How do you model seismic and wind loads?

1 Seismic loads

Seismic loads are the forces and motions that result from earthquakes. They depend on the magnitude, location, and duration of the earthquake, as well as the soil and structural properties. To model seismic loads, you need to consider two aspects: the ground motion and the structural response. The ground motion is the input that describes the intensity and frequency of the earthquake shaking. It can be obtained from historical records, probabilistic analysis, or synthetic generation. The structural response is the output that describes how the structure behaves under the ground motion. It can be calculated using various methods, such as linear or nonlinear static analysis, linear or nonlinear dynamic analysis, or response spectrum analysis. You also need to account for the effects of damping, soil-structure interaction, and inelastic behavior.

2 Wind loads

Wind loads are the forces and pressures that result from the flow of air around structures. They depend on the wind speed, direction, and turbulence, as well as the shape, size, and orientation of the structures. To model wind loads, you need to consider two aspects: the wind characteristics and the aerodynamic coefficients. The wind characteristics are the input that describes the statistical and spatial distribution of the wind speed and direction. They can be obtained from meteorological data, wind tunnel tests, or numerical simulations. The aerodynamic coefficients are the output that describe the drag, lift, and moment forces that act on the structures. They can be obtained from empirical formulas, wind tunnel tests, or numerical simulations. You also need to account for the effects of dynamic response, wind-induced vibration, and gust factor.

3 Modeling tools

To model seismic and wind loads, you need to use appropriate tools that can handle the complexity and uncertainty of these phenomena. Various tools are available for civil engineering design, from simple spreadsheets and calculators to sophisticated software and hardware. ASCE 7 is a standard that provides minimum design loads for buildings and other structures, covering both seismic and wind loads, as well as other types of loads. SAP2000 is a software that can perform structural analysis and design for various types of structures, with the ability to model seismic and wind loads using different methods. OpenSees is a software that can perform advanced simulation of structural and geotechnical systems under seismic and wind loads, with the capability to model nonlinear and inelastic behavior, soil-structure interaction, fluid-structure interaction, material degradation, probabilistic and stochastic analysis, parameter identification, and sensitivity analysis.

4 Modeling tips

To model seismic and wind loads effectively and efficiently, you should adhere to certain tips and best practices. Firstly, use realistic and reliable data that reflects the actual or expected conditions of the site, the structure, and the loading. Avoid outdated, inaccurate, or incomplete data that can lead to errors or uncertainties; verify and validate your data using multiple sources and methods. Secondly, simplify your model to reduce computational cost and complexity; avoid unnecessary or excessive details, elements, or parameters that can increase the error or uncertainty. Utilize appropriate assumptions and simplifications that can preserve the essential features and behavior of the system. Lastly, check your results to ensure they are reasonable and consistent; avoid results that are unrealistic, contradictory, or suspicious. Compare and contrast your results with other methods, tools, or references.

5 Modeling challenges

Modeling seismic and wind loads is a difficult task. There are many challenges and difficulties that need to be addressed, such as uncertainty and variability, complexity and interdependence, and standards and regulations. Seismic and wind loads are uncertain and variable phenomena that can change over time and space due to many unpredictable factors. They also have a high degree of randomness and nonlinearity, which can cause unexpected or extreme events. In addition, seismic and wind loads are complex and interdependent phenomena that can interact with each other and with other systems, causing multiple simultaneous effects like resonance, coupling, or feedback. Moreover, seismic and wind loads are subject to various standards and regulations that can vary by country, region, or industry. These regulations can impose different requirements, criteria, or limitations on the modeling and design process. They can also change or update due to new research, technology, or experience.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?