Correction for Prestress Final Project problems (will always be updated) :
1. Es (for prestressing tendon) = 186 GPa or 186.000 MPa
2. Use 4 (four) girders for main bridge design, otherwise each girder wouldn't support the loads
The distance between girders is clearly stated in the problem. The value is 3.25 m. The total road width is also fixed at 11.7 m. Use these value to calculate the distance for exterior girder to the end of road width (11.7-3*3.25)/2.
we unsure about the area of one strand because in the question sheet the area of one strand is 98,7 mm^2 and the diameter of one strand is 12,7mm. But if we calculate it the area from the given diameter, is not suit with the area that given.
the calculate is 1/4*pi*12,7^2=126,677 mm^2.
and there's a problem when we made magnel diagram. we did't get the acceptable region. What should we do?
The value of strand's diameter 98,7 mm is usually defined as nominal diameter of strand. The actual value of strand's diameter should not be the same with the nominal diameter, so the actual area of strand (98,7 mm^2) might be used in design process. But, for (strand) stress calculation, especially for yield and/or ultimate stress limit, the nominal value should be used as design basis, so the nominal area (126,67 mm^2) shall be used in this case.
I believe the acceptable region is exist in magnel diagram, you should check the numbers again, and consult with me (with your preliminary report about your magnel diagram)if the problem still exist. But if you believe that the acceptable region is not exist, you may propose solution for the problem.
I want to ask you about the eccentricity which is used to plot in Magnel Diagram. There is two eccentricities: girder and composite, which one should I choose?
You should use the girder properties for eccentricity plotting. Composite properties are used for deflection and stress calculation, but you may use the composite properties for Magnel diagram (long term condition).
i want to ask about anchorage zone 1. is the calculation of Mb at page 83 from 'diktat' right? i think it should be Mb= (5,3*(231,8^2)/2 + 2*1,53*231,8^2/6 - 7,55*139,3^2/2)*10^-3 2. If i want to calculate 2 anchor from 1 side, i must calculate for each anchor that pulled alone and both of them pulled together right? But I confused how to calculate both of anchor pulled together, we can't use end block symmetric like in the 'diktat' right? thx
I must check the book again for your correction about Mb. You can use simplification for case in which both of the anchors are pulled together. In this case, you can assume that the anchors react together in one combined force. This single force is then assumed to be effectively applied on its combined center gravity of steel. Based on that assumption, you will get a single (maybe) eccentric tendon with single anchorage zone (end block).
About the Mb calculation on page 83, it needs a little correction like have been mentioned before. The value 231,6 in first operation must be changed into 231,8 (the value comes from calculation before Mb). But I have calculated the result for Mb is not significantly different from the old ones. The value changes from 55,5 into 55,4 KN.m.
how long is the space between the girder?
ReplyDeleteis it 3250 mm? so the length of the bridge is 3250*4=13000mm^2
or is it 11700/4=2925 mm?
thx :)
The distance between girders is clearly stated in the problem. The value is 3.25 m. The total road width is also fixed at 11.7 m. Use these value to calculate the distance for exterior girder to the end of road width (11.7-3*3.25)/2.
ReplyDeletewe unsure about the area of one strand because in the question sheet the area of one strand is 98,7 mm^2 and the diameter of one strand is 12,7mm. But if we calculate it the area from the given diameter, is not suit with the area that given.
ReplyDeletethe calculate is 1/4*pi*12,7^2=126,677 mm^2.
and there's a problem when we made magnel diagram. we did't get the acceptable region.
What should we do?
thx
The value of strand's diameter 98,7 mm is usually defined as nominal diameter of strand. The actual value of strand's diameter should not be the same with the nominal diameter, so the actual area of strand (98,7 mm^2) might be used in design process. But, for (strand) stress calculation, especially for yield and/or ultimate stress limit, the nominal value should be used as design basis, so the nominal area (126,67 mm^2) shall be used in this case.
ReplyDeleteI believe the acceptable region is exist in magnel diagram, you should check the numbers again, and consult with me (with your preliminary report about your magnel diagram)if the problem still exist. But if you believe that the acceptable region is not exist, you may propose solution for the problem.
I want to ask you about the eccentricity which is used to plot in Magnel Diagram. There is two eccentricities: girder and composite, which one should I choose?
ReplyDeletethx :)
You should use the girder properties for eccentricity plotting.
ReplyDeleteComposite properties are used for deflection and stress calculation, but you may use the composite properties for Magnel diagram (long term condition).
i want to ask about anchorage zone
ReplyDelete1. is the calculation of Mb at page 83 from 'diktat' right? i think it should be
Mb= (5,3*(231,8^2)/2 + 2*1,53*231,8^2/6 - 7,55*139,3^2/2)*10^-3
2. If i want to calculate 2 anchor from 1 side, i must calculate for each anchor that pulled alone and both of them pulled together right? But I confused how to calculate both of anchor pulled together, we can't use end block symmetric like in the 'diktat' right?
thx
I must check the book again for your correction about Mb.
ReplyDeleteYou can use simplification for case in which both of the anchors are pulled together. In this case, you can assume that the anchors react together in one combined force. This single force is then assumed to be effectively applied on its combined center gravity of steel.
Based on that assumption, you will get a single (maybe) eccentric tendon with single anchorage zone (end block).
About the Mb calculation on page 83, it needs a little correction like have been mentioned before. The value 231,6 in first operation must be changed into 231,8 (the value comes from calculation before Mb). But I have calculated the result for Mb is not significantly different from the old ones. The value changes from 55,5 into 55,4 KN.m.
ReplyDeleteThank you for your correction.