Construction Technology and Environmental Services

Question 1

Types of foundation

Answer 1

Strip
Raft
Pad
Piled

Question 2

What are the advantages of a pre-cast concrete plank floor?

Answer 2

Floors using precast units offer a number of benefits. The spanning ability of the units is such that the spacing of secondary beams can be increased (compared to when traditional decking profiles are used). The construction system is most efficient for column grids of approximately 9 m by 9 m. The units provide a flat soffit. Advantages:
− Less formwork required
− Curing time of concrete eliminated (Programme)
− H&S advantages
− Quality control easier
− Aesthetics – as fabricated in a controlled environment, range of shapes and sizes with smooth finishing.

Question 3

What are the disadvantages of a precast concrete plank floor?

Answer 3

Disadvantages:
− Less flexible design terms
− Requires use of heavy duty craneage
− High degree of site accuracy required to ensure pre-cast concrete unit can be accommodated without any alterations or making good

Question 4

What are the advantages of a composite deck?

Answer 4

Composite slabs are an excellent choice when speed of construction is important. Bundles of decking are lifted into place on the steel structure, for distribution by hand.
The number of crane lifts needed, when compared with the precast alternative, is greatly reduced.
The ability to stack the pieces of decking into bundles also reduces transport time and costs.

Question 5

What are the disadvantages of a composite deck?

Answer 5

More time on site required, propping and deliveries of concrete to site required,

Question 6

What are alternatives to the above (precast/composite deck)?

Answer 6

Post tensioned slab foor:
Post-tensioned slab benefits as opposed to RC slabs:
* For span lengths over 6 metres, PT slabs are often more cost effective. Concrete reductions up to 25%, and rebar reductions up to 65% are typical.
* It allows design of longer spans in elevated members such as floors or beams.
* It allows slabs and other structural members to be thinner.
* Post-tensioned slabs typically have less cracking and less permeability when detailed properly.
Main Disadvantages:
* High degree of control over materials, design and quality of workmanship is required.
* Special alloy steels are dearer than most traditional steels used in reinforced concrete.
* Extra cost of special equipment required to carry out the prestressing activities.
* Cost of extra safety requirements needed whilst stressing tendons.

Question 7

What are the UK reduction targets?

Answer 7

Climate Change Act 2008 Establishes a legally binding target for the UK to reduce its GHG emissions by at least 80% from the 1990 baseline to 2050.
To outline how the government intends to achieve this aim, it has published The Carbon Plan: Delivering our Low Carbon Future. Measures include:
− reducing demand for energy, by e.g. incentivising business to use less energy through the Climate Change Levy.
− putting a price on GHG through the EU Emissions Trading System.
− use of smart meters.
− providing reporting requirements through the Streamlined Energy and Carbon Reporting (SECR) policy.
− Investing in, and promoting, low-carbon technologies.

Question 8

What legislation required the UK to reduce its carbon emissions?

Answer 8

Kyoto Agreement – international treaty signatories agree to reduce greenhouse gases and emissions.
UK Climate Act 2008 – as previous question
Environmental Protection Act 1990 – deals with waste and disposal of hazardous materials

Question 9

What legislation is there within the construction industry?

Answer 9

Part L – Conservation of Fuel and Power:
* Limiting heat gain and losses
* Providing building services which are efficient
* Effective controls
* Properly commissioned
* Information to be provided so that the building can be operated efficiently

Question 10

What is the build of a traditional plasterboard and stud wall?

Answer 10

Plasterboard, gypframe, insulation, breezeblocks, metsec, brickslips.

Question 11

Tell me about these assumptions?

Question 12

How accurately were you able to present these costs if there was no design?

Answer 12

I based the costs on similar projects where extensions were used as part of the project, I also had the cost data and returns for the ground floor wall infill where a floor to ceiling window was being replaced with a wall of the same construction. However, know that these walls were to be load bearing I added in a budget allowance for any structural elements (steel).

Question 13

What is the advantage of using secant piling?

Answer 13

Acts as a retaining wall
As basement was also being constructed secant piling had other advantages as a primary layer of waterproofing
By using rebar cages the piles could be tied into the pile cap which was extending out as a toe for the façade

Question 14

Name 2 other types of frequently used piling?

Answer 14

Contiguous
Sheet piling
Bored piles – off site manufacture
Driven concrete piles – on site installation

End Bearing piles – rest on bedrock or firmer ground
Friction piles – rely on the physical transfer of sheer forces between soil and the pile

Question 15

Why would you choose secant over contiguous piling?

Answer 15

Secant acts as a retaining wall.

Question 16

What was the cost change for using secant foundation as an alternative to hand dug underpinning?

Answer 16

There was a potential saving of £550k
There was a programme saving of 5 weeks
There was an NIA loss of 150m2 in B1

Question 17

Was it a worthwhile exercise using secant foundation as an alternative to hand dug underpinning?

Answer 17

Yes, it was decided that this method should be used as the loss of NIA was minimal the overall project but the time and cost savings, as well as buildability were advantageous.
It is important to note that the piling rig would already have been on site and that the overall increase to the amount of piling on the project overall was 25%

Question 18

What impact would a composite deck have on the existing structure below?

Answer 18

The existing structure was examined by the structural engineer on the project and found to be suitable to a composite deck with very minimal changes. A further study would be used to determine if the structural steel elements could be reduced.

Question 19

Could the reduced weight of the composite deck have further savings in the structure (i.e. columns etc… not requiring the same strength, did you consider this?

Answer 19

Yes, I considered this, and had asked the structural engineer to review the Steel requirement and indicate if there was a reduction, due to a lack of certainty I decided to leave the budget for the steelwork in place.

Question 20

At what stage did this happen?

Answer 20

This was during the Stage 3-4 design phase, also during the MC PCSA.

Question 21

What were the benefits of using the precast concrete plank construction? You mention considerable crane time - what effect did this have on the programme/ prelims? How was the 550k saving built up?

Answer 21

• Manufactured off site so works on site can progress while planks are constructed
• delivered when required - no need for lots of storage
• Uniform sizes and quality as not manufactured on site
• reduces requirement for temporary works (propping, formworks etc.)
• Because the precast planks became non uniform and increasing in size the crane time was increasing, this also meant access was an issue as the steel frame could not be erected simultaneously
• Lifting every beam into place can be more time consuming than just lifting steel decking once, installing it, and having the concrete pumped by a separate machine, allowing steel frame erection to continue
• Higher transportation cost and risk due to the increasingly non-uniform design of the planks
• procurement issues - there was considerable issues with procuring the precast planks in the sizes and quantities, usually the building (i.e. a car park) uses the standard sizes available and designs around that, rather than designing the building and procuring the sizes post design.

Question 22

What would be the risks to building integrity with a rainwater pipe running through?

Answer 22

• Water ingress
• Damage to internal finishes
• Flooding
• Damp & Mould

Question 23

CLT - Was the CLT a structural element on hopton street? What was the structure?

Answer 23

• CLT Wall
• Insulation and waterproofing
• Metsec brick slip carrier frame
• Brick slips

Question 24

What assumptions did you make for the studwork wall?

Answer 24

• Structural steel columns as load bearing element
• External brick slips or traditional brickwork
• Insulation and waterproofing
• Internal plasterboard
• tape and joint
• painted

Question 25

What is a secant wall piling foundation?

Question 26

What are the waterproofing grades?

Answer 26

GRADE 1a Seepage and damp areas from internal and external sources are tolerable, where this does not impact on the proposed use of below ground structure.

GRADE 1b No seepage. Damp areas from internal and external sources are tolerable.

GRADE 2 No seepage is acceptable. Damp areas as a result of internal air moisture/ condensation are tolerable; measures might be required to manage water vapour/condensation.

GRADE 3 No water ingress or damp areas is acceptable. Ventilation, dehumidification or air conditioning necessary; appropriate to the intended use.

The agreed grade should meet with client’s expectations for the intended use of the below ground space. Reducing the grade could increase the risk of not meeting the expectations of the client.

The grade of waterproofing protection should be agreed at the earliest stage. Reducing the grade increases the risk.

Seepage has been defined separately to damp, and specifically mentioned as either acceptable or unacceptable depending on the Grade of protection.