Unit 1: Analysis with FEA Method

unit_1_icon.jpg

An introduction to modern structural engineering basics.

Man is an inherently creative being. Because of this, structural engineering has existed for as long as man has needed a shelter. Since the first bundle of twigs were tied together to shield against the rain and wind, this field of study has grown in scope and beauty. From primitive huts in the rain forests of South America, to the pyramids in Giza, to the Burj Khalifa in Dubai, structural engineering has accomplished staggering achievements.

Learning Objectives

After completing this unit students will have an introductory grasp of:

  • Finite Element Analysis and its advantages to modern engineering
  • Degrees of freedom and stability in structures
  • Design rules of thumb and their great importance today
  • Dead, live, seismic, and hydrostatic loads and load combinations
  • Ability to create graph paper Autodesk Revit 2015 
  • Draw structural elements to scale
  • Use Robot Structural Analysis 2015 to solve a finite element analysis problem

Introduction

Man is an inherently creative being. Because of this, structural engineering has existed for as long as man has needed a shelter.  Since the first bundle of twigs were tied together to shield against the rain and wind, this field of study has grown in scope and beauty.  From primitive huts in the rain forests of South America, to the pyramids in Giza, to the Burj Khalifa in Dubai, structural engineering has accomplished staggering achievements.  In this chapter students will be introduced to the basic principles of structural engineering, shown how modern advances in computer technology have affected design, and taught useful skills for building design intuition.

Loads and Codes

The basic problem of structural engineering revolves around the desire to keep structures in static equilibrium.  This means we want everything to remain motionless.  If a system is free to move, it becomes a dynamic system and is no longer a static one.  In order for a system to remain stable, it must be arranged so that all the members support each other.  In other words, a structure must be designed to hold its own weight.  Weight is a force which causes acceleration.  If it is not balanced by another force equal and opposite to it, the system will fail.  In the field of structural engineering, forces like this are classified as a “load.”

There are several different load type classifications, but the two most basic are live loads and dead loads.   The American Society of Civil Engineers (ASCE) handbook, Minimum Design Loads for Buildings and Other Structures , defines these terms as follows: 

Dead Loads

Dead loads are the weight of the structure itself. 

Dead Loads: “Dead loads consist of the weight of all materials of construction incorporated into the building including, but not limited to, walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items, and fixed service equipment including the weight of cranes.”

Live Loads

Live loads are the weight applied by the occupants and furnishing of a building. 

Live Loads: “A load produced by the use and occupancy of the building or other structure that does not include construction or environmental loads, such as wind load, snow load, rain load, earthquake load, flood load, or dead load.”

There remain several other types of loads for different situations.  The ASCE handbook defines hydrostatics loads as loads “caused by water either above or below the ground surface, free or confined, which is either stagnant or moves at velocities less than 5 ft/s.  These loads are equal to the product of the water pressure multiplied by surface area on which the pressure acts.”  Just as this load defines the pressure of underground water on a building, there are also loads describing water bearing down on top of structures.  Snow load describes an accumulation of snow that becomes large enough to affect building design; and water or rain loads describe the weight of pooling water on the roof of the building.  Several other loads exist besides these, and they must all be accounted for if a building is to remain firm and unyielding. 

Another important topic that will be discussed more in Unit 2 is load combinations.  When designing a structure, an engineer must design for not only one type of load but for any case of multiple loads acting together.  For example, if the building is located in a climate with frequent blizzards, it must be designed to withstand maximum wind loads as well as snow loads.  Any combination of loads, as outlined per the governing design code, will need to be considered depending on the situation

Global Perspective

Robot Structural Analysis is a mature program that can run a large variety of design codes.  With its international platform, it supports 70 design codes from different countries. For example, Robot is compatible with Indian Standard Codes for structural design, as well as the GB 50009-2001 Load Code for the design of building structures used by China.  Even in North America, there is a diversity of codes and several of these are available for use in Robot, such as the American Institute of Steel Construction (AISC) Steel Construction Manual or the American Concrete Institute (ACI) 318 Building Code Requirements for Structural Concrete. These will be referenced later in this curriculum.

Almost all countries utilize a governing code with provisions that give direction and standards on structural design and engineering.  Often these codes are tailored specifically to that region’s unique conditions.  For instance, Germany, along with several other countries, utilize the Eurocode.  Users find the Eurocode to be detailed but broad, covering a large range of structures, while other codes tend to be focused on building and building-like structures only. In many codes, the primary technical subject matters are treated similarly and even some subjects that are covered in one country’s code can be referenced to by another country’s code.  An understanding of the governing design code for your local jurisdiction is one of the top priorities for a structural engineer.  

In addition to incorporating country-specific codes, the international platform of Robot enables engineers to work with different international structural shapes and units.  Furthermore, Robot is multilingual and allows designers to input their data in one unit format and publish their reports in a different unit format.  Reference Job Preferences in Robot Structural Analysis to learn more.

Stability

Stability

The basic problem of structural engineering revolves around the desire to keep structures in static equilibrium.  This means we want everything to remain motionless.  If a system is free to move, it becomes a dynamic system and is no longer a static one.  

Complex Geometry in Structural Analysis

Complex Geometry in Structural Analysis

Finite element analysis (FEA), or the finite element method (FEM), is a numerical technique for analyzing the stresses and reactions in structures. Its computational power enables it to be used to solve structures with complex geometries.  

Structural Engineering Rules of Thumb

Structural Engineering Rules of Thumb

Previous generations of engineers known for mastering their craft functioned with “rules of thumb” and with old habits that were proven reliable through simple experience.  Learn more about these rules of thumb and the art of sketching by hand.

Sketching

Videos: Sketching to Scale

Previous generations of engineers known for mastering their craft functioned with “rules of thumb” and with old habits that were proven reliable through simple experience.  Learn more about these rules of thumb and the art of sketching by hand.