environmental statement vol 3 appendix e part 54 of 56_tcm21-162474

7/27/2019 Environmental Statement Vol 3 Appendix E Part 54 of 56_tcm21-162474

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Walsh Associates SEAGRAVE ROAD

Consulting Structural & Civil Engineers

Structural Principles Report Page: 15

5.0 Structural Design Criteria

This section describes the methods used to design the various structural element

systems and types. The following assumptions have been made by Walsh

Associates:

5.1 Dead Loads

Dead loads should generally be kept to a minimum given the number of

floors to be supported. This should be achieved by:

Partitions should be drywall construction rather than stud

External cladding should be lightweight, rather than block

Floor finishes should avoid the use of screeds.

In general blockwork should be avoided due to both its weight and also

because it is a brittle material with onerous deflection criteria.

Assumed dead loads for a typical floor are shown in Table 2

Table 2 Superimposed Dead Loads

Component LoadingFloating floor 0.3Finishes & ceiling 0.5

Partitions 1.0Total 1.8

Cladding assumed to be Glazing plus backing, taken as 1.5kNm-2

5.2 Live Loads

Live loads have been assessed in accordance with BS 6399 Pt1 and are

summarised in Table 3. Live load reduction will be carried out in accordance

with Bs6399 Pt 1, Table 3, repeated below in Table 4.

Table 3 Live Loads

Use Loading kN/m Residential 1.5Retail / Commercial 4.0Car Parking 2.5

Table 4 Live Load Reduction

No of Floors Supported % Reduction in Total Imposed Load1 02 103 204 305-10 40

Above 10 50

5.3 Wind Loads

The main stability forces to be resisted are wind loads. Loads have been

initially assessed based on BS 6399 Pt 2 1997. Due allowance in the design

has been made for shape factors, dynamic augmentation and dominant wind

direction. However a wind tunnel test will be required to establish the wind

regime on the structure, the cladding and surrounding environment.

5.4 Hydrostatic Loading

The basement structure will be designed for water 1.0m below grade level,

as required by BS 8102 Protection of Structures against Water From the

Ground


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5.5 Fire Resistance

The required fire resistance is yet to be established. However the current

climate of opinion may require up to 4 hours in the basement and 2 hours for

the superstructure. These can be achieved without major impact on the

structure. Fire resistance will be achieved by specifying a minimum cover to

reinforcement. A concrete structure will provide inherent fires resistance and

the core will provide a natural save haven.

5.6 Robustness

The size of structural elements required to support the lateral and vertical

loading will provide inherent resistance to accidental loads. Robustness as

required by BS 8110 Pt 1 Clause 3.1.4 will be achieved in the structural

design by:

i) The provision of both lateral and vertical ties via reinforcement.

ii) Key elements which if removed would cause unacceptable will

be designed in accordance with BS 8110 Pt 2 Clause 2.6

iii) Columns at ground floor will either be protected from vehicle

impact or designed for impact loading.

5.7 Durability

Concrete mixes and cover will be provided to protect the reinforcement

against corrosion according to the exposure conditions defined in BS8110 Pt

1 Section 6.2, as in Table 5.

Table 5 Durability Requirements

Condition ExposureResidential slabs mildBalconies moderateCar Park Severe

Foundations & structure in contact with ground TBC

The exposure for elements in contact with the ground will be determined in

accordance with BRE Digest 363 based on the level of sulphates in the

ground as determined by the site investigation

5.8 Basement Design Criteria

The basement will be designed to CIRIA guide 139 for the degree of

watertightness given below in Table 6.

Table 6 Basement Design Criteria

Use Grade

Car Parking Grade 1; minor seepage acceptable

Plant Grade 2; Seepage not acceptable

We note that NHBC now specify grade 2 as a minimum, however this can be

limited to the roof only if queried.

5.9 Deflection

The structure will be designed to the following criteria. These are derived

from BS 8110, BS8004 and the CIRIA guide to movement in buildings.

These criteria are established to prevent damage to non structural elements

and to prevent deflections from being visible.


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Table 7 Deflection Criteria

Element Criteria

Total vertical deflection of concrete

floors and beams under service

loads

Span/250

Vertical post installation deflection

of concrete floors and beams after

installation of finishes

The lesser of span/350 or 20mm

Total vertical deflection of steel

beams

Span/200

Vertical live load deflection of steel

beams

Span/360

Lateral sway under service wind

loads

Height/500

The structure will be designed for additional moments induced by

deflection (buckling) as per CIB FIP Model Code 1990.

In domestic structures a maximum foundation settlement of 25mm is

normally used as a deflection criteria, along with a differential settlement

between foundations of 19mm. These limits are not appropriate for high

rise structures given the magnitude of foundation loading. Instead

deflections are minimised and actions taken to mitigate against the

anticipated deflections. These measures will include:

Pre-cambering out deflections

Articulating finishes to accommodate movement

Building out deflections as the structure is built.

5.10 Human Comfort

As well as the criteria above the structure will be designed to the

following criteria, based on acceptability limits of humans to motion.

5.11 Design Standards and ReferencesWe shall design to all the appropriate British Standards and documents

approved by Building Regulations.

6.0 Construction Strategy

The construciton strategy has yet to be developed. It is envisaged that the site

will be developed in Phases above podium. It is unlikely to be feasible to

construct the podium in more than 2 Phases, for logistical reasons. The

fololwing strategy is proposed:

West Zone

Secant pile west zone perimeter

Install sheet piling along East / West zone split

Install bearing piles from ground

Excavate central area, leaving berm

Cast basement slab

Cast podium slab

Remove Berm, cast perimeter

Hand over basement for car parking & Fit out Commence construction superstructure

Commence construction of East zone and or Sueprstructure


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East Zone

Secant pile east zone perimeter

Excavate central area

Cast basement slab

Cast podium slab

Remove Berm, cast perimeter

Remove sheet piling

Hand over basement for car parking

Commence construction superstructure

This strategy was used at the Greenwich Reach project.

7.0 Sustainability

7.1 General

The engineering design of the project is to be developed in a holistic manner

in conjunction with both the Architectural and Environmental design in order

to minimise the effect the project has on the environment. This will be

achieved by considering both the structural arrangement and the materials

used.

Examples of positive environmental aspects that will be reviewed for

incorporation into our structural schemes include:

Using the inherent thermal mass of the concrete frame as a key

element of the environmental strategy.

Reducing the dead weight of the floor slabs by using a power floated

concrete finish, alleviating the requirement for a non-structural

levelling screed and thus reducing slab reinforcement and foundation

loads.

Using inherently robust, durable, self finished materials requiring little

maintenance.

Choosing a structural system with an eye to initial low cost and

reasonable embodied energy.

Focusing on design loads as just adequate for proposed use, i.e.

do not over design the structure computer software enables efficient

design.

environmental statement vol 3 appendix e part 54 of 56_tcm21-162474

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