THE 10 Zandard 200
SENIONAL SLEVORLA SECONDE ARMABLY OF VAUDE
COMPOUND REINFORCEMENTS
Fig. 33
are
·
and the pipes are compressed by means of end anchorages, Grout is filled into the central hole and establishes solid connection between the wires and the pipes. The end fittings
re. moved after the grout has hardened.
Although the compound reinforce ment is a prestressed unit, the concrete structure in which it is used is, for all intents and purposes, an crdinary re- inforced concrete structure, and the builder is not concerned with any pre- stressing apparatus. This proposal is an attempt to obtain in ordinary con- crete construction the 80-85% saving
in steel which is one of the paramount advantages of prestressed concrete without applying prestresses to the
actual structure.
Stretching devices, For the stretch ing of one or two wires or wire strands, a 3-ton hydraulic jack was used, such as are employed as shock absorbers in Equipment Developed During Expert the undercarriage of heavy aircraft, mental Production
Fig. 36. Diameter of piston 2 in., Gripping devices. By a process of run-out 9 in., hydraulic pressure 1 ton trial and error, a number of mechanical per sq. in. The jack is suspended on grips in form of tapered pins, serrated a steel frame in balanced condition, wedges and split conical wedges with so that it can be easily moved from with central thread were developed one position to another, and the break to the state as shewn previously. In in direction of the wires never II. a similar way, gripping blocks cast ceeds 5 degrees. of rope expping metal, Fig. 34, were developed as means of anchoring whole groups of wires. In the test production of joists and poles, groups of up to 28 wire strands were gripped in such metal blocks. The moulds of the blocks were made of structural steel; they abutted against the cross head which Was moved by the pistons of the by leaulic jacks.
The usual way of fixing wires in the grid plate and cross head was by means of tapered pins with or without grooves, Fig. 35, The pins and bush- ings of the holes must be of specially hard steel, otherwise they wear very quickly. As soon as the hydrau. lic jacks have attained the full speci fied elongation, the whole reaction of the prestressing force is taken over by The experimental stretching bed, four screw jacks, two of which are shown in Fig. 38, is of the deep foun- visible here above the rams. The dation type where the reaction of the hydraulic jacks are used only for the stretching force is transferred from actual stretching process and then the vertical anchorage joists through they are released.
out
Universal cross head and grid plate, Fig. 37. For the production of the early prototypes, cross heads and pat tern plates were made for each unit separately to fit the pattern of the Later we construct- compressor wires, ed a universal cross head and a stan dard grid plate which could be used for the production of practically any unit within the power of the stretch- ing bed. The cross head is a stiff steel frame, completely open over 12"
p
169
x 18" so as not to interfere with the passing of the wires. The grid plate has 13 x 13
tapered holes, positioned at 1 inch e/e each way, in which up to 169 wires or wire strands can be gripped,
heavy foundation blocks
into
the
¡
Fig. 34
Fig. 36
Fig. 35
Fig. 37
50