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Civil Engineering/the effect of cantilever in dynamic analyzing

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Expert: - 7/18/2009


Question
QUESTION: hi sir
in my project there is along cantilever so when i analyzed the model usin dynamic anlyzing i noticed that the value of
fundamental period time exceed 3000 sec and modal participation  is zero for all modes
could i remove the cantilever and put its load on abeam to solve this problem and whats your advise to me


ANSWER: Hi Maher,

Yes, if the cantilever is just a very small part of the whole structure, you can remove it and just apply equivalent vertical and torsional moment to the supporting beam.

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

typical slab
typical slab  
QUESTION: hi sir,thank you for your answer
but could you please tell me, what is the reason of the problem which occur if you model the cantilever in dynamic analyzing ,where all the result come in wrong
note(the length of the cantilever is 4m )
please check the enclosed drawing


Answer
Hi Maher,

It seems that your cantilever is actually a slab varying in span. If the maximum span is 4m and the depth of the slab is at least 450mm, then you should not get such a long time period. I suggest you re-check your model and also the units.

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Arshad Khan

Expertise

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: 36 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

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 date)

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