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Prestress creates an upward deflection on the beam due to the combination of elastic strain, creep and shrinkage in the unloaded beam. This negative deflection will bend back to a straight stance or at least minimize much of the deflection of the beam after the loading. The equations of the deflection of a prestressed concrete beam depend on the curvature ...


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The short answer would be "yes", but there is a lot of things to be aware: First of all, you should check that the building code you are following allows you to do so. You should check adherence between steel and concrete. Since the ratio between strength and lateral surface is a lot higher for tendons than for passive reinforcing steel, adherence ...


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@hazzey has answered your main question quite effectively, so I'll just add two comments. While I agree that partially filling rows is perfectly fine, I would just like to add that it may be better to distribute the strands along their rows instead of bunching them all near the centerline (but keep the strands of different rows aligned) as in the figure ...


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Strands in Upper Rows Versus Debonded Strands You have the right idea that placing strands in upper rows is better than debonding strands. Debonded strands are more time consuming (e.g. cost more) than bonded strands. Also, placing a strand or two in the very top row usually helps to reduce the number of debonded strands needed. It is relatively easy to ...


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I have no resources to point to in regards to this, but I'm fairly certain your gut-feeling is correct. In fact, end diaphragms exist in bridges primarily to hold the soil on the approach. They can also be useful for temporary lateral stability of the beams, but if that were the only reason, temporary metallic bracing would be much easier and cheaper. ...


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The questions in your title and in your body-text are slightly different. Prestressed girder camber should usually be upwards. This is because one usually applies sufficient prestressing to cancel out (or overcome) all possible dead loads and some fraction of live loads. This means that without live loads the prestressing will probably be larger than the ...


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The Los Angeles Tall Buildings Structural Design Council (LATBSDC) 2017 guidelines suggest using the following (Table 3, LATBSDC 2017): Service-Level Evaluation: Axial : $0.8E_cA_g$ Flexural : $0.8E_cI_g$ Shear : $0.4E_cA_g$ MCE-Level Evaluation: Axial : $0.5E_cA_g$ Flexural : $0.5E_cI_g$ Shear : $0.2E_cA_g$ For code-level evaluation you could use some ...


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Because there are rebars designed for this exact task on the top layer of the beam rebars. These are in addition to other rebars required for other loads, such as negative moment rebars at the supports. the codes allow certain bars to share loads.


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Unless I'm misunderstanding your are referring to this process of pre-stressing concrete, where a steel reinforcement/tendon is put under tensile loading the concrete is cast the steel reinforcement/tendon is released. In step 3, (i.e. when the tendons are released), the tendons which is extended tries to return to his original size (that is what you ...


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Concrete is strong in compression but weak in tension. In tension, it will crack at a much lower stress than the allowable compression stress. A reinforced concrete beam without any prestressing will generally have compression in concrete and tension in the rebars. If there are any significant tension stresses in the concrete, the concrete will crack and ...


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Based on your most recent comment, you seem to be looking for a DIY improvised way of drying your painting. I'm thinking of something, but it depends on the scale of the painting you do in the winter. I think it's way better, more efficient, and less risky to actually dry the paint from the outside given it'll take quite a lot of energy and temperature ...


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Yes, theoretically... But electric underfloor heating is done with thin wire to limit the current. Concrete rebar is 1/2" or 3/4" in diameter so will need a lot of current - have you considered a source for that... Also the connections with the rebar were not designed for electricity and you may find bars that you only get to one end.


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Comments by @Mr.P nudged me to realize that there is a redistribution of equivalent loads due to losses which cannot be trivially encompassed by Lin's method. To demonstrate this, take the following simply-supported beam (ignore all concepts of units or scale here, this is a thought exercise). The bending moment diagram solely due to prestress for this ...


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The PCI manual (3rd Edition, Section 8.7.1) states: It is not recommended that prestressing levels be increased in order to reduce or eliminate long-term downward deflection that might be predicted if the multipliers in Table 8.7.1-1 are used.


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After the discussion with @sanchises in the comments, the answer is that, yes, the order of operations in jacking does affect the final tension diagram of the cable. A symmetric cable simultaneously jacked will have a symmetric tension diagram, while the same cable jacked from one side and then the other will not. The diagram actually ends up as a line ...


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