The carrying capacity of the Holmenbrua bridge in Norway is weakened
The load that today’s traffic inflicts on Holmenbrua in Drammen is much higher than what was originally predicted when the bridge was built in the early 1960’s.
Due to a significant increase in traffic volume, examinations of the bridge’s construction was initiated to determine if it could withstand the burden it was exposed to or whether improvements were needed.
To analyze the impact the increased traffic volume had on Holmenbrua’s construction, HBK was assigned by Rambøll Norge to conduct the necessary measurements on a given area of the underside of the bridge using strain gauges.
The strain gauges were attached to five longitudinal steel rods, or rebars, to log tension and compression in the material by the passing of a truck weighing 50 ton. For full exposure of the rebars and to get the best utilization of the strain gauges possible, a part of the concrete around the rebars was removed.
“It was essential that the surface of material where we attached the strain gauges was treated” says Herman Lingefelt, project engineer at HBK.
“We do this to make sure the strain gauges provide the correct measurements. Even wrong coarseness on the surface can result in the glue not transmitting the strain of steel correctly.In this case, we had to grind away the rust and then brush with sandpaper. It may seem simple, but it requires a lot of practical know-how.”
The strain gauges were adjusted to the environment in which they were to operate in, taking into consideration temperature variations in the area. This was so that they would follow the natural expansion and compression in the material caused by temperature.
Because Holmenbrua is located in a moist environment, HBK also used a coating over the measuring points to prevent the gauges from losing their grip due to rust or short circuits in the steel.
The results of the measurements were consistent with the deflection the bridge experienced and, based on the measurements made by HBK, Rambøll concluded that the bridge’s capacity was so weakened, that reduced weight limits were recommended.
“Measurements like these are very important to uncover security implications that increased load may have on the material in a construction, and shows how important it is to use reliable measurement techniques. Exact knowledge of the bridge's condition is essential for municipal and transport managers,” says Bjarne Hauge of HBK Norway.
Rambøll is satisfied with HBK’s cooperation: ”Using one supplier to conduct the measurements was efficient and saved us time. The work HBK did on Holmenbrua was conducted in a precise and accurate way, and we are very pleased with our cooperation”, says Jon Halden at Rambøll Norge.
Ramboll is a global architecture, engineering, and consultancy company, delivering expertise and sustainable solutions to clients and partners.
Founded in Denmark in 1945, Ramboll today operates across 35 countries. We combine deep local insight and experience with a global knowledge base to create sustainable societies and drive positive change for our clients. We call it: Bright Ideas. Sustainable change.
As The Partner for Sustainable Change, we enable our stakeholders to realise their goals and navigate the transition to a more sustainable future.
Using one supplier to conduct the measurements was efficient and saved us time. The work HBK did on Holmenbrua was conducted in a precise and accurate way, and we are very pleased with our cooperation.
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This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
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