Questions tagged [prestressed-concrete]

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2answers
40 views

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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0answers
25 views

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 ...
2
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3answers
81 views

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? ...
1
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0answers
113 views

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 ...
3
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1answer
607 views

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-...
1
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0answers
34 views

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 ...
3
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1answer
222 views

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 ...
4
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2answers
612 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 ...
2
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1answer
110 views

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 ...
9
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1answer
3k views

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 ...
3
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2answers
439 views

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 ...
6
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1answer
637 views

(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 ...
4
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1answer
138 views

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 ...