Â to Â span Â from Â wall Â to Â wall, Â bearers Â are Â used Â in-Ââ€?between Â to Â cut Â down Â the Â size Â o Â the Â material. Â Â Concrete Â Â Concrete Â is Â artificial Â stone. Â Concrete Â Components Â When Â cement Â is Â mixed Â with Â water Â it Â binds Â the Â sand Â gravel Â aggregates Â together Â to Â make Â the Â hard, Â solid Â material Â we Â call Â concrete. Â
Common Â concrete Â mix Â is Â Â 1: 2: 4: 0.4 âˆ’ 0.5 Â đ??śđ?‘’đ?‘šđ?‘’đ?‘›đ?‘Ą: đ??šđ?‘–đ?‘›đ?‘’ Â đ??´đ?‘”đ?‘”đ?‘&#x;đ?‘’đ?‘”đ?‘Žđ?‘Ąđ?‘’: đ??śđ?‘œđ?‘Žđ?‘&#x;đ?‘ đ?‘’ Â đ??´đ?‘”đ?‘”đ?‘&#x;đ?‘’đ?‘Žđ?‘”đ?‘Žđ?‘Ąđ?‘’: đ?‘¤đ?‘Žđ?‘Ąđ?‘’đ?‘&#x; Â Â Cement Â Â Fine Â Coarse Â Aggregates Â Aggregate Â Portland Â Sand Â Crushed Â rocks Â Lime Â Â Â
Provenance Â When Â the Â cement Â powder Â and Â water Â are Â mixed, Â a Â chemical Â reaction Â takes Â place Â and Â heat Â is Â released. Â This Â process Â is Â called Â hydration. Â During Â this Â process Â crystals Â are Â formed Â that Â interlock Â and Â bind Â the Â sand, Â crusted Â rock Â and Â cement/water Â paste Â together. Â If Â too Â much Â water Â is Â added Â to Â the Â concrete Â mix, Â the Â final Â concrete Â will Â not Â be Â strong Â enough Â (weak). Â If Â too Â little Â water Â is Â added, Â the Â concrete Â mixture Â will Â be Â too Â stiff Â and Â it Â will Â be Â difficult Â to Â work Â with Â (unworkable). Â Process Â An Â advantage Â of Â concrete Â is Â that Â it Â is Â plastic Â before Â it Â set. Â One Â of Â the Â great Â advantages Â of Â concrete Â is Â that Â it Â is Â fluid Â
and shapeless before it hardens. It can be formed in to any shape we desire. Formwork is the term used for the temporary support or moulds used to hold the liquid concrete in place until it becomes hard. Formwork can be built at the building site (IN SITU) or in a factory (Pre Cast) out of a range of different
materials: timber, plastic, formply etc. During the curing process the framework needs to be supported, as the weight of the wet concrete is very heavy. As the concrete sets, it carries its own weight transferring the load through the support, which could be the floor, column or walls. This is achieved
by using props and bracings of various types. Concrete generally reaches 75% of its compressive strength in approx.. 7 days with testing for the required strength occurring at 28 days. Once the concrete is hardened and strong enough, the formwork is carefully removed. Formwork is often removed, stored and reused or it may stay in place forever (sacrificial formwork). Finishes There are many finishes of concrete such as: • Sand –blasted • Exposed aggregate • Raked finish • Bush hammered • Board – marked • Board & batten. Reinforcement Concrete is also known as ‘artificial stone’. This suggests that the properties of concrete and stone are similar. Concrete is very strong in compression but is weak in tension. To improve its structural performance, a steel (very strong in tension) reinforcement in the form of mesh or bars is added.
The resulting material is known as reinforced concrete, which is strong in both compression and tension. Reinforcement is often used to form a fixed or rigid joint between a slab or wall. Reinforcement bars extend out of the concrete so another concrete can be placed onto it. The amount of reinforcement is adjusted by different level of loading. Properties The properties in the ‘fresh wet; -‐ plastic state and hardened state depend on the physical characteristics, chemical composition and the proportions of the components. The list below addresses the hardened state. Hardness – High. Can be scratches with a metallic object Fragility – low. Can be chipped with a hammer Ductility – very low ductility Flexibility/ Plasticity -‐ low flexibility and plasticity Porosity/ Permeability – medium-‐low. Depending on proportions and components Density – Medium-‐high. Approx. 2.5x dense than water.
Conductivity – poor conductor of heat and electricity Durability/Life Span – typically very durable Reusability/Recyclability – medium-‐ low. Can be partially re-‐used when crushed to be used as aggregate for new concrete elements. Sustainability and Carbon Footprint – High embodied energy. Non renewable, long lasting. Cost – Generally cost effective. Labour dependent for formwork and pouring. Considerations Concrete is permeable (not completely waterproof). This is one of the main sources of problems in concrete. If the steel bars are too close to the surface they will not be protected from moisture and oxidation. This will cause both aesthetic and structural degradation of the concrete. Another common cause of problems is poor vibration of the concrete during the pouring process. Concrete is vibrated to get rid of the air bubbles that get caught during the pouring process. These bubbles can lead to the element failing.
In situ Concrete In situ concrete are added on the construction site. Trucks deliver this liquid to the site. This is any concrete element that has been poured into formwork and cured on the building site. This process includes the fabrication and assembly of the formwork, placing any required reinforcement, the pouring, vibration and the curing of the concrete. Once the concrete has been poured, there is a limited time before the concrete starts to harden and become unworkable to ensure that the concrete is placed in the proper position, the air bubbles removed (vibrated) and the desired finish applied. This is labour intensive process, resulting in congestion of the construction site. Uses floats to make a flat finish. This is done by hand. Note that it is difficult to control strength and quality of the In Situ concrete. Uses When to use In Situ? In Situ concrete in a great many applications. It is generally used for structural purposes (either self supporting or as primary structure)
Widely used in footings, retaining walls and all bespoke (non standard) structural elements. Sometimes concrete is sprayed into place using a pressure hose (shotcrete). This is useful for landscapes, swimming pools, and basements walls between piers or overhead surfaces. Joints There are wo types of joints in In Situ concrete: construction and control joints. 1. Construction joints – used to divide the construction into smaller and more manageable sections of work. We can’t lay all the concrete on the site at once. 2. Control Joints – Required to absorb the expansions and contractions that thermal variations cause and the long term tendency variations cause and the long term tendency of concrete to shrink over time. The elongation/shrinkage is proportional to the temperature differential, the material coefficient and the dimensions of the piece.
Both construction and control joints are potential weak points and must ensure that be detailed appropriately, especially in terms of water and moisture control. Pre-‐cast Concrete Pre-‐cast concrete is any concrete element that has been fabricated in a controlled environment and then transported to site for installation. This process ensures a much more standardized outcome that avoids many of the quality control issues associated with In Situ concrete. Pre-‐cast concrete elements also allow work on site to progress at a much faster rate.
Pre-‐cast concrete is widely used in many different applications. It is often associated with the structure of a building, bridge or civil works, forming part of the primary structure or self-‐ support panel type elements. Although rarely used in footings, it is common in retaining walls, walls and columns. Joints There are two joints: construction and structural joints. 1. Construction joints – the panel/elemental nature of pre-‐ cast concrete mean that joints natural occur when one precast element meets another. 2. Structural Joints – the type and performance of the structural connections joining the precast elements to each other and to other parts of the structure are critical for the overall performance of the building. Construction and structural joints will greatly depend on the desired aesthetic outcome. If joints are visible, it needs to be looked after carefully.
Finishes They need to be taken care of when transferring it to the site. Considerations Pre-‐cast concrete elements can be limited in size due to the transport in the city. On site changed are very difficult to incorporate. Also the cost benefits in repetition where it can be re-‐used with multiple panels. Beams and Cantilevers Beams A beam is a (mostly) horizontal element. The function of the beam is to carry loads along the length of the beam and transfer these loads to the vertical supports. • A beam can be supported at both ends of the beams • Supported at numerous points along the length of beam • Supported at points away from the ends of the beam (creating overhangs/cantilevers beyond the supports)
on of a BEAM is to carry loads along the length of the beam and transfer these loads to the vertical supports. A BEAM can be: CANTILEVER OF - supported at both ends of the beam PORTION THE COLUMN! - supported at numerous points along the FLOOR! length of beam - supported at points away from the ends of the beam COLUMN!
A CANTILEVER is created when a structural element is supported at only one end (or the overhanging portions of a member are significant). The function of a CANTILEVER is to carry loads along the length of the member and transfer these loads to the support.
(creating overhangs / cantilevers beyond the supports)
Supported at only one end of the - •supported at only one end of the beam (these beams are called cantilevers) beam (these beams are called FLOOR! cantilevers)
A CANTILEVER can be: - horizontal - vertical - angled
FLOOR LOAD! CANTILEVER!
Illustration from CHING ‘ Building Construction Illustrated”, 4.02 (2008) Illustration from CHING ‘ Building Construction Illustrated”, 5.36 (2008)
Cantilevers A cantilever is created when a structural element is supported at only one end (or the overhanging portions of a member are significant). The function of a cantilever is to carry loads along the length of the member and transfer these loads to the support. A cantilever can be: • Horizontal • Vertical • Angled
SUPPORT! Illustration from CHING ‘ Building Construction Illustrated”, 4.11 (2008)
Published on May 19, 2014