Dynamic loads and turbulent wake

The requirements concerning protection of steel chimneys against vibrations have become more stringent pursuant to binding European standards. New procedures of calculating turbulent wake loads mean that most chimneys, designed and built nowadays, require dampers. This issue is vital as vibrations may pose considerable risks to structures. Significant, uncontrolled vibration amplitudes lead to material fatigue, and in extreme cases may even cause a sudden collapse of the structure. The requirements pursuant to the standards stem from current designing trends. The availability of construction materials capable of withstanding high loads (steel) and modern construction solutions (e.g. sprężane połączenia śrubowe) and using advanced, computer-assisted designing methods allow to build more cost-effective structures. This means, however, that despite enhanced resistance, the structures are becoming increasingly lighter, and hence their damping capacity is smaller. Consequently, such structures are highly susceptible to various vibrations and dynamic loads. This is especially relevant for self-supported chimneys.

Cost-effectiveness vs. safety

When designing and later using steel chimneys one should not forget about very important economic factors, as well as safety and reliability concerns. Competitive market and the need to decrease energy absorption calls for optimization of all structural elements and equipment. However, nothing can be done at zero cost. Structural solutions are more and more complex and need advanced designing methods, higher technical skills during construction and advanced quality control. The European standards to a great extend take those considerations into account, but it results in rigorous requirements for protection of chimneys against vibrations resulting from wind resonance. Our estimates show that around 90% of self-supported chimneys designed according to the new standards must be equipped with dampers reducing vibration amplitudes and fatigue strength of steel. Pursuant to PN-EN 1993-3-2. EUROKOD 3: Design of steel structures. Towers, masts and chimneys – Chimneys, post-installation inspections should be carried out to verify the effectiveness of damper systems.

State-of-the-art dampers

Our innovative vibration dampers were created to meet rigorous safety requirements and optimise costs. They are a combination of tuned mass and viscous dampers. Their moving elements use specially designed bearing systems guaranteeing high durability, reliability and precision of the joints. At the same time they are extremely easy to use. Their adjustable settings allow us to tune the dampers to dynamic properties of the chimney and to correct the adjustments after some time, if there is such a need. All moving parts and viscous fluid are enclosed in a compact, hermetic casing, which secures the device against aggressive environment at the chimney outlet. The above structural features and the fact that usually a number of independent dampers are used at one structure contribute to extremely high reliability of our dampers. The unique design of our devices is protected by a patent.

Advantages of our dampers::

The main advantages of our horizontal vibration dampers::

• they can be used both at newly-designed chimneys and at existing structures with no major structural changes
• their parameters can be regulated and, after some time, adjusted to changing dynamic conditions at the chimney ( e.g. due to corrosion, after modernisation or after installing additional telecommunication equipment)
• we choose and install optimal solutions after testing dynamic loads at the structure;  it allows us to establish actual dynamic values (which may differ from those theoretically calculated) and to verify the effectiveness of the dampers after the assembly.
• the dampers are relatively light and small (in comparison to other available mass and fluid dampers) and, hence, they do not significantly increase the loads at the structure
• they can be adjusted to common structural designs of chimneys, which enables their servicing from standard access platforms
• they are highly reliable and durable (durability of >30 years) in aggressive industrial atmosphere

Possible applications

So far, we have used our dampers to secure steel chimneys ranging from 25m to 120m in height against vibrations. We have tested the devices not only at structures with uniform dynamic parameters for both vibration directions, but also at asymmetric chimneys, where special solutions had to be implemented. Our dampers have been used at new structures built by us and also as auxiliary equipment in projects by other designers. We have also installed damping systems for existing chimneys, including structures where other types of dampers failed and old chimneys in need of safety upgrade to extend their life cycle.

Comprehensive service

We offer comprehensive solutions for securing high-rise structures against horizontal vibrations. We:

• perform initial dynamic load testing for existing structures
• conduct a comprehensive analysis of dynamic parameters of the structure.
• choose optimal solution and often design custom-made dampers tailored to your actual needs.
• provide design documentation, components, mechanical and structural parts and  assemble ready devices.
• conduct initial laboratory tests, assemble and tune the dampers at the structure.
• verify the effectiveness of the dampers through testing after assembly and provide testing reports (required pursuant to Eurokod).
• provide warranty and after warranty service of the dampers.