DESIGN CHANGE APPROACH OF BS EN 1997 IN THE UK
A new European suite of geotechnical design, proving and building paperss will in due class mostly replace British codifications and criterions. This intent of this paper is to analyze the alterations in design and buildings one time the new Eurocode is to the full implemented in the UK. In this context, this paper highlights the of import characteristics of the new Eurocode system and seeks to demo how they may impact pattern. Some old surveies have been the beginning of this scrutiny and rating. For illustration, the study published by the Institution of Structural Engineers ( 2004 ) has highlighted the challenges confronting applied scientists in accommodating to the Eurocodes. The intent of this study is to help the applied scientists to understand the most of import differences that geotechnical applied scientists are meeting while implementing new suit of geotechnical Eurocode and advocates the readying of counsel to ease their transition into pattern.
The chief alterations to geotechnical pattern introduced in the Eurocodes are concentrated in Eurocode 7 Geotechnical design. It is of import to appreciate that the new European suite of geotechnical paperss is a comprehensive, coupled system of codifications, criterions and proficient specifications. These bespeak how information on the land is to be acquired, how it is to be interpreted and transformed into design parametric quantities and the geometry of geotechnical constructions, and how these constructions are to be built and maintained, with suited monitoring and quality confidence.
Figure 1 illustrates the system of new European paperss while Tables 11 and 2 show the current BS codifications and criterions and their approximative relationships with those European paperss that exist or are anticipated. There is direct correspondence for some paperss ( for illustration, some parts of BS 1377 are being and will go on to be replaced by an tantamount criterion from CEN Technical Committee 341, see Powell and Norbury, 2007 for illustrations ) while in most other instances there is limited convergence between the stuff ( for illustration, BS 8004 covers facets of the building ( “execution” ) of heap foundations found in BS EN 1536:1999 ) .
EC7 introduces a figure of of import alterations in the codification of design patterns. In peculiar it:
* Presents, for the first clip, a incorporate set of Principles for all geotechnical design
* Bridges the philosophical divide between geotechnical design and superstructure design that has existed since BS 8110, explicitly using bound province design and partial factors, was introduced in the UK
* Makes a clear differentiation between the turning away of an ultimate bound province ( failure of the land and prostration of all or portion of a ground-supported construction ) and of a serviceableness bound province ( undue motion and its effects ) . Much “routine” geotechnical design has historically blurred these two demands. The Eurocode should motivate greater idea about planing to forestall unacceptable motion, which should be good
* Requires more systematic idea about the grade of uncertainness in the values of geotechnical stuff parametric quantities for usage in design computations
* Introduces a grade of irresistible impulse by bespeaking that certain ( Principle ) activities “shall” be undertaken in both design and land investigation6.
EC7-1 is non merely about transporting out design but is besides approximately look intoing that a design will non make a confining status in prescribed design state of affairss. The codification does non state the reader how to plan, instead it lays down a set of steering design Principles, lists the many physical conditions that the land and the construction it supports may exhibit, and states how the constructed result must act.
The application of safety in bound province design computations
Current British codifications contain a scope of different ways of presenting safety into a geotechnical design, from the “working state” method utilizing a planetary safety factor, by and large adopted in BS 8004, to the partial factor method adopted in BS 8081. BS 8002 adopts yet another attack, that of the “ ( strength ) mobilization factor” whereby motion is limited by cut downing in the computation the value of strength ( and therefore strain ) mobilised in the land.
Most users of BS 8004 will hold performed a design computation that, by virtuousness of the ( big ) planetary factor of safety employed will hold ensured non merely that a ULS is avoided but besides that colonies are tolerably little. In contrast, EC7-1, in ULS computations, uses partial factor values that are intended to guarantee that geotechnical failure is avoided, and may non be big plenty to maintain colonies to an acceptable degree, peculiarly for softer, more compressible land such as normally-consolidated or lightly over-consolidated clay or farinaceous dirt ( BS 8004 Clause 184.108.40.206.2.1, p 9 ) .
Once implemented in the UK, the Eurocode paperss will hold the position of current BS codifications and criterions. It is expected that all mentions to BS paperss in the Building Regulations and other regulative paperss such as those of the Highways Agency and Network Rail will be replaced by mentions to the new BS ENs. The Eurocodes contain “Principles” that are “mandatory” ie they contain the word “shall” , as highlighted subsequently in this book. This means that if and when the new BS ENs are used to plan or to look into a design, these compulsory demands must be satisfied.
Institution Of Structural Engineers ( 2004 ) National scheme for execution of the structural Eurocodes: Design counsel Report prepared for The Office of the Deputy Prime Minister, IStructE, London
Powell, J ( 2003 ) A simple usher to unmoved land proving – in 7 parts. Part 2: Cone incursion proving 144065, BRE Bookshop, London
Powell, J J M and Norbury, D R ( 2007 ) “An update on execution of EC7” In: Land Engineering, June 2007, pp 14-17