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Do you know how to balance structural strength with comfort for daily use in a design?
In today's architectural design field, how to strike a balance between structural strength and daily comfort has become a major challenge for engineers and designers. With the advancement of technology and the evolution of building materials, designers must consider every detail to ensure that the building meets structural safety while also providing a comfortable living environment for users.
Limit State Design (LSD) is a structural engineering design method whose purpose is to ensure that the structure can withstand possible loads during its design life while maintaining suitability for use.
According to the principles of limit state design, a structure must meet two main criteria: Ultimate Limit State (ULS) and Serviceability Limit State (SLS). These standards not only ensure the strength and stability of the structure, but also require the structure to maintain functionality during daily use and avoid causing discomfort to users, and these standards are the core of the design.
Ultimate limit state (ULS)
Ultimate limit state (ULS) is an important concept in design that focuses on the ability of a structure to withstand the maximum design load. When a structure encounters conditions that exceed its design load, structural failure may occur, resulting in irreversible damage or collapse. Therefore, all bending, shear, and tensile or compressive stresses must be below the calculated material load-bearing capacity.
The design process requires estimating the loads the structure will bear, selecting member dimensions to inspect, and setting design criteria. The common goal of all engineering design standards is to ensure the safety and functionality of a structure.
The calculation method of ULS involves adding Magnification Factors to the load to determine the stress, and using Reduction Factors to calculate the material's load-bearing capacity. This means that structures must maintain their safety and reliability in a changing environment.
Serviceability Limit State (SLS)
Another important criterion is the Serviceability Limit State (SLS), the main purpose of which is to ensure the functional effectiveness of a structure in daily use. For example, the structure must prevent uncomfortable conditions during daily operation, such as excessive deformation, noise and other problems. SLS is not a physical phenomenon, but a computational check that must ensure that the structure can function properly under normal loads.
These inspections involve various pressure limits, deformation limits, flexibility or rigidity limits, etc., as well as crack control requirements, which can affect the durability and comfort of the structure. Especially when considering non-structural factors, limitations such as acoustics and thermal conduction may also be involved, which also reflect the comfort of daily life.
When designing for extreme states, the design must meet the comfort of daily use, which is also a key consideration in modern architectural design.
Development of load and resistance factors
In limit state design, load and resistance factors are determined using statistics and the probability of failure is preset. The performance changes of different materials will affect their factor settings. Usually the load-bearing factor of the material will be less than or equal to 1, while the load factor will be greater than or equal to 1. This may result in structures that may respond to uncertainty in different ways in different designs.
For example, when dealing with structural safety, wood and masonry will generally have smaller resistance factors than concrete, which in turn will have smaller resistance factors than steel. The use of these factors can ensure that each structural element has a similar probability of failure when faced with various situations, thus improving the consistency of the design.
Global practice
In many countries, including Europe, Australia, Canada and China, extreme state design has become a mainstream architectural design standard. Building regulations in these countries are generally based on limit state design, ensuring that structures can bear heavy loads while maintaining user comfort.
Limit state design has replaced early allowable stress design in most civil engineering projects, which shows the effectiveness and forward-lookingness of this design method.
However, due to the slow progress in implementation in this area in the United States, many building standards still use allowable strength design. In this case, designers must consider the reliability and comfort of the structure more carefully, as this directly affects the end user's experience.
Conclusion
In extreme state design, finding the balance between structural strength and daily comfort is undoubtedly a major issue that designers need to solve. How to maintain this balance in an increasingly complex environment will be an ongoing challenge and inspire innovative thinking in future architectural design?
