Since its closure it has lain unused for almost three decades – for more than a quarter of its lifetime in fact – and initial attempts at renovation ground to a halt (see box below).
But with the false starts now in the past, and backed by the enthusiastic support of the state governor, a complex renovation project costing around US$95 million is now in full swing. The historic bridge, the superstructure of which has been largely dismantled to enable replacement of corroded elements, is being extensively strengthened to enable it to be reopened to traffic in December 2018.
The bridge first opened to traffic in 1926 and incorporates an unusual combination of eye-bar suspension elements, with the stiffening truss above the deck on the main span – one of only a handful in the world with this structural form. But now a major renovation project being driven by the governor of the state of Santa Catarina intends to bring it back into use later this year, and contractor Teixeira Duarte is moving steadily towards the deadline.
At the end of next month (March) the first of 360 new eye-bars will be installed on the bridge superstructure, marking the start of a six-month phase of work which is set to continue until October. The contractor is currently carrying out the the rehabilitation of the truss on the central span and assembling the auxiliary structures to replace the saddles. Work is also under way to rehabilitate the anchorage blocks at both ends of the structure.
Later life has been troubled for the Hercílio Luz, which was first closed to traffic in 1981 after an eyebar ruptured – and although it was subsequently reopened, it closed permanently in 1991 and has been shut ever since. The bridge was commissioned by the state governor of the time, Hercílio Luz, and created the first fixed link between Santa Catarina island and the Brazilian mainland over the Atlantic Ocean. However when the structure started to fail, the fact that additional bridges had been built in the intervening years, meant that authorities were not under any immediate pressure to repair and reopen the bridge.
The complexity of the repair work that has been required also no doubt contributed to the delays. Not only were the superstructure and substructure of the bridge in poor shape, but the condition of the tower foundations, believed to be wooden piles, was not only unknown, it was difficult to establish with any certainty.
Construction of the original bridge, the design for which was conceived in the 1920s by American engineers HD Robinson and David Steinman, began in 1922. The steel structure was manufactured in the USA and assembled in Brazil by American Bridge Company. The bridge was opened to traffic on 13 May, 1926; it was designed to carry a highway, an electric railway and a water supply and is almost 820m long with a main span of 340m and side spans of 259m on the island and 221m on the mainland. The steel towers rise 75m above sea level and the main span has a navigation clearance of 30m above sea level.
The steel structure weighs approximately 5,000t and the foundations and piers incorporate some 14,250m³ of concrete. The maximum height of the main span truss occurs at the quarter points of the span, where the bending moment is at its greatest, and over the middle of the span, the eye-bars that form the main support are incorporated into the truss, where they also act as an upper chord. Over the rest of the span, the upper chord of the truss is connected to the eye-bars by vertical hangers.
Towards the end of the last century, corrosion took its toll, and the Hercílio Luz Bridge was temporarily closed for the first time in 1981 after the rupture of an eye-bar. Although it subsequently reopened, problems remained and in 1991 the bridge was permanently closed to traffic.
The last visual inspections, which were carried out between the years of 2009 and 2013, revealed fissures and high levels of corrosion at the base of the tower and in the steel deck. Due to the fact that the original project is very old, there were no records of the composition of the steel, and so hardness tests were carried out to enable yield limits to be defined.
The renovation project involves replacement of the damaged elements and strengthening of the foundations. Around 2,000t of steel, out of a total of 5,000t on the bridge, is set be replaced. Massive temporary works have been installed to support the central span during the rehabilitation process. A carefully analysed load-transfer process, in which the main span loading is transferred from the eye-bars into the temporary structure, has already taken place. For this purpose, a synchronised jacking sequence was used, the procedure for which was determined through numerical model analysis.
The temporary structure is composed of a space truss with four bases, supported by independent foundations.
All permanent foundations had to be reinforced because of the uncertainty as to their structural condition; the anchor blocks and bases have been reinforced by surrounding them with a new jacket of concrete which is supported on newly installed concrete piles. An alternative solution for the rehabilitation work was evaluated, which involved supporting the central span on auxiliary cables which would be placed over the eye-bars. This alternative is similar to the procedure that was used for the initial assembly of the structure, but would not have improved the situation at the tower foundations. It would have required even more reinforcement and bigger jacking loads to enable the bearings to be replaced; it would also not have been as safe as the adopted solution, because it would have relied on damaged elements to sustain and stabilise the structure
Once the temporary structure was assembled, the load was transferred from the eye-bars to the temporary structure by the synchronised vertical jacking of 54 truss points to impose the bridge displacements in a parabolic form. The whole process was monitored by a topographical survey and data analysis from sensors on the structure, including extensometers, displacement sensors, thermometers and so on.
To define the configuration needed to minimise the forces at the eye-bars, a geometric non-linear finite-element model was developed in SAP2000.
Incremental displacements were imposed in the truss with the intention of reducing the loading at the eye-bars to the minimum. The confirmation of the hypothesis of zero loading in each element was verified experimentally by analysing the stress measured by triaxial strain gauges. The load transfer process was carried out in two main phases.
The first phase was jacking of 54 points in a parabolic form, with upward displacements in order to reach a zero loading condition in the external eye-bars of the truss. After completion of phase one, these eye-bars were disconnected from the truss. But even with the disconnected truss structure, there was an axial tension load in the internal eye-bars, due to the original bridge assembly method employed. A total vertical upward displacement of 550mm was proposed, made up of five steps of 110mm each.
The second phase involved the jacking of 54 points in a parabolic form, with downward displacements, with the intention of reaching compression loading in the upper chord of the truss. This compression load cancelled out the residual tension load, resulting in zero loading on those elements. Ultimately the eye-bar symmetrical pairs will have zero load and can be removed.
Once the structure had been disconnected and the eye-bars opened, all the replacement and reinforcement work could be started; reassembly of the structure will follow the reverse sequence.
The access span foundations were originally designed as rock-supported concrete blocks. But as it was not possible to verify the actual condition of these blocks, a strengthening scheme was developed. The blocks were made larger and strengthened by being surrounded by a new, bigger block supported on 450mm-diameter concrete piles.
Reinforcement of the main span tower foundations follows the same logic as that used for the access spans foundations, but steel bars were used to tie the new block into the existing one. Precast concrete cofferdams were used as formwork around the existing block and reinforcement was fixed within. The anchor blocks, which have to resist very high loads, will be increased in size by having a new concrete block built around them, supported on piles and micropiles.
The most damaged parts of the Hercílio Luz Bridge were the steel structures that had suffered extensive corrosion over time. The original bridge deck, which was made of steel beams covered by wooden planks, will be replaced by press-welded steel gratings, supported on new steel beams on the roadway, and orthotropic steel decks in the sidewalks. The residual strength of all elements with complex geometries was evaluated by the use of finite element models. The tower bases and the eye-bar supports will be replaced by new castings and the eye-bars will be replaced by new machine-made elements of high resistance steel with a yield strength of 900MPa.
No additional corrosion prevention measures are proposed, but the paint scheme that is being used is designed to form an effective barrier to the mitigation of corrosion: primary and secondary aluminium base layers with a polyurethane finish.
José Luis Silva is project manager, Pedro Faro is steelwork manager, and João Pedro Lopes is construction director, all at Teixeira Duarte; Hermes de Carvalho is project designer and professor of structural engineering at the Federal University of Minas Gerais (UFMG)
The renovation process has not been straightforward and although the first parts of the work were carried out more than a decade ago, there have been a number of hurdles to clear to get to this stage.
In 2005, the state government first revealed its plans to rehabilitate the Hercílio Luz Bridge, and soon after the tender documents were issued for the first stage of the work – to repair the approach structures on both sides of the bridge and provide access to the main bridge. This contract, which was won by a consortium of local companies, began in 2006 and was completed two and a half years later.
Efforts to complete the final phase have taken longer than expected. In 2009, the state government signed a contract with another consortium to renovate the entire central span and the main towers, as well as the pedestrian walkways. This involved construction of four temporary support towers below the main span, requiring the use of divers in 30m-deep water that is also subject to strong sea currents. The divers could only remain submerged for a few minutes at a time and had to carry out underwater welding with high precision. But even when the difficult underwater work had been successfully completed, the consortium contractor was unable to meet the contract deadlines.
In August 2014, after successive delays to the completion date, the state government took the drastic step of terminating the contract with the consortium. This process itself did not just cause bureaucratic problems; the impact of further delays on the condition of the incomplete temporary towers was, however, a significant issue.
The state had to act quickly to prevent the welds, material and structure from deteriorating, and to ensure that the temporary structure would be able to support the weight of the bridge throughout the final phase of the work, which was intended to take two and a half years.
So plan B was brought into action, which involved carrying out the remainder of the work in two parts. The first stage was to complete construction of the four temporary support towers; the second stage, which is currently under way, involves the construction of the truss, the transfer of load, the replacement of the joints and the dismantling and exchange of eye-bolts.
Contractor Empa, which is a division of the Portuguese group Teixeira Duarte, was appointed for the first phase of the work, which started in April 2015 and was completed on time in October of the same year.
As a result of successfully completing the first phase, Teixeira Duarte was hired to carry out the remaining work. The construction contract requires that the works be performed almost exclusively by Teixeira Duarte, without recourse to subcontracting, because one of the justifications for letting the work without going through the usual bidding process was the company’s proven experience in the required metallurgical and geotechnical engineering.
Once work is completed and the Hercílio Luz Bridge is reopened, it is expected to absorb around 20% of the traffic currently on the other two bridges.