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Civil Engineering/Beam spans with different sections


QUESTION: hello e. Arshad Khan
please , I want to know , when we have a beam with 2 spans , from the next cases , what cases in which we consider this beam discontinuous ?  
1 - the width of the section differs through the two spans
2 - the depth of the section differs through the two spans
3- the reinforcement  differs through the two spans
4- cases 1&2 together
5- cases 1&3 together
6- cases 2&3 together
7- cases 1&2&3 together
I ask this question to know when I release the ends of beam in etabs .
thanks very much

ANSWER: Hi Ehassan,

I presume that there will be a supporting column where the beam section changes. So:

1. and 2 basically affect the section property, so model them as per actual sizes (apply stiffness modifiers to applicable code).

3. Makes little difference for the analysis, so ignore. But take care when detailing after design.

4. As per my answer 1 above

5. Ditto

6. Ditto

7. Ditto

Basically you have to decide whether the wider beam can have effective continuity into the supporting column- if the answer is yes, then you do not need to assign any releases.

---------- FOLLOW-UP ----------

QUESTION: thank you very much for your quick answer
I understood most your answers but I didn't understand what i have to do for the cases 1 & 2 , release or no .
for that I attach image to explain my question clearly
please tell me which choice I select a or b for cases 1 and 2 , then consider this image as basic for my other cases and tell my if any of your answers changed
thank you

Hi Ehassan,

From what I can see, both beams are hidden beams which means that they are within a 300mm deep slab? If so, just do as I suggested earlier and then anchor the rebar of the wider bit of the beam through the column and into the slab. The column seems a bit narrow to be easily buildable, though.

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Arshad Khan


I can answer any questions to do with civil and structural engineering consultancy and construction industry in East Africa and the Middle East, and specifically with the analysis and design of reinforced concrete structures. My particular expertise is in the aseismic design and optimisation of tall buildings.


Employment history: 40 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Zambia, Austria, Bahrain, Kuwait, Doha and the U.A.E.

.Fellow of Institution of Structural Engineers (UK) .Fellow of Institution of Civil Engineers(UK) .Member of the Institution of Engineers, Kenya .Registered Engineer, ERB, Kenya .Member of the Architectural Association of Kenya (Engineers Chapter) .Chartered Engineer (UK)

•1984: International Conference on the Art and Practice of Structural Design, London •1994: 3rd Int. Kerensky Conference in Structural Engineering, Singapore •2008: International Conference on High-Rise Towers, Abu Dhabi •2013: IEK International Conference, Kisumu, Kenya

BSc, 1st Class Hons, in Building Engineering, University of Bath, UK MSc in Concrete Structures and Technology, University of London. Diploma of Imperial College, UK.

Awards and Honors
•Science Congress Special Award (for 2-seater Hovercraft - 1968) •Institution of Civil Engineers Award for outstanding performance at Bath University (1975) •Concrete Society Postgraduate study Bursary Award (1976) •Consular Representative for British High Commission, Nairobi. (1995 to 1998) •Examiner for Institution of Civil Engineers Professional Interviews, Nairobi. (1997 to 1998) •Branch Representative in Vienna for PI assessment for Inst. of Struct. Engrs. (1999 to 2010)

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