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Civil Engineering/how to analyze the structure


QUESTION: A two storey building,say 12m by 15 m, already exists; and it is to be proposed that an extension  of a like similar structure(also a two storey) be attached by connecting the integral parts(so that it looks unified).  How do i analyze the said extension? Do i analyze it as an independent structure, also 15m by 12m,because the previous sructure already existed long its lifespan? Or do i consider when designing the new extension the previous structure since it might "react" and be a loading to the new structure. please clarify this for me. In that case the dimensions might be bigger in the new structure(although their floor plan is the same), correct?

Also,what is the unit wt. of reinforced concrete?

How do i usually determine the magnitude of seismic loading? many tnx

ANSWER: Hi Nordz,

This depends on the foundation material- if it is not rock (or hard material), then there should be a settlement joint between the two halves and you should analyse the new separately. If they are to be joined together, you can model both together.

Weight of reinforced concrete is around 24 kN/m3

Seismic loading is determined in accordance with local zoning and codes and can vary between 5% and 20% of weight of the building depending on zone and type/size of structure.

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

QUESTION: tnks for your answer..But what basically a settlement joint. That's the problem do i model both together? I know how to analyze frames and design beams, but i still know a little on how to model..tnx agen

Hi Nordz,

What a settlement joint means that you have a separation of say 20-25mm between the two structures, filled with compressible material and a sealant at the surfaces. Then you can model and analyse the new structure by itself, as it will have its own foundations.

If you decide not to have a separation joint then model both structures together, in which case the new structure will impose additional forces into the old one.

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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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