Long Term Deflection Analysis using SAFE Program | | The Structural World

Long Term Deflection Analysis using SAFE Program

 

 

Long Term-Deflection in slabs/beams is the deflection or the deformation that occurs over time due to shrinkage and temperature. It is also influenced by the condition of the cracking before loading, then creeping, which depends on the time passed to the time of the first loading, the environment, and other factors.

In this article, we will focus on the analysis of long-term deflections on slabs.

Analysis of Long-term deflection of the slab using  SAFE program is often confusing especially for those newbies in structural design, but that’s already a few steps away of knowing. This article will guide you with easy to understand step by step on doing slab’s long-term deflection analysis using the SAFE program. Before we proceed further, let us define the following parameters used. As we commonly encountered in the design, DL stands for dead loads, LL designates the live loads and SDL denotes superimposed dead loads.

In SAFE, the following principle may apply on the modeling; LONG TERM DEFLECTION– is the sum of immediate deflection for 75% Live load, (DL+SDL+LL) – (DL+SDL+0.25LL) and Long-Term Deflection for DL+SDL+25% Sustained Live Load. Which means:

Long-term Deflection = 75%LL (immediate effect) + 25% LL+DL+SDL (long-term effect).

But, how to apply these principles to the SAFE program? Supposed that we had already a SAFE model of the slab that we are going to analyze and ready to run. The next procedure is listed as follows:

Below are the procedures for applying the above principles of Long Term Deflection Analysis:

1. Defining a Load Pattern: 

  • Go to Define>Load Patterns
READ ALSO:   Design Strips in CSI SAFE

2. Define a Load Case for Immediate All Loads

  • Go to Define>Load Cases>Add New Case > tick nonlinear (cracked) for the analysis type

3. Define a Load Case for Long-Term- Sustained

  • Go to Define>Load Cases>Add New Case > tick nonlinear (long-term cracked) for the analysis type 

4. Define a Load Case for Immediate-Sustained

  • Go to Define>Load Cases>Add New Case > tick nonlinear (cracked) for the analysis type 

5. Define Load Combination:

“Elastic”-to display elastic deflection for service loads.

  • Go to Define>Load Combinations>Add new combinations

6. Define Load Combination:

“Long Term” – this is to combined 3 load cases for long-term analysis principle.

  • Go to Define>Load Combinations>Add new combinations

7. Run Analysis.

  • Go to Run>Run Analysis & Design

Be sure to check the design preferences and edit the design parameters accordingly.

As well as the Cracking Analysis Options.


What are your thoughts on the procedure discussed above? We’d love to hear from you. Leave your message in the comment section below. Feel free to share this article, subscribe to our newsletter and follow us on our social media pages.

Visit Us On FacebookVisit Us On TwitterVisit Us On PinterestVisit Us On Google PlusVisit Us On Youtube

2,716 total views, 17 views today

Digiprove sealCopyright secured by Digiprove © 2018 The Structural World

5 Comments

  1. velimir kazic

    I have some remarks on the article, and I think they are important to younger engineers.
    Right at the beginning, a sentence was written that was wrong
    Cite ” Long Term-Deflection in slabs/beams is the deflection that occurs over time due to shrinkage and temperature”
    Long-lasting deformation also depends on the condition of the cracking before loading, then cracking, which depends on the time passed to the time of the first load, the effect on the environment and on a whole range of factors. All I’m saying is to avoid confusion for the novices.

    Reply
  2. thestructuralworld (Post author)

    Thanks, Mr. Velimir for pointing out, we incorporated your remarks on the article.

    Reply
  3. Mohit D

    what is the role of soil subgrade reaction in these calculation ?

    Reply
  4. thestructuralworld (Post author)

    No subgrade reactions to consider in the Long Term Deflection analysis. Subgrade reactions are usually considered in raft/mat foundations design.

    Reply
  5. Sherif Mohamed Moselhi

    Dear Sir
    I’d like to know when we can consider the slab and a restrained or un-restrained slab.
    in Other words the tension stress of concrete to be 0.33 or 0.62 root square Fc’

    Reply

Leave a Comment

Your email address will not be published. Required fields are marked *

All original content on these pages is fingerprinted and certified by Digiprove