04-09-2012, 05:02 PM
DESIGN OF LIQUID MANURE TANK ROOF SLABS
1DESIGN OF LIQUID.pdf (Size: 3.33 MB / Downloads: 123)
ABSTRACT
In many cases, it is desirable to coverliquidmanuretanks. The roof slabwill often be subjected to trafficloadsfrom tractors,
wagons and other farm implements. When substantial wheel loads areto bedesigned for,a poured concrete flat slabvery often
provides an economical solution. This paper deals withthe effectof concentrated loads on rectangular flat slab panels. It also
deals withtheanalysis anddesign ofaroofslab forcircular tanksthatare too large forasingle central columnsupport. Theresults
of the various analyses havebeen used to provide design recommendations that can be used directly by the designer if used in
conjunction with the Canadian Farm Building Code and concrete design code, CSA A23.3.
INTRODUCTION
An increasing number of liquid manure
tanks are being covered to satisfy
environmental considerations. If the roof of
a liquid manure tank is at ground level,
traffic loads should be allowed for in the
design of such a roof. The Canadian Farm
Building Code (1977) requires a minimum
design uniform live load of 150 psf (7.18
kN/m2) for farm machinery traffic areas. If
it is anticipated that the area will be occupied
by loaded farm trucks or large tractors,
larger design live loads have to be used.
General traffic areas also have to be
investigated for a concentrated load of 5,000
lb (240 kN).
Liquid manure tanks may be rectangular
or circular. The design of roof slabs for
rectangular tanks is adequately covered in
Section 11 of CSA A23.3-1973 where it
concerns uniformly distributed loads.
Design information for small circular tank
roofs without columns and with a single
central column is contained in a Portland
Cement Association publication on circular
concrete tanks without prestressing.
CIRCULAR TANK FLAT PLATE ROOF
SLAB
Flat slab roof slabs of circular tanks of
50-80-ft (15.2 - 24.4-m) diam subjected to
loads typical for the cover of a liquid manure
tank require interior column supports. The
optimum arrangement of columns allows an
arrangement of slab reinforcement in a
radial and circumferential pattern so that a
large number of bars are of equal length.
The chosen layout of columns results in
maximum positive and average negative
moments that are approximately equal. The
layout provides for six columns placed
equidistant on a circle with a radius one-half
of the radius of the tank (see Fig. 5). The
columns were modelled as point supports
with linear rotational springs in both
bending directions to provide for the
bending stiffness of the columns.
SUMMARY
The results of a number of finite element
bending analyses of manure tank roof slabs
have been used to provide design
recommendations for concentrated loads on
rectangular flat slab panels. Also, a
particular circular roof slab configuration
suitable for tanks in the 50 - 80-ft (15.2- 24.4-
m) diam range have been analyzed for
uniformly distributed live and dead loads
and for concentrated loads. Design
moments are provided. The recommended
values for the circumferential positive
moments are based on a live to dead load
ratio of one and one-half.