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Showing content with the highest reputation since 02/25/2017 in all areas

  1. 12 points

    Welcome Everyone! :)

    Asalam-o-alikum wr wb everyone! I am very excited to announce the launch of "Structural Engineering Forum of Pakistan". Its a open discussion forum directed to Civil/Structural Engineers. The purpose is to have discussions, to shun ambiguity and to overall uplift the structural design practice. I welcome everyone aboard. I hope this forum meets serves its purpose, May Almighty ALLAH bless you all. Warm Regards, Makhzumi!
  2. 6 points

    Beam/column Capacity

    Ratio of flexural capacity of Beam/column is computed to preclude the formation of plastic hinges in columns for obvious reasons, refer to section 21.6.2 of ACI 318-11. Sum of flexural capacities of column at a joint should be 1.2 times the capacities of beam framing into the joint in particular direction. Etabs alerts user when the ratio exceeds; if it does not alert, it means either you are ok, or you have not activated corresponding seismic category (I think it calculates for category D E & F) for which this capacity needs to be computed. When capacity is exceeded, we can increase the size of column, or reduce the size of beam, or play with reinforcement of members. It has nothing to do with redistribution of moments; If both end of column will yield, during a seismic event, in a particular story, structure will most probably collapse. In a frame, that is resisting lateral loads, you cannot take away the ability of beam to develop negative moment; if you do not provide top reinforcement, it will not be called a moment resisting frame, and will not resist lateral loads..
  3. 6 points

    Building Drifts In Etabs

    Good article; I will throw my two cents. Seismic drift values are much larger than wind values. UBC uses maximum inelastic response displacements rather than the design level displacements to verify the performance of the building. As stated above, the seismic drift limits are 2% & 2.5% of the story height for long and short -period buildings. So, for a floor to floor height of 12 feet the max. allowable inelastic drift value would be 2% of 12 feet= 0.02*12*12inches=2.88 inches. For wind for a 12 story height, drift would be L/400=12*12/400 =0.36 inches, A comparison of both wind and seismic drift limits shows that earthquake inelastic displacements are quiet large compared to wind displacements. That is why proper detailing is emphasied in seismic design. Moreover, when calculating ΔS for seismic, make sure: you have included accidental torsion in your analysis.use strength design load combinations: 1.2D + 1.0E + 0.5L & 0.9D + 1.0EYou are using cracked section properties for reinforced concrete buildings. Typical values are Icr walls= 0.5EcIg, Beams = 0.5EcI g & for Columns 0.5 - 0.7 EcIg.
  4. 5 points
    Dear Fellows I have encountered an issue; draftsmen/architects take projects from clients and make structural drawings without calculations and there are engineers whose stamps are available at printing shops which are stamped for very minimal charges. Structural engineers who are stamping as designer and as vetter are having filthy money without fulfilling their duties. These designers and vetters disregard the profession and engineering community, they do not have any ethics and sense of humanity. PEC do nothing or there is no complain against them. Being engineers and specially as structural engineers this is our responsibility to raise this issue to PEC or any other authorities and more to educate our engineering community that have respect and dignity in the profession, one must not disrespect his profession or let disrespected by such black sheep in the community. If a system/community have the ability to spit the wrong things out it remains alive and working perfectly. when system/community allows everything without check, such community is already dead. Structural engineers do not get projects who are working earnestly due to such people. Main aspect of design safety of humanity is at stack . This is totally against the PEC Code of Ethics. This is against the PEC Code of Conduct. Allah has bestowed us with great knowledge and brain to use for serving humanity and earning rizq e halal. We do use our brains rightly. We should stop this corruption by whatever means we can do.We must spit these non-professionals out of our community. This forum is one of the unique voice of structural engineering community, people comes here to get and share knowledge. I request to all the members that will stand with me on this issue. There is immense need to educate people that structural engineering is a business of life/economy saving, the fees structural engineers charge is nothing in comparison to the cost of lives lost during any incident due to incomplete and false designs or more accurate no designs. Regards
  5. 4 points

    Tie Spacing Smrf

    Dear waqar saleem, Here are my 2 cents: 1. Section of ACI 318-08 deals with flexural members i.e., beams and NOT columns. In case of columns of SMRF, ACI section is applicable. 2. For calculating the tie spacing, the applicable member parameter is 'minimum member dimension' of the column, which is 12 inches in case of 12"x15" column. So, the controlling tie spacing for seismic zone 3 will be 12"/4 = 3" (and, NOT 2.625", as calculated in your post.) 3. A column tie spacing of 3" has generally no problem in concreting, even if commonly used nominal maximum aggregate size of 3/4 inch is used. I frequently use this spacing in concrete columns, for buildings located in seismic zones 3 & 4 areas, without getting a single complaint due to closeness of ties. 4. As clarified in the commentary section R21.6.4.3, this maximum tie spacing is for confinement of concrete, rather than for shear. As such, use of a larger size tie bar would not help increase required spacing of ties in case of an SMRF. IMHO, The only parameter that may be helpful in increasing the required tie spacing, is the 'smaller dimension of the column'. However, in a double storey building, I do not see a need to increase smaller dimension of the column beyond 12", solely for providing ties at a spacing larger than 3". Regards.
  6. 4 points
    All I can understand from your post is that you are doing a comparison between two codes for Saudi and trying to find out quantitative difference of base shear? Also, I believe you want someone to check your numbers? Before you do that you need to understand the differences between UBC and IBC Seismic Design Philosophy; you aren't comparing apples to apples if you just compare numbers. There is a lot different between two codes. Both codes design to a different Maximum Considered Earthquake (MCE). Considering everything is constant, IBC will give you a higher base shear. Read the attached article:IBC and UBC Comparison.PDF Use the method provided in code to identify your seismic response coefficients. Ss=Ground acceleration at short (0.2 second) period, which will allow you to determine Sms and subsequently Sds. Code outlines the procedure to calculate all these components. I don't know why are you calculating Ss like you did. Documents attached are result output, and calculation is not attached. Without a calculation, no one knows how you came up with the numbers. My best advice to you, to check your numbers is to compare them with a solved example. You can't go wrong.
  7. 3 points

    column to foundation reinforcement hook

    Hooks bent inwards provide confinement and increase ductility. Thanks.
  8. 3 points
    (1). Structure Aspect Ratios The Horizontal/plan aspect ratio (Length to Width ratio) of the side block is 160/18=8.8 While its vertical/slenderness ratio (height to width ratio) is 60/18=3.33 I didn't come across any code limitations regarding these ratios But an indian research paper "Effect of Aspect Ratio & Plan Configurations on Seismic Performance of Multistoreyed Regular R.C.C. Buildings: An Evaluation by Static Analysis" concludes that, (a) The buildings with Horizontal Aspect Ratios 4 or less than 4, the seismic performance is reasonable. Above this, the worse effects of excessive forces, storey drift and displacement values may be obtained. Hence they should be discarded due to their unsatisfactory, weaker and unreasonable performances on the bases of above seismic parameters, which can cause detrimental and disastrous effects or otherwise be treated with the enough earthquake resistant elements. (b) The buildings with Vertical Aspect Ratios less than 4, the seismic performance is reasonable. Above this, the worse effects of excessive overturning, storey drift and displacement, period of vibration, etc. values may cause detrimental and disastrous effects to the buildings. Hence slender building configuration, as far as possible, should not be chosen, or otherwise be provided with the adequate earthquake resistant solutions. (2). Flexible Tower on Rigid podium UBC-97 Section 1629.8.3 item 4 says "Structures having a flexible upper portion supported on a rigid lower portion where both portions of the structure considered separately can be classified as being regular, the average story stiffness of the lower portion is at least 10 times the average story stiffness of the upper portion and the period of the entire structure is not greater than 1.1 times the period of the upper portion considered as a separate structure fixed at the base." And UBC-97 Section 1630.4.2 Item 2 says 2. The following two-stage static analysis procedures may be used for structures conforming to Section 1629.8.3, Item 4. 2.1 The flexible upper portion shall be designed as a separate structure, supported laterally by the rigid lower portion, using the appropriate values of R and ρ. 2.2 The rigid lower portion shall be designed as a separate structure using the appropriate values of R and rho. The reactions from the upper portion shall be those determined from the analysis of the upper portion amplified by the ratio of the (R/ρ ) of the upper portion over (R/ρ ) of the lower portion.
  9. 3 points

    Special Seismic Data Input In Etabs

    Special seismic data in ETABS, is used for the enhancement of normally calculated seismic forces, in specific conditions as required by Division IV of Chapter 16, or Chapters 18 through 23 of UBC-97. Inclusion of special seismic data, results in the use of special seismic load combinations of UBC section 1612.4, for the design of structural members. Parameter 'Em', used in these special load combinations, is described in section 1630.1.1 of the code. Generally, special seismic load effects should be included in ETABS models, for all those structural elements for which the code (UBC) requires the use of special seismic load combinations of section 16.12.4. According to Division IV of UBC Chapter 16, special seismic load combinations are to be used in following cases, among others: a. For elements supporting discontinuous systems, as described in Section 1630.8.2. b. For collector elements, splices, and their connections, in accordance with Section 1633.2.6. Regards.
  10. 2 points
    SEs United

    Etabs Analysis Warning Kindly Help

    Dear Umar Thanks for your reply well i am gonna look into that auto line constraint i.e. what it does. but i resolved the issue some other way around. this is what happened. 1. When i selected all shell objects to mesh them. it so happened that etabs also selected the slab in which i had marked opening. and after the meshing was done etabs subdivided the opening too. 2. when i selected all shell objects to apply loads etabs selected the opening too and applied load on it as well. so when i ran the model check i found the slab label in which problem was present and well it was the opening and etabs could not transfer the load there. so that was the problem. Solution : i deleted the subdivided (Meshed) opening therefore the load applied on it was also gone. then i created the new opening. and there is not warning now.. Thank you again for replying
  11. 2 points
    Saad Pervez

    Re entrant Corners and Vertical Irregularity

    A: In my opinion, both sides, this is to exclude an architectural projection e.g. a patio roof from this definition. A: ACI318-11 R21.11.7.5: "....collector elements of diaphragms are designed for force amplified by a factor Ω ..." so collector elements will be designed using overstrength factor in strength design method. A: diaphragm chord and drag members are not separate elements, they are part of the diaphragm. The components at the diaphragm boundary acting in tension and compression are known as tension chord and compression chord. Drag members have 2 types, collectors and distributors. Both are part of the diaphragm, a collector is an element that takes distributed load from the diaphragms and delivers it to the vertical element, a distributor takes force from the vertical element and distributes it into the diaphragm. See attached images. A: Motion of projecting wings can be ignored if dynamic analysis is performed along with finite element analysis aka ETABS model. A: If your stair case is not forming part of the lateral force resisting system and is not connected to diaphragm you can ignore this. A: Please see the attached flowchart published by SK Ghosh, it is very helpful.
  12. 2 points

    Torsional Irregularity according to UBC97

    Yes you are right. If loading direction is X, check x displacements on point 1 and 2 on the edge that is perpendicular to loading direction. Following will clarify; 1. Load in Y Direction Source: FEMA; https://c.ymcdn.com/sites/www.nibs.org/resource/resmgr/BSSC/Topic09-SeismicLoadAnalysis.pdf and 2. Load in X direction: Source: Reinforced Concrete Design by Tranath
  13. 2 points

    Shear wall location

    Divide the structure into blocks with regular shape (like center portion with open yard being a block separate by joint). The multipurpose hall (only this has basement??? provide more sections) so separate it from rest of building. Then analyze and design it like regular frame structure for zone 4 and steady the results. Only then you can go for Shear Walls.
  14. 2 points
    1. Your observation is correct that Sin(6.8) on calculator = sin(radians(6.8) provided your calculator is set in degree units. What you have used in Excel formulas [ sin(radians(6.8) ] is correct if; the angle 6.8 originally was in degrees. Was it in degrees? See the formulas you have attached in Excel. I do not think so. Why? Because circular frequency (w) is usually is rad/s. So your units are already in rad and you do not need convert them further and Excel is already set in rad units so just use directly the sin(6.8). This is what @Saad Pervez pointed out.
  15. 2 points
    In Excel, default unit for trigonometric functions is Radians. You're using the formula SIN(RADIANS(VALUE)). You're forcing excel to assume that the value already in radians is in degrees. SIN(6.28 radians) should be zero, using your formula the value is 0.11. Remove the RADIANS(), use SIN(VALUE) instead.
  16. 2 points

    Shear wall location

    1. You need to divide the buildings to avoid irregularities especially in zone 4. 2. start with a crude model, no shear wall (only columns) and try to get the general feel of the structure. For that you could also roughly estimate the gravity loads (for mass source). For example 15-20 kpa let say (including sw+sdl+ll) as gravity load. 3. Iterate by putting in shear walls where you need it. Once the crude geometry is finalized you can go for detailed modelling/design and you will find out the importance of concept stage design at early stage.
  17. 2 points

    Detailing Software

    CSI SAFE also has a Detailer. You may export ETABS results to SAFE and using the commands available under its 'Detailing' menu option, it will prepare structural drawings for you. You may give it a try to see whether it fulfills your requirements or not. Regards.
  18. 1 point
    Saad Pervez

    Quantity Takeoff software

    You can take off quantities from etabs as well, I have worked on BlueBeam Revu, quantity take off is severely limited, you still have to draw and mark everything on plan, it is not automatic.
  19. 1 point
    See the attachments. It answers your question and explains the fundamentals as well. Inelastic_Seismic_Behavior_Notes.pdf
  20. 1 point

    STAMPING Structural DWGS; a crime or corruption

    I think one do not need a PhD to differentiate right from wrong, if he ask himself. The minimal should be "Does my action causes danger to the life of any human being?" Rest paves out as we go from time to time, and from moment to moment. But then there are engineer who act against another engineer, or he's not ready to help a fellow engineer. That's a problem specially in Pakistani engineers. Like Pakistani architects use AutoCad (Cracked) and he does not impose himself on another Architect, by saying "Go! and buy a licensed AutoCad!!!!!!". They just work and help another architect. Sadly, you can not say this for engineers. Same goes for PEC..... Architects register with PCATP once. They do not register again if they want to be a consultant and pay in thousands. Similarly, they do not pay again and again if they want to be a contractor/constructor. ....... Engineer Engineer Ka Dushman Hai !!!!!!!!! (Buhut maazrat K sath)
  21. 1 point
    You can assign end releases for moment to beam connecting at a joint with column, for that joint specifically. This will model the end condition transferring all the forces except moments from column to beam end.
  22. 1 point
    Hi Suveksa, You can model the connecting ends of column and beam as pinned. Thanks.
  23. 1 point

    Expansion joint in irregular building

    Yes it looks okay.
  24. 1 point
    That is a common FEA problem. You get infinite stress at supports due to infinite stiffness.This is a problem of stress concentration. For commercial design purposes what you did is okay.
  25. 1 point

    Welcome Everyone! :)

    Welcome aboard Fatma. Bienvenue à bord!
  26. 1 point
    Assalamualaikum SE Pakistan in this pca seismic guide detailing it says that the rebar hook shall be bends towards to the center of column but i always see the bend is towards to the outer of column, which one is right? and why? all the best
  27. 1 point

    Joint reactions along local axes in ETABS

    Solutions; 1. Why dont you import the cad drawing (as shown in image) into SAFE and draw footings with proper orientation? 2. Like you got reactions under so many combinations from ETABS for each column, in the same way, you could select all columns and export to EXCEL the local forces at and then filter for zero location and proceed with manual design. 3. Get global reactions (like you did already) but one group at a time. By one group i mean all the columns on one radial grid line. All columns on that grid will have same orientation and angle right. Export to EXCEL, transform forces in XY to that angle. New rotated forces will be; Fx' = Fx Cos theta + Fy Sin theta Fy' = -Fx Sin theta + Fy Cos theta there you go, you now have the new rotated forces. Repeat it for each radial line and then design footings manually.
  28. 1 point

    Purpose of design strips in safe

    Generally to keep construction simple, people go with maximum reinfo throughout unless the max reinfo is too big. If that is the case, they use additional bars at critical locations.
  29. 1 point

    Building Drifts In Etabs

    "Ever since strength-level (as opposed to service-level) design earthquake forces were introduced in the 1997 Uniform Building Code (UBC), as indicated by a load factor of 1.0 on E in strength design load combinations, it has been required that drift computations be done directly under those strength-level forces. The drift limits were adjusted accordingly. You never reduce the strength-level design earthquake forces to service-level forces for the purposes of drift computation. This is true of the 1997 UBC, all editions of the IBC, and all editions of ASCE 7 since 1993." My original post is referring to use strength level load combos in the light of justification provided. In addition to that, using dead and live loads with earthquake is a good idea as they cover any lateral deflection due to gravity load (mostly observed in non-symmetric frames) which wouldn't be accounted if only earthquake load case is used. Thanks.
  30. 1 point

    P-Delta Analysis In Etabs

    There are a number of resources. You can start from here: Thanks.
  31. 1 point

    Building Drifts In Etabs

    Inter-story drift limitation is intended to limit the damage. Abs disp of max point of upper stories wrt to base is to check for seismic separation. Both checks are must.