Now you see it. Now you don’t!

Posted on: 25 June 2020

During construction we occasionally have had items stolen from site but this is rare. Bridges are occasionally damaged superficially by vandals but this is less common than one might expect. This week we have had the entire parapet stolen from one of our bridges on a remote nature reserve. Before After  They have not been stolen for scrap as the price of galvanised steel is very low and the effort to remove them and extract them from a difficult site would not be justified. They have been recognised for the high quality they are and have been stolen for another project!    

What is a Catch Pit?

Posted on: 11 June 2020

I am sure you have noticed that our weather in changing? When it rains it does so more intensively. Today in South Wales at The Mumbles 68mm (two and a half inches) fell in 24 hours. When this happens it can overwhelm drainage systems if there are any.   In rural areas roads become rivers as the water runs off fields to add to the water which has fallen on the rad itself. With the drains choked the water will run downhill until it finds a route off the road. If you are unlucky this may be into your drive. Hundreds of gallons can flood into your property and if you are unlucky into your home.   There are some measures you can take to reduce the impact. One is to collect the water as it comes into your property and divert it ideally back off your property away from vulnerable places. A catch pit does this. The unit needs to be able to cope with high in coming flows but also needs...

What is vibration Serviceability?

Posted on: 29 May 2020

When an opera singer shatters a glass this is because the Natural Frequency of her voice is the same as the Natural Frequency of the glass. Most structures have a Natural Frequency. As steel bridges (or steel and timber bridges) increase in length they become prone to this – typically in the middle to upper 20’s of metres. An equation predicts this and it contains length, weight per metre and length. As length increases it is necessary to increase the depth of the beams to increase the resistance to deflection (increased I Value). Increasing the depth usually also increases the weight per metre. There comes a point when the natural frequency of the structure comes close to that imposed by a person walking across it. At this point very small inputs excite a disproportionate response in the bridge. Your bridge designer has seen a dog crossing a sensitive bridge make the bridge and the dog jump violently about. Cambering is useful but the maths are di...

Elena has arrived!

Posted on: 26 May 2020

Collecting and efficiently removing the water which percolates through permeable surfaces can be a problem. The Elena Collection System is the answer.   Water percolates down until it reaches an impermeable layer. It then travels along this surface until it encounters the duct. Slots in the side faces of the duct allow the water to enter when it is carried to a suitable drain and discharged. Depending on the water volumes single or twin ducts can be used. The ducts are set into the impermeable surface level with the inlet slots. The entire duct is then covered in bonded aggregate. Access covers are incorporated to permit inspection and maintenance. These are securely fitted and have an attractive appearance.  

Is it important what kind of fixings are used on bridges?

Posted on: 06 May 2020

There are a huge number of fixings and good design requires that the correct fixing is used in every place. The fixings are made from different materials and have a range of different finishes. Cost should never be allowed to be in conflict with safety and long term service. A cheaper fixing with poor resistance to weather will be a poor choice in 30 years time when its failure leads to the scrapping of an otherwise sound bridge. The strength of some fixings needs to be greater than others. Some fixings are used in relatively more hostile environments. The bolts used to assemble the sub structure of bridges for example have to have two features. Firstly they will be wet for much of their lives and a galvanised finish is the preferred one. BZP (bright zinc plate) will offer protection for almost 3 weeks before rusting begins! Secondly the bolt needs to be made from a High Tensile Steel (HTS). One indication of this is if 8:8 is cast into the bolt head.   Other...

What are the best value bridges?

Posted on: 24 April 2020

What are the best value bridges? There are two costs to take into account when looking at a the purchase of bridge. Firstly the Capital Cost to buy and install the bridge. This will be minimised if the foundations are provided by the bridge deck supplier. Most manufacturers do not offer this service but can put you in touch with a specialist installer. Joined up projects are the least problematic. Secondly the future maintenance costs of the bridge over its life. Decisions taken at the procurement stage will impact the bridge all through its life. Sadly vandalism is an increasing issue. Money to maintain bridges is and is likely to remain in short supply. There is little doubt that steel bridges last longer than timber ones and even longer if galvanied rather than painted. They are less prone to vandalism other than graffiti.   Steel bridges do not burn.   Your Bridge designer thinks that steel bridges with a galvanised finish are...

What is a compliant bridge ?

Posted on: 16 April 2020

It is desirable to practice defensive purchasing when sourcing a bridge.   In the event of an accident and a law suit the question will be asked “Is the bridge a Compliant Structure?” This begs the question about what is a Compliant Structure.   The answer is not simple. The bridge should be designed by competent people (suitably qualified and experienced), it should be precisely made from the materials specified by The Designer and by competent trades people and it should be installed onto a suitable foundation by competent and experienced people.   In more detail the bridge should be designed to the relevant Euro Codes (which have replaced BS)   Manufacture should be carried out with in an appropriate Quality Assured system by people with relevant expertise.