What is the overview of ‘Load Transferring’?
Load -> Beams -> Structural columns -> Sub soil layer
What are the 3 axes?
- Longitudinal axis (length of beam/height of column)
- Major axis (longer than minor)
- Minor axis (shorter than major)
What are the 2 types of beam support conditions?
- Pinned (simply supported) (less than 90deg with load)
- Fixed (rigid) (Kept at 90deg with load)
What zone of a concrete beam would reinforcement steel be placed?
Tension zone.
Concrete is weak in tension but strong in compression
What are the bending stresses of simply supported/pinned connection?
- The bending moment at the supports are zero
- The maximum bending moment occurs at the mid span
- The area of tensile reinforcement steel is highest at the mid span (most bending)
What are the bending stresses of fixed/rigid connection?
Two bending moment types:
1. Hogging moments near the support (maximum hogging moment is at the support)
2. Sagging moments near the mid span (maximum sagging moment is at the mid span)
- The maximum sagging moment is significantly smaller than in the maximum sagging moment in the simply supported case.
- Therefore smaller cross-sections for beams with fixed connections can be used
What are the shear stresses of concrete beams?
- Tends to deform the beam
- Concrete is weak in shear (shear-links/stirrups) are used in beams to resist shear stresses developed by transverse loading
- The stirrups have longitudinal bars top and bottom -> for tensile strength requirements, and minimise shrinkage and cracks in concrete
What is axial loading?
Pure compression, generally upright beams
What is eccentric loading?
Load that is along the X-X, Y-Y, or X-Y axis (not centre)
What is pad footing?
- Interface between structural column and foundation material
- Reduces the stress transferred to the sub-soil by structural columns
What are the 4 minimum cover requirements are specified to AS 3600?
- Concrete grade used
- Exposure classification
- Method of formwork
- Method of compaction
What are cover blocks used for?
- Attatched between the formwork and the bottom of the outermost reinforcements
- Ensures minimum cover requirements
What is Newtons Law?
(In reference to support beams)
- Must be an equal and opposite force (‘T’)
- Counter balance is created by bond between the rebar and surrounding concrete
What is splicing of reinforcement bars?
- Joining two bars to provide a required length, a splice shall be provided
- Splicing transfers stress between two bars
- Overall length of two bars -> ‘Lap Length’
- Staggering splicing minimises weak points
What loads do suspended floors withstand?
- Dead loads: weight of the structural elements (for example, self-weight of the slab)
- Superimposed dead loads: weight of the non-structural elements (such as weight of floor finishes)
- Live load: weight of furniture and people
What stresses do suspended floors withstand?
- Bending stresses
- Shear stresses
- Torsional stresses
List 2 characteristics of thermal resistance in suspended floors.
- Suspended floors do not always need thermal insulation
- Suspended slabs with in-slab heating/cooling systems should be insulated
(min. R value should be 1.0)
What is slab action?
How applied load on a suspended floor is distributed/transferred to its structural supports
What is a ‘one-way slab’?
Slab supported at two edges
What is a ‘two-way slab’?
Slab supported at four edges
List the 5 benefits of concrete over timber floors.
- High level of durability
- Sufficient stiffness to avoid deflection under load (will not affect other elements of the building)
- Energy efficient because of their high thermal mass
- High level of acoustic performance which meets BCA requirements
- Constructed quickly where precast or composite elements are used
What are ‘composite concrete floors’?
- Made of concrete & steel
- Steel decking acts as permanent formwork
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What are ‘insitu concrete floors’?
- Designed to support walls anywhere within a slab
- The most flexible concrete floor type
What are ‘precast concrete floors’?
