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Technical Note (National Research Council of Canada. Division of Building Research), 1966-12-01
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Design Live Loads for Libraries
Amos, D. B.
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DIVISION OF BUILDING RESEARCH
'f
E
C
1HI N ][ CAlL
NOTlE
477
PREPARED BY D. Bruce Amos CHECKED BY W. R. S. APPROVED BY N. B. H.
DATE Decomber 1ｾＶＶ
PREPARED FOR Inquiry and record purposes
SUBJECT DESIGN LIVE LOADS FOR LIBRARIES
This investigation was prompted by an inql1iry from a consulting engineering firm to the Building Structur es Section. In their design of a new law library this firm encounter ed
the figur e of 150 psf given in the National Building Code (NBC) (l)
and questioned the validity of a single value for different conditions of librar y loading.
Books ar e heavy and when they ar e stacked in a library the resulting live loads are the heaviest encountered in office occupancies. There ar e many differ ent kinds of libraries, however, so it seemed desirable to study actual loads and to cOmpare them with the NBC figure of 150 psf.
Some libraries were visited to determine the range
of values for the several controlling factors and the combinations of factors that were likely to result in a maximum load.
Libraries visited wer e:
Department of Agriculture Library - Neatby Building NRC Library - Sussex Drive
- 2
MEASUREMENTS
Samples of books of all types were measur.ed and weighed, and the physical arrangement of books and stacks was investigated. In an attempt to simplify the calculation of loads, several factors wer e combined, using two differ ent methods.
(a) lIEnd Ar ea" Method - The depth of books in a shelf can vary greatly, but a library must be designed for books that fill the shelf. Ther efor e, a maximum depth was assumed and the weight of the books on one stack on a library floor was a function of the total end ar ea of the books and the weight of the stack itself. The unit load acting on the floor was then governed by the stack width and the fraction of floor area cover ed by stacks, in addition to the weight of stacks and books.
Figure 1 shows the weight of books in a unit end ar ea for differ ent book depths and differ ent types of paper. Assuming a maximum book depth of approximately 9 in., the resulting book weights are 50 psf of end area for heavy, glossy paper, and 40 psf for ordinary paper. The total end area of a
lineal foot of stack is the total book height multiplied by the number of rows (or the net book height). For the usual
two-sided shelf, the total weight of books on one side must be doubled. The weight of a stack is small compared with the weight of books which it is supporting, but stack weight can be
approximately allowed for by including the shelf thickness with the maximum book height.
The floor ar ea upon which the weight of a lineal foot of books is acting is the width of a double stack in sq ft, but only a fraction of the floor area is covered by stacks, the remainder being aisles and open areas. Thus, the load
acting over the whole floor is that load directly under the stack, multiplied by the fraction of floor area covered by stacks.
If W
=
b=
w=
f=
thenweight of books per sq ft of end ar ea (psf) net book height (ft)
double stack width (ft)
fraction of floor area covered
live load
=
2WbfAs a result of observations made in the libraries visited and based on recent published material(2), it can be reliably
concluded that a book height of 7. 0 ft and a stack width of 2. 0 ft
represent maximum and minimum conditions, respectively, and that the fraction of floor area covered seldom exceeds 0.45. These figures can thus be expected to produce the greatest load that needs to be considered. Higher stacks and narrower aisles would make access impractical.
Figure 2 is a plot of loads resulting from different densities of stacks for various types of books as a function of f. It was drawn using Eq. (1) and the following assumptions:
7.0 ft
= 2. 0 ft.
net book height =
shelf width
This figure would appear to indicate that the live load for maximum loading conditions (f
=
O. 45) would seldom exceed the National Building Code figur e of 150 psf. It has been assumed for this graph that all books are fairly deep (>9 in.) and the shelves are completely filled with books. The maximum loads then ar e between 100 psf and 150 psf, depending on the type of paper.(b) "Stack Density" Method - Using the weight and size measurements of the sampled books, the density of books was determined. The density of the entir e stack with books was then approximated by assuming the volume enclosed by a stack to be 35 per cent air. The heaviest books (those printed on 3 glossy paper) had a density slightly greater than water (,... 65 lb/ft ), while paperback editions were as light as 30 lb/ft 3 •
For one lineal foot of stack, the total weight on the floor is the density of the stack multiplied by the volume of the stack. Again the floor ar ea is the width of a double shelf, in sq ft, and the fraction of floor area covered is a reducing factor.
If p
=
h'=
w=
f=
t=
stack density in pef (i. e. book density x O. 65) stack height in ft
stack width in ft
fr action of floor ar ea cover ed stack length
- 4
-then
live load
=
e...h'
w tw
1-= PhI f
f
(psf) • .. (2)
From the observations mentioned earlier the following values for book densities and stack densities were obtained.
Paper type light medium heavy Book Density (lb/ft3) 35 50 70 Stack Density (lb/ft3} 25 35 45
The live loads calculated with the "stack density" method are also indicated in Figure 2 and are plotted as the dashed lines. The results are similar to those obtained using the fiend area" method.
CONCLUSIONS
1. Density of books varies considerably.
2. Maximum stack width and floor ar ea coverage found in libraries appear to be fairly constant. 3. If one assumes that any area of a library could be
used for the storage of deep and heavy (glossy) books, as one should, the present NBC value of 150 psf seems to be a reasonable and a safe load.
4. In the design of structural members for a library building, it appears reasonable to assume that as the tributary floor area becomes greater, the chance of complete stacking, with the heaviest books and ther efor e of maximum loads, is decr eased. This is taken into account in the National Building Code by the reduction of load with increasing tributary floor area (see Article 4.1. 3.1(3».
REFERENCES
1. National Building Code of Canada 1965. Part 4, Section 4. 1.
2. Metcalf, K. D. buildings.
Planning academic and research library McGraw -Hill, New York, 1965, 431 p.
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