Civil Engineering/SAP modelling


Hello sir!
I have modeled a 8 storey RCC building with basement walls and shear(in lift)walls.
However i am not sure of the support condition in basement walls. Since the drift pattern below and above the ground differs(the soil would not allow the basement wall to drift freely as the upper floors do in case of earthquake loads), do I need to idealize any supporting conditions around the basement wall(like spring or something)
Also i have an open well stair case with a lift in the well. Since I have not modeled the staircase i.e. I have not put any slab in place of stairs and applied the loads manually to the beams. The lift wall has only connection at top and bottom(and not at every floor level)
How can i rectify these two problems?

Hi Rohit,

1. For the basements, it is good enough to model the walls and slabs and just place supports at the base (bottom). The much stiffer basement will not drift much from lateral loading, so you do not need to model any other lateral supports for most normal cases.

2. The way you have modelled the stair well is correct as the diaphragm is punctured/interupped at these locations. Just ensure that you assign the correct DL and LL to the stairs landing beams from the stairs flights. Any mid-height landing reactions can be applied to the main floor level too.

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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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