Civil Engineering/Force on a hinge

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Expert: - 9/30/2011


Question
Hello,

I'm sorry if this question is not appropriate for your expertise, but I'm not sure who else to try, so I'm trying you.  I'm building a fence with a gate and I'm trying to figure out how strong a hinge I need.  The gate weighs 60 lbs and it is 12 feet long made up of two 6 foot panels with a hinge strap between them.  At this point, I think, the hinge strap is sufficiently strong, so I just want to calculate the force on the hinges that will attach to the post.  I'm guessing on the weight of the gate, so if you could include formulas you use, so I can adjust if necessary, I would appreciate it.  Thanks for your help.

Matt

Answer
Hi Matt,

You have not indicated the height of the gate, or more importantly the vertical distance between the, I presume, two number hinges. Let's say that distance is z ft.

So, the 2 hinges will be subjected to vertical shear (assume both will be subjected to 30 lbs each) and horizontal forces as a couple to resist the bending moment due to the cantilevering gate. The top hinge will have a horizontal force towards the far end of the gate, and the bottom hinge will have a force in th opposite direction.

The overall moment at the position of the gate post will be 60 x 12/2 = 360 lbs ft.

So, the horizontal forces on the hinges will be 360/z ibs. Remember that the orientation of this horizontal force will move as you open the gate- it will always be along the plane of the gate.

If you provide 3 number hinges, then the one in the middle will have no horizontal force, but will share the vertical shear force, so that each will carry around 20 lbs.

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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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