Civil Engineering/ETABS


QUESTION: Dear sir

We can model analyse and design using ETABS. In case of column ETABS IT GIVES r/f after design. How that load case (controlling combo) selected by the ETABS.

sometimes it gives very low values for r/f while other load cases require more r/f

ANSWER: Hi Priyantha,

If by r/f you mean rebar (reinforcement steel, then the answer is that ETABS gives the design output based on the concrete stress interaction diagram, so that in some cases high axial load will be governing and in other high moments/low axial force (e.g at top floors) will be governing.

Read the ETABS manuals in the help menu and it has all the details.

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8 story building (without shear wall) was modeled analysed and design using ETABS for BS code. It was found that governing load case ( controlling ),for all columns is (1.4Gk+1.6Qk) (dead load + imposed load). Deflection of the building is ok.

Is there any purpose of introducing shear wall to this building. (ex by introducing shear wall we can reduce column sizes)

Hi Priyantha,

Without knowing the framing dimensions or sizes of members it is difficult to advise but as a general rule an 8-story building must require liftshafts and stairwells, which should be used as part of the structure, and yes it should reduce the sizes/rebar of columns and beams as they will not need to be a full MRF (Moment Resisting Frame)for lateral loading

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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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