The Waioeka River (Opotiki) Bridge is a 305m long 25-span bridge in Tauranga, NZ constructed circa 1927. In late 2016 we worked with Beca Ltd (on behalf of NZTA) to assess the existing pedestrian clip-on structure and perform detailed design for bridge strengthening of the Waioeka River Bridge. Strengthening of bridges to accommodate higher productivity motor vehicles (HPMV) is part of NZTA’s strive for an improved but sustainable network. By helping develop cost effective strengthening we were able to prolong the life of this key asset and reduce the energy and resources needed for new construction.
The existing bridge comprises four cast in-situ reinforced concrete T-beams supported by reinforced concrete abutments and piers. Each of the spans is 12.2m long. The superstructure is divided into five uniform continuous girders connected to piers integrally at the inner supports and simply supported at the end supports. The design for the strengthening features external post-tensioning installed on both sides of the existing concrete to enhance their flexural capacity. Tendons are installed on each side of each longitudinal beam and anchored as close as possible to the underside of the deck slab, at each end of the beams.
The Freyssinet external post-tensioning system using the 1R15 anchorages and 15.7mm pre-stressing strands was used. The main advantages of the system are:
- Minimum amount of drilling into the existing beams for end anchorages.
- Anchorages are factory produced castings with a bonded nylon coating.
- Anchorages can be located at the ends of the beams.
- The system is designed by a leading pre-stressing / post tensioning equipment supplier.
Longitudinal shear strengthening of the interface between the deck and the top of the beams was also designed to accommodate the additional horizontal shear loads arising from the strengthening. These brackets are located along the beams and installed from below the bridge to avoid disruption to traffic.
To facilitate successful strengthening we developed a simple 3D model as part of the works. This approach to design enabled us to confirm the suitability and positioning of strengthening concepts prior to arriving on site. This saved the site team a lot of headache. See images below.
Design was completed November 2016 and the physical works were tendered April 2017.
Waioeka River Bridge Tauranga NZ
Waioeka Strengthening – Example of 3D models compared against existing photos
GRP Walkway Concept
