Questions tagged [prestressed-concrete]

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Design of prestressed beams and bridge decks

When we are designing bridge decks and beams for class 1 or 2 (i.e. uncracked) we have to check both the compressive stresses (in Eurocode design we use the characteristic value of $f_{ck}$ i.e. 0.45 ...
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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 ...
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3 answers
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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 ...
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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 ...
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Is it possible to measure the concrete workability by a mobile app one day? [closed]

After studying all methods that can measure the concrete slump, I found 62 devices that service this purpose at the same time these devices are expensive and not practical enough, for this reason the ...
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How to choose the dimensions for a prestressed I-beam?

I need to design a simply supported symmetric I-beam (for a school problem). However, I can't find much information about the selection of the section or if there exist any standards for that. the ...
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Why does rebar in reinforced pre-stressed conrete reduce in deflection if compressive stress is applied to member?

According to What is Prestressed Concrete? - Practical Engineering, one way to reduce deflection in the steel rebar is to pre-stress the rebar by applying compressive stress in the member before ...
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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 ...
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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? ...
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What are the general consideration for tendon profile in a post tension slab?

How the tendon profile is calculated for banded-distributed disposition? In the following figure why is the tendons profile one in the top fiber and the second in the bottom fiber? If the location is ...
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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-...
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Effort applied on the cement silo [closed]

As mentioned in the question above, I am working on a clinker silo, I want to know if the forces applied on the cone of the silo are exclusively coming from the weight of the material stocked or their ...
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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 ...
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4 votes
2 answers
985 views

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 ...
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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 ...
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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 ...
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3 votes
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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 ...
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7 votes
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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 ...
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4 votes
1 answer
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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 ...
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