The South African branch of the Italian construction company CMC di Ravenna looked to Pilosio to provide solutions for the construction of a new bridge in Durban, currently given the project name of the N2/Cornubia Interchange. This overpass will serve to streamline traffic by linking the Umhlanga industrial zone with Cornubia’s new development area (Tongaat). The two companies had established a strong working relationship when they collaborated on the construction of the major Mount Edgecombe Interchange motorway junction, which included two of the longest viaducts in the country. Their latest project has reaffirmed the partnership.
Project name: N2/Cornubia Interchange
Customer: eThekwini Municipality
Builder: CMC South Africa Branch
Material supplied by Pilosio: MP shoring, MP heavy-duty walls, MAXIMIX modular formwork for decks, MP stairway access.
Project: three-span bridge, length 127 m and width of the spans from 33.5 m to 43.6 m
Pilosio and CMC partnership
Thanks to technical skills acquired over the years in the infrastructure sector, Pilosio was the ideal choice of partner for CMC, offering strong solutions, quality products, not to mention support and assistance during the design phase and throughout all the delicate stages on site. Given that Pilosio had previously provided CMC with a custom made system for another bridge, engineers at both companies decided to reuse the same system. They had a tried and tested system, and they could take advantage of their assets. In contrast, the solutions offered by competitors involved non-reusable wooden ribs.
The Cornubia Boulevard Overpass is a three-box, cast-in-situ concrete deck 127 m in length, divided into three spans.
One of the complexities of the project lay in the fact that construction of the bridge had to take place without interrupting the normal traffic flow of the highway. To accommodate this need large portholes were constructed above the highway to enable the preassembling of formworks panels, installation of the rebars, and deck casting operations in complete safety.
Another major complexity for the construction was due to the fact that the viaduct had a longitudinal slope of 2.4°, a transversal slope of the cross section plus a pre-camber casting deck.
An MP Heavy-duty support system was provided for porthole support in order to pass over the highway with HD Walls that were 19.20 m long and 12.27 m high spanning a clearance of 16 m and with a total load capacity of 1,451 kN.
The deck and the wings of the bridge were poured on a plywood surface installed on a grid of secondary timber beams and main steel walings (double UPN100 profiles) formwork (to allow for structures that might have to pass over the roads). In this case, the deck of the bridge was installed over supporting truss beams 150 cm high, made of HE340A and double L-shaped beams, coupled by vertical braces. Adjustable foot plates, placed between the steel walings of the bridge deck and the trusses, made it possible to give pre-camber to the casting. The steel trusses were supported by steel beams placed over MP Heavy Duty towers. In the horizontal plane, the trusses were stiffened by means of tubes and fittings, both on the upper and on the lower cords of the trusses. The stresses in the steel elements of main beams and the nodal reactions were obtained from a 3D FEM dedicated model of the structure, carried out with SAP2000 software. All the static checks were carried out by Pilosio engineers according to the EN 1993 Standard.
Adjustable foot plates
The foot plate extraction had to guarantee the transversal sloping of the cross section plus the pre-camber that allows the casting to have a horizontal bottom deck after falsework dismantling. The pre-camber was obtained from the 3D FEM model of the supporting structure.
A gross longitudinal sloping of the bridge of 2.4° was obtained with the inclination of the main trusses. The steel trusses were fixed on the left support of the portal (bolt connection) and free to move horizontally on the right support. Thus, the horizontal action due to sloping was all applied on the left support (MP Heavy Duty support tower). The MP Heavy Duty tower base jacks were fixed to the ground and braced to the lateral MP standard platform in order to avoid any risk of tipping. Cables or ballast could have been used as an alternative.
Lateral support platforms
As a temporary support platform, the MP Pilosio multidirectional shoring system fit perfectly with all the site requirements. The support platforms were obtained by connecting square or rectangular modules together. A height variation from 6.5 m to 12.7 m was easily covered thanks to the flexibility of the MP system. Different capacities were reached with various configurations of braces and ledgers.
Two casting phases were performed: the first phase was the pouring of the bottom deck and the second phase was the pour of the lateral vertical walls and upper slab with lateral wings. For the deck casting, the builder chose MAXIMIX, a formwork system made of wooden beams, steel beams and plywood panels that allows for the covering of large surfaces to be run in site and complex shapes with high capacity and limited weight. The capacity can be adapted to the requirements of the project by varying the distance between the beams. Pilosio engineers made the design of the wooden deck.
On site assistance
Pilosio gave on site assistance with training for the assembling of Maximix panels, providing dedicated shop drawings for each single module (typically designs require interpretation by the workers on site) and day by day assistance for the various problems that arose during assembly and installation of the MP towers, such as dealing with discrepancies detected on site in measurements and so on.