Civil Engineering/Shear Wall

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Question
I am having following question relevant to ETABs

1) what is the difference in column and shear wall in reality ..i read that one is area section ant the later is frame ..but i am still not sure that both can take axial loads and moments but are differed from each other ..kindly elaborate

2) while modelling a shear wall in ETABs , e.g at the corner of building the shear wall from perpendicular direction meet there ..is there requirement of providing a column at their junction ..as a did this in order to support beams on that column instead of resting it on shear wall..

3) i am having an irregular building ..if i reduce the percentage difference between the center of mass and center of rigidity up to 12-14 % is it fine or i should further bring them closer to each other ???

4) In designing the Raft of 3o'x60' (under entire area) for the bullring the soil reaction is coming more than allowable bearing pressure , i cant increase the dimensions of the raft anymore..what could be the solution ..the Bearing capacity of site is good ( 1.8 t /ft2)...what could be other solution ??

Answer
Hi Zain,

1. They act in the same way, except that when the column L:W ratio exceeds about 4 to 5, it should be considered a wall (different codes have slightly different rules)

2. You can rest on the corner, but this should be treated as a boundary zone, with extra rebar (min. 1%, with closely spaced links, at 100mm centers). If you model a nominal column (say 200x200) at the corner, the ETABS output will guide you on the %age rebar required at the corner.

3. That should be fine.

4. Either stiffen up the raft, so that the maximum pressure is spread over larger area, or deepen the foundation to get better soil bearing capacity or get benefit from extra capacity due to soil removed. e.g. for every meter removed you will gain an extra 18-20 kN/m2 bearing capacity.

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Arshad Khan

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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.

Experience

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.

Organizations
.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)

Publications
•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

Education/Credentials
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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