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Braithwaite Pressed Steel Sectional Water Tanks

by
Dale Price
BEng(Hons), CEng, FIStructE, MICE
Structural Science Ltd.

Structural Science Ltd, in cooperation with Braithwaite Engineers, are implementing IDEA StatiCa Connection software to continually research and design various bespoke connections in their steel water tanks and with over 125 years of experience in the design and manufacturer of steel sectional water tanks they have installed thousands of tanks both domestically and internationally across the world.
In the construction of sectional steel pressed tanks, a variety of connections is used, and in this short case study written by Dale Price, structural engineer at Structural Science Ltd., the stay connection is discussed which supports the horizontal hydrostatic water pressures exerted on the walls of the tank.

About the connection that has been tested

As you can see in Figure 1, the steel bolted stay connection or cleats consists of a thin baseplate with a welded fin plate connecting the angle stay between the base and walls or the wall corners of the tank and can be subjected to 75 kN design tension force in normal cases.

Historically, design is normally undertaken by hand calculations and verification of connections has been confirmed by preparing expensive full scale laboratory testing of components and testing full scale site mock ups of tanks.

Figure 1

Figure 2 shows recent full scale testing of a tank where a stay is connected to strain gauges which continually monitor the load on tank stays during water filling and long static water tests.

Figure 2

Back in the laboratory, Figure 3 shows the stay connection being proof tested to code requirements (and of course other strength and failure tests not shown here).

Figure 3

The stay connection has been analyzed with IDEA StatiCa, and the below screen shots summaries the procedure:

Figure 4, describes the overall arrangement of the connection with bolts and welds with 75 kN design axial load to the stays.

Figure 5, highlights the equivalent stress plots indicating the areas of highly stressed components and

Figure 6, indicates developed plastic strains on the baseplate.

Figure 4

Figure 5

Figure 6

Of course, except from pure analysis results, more importantly, IDEA StatiCa provides the overall EC/AISC checks for all elements, as it is shown in Fig.7, giving us very clear Pass/Fail results (Fig.8)

Figure 7

Figure 8

In conclusion, the connection behaviour and load correlation between full scale/laboratory testing and CBFEM software was very good and therefore, full scale testing program confirmed the validity and accuracy of the IDEA StatiCa software for connection design.
In general, future bespoke connection designs can now quickly realised using this software without implementing and planning costly and long period testing programs.
The software is currently being used to rationalise and develop better connection designs with benefit saving in cost and manufacturing processes.
Other difficult bespoke connections related to the tank design are now being investigated using the IDEA StatiCa software.

Fig.9 – Deformed shape representation help the engineer to have a better understanding of the connection’s behavior

Summarizing, some of the key benefits of using IDEA StatiCa are:

  • Reduce the period of the desk based and repetitive connection design work.
  • The ability to model of all the components of the connection in one design, i.e. weld, bolts, plates and section in one assembly and understand the better interaction between individual components and comparing this against breaking up the connection into individual design component.
  • Continually investigate, develop and research old and new bespoke connections without planning long and expensive full scale test programs to verify connection designs.
  • Improve existing connections by rationalising plate or section sizes, vary configurations for cost manufacture and verify increased design forces from the normal design for example earthquake forces subjected to tank walls.
  • The full-scale testing has provided confidence in the implementation of designing such connections using finite elements and specifically IDEA StatiCa Steel software which is based on the new CBFEM method.
  • Switch designs with updated different country connection standards.

About Braithwaite Engineers:

 Braithwaite is an international company with a reputation for technical excellence founded on more than 125 years of experience in bridges and storage tanks. The name Braithwaite is synonymous with a comprehensive range of liquid storage tanks and ancillary products. Our range of Steel and GRP modular tanks has gained an enviable reputation worldwide.

http://www.braithwaite.co.uk/

About Structural Science Ltd:

Structural Science a small international structural engineering consultancy based in the South West of England and provide engineering consultancy to Braithwaite and Engineering Consultancies.  With over 30 years of experience in tall buildings, long span structures, stadiums, airports, and special structures.

http://www.structuralscience.co.uk/