Waqas Haider

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Waqas Haider last won the day on May 13

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About Waqas Haider

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    UET Lahore
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    Kashif Aslam and Associates

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  1. Yeah. I always use to amaze who is funding this website except you sir. It really need fiances, time and extreme effort to arrange and manage such a website having a good interface along with updating options of social world. It is really good sir. You have initiated a chain and it is really making change in Pakistani community of engineers who rely on internet a lot for learning. We try our level best to spread this forum as much we can. At end, heartily thanks to the moderators and all other members of the forum who are sharing their knowledge and time with people. Thanks.
  2. A very interesting and explanatory document along with example..... design of dome.pdf
  3. This is what i found in "Structural Concrete theory and Design by Nadeem Hussen" Here it also reports the same thing that we should design for torsion for atleast φ4λ Sqrt(fc ′) A2cp / Pcp Which is also specified by ACI that we can reduce our torsion upto phi.Tcr i.e. cracking torsion and not below this. Even if we neglect the remaining torsion for compatibility, we should atleast perform design for phi.Tcr or should at least provide minimum longitudinal and transverse reinforcemet for torsion. This is to control crack width to satisfy servicability. ACI, Nilson and Nadeem hussen all quote the same thing. Hence reducing the modifier upto such a little value is not good at start. At start we should go for a value of 1, 0.3 or any other suitable value which user think is small enough to release majority of compatibility torsion and will sustain only smaler torsional moments. After designing, if still some indeterminate beams are being failed, then for the specific beams we can reduce value unless we get Tu equall to phi.Tcr or a bit larger than that. Because putting Torsional modifier to 0.001 would not report any torsional reinforcement and hence adding no torsional reinforcement at all would cause excessive crack widths affecting serviceability of the structure.
  4. please go through this thread. Thanks.
  5. Last month, i design a structure with shear walls. I will attach more documents. What i know/remember i will share with you. In simple, Pier is similar to column and Spandrel is similar to beam. Shear wall is modeled in etabs as shell element. You are to assign it either pier label or spandrel label (Depending on situation of shear wall) to design a shear wall. If you want to design a shear wall, it mostly needs peir label to be assigned. But for the portions of shear wall above openings, as its behavior is somewhat like beam resting on two supports, you need to assign it a spandrel label. I have attached screen shots of my model where you can see i have assigned pier label to the vertical elements and i have assigned spandrel labels to the elements spaning horizontally above openings. The reason behind is detailing based. The detailing in vertical elements of shear wall is similar to wall (or column) and its design is based on considering it as an element resisting majorly AXIAL FORCES + MOMENTS along with inplane shear forces. (Theoratically it acts as a cantilever beam spaning vertically which again represent behavoiur similar to column). I have also attached screen shot of design detail of pier which reports total vertical steel in wall with respect to section area for resisting moments, horizontal steel for resisting shear and some times boundry elemtns (i.e. special detailing at ends of shear wall exactly as in column i.e. shear rings confining vertical bars). I have also attached screen shot of design detail of spanderal which reports top steel, bottom steel, to resist moments similar to beam and vertical steel to resist shear along with DIAGONAL reinforcement some times needed to account for reversal of forces. I will attach more documents throwing detailed light on shear wall design i found few weeks ago. Also my model is attached (it is in seismic zone 4 from where you can get idea about pier labeling and spanderal labeling) One important thing is that, pier label and spanderal label also meant to integrate forces. i.e. if you assign same pier label to all walls in a floor connected with each other, the software will report results only for one and critical wall because all walls were assigned only one pier label. If you want to have multiple outputs at multiple walls, you should assign them different pier label. in image number 5, note that i have not assigned any pier to the selected portion of wall. hence no reporting of results is done. Etabs Center Portion.e2k
  6. Assalam o alaikum, There is a job opening for structural draftsman in Kashif Aslam and Associates, Lahore, with minimum of 3 to 4 years of experience in structural drafting. Interested candidates may send their CV at waqas.haider@kaa.com.pk Please forward to the concerned person in your circle also. Thanks.
  7. I am confused regarding this approach of reducing torsional modifier to such great extent. According to ACI In a statically indeterminate structure where reduction of the torsional moment in a member can occur due to redistribution of internal forces upon cracking, the maximum Tu shall be permitted to be reduced to the values given in (a), (b), or (c), as applicable: (a) For nonprestressed members, at the sections described in φ4λ Sqrt(fc ′) A2cp / Pcp It says that we can reduce torsional moment upto a specified limit. Not to zero or 0.001. In its commentary it says, For this condition, illustrated in Fig. R11.5.2.2, the torsional stiffness before cracking corresponds to that of the uncracked section according to St. Venant’s theory. At torsional cracking, however, a large twist occurs under an essentially constant torque, resulting in a large redistribution of forces in the structure.11.34,11.35 The cracking torque under combined shear, flexure, and torsion corresponds to a principal tensile stress somewhat less than the quoted in R11.5.1. When the torsional moment exceeds the cracking torque, a maximum factored torsional moment equal to the cracking torque may be assumed to occur at the critical sections near the faces of the supports. This limit has been established to control the width of torsional cracks. Also according to Nislon, this distribution is only possible after extensive cracking as highlighted in below pic. So I doubt the approach used to neglect torsion upto 0.001 level What i got from the 2nd attachement of Zain Saeed the author is dividing Tcr with Tu to find how much reduction in Tu is needed to reduce torsion upto Tcr which is, as mentioned above, is necessary to keep torsional crack widths in control. and hence using the modifier for each section defined for beam. It might be a bit lengthy task to evaluate for each type of section ( most loaded members of a type of beam may be checked only), but the approach seems more realistic. Kindly comment as I think if even we reduce to 0.001, still this redistribution in torsion is not possible without large twisting which is not possible without excessive cracking. So reucing upto such a low value does not seem good.
  8. Sir link is not working. Their website is not being loaded. Is there any other alternate to know the details?
  9. This is from Book "Reinforced Concrete Design of Tall Buildings by Bungale S. Taranath" From an inspection of the given problem, determine if the design torsion, Tu, is due to equilibrium torsion or due to compatibility torsion. If it is due to equilibrium, design of member for the entire calculated torsion. If Tu is due to compatibility requirements, as in statically indeterminate structures, it is permissible to reduce Tu to a maximum value, To given by φ4λ fc ′. Sqrt(Acp^2/pcp) Why ACI is putting limit on reduction if we can reduce upto negligible values? Moreover,kindly explain the following wording by the same book. Overall Building Torsion Regarding the simultaneous application of loads in two mutually perpendicular directions, it is worth noting that for buildings in SDC B, the earthquake loads are assumed to act independently along the two orthogonal axes of the buildings. For SDC C buildings having nonparallel lateral load–resisting systems, and for all buildings in SDC D and higher, 100% of the forces for one direction are added to 30% of the forces in the perpendicular direction, the directions chosen to give the worst effect for the member being designed. Is it necessary for every type of building in SDC D and higher? I though this clause is for only non parallel lateral load resisting systems.
  10. Here I am confused regarding two things... 1st is how much we can reduce our design torsion Tu? If we reduce modifier to 0 or 0.01 it means we are reducing Tu completely... But according to ACI — In a statically indeterminate structure where reduction of the torsional moment in a member can occur due to redistribution of internal forces upon cracking, the maximum Tu shall be permitted to be reduced to the values given in (a), (b), or (c), as applicable: (a) For nonprestressed members, at the sections described in φ4λ fc ′. Sqrt(Acp^2/pcp) ans Section says " — In nonprestressed members, sections located less than a distance d from the face of a support shall be designed for not less than Tu computed at a distance d. If a concentrated torque occurs within this distance, the critical section for design shall be at the face of the support." It is saying in first clause that we can reduced our torsion upto minimum of φ4λ fc ′. Sqrt(Acp^2/pcp). So reducing modifier upto negligible value is confusing me. More over how to cater this reduction upto specified limiit of φ4λ fc ′. Sqrt(Acp^2/pcp)? In 2nd paragraph it is relating torison design for distance less than d to the distance equal or greater than d. Is it a generalized statement or it is specifically saying that this minimum Tu requirement is for the distances less than d and for distances greater than d these can be ignored? Thanks.
  11. If i reduce my torsion constant to 0.01, having in mind that it is only needed for compatibility, The moment will transfer to slab and secondary beams and ultimately equilibrium will be obtained. But I m confused to achieve this equilibrium, the main beam need to twist for compatibility until equilibrium is achieved. This will induce diagonal cracks in main beam. Is it acceptable and with in serviceable limits? Are these hairline cracks dont affecting any thing especially appearance or any other design force? I have also seen an approach of providing moment release to secondary beams to avoid excessive torsion and to get same condition physically reinforcement at joints of secondary beams is provided to resemble pin support. But still i m confuse if this type of reinforcement is provided, the secondary beam section will crack. Are these cracks in acceptable limit?
  12. Assalam o alaikum, Is there any suitable software available for concrete and steel quantities take of for all members like slab, column, beam, shear wall and foundation? especially which may work in conjunction with ETABS/SAP2000/SAFE. I found suggestions of some seniors to use SAFE for slab footing beam quantities but I want some specialized software where I can export my model of etabs or safe for quantity estimation? I just want to avoid time consumption for this purpose and speed up the process. Has any one listen about BLUEBEAM REVU software? I have heard about it but dont know in details.
  13. Neither I m aware of dynamic analysis procedure nor with seismic calculations by ASCE. And i dont have enough time to study for this project because of deadline of project. After understanding UBC 97 for static analysis, once this project is complete, I will obviously go through ASCE and Dynamic analysis. I m using rigid diaphragm but the checks like torsional irregularity or re-entrant corners are not specific to rigid or semi rigid diaphragms i think. I may be wrong. But i dont find any of difference between application of relevant clauses of irregularity by UBC. For what purpose sir?
  14. Thank you so much for so detailed explanations. The best thing of this forum is we come here with blank mind and get clear answers for our specific confusions instead of generalized replies. Can you please tell me from which book or study material are these excerpts of images? Now since my building has less than 5 stories and less than 65ft ht, so i m not going to perform dynamic analysis. Now how can i get this condition satisfied using static analysis using ETABS? My stair case also have same framing of column beam as SMRF and it is connected with the Part 2 and 3. But the only landing slab at floor levels will be connected with remaining concrete slab. Whether I need to consider 1633.2.9 item 6 and 7? Also as you mentioned, we need to check slab stresses in ETABS to decide whether it is greater than 0.2fc' or not or if we r using Omega factor it will be 0.5 fc'. But i think Omega factor is only used in special seismic combos which are uses if system is a discontinuous structural system having horizontal or vertical offset of lateral force resisting system. In my case, no need to use this Omega. Am i right?