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Design of Helical stair case
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k.gangadharan
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PostPosted: Fri Nov 27, 2009 6:48 am    Post subject: Design of Helical stair case Reply with quote

Kind Attention of SEFI members

Helical Stair analysis and design

For design of helical stairs (where the plan shape is circular) a method of solution is given in reinforced concrete designer’s hand book by Reynolds & Steedman (10th edition). We have lengthy equations & graphs for computing BM, Shear, Torsion. Normal Thrust etc and it is for helical stair, whose plan shape is circular.

An example of a helical stair (with circular plan shape) is also worked out in Hand Book for Building Design by Dr. Krishnamurthy & Madhumalathi.

We have to design a helical stair whose plan shape is ellipse. The dimensions of which are as follows. The major axis of
Ellipse = 7.8m
Minor axis = 4.8m
Floor height = 4m.

The helical stair has a level mid landing halfway (at centre). It is inside a space of 8.10m x 5.1m and you have columns and beams on all four sites. The helical stair case is inside a framed building (Commercial)  and is continued for 2 floors.

I have seen almost a similar stair case in CBRI administrative building in Roorkee which was designed by famous architect Kanvinde & Roy of Delhi in 1960s. Some guidance is required for design of such a staircase, SEFI members are requested to share their knowledge & put forth suggestions for solutions of this stair design.

A sketch of the stair case is also attached.

Regards

K. Gangadharan
Structural Consultant

Encl: Sketch



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sakumar79
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PostPosted: Fri Nov 27, 2009 7:50 am    Post subject: Reply with quote

Is the staircase supported on the beam along grid B only or is it supported by any other member? Is it possible to shift the staircase closer to grid B to reduce span? You can start by modelling the centerline of the staircase treads and connecting it to form the geometry of the staircase. Each member can be assigned properties based on the width of the staircase and the thickness (start by assumption and then after verification of safety, refine for design). Then, the loads can be applied and the support conditions modelled. After analysis, check shear and torsion in the section and verify if shear stress (including effect of torsion) is within limits and design for the bending moments (including effect of torsion here also).

Arun
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RENJITH C
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PostPosted: Fri Nov 27, 2009 8:48 am    Post subject: Reply with quote

Sir

       If it  difficult  to introduce a column at 2'A.
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k.gangadharan
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PostPosted: Sat Nov 28, 2009 9:52 am    Post subject: Design of Helical stair case Reply with quote

Dear Mr. Arun
 
Thank you for the response. A clear sketch is attached – As you suggested mathematical modelling is a bit difficult. The horizontal co-ordinates can be found out from the geometry of the ellipse. When it becomes a helical stair, the helical vertical ordinates cannot be accurately calculated. It coordinates can be correctly computed, the slab can be properly modelled and analysed with load. Can you please suggest how to model the helical stair, accurately. The stair has connection at the ground slab level at entrance of the ground floor. There is a basement floor below ground floor, for parking. There are no connections on three sides of the stair.  
Regards
K. Gangadharan
Structural Consultant
 
Encl: Sketch (PDF file)

 
On 27/11/2009, sakumar79 <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Is the staircase supported on the beam along grid B only or is it supported by any other member? Is it possible to shift the staircase closer to grid B to reduce span? You can start by modelling the centerline of the staircase treads and connecting it to form the geometry of the staircase. Each member can be assigned properties based on the width of the staircase and the thickness (start by assumption and then after verification of safety, refine for design). Then, the loads can be applied and the support conditions modelled. After analysis, check shear and torsion in the section and verify if shear stress (including effect of torsion) is within limits and design for the bending moments (including effect of torsion here also).

Arun







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PostPosted: Sun Nov 29, 2009 3:03 am    Post subject: Reply with quote

Since you are modelling the center line of the steps, the vertical coordinate becomes the level of the step which can be easily calculated based on the rise.

Arun
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P.V.Ramakumar
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PostPosted: Mon Nov 30, 2009 8:07 am    Post subject: Reply with quote

dear Mr. Gangadhar,
The book Staircases:analysis and design, T.bangash and SMH.bangash is exclusive for staircases covers the helical staircase design.

regards
Ramakumar
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k.gangadharan
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PostPosted: Tue Dec 01, 2009 2:13 pm    Post subject: staircase design by Bangash Reply with quote

dear sir,
Can you  please give the publisher of this book, so that I can purchase the book. Is it available now for purchase.
thanks

regards
K.Gangadharan
Structural consultant
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Dr. N. Subramanian
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PostPosted: Tue Dec 01, 2009 7:07 pm    Post subject: Re: staircase design by Bangash Reply with quote

Hi Sir,

The details of the book are given below. But I am not sure whether it has the details you are looking for.

Staircases: Structural Analysis and Design
by M.Y.H. Bangash and T. Bangash,Taylor & Francis, 1999, 348pp.£114.95
Contents:
# 1. Specifications and basic data on staircases;
# 2. Structural analysis of staircases: classical methods;
# 3. Structural analysis of staircases: modern methods;
# 4. Staircases and their analyses: a comparative study;
# 5. Design analysis and structural detailing;
# Appendix 1: Supporting analyses;
# Appendix 2: Structural details for practising engineers;
# References.

Regards
NS
assekg wrote:
dear sir,
Can you  please give the publisher of this book, so that I can purchase the book. Is it available now for purchase.
thanks

regards
K.Gangadharan
Structural consultant
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thirumalaichettiar
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PostPosted: Wed Dec 02, 2009 1:47 am    Post subject: Reply with quote

the book by Bangash on Staicase is available with Amazon.com and costs $75 and I went through the book once a lonfg time back and still remember that it gives an elobarate methods of staircase design even for eliptical shapes.

I had the copy but in India.

T.Rangarajan.
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sdec.in
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PostPosted: Wed Dec 02, 2009 11:07 am    Post subject: Design of Helical stair case Reply with quote

The price is painfully steep!!
Quote:
----- Original Message -----
From: drnsmani (forum@sefindia.org)
To: general@sefindia.org (general@sefindia.org)
Sent: 02 December, 2009 12:37 AM
Subject: [SEFI] Re: Design of Helical stair case


Hi Sir,

The details of the book are given below. But I am not sure whether it has the details you are looking for.

Staircases: Structural Analysis and Design
by M.Y.H. Bangash and T. Bangash,Taylor & Francis, 1999, 348pp.£114.95
Contents:
# 1. Specifications and basic data on staircases;
# 2. Structural analysis of staircases: classical methods;
# 3. Structural analysis of staircases: modern methods;
# 4. Staircases and their analyses: a comparative study;
# 5. Design analysis and structural detailing;
# Appendix 1: Supporting analyses;
# Appendix 2: Structural details for practising engineers;
# References.

Regards
NS
assekg wrote:  dear sir,
Can you please give the publisher of this book, so that I can purchase the book. Is it available now for purchase.
thanks

regards
K.Gangadharan
Structural consultant






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