Wind Loading of Buildings & Structures

Strong winds can generate large loads on tall buildings and slender structures, often triggering dynamic responses. For this reason, wind loading is generally considered to be one of the most important factors when designing tall structures. Because of the complex interaction of turbulent wind flows and the flexibility of structures, wind loading on buildings can only be measured accurately by wind tunnel testing.

At Gradient Wind, we create model replicas of study sites and their surroundings (typically at a scale of 1:400), install them in the wind tunnel, and perform tests for the full 360O azimuth of wind directions. We then combine the raw data with statistical models of the wind climate for the building’s location to predict wind loads and building accelerations. At Gradient Wind, we have experienced engineers and technicians who are capable of accomplishing project goals quickly and efficiently using our in-house testing and fabrication facilities.

Our studies are conducted using either the high-frequency force-balance (HFFB) technique or the high-frequency pressure-integration (HFPI) technique, which provide the loading and deformation information necessary to design safe structures. Gradient Wind staff also have experience with more complex aeroelastic modelling for unique situations.

After wind loading, occupant comfort and functionality of buildings are the most important priorities in tall building design. Adequate serviceability of a building is assured by controlling accelerations at top occupied floors. Accelerations influencing occupant comfort are related to building deflection (inter-storey drifts) and the interaction of building components.

Building motions increase under stronger wind, but decrease when a building becomes stiffer or has more inherent damping. Beyond these factors, good aerodynamic design of tall buildings can avoid the largest resonant vibrations by detuning the building’s natural vibration from vortex shedding around the building corners for prominent wind speeds.

When detuning by structural stiffening or geometric modification is not feasible or economical, the problematic vibrations can be mitigated by introducing supplemental damping such as Tuned Mass Dampers (TMD) or Tuned Liquid Sloshing Dampers, among other options. Information relating to building motions and accelerations are also derived from wind tunnel testing using the HFFB and HFPI approaches. Gradient Wind engineers routinely interact with the design team members to provide advice for the most economical solutions to building motion and wind-loading problems.

Supplemental Damping Of Buildings & Structures

In many cases, stiffening lively buildings or structures is costly and reduces the amount of useable floor space. Alternatively, the process of supplemental damping provides an economical and effective option to control building accelerations and deflections. At Gradient Wind, we have designed, tested, fabricated and overseen the installation of supplemental dampers in numerous buildings across North America.

The Tuned Mass Damper (TMD) is one of the most efficient types of dampers to control excessive building motions. Leveraging solid mass made of steel or concrete, TMDs provide greater damping for a given space, and their maintenance is much easier compared to other dampers, such as Tuned Liquid Sloshing Dampers (TLSD) or Tuned Liquid Column Dampers (TLCD). Compared to  pendulum or double-pendulum type TMDs, which have large space requirements, Gradient Wind’s TMDs are designed to fit in much smaller spaces while providing similar or even greater damping effects. This efficiency is accomplished through compact design that involves moving mass gliding on linear guides or multi layered-rubber bearings. Gradient Wind provides TMD design, fabrication, installation and maintenance services.

The Tuned Liquid Sloshing Damper (TLSD) is the most widely-used and economical apparatus to control building motions. This device is installed near the top of a building and consists of one or more water-filled tanks fitted with internal baffles. The motion of the water in the tank, tuned to the natural frequency of the building, passes through the baffles and dissipates the energy of the moving structure. At Gradient Wind, we can provide initial consultation for damping options, and when necessary, detailed design of the TLSD using our dynamic test rig. This rig simulates the damping effect that the TLSD would impose upon the fullscale building.

Modular Dampers

As a variation of the TLSD, Gradient Wind has invented modular dampers that facilitate simple and more flexible damper installation. Unlike the one large tank of a TLSD, modular dampers consist of many modules (50 to 100) of small size fiberglass tanks with an approximate dimension of 9’ (L) ×4 (2)’ (W) ×1’(H). Due to the small size, modular dampers can be flexibly stacked in smaller spaces while providing damping effects similar to a large TLSD. Other benefits of modular dampers are that they are virtually leak-free with easy installation and replacement. Moreover, modular dampers do not require large concrete tanks and can be used in the rehabilitation of existing buildings. Lastly, since the installation time can be delayed to follow field monitoring, the most economic damper design is possible after knowing the exact design parameters, such as required supplemental damping levels and building frequencies. As the inventor, Gradient Wind designs, fabricates and installs the modular dampers.

To suppress the vibration of slender structures such as bridge decks, slender towers and flexible sculptures, special damping solutions are sometimes necessary. These include smaller versions of the TMDs used for buildings, Impact Chain Dampers (ICD), and Viscoelastic Dampers (VD). While TMDs and ICDs dissipate vibration energy through “tuned” secondary masses, VDs dissipate the energy through the viscous dissipation of fluid or the plastic deformation of the interfacing material itself. A wide variety of dampers can be used to satisfy different design requirements and unique site conditions.

At Gradient Wind, we have practical experience with a wide array of economical damping solutions.

Empty Tank With Screens and Water

Monitoring Of Building Motion

Occupants of tall buildings and slender towers can experience uncomfortable motions and accelerations. At Gradient Wind, we predict structural accelerations based on wind tunnel testing and analysis of theoretical building properties. These techniques provide us with the initial estimates of motions. Later, we can perform full-scale measurements on the completed structure to validate our predictions. Finally, we use the information gathered through predictive modelling and physical measurements to mitigate uncomfortable accelerations.

Gradient Wind staff have practical experience monitoring the motions of buildings and structures, the knowledge to design cost-effective damping devices, and the judgement to apply solutions to mitigate excessive accelerations where required. We use state-of-the-art technologies to monitor, retrieve and analyze essential structural properties and structure response data.