CSP’s expertise called on for repair of bridge

In May 2013 a small truck travelling west towards Havelock North struck the concrete barrier of the Maraetotara Bridge, breaching the railings and coming to rest on the river-bed below, seriously injuring the driver. This left the Hastings District Council (HDC) with a dilemma. How should they repair the existing concrete bridge – which was built in 1953 and not due for replacement for at least another 50 years?

MWH were appointed to carry out the design of the new barrier system and soon discovered that the bridge beam was probably not capable of sustaining a TL–4 barrier impact - using standard CSP 20mm necked holding down bolts - without structural damage. The barrier’s original fittings had failed immediately during the collision – as they are designed to do – preserving the beam structure from damage.

“After consultation with CSP, MHW came to the conclusion that a reduced bolt strength (necked to 12mm) would result in more bolts failing in an impact event, resulting in increased barrier deflection,” said Tim Bateman, Transportation Operations Engineer for HDC. “To counter this the Thriebeam barrier was installed, nested in two layers to increase barrier stiffness and limit barrier deflection. This will ensure that any colliding vehicle is retained roadside.”

We worked with MWH and Fulton Hogan to help come up with a solution for the repair of the bridge,” says Jeremy Mallender, Sales Engineer for CSP. “We helped with the design of the special bridge posts and also assisted with the new bolt design to ensure the bridge would not be damaged in any future impacts but, most importantly, to ensure vehicles would remain on the bridge. Necked bolts, specially reduced in diameter from 16mm to 12mm, will ensure they successfully shear off if impacted to protect the integrity of the concrete bridge deck. It was not a standard fix!”