Structural Modeling of Buildings – Simplified Guideline of Modeling Techniques

Structural analysis is a key part of design in civil structural engineering. The structural analysis is the procedure that enables the determination of the structural response (the internal forces and the movement components) considering the applied external effects (loads, displacements, thermal…) and the boundary conditions. It was not too long ago that structural analysis methods were performed manually using the various conventional theory of structures methods such as the moment distribution method, the slope deflection method, the matrix method….

The use of these conventional manual methods is commonly accompanied with difficulties when conducting complex structural analysis such as the study of three dimensional structures, the dynamic analysis, the non-linear behavior…Moreover, these methods require long time for calculation and may result in inaccuracy of the obtained results.

Another method of calculation is the finite element method (FEM). The FEM, developed long time ago from the matrix analysis method, provides high level of accuracy when used in the structural analysis, but the mathematical complexity of the method made it impractical for manual analysis. The development of the computers and the evolution of their capacity in the previous decades allowed for the integration of the FEM as numerical method for the use in the structural analysis. Accordingly, the FEM became typically the base for the modern structural analysis.
The FEM software represent powerful and flexible means to model a wide range of structures and straining effects on the structures. However, the use of this powerful means may embrace important peril within the obtained solutions if some precautions are not properly incorporated in the numerical model.

Performing adequate numerical structural studies requires basic knowledge in the FEM and strong theoretical structural background (Theory of Structures, structural behavior of Tall Buildings…). In other words, The behavior of a structure ,when subjected to more or less complex effects (dynamic, non-linearity…), should be predictable by the user based on his former theoretical knowledge and experience in the structural domain. ACI President’s Memo José M. Izquierdo- Encarnación 2003 highlighted the importance of the above concept:

“As a rule, a program should be used only if engineers can predict the general deflection and distribution of moments in the structure prior to obtaining a solution. The computed solution is used to verify the results previously predicted by the engineers. If the solution is significantly different from the prediction, engineers should use the results only if they can satisfactorily explain the reason for the discrepancy and find it acceptable.”

The type of expected results may include:
 Approximate values of some structural response components such as the slabs/beams deflections or the sway/drifts buildings. The approximate values may be obtained from simplified theory of structures methods (moment distributions...)
 Recognizing the deformed shape of the whole structure and the structural elements under the applied loads

Despite their continuous development, most of commercial structural software have practical limitations such as the size limitation of the model and the linear behavior of materials. Commonly a single model of the structure cannot be used to provide all aspects of a structural behavior. For the same structure, several analysis models are often needed, each with different set of parameters or different elements type, to generate a specific structural response (elements forces, deformations...). Since most of the software manuals provide guidelines for the use of specific software assuming the user has already the required theoretical knowledge and adequate experience, the intent of this manual is to provide simplified basic guidelines of the structural modeling techniques combining:
 The complexity of numerical analysis by using Finite Element Method (FEM).
 The systematic procedures to use these software that are stated in the software help manuals. However, the user manuals of software do not include all necessary modeling techniques, tips, and the adequate assumptions for specific cases of study.

The aim is to enable the user to construct a numerical model that properly generate the expected responses of a structure. In other words, it is a simplified framework to provide guidelines for all structural engineers including fresh graduates and undergraduate students. It presents clarifications and answers that help the user comprehend the different aspects of structural modeling by understanding the concepts of analysis of the structural elements and the various ways to reflect this analysis as given inputs within the software. It tackles the structural elements as separate subjects clarifying the different ways to deal with these elements based on given criteria.
Hoping this manual to serve its purpose, it is only the first edition. Your comments, feedbacks, suggestions and queries are all welcomed to bring out the best of and enhance the editions yet to come. 

Structural Modeling of Buildings - Simplified Guideline of Modeling Techniques
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