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Questions tagged [prestressed-concrete]

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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 ...
Shear at its finest's user avatar
2 votes
2 answers
283 views

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 ...
Sagierian's user avatar
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2 answers
113 views

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 ...
Stergios Aristoteles Mitoulis's user avatar
2 votes
2 answers
764 views

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 ...
Abdellatif Hannachi's user avatar
2 votes
3 answers
186 views

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 ...
S. Rotos's user avatar
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1 vote
3 answers
248 views

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 ...
aNONYMOUS SHAHMAN's user avatar
1 vote
0 answers
68 views

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 ...
Amro's user avatar
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-1 votes
1 answer
162 views

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 ...
MaxSmith060's user avatar
0 votes
2 answers
360 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 ...
Zirc's user avatar
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2 votes
0 answers
339 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 ...
chromechris's user avatar
2 votes
3 answers
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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? ...
chromechris's user avatar
1 vote
0 answers
344 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 ...
J.Daou's user avatar
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3 votes
1 answer
2k 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-...
J.Daou's user avatar
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1 vote
0 answers
42 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 ...
Houss_gc's user avatar
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3 votes
1 answer
409 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 ...
steinbock's user avatar
4 votes
2 answers
1k 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 ...
CableStay's user avatar
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2 votes
1 answer
172 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 ...
Wasabi's user avatar
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9 votes
1 answer
5k 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 ...
CableStay's user avatar
  • 2,760
3 votes
2 answers
812 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 ...
CableStay's user avatar
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7 votes
1 answer
799 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 ...
Wasabi's user avatar
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4 votes
1 answer
207 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 ...
Wasabi's user avatar
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