Book Weights

8/11/2019 Book Weights

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Geoff's Woodwork

for Students of Woodwork

Using timber structurally

calculating strength properties

modulus of elasticity

useful facts and data

weights for common books

Using timber structurally

The table below gives the approximate weight of various sized books per 500 mm run. It does not give thematerial or thickness, etc. of the required board. For this, you should calculate using the materials MoE

(modulus of elasticity) and the various bending formulas. You may obtain these and a good working

explanation from Bruce Hoadleys book "Understanding Wood". Another excellent book about shelf loads

and other formula is the "Woodworkers Essential" by Ken Horner. I have included some formula and

calculations collected from various sources over my teaching and learning career. I must confess that I am

not entirely happy using raw data or formula without carrying out a practical test of the likely loads on a

mock up using the proposed material and spans. The formulas do not include a margin for safety and I

would reduce the predicted spans to give a degree of tolerance especially those calculated with fixed ends. A

batten added to the front and the rear of the shelf will provide a greater load potential.

To get an idea of the safe loading you could always preload your shelf with an approximate weight that you

intend to load. Even if it is only the proposed board set out between a couple of supports. Weigh a singlebrick (or similar common unit) and then load the board with them until the board starts to dip. If you

multiply the single units weight by the total number of units that it safely took (with a safety allowance) you

will have an idea what weight the given board (material, span, thickness and depth) will take. You may then

modify the span, thickness, etc. accordingly before committing yourself. In my calculations I use a deflection

of an eighth of an inch (about 2.54 mm). This is a tolerable deflection but the amount should be changed to

that required for the job. When designing shelves for bookcases and similar loading start at a finished

thickness of one inch (25mm) anything less calls for quite short spans.

It is surprising how heavy books and other ornaments are. You should err on shorter shelving rather than the

longer variety unless you are confident that the thickness of your chosen board can take it. I note that many

designers and writers are loathe to quote loading tables nowadays. Failure could be expensive. Remember,

if you make someone a piece of furniture and it fails and someone gets injured it is you the designer who isresponsible. As the manufacturer you are responsible for any production errors and failures. Try to obtain

the customers written plans and specifications but use your good judgment before production and if you are

not sure, check.

Please be careful when making bookcases and shelving or anything that may take a lot of weight. If in doubt

ask an expert. Although in my opinion, it is difficult to get one to commit themselves. Remember, make

practical tests before you use such tables and formulaes. They are a good starting guide but not final proof!

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Calculating Strength properties of timber

These formulas do not include a safe operating margin. Users should satisfy themselves that the formula is

correct for their application and carry out physical checks to confirm safety.

Sayfa 1 / 5weight of books

29.07.2013http://www.geoffswoodwork.co.uk/book%20weights.htm


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1. Uniformly distributed load, with supported ends such as adjustable shelving, etc

s = (5 x F x L ) (384 x E x I)

L = v ((384 x s x E x I) (5 x F))

I = b x h 12

Where:

s = deflection

F = Force in Newtons

L = Span

E = Modulus of Elasticity in N/mm

I = Moment of inertia

b = breadth (depth) in mm

h = height (thickness) in mm

2. Uniformly distributed load, with fixed ends i.e. secured in housings or dado:

s = (F x L ) (384 x E x I)

L = v ((384 x s x E x I) F)

I = (b x h) 12

Note when the ends are securely fixed such as in a glued housings or dado the increase in load capacity. To

obtain the advantage of these spans the ends must be held extremely stiff because any movement will reduce

the load potential. I doubt if the full advantage would be obtained using standard timber shelving and

normal jointing methods. However it is included for comparison purposes and to demonstrate the obvious

advantage of fixing the ends securely as possible.

Summary of methods toincrease load capacity:

a. Ends firmly fixed into supports.

b. Wider the board - the amount of load may increase by twice the load by increasing twice the width.

c. Thicker the board - the amount of sag in the board may decreased by a factor of eight by doubling

the thickness.

d. Shorter the span - on the other hand by doubling the supported span the amount of sag increases

by a factor of 8.

By scrutiny of the E values below you will see the stronger timbers to use and the obvious weakness of

using man-made boards such as plywood and MDF despite its wide use in the shelving business.

If a certain span is required that would otherwise would sag due to its thickness the remedy is to providedividers to decrease the span or increase the load capability by using a wider board.

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Modulus of Elasticity. E value

Users should obtain their specific data from the manufactures or suppliers specification sheets.

The data supplied below is some that the author has collected from various sources and is quoted only below

to show the range available. No apologies are made for the wide values shown against some timbers. This

information is collated from sources such as technical publications, data sheets from TRADA, and BRE.(see

for web sites) The wider variations are generally for differing characteristics between similar species, theircountry of origin and always, the local conditions that the tree grew in. You should obtain E values from

your supplier and when using the boards in a critical situation take physical checks to ensure the material is

up to the stability for the use you are putting it. There are further factors that affect the strength of timber

such as the temperature, the amount of moisture, the grain direction and slope, the physical defects such as

knots, shakes, splits, mature or juvenile wood, etc. All this leads to the absolute need to provide practical

tests before using boards to carry weight.

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Material Densi ty = Kg/m E in N/mm2Ash European 689 11,900

Balsa 176 3200Birch European 670 13300

Beech European 673 12600Cedar UK 417 5400

Cherry USA 580 10,200

Chestnut sweet 560 8,200

Douglas Fir Canada 545 12700

Hemlock Canada 465 10400Iroko 655 9,400

Larch European 545 9900

Keruing/Luan spp. 641-849 13,700 - 17600

Mahogany var. spp 495-850 7,800 10,600Meranti/ 481 10500

Oak European 689 10,100Parano Pine 529 10400

Spruce sitka Canada 384 8100Sapele 673 11,700

Scots Pine 513 10000Sycamore European 561 9400

Teak 641 10000Utile 660 10800

Walnut African 545 9,200Western Red Cedar 368 7000

Whitewood European 417 10200MDF HD 17-19 mm 3,450 5,000

MDF Std 18 19 mm 3,000

Chipboard 12 19 mm 1,600 3,400

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Useful facts and data

When gathering data for your calculations you will find the tables will reveal the material you are

looking for but often in the wrong unit. The table below gives some conversion factors that might

be useful to convert the information to the correct format.

Stress (s) s = load/area (MN/m or lb/inch or psi)

Strain (e) e = amount of stretch/original length (nounits)

Youngs modulus (E) E = stress/strain = s/e (N/mn)




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Weight of

books

The average weight of standard books per 500 mm run:

Small paperback 8 X 5 inches 10.29 Kg

Small modern compact paper backs 8 X 6 inches 15.7 Kg

Small hardback older book 9 X 6 inches 11.84 Kg

Medium hardback book 10 X 7 inches 17.4 Kg

Large hardback book 12 X 9 inches 37.2 Kg

I have been asked a number of times the source of the book weights.The weights are purely average based on Practical Observations.I took say 4 or 5 books each of the same sizes, weighed them and measured the total thickness of the bundle in mm.The weight was divided by the total thickness and multiplied by 500.Therefore the 'weight per 500mm run' is purely as a guide to how heavy books of given sizes represent a shelfof span 500 mm loaded with books to fill the shelf.I did this to each size range of book. Now you may well have a heavier paper and book boards so CHECK!

I recommend that you carry out and check the exercise yourself if you are going to do design work.

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text and grafics Geoff Malthouse

home foundation basics resources safety

key skills trade needs technology photos links

density = Wt Kg / vol cm

mass = volume x density

specific gravity (sg) = Kg/m

1 psi = 0.00685 MN/m

= 0.07 Kg/cm

1 kg/cm = 0.098 MN/m

= 14.2 psi

1 MN/m = 10.2 Kg/cm = 146 psi

KN/mm = 1000N/mm

N/mm = 1MPa

= 1 N/m x 10^6

KN/mm = 1GPa

= 1 N/m x 10^9

1 Pascal = 1 N/m

1Kg force = 9.8N

1 m = 1000000 cm

= 1000000000 mm

1 cc ( mass of 1 gram) = 1 millilitres or 1ml= 0.001 Litres

= 0.000001 m

1 Litre = volume of 1 Kg of pure water @ 40C

= 1000 cc = 100 cl

= 1000 ml

= 1000 cm

1 m = 1000 Litres

1 grain = 1/7000 lb

1 Lb/foot = 4.88 Kg/m

1 lb/Cu.Ft = 16.0185 Kg/m

1 Lb/Cu.Inch = 27679.90 Kg/m




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revised and uploaded 3rd March 2010


29 07 2013h // ff d k k/b k%20 i h h

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