INTRODUCTION TO

AUTO DIAPHRAGM

An Enhanced Software for Analysis and Design of RC Diaphragms

Using Strut and Tie Analysis

By:

Mohammad Ebrahimi Koopaee, Senior Structural Engineer

and

Amirhossein Najafi, Engineering Programme Developer

Presentation Outline

• Necessity of strut and tie in NZ standards

• Generation of building geometry at Auto Diaphragm

• Strut and Tie grillage

• Assignment of Strut and Tie sections

• Seismic load distribution to strut and tie nodes

• Strut and Tie analysis

• Verification

• Exceptional abilities

STRUT AND TIE IN NZ CODE

Design of diaphragms based upon strut and tie method is mandatory in NZS3101

Engineers are hard pressed within the timeframe and budget restraint of projects to

perform reasonable strut and tie analysis for diaphragms

THE NEED FOR ITERTATIVE ANALYSIS AND

DESIGN

COMMON PRACTICE FOR DESIGN OF

DIAPGRAGM

Figure from Holmes Consulting

ISSUES IN THE CURRENT PRACTICE FOR

DESIGN OF DIAPHRAGMS

❑ The process is time-consuming

❑ It does not allow trying grillage with different parameters such as grillage

spacing, etc.

❑ The floor geometry needs to be simplified often resulting in different floor

layout than the original floor layout

❑ Transfer forces and stiffness of supports will need to be calculated manually

❑ A single section size is typically given to strut and tie section rather than

precisely based on the grid spacing

❑ Transfer forces are sometimes missed

❑ Analysis models are often un-stable

Generation of Building Geometry at Auto Diaphragm

Reads an existing ETABS (or Sap2000) model

Building geometry including diaphragm supports

and stiffness Automatically imported into Auto

Diaphragm from the ETABS model

→ no need to define support springs or calculate

stiffness of supports for the diaphragm

The programme loads the floor levels from an ETABS model into Auto Diaphragm

User selects a floor level for strut and tie analysis

User selects critical points which must be part of the grillage

User defines maximum spacing of the grillage

Generation of Building Geometry at Auto Diaphragm

Strut and Tie Grillage

The programme forms the grillage based on the specified maximum mesh spacing and the base points

Assignment of Strut and Tie Sections

The programme automatically assigns section properties to generated strut and tie elements based on the floor thickness and grid spacing

User can specify the width of strut and tie elements in relation to grid spacing

User can define different thickness for orthogonal members in two horizontal directions

Seismic Load Distribution to Nodes

The programme automatically distributes user-defined lateral forces to strut and tie nodes

User can specify the width of strut and tie elements in relation to grid spacing

User can define different thickness for orthogonal members in two horizontal directions

Strut and Tie Analysis

The programme automatically creates nonlinear load cases for diaphragm analysis

Nonlinear is performed to calculate the strut and tie forces

Strut and tie forces can be easily checked and elements can be designed

AUTO DIAPHRAGM

It has been verified for the most complicated building shapes and configurations

AUTO DIAPHRAGM

It has been verified for the most complicated building shapes and configurations

EXCEPTIONAL ABILITIES

❖ User can mesh walls at the joints with strut and tie sections to engage supports in the

analysis

❖ User has the option to include or exclude beams as part of the diaphragm design

❖ Grillage spacing can be readily changed by user

❖ Transfer loads to diaphragm are automatically captured

❖ Section sizes are defined and assigned automatically based on grid spacing and floor

thickness

❖ Lateral loads are automatically applied at joints

❖ Lateral loads are distributed based on tributary mass, rather than simplifying to

tributary area

BENEFITS OF AUTO DIAPHRAGM

We have developed a tool to revolutionise strut and tie analysis of diaphragms

We believe that we have developed the best tool currently available for the purpose

The software significantly simplifies the design process but also enables conducting more

accurate and precise Strut and Tie analysis

which

❖ Saves the time of engineers

❖ delivers a more accurate yet more economical design

❖ Which will reduce the overall construction costs

THANK YOU!