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Commissioned Reports - Round Wood


Date: 2005
Title: Improved durability timber piles and utility poles (225817)
Authors: Report commissioned from BRE
Full Report: PDF

Summary
This project produced a BRE Digest following a comprehensive review of the options available for enhanced durability specifications and other measures to protect timber, particularly in ground or water contact. Information from a large number of sources including industry participants was summarised in this report.

During the course of the project, as a result of EU legislation, chromium based wood preservatives were withdrawn from the market, emphasising the need for this work.

The following potential enhanced durability processes for timber elements such as piling, poles and bridge beams were the subject of practical investigation as pre-installation of borate preservative via centre borings and by polymer wrapping.

Barrier coatings are used for post foundations for buildings in North America. Remedial and supplementary treatment using borate and sodium fluoride is also practiced in the US, and elsewhere, on items such as utility poles and railroad ties. There are methods that are practical and effective for improving the durability of timber elements. For the most part these have not been taken up in the UK.

A review of the suitability for untreated timber piling installed below the water table in the UK has been carried out, in collaboration with Green Piling Ltd. In a unique piece of work, test driving of Sitka spruce log poles was carried out at site near Middlesbrough. It was found that Sitka spruce had high compressive strength and was resilient to pile driving forces. The log poles obtained were noted to be good quality in terms of straightness, with good development of latewood and low knot content. The potential of timber piling is enormous; however more research is needed to remove doubt on the issue of long term durability, in particular the effect of bacterial degradation. The work so far has highlighted the opportunities for UK grown timber, in particular Sitka spruce, in a new application.
Further work on developing the use of UK grown timber for engineering applications, including piling, would be worthwhile. This could provide the basis for longer term monitoring of test items, together with further development of links between interested parties.


Date: 2004
Title: UK Timber for Marine and Geotechnical Applications (217144)
Authors: Report commissioned from BRE
Full Reports: PDF. BRE Digest 479 available from www.brebookshop.com
BRE Digest 479 cover: PDF.

Summary
The project objective was to investigate and provide guidance on the usage of UK hardwood and softwood timber for piles, marine use, retaining walls and foundations. BRE Digest 479 Timber Piles and Foundations was based on this report.

This report also details the further work carried out on Copper Chrome treated sycamore, Fibre Reinforced Polymer coated timber, full scale axial load testing on Sitka spruce logs and compression strength tests on small scale samples.

Wooden piles are widely used overseas, but are not often considered in the UK for on-shore structures because of the perceived reliability and drivability of the principal alternative, pre cast concrete piles. Doubts about long term performance count against the use of timber. However, timber piles driven below the water table can last indefinitely; treated timber can withstand acidic and alkaline soil conditions better than concrete. The Canadian Permanent Wood Foundation (PWF) system using timber bearers on a drained gravel base will be viable for some types of structure in the UK, particularly in positions with poor access. Timber can and is used for retaining walls, and offers an attractive alternative to concrete.

For marine structures greenheart is the principal species used because of its availability in large sizes, drivability, marine borer and abrasion resistance. UK timbers such as oak and Douglas fir are being used for marine works, but in limited quantities, and are considered less durable. Waste plastic piles and Fibre Reinforced Polymer piles are beginning to enter the UK market and have been extensively used in place of timber in the US. The use of UK timber as a geotechnical material requires promotion and development, but will probably remain a niche market for on shore use. Tropical hardwoods for marine works are hard to match for durability and strength. UK grown timbers can offer viable alternatives for many of the less demanding geotechnical and marine roles, and should be used wherever possible. BRE Digest 479 Timber Piles and Foundations aims to provide suitable stimulus and guidance for the use of British grown timber in this respect.

Timber is a hugely capable civil engineering material, with the additional advantage of being sustainable. Trees, in particular conifers, make natural piles. Timber foundations may be particularly suitable for countryside structures such as bridges, forest chalets and activity centres, as well as post and beam timber buildings in waterfront or flood prone locations. Home grown treated softwood and hardwood timber should be considered as alternatives to imported tropical hardwoods wherever possible.  Although CCA treated timber cannot from June 2004 be used for marine structures, it can still be used for freshwater and brackish water piles, as well as on shore. One of the suggested methods of reducing global warming has been to bury timber to create carbon dumps. Using timber for piled foundations would effectively achieve this. There is likely to be increased interest in the use of sustainable foundation materials in the future, and timber is a suitable alternative to concrete in a number of forms ranging from driven piles, to pads and retaining walls.



Date: 2003
Title: Round timber in construction: an introduction
Author: Report commissioned from TRADA
Full report: PDF

Summary
Prior to the introduction of tools such as saws timber was largely used in its natural round form, often connected together with lashings rather than by mechanical jointing. This sheet outlines the processes to create these constructions.


Date: 2003
Title: Round timber in construction: Notes for structural design
Author: Report commissioned from TRADA
Full report: PDF

Summary
Structural Engineers designing round timber elements are often faced with limited information with which to support design evaluations and connection detailing. This sheet gives a technical and normative background to the design of round timber structures. It brings together basic terminology, grading and species selection advice together with suggested simplified design approaches and key references for further detailed information.