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.  

Elena is coming

Posted on: 09 April 2020

Elena is coming! Blackburn and Roberts have always been innovators. The Rowsander Path Pipe was a product for the 1980s The Kingshurst Bypass kerb for the 1990s The Nib Nobbler tool the 2000s by storm and the Servisafe Data Duct caused waves in the 2010s Now Elena is coming. A unit to collect water which has percolated though permeable drainage. Embedded in an impermeable coating it is completely covered by the permeable surface – except for access and rodding points. Water enters through openings in the side walls and travels along the duct to be discharged into drains.  

Galvanise Or Paint

Posted on: 02 April 2020

At some point the finish on the steelwork arises on every project. The choice is between painting or galvanising. Our clients favour galvanising. This is a process which offers the best long term protection. Painting is less resistant to vandalism and when it is vandalised it looks worse than a galvanised finish. Both finishes look good with wooden deck and parapet When we make trusses the galvanising gets inside the sections and stops them rusting from the inside out. Installers also prefer the galvanised finish as it is less prone to damage during delivery and installation. When used by Utility Companies they prefer the galvanised effect. Future Maintenance costs are a major issue. It is difficult and expensive to repaint a bridge in position. Preventing pollution of the river/reservoir is costly. A painted bridge will need a re-paint every 15/20 years but galvanised steelwork will last for up to 70 years before it needs attention.