Services

Structural Design

GC Robertson and Associates can provide structural design work within several different disciplines, see below for more detail;


Residential        Commercial, Industrial         Listed/Historic Buildings


Foundation Design     Statutory Background












Residential

The complexity of structural engineering work required for the construction of new dwellings and the extensions and alterations to existing ones can often be underestimated, for although in the main the structures are small in civil engineering terms, an appropriately designed and well detailed scheme can save time, reduce cost and simply make life less stressful for all involved in the project. This is doubly important when someone is living in the structure in question. With existing buildings time taken to find out about the form of the existing construction including any previous alterations is rarely wasted.

We have very wide experience of both new build and alteration works on residential buildings from clay lump and traditional timber frame through all kinds of masonry construction to timber panel construction, and concrete / steel framed houses.


Commercial, Industrial

The requirements of work on commercial and industrial buildings largely stems from the fact that their function is paramount and often the building form simply follows the required function. The structural design should follow this principle to give a practical, buildable economic solution.

The commercial and industrial sectors are often less conservative than the residential market in embracing recent construction technology and the economic benefits this can bring.

Alterations to commercial and industrial buildings are often primarily governed by the need to minimize disruption to the main activity of the concern, and care and planning taken at the design stage can minimize disruption during the work itself.

G C Robertson & Associates have long experience in both the structural design of new commercial & industrial buildings and of alterations to them from portal framed industrial buildings, restaurants, schools, lifeboat stations to golf driving ranges.


Listed/ Historic Buildings

Structural work on listed or historic buildings can either be to deal with defects or to extend / alter or change their use.

Any structural work to a Listed Building will require investigation to determine the form of the original structure, how it works and its capacity. In general the philosophy governing repairs and alterations to listed buildings is to maximize the retention of the existing structure and finishes, though there are wildly divergent approaches to this all with their own benefits.

  • Repairs can be carried out using exactly the same methods as the original construction, thus preserving the way the structure works.

  • Using 'modern' techniques e.g. steel plates, posts, resin injection etc. on traditional timber structures can allow retention of more parts of an original structure than replacement of like for like and can be seen to provide a more 'honest' repair - the repairs can be seen for what they are.

  • Minimum intervention. Modern day methods of structural analysis and design Codes of Practice have generous factors of safety built in and often existing buildings will perform satisfactorily even though they may be woefully under designed by modern standards. It is possible to take the view that if a building has been in use for several hundred years it is bound to stand up for a few more years and to keep any repairs / replacements to an absolute minimum. This however can be taken too far and knowing when and how far to intervene is a matter for engineering judgement.

  • The use of modern day finishes e.g. cement render and modern masonry paints on traditional timber framed buildings can promote decay, and the use of lime mortar and other traditional finishes allows the timber frame and infill to breathe but some conservation evangelists would have you believe that traditionally finished buildings will never decay - this is simply not true!

  • Conventional conservation practice recommends that repairs to oak framed buildings are carried out in new green (unseasoned) oak which is much easier to work and is less likely to have nails etc. embedded in it, also as the oak then dries and shrinks it can lock joints together. In contrast however recent advice on reducing construction waste is pushing the use of recycled timber for such projects.

  • Very few historic buildings have remained unchanged since they were built, most have been repaired or altered at some stage, others repeatedly so that one can often find a sixteenth century timber framed building hiding behind a Georgian rendered facade or a Victorian brick facade. It is important to have an in depth knowledge of the local traditions in construction over the centuries to be able to read the way the building has been altered and understand the likely construction forms at different times in order to be able to design repairs and alterations that will work with the existing structure.

  • G C Robertson & Associates Ltd have worked on a large variety of listed and historic buildings and we can appreciate the depth of the heritage of historic buildings that abound in Suffolk and we believe that we have helped in a small way to ensure that this heritage is passed on for future generations to enjoy.

It can be seen from the above that repairs and alterations to listed / historic buildings require a depth of knowledge of materials and building techniques beyond that of the structural design of new buildings.

It is important that the Conservation Officer of the Local Authority is consulted prior to any work on a listed building to check whether Listed Building Consent is required - see below (Statutory Background).



Foundation Design

This short article gives an overview of the common factors governing foundation design of residential or small commercial buildings in East Anglia and a summary of commonly used foundation types.

Most of East Anglia is relatively flat and is composed of either sands or clays with adequate capacity to withstand the loads imposed on them by low rise buildings, so on the face of it most foundation design in this part of the world should not be particularly onerous and this is indeed the case with the simple approach of digging a trench 1 metre deep and filling it with concrete, sufficing in most cases. However in the following cases this is not sufficient and special foundations can be needed.

  • On clay sites the roots of trees (or even large shrubs) can rip off by osmosis water molecules that are chemically adsorbed to the surface of the molecules of the clay causing large volume changes (shrinkage / heave) of the clay which can cause movement of foundations bearing onto the clay. Conventional foundations can be deepened to get below the level of the clay affected by the roots or piled foundations can be used instead. The recent increases in Landfill Tax have favoured the use of piled foundations or reinforced rafts for small stand alone buildings.

  • Made Ground. Unlike the North of England, East Anglia does not have a history of widespread mining, but small pits and quarries for the extraction of sand, gravel or clay were common and these were often subsequently infilled with soil or refuse. These pits are not always picked up by site investigations unless the site is peppered with boreholes or trial holes though they are sometimes recorded on historic Ordinance Survey maps. Old wells are often found during work on domestic extensions and they were, unsurprisingly placed as near as possible to the back of the original building and deep sewers or surface water drains can also be problematical.

  • Alluvium. Recently deposited river bed material is often so soft that it is unsuitable for taking the loads from conventional foundations or contains large amounts of peat which undergoes large volume changes with changes of loading.

  • On sandy soil the presence of a high water table means that the sides of excavations for conventional foundations can fall in before the concrete can be poured into a footing so other solutions need to be found.

With all of these, alternatives to conventional foundations can be required and we can provide designs for a variety of special foundation types to cover these situations.





Statutory Background

If you are new to the world of building construction it can be useful to have a broad outline of some of the legal hoops that need to be jumped through in order to construct or significantly alter a building.

Planning Permission - If you are proposing to construct a building or to modify a building so as to alter its external appearance Planning Permission is likely to be required and advice of the Local Authority should be sought.

Local Building Control Building Regulations Approval - There are a myriad of government regulations concerning the details of design and construction of buildings and these need to be complied with when constructing or altering a building. Part of these regulations govern structural design and construction requirements, and normally an application is made to the Building Control section of the Local Authority to gain approval of the design, and then the construction is checked on site at various stages by a Building Inspector.

Listed Building Consent - Some existing buildings, usually of special architectural or historical interest are listed and for these any significant extensions or alterations (even internally) require Listed Building Consent. The Conservation officer of the Local Authority can advise on whether a building is listed and if so what is required to gain consent. More details of this are given in the article above on Structural Design for Listed / Historic Buildings.

Construction Design & Management (CDM) Regulations - see CDM Co-ordinator.