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  1. 3 points
    Great question. Current ACI design (2002 onwards) is based on strain limit and based on that you end up with tension controlled or compression controlled sections. Tension controlled being the sections where strain is steel is equal or greater than the limit provided by code (0.005 I believe). Previously (1963 to 2002), the reinforcement design was based on reinforcement ratios. This is where the terminology "under-reinforced", "over reinforced" and "balanced reinforcement" comes from. The simplest word to put this is that any steel that has strain greater than 0.005 (or whatever the code says) at time of concrete failure is termed as tension controlled. Both under-reinforced and balanced reinforcement sections will meet this criteria.
  2. 3 points
    EngrUzair

    Steel Truss Access Bridge

    1. Section 1.3.1 of AASHTO's Guide Specifications for Design of Pedestrian Bridges, 1997, states the following regarding the deflections:- "Members should be designed so that the deflection due to the service pedestrian live load does not exceed 1/500 of the length of the span. The deflection of cantilever arms due to service pedestrian live load should be limited to 1/300 of the cantilever arm. The horizontal deflection due to lateral wind load shall not exceed 1/500 of the length of the span." On the other hand, Section 5 of AASHTO's LRFD Guide Specifications for Design of Pedestrian Bridges, 2009, describes the following regarding the deflections:- "Deflections should be investigated at the service limit state using load combination Service I in Table 3.4.1-1 of AASHTO LRFD. For spans other than cantilever arms, the deflection of the bridge due to the unfactored pedestrian live loading shall not exceed 1/360 of the span length. Deflection in cantilever arms due to the pedestrian live loading shall not exceed 1/220 of the cantilever length. Horizontal deflections under unfactored wind loading shall not exceed 1/360 of the span length." 2. AFAIK ETABS 2016 can design steel connections. However, SAP2000 does not have this option. Regards.
  3. 3 points
    UmarMakhzumi

    Design Theories

    WSalaam.. ASD is design based on actual non-factored loads considering reduced material strength capacties. For example, for 100 kN load on a steel beam with yield of 350 MPa, you will design it using 100 Kn load and a strength of 2/3*350 MPa= 232 MPa. The reduction in material strength would provide safety, calculated as ratio of actual strength/ (reduction factor * actual strength). This ratio is called Factor of Safety (FOS). FOS would vary for foundations, steel or concrete design etc. ULS is based on factored loads (load factor as per the statistical probability of likely hood of occurance causing failure) with reduced material capacites. The reduction in material capacites is lower than what ASD has. Like for steel design, material reduction factor is 0.9 only which is a mere 10% reduction. ULS is improved and currently the way to go in most building codes worldwide. Some building codes even prohibit using ASD. The following link contains an excellent reply by @EngrUzair about cost Compairson b/w ASD and LRFD. WSD is same as ASD. Secant modulus represents elastic behavior between stress and strain values (as it is a straight line) whereas tangent modulus gives you relationship in any portion of stress strain curve (elastic, plastic etc). Thanks.
  4. 3 points
    Salam Alaikom fellow Engineers! I have found the "The Seismic Performance of RC Frame Buildings with Masonry Infill Walls" article very useful. So I would like to share it with you, especially for junior structure design engineers. Regards The Seismic Performance of RC Frame Buildings with Masonry Infill Walls.pdf
  5. 2 points
    Fatima Khalid

    Performance Point in Pushover Analysis

    to calculate participation factor, you first do modal analysis.. from first mode.. take the eigen values that would be the mode shapes at each storey... Take storey mass of each storey and solve it manually or using excel file.. By the way, if you want performance point, you can directly get from the SAP result where it shows caapcity and demand spectra. See the attached research paper for ur reference IRJET-V3I5479.pdf
  6. 2 points
    Ayesha

    SAGRODS AND SAP2000

    Legit request. Find attachment. 2011-12-lateral-stability-of-purlins-and-girts.pdf
  7. 2 points
    EngrUzair

    .

    Zebi, Please provide following information regarding degree program and the institution you have attended, to proceed with PEC:- 1. Full Name of the University with mailing address 2. Contact information of the University (web and email address) 3. Duration and Official Start and Completion dates of the degree program attended. Regards.
  8. 1 point
    BAZ

    Modelling Issues/consideration in ETABS

    I want to comment on some modelling issues in ETABS. Though some of these things are discussed elsewhere in the forum, I hope to extract some more useful conclusions. First thing is related to modelling the bending stiffness of flexural members, for strength level loads, that is representative of their condition near failure. The ACI code specifies the modifier of 0.35 on gross moment of inertia to represent its condition at yielding. Some people say that the factor should be multiplied by 2 to represent the stiffness of T-beam. This approach would be justified if you are not taking into the account the out of plan bending stiffness of slab. But, ETABS does include the out of plane bending stiffness if you have modelled the slab by using shell elements. So, a factor of 0.7 would overestimate the stiffness of your structure in this case, and will lead to under-design. If one has used the modifier of 0.35 in ETABS for beams in beam-slab floor system, then what value should be adopted for slab? It should not be 0.25, as this value has been specified for flat plates and flat sab floor system. If one is using some value of modifier for out of plane bending stiffness on shells, then the share of the bending moment in beams will be reduced accordingly. This approach is correct if one will be providing the reinforcement in column strips of slab. But, if you are providing reinforcement in slab in the direction perpendicular to supports only, i.e. beams, as is the general practice in Pakistan, then you are under-estimating the flexural demand in beams. Now, there is also a question of factors to be used while deciding the amount of reinforcement required in beams, columns and shear walls. If you are using factors 0.35 for beams and shear walls, and 0.7 for columns, then you are finding out the demand in members at the point of yielding, and this conforms to the code. But, this also means that the structure might experience unacceptable cracks widths. So, if you are using 0.35 for calculating the demand at strength-level forces, then you should also perform crack-control-check at service-level loads by using the factor of 1. If you are calculating the strength-level demand with a modifier of 1 for all structural members, after you have decided the location and the number of shear walls with modifier of 0.35, then you are overestimating seismic forces, as you are underestimating the time-period. But, the structural performance will improve.
  9. 1 point
    Salam, What is the difference between the under reinforced and tension controlled section? Are they same with the exception of strain values of steel.? Many Thanks
  10. 1 point
    ACI Code has not specified any stain-range for under reinforced beams. They just say that the beam should fail in tension before failure of compression region. By that definition, the tensile strain in steel must have a value of more than 0.002 before the compression strain in concrete reaches 0.003 for under-reinforced section.
  11. 1 point
    BAZ

    Building Joint Displacement/ Drift in Etabs

    After running the analysis, one way is to look for the symbol that is used for displaying the deformed shape of your structure. The deformed shape will be displayed against a load case, or load combination. Once you have deformed shape, right click on the node where you want displacements. Limits are already discussed in the forum. Use the search facility, either on google, or in the forum.
  12. 1 point
    Hira Malik

    Pile Foundation Book Muni Budhu

    BTW GOT THE BOOK AT [URL Deleted as it violates Forum Posting Rules]
  13. 1 point
    EngrUzair

    Pile Foundation Book Muni Budhu

    Check the following link. May be it could help. http://www.sepakistan.com/topic/115-pile-design/?do=findComment&comment=860 Regards.
  14. 1 point
    Ahmad Shafiq

    Performance Point in Pushover Analysis

    In addition to pushover curver (Base shear Vs displacement) SAP gives you the option of ATC -40 curve. So you can select that. Then go to the properties table of the curve and you can get the Sa and Sd values.
  15. 1 point
    Ayesha

    SAGRODS AND SAP2000

    You can model sag rod as bracing (Sag rod properties can be defined in a frame section and modelled as a brace) provided your design condition allows the sag rod to behave like a brace as I mentioned in the previous post. Once you model them, see the forces and design accordingly.
  16. 1 point
    Ayesha

    Steel Truss Access Bridge

    I think Uzair has replied to your question well. I was about to say the same thing for number 1 after checking my self. Try using a 4x4x1/2" or 3x3x3/4" as bracing. For top and bottom cord, go with a lightweight 8" section (like W200x36). Using 8" will allow you to do field bolts easily as 6" or less are tight for even 2 bolts. For L/r > 60, I am not sure what that is.
  17. 1 point
    EngrUzair

    Steel Truss Access Bridge

    For Seismic Design requirements, you may refer to AISC 341-10 specification, that can be downloaded from here for free. Seismic compactness requirement are given in Chapter D. In order to avoid above error, you will have to try ONLY those sections that are seismically compact according to AISC 341. To avoid this error, the slenderness ratio (l/r) of the steel sections to be used for concerned members must not exceed 60. You will most probably need to reduce spacing (or increase number) of column bracing for this purpose. Regards.
  18. 1 point
    Ayesha

    Steel Truss Access Bridge

    1) What are the section sizes that you are using. Please list the original ones as well as the updated ones. 2) What is the Sap2k error code of l/r > 60 message?
  19. 1 point
    EngrUzair

    STAAD FLOOR LOADS

    Yes. It is possible. But you must make sure, either by confirming from the architectural drawings, or the designer. Because the software model must conform to actual loading requirements, as indicated in architectural plans & relevant loading code. No. Floor Load is a specific command, indicating two-way load distribution. For one-way load distribution, STAAD uses ONEWAY command. Self weight of members defined under MEMBER PROPERTY command is automatically calculated by the software, when SELFWEIGHT command is used (as shown in second line of the following quote). Hopefully, it should be clear now. Regards.
  20. 1 point
    EngrUzair

    New system of categorizing posts - SEFP

    Here are my thoughts on the topic under discussion:- 1. The idea of re-categorizing the posts appears to be attractive. However, following points must be kept in mind in this connection: a. IMHO qualitative ranking of questions will certainly be a challenge to deal with. Firstly, because unfortunately even engineering education in our country is not upto the desired standard (as compared to that in advanced countries). Our students do get very good grades during studies, but their level of understanding & practical knowledge regarding engineering matters is not that good. Accordingly, many engineering concepts that are basic internationally, are not that easy to understand for our young engineers. Secondly, a piece of knowledge, no matter how basic or simple, will be difficult for me, in case I have not read about that earlier or have not been exposed to somehow during my field practice. Similarly, any engineering knowledge, no matter how much advanced or complicated, will be a piece of cake for me, if I already have know or have exposure to it. b. In case, we are determined to accept the challenge, than we will have to develop basic FAQ to a greater depth and to the most basic level, keeping in view general level of perception of our own engineers. 2. Assigning various forums to different moderators might not be beneficial for the forum or the members, as it might result in delayed replies to the queries, in case the concerned moderator is unable to see or reply the question, because of other commitments / unavoidable circumstances. 3. In addition, it would also a very good idea to add professional type sample Design Calculations in the forum (based on our own professional knowledge and experience) for various kind of civil engineering structures. This would certainly be helpful in developing professional sense in the engineering output of our young and fresh engineers. In the end, the idea of ranking the questions, addition of new sub-forums & improving the quality level of forum is appreciated and supported. Regards.
  21. 1 point
    EngrUzair

    STAAD FLOOR LOADS

    1. Above is an extract from your attached STAAD Input file. The last two lines indicate that two different uniform dead load values have been applied to the same floor area (ranging from 0 to 20 ft in X direction and 0 to 30 ft in Z direction), which is illogical & most probably indicated by mistake. In actual situation, these two load values will be for two different floor areas, for which at least one of the XRANGE & ZRANGE values must be different. 2. Here are two different sample situations for elaborating correct application of given dead loads: Situation A. 50 psf dead load for XRANGE from 0 to 10 ft and whole ZRANGE from 0 to 30 ft 122 psf dead load for XRANGE from 10 to 20 ft and whole ZRANGE from 0 to 30 ft STAAD commands for this situation are as under: YRANGE -10 0 ONE -50 XRANGE 0 10 ZRANGE 0 30 GY YRANGE -10 0 ONE -122 XRANGE 10 20 ZRANGE 0 30 GY Situation B. 50 psf dead load for whole XRANGE from 0 to 20 ft, but ZRANGE from 0 to 20 ft only 122 psf dead load for whole XRANGE from 0 to 20 ft, but for remaining ZRANGE from 20 to 30 ft STAAD commands for this situation are as under: YRANGE -10 0 ONE -50 XRANGE 0 20 ZRANGE 0 10 GY YRANGE -10 0 ONE -122 XRANGE 0 20 ZRANGE 20 30 GY 3. Now, what should be the actual values of XRANGE & YRANGE in your case? This will be clear from the floor details, as given in architectural drawings. You may ask the original designer to explain how he/she arrived at the floor load values (and even the other loads & design parameters) used in the STAAD model, if you are still unable to understand their basis. HTH Regards.
  22. 1 point
    Rana

    Lateral displacement due to earthquake

    AQ, there is nothing wrong with the conversion. I stated "87.5mmx10=87.5cm" which is 87.5mm for each storey x 10 storeys = 875mm = 87.5cm. This is the total drift of top floor relative to base 0,0.
  23. 1 point
    EngrUzair

    manual mesh vs auto mesh

    Please check the following link for clarification:- https://wiki.csiamerica.com/display/etabs/Auto+vs.+Manual+meshing Regards.
  24. 1 point
    EngrUzair

    STAAD FLOOR LOADS

    Floor loads may consist of several layers (slab itself, floor finish, ceiling plaster, weight of sand for sunken portion of slab to accommodate bath/kitchen piping to be laid under normal floor, etc). These may have different load types (e.g., dead or live) as well. Moreover, it is practically possible that two adjacent portions of a floor slab have different load values. For example, if one portion of a slab is to be made thicker for creating a raised platform, dead load being carried by thicker slab portion will be higher and different from the one having normal / lower thickness. All structural software (ETABS, SAP2000, etc.) have capabilities of applying above mentioned loads, through their basic commands & menu options. As such, STAAD surely has this capability too. I have used STAAD in the past. As such, if you could attach text input file of your model, I might be able to help clear your doubts. Regards.
  25. 1 point
    BAZ

    One day International Seminar (26 April 2017)

    A two hour session will be held in the Wah campus of CIIT. The attendees will receive a certificate which can be helpful for engineers in matters of PEC-registration. The speaker will be discussing the topic of performance-based design and evaluation of tall buildings. It is good opportunity for structural engineers to equip themselves with recent advancements regarding the structural analysis and design of tall buildings. The speaker, Dr. NAVEED ANWAR, who is executive director at AIT Solutions, is not only a Structural engineer, but also has been actively involved in software-development of CSI products such as ETABS, SAP2000 and CsiCol. Please find the brochure in the attachment for further details. CPD_Dr Naveed_1.pdf
  26. 1 point
    Saurav Bomzon Chettri

    Pushover analysis

    Push over analysis is mostly related to get the capacity of a building for max. displacement. Mainly used for retrofitting of old buildings.. Pushover curve is a strength-deflection curve.. Plot force vs displacement curve.. The pt. where the strength drops drastically is the limit of the storey, its the state describing the collapse of the frame..
  27. 1 point
    Rana

    New system of categorizing posts - SEFP

    I invite other members to also shed some light. For example it could be something like this; If a post is related to let's say wood design (and not to a specific software) we could ask the user to include tags such as "wood" in the question. I am opposed to making so many categories. That would create mess. We could control the sub categories by appropriate tags (strict policy to be imposed on users to input appropriate tags based on the materials /pre-defined sub-categories). All users to be requested politely to contribute in the proper section. For example some one asking how to calculate the time period should directly go to BASIC FAQs section and search the thread, if not found then post the question. Or we could enforce new users to post only in the #4 section, unless we see that the user is not a university student but a more experienced one. So we, as moderator team, could grant him permissions to post in all the forum anywhere he/she likes. This could be a bit more work for moderators but how many 'ACTIVE' users we have? Also this would keep the forum 'clean' and decluttered. Don't you think each and every group on Linkedin and other places are full of one famous question about ETABS i.e. stiffness modifiers? Every new comer post the same question. And also don't you think following two questions should be in two different categories; 1. What is the purpose of stiffness modifiers in ETABS. 2. Although not required by ACI codes, how do you guys model the shear stiffness of shear walls? To reduce f12 or not? etc. Most of the times a design issue is always related to a specific software issue, such as no.1 . So the categories I have recommended are not the final words. Just a direction to start the discussion on the topic.
  28. 1 point
    BAZ

    Existing Column joined to New Wall

    What is the question?
  29. 1 point
    rummaan17

    Slender Column Design - Second Order Moment

    Dear Mr.Rana Waseem, Thanks for your response. I am working on a tall building for which column magnification procedure is found to give inconsistent result. For elastic linear second-order analysis from what I understood, I am approaching as follows: 1. Assigning stiffness modifier to all structural members as indicated in ACI 318-11 10.10.4.1 2. Assigning eccentric column by using Frame insertion point option to option for addition moment from M=P.e. 3. For columns which have problem, I am dividing it into 5-6 segments depending on judgement to capture local P-delta effect of second order moment resulting from deflection in the chord of the frame element between nodes. i.e. M=P x d ( Small delta ) 4. Enabling p-Delta option in Etabs so that it can calculate moment that will result from deflection indicated in Step.3. 5. In design preference, I modified consider eccentricity option to "No" so that it doesn't consider additional moment as I have already defined it in Step2 and also put magnifier to 1. 6. After running the analysis, column with problem in loads that are close to Buckling load will give error. (Though I am still not in favor of conservative buckling load calculation made by ETABS). Any Addition would be appreciated.