SQVe Consultants
For safety and cost optimization of the structures, interface between geotechnical engineer and structural engineer is one of the important area. It is required that the interface should be carried out throughout the project cycle. In the next session of 4-OCT-20 (11:00am), we will attempt to highlight such important interface areas. The overall idea is to discuss and collate the important interface gap areas. Possible solutions for the collated areas may be taken up in the future sessions.
In the session, Vivek Kumar MITRA will join us as a Guest Expert. He is a geotechnical engineer having around 25 years of experience. He has worked in projects in the areas of Offshore, Infrastructure, Power, Refinery, Petrochemicals & Marine. He also handled with distinction various projects in Ports & Harbors, Artificial Islands, Dredging / Land Reclamation and Oil & Gas and Ground Improvement for ultra-soft soil. He is the Founder & CEO of VKM GEOTECHNICS which he started in 2019.
Link for attending all live sessions :
https://youtube.com/c/StructuralEngineering/Live
Link of the recorded session is attached below. Your further comments/suggestions are welcome on the stiffness modifiers.
You may also suggest topics which may be taken up in the next weekly sessions (Sunday at 11:00am).
Bhavin Shah
Founder & CEO, SQVe Consultants
Link for attending live session of 27-SEP-20 : https://youtu.be/wEom_O1i7LY
his is a very good question. Let me try to explain this with the simple language based on my understanding. For wind resistant design, the structure is designed to resist wind load under elastic limit. However, for earthquake resistant design, it is not economically feasible to design the structure to resist the earthquake loads under elastic limit. Hence, during extreme seismic event, the structure is expected to experience the inelastic displacements. In view of the above, the structure will be under elastic stress for the wind load case and will be designed to respond inelastically under the effect of earthquake loads. Due to the same, stiffness modifier concept might not have been considered for the wind resistant design for buildings less than 50m height (IS 1893 (Part 1) : 2016). IS 16700 : 2017 defines stiffness modifiers for wind load case as well (table no. 6).
stiffness modifiers are independent to the nature of the force but they are dependent upon the extent of cracks in the member. The structures are designed to resist the wind force within elastic limit whereas for earthquake resistant design, the structure has to undergo inelastic displacement. Due to this the extent of cracks will be lesser in the structural members for wind resistant design as compared to the earthquake resistant design. Hence, the stiffness modifiers values are different for wind load and earthquake load.
For buildings having height up to 50m, IS 1893 (Part 1) : 2016 to be referred. IS 16700 : 2017 to be referred for buildings of height greater than 50m but less than or equal to 250m. It is mentioned in Cl. no. 1.4 of IS 16700 : 2017 that the standard may be used for buildings of height equal to or less than 50m. It is recommended that IS 16700 : 2017 may be used for such buildings as it may add values to the design. However, it is not mandatory to use IS 16700 : 2017 for design of buildings up to height of 50m. It is mentioned in Cl. no. 1.4 of IS 16700 : 2017 that the standard is not applicable for buildings of height more than 250m. Buildings of height greater than 250m are considered as Super Tall Building (Cl. no. 3.13). I believe that special issues associated with the Super Tall buildings like safety of structure, serviceability criteria, different structural systems, wind effects, etc. might not have been covered in the code. Hence, it might have been mentioned that the code is not applicable for Super Tall Buildings.
Let me correct your understanding based on my experience. As per IS 1893 (Part 1) : 2016, only one model is required and the stiffness modifiers to be considered only for seismic load. As per IS 16700 : 2017, two separate models will be required as there are different stiffness modifiers for wind load (serviceability state) and seismic load (ultimate state). I hope it is clear. May share further doubts, if any.
In IS 1893 (Part 1) : 2016, there are separate stiffness modifiers for beams and columns. IS 16700 : 2017 defines separate stiffness modifiers for slab, beam, column and wall in table no. 6 (Cl. no. 7.2). As per IS 16700 : 2017, the sensitivity analysis is to be performed for multiple tall buildings connected with a common podium (Cl. no. 8.1.3). Table 7 indicates stiffness modifiers to be used for upper and lower bound solution while performing the sensitivity analysis. The sensitivity analysis is to be performed in addition to the analysis based on the cracked RC section properties, as defined in Table no. 6 (Cl. no. 7.2). I hope it answers your query.
As per clause no. 8.1.3.2.1 of IS 16700 : 2017, the stiffness modifiers are defined for upper-bound and lower-bound cracked section properties of floor diaphragms and diaphragms & perimeter wall of podium. Hence, there are unique values of the stiffness modifier. For more details, pl refer to the clause.
I agree with your views that stiffness modifiers may be included for shear wall as well. I believe it may be included in the next revision of the code.
As per my understanding the values might have been derived based on testing of the structures which are designed using conventional limit state design method principles. I think if we are limiting the crack widths as per requirements of un-cracked concrete then the values of stiffness modifiers may be increased. However, at present in the code, there are no different values of the modifiers defined for the structures which are designed considering the principles of un-cracked concrete.
As I understand that the stiffness modifiers are to be used only for structural analysis. After deriving the analysis results, the flexural / shear design to be performed using the conventional procedure of limit state design method.
In IS 1893 (Part 1) : 2016, stiffness modifiers are defined for structural analysis for seismic load case. The analysis results to be derived considering the stiffness modifiers. Thereafter, the design to be performed as per the conventional procedure.
Stiffness modifiers are defined with a fact that the RC structural elements would have cracks during their service life. For seismic evaluation and retrofitting of the existing RCC structures, you can refer IS 15988:2013.
The intention for introducing the stiffness modifier is not for load distribution, instead it is to account for reduced moment of inertia of different members due to cracking.
The seismic force values are inversely proportional to time period of the building, i.e. higher the time period lesser is the seismic force. The time period is again inversely proportional to the stiffness of the structure. Hence, even if for the constant mass values, relatively lower stiffness will result in the higher time period and the higher time period will reduce the seismic force on the structure. I hope it will clarify your doubts.
Bhavin Shah
Founder & CEO, SQVe Consultants
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(Clause 7.2.3)
Flexural Rigidity
(clause no. 7.2)
Element Unfactored loads Factored loads
Clause no. 8.1.3.2.1 (a)
Diaphragms & Perimeter walls of podium and below the level
Of backstay – Ieff / Ig – 0.5 (upper bound) , 0.15 (lower bound)
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Feedback of participants from the previous online courses:
After attending the course WIND-STR-001, I change my prospective towards structure and learn many concept.
The course GEO-STR-001 effectively addressed the gap between geotechnical and structural engineer. It not only covers important interface areas but also discusses consequences of poor interface. Subject experts have in depth knowledge and experience to address expectations of various participants ranging from fresh engineering graduate to highly experienced professionals. The course is interactive and experts are more than willing to address any queries of the participant. The course content is appropriately divided into multiple sessions over the weekend to allow flexibility to participants to participate and reflect during the week at their convenience. Overall, this course is highly recommended for structural and geotechnical engineers for gaining and enhancing the understanding of the very important interface between geotechnical and structural engineering work.
On attending to STEEL-STR-01 course with the multi discipline participates from across India is the best part of this course. As the questions raised and its solutions, are many a times very new for each other during the sessions which enhance our knowledge in different practical applications and approach towards it’s solution. I Recommend to join STEEL-STR-01 to all upcoming Structural Engineers.
This course related to STAAD.Pro and case studies was beyond the conventional software training. It helped me conceptualise the idea behind the behaviour of any structure, understand the special requirements between steel and concrete structures. Real life case study and interactive sessions made the learning more impactful.
STEEL-STR-001 was the best package for understanding the limit state design of steel structures using IS800:2007 along with its application in STAAD.Pro. Tremendous wealth of knowledge from Bhavin sir combined with queries by other participants really facilitated a great learning experience. Thank you for such an amazing course. I hope more such courses are on the way.
I am very grateful to Er. Dr. Abhay Gupta and Mr. Bhavin Shah for sharing your knowledge with us even though we have the same profession. Your course WIND-STR-002 helped me to clear many of the doubts I had sine the past 20 years.
At first I never expected the sessions which are going to be conducted would be so knowledgeable. Day by day listening to Abhay sir touching every aspect from the codal point of view, few from his own experience. The mixture of everything made this course WIND-STR-002 very valuable and useful. Before this course I was trying to learn from everywhere how does this wind dynamic forces are to be calculated but through SQVE consultants arranging this webinar and learning under experience fraternity was worthwhile.
I heard somewhere that we shall never use STAAD for dynamic analysis. But that wrong interpretation of the software was cleared through the course : STAAD-STR-001.
The course WIND-STR-001 is very informative. It clears basics of overall concept of wind flow. Thanks to Bhavin sir and Gupta sir for your guidance on wind loading.
STEEL-STR-001 is much awaited course. Finally the industry expert teaching the right thing with right methodology. I had never seen such an excellent online course like this. The amount of knowledge and engagement was extremely good. Thank you so much for the wonderful course.
Topics covered in WIND-STR-002 were new for me to understand, as it has never been covered in syllabus. But the way Dr. Abhay Gupta sir taught, explained the problems and shared his experiences, the subject got easy to understand. I feel proud of being his student.
The course WIND-STR-002 is very much informative as well as useful for practicing engineers considering the non availability of easy to detailed literatures and practical examples.
I am pursuing masters in structural engineering and steel was the topic that I found always challenging since my B.Tech times. Moreover this is also a missing topic for the syllabus of many universities in masters program. To understand its theory ,and execute it practically in software is really challenging and need a mentor for that. I’ve been following Bhavin sir from last few months and was it was my good decision to choose him as a guide. By the course STEEL-STR-001, now I can feel that I am in a position to explore boundaries of IS code, and also I’m enthusiastic to see how Euro code, AISC code and other countries code tackles the problem which sounds to be complicated in IS code.
STEEL-STR-001 is very wonderful course. I have learned many things through this course. During session Bhavin sir interaction with the participants is very great with clear explanations. We are expecting these type of courses in future also.
The Course WIND-STR-002 was very effective. It changed my perspective on not only wind engineering but also seismic loading analysis. Dr.Gupta also referred some excellent books which would not have been possible otherwise. Last but not the least, Dr. Gupta was kind enough to give me the charges of highlighting the errata for the Explanatory Handbook on Wind Engineering.
I would like to thanks and appreciate for this helpful course comprising of STAAD PRO Training and Design concepts for RCC and Steel. In this module I have learned in detail about essential concepts for designing industrial buildings and gained an understanding of different types of Analysis. I also acquired the knowledge of different types of Codes. Moreover, l was introduced with FEM, design of foundation, anchor bolts and connections. All the sessions were very interactive and engaging. The valuable knowledge that i have gained in these two months will certainly be propitious to start my career as a structural engineer.
I appreciate the course structure designed by Er. Bhavin Shah , which includes the theory and implementation of coddle provisions to software and interpretation of results. By attending it, I am able to learn and explore the analogy of a software – Staad Pro. Thank you very much for sharing the knowledge and make my doubts crystal clear…
I must say that he is a true professional academician…
Like a bridge between Institute and industry…
Bhavin Shah is a fantastic trainer, very friendly and encouraging, it was a well-delivered and presented course (STAAD-STR-001) that was well received by the group. There was a great balance between theory and practice and the concepts were clearly and professionally explained.
I am a budding geotechnical engineering professional. For three years I have worked as faculty in NIT and recently joined as project fellow- geotechnical engineering in a research Institute. Now I am in the transition phase of my career ie, shifting from academics to industry. My desire to become a geotechnical engineering consultant inspired me to join this course. As I don’t have much industrial exposure, attending the course GEO-STR-001 helped me to gain a lot of practical knowledge related to geotechnical engineering. Especially the discussions related to soil investigation, interpretation of soil report and interactive sessions were really amazing. Queries of other participants and the discussions associated with it,were really informative, as it mainly focussed on current industrial practices. Thank you Vivek sir and Bhavin sir for giving this wonderful opportunity. Hoping for a better support in my future endeavours too. Also expecting further courses related to this, in the coming future.
It has been an excellent course and given me an in-depth understanding on ETABS and STAAD.Pro software . I feel more confident in my understanding and it helped me complete my major project in my B. Tech course .Thank you for all the support and excellent teaching. During the training program all my queries were answered quickly.
The course STAAD-STR-001 was really amazing an knowledgeable. As I fresher I gained so much knowledge about all the little things I didn’t know that were so much important. Troubleshooting of the software was the most important topic as a single wrong interpretation of the warning can totally change the outcome. I heartily thanks Shri Bhavin bhai and SQVE consultants for introducing such wonderful courses so that we can perform good in practice.
The course WIND-STR-002 was so interactive and Dr. Abhay Gupta was so kind enough to listen to all queries and answer them in very great detail. Also time spent by Dr. Gupta is highly appreciated. Great job Dr. Gupta in spreading the knowledge.
REC-STR-001: The recorded sessions are more than anything for tackling practical difficulties…. and you bring some other professionals like dr. Jain and dr. Gupta is just like awesome experience for the student like me who are from tier-3 college who won’t get such a precious information… thanks to you also for the knowledge you impart… best luck to you and your team for this your initiative to resolve practical difficulties among aspiring structural engineers… 🙏🏻 once again thank you so much… because nobody in today’s era from structural engineering domain is wants to share the information, but you do… kudos!
Dear Sir thank you so much for your Course ETABS-STR-001. We learn Lot from here. Happy to Join this Course we are waiting for next Upcoming Courses.
The Staad Pro Training sessions were extremely fruitful, informative and it gave deeper insights into the field of structural engineering. Bhavin sir had not only taught us the software of Staad Pro, but he had explained us several technical concepts based on his field experiences. It was an interactive session where sir had asked us questions and it helped us think a lot and come up with solutions. Overall, it’s been a great experience and this 25 day of training has taught me a lot and has inspired me to develop greater passion towards civil engineering.
STEEL-STR-001 is very useful course for updating to new code for steel design of buildings.
It gives a good awareness about software as well as corresponding codal provisions. So one can get technical knowledge as well as how software using clauses giving in codes. Teacher is very patient, soft spoken and knowledgeable person. Topics selected in the course STEEL-STR-001 are very relevant, useful and to the point for design and analysis of steel structure.
STEEL-STR-001 was the best interactive course ,wherein all practical facts and limitations those are related with prevailing standards, software and practices were discussed. Vision was provided to participate towards solving such prevailing limitations rather following the same collaboratively. Course content was described very effectively and constant encouragement on experiments of the course deliverables and raising doubts and solving the same. Effective time management by faculty to satisfy all participants’ queries along with effective delivery of course content. 24 hour interaction facility was made available for solving course related queries.
STEEL-STR-001 : Excellent initiative to bring clarity of concepts to professionals.
The course content for STEEL-STR-001 has been thoroughly devised to be effective in best manner. Sharing of Recorded Sessions was the best part as I myself missed few end sessions due to office pressure but I could complete these later on. Making a permanent whatsapp group for discussion was also a good idea.
I really enjoyed throughout the journey of the course STEEL-STR-001 wherein I improved by Fundamental Knowledge in the Design of Steel Structures. Bhavin Sir’s explanation on Lateral Torsional Buckling and other critical areas, really helped me to become sound in manual calculations. Keep continuing the good work!
Bhavin Shah conducted very interesting discussion on the concept of stiffness modifiers (SM) as per IS 1893 (Part 1):2016. The participants raised many interesting questions. Few of them are mentioned below:
· What is the value of SM for PT beams?
· What are the values of SM for composite beams?
· What are the impact on analysis due to consideration of SM?
· What are the impact of SM on strong column weak beam concept (IS 13920:2016) ?
· And many more…
Please refer the recording of video for details. Your further comments/suggestions on the subject are welcome.
The concept of stiffness modifiers is introduced for the first time in IS 1893 (Part 1) : 2016. The clause no. 6.4.3.1 of the code defines requirements for structural analysis. It is mentioned in the clause that for structural analysis, we should consider reduced moment of inertial for RCC structures. For columns, 70 percent of Igross should be considered and for beams, 35 percent of Igross to be considered. This clause has generated many questions among the group of structural engineers. The overall objective of writing this article is to collate views/suggestions from the wider group of engineers. In the following section, I have attempted to give answers to few questions, received from different engineers. The answers are given for buildings having height less than 50 m. The comparison of stiffness modifiers with IS 16700 : 2017 & IS 15988 : 2013 will be done in the subsequent article.
Before this clause, in the structural analysis, we were considering 100% of moment of inertia for RCC beams and columns. In RCC member, the cracks will generate in the tension zone of concrete due to application of different loads. Due to these cracks, the moment of inertia of RCC member will be lesser than the gross moment of inertia. Hence, to account for the reduced moment of inertia of the cracked section, the concept of stiffness modifiers is introduced in the code.
The pattern and extent of cracks will vary substantially from structure to structures and members to members even in a similar structure. It is very difficult to assign the unique values of the stiffness modifiers for different members. The values which are suggested in the code are based on the numerous experiments and might have been referred from different international standards. The stiffness modifier value for column is higher than the beam since the columns will have higher axial compression than the beam. Hence, the extent of cracks would be lesser in the columns as compared to the beams. Hence, the stiffness modifier value for column is higher than the beams.
There will be two major impacts in the structural analysis results as compared to the model using 100% of gross moment of inertia:
1) Since we are considering the reduced moment of inertia, the overall stiffness of the structure will reduce. Due to the reduced stiffness, the structure will be relatively flexible and hence would attract the lower seismic forces.
2) Drift of the structure will increase because it is relatively flexible.
The stiffness modifiers should be considered only for the structural analysis. The analysis results to be derived considering the stiffness modifiers. The structural design to be done with the conventional procedure considering the analysis results.
The stiffness modifiers mentioned in IS 1893 (Part 1) : 2016 are only for ultimate condition, i.e. for seismic load case. The same modifiers should not be considered for the other load cases.
As per IS 1893 (Part 1) : 2016, no reduction to be considered for torsion constant, i.e. 100% of torsion constant to be considered for the structural analysis.
Generally, the stiffness modifiers are different for serviceability and the ultimate conditions. As discussed above, the stiffness modifiers defined in IS 1893(Part 1) : 2016 are for the ultimate condition. If we consider the same stiffness modifiers for the serviceability condition as well then the moment at beam column junction will be higher and the span moment will be lesser as compared to the model without stiffness modifiers. In my opinion, the span moment may err on the unconservative side, if we consider the same stiffness modifiers for the serviceability condition.
At present, I think it is not required for the shear wall & slab as per IS 1893 (Part 1) : 2016. It is only required for RCC beams and columns.
As mentioned above, the stiffness modifiers to be considered only for seismic load case. The structural analysis is to be performed with the seismic loads having stiffness modifiers. Thereafter, the analysis results should be used for design of the foundation.
Consideration of the stiffness modifiers will reduce the seismic demand on the structure. But at the same time, it will result in relatively higher drifts due to increased flexibility of the structure. The stiffness modifiers value should be different for the serviceability and the ultimate conditions. The stiffness modifiers are to be used only for structural analysis. The comparison of stiffness modifiers with IS 16700 : 2017 & IS 15988 : 2013 will be done in the subsequent article. The above mentioned answers are based on my understanding. If you have further questions / difference of opinion, then please share details in the below comment box.
Bhavin Shah
Founder & CEO, SQVe Consultants
As a part of a “weekly live technical discussion” series, Bhavin Shah conducted a live session for design of the gravity columns as per IS 13920:2016. We had a highly interactive session today on design of gravity columns as per IS 13920:2016. The recording of the same is attached below.
Your views/suggestions are welcome for the next topics.
For design of steel structures, IS 800:2007 was published before ~13 years. However, till today there are practical difficulties for performing the design in total compliance of the code may be due to several reasons like unavailability of detailed handbook with practical examples, gap between current software and IS code, doubts related to certain clauses of the code, interface gap areas between different IS codes, etc.
To bridge this gap area, we are glad to announce an online workshop which is specifically designed to address some of the above-mentioned practical difficulties. We intend to share the collated discussion with the concerned BIS technical committee for their perusal. The areas related to the software will be shared with the concerned software developer for further action at their end.
Let’s work together for improvement in our IS codes.
Bhavin Shah will be conducting the unique workshop named as “Decoding of IS 800:2007 for design of steel structures”on 18-SEP-20 at 3:30pm. The event is organised by Steel Structures & Metal Buildings (SSMB). The three-hour online workshop is specifically designed to address some of the practical difficulties being faced while design of the steel structures.
For registration and further details, pl visit : https://zoom.us/webinar/register/8916000766713/WN_dzSJQZv2SROlsoFtruNmjQ
We are going to initiate “Weekly Live Technical Discussion” series on the topics for which industry is facing difficulties. The topic will be decided in advance and the technical discussion will be conducted through the live stream at youtube. The sessions will be organized on every Sunday at 11:00am.
The topic for upcoming Sunday (13-Sep-20) is “Gravity Columns”. The concept of gravity column is included in the latest IS codes related to earthquake resistant design. I have received many questions from the practicing engineers like how to model the gravity columns, design of gravity columns, which columns can be considered as gravity columns, etc. In the upcoming session on Sunday, the technical discussion will be focused on the gravity columns.
The brief note prepared by Bhavin Shah can be downloaded from the below link. The note was prepared and shared with a purpose of initiating the discussion in the structures group at telegram ( link for joining the group : https://t.me/structuresgroup ). Bhavin Shah will give overview of the note and take up each comment/question/suggestion, etc. sequentially. You may post your comments/details in advance. While, posting the comment, pl mention your name, city & organisation (optional).
For participating in the session, simply click on the youtube channel link : https://www.youtube.com/c/StructuralEngineering/live
You may like or subscribe the channel to get notification when we are live as well as to get update about the future sessions.
Your input / suggestions are welcome for the next topics.