Newnham Road Cycle Suspension Bridge was a design we did for Edifice Contracts Limited (Edifice) as part of the July 2017 “Omokoroa 3 Bridges” Tender. The project was for the design and construction of three cyclebridges for Western Bay of Plenty. Our design for the Newnham Road cyclebridge is a long span suspension bridge with a 70m main span to the northern side of the existing railway bridge. The suspension bridge has a usable width of 2.4m and is constructed mainly from glulaminated timber which makes it a very environmentally conscious and durable bridge form for the marine environment. The main cables are made from stainless steel to prevent main cable maintenance issues normally synonymous with suspension bridges and the rest of the (easily replaced or accessed) components are made from galvanized and painted mild steel.
By working closely with the contractor, we were able to present the most competitively priced design and construct package which was $200,000 below the original $1.5M project estimate. Also see Plummers Point Cycle Bridge.
Newnham Rd Cycle bridge – DC Structures Studio & Edifice 2017
Key Suspension Bridge Design Criteria
The overall Omokora Cycleway is to be a Grade 2 cycle track (easy) as per NZCTDG. As such it was considered appropriate to design bridges (which are generally less than 100m of the track at any point) for one grade higher and the bridges are therefore designed to Grade 3 requirements as set out by NZCTDG. This improved our ability to design economic bridges and was particularly relevant to bridge grades, turning radii, and barrier design loads:
- Clear span = 70m;
- Minimum bridge width = 2.4m measured at the deck surface;
- Minimum barrier height = 1.4m;
- Sloped surfaces to have non-slip surfacing;
- Barrier infill to be non-climbable as per NZBC F4;
- Longitudinal joints are not be used;
- Minimum headroom to cycle-path and bridges = 2.4m;
- Maximum allowable pathway gradient = 7.5% (Grade 3);
- Radius of turns: 2.5 m minimum with at least 4 m desirable to outside of turn (Grade 3);
- Design life for all structural elements is 50 years minimum;
- 25 years to first maintenance for all steelwork protective coatings.
Newnham Rd CycleBridge – Long Section of suspension bridge
Newnham Rd Bridge – Suspension Bridge Pier Details
Cycle Suspension Bridge Clearance
Plummers Point Bridge and Newnham Road Bridge will have a soffit of all superstructure elements 1500mm minimum above MHWS. This is considered suitable to accommodate flooding, freeboard and climate change during the life of the structure. This elevation is also assumed to put superstructure elements outside of the salt water splash zone.
A zone of 3m wide through the centre of the Plummer Point Bridge and Newnham Road Bridge crossings will be designed to have a minimum clearance of 2.5m above MHWS to accommodate the passage of small watercraft such as kayaks and canoes.
Suspension Bridge Design and Construct (D&C) Process
During early collaborative discussions between Edifice and DC Structures Studio (DCSS) it was quickly agreed that piling in the waterway was the most expensive part of the build and a key area for innovation. Based on these fruitful discussions the focus quickly turned to long-span structures that could span the waterway without needing piles and piers in the waterway. Our design for the Newnham Road cyclebridge is a long span suspension bridge with a 70m main span to the northern side of the existing railway bridge. This design is preferred as it prevents the need for any piling or lifting to be done from the water. This bridge form also played to the strengths of Edifice who have extensive experience constructing suspension bridges for Department of Conservation.
Services provided by DC Structures Studio:
- Developed in consultation with contractor efficient bridge types specific to the site (use of a suspension bridge prevented costly piling in the waterway);
- Sourced and coordinated Geotech, Planning, and Peer Reviewer inputs (preference was to use locally available Planning and Geotech);
- 3D Sketchup models created showing bridge in local topography (done in-house and helps with the Constructor’s ability to understand and plan around existing site constraints);
- Produced CAD General Arrangement (GA) drawings;
- 3D visualisations (a great way to show the client what they are getting!);
- Tender design Statement. This was a discussion document identifying key assumptions, exclusions, design codes, materials, durability, etc.;
- Design stage programme (showing how planning, investigation, Geotech and design would all need to overlap);
- Tender design analysis on key structural elements and provided info and assumptions to Contractor pricing team;
- Developed competitive pricing for the Structural, Geotechnical, Planning and Peer Reviewer detailed design and construction phase fees.
Newnham Rd Cycle bridge 3D modelling as used for construction planning – DC Structures Studio & Edifice 2017
DC Structures Studio – Bridge Design
