Improvements in the Construction of Joists, Girders and the like of Cement Strengthened with Iron or the like.
Year: 1897

page_text: Date of Application, 20th Dec., 1897-Accepted, 12th Feb., 1898
Improvements in the Construction of Joists, Girders and the like of
Cement Strengthened with Iron or the like.
I, FRANÇOIS HENNEBIQUE, of 54, Boulevard Saint Michel, Paris, in the Republic
of France, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement:—
The use of strengthened beton in buildings has within recent years greatly
developed. It has been thought possible by mixing beton and iron or steel to
replace the purely metallic elements of building construction by parts equally
incombustible but lighter and more simply and rapidly made. In any case the
mixture of cement or hydraulic lime which resists perfectly compression, with
iron or steel which more particularly resists tension and flexion, has not hitherto
been capable of being carried out in a judicious and rational manner.
By arranging at useful points in a mass of beton of suitable form, longitudinal
bars of iron of a given shape in order to constitute the tension chord, by dis-
tributing them in the mass in a judicious manner in order that the whole mass of
iron and beton may have at every point of the piece formed the desired resistance
to flexion and breaking strain, and by further connecting the longitudinal bars
by brace pieces or stirrups of suitable form, I have succeeded in producing the
practical joists, girders and the like which form the object of my present invention.
I have shown diagrammatically in Figure 1 of the accompanying drawings a
practical continuous joist or girder of beton strengthened with iron arranged
according to these principles.
This joist encased or built in at one of its ends A is placed on a series of inter-
mediate supports C.
The characteristic of the metallic core or strengthening is the addition to
longitudinal bars 1 arranged parallel to the lower side of the joist, of inwardly
bent bars 2 21 211 2111 arranged in the same vertical plane. These bars are parallel
to the bars 1 in the mean central part of the joist that is to say in the part where
the effects of the breaking strain are almost nil. They are placed parallel to the
bars 1 and in their vicinity they double the resistance of the latter to tension.
They are carried by the same supports or stirrups 3, and these latter thus connect
the chord of tension formed by the bars with the chord of compression formed by
the beton.
One of these stirrup pieces is shown in perspective in Figure 2. It is formed of
a band of sheet iron of U shape having straight arms terminated by a little hook
which facilitates their fixing in the beton. These straight stirrup pieces play, in
the joist of strengthened beton, the part which the suspension rods play in the
trussing of metallic girders.
As in the extreme parts of the girder the breaking strain increases in proportion
as the wall A and the support C is approached, I raise the bar. The inclined arms 21
of this bar are connected with the horizontal bar 1 by stirrup pieces 3 approached
more and more closely together. I thus form a triangle of resistance, the apex
of which is at the point of divergence of the bars at 21.
This triangle in consequence of the stirrup pieces 3 being progressively placed

page_text: nearer one another, and of the growing mass of beton which it encloses between
the bars 1 and 21, offers a proportionate increasing resistance to the breaking strain.
The bar 2 after having been raised at 2¹ runs horizontally at 2" and then again
descends in order to be secured in the wall A.
Figure 3 shows a transverse vertical section on the line st of Figure 1 of the
girder in the neighbourhood of the walling A.
Figure 4 is a view in sectional perspective on the line -y of Figure 3, the
longitudinal half of the girder being supposed to be removed.
At the point where the continuous girder passes on to an intermediate support C,
I prolong the bar 21 to 21 in the adjoining compartment or bay, which is thereby
strengthened and in order to ensure that the reaction of the beton on this prolonga-
tion shall not raise the latter I crown it with reversed stirrups a which maintain
the bar perfectly firmly.
Figure 5 shows in detail the passing over an intermediate support C. The
crossing of the arms 2111 consolidates the girder in a practical manner on the
support C where the bending strain is greatest.
It will be seen therefore that owing to the addition of a single bar 2 the arms 21
21 21 of which are suitably inclined connected and arranged in the beton and
further owing to the rational distribution of the straight stirrups 3 it is possible
to construct girders resistant in all their parts in a perfect manner to the effects of
tension, the effects of compression, the breaking effects and the bending effects,
whilst reducing to a minimum the quantity of iron employed, and suppressing or
dispensing with iron in the part under compression, thereby avoiding between the
irons 1 and 2 any cross fastening by inclined stirrups or by wire lattice work.
It is needless to state that the principles hereinbefore described may be applied to
the manufacture of any suitable girders or joists for ceilings or floors and in fact
to any constructions formed of beton strengthened with metal which as regards
the strains which they will support may be likened to girders placed on supports
or encased in masonry.
It is also understood that according to the dimensions of the girder the trans-
verse section of which is not necessarily rectangular the number of bars 1 and 2
placed in the same vertical plane may vary.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. In the construction of joists girders and the 'like of cement strengthened
with iron or the like, the use of inwardly bent bars 2 21 211 2111 of which the central
branch 2 is horizontal and arranged in the plane of the bar 1 which forms. the
chord of tension of the girder and of which the arms 21 are always raised in the
same vertical plane and in the direction of the point where they are fitted into
the wall A or on the supports C, in order to obtain a better resistance to the increas-
ing breaking strain, whilst the branch 21 is bent down in order to be fitted securely
in the masonry or prolonged at 2111 into the next compartnient or span, substantially
as hereinbefore described.
2. In the construction of joists, girders, or the like of the kind described, the use
of straight stirrup pieces 3 of hoop iron in a U form for connecting the bars 1
and the inwardly bent bars 2 21 21 2111, the said stirrup pieces being judiciously
distributed in the girder, substantially as herein before described.
Dated to
1
C
ד
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.