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...