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CIVL4903/9903: Civil Engineering Design
Semester 1 - 2024
Structural Floor Systems
Reinforced Concrete, Prestressed Concrete, Composite Steel & Mass Timber
Weeks 9 to 12
This week (Week 9)
• Design brief
• Floor systems
• Reinforced and Post-tensioned concrete,
• Tutorial 2
• 2nd lecture - step through Tutorial 1, view online
Next week (Week 10)
• Composite Steel
• Case studies, view online
Weeks 11 and 12
• Timber and roof design
Assignment 4 – due in Week 13 Friday 24th May at 11.59pm, submitted on Canvas
People
Services
What is a building?
Ground
Level
Soil
Columns
Foundations
Stability
Floors
Walls/cladding
Roof
Design brief: A new Sydney tower
Example: 8 Chifley Sq - 2013
Example: 100 Mount St – 2019
7
5
0
0
1
0
,0
0
0
7
5
0
0
1000 42,500
N
o
rth
Reinforced
concrete core
(10m x10m
preliminary)
Steel
frame
Design brief: Typical floor plan
East/West Section
Roof 130.7m
Level 32 126.7m
Level 31 122.7m
Level 30 118.7m
Level 29 115m
Level 28 111.3m
Level 3 18.8m
Level 2 15.1m
Level 1 11.4m
Ground level 6.4m
Basement 1 3.2m
Basement 2 0m
Column number and
positions indicative TBC
Assignment 3
Lateral stabilty
Assignment 2
Foundations and Geotech
Assignment 1 Bridge
Assignment 4
Floor structures
Design parameters
• What column spacing to use?
– At least 12m x 8m (timber floors less)
– Main columns straight down to foundation. Avoid transfer
structures – needs to work through car park
• What type of structure?
– Reinforced Concrete? Prestressed Concrete? Steel?
Timber?
• Design loads:
– Self weight 1.5kPa Superimposed Deal Load SDL,
– 3kPa Live Load
• Façade load: 2.5kN/m dead load around perimeter
• Design issues
– Cost, depth, weight, constructability, durability
CIVL4903/9903 – Week 9 to 12
• Intro to common structural floor systems
• Concepts for:
– Reinforced concrete
– Post tensioned concrete
– Composite steel
– Timber
• Simple scheme guidance for preliminary design
– Week 9 - RC and P/T concrete
– Week 10 – Composite steel
– Week 11 & 12- Timber and roof
Tutorial 2 and Assignment 1
Assignment
• Part 1 for Week 9 . Work out and draw a column grid
• Preliminary scheme in P/T concrete – Typical bay
• Preliminary scheme in composite steel/concrete
• Preliminary scheme in timber
• Cost estimates
• Comparison
Tutorial 2 – Post tensioned concrete – Week 9
• Explore ‘Rules of Thumb’ and P/T concepts
Assignment 4 - Part 1- Typical Office Floor Assingment will be submitted individually
1. Structural Layout (5 marks out of 20)
• The builder (your client) is considering composite steel or post-tensioned (P/T) concrete construction for the typical office
floors. In this assignment you will develop preliminary designs using each of these systems to contribute to the tender cost
plan.
• The brief requires a minimum typical column grid of at least 12m x 8m, and you will need to think how best to lay out columns
to best suit the plan and achieve a good balance between flexible open space, structural depth, and economy. You are
considering two main options for structural layout in the typical areas of the floor, one in P/T and one in steel composite
construction:
• Option 1 - Two internal columns per bay spaced at 15m with a 5m cantilever zone at each end and no perimeter columns –
using P/T concrete
• Option 2 - One internal column and two perimeter columns per bay to create two 12m spans (allowing for columns) - using
composite steel/concrete
• Make A4 sketches to 1:200 scale showing the two options for structure on a typical floor. Show edge of slab, columns
(draw as 900mm diameter although they may vary at different levels), beams (steel beams as a single thick line, concrete
beams as two dashed lines) core outline (assume 10m x10m) and gridlines. No need to show structural sizes yet (typical
sizes will be assessed in following parts).
• Near the core, column spacing can vary. Try to avoid columns very close to the core (why? – ask a tutor). Note: Use an E/W
grid spacing generally of 8.4m so that at basement levels, columns can align with car park spaces (not required to design the car
park in this assignment).
• At the west end, the floor will be supported fully on the braced steel structure
Structural floor systems – some basic concepts
▪ Horizontal spanning
▪ Transfer gravity loads to the vertical
system
▪ A significant % of the structural cost
▪ Highly repetitive, therefore, efficiencies
will be realised throughout the building
>> cost savings
▪ Categorised as one and two way
spanning
Concrete vs Steel Floor Systems
Concrete
▪ Traditionally more cost effective in Australia
▪ ‘Formed’ and adapted into many ‘systems’
▪ Reinforced or Prestressed
Steelwork
▪ Used extensively in the UK and USA
▪ Offers relative speed of construction.
▪ Lighter floor loads.
▪ Additional strength through composite
action
One way systems
▪ There are very few true one way
systems
▪ Mostly in houses and low rise units that
use fixed internal wall systems
▪ Introduction of beams and columns
creates a hybrid system:
➢Individual elements span one way
➢All loads have to be carried two ways to
reach the columns
▪ This is an important principle when
designing two way slabs.
Two way systems
▪ Reinforced & Prestressed concrete:
➢ Ribbed slab and beam
➢ Beam and slab
➢ Band beam and slab
➢ Flat plate
➢ Flat slab
▪ Structural Steel
➢ Beam grid with permanent metal
deck formwork
▪ Span in two directions to bring
loads back to a column grid.
▪ Opens up the floor space - much
greater flexibility of use.
▪ Used widely in all major structures.
▪ offices; car-parks, high rise
apartments; exhibition floors and
so forth.
Concrete vs Steel Floor vs Timber Systems - Continuity
Concrete
▪ Generally designed as ‘continuous’,. Ie
multi-span beams
▪ Benefit of using shorter end spans and
cantilevers
Steelwork and Timber
▪ Generally designed as a series of simply-
supported beams so simple joints
▪ More difficult to achieve cantilevers
▪ But can create continuity, but with more
complex joints (steel loses composite
action in hogging zone)
Concrete Floor Structures
Reinforced and Prestressed Concrete
Ribbed slab and beam Beam and (2 way) slab Band-beam and slab
Flat plate – 2 way Flat slab – two way
Reinforced and Prestressed Concrete
Ribbed slab and beam Beam and (2 way) slab Band-beam and slab
