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Psc irc 112-2012 PSC Composite-General section type can now be designed as per IRC 112-2012 as well as composite typical section types. This new feature will be useful for the design of composite sections with irregular section shape. Prestressing force and the estimation prestress losses are done. Study of effect of curbs on solid deck slab bridges using conventional and finite element method. Comparative study of IRC: 112-2011 with IRC: 18 and IRC:21. 1.3 Deck Slab Bridge A deck slab bridge is the simplest type of.
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Introduction to prestressed concrete.1.PRESTRESSED CONCRETE STRUCTURES.Reinforced concrete: Concrete is strong in compression weak in tension. Steel in strong in tension Reinforced concrete uses concrete to resist compression and to hold bars in position and uses steel to resist tension. Tensile strength of concrete is neglected (i.e. Zero ) R.C beams allows crack under service load.Pre-stressed Concrete What is Pre-stressed Concrete?: Internal stresses are induced to counteract external stresses. In 1904, Freyssinet attempted to introduce permanent acting forces in conc. To resist elastic forces under loads and was named “ Pre stressing”.Concept of pre-stressing: i. The concept of pre stressing was invented invented years ago when metal brands were wound around wooden pieces to form barrels.
The metal brands were tighten under tensile stress which creates compression between the staves allowing them to resist internal liquid pressure.Principle of pre-stressing: Pre-stressing is a method in which compression force is applied to the reinforced concrete section. The effect of pre stressing is to reduce the tensile stress in the section to the point till the tensile stress is below the cracking stress. Thus the concrete does not crack. It is then possible to treat concrete as a elastic material. The concrete can be visualized to have two compressive force i. Internal pre-stressing force. External forces (d.l, l.l etc ) These two forces must counteract each other.Principle of Pre-stressing: Stress in concrete when pre stressing is applied at the c.g of the section.Principle of Pre-stressing: Stress in concrete when pre stressing is applied eccentrically with respect to the c.g of the section.Pre-stressed Concrete: Methods There are two basic methods of applying pre-stress to a concrete member Pre-tensioning – most often used in factory situations Post-tensioning – site use.Types of pre-stressing: I.
Pre-tensioning In Pre-tension, the tendons are tensioned against some abutments before the concrete is place. After the concrete hardened, the tension force is released. The tendon tries to shrink back to the initial length but the concrete resists it through the bond between them, thus, compression force is induced in concrete. Pretension is usually done with precast members.II.
Post tensioning In Post tension, the tendons are tensioned after the concrete has hardened. Commonly, metal or plastic ducts are placed inside the concrete before casting. After the concrete hardened and had enough strength, the tendon was placed inside the duct, stressed, and anchored against concrete. Grout may be injected into the duct later. This can be done either as precast or cast-in-place.
Fundamentals of Prestressed Concrete Bridge (with solved example)Introduction: In prestressed concrete, a prestress force is applied to a concrete member and this induces an axial compression that counteracts all, or part of, the tensile stresses set up in the member by applied loading. In the field of bridge engineering, the introduction of prestressed concrete has aided the construction of long-span concrete bridges.
These often comprise precast units, lifted into position and then tensioned against the units already in place, the process being continued until the span is complete. For smaller bridges, the use of simply supported precast prestressed concrete beams has proved an economical form of construction.
The introduction of ranges of standard beam section has simplified the design and construction of these bridges. Methods of Prestressing. Elastic deflection due to prestress. Elastic deflection due to initial loading.
Creep deflection under sustained stresses. Deflection due to loss of prestress. Additional deflection due to live loadThe deflection due to prestress may be calculated by treating the prestress as an equivalent normal loading. Since concrete deforms both instantaneously under load and also with time, due to creep, the deflections of concrete structures should be assessed under both short-term and long-term conditions.
End Block Design. There are 2 problems associated with end-block design namely, the assessment of the bursting tensile stresses and the compressive bearing stresses directly beneath the bearing plate. For post-tensioned members, the prestressing force in a tendon is applied through the anchorages as a concentrated force. By St. Venant’s principle, the stress distribution in a member is reasonably uniform away from the anchorage but in the region of the anchorage itself the stress distribution is complex.Composite Construction:.
Many applications of prestressed concrete involve the combination of precast prestressed concrete beams and in-situ reinforced concrete slab. A common example is the in-situ infill between precast bridge beams.
The beams are designed to act alone under their own weights plus the weight of the wet concrete of the slab. Once the concrete in the slab has hardened, provided that there is adequate horizontal shear connection between the slab and beam, they behave as a composite section under service load. The beam acts as permanent formwork for the slab, which provides the compression flange of the composite section. The section size of the beam can thus be kept to a minimum, since a compression flange is only required at the soffit at transfer. This leads to the use of inverted T sections.Complete topic is covered in the form of a PowerPoint presentation embedded below along with the solved example on post-tensioned Concrete Slab Bridge.