r - The Hong Kong Polytechnic University

adopting method of grouping and categorization of elements of similar properties or deterioration performance.
INTERNATIONAL CODES AND PRECODES ON SERVICE LIFE
There has been much development in the concrete of service life design and planning in the last 15 years or so.
There has been a growing acceptance that safety levels of both new designs and existing structures to be
mandated should be in reliability or probabilistic terms. Considerable work has been done towards codification
of methods of assessment. The ISO 2394:1998 (ISO 1998) sets out the general principles of reliability-based
design of structures as well as the target reliability levels for the different limit states designs. 2001 saw three
heavy-weight publications on reliability-based assessment of existing structures. These are the ISO 13822:
Bases for Design of Structures – Assessment of Existing Structures (ISO 2001), and Probabilistic Assessment of
Existing Structures (JCSS 2001) and Probabilistic Mode Code (JCSS 2001a) by the Joint Committee on
Structural Safety (JCSS). Whilst (JCSS 2001a) details the general concepts and the framework of code
calibration, (JCSS 2001) and (JCSS 2001a) provide further guidelines for assessment related to existing
structure. The concepts of reliability and limited states, including the reversible serviceability limit states, the
management and levels of reliability contained in these documents are filtered into the Eurocode EN 1990:2002
Basis of Structural Design (BSI 2002). EN1990 explains the calibrations of the partial factors method against
the target reliability levels. The fib Model Code for Service Life Design 2006 (fib 2006) and the ten-part ISO
15686: Buildings and Constructed Assets- Service Life Planning (ISO 2000-2010) outline methods for planning,
designing and predicting service life. The concept of reliability is embedded in the recently published fib Model
Code 2010 (fib 2010).
These publications issued by international research bodies provide operational rules as well as the background,
trends and design recommendations. The “model codes” provide framework for the code drafters to calibrate or
produce standards and code of practices for use by practitioners. The relationship between these references can
best be illustrated in “Figure 1” below.
Fib Model Code for
Fib Model
Service Life Design: 2006
Code 2010
Model codes
Codes and
Standards
Fib
International federation
for concrete structures
Euro Codes
ISO
Other international
organizations: CIB, RILEM,
IABSE, JCSS, etc
JCCS Probabilistic
RILEM 2001 Probabilistic
Model Code: 2001
assessment of existing
structures
EN1990:2002
Basis of
structural
design
ISO 15686
(10 parts, 2000-2010)
Service Life Planning
ISO 2394:1998
general principles on
reliability of
structures
ISO 13822: 2001
bases for design of
structures-assessment of
existing structures
Figure 1 The world knowledge map of service life
Though principles are said to be applicable for the assessment of existing structures, direct application is
however extremely difficult due to the specific conditions of HKHA buildings and the large amount of variables
in the same building. Methodology developed for HKHA’s aged buildings has taken the advantage of
availability of huge amount of corrosion-related field data collected from CSIP and is based on the above
international models codes and standards with suitable adaptation.
THE CONCEPTS
Cost-effective of repairs as a serviceability limit state
Concrete spalling in domestic buildings is normally an acceptable defect which can be repaired. It can thus be
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