When designing a building, it is essential to consider various loads to ensure resistance to shear forces and moments, as well as usability considerations for vibration and deflection for user comfort. This allows us to pursue structural stability and a safe living environment at the same time.
Buildings are subjected to various kinds of forces by various factors, such as the weight of the building itself, the weight of users, and the external environment, which are called loads. All objects on Earth are subject to a force called gravity in a straight line. This is because the Earth and objects on Earth are attracted to each other. This is Newton’s law of universal gravitation, and no object on Earth is free from this force. Buildings are subject to the same universal gravitational force, which is called vertical load.
Vertical loads can be divided into two main types: dead loads, which are caused by the weight of the building itself, and live loads, which are caused by people living in or moving around the building, furniture, etc. These two loads are the most basic loads acting on a building and are the first to be considered in structural design. Accurate calculation of these loads is essential in building design, and they should be analyzed and simulated in detail from the earliest stages of design to ensure that they are properly addressed. In addition to these, buildings are subjected to a combination of other loads, including wind loads from wind, seismic loads from earthquakes, rainfall loads from rain and snow, and snow loads. These loads vary depending on the geography, climate, and the building’s intended use, and designers must consider them all to ensure a safe structure.
Structural engineers use the right combination of these different loads in their designs. When loads act on a building, they create forces called shear forces and moments in each major structural member (columns, beams, load-bearing walls, etc.). A shear force is a force acting on any side of a member, and it has the property of causing two opposing sides of a member’s cross-section to slide against each other. For example, if you ask a friend to lend you their arm, you can push up and down on their arm with both hands as hard as you can. The force on your friend’s arm is called shear force. If the force becomes very large, your friend’s arm will break. This is called shear failure. In architecture, to resist shear forces, members are enlarged or reinforced with reinforcing bars in the middle of the member.
The bending moment is the product of the moment arm length, which is the shortest distance from a reference point to the point of action when an external force is applied, and the external force. It is a measure of bending. Let’s borrow a friend’s arm again. Stretch out your friend’s arm and place it across the end of your desk so that your hand is sticking out of the desk. Now, press down firmly on your friend’s palm. At this point, the end of your friend’s arm will have a bending moment. If you were to extend your arm further out to increase the arm length of the moment, your friend would feel more pain for the same force. This is because the magnitude of the bending moment has increased due to the increased arm length. This is how structural engineers design all structural members of a building to resist both effects of loads (shear and moment).
However, resisting only shear forces and moments does not mean that a building is perfectly designed. Unlike art structures on the street, buildings are meant to be used by people, so they require usability studies that consider vibration and deflection to ensure user comfort. For example, wind-induced vibrations can be a problem in high-rise buildings. If these vibrations are excessive, they can cause dizziness or anxiety for people in the building. Therefore, structural design requires devices to minimize these vibrations, and in recent years, vibration control systems using advanced technology have been developed and applied.
Many years ago, there was a disturbance when a building was reported to be about to collapse. The building was evacuated after users inside felt a large vibration that felt like an earthquake. When we investigated, we found out that a group of women were taking aerobics classes in the building’s gym, and they were all running in a regular cycle. The frequency of the women’s jogging coincided with the natural frequency of the building, causing the building to shake due to resonance. While this was an isolated incident, it’s a great example of how important it is to review the usability of a building. No matter how sturdy a building is built, the slightest thump can cause significant vibration or excessive floor sagging, which can cause anxiety and fear for the people living inside. To avoid these problems, usability reviews should become an integral part of the design process.
This is just a brief overview of the factors that go into a building’s ability to stand. When structural engineers design a building’s structure, they first look at the various loads that can affect it. Then, they design for a member’s ability to resist more than the shear forces and moments caused by the load. Lastly, in addition to structural issues, a usability review should be completed to ensure that the building’s users are safe and comfortable inside.
Building collapse incidents result in many casualties. Recent building collapses around the world are a stark reminder of the seriousness of the problem. Structural engineers should strive to design buildings that are resistant to collapse by comprehensively considering a variety of circumstances. This effort should extend beyond simply ensuring the safety of the building to include the daily convenience and comfort of the people living in it. Only such a thorough approach will be the foundation of safe and sustainable building design.
