Thursday, August 7, 2008

MRR2 FAILURES: Would the TRUTH be told?

Yesterday, sun2surf columnist Citizen-Nades in his article "Former minister wins uncivil war" wrote:

[quote]

The asking price by the new firm – Leonard Andre and Partners (LAP) was a mere RM18 million – just RM6 million more and they were providing space-age technology – carbon-fibre to save the cracking pillars.

Can we anticipate someone standing up and saying: "Yes, I take responsibility. It was me who approved the use of carbon-fibre technology which had never been tested or used in Malaysia previously."

[unquote]

I would like to tell Nadeswaran that Carbon-Fibre Technology (CFRP) is not space-technology and the proposed methodology for strengthening the reinforced concrete structure using CFRP is not something new and surely is not a space-technology, neither is it used for the first time in Malaysia.

The peeling of the plastic strap do not mean the strengthening works had failed. It is neither about taking responsibility for a failed technology or methodology. If ever we are to discuss failure, we should be discussing about the structural failures which was occasioned by the design failure during the construction stage.

How many of us gets to know the truth of the failure? To make matter worse, we have non-engineers who were fed with surreal knowledge of engineering design and construction technology. Equally we are puzzled by the statement made by Halcrow senior consultant (bridge engineering) Roger Bucky who said he had in 2005 advised PWD not to use carbon fibre straps because the plastic straps used to strengthen the pillars have limited ductility; but JKR proceeded with the use of the carbon fibre straps.

3 of the 18 carbon fibre straps on Pillar 18 had since peeled off.

Roger Bucky in his diagnosis attributed delayed ettringite formation (DEF) as the cause of the peeling of the straps.

For non-structural engineers they may think that DEF is some kind of a cancerous virus in structural concrete. So what is DEF?

Generally, DEF is seen as a form of internal sulphate attack. A number of factors such as concrete composition, curing conditions and exposure conditions influence the potential for DEF. DEF is believed to be a result of improper heat curing of the concrete where the normal ettringite formation is suppressed. The sulfate concentration in the pore liquid is high for an unusually long period of time in the hardened concrete. Eventually, the sulfate reacts with calcium and aluminium containing phases of the cement paste and the cement paste expands. Due to this expansion empty cracks (gaps) are formed around aggregates. The cracks may remain empty or later be partly or even completely filled with ettringite.

(Source: www.concrete-experts.com)

Self-desiccation of normal density (ND) high strength concrete may prevent delayed ettringite formation (DEF).

Was DEF as espoused by Halcrow the reason of the structural failures? It wasn't!

So what cause the failure? What caused the cracks in the crossbeams?

The investigation carried out by the experts into the cracking has comprised of both field investigations and design assessment. The field investigations included site inspections; data gathering; crack mapping; cover-meter tests, concrete strength sampling; chemical tests and crack width monitoring.

The design assessment comprised of both load assessment and structural analysis by a number of methods including Code Assessment, 2D Strut and Tie Modelling, and Non-Linear Finite Element Modelling. The analysis covered both construction phase loading (from temporary overhead erection loading used to erect the precast superstructure segments) and in–Service Phase loading from permanent loads and traffic.

Based on Site Investigations and Design Assessment, the primary causes of the cracking at the critical sections for the Typical Piers and Abutment B are a result of temporary gantry erection loading and early thermal and shrinkage cracking which occurred during the Construction Phase. These load conditions were far more onerous for the structure than any In-Service load conditions.

For the In-Service Phase, calculations by both traditional Bernoulli methods and by Strut and Tie methods have demonstrated that the Pier structure has more than the required capacity to carry the factored In-Service loads in-accordance with BS 5400 Code requirements.

In the analysis the development of bond stresses in the reinforcing bars has been checked and found to comply with Code requirements.

The FE Model predicts that the Ultimate Capacity of the pier cantilever is in the order of 2.6 times the applied Nominal Loads, which far exceeds the Code required factor of safety. Ultimate failure at this level of overload is ductile as required by the Code. Sudden failure would not occur even at this extreme overload condition.

This was the structural analysis reported. However, the recommended solution was not acceptable and was considered as superficial. The engineers wanted a comprehensive rectification methodology, which would ensure that the structural integrity would comply with the Need Statement and in accordance with the Government's Requirement as postulated in the Contract Document. JKR holds the contractor fully responsible for the default which constituted a breach of contract and wanted the contractor to make good the defective works in full compliance of the agreed design integrity.

Under the PWD From DB/T Contract Terms and Conditions, it was stipulated that the Contractor shall check the design and accept responsibility (Read Clause 2.3.2).

As stipulated under Clause 2.2 of the Conditions of Contract: "The Contractor shall be fully responsible for the design, execution and maintenance of the Work/portion of the Works for which the design have been accepted by the Government, and shall absolutely guarantee the Government independent of fault that the design, materials and workmanship for the Works or portion of the works is suitable for the known requirement of the Government."

Under Clause 2.6, The Contractor shall take full and unequivocal responsibility for the safety of the design and for the adequacy, stability and safety of all site operations and methods of construction.

And in Clause 2.7.1, the Contractor shall be liable for any damage to the Works occasioned by him in the course of any operations carried out by him.

Clause 2.8.4 states that, if there is any failure, either during the execution of the Works or during the Defect Liability Period, any remedial or repair works shall, in the opinion of the Project Director (Ketua Pengarah JKR) be urgently necessary for the safety of the Works or the public, the Government may employ and pay other persons to carry out such work or repair as the PD may consider necessary; and the costs and charges properly incurred by the Government in so doing shall be recoverable from the Contractor by the Government.

Nadeswaran posed the question: "Who is going to be held accountable for this monumental man-made disaster?"

Mr. Nades, who else? There is a contract and the contract had spelt out the terms and conditions. The German structural engineers had confirm it was design error. The British Halcrow had confirmed it was design fault. The Australian Consultant had reported that the causes of cracking were due to negligence in their design work which have resulted in the design failure. The primary causes of the cracks at the critical sections for the Typical Piers and Abutment B are a result of temporary gantry erection loading and early thermal and shrinkage cracking which occurred during the Construction Phase. Both of these design effects were in the scope of design works provided under the terms and conditions of contract.

So, who else should be responsible? Who is going to be accountable?

I'm sorry; it would have to be the contractor.

I hope Samy Vellu do not come up with another different version of explanation. Let's wait for him to tell us.




3 comments:

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A number of factors such as concrete composition, curing conditions and exposure conditions influence the potential for DEF. DEF is believed to be a result of improper heat curing of the concrete where the normal ettringite formation is suppressed. right!

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