Effects of wind load on ‘E’ plan shaped tall building under interference conditions

Wind is an invisible force that constantly pushes against the structures we live in, but its behavior changes dramatically when buildings stand close together. In the crowded skylines of modern cities, where space is at a premium, architects often design towers with complex, irregular shapes to fit more living space onto a small plot of land. While engineers have long understood how wind hits a single, isolated tower, the physics become far more complicated when one building stands near another. The presence of a neighbor can block the wind, funnel it through narrow gaps, or create swirling pockets of air that exert unexpected pressure on the main structure. Understanding these interactions is critical for safety, as the wind loads on a building in a dense cluster can be significantly different from those on a solitary tower, potentially leading to structural failure if not properly calculated.

Researchers Sumanta Mandal and Sujit Kumar Dalui from the Indian Institute of Engineering Science and Technology in Shibpur set out to investigate these hidden forces on a specific, complex architectural form: a tall building with an "E" shaped floor plan. This shape, resembling the letter E, presents twelve distinct faces that can catch the wind from any direction. To understand how this shape behaves when surrounded by other buildings, the team combined two powerful methods. First, they built a physical model of the "E" building and placed it in a wind tunnel, a large laboratory chamber where air is blown at controlled speeds to simulate real-world storms. They measured the actual forces and twisting moments acting on the model. Second, they used a sophisticated computer simulation technique known as computational fluid dynamics. This method creates a virtual wind tunnel, allowing them to model the flow of air with extreme precision and to test scenarios that would be difficult or impossible to replicate physically.

The study focused on how the wind load changes when two smaller, square-shaped buildings are placed near the main "E" building. The researchers tested these interfering neighbors at various distances, ranging from very close proximity to several building-widths away. They also rotated the wind direction, testing angles from zero to one hundred and eighty degrees to see how the building reacted to wind hitting it from the front, the side, or the corner. The goal was to determine a specific value called the interference factor, which compares the wind pressure on the main building when it is alone versus when it is surrounded by neighbors. If this factor is greater than one, the neighbor is making the wind load worse; if it is less than one, the neighbor is actually shielding the main building from the wind.

The experiments and simulations revealed that the distance between buildings and the angle of the wind are the most critical factors. When the interfering buildings were placed very close to the main "E" structure, the wind behavior changed drastically. In some specific situations, the presence of a neighbor actually increased the wind pressure on certain faces of the main building by a significant margin. For instance, when the wind hit at a thirty-degree angle, a neighbor placed three hundred millimeters away caused the pressure on one specific face to more than double compared to when the building stood alone. Conversely, in other configurations, the neighboring buildings acted as a shield, reducing the wind pressure on the main structure. The researchers found that when the interfering buildings were placed at a distance of three thousand millimeters, the wind load on the main building returned to the same level as if it were standing completely alone, indicating that beyond this distance, the neighbors no longer influenced the wind forces.

One of the most striking findings was the discovery of "channeling" effects. When the wind blew directly at the gap between the main building and a neighbor, the air was forced through the narrow space, speeding up as it squeezed through. This acceleration created a localized increase in wind speed and pressure that would not exist if the building were isolated. On the other hand, when the wind hit the side of the interfering building, it created a blockage that reduced the wind speed reaching the main building, effectively lowering the force it had to withstand. The study also identified specific faces of the "E" building that were particularly vulnerable. For example, at certain wind angles, the interference caused a suction effect on the rear faces, pulling the building outward rather than just pushing against it. These negative pressure values, which indicate a pulling force, were found to be significant and varied depending on how close the neighbors were.

The researchers validated their computer models against the physical wind tunnel tests and found a strong agreement between the two, with errors generally remaining below fifteen percent. This confirmation gave them confidence in using the computer simulations to explore a wide range of distances and angles. The data showed that the maximum force the building experienced occurred when the wind hit it head-on, while the minimum force happened when the wind came from the side. However, the presence of neighbors shifted these values. In the most extreme case of interference, the force on the main building dropped to a fraction of what it would be in isolation, while in other cases, it surged. The study concluded that for the specific "E" shaped building analyzed, the influence of neighboring structures is highly localized. Once the distance between buildings exceeds a certain threshold, the complex interactions fade, and the building behaves as if it were standing in an open field. This precise mapping of how wind forces change with distance and angle provides essential data for engineers designing tall, irregular buildings in dense urban environments, ensuring they are built to withstand the unique and often unpredictable forces of the city wind.