Bridge Maintenance. Essential Things to Check.
We build bridges to stand the test of time. But like any high-value structure, regular inspection and maintenance is important to extend longevity.
Visually inspecting your bridge at least once a year is a good idea, especially if you rely on it for access to your home or business. If it starts to degrade, it can cause major disruption and potentially be very expensive to repair or replace.
What to look for
Check both the bridge itself and the surrounding stream or land. Here is a quick inspection check-list and points we recommend you consider. If you want us to cast an expert eye over your bridge for you, just get in touch.
Things to look for on your bridge:
Abutments
Is there any sign of cracks, chips, rust stains (which indicate corrosion) or is the reinforcing steel exposed? Is there any signs of movement such as gaps between the soil and concrete or are items not entirely straight? Do the abutments provide protection to the adjacent embankments? Look for evidence of any settlement behind the abutments on both approaches.
Deck
Are there any broken, rotten or loose boards on your timber deck? Or is there cracking in your concrete? If your bridge deck is covered in a thick layer of mud, it could burden the bridge with unnecessary load. It’s also worth noting that timber deck boards need to be an adequate size for your bridge load . If you have a timber deck bridge there should be running boards along the wheel paths to avoid wear to the main structural timber deck members. Other safety checks should include making sure kerbs and balustrades are present and adequate. If they’re not, consider installing or upgrading them.
Steel beams
Is there any evidence of corrosion (especially at the end of beams or at the joint between underside of deck and top of beams)? Debris washed down waterways during floods can damage bridge beams. Is there any sign of impact damage on the bridge (i.e. unusual bending in beams, dents etc)? Do your abutments provide adequate support for your beams? Sometimes steel beams are installed in contact with the ground which leads to corrosion occurring faster as the steel doesn’t get the chance to dry. Ideally there should be separation between ground and steel members. Is there any effluent build up on the beams? If so, clean it off as this will also accelerate corrosion. Also look to ensure that all nuts and bolts are installed, in good condition and tight.
Corrosion
There are three types of corrosion to check for on your bridge. Corrosion is generally easy to identify – you can physically see rust or other signs such as flaking or bubbling paint:
Localised Corrosion is corrosion in isolated areas and may occur anywhere on steel surfaces. It could be caused by scratches in the paintwork or where modifications have been made but correct re-coating procedures haven’t been followed.
General Corrosion is uniform loss of material over a surface. While it may look in poor condition, it doesn’t necessarily affect the structural component of the steel. A typical steel beam consists of two horizontal plates (flanges) located top and bottom and a vertical steel plate between (web). Generally the flanges will deteriorate the fastest as their horizontal alignment means they have the tendency to hold debris or moisture. Flanges are important to check . Often the worst corrosion can be found between the top flange and deck, especially in timber decks as the interface between timber and steel holds moisture and debris – especially effluent on farm bridges. This is also one of the more difficult locations to check for corrosion but it is generally visible on the top edges of the top flange as shown in the picture.
Pitting Corrosion is where small corrosion craters appear in the steel when corrosion has been underway for some time. It’s often seen on exposed pipework and unprotected steel structures. The pitting can fully penetrate a steel flange of metal (compromising structural integrity) but only a small amount of damage is actually visible. This can be treated and preserved with a coating, but if the pitting is too deep and has created holes in the steel, it needs to be replaced to an engineer’s specification to bring the structural integrity back up to standard. All rust needs to be removed before any new coating is applied.
Things to look for in the waterway and surrounding area:
Vegetation
Is there a tree nearby which might fall and damage your bridge? Are overgrown bushes preventing access to check beneath the bridge? If trees (e.g. willows) are growing on the side of the bank and dangling their branches into the water, they can stop water from flowing freely and create a dam. Old trees or stumps can also rot and cause embankment instability.
Ground conditions
Is the soil dropping away or slumping near the abutments? If so, water could be causing scour (the removal of sediment from around bridge abutments or piers), potentially undermining bridge stability. Are there any areas of exposed ground along otherwise vegetated banks? This is a sign of scour or erosion.
Stream / riverbed
Has a large amount of sediment been transported (by water) and changed the height or shape of the stream channel? If so, this can alter the water levels during flood events and potentially put your bridge at risk. Erodible material (gravel and silt) needs to be protected so piers and abutments are not undermined. Is there any localised variation in the stream bed upstream or downstream of the bridge? If so, this is an indication that the bridge may be impacting the stream.
Debris / dead vegetation
If present in the water or within the flood plain, this can prevent water from flowing freely and scour out the banks. Large debris can potentially hit and damage the bridge during flood events so remove as much as you can.
As you can see, there’s a fair number of visual checks and issues to be aware of. Bridge It NZ can carry out a full bridge inspection for you and provide a written report of its current condition including maintenance recommendations. We’ll check your bridge and associated items for their overall condition and can assess your bridge’s current load capacity. We will also identify any maintenance items which need to be undertaken and indicate costs and methodologies to ensure your bridge remains serviceable for as long as possible.
If you would like a hand to assess your bridge, get in touch with us today.
