Introduction to Structural Design

© 2010 Project Lead The Way, Inc.Civil Engineering and Architecture

Architecture has recorded the great ideas of the human race. Not only every religious symbol, but every human thought has its page in that vast book.

- Victor Hugo

Structure of a Building

The primary function of a building structure is to support and transmit the building loads and forces to the ground.

Photos courtesy Tilt-up Concrete Association

Characteristics of a Structure

• Strength

• Stability

• Economic Value

Structural System

• Made up of many smaller structural sub-systems that work together to provide a strong, stable, and cost-effective structure.

• Examples of these smaller structural sub-systems include:

Structural engineers design these structural systems.

Structural Sub-System

• Made up of many structural elements that work together to provide a strong, stable, and cost-effective system.

• Basic structural elements include:

Structural engineers design these structural systems.

Forces and Loads

• A force is any action that causes a change in the shape or motion of an object.

• A load is a force that is supported by a structural element.

• The terms force and load are often used interchangeably.

SNOWWIND

Structural Member Forces

Tension – A force that stretches or pulls apart a member, resulting in the member elongating.

Compression – A force that squeezes or presses a member together, resulting in the member shortening.

Shear – A force that acts perpendicular to the axis of the member, causing the internal particles of the member to slide against each other.

Beam

• A structural element that carries a load that is applied transverse (perpendicular) to its length.

• Usually a horizontal member that carries a vertical applied load.

• The top fibers of a beam are in compression; the bottom fibers are in tension.

Cantilever Beam

• A special type of beam that is supported only at one end

• The top fibers of the cantilever are in tension; the bottom fibers are in compression

Column

A vertical structural element that carries an axial force in compression

COLUMN

Truss• A structural element that is composed of

smaller structural members typically configured in triangular arrangements

• Some truss members carry a tension force; others carry a compression force

Arch

• A curved structural element that spans over an open space

• In stone arches, the last stone to be placed at the top is called the keystone

KEYSTONE

Vault

A continuous arch that forms a ceiling or roof

Dome

A structural element that is made up of arches that radiate around a center point to create a half sphere

Hybrid Forms

• An infinite number of combinations of these forms exist

Design Process

The same design process used by engineers and designers in other disciplines can be used to design structural systems.

This design process was developed based on the University of Maryland - College Park - IRB Research Project

Architectural Program

• Defines the Problem

• Establishes overall concept and design philosophy

• Includes– Location of building on site– Architectural style– Interior space planning– Design elements– Construction materials– Building systems

Architectural Program• An architectural program establishes preliminary

structural systems.

• The structural engineer must analyze the structural systems and provide a strong, stable, and cost-effective design.

• Additional criteria needed:– Types and magnitudes of applied loads– Load path that each load will follow to the ground

Structural Design Process

Generate Concepts– Consider alternate

structural configurations, materials, and spacing to improve the design or reduce costs

Structural Design Process

Generate Concepts– Select an Approach

• Based on structural performance, compatibility with the architectural program, and cost

• Based on the possibilities explored, select the optimal design

Structural Design Process

Develop a Solution– Create a preliminary

structural design incorporating the selections for all structural elements

– Create technical drawings to represent your solution

Structural Design Process

Construct and Test Prototype– Create a model to

represent your structural design

• Structural analysis software

• 3D architectural software

• Physical model

– Test model

Structural Design Process

Evaluate the Solution– Assess the

effectiveness of the design

– Revise the design as necessary to correct problems with strength, stability, and compatibility with other systems

Structural Design Process

Present the SolutionIf the proposed design

solves the problem• Document the project

– Create working drawings and specifications for the structural design

• Communicate the project

Image Sources

• Tilt-up Concrete Association

(www.tilt-up.org)