Hospital – Basic design criterion, influences and consideration for controlled Defects & Structure Repairs (Rehabilitation Work)

Post date: Oct 18, 2009 2:44:31 AM

INTRODUCTION

Buildings are structures which are designed with certain life span however with proper maintenance and sufficient knowledge on rehabilitation work, the life span of the building could be prolong (50 years, if the designer is designing in the light of BS 8110, Table 3.3) and continue to provide intended service(s).

EN1504: THE GENERAL REQUIREMENTS

Previous postings/paper discussed about the method in preparing appraisal for repair/rehabilitation/ maintenance work for the concrete structures. Nevertheless, we will highlight once more the methods as specified in EN1504 which are:-

• Assessment of the registered state of a concrete structure

• Determination of the courses of damage

• Determination of the objective of the rehabilitation of a damaged concrete structure

• Choice of relevant principles for rehabilitation of a damaged concrete structure

• Choice of methods for rehabilitation of a damaged concrete structure

• Definition of the properties for repair materials and systems for rehabilitation of a damaged concrete structure or its members

• Specification of requirements for the maintenance that should always follow rehabilitation of a damaged concrete structure or its members.

THE SINGLE MAIN IMPORTANT CRITERION IN DESIGN

Aside from the repair and rehabilitation works, the defects can be control prior to construction by determining the type and class of concrete for every members of the concrete structure. The determination and consideration should be based on BS EN 206-1 which is relevant to BS8110 (Part 1, Clause 2.4.7 Material properties for durability) and also Eurocode 2 (Part 1, Clause 1.2.2 – Other reference standards). Previously in BS 8110, the guidance for this was underlined in BS 5328 which is superseded by BS EN 206-1:2000; New European Standard for Concrete. The BS 8500 is the complimentary copy of BS EN 206-1:2000 to the British Standard. It is highly recommended that one should use Figure1 at page 7 of BS 206-1:2000 for more information and the relationship of BS 206-1:2000 to other codes. This code shall assist designer to determine the concrete cover and durability for their intended design.

In the normal construction process, the use of the said code has been applied in most of the highly toxic or chemical facilities. It is been normal practice for most designers not to take into consideration the exposure type in their design for durability and robustness; the design is totally based on BS 8110 only and not in the light of EN BS 206-1 although it has been highlighted clearly in Table 3.3 in BS 8110.

This article shall discuss the general issues in regards of using proper reference(s) since it is well understood to designer, Structural Engineer and Consultant in their Term of Reference when appointed by the Client; they are exposed to risks and to guarantee their sufficient/proper/value design safe and functional to intended inhabitant. Eurocode 8 - Design of structures for earthquake resistance will not be discuss at this moment as Malaysia is sitting relatively outside of the Ring of Fire Map and skeptically in regard to tsunami; most of the shores are armored with wave breaker and/or break water or buffer zone(s) which would reduce the amplitude of possible gigantic waves. However, it would be appropriate for designer to counter check to hydrographic map of the region or a simple consideration based on the vessel’s draft. This consideration will give the client the edge in case of possible natural disaster, this facility will remain intact and provide continuity in services (parallel to MAMPU requirements and recommendation in their letter MAMPU.BPICT.700-4/2/11(3) dated on the 22th January 2010 to all Head of Government Ministry, Department, State Secretary and Local Authority). There are high possibilities that the Malaysian Government is going toward integrating SOx into their management.

The hospital is a facility which is fully equipped with systems and functions which are relative to the usage of chemical for various usages. Therefore, it would be appropriate for designer to divide them into zones in their design. The criterion and considerations are very subjective, thus the article shall highlight possibilities for consideration.

STRUCTURE DESIGN REQUIREMENTS (BRITISH AND EUROPEAN STANDARD)

This article will take Queen Elizabeth Hospital of Kota Kinabalu, Sabah as an example (Disclaimer – This article is only for discussion and shall not be use and considered as a guide in scrutinizing/severing design(s) of the said hospital or any other hospitals)

Based on Table 1 of BS EN 206-1:2000

X0 Consider Inside building with normal functions

XC1 Consider Sewage treatment plant and some storage pit

XC2 Consider Foundations

XC3 Consider RC wall and roof

XC4 Consider Drains, block thrusts, sumps, chambers and manholes

XD1 Consider Surfaces exposed to chlorides - stores, etc

XD2 Partly Pits/structure member most time exposed to chlorides - stores, etc

Based on Table 2 of BS EN 206-1:2000

The designer should consider if not simulate possible risk(s) based on the inventory of sludge formed from hospital processes and the infrastructure/ facility’s connection(s) in transporting the sludge, leakage, surface water, contamination and others. The existing parameters available in the table are SO4 2-, CO2, NH4+, Mg2+, pH for ground water and soil, and acidity of the soil. For other chemicals exposure, it would be highly recommended to review it with chemist for possible chemical reactions and their properties.

CONCLUSION

Although the BS EN 206-1:2000 might specify cover thickness in determining the durability, it is highly recommended that designers and builders to consider the other possibilities which would or might or possibly contributes toward deterioration such as;-

• Half cell potential due to chemical reaction which will react to corrode the reinforcement bars

• Cracks during construction due to cold joining (due to inability to pour within 45 minutes of concrete casting)

• Other possible and tangible cause(s) which enhance/expedite/cause the degradation of the concrete structure's strength and/or durability.

For detail discussions and guidance (in design criterion and structural repair), please contact the Principal of MCS.