LEC 1 Flashcards
(23 cards)
It is a preloading of a structure, before application of service load, so as to improve its performance.
Prestressing
Prestressing in concrete involves application of ___________ loading prior to applying of the anticipated service loads, so that the _______ stresses that otherwise would occur are reduced and eliminated.
compressive, tensile
T/F
Prestressing completel eliminate all tension in concrete
F
The beams can be designed to zero deflection at the specific combination of ___________ and _________ loading.
prestress, external
Where to pre-compress the concrete?
At TENSILE STRESS REGION under working load
Prestressed works due to bond and/or bearing mechanisms to transfer stress to _____________.
concrete
cracks in beams lower the ___________________ of the section, thereby increases deflection.
moment of inertia
cracks tend to develop at ______ stages of loading in flexural members such as beams and slabs.
early
Early attempts of prestressing were not successful because concrete _________ with time.
shrinks
under sustained load, the strain in concrete increases with increase in time, this is known as _________________.
creep strain
The reduction in length due to creep and shrinkage is also applicable to the ________________, resulting in significant loss in the tensile strain.
embedded
obtained a patent for the manufacture of Portland cement
Aspdin, J.
introduced steel wires in concrete to make flower pots, pipes, arches, and slabs.
Monier, J.
Introduced the concept of tightening steel tie rods in artificial stone and concrete arches.
Jackson, P.H.
Manufactured concrete slabs and small beams with embedded tensioned steel
Doehring, C.E.
Recognized losses due to shrinkage and creep, and sugested retightening the rods to recover lost prestress.
Stainer, C.R.
Developed a method of winding and pretensioning high tensile wires around concrete pipes.
Emperger, F.
Developed ‘long line’ pretensioning method.
Hoyer, E.
Developed an anchoring system for post tensioning, using flat wedges.
Magnel, G.
Used high tensile steel wires, with ultimate strength as high as 1725 MPa and yield stress over 1240 MPa. In 1939, he developed CONICAL WEDGES for end anchoraged for post - tensioning and developed double - acting jacks.
Eugene Freyssinet
used high strength unbonded steel rods. The rods were tensioned and anchored after hardening of the concrete.
Drill, R.H.
