Engr Waqas

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Everything posted by Engr Waqas

  1. Why r u asumimg only two bolts effective in shear? R u assuming bolts in tension would not be effective in shear or what? Also why earth quack load is not being used to calculated base forces? @waqar saleem as umer said your bolts will not only be designed for tension only but also for some failure moods associated with bolts i.e. breakout failure, pryout failure etc. so appendix D of ACI deals with it.
  2. Assalam i alikum friends, What are good consultants in karachi which have experties in building design of low height as well as high rise. Kindly share ur experience and info. Major element i m looking for is good learning environment where we can learn real and correct design practices instead of faulty ones. Also kindly comment whether EA CONSULTANTS from karachi are good in technicalities in structural design or not? If u also can comment or comparison between EA and bilan nd mushtaq consultants it would be of great help. Thanks.
  3. If beam is wide it reduces one way shear force by reducing cantilever part. but providing beam or not, is purely dependant on situation and loading. I believe it is mostly differential settlement that happens and when one part of wall exerts more load and soil loses its strength and settles, then the beam provided will behave as bridge between this settled soil and hence will not allow wall to settle even if soil has settled( as in loose pockets).
  4. Depends on loading nd settlement. If loads are high, go for beam. Difference i have mentioned above. It is you who will have final judgement.
  5. Tell me why are you not designing it using software to take care of all the forces for design? More over in my opinion, tie beam grade beam ground beam and plinth beam are not different necessarily. They are just terms to define the type of beam. Tie beam is a beam used to tie two columns for two movememts. Vertically and horizontaly by increasing stiffness of structure there. For example column A and column B are tied.if column B settles, the tie beam will offer a resistance to its settlement by transfering force to column A. Also if column B moves horizontaly, tie beam will tie column B with column A and hence offering a frame actiom to reduce horizontal deflectiom. Tie beams may be at any level. If these are at plinth evel they are called plinth beams where it also helps in soil retaining of inner house area and offer also as support for walls. Plinth beams my also be designed as tie beams or just as plinth beams to support walls etc. Grade beam is a beam cast against earth. If below plinth there is not brick foundation and plinth is supporting wall then this plinth beam also called as grade beam. And grade beam and ground beam is same.
  6. If you are worring about settlement of foundation, i think it can be checked in safe. If beam without bem satisfies, strap footing must be enough.
  7. Assalam o alaikum. Why dont we model masonary wall in etabs while modeling frame? Walls are there with their stiffness participation by reducimg displacements in an earthquack. Is it because we consider walls will fall when seismic force will act on walls perpendicular to plan of walls? More over one of my friend told me that now a days practice of construction in islamabad, quetta and kashmir , houses are built with masorany walls along with columns. The frame provided is designed for lower seismic zone than original and for lower ductility. My question is does it act as dual system? Means walls are considered to resist lateral forces and the frame ( in which beam is not designed to take slab load) is provided just to have some extra stiffness.... what exact concept is used behind such design, if any one is familiar with?
  8. Thanks a lot. Keep it up. You are serving engineering community a lot...
  9. For design of beam footing, either you cand consult PRC 1 by Z A SIDDIQUE or search the forum. There are other discussions also.
  10. My opinion is that, beam foundation is mostly suited when loads coming from super structure are excessive and causing punching shear in footing. So instead of increaisg depth of whole footing, we provide tapered footing or we go for beam footing. But since in case of wall, there is no case of punching shear. And only one way shear exists. Which is nearly same either you provide beam or not. Again if u r having excessive one way shear u can again go for beam footing or tapered footing. again if u think tapering will cost more go for localized thickneing by providing beam. More over, providing beam also causes increment in rigitiy of footing. I will personally provide strap footing.
  11. The dimension of column is very big. R u sure? What is the project exactly? More over why r u facing problem in design of footing? It must be same and dimension of column should be taken at bottom of column.
  12. @UmarMakhzumi So for model 2, frame only, instead of playing with modifiers, can we go to reduce effective mass multiplier to 0.25 as Ilyas said?
  13. Does vertical distribution depends on time period? It must depends on weight participation and stiffness of floors.
  14. As umer makhzumi bhai said, for seperate model without shear walls, the approach told by ilyas should be ok. But I doubt the interaction with shear walls is not taken into account if we design frame for 25% shear separately. Kindly share you solution how to cater it in etabs.
  15. If you share your found solution with this forum it would be of great help for others. Thanks in advance.
  16. Is it from some document? Kindly give reference. I would like to study more about it. thanks.
  17. Kindly explain for what purpose? Because for seismic drift, @Rana Waseem sir has explained only seismic CASE should be used. instead of Ex or Ey with any combination.
  18. I think for single column or single beam, This statement seems true but for a frame in ETABS, relative difference between stiffness of column and beam must be provided so in any case 50% difference between stiffness of both beam and column must be provided. Am I right? I have few questions here. 1) For serviceability, we cant go for 0.5 for beam and 1.0 for columns because here lateral deflections are calculated against real cracking by 0.35 and 0.7. For strength design only we can go for 0.5 for beam (this 0.5 may also be skipped as Nilson said) and 1.0 for columns. Am I right? 2) Does ETABS design beam for positive region as T-beam or Rectangular beam? Mean does it takes into account monolithic behavior of beam with slab and make part of slab acting as flanges or not? 3) If it only design as rectangular beam, why it has algorithm of T-beam design in its manual? 4) If it design as T-beam also depending on neutral axis depth, Then as Engineer Suliman said, We will have to provide 0.7 modifier for beams also.
  19. If you are having a geotechnical report with you, there must be clearly stated value of spring constant with the name Modulus of Subgrade Reaction. Incase soil investigation have not been done on site for any reasons, you can use a tentative value for k by following relation. k = 3 x qa x 12 (in FPS in k/ft3) k = 3 x qa x 40 (in SI in KN/m3) where qa = allowable bearing capacity. and 3 is Factor of safety applied on soil while determining bearing capacity of soil. For the reference of this formula, please read the attached document. Correlation_BC_and_K.pdf
  20. Great..!!! I m only familiar with Engr Junaid because he is my class fellow, with Umar Makhzumi Bhai, and With Waqar Saleem Brother. Today I came to know what is full form of BAZ And he has changed his looks also. By the way, I used to think Engr Uzair Sir quite younger but he is quite senior to us. Mostly people after getting senior does not use social media forums much.. especially for responding people.. Really nice to know the members. This forum is really great.!!
  21. You must export combos related to all loads i.e. gravity and lateral loads because ultimately effects due to all the loads is going to be transferred to foundation. Designing foundation only for gravity loading is not correct approach. But remember, since mostly bearing capacity provided by Geotechnical consultant is safe bearing capacity instead of ultimate bearing capacity (safe bearing capacity means full factor of safety has been applied to bearing capacity as we do in ASD approach). Hence if we use this bearing capacity for design of foundations, loading combos of ASD or unfactored loading combos must be used. UBC and IBC provides these laod combos and footing must be designed for all this loading combos instead of autogenerated loading combos of ETABS which are factored. Either define these loading combos in etabs and export to safe or directly define then in safe. Increase of bearing capacity upto 33% is not allowed in all the cases. It can only be used where in loading combos having two or more variable/Transient loads togather, we have not reduced the intensity of transient loads. If we have reduced these loads by 0.75 factor then bearing capacity can not be increased by 33%. Basically it is not the case with bearing capacity only. Any strength determined by using ASD approach (i.e. full factor of safety applied on strength of member, ) can be increased by this approach but only if in loading combos transient loads have not been reduced. UBC and IBC proposes two types of loading combos for ASD. in first type of combos you may find for example a combo D+L+W and in 2nd type you can find the same combo as D+0.75L+0.75W. if you use first type of combo you can increase by 33% and if u r using 2nd type of combo, note that the loads have been reduced by 1/1.33 = 0.75 times instead of increasing strength. so same factor of 1.33 has been applied on load side so in this case no increase can be made in strength. For a detailed study refer to following document. 1-3rd stress increase AISC.pdf
  22. Kindly mention names of members as we are unfamiliar with faces. Thanks..
  23. Can you please provide the complete document? thanks.
  24. In regular non inverted beams, the negative steel of slab rests on the upper portion of beam which is in compression and hence fully available for end bearing load of slab. But in inverted beams, this negative steel rests on the lower portion of beam which is in tension (in middle span) and hence will be having flexural cracks (though up to minor crack widths), I m amazed if this cracking affects the bearing strength in any way.