THE 11.8 kilometre Third Mainland Bridge in Lagos has been in the news in the last three weeks, albeit, for the wrong reasons. The whistle that the bridge, touted as the longest in Africa, is on the verge of collapsing, was blown by Senator Gbanga Ashafa, representing Lagos East Senatorial District in the Senate.

Ashafa has in a motion co-sponsored by 55 other senators, alleged that a report produced by a company experienced in underwater surveys indicated that the underwater metal casings housing the concrete piles on which the bridge stands, have rusted and this accounts for the vibration experienced in some portions of the bridge.

The report was attributed to Professor JHT Kim, Head of the Concrete Structural Engineering Laboratory at Yousei University, Seoul, South Korea, who came to Nigeria for research work in December 2012. The Korean professor who allegedly conducted an underwater examination of the structures holding the bridge, had reported that the damage to the structure was worse than what he had been revealed.

Ashafa's observation, although not stated in his submission at the Senate session, must have been informed by fears of what happened several years ago, when a lateral displacement occurred at the Five Cowrie Bridge in Lagos. The lateral displacement occurred when one of the piers caved in, and construction giants, Messrs Julius Berger Niger Plc, were contracted to fix the bridge which links Lagos Island and Ikoyi.

The Senator lamented that the repair works done on Third Mainland Bridge during the last quarter of 2012 by the Ministry of Works, were mere window dressing on the expansion joints of which reports had confirmed that some parts had since become disjointed.

"The implication is that the Third Mainland Bridge between Adeniji Adele, Adekunle and Oworonshoki ends could collapse and therefore require comprehensive works to be carried out on the foundation immediately," he claimed.

A FORMER President of the Nigerian Institution of Structural Engineers, NIStructE, a division of the Nigerian Society of Engineers, NSE, Kunle Adebajo, who reacted to claims that the bridge is under severe threat stated that "as a professional engineer, it worries me when major issues such as the structural stability of a significant bridge are being speculated upon in public by non-experts. This can certainly cause alarm in the minds of the general public and this does not do anyone any good".

Adebajo who is the Chief Executive Officer, CEO of Ove Arup & Partners Nigeria, suggested that the issue should be immediately referred to engineers who are better positioned to scientifically assess the true state of the bridge.

Adebajo called for "a full-scale structural investigation, particularly of the bridge piers and their supporting piles, to ascertain the veracity or otherwise of the reported claims". He did not stop there.

"Until otherwise informed, to the best of our knowledge, there is no evidence to indicate that the bridge is in danger of imminent collapse, as no significant signs on the superstructure support that assertion," he said..

The former NIStructE boss was quick to point out that there is usually no smoke without fire. "The Federal Ministry of Works would certainly have in the past conducted investigations into the reported structural distress of the Third Mainland Bridge.

Such investigations should normally involve reports of deep sea divers who would take underwater pictures and observations. It could well be that there has recently been some evidence discovered that gives some cause for concern. This would not be readily available in the public domain.

If, for example, any of the piles supporting the piers have become badly corroded or damaged, such conditions cannot and must not be swept under the carpet as real corrective measures must immediately be undertaken. In addition, some parts of the bridge may have been subject to the negative effects of scouring due to the activities of sand miners. Again, in such instances, urgent and decisive action must be taken," he said.

Continuing, Adebajo who called for a comprehensive structural investigation of the bridge, declared: " A bridge such as the Third Mainland Bridge is much too strategic to be ignored. This is why a comprehensive structural investigation must be carried out now, and done by suitably competent consultants".

On how long it would take before repairs are carried out on such a national infrastructure, Adebajo explained that maintenance should be done regularly. "If you buy a car today, it is likely that you may not visit a mechanic workshop for the next two years.

But after that, wear and tear sets in and it becomes necessary for you to regularly maintain the car. In like manner, a bridge such as the Third Mainland Bridge may not have problems within the first few years but with usage, the bridge will begin to deteriorate and requires constant maintenance to keep it in good shape," he said.

Also reacting to the alarm raised about the health of the Third Mainland Bridge, another Lagos-based civil engineer, Mr. Afolabi Adedeji, called for the constitution of a joint ad-hoc panel of the Nigerian Society of Engineers, NSE, Council for the Regulation of Engineering in Nigeria, COREN; Federation of Construction Industry, FOCI, which is the umbrella body for all the major construction companies in Nigeria and the Nigerian Institution of Surveyors, NIS, to study the report of the Korean professor and advise government on an appropriate line of action to be taken concerning the report.

Adedeji who warned against what he called an 'alarmist'-cum-'panic' response, maintained that although the safety of commuters is vital, "primordial job for the boys instincts must also be tempered by sound engineering judgement".

REACTING to speculations that the Third Mainland Bridge may soon collapse, the Director, Highways Design (Bridges) in the Federal Ministry of Works, A.O. Effiong, outlined measures taken by the government to protect and keep the ever-busy bridge in an acceptable state.

In a statement titled "Facts File on Third Mainland Bridge in Lagos", Effiong, an engineer, disclosed that the Federal Ministry of Works has commenced the process of engaging a consultant to urgently carry out investigation/assessment on the entire bridge sub-structure so as to determine the extent of maintenance work required.

The scope of works to be covered, according to him, include* echometric test to check the structural integrity of the piles in water and selected piles on land (total of 988 No. piles), including coring on selected piles, testing and chemical analysis.

Underwater inspection report

*Underwater Inspection of 658 No. piles and submission of Report of the Inspection/Assessment of Foundation piles with appropriate recommendations.

The statement reads in parts: "Following reports of oscillation and excessive vibrations of the bridge under traffic load, the Federal Ministry of Works in 2008 engaged the services of Messrs JBN Plc. to conduct preliminary investigations of the structure and later Dynamic tests were carried out by Messrs 4EMME, an internationally acclaimed bridge engineering consulting firm. The reports of the investigations and tests at the time indicated that the bridge was structurally adequate but required the replacement of bad expansion joints and bearings.

Consequently, Messrs Borini Prono & Co. Nigeria Ltd. carried out the replacement of four critically affected expansion joints (Phase I) which drastically reduced the vibrations on the bridge to tolerable limits and allayed the fears of members of the public.

Following yet another report of subsidence and oscillation of the bridge structure exceeding tolerable limits under minimal load stress, the Ministry's engineers inspected the bridge and their Site Inspection Report indicated that:

*Excessive vibrations occurred at damaged expansion joints locations whenever heavy vehicles crossed over them;

* Rubber accessories of the expansion joints at the Ebute Metta axis of the bridge had been damaged and were therefore not water-tight;

* Significant horizontal displacement of a retaining wall at an intermediate abutment of the bridge was observed;

*Dredging activities around the bridge piers from where large quantity of sand was being excavated on a daily basis might undermine the integrity of the bridge foundations.

Site Inspection Report

The Site Inspection Report recommended the immediate replacement of more damaged expansion joints since the vibrations were still traced to them and also underwater inspection to ascertain the current state of the bridge substructure/foundation. Accordingly, and following the approval by the Federal Executive Council in October 2011, eight additional joints (Phase II) adjudged to be border line cases in 2008 were replaced by the same contractor in 2012.

In recognition of the importance of the bridge, the Ministry commissioned Messrs Nigerian Submarine Divers Limited, NSD in December 2010 to undertake the underwater inspection of the Third Mainland bridge and Eko bridge in Lagos in order to ascertain the state of the underwater structural elements which had hitherto not been inspected since the bridges were constructed and opened to traffic some 35 and 25 years ago respectively for the two sections. An initial report of the underwater inspection presented by NSD in July 2011 showed "alarming" deterioration and serious damages on numerous pile foundations of the Third Mainland Bridge.

The Final Report submitted by NSD in November, 2011 indicated "extensive" deterioration of embedded steel reinforcement in piles, concrete degradation and appreciable loss of concrete material as well as discontinuities in some foundation piles which apparently has affected the load bearing capacity of the piles.

They recommended the replacement of some piles, encapsulation of others, cleaning piles of marine growths using high pressure water jets and discontinuation of organic effluents discharge into the water. Hence, Advanced Integrity Assessment tests of the affected foundation piles and chemical analysis of the concrete samples were recommended.

Following further review of Messrs NSD Ltd's Final Report, it was observed that not all piles were inspected due to various reasons advanced such as obstruction by human activities and inaccessibility. To ensure that their report was adequate and comprehensive in accordance with the contract's terms of reference, the Ministry directed that all piles, whether in water or on land, be duly investigated which culminated in the submission of an addendum to the Final Report in December, 2012.

It is pertinent to note that the Addendum to the Final Report submitted by Nigerian Submarine Divers Limited in December 2012 confirmed some deterioration and defects at the underwater sections of some of the foundation piles as follows:

* Concrete degradation and appreciable loss of concrete infill materials

*Extensive deterioration of embedded steel reinforcement in piles

* Progressive deterioration of steel caisson of foundation piles.

THE findings of Messrs Nigerian Submarine Divers

THE findings of Messrs Nigerian Submarine Divers Ltd, NSD were strictly based on visual inspection and under water photos. For this reason, and following meetings between officials of the ministry, Messrs NSD, Julius Berger and Borini Prono, it was decided that Advanced Integrity Assessment, including high technology chemical analysis of concrete samples from piles was inevitable, and in order to authenticate the findings of NSD as contained in their reports. Moreover, since Messrs NSD Ltd is not a civil engineering consultancy firm, their capacity and professional competence to carry out such works was doubtful.

Therefore, in recognition of the fact that the required integrity test has not been exhaustively conducted on the entire bridge, even as various investigations had been concluded, the Ministry felt obliged to request Messrs Borini Prono & Co. (Nigeria) Limited, a member of the PGH Consortium that constructed the first section of the bridge to assess the condition of some foundation piles of the first section of the Third Mainland Bridge which was mostly impacted in the reports by studying the original designs, conducting site investigation in collaboration with Messrs Trevi Foundations Nigeria Limited, the foundation specialist that undertook the piling works in the first place. Messrs ICECON Nigeria Limited, specialist in bridge investigations, was also engaged by Messrs Borini Prono to independently confirm the results of their investigation. A report was submitted in November 2012 and the major findings were: * The visual underwater inspection, the Non Destructive Tests and coring campaign carried out on

the Third Mainland Bridge in Lagos confirmed the adequacy of pile concrete quality. *Some degradation was observed particularly in the first few meters of pile shaft, a consequence of 35 years of bridge life;

*Although serious steel casing corrosion was noticeable, it was pointed out that the steel casing has no structural function regarding pile bearing capacity, as they simply served as formworks to the R.C. piles;

*No cases of total loss of piles, clearance between the pile and pile cap or other major anomalies were reported on the tested piles;

* Based on the results of the investigations, there is no evidence of immediate threat of failure of the pilings.

In their conclusion, they made recommendations that elaborate maintenance programme based on systemic assessment of all the piles be put in place.

The Bridge

THE Third Mainland Bridge is the longest of three bridges connecting Lagos Island to the mainland, the other two being the Eko and Carter bridges. Touted as the longest bridge in Africa, the bridge which was built by former military President, Ibrahim Babangida, starts from Oworonsoki which is linked to the Apapa-Oshodi Express way and Lagos-Ibadan Express way, and ends at the Adeniji Adele Interchange on Lagos Island. The 11.8 km long Bridge was constructed in two sections. The first section, from Lagos Island to Ebute Metta (Adeniji Adele Interchange - Adekunle Interchange) which has a box girder arrangement cantilevered from the pier to the mid-span was completed in 1979 by PGH, a consortium made up of Messrs Borini Prono, Messrs Girola and Messrs Hiconi. The second section from Ebute Metta to Oworonshoki which was later completed in 1990 by Messrs Julius Berger Nigeria Plc. JBN is a multi-span structure.