Civil engineering and building works

cylinders and pre-cast beam or deck sections offers the advantage of simplicity and speed. Flexibility of con­ struction and type of pile is also advantageous. Accept­ able alternatives should be able to be driven, vibrated or jetted to the level or permission given to use any combination of these methods. Soffit shuttering should be avoided and pre-cast work used where possible. Insitu concrete, where necessary, may even be placed more economically by helicopter from a shore-based batcher.

The decision on how much energy absorption to take in the structure and how much in the tendering depends largely on external factors such as current, wind, type and size of ship and how closely-coupled the vessel needs to be during loading or unloading. A tanker, for instance, requires much less rigidity than a collier or container ship, as all shore connections are flexible.

11Loadings

11.1Definitions

When designing any structural element in a building it is necessary to ascertain the imposed loads in addition to the dead load of the frame, cladding and other components making up the building. The imposed loads are the result of static plant, dismantled plant being placed on floors, impact operation of plant, vibration and dynamic forces, foot and wheeled traffic and also wind and snow loads.

11.2 Imposed loads due <o plant

Loads due to plant items may vary from less than one tonne on small pipe supports and similar items to those up to 13 000 tonnes for slung boilers, turbine and

Chapter 3

generator components. If maintenance of the heavier plant is not carried out by station personnel, no provision is made for accommodating plant com­ ponents on the boiler house and turbine hall operating floors, and the crane is used to move equipment directly to transporters in the loading bay. The loading bay floor in the turbine hall is designed to carry transporters and loads up to 310 tonnes.

11.3 Distributed imposed loads

Although it is necessary to limit the positions on which heavy loads can be set down on floors, it is not practical to do this with smaller items and it is therefore usual to decide on a floor loading per square metre which will cater for this form of loading. Foot traffic and the movement of materials are also taken into account when assessing the imposed distributed load. At the time that the design of the frame is prepared it is not possible to ascertain all the smaller individual imposed plant loading requirements, especially loading on linens due to undcrslung pipework and similar items, and it is common practice to increase the distributed imposed load per square metre by an amount which will cater for these requirements.

It should be noted that the loadings in Table 3.5 are in addition to individual items of heavy static plant, the positions and weights of which are accurately deter­ mined and which in some cases have their own separate foundations.

The recommendations given in BS6399 — Loading for Buildings: Part 1: Code of Practice for Dead and Imposed Loads [15] are normally used to establish the design imposed loads for offices, canteens, laborato­ ries, etc. Typical imposed distributed loads lor offices from BS6399 are 2.5 kN/m2 for offices for genetai use and 3.5 kN/m2 for offices with fixed computers or