Leaderboard

Thanks...I hope it will work . I will get back to this forum if i need further help.This idea will make our work easy.

First-off, I am not sure about your system, is it a moment resting frame, dual frame or shear wall frame interaction? I assume it is a building frame system where lateral loads (all) are taken by shear walls (in-plane) and all gravity (mostly ~ 90%) is taken by columns. The above assumption can be checked by checking reactions after applying 0.7,0.35 modifiers to walls and 0.7 modifiers to columns. This is your routine design..Right? Now comes the question of temperature loading, for that please update what is the temperature magnitude you are using? What is the use of building? It is heated/un-heated structure? For example if its a parking structure where under-sides of beams also have temperature loading, slab stresses will be minimal (almost zero if equal values). Also for parking structure, the first slab will have huge stresses due to fixity of base. And as @UmarMakhzumi pointed out, you also need to check bending under temperature gradient (manually by using C and T approach for a single reinforced section or by computer using complex analysis). Anyway, In my view, I hope that authorities would not go for that. But for normal temperature analysis, I would recommend you to make a 1 page A4 calculation, stating the design philosophy for temperature loads and put it as appendix or part of your report. In that report you would mention, 1. use of semi-rigid option 2. use of reduced modifiers for tension cracking for walls (even for columns if they are showing tension). You can use 0.25 and if it not working reduced further. It would be nAs/Ag for the members where you havee tension. 3. show formula for modulus of rupture for restrained slabs and subtract that capacity from ETABS values. 4. Assign piers or average manually the axial force over whole length of wall piers to reduce magnitude further. Make sure that reinforcement provided for temperature is same on both sides for slabs/walls and same on all sides for beams/columns. Now next question is regarding lateral load RE-distribution. If you reduced the stiffness of walls and columns both by same amount, that would not affect re-distribution of lateral forces. But if you just reduced stiffness of walls, columns will start taking more lateral loads (depends on relative stiffness of wall/columns, I do not know the dimensions) so As @UmarMakhzumi pointed out, you should this design too. Because axial stiffness of walls/shells = in-plane stiffness of walls/shells so changing axial stiffness will also change the bending stiffness for lateral loads and re-distribution will happen. So check for this condition too, you might need to increase some columns that again depend on dimensions and framing system. In that case, read Tranath book on tall buildings chapter 3 on lateral loads to see what you actually need to increase, columns or beams? Please update us what happens.

Ofcourse, you should use semi-rigid diaphragm for temperature analysis or other axial loads.

1. I forgot to mention and as is Rummann understood correctly, that reason for using reduced stiffness for axial tension is that we will get less tension from analysis (due to less stiffness/restraint). 2. Negative temperature will produce tension near restraint (like slab supported on heavy walls). 3. What is the use of building? Is it a car park where you need to apply temperature to all the structure? Otherwise as Umar and you already pointed out, its the top slab where you need to consider differential temperature between top and bottom slab and thats not possible with ETABS 9 atleast. 4. Yes, tension should be checked on appropriate combination with other loads and that is 1.2D+1.6L+1.2T plus other loads if you have. If still you are getting tension that means it will be carried by modulus of rupture + steel only. 5. I would recommend you to use reduced stiffness of 0.25 and then also subtract the tension capacity of concrete (equal to half of 0.62(f'c^0.5)xthicknes in Mpa), half because slabs are restrained as per ACI. 6. For compression, cracking modifier should be increased but walls are quite stronger in compression. So just use 0.25. This is your separate model for temperature analysis. Keep it separate from lateral analysis where you might be using 0.7 or 0.35 modifiers for shear walls. Or it will affect the distribution of lateral forces to columns as you pointed out. But keep in mind, that is the real situation, if temperature cracks walls before earthquake hits, walls would be very weak transferring lateral forces to columns. Others can shed light on this more.

Yes, that would be correct for columns stiffer than beam. Thanks.

Sohaib, I will try to explain to you the procedures involved in designing a pile. 1) Pile design involves meeting the two limit states: Axial and Lateral (also called serviceability for piles) Considering ULS design for piles, you need a geotechnical report that contains skin friction values for pile design along with recommended factors for tensions, compression and frost loads. Geotechnical report will also provide you either parameters for lateral design or load deflection graphs. 2) Once you have the geotechnical report, you do initial sizing of the pile based on the load. Geotechnical report recommendations will allow you to size the pile based on geotechnical capacity, which is how much load can be transferred from pile to soil based on pile geometry. 3) Once you have sized the piles based on geotechnical, you will need to do structural checks to make sure pile structural capacity is greater than geotechnical capacity. 4) For literature, you can have a look at attached. Foundation Analysis and Design - FEMA.pdf Thanks.