CO ee ae. 1), 
t 2 mi 
ON THE ERECTION OF ALEXANDER III. BRIDGE IN PARIS. 475 
| The time necessary to hold a voussoir, to present, and to connect it to 
the next one, and also to secure it with oak wedges, was only about ten 
minutes. The successive operations were really a little longer because it 
was not possible, within ten minutes, to clean the surfaces of the table- 
joint from the coat of paint which kept them from rusting. Nevertheless, 
as every half-arch consisted only of sixteen voussoirs, two sets of six 
workmen with good foremen easily connected up two arches within two 
days. 
UDeitig the work of connection the foreman noted with a gauge that 
the arches were at the proper distance, so that when it was completed the 
direction of each half-arch was almost correct. But as it was indispensable 
on account of the necessity both of assuring a good transmission of the 
enormous thrust and of mounting the flooring, which was manufactured 
in shops at a great distance from the steel foundries, to get a very high 
degree of exactness in the setting of the arches, the chief erector accu- 
rately provided for it. When by small removals, obtained by means 
of crowbars and wedges, he judged the arches to have been brought in 
their proper places, when the inspectors had stated that the spring- 
ing articulations were at the proper level, that the two parts of 
each arch were exactly in the prolongation of each other, and that the 
sockets were satisfactorily in connection with the pins, then the thrust 
sockets were sealed in the thrust-stones with liquid cement forced into 
the joint. 
Four days after they were filled, the cement joints were fast enough 
to support the thrust of the arches, so that it was possible to take away 
the centreings. 
In spite of the precautions taken at the steel works, the engineers did 
not rely on the measurements made at a distance for the regulation of the 
arches ; they had purposely arranged the length of the voussoirs to be in 
the total three centimetres (one inch) shorter than the arches, the difference 
being filled in by sheets of rolled steel placed at the joints of each of the 
two central socket voussoirs. A sufficient number of rolled steel sheets of 
various thicknesses having been cut beforehand, drilled and prepared, it 
was possible to fit at once, by a proper combination of them, joints of any 
required thickness. 
The last operation to be described is the method of removing the 
centreings from the arches. 
The processes commonly used for such operations did not seem satis- 
factory because the stresses developed in the supports as well as in the 
arches could not be well known, and it was equally inconvenient, even 
dangerous, both to develop extension stresses in the arches—for which 
the joints were not made—and to bring the loads in the central part of 
the rolling bridge to an excessive amount. Moreover, it was indispensable 
to secure the possibility of putting the arches again in connection with the 
centreings, in order to change, if necessary, the size of a regulating joint. 
It was decided on these accounts that the operation should be completed 
by means of screw cranes, and that the screw cranes should be dynamo- 
metric. The screws were fitted with Belleville washer springs constructed 
by Schneider & Co. 
The time required for the successive operations should have been 
160 days ; it was really six months and a half, from the end of November 
to June 9. The increase in the time was only due to the delay in deliver- 
ing metal for the upper part of the bridge, on account of which the 
