Questions tagged [prestressed-concrete]
21 questions
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What is the effect of end diaphragms on prestressed girder forces/deflections?
I'm encasing the abutment ends of prestressed concrete bridge girders in concrete before the deck pour. (For lateral stability and to prevent the soil from spilling through.)
Discussion of intermediate diaphragms for prestressed girders abounds, but…
CableStay
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(Non)simultaneous prestressing anchorage slip losses
Post-tensioned prestressed concrete beams suffer from a multitude of losses. When jacked, they suffer friction losses and their tension diagram is, for example (to simplify the drawing, I'm using the linearized version of the friction loss equation…
Wasabi
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Strand layout in prestressed concrete girders: is a partially filled bottom row acceptable/advisable?
My state (USA - Nebraska) uses "NU" type prestressed girders (though the question should equally apply to all geometric variants of prestressed concrete "I" girders).
There are 6 "rows" available for the prestressing strand. Moving from the bottom…
CableStay
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Is the order of operations in jacking a cable relevant?
If you have a prestressed concrete beam or slab and are jacking a cable from both ends, does the order of operations alter the result?
For a symmetric curve, the tension diagram along the cable's span after friction losses is always shown as…
Wasabi
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Should long-term prestressed girder camber always be upward?
When considering long-term prestressed girder camber (for a bridge), what are the implications (if any) of long-term downward deflection on girder performance? Should prestressing be designed to ensure that long term camber is always upward?
I'm…
CableStay
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What is the stiffness modifiers for a prestressed slab?
According to ACI the stiffness modifier for moment of inertia for flat plate and flat slabs is 0.25 (ACI318/318R-02 10.11.1) to mitigate for the cracked section.
But in a prestressed slab (post-tensioned) the crack is controlled can the stiffness…
J.Daou
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do prestressing tendons located in the compression zone contribute to compression reinforcement?
when doing the normal RC design of an RC beam, it is determined that compression steel reinforcement is required, does a prestressed tendon in the compression zone contribute to the area of compression steel?
Possibly it could contribute, but with…
steinbock
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How is prestressing with losses self-balanced?
By definition, prestressing is a self-balanced load. This is because it is in fact merely an applied state of internal stresses.
This can also be demonstrated mathematically (in this case for a simple parabolic cable) via Lin's load-balancing…
Wasabi
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In a pre stressed concrete? Why is the top fiber considered as under compressive stress?
I have been solving problems involving pre stress concrete, i want to clarify why is the top fiber always considered as under compressive force, in my understanding the concrete would bend positively to due pre stressing and thus top fiber would be…
Shear at its finest
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Why are expansion joints on prestressed concrete box girder bridges sometimes not located directly above the bridge piers?
Here is an example of what I am referring to. This bridge is part of the Tom Moreland Interchange in Atlanta, more commonly known as "Spaghetti Junction". This interchange has several flyover bridges, all of which have expansion joints that are not…
Sagierian
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How to calculate the required prestressed jacking pressure to apply to a pre-tension concrete beam?
How does the fabricant of prestressed pre-tensioned beams calculate the equivalent pressure in the hydraulic jack (in bars) to the design prestress force (in kN)? Are there factors to multiply like a jack efficiency factor or are there some losses…
Abdellatif Hannachi
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Why doesn't prestressed concrete crack at the top before the load is applied?
In prestressed concrete, we add a tensioned steel cable at the bottom half of the beam to balance out the tensile forces resulting from the applied load. But before the load is added, doesn't the beam deflect upwards and cause tensile cracks now at…
S. Rotos
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Maximum allowable crack in Post Tension concrete
What is the maximum allowable crack size dimension in a post-tension concrete slab before it is considered a "structural" crack, in Arizona, USA? Is there a certain standard for this. I have tried looking for it in my state's ROC rules but they have…
chromechris
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Using electricity to heat up a slab through post-tension cables?
Would a passive and controlled amount of electricity fed through post-tension cables, heat up a slab, without ruining the dependability and health of the post-tension cables, and the concrete itself?
I am wondering because I coat concrete slabs with…
chromechris
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Is the strain in the pre tensioned steel after cutting of tendons compressive or tensile in nature for pre-stressed concrete?
When we cut the tendons of the pre-tensioned steel, the steel undergoes compression, therefore the steel should have compressive strain. But when we calculate the residual strain, the strain in steel and the compressive strains in concrete due to…
aNONYMOUS SHAHMAN
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