Modeling Pedestrian Bridges Using Autodesk Robot | Part 4 - Wrapping up

[@donaldkhanye9011]

Hello CEE, I would like to dispel the notion that last videos in a series may be inherently less interesting. As is mentioned by yourself, it is important to wrap-up things properly. These videos do just that, and they additional help to connect the final dots, to confirm, and to reinforce the application of the ideas learned and introduced throughout the rest of the series. For me this is an important learning step on its own; what may seem obvious and simple often turns out to be something else and it is good when there is a wrap up video that shows and confirms the work. I do not find these videos disappointing, I find them necessary and they serve as important “….haah….and…..aha....moments…..” Thank you for making these the way that you do. 0:18 I am glad that the CEE “…did not just hand wave…..” 😊😊😊 the lateral stability discussion. Indeed, most codes do have similar provisions and guidelines for beams slenderness limits and associated limits on the distance between lateral restraints. Clause 5.9 of Eurocode 2 (EN 1992-1-1) for example is one such code that certainly make a curious reading in this regard. 15:51 😊 I like these “Rabbit holes”, they leave “bread crumbs” and gives necessary hints to the “behind the scenes” and to the real extents of many issues and topics that are covered in this channel. About the “influence surfaces”, maybe Mr. Editor could add this to the “Current Video Ideas for the Future list”? 20:44 I concur with the various loads’ types and the general estimates that have been included. I think these loads have covered all the key areas of the loads that are required. The WisDOT guide that CEE shared in part I is a huge eye-opener with regards to what is to be included in this regard. 23:35 Nice tip on Contour v/s Contour Edge (#); simple as it seems, this could become handy in other models and applications, thank you for this. 27:40 Mr. Editor sir, you make very good points, keep it up! 29:10 ***1.6 LIVE !!!!!*** 😂🤣😂. With regards to Mr. Recorder performance, my view is that Mr Recorder is actually doing great, all things considered 😊. He does cover pertinent details to rouse interest throughout from the beginning of the video to the end. 30:33 With regards to the deflections that Mr. Editor is pointing out and considering that the beams and the deck slab used in this model are currently modelled as concrete, and that concrete deflections are influenced by its reinforcements and also by the period of loading (long term deflections). How meaningful are the immediate deflections from the analysis in case of a concrete model? Is it possible to display long-tern deflections for RC concrete elements as part of the entire model in RSAP? (I know that the RC beam element design module does display long-term deflections and incorporates rebars effects on deflections) General Questions: A) Releases (😊): I have released both ends of my beams and both ends of my deck slabs [I have made NO releases on any of the piers themselves]. All pier supports are behaving as expected (simply supported in the same way as it is showing with the center support @18:37 on this tutorial video) [but in my case, this is so for all the support piers, and not just for the central pier] I am happy with this arrangement and all seem to be working as I want it to. The challenge I have is as follows: 1. I had “assumed” that by doing the above releases in the way that I did, it means that “the deck slab is now primarily a one-way spanning slab that is supported on the beams only. Therefore, minimal to none bending moments will be present on the deck slab in the direction parallel to the supporting beams [the x-axis direction in the current model]? 2. To my surprise, when I create a panel cut (say for a Dead Load Moment along the xx direction) parallel to the XZ plane along the centre line of the deck slab from one pier to another, I get a simply supported BM diagram between the piers. This is theoretically correct and it is as expected except that the value of this moment in my case is about 60kN.m at mid-span along the deck slab centre line; And if I now create another panel cut (for the same Dead Load Moment but now along the yy direction, i.e. along the direction of the supposed one-way spanning deck slab) in the perpendicular direction (along the YZ plane) at the same mid-span position only now crossing or cutting through both the supporting beams and the deck slab, I do get the expected BM diagram shape of a simply supported beam with extended cantilever ends on both sides as expected BUT the value of this BM diagram at the mid-span position (this position coincide with the same last position from which I read the 60kN.m when looking at the XZ panel cut discussed above) is now 1.3kN.m ??? What gives? If the deck slab was indeed spanning one-way in this direction, shouldn’t its BM be the largest in this one-way spanning direction as compared to the long (unsupported) perpendicular direction to this one-way spanning direction? If one were to design rebars using these BM moment values, the most rebars would be along the XZ plane and this is not right? There is hardly any support for the deck slab along this plane. What am I missing? 3. How can one make sure that the deck slab is indeed one-way spanning between the beams in this case? B) Cast-in-place RC, Precast RC, and Prestressed beams options for the pedestrian bridge: A pedestrian bridge is usually constructed over existing “busy” roadway, and as such the conventional in-situ construction of RC elements which requires temporary support scaffolding (located at and blocking the use of the roadway for the duration of the construction period) is not ideal. I would therefore imagine that the analysis results from a model such as the one here are used to (for example) select or to design pre-cast or prestressed concrete beams capable of resisting the maximum BM and SF? And spanning the considerable spans that are involved? I know that I have asked a similar question before and CEE indicated that it may be considered on the highway bridge series that may be yet to come? For now, is there a quick way to size say an AASHTO/PCI STANDARD I BEAM(S) based on the analysis results obtained from our model in this series? Which key outputs are required? Perhaps CEE could consider a tangent video to touch-up on this? The span of the simply supported beams in this model is 13.25m c/c of the supports. In a “perfect engineering world - which unfortunately does not exist 😊” Which option would CEE consider to be ideal for such a pedestrian bridge? a reinforced or prestressed beam option? What would be the main or key engineering related influencing factors to this decision other than cost? (of course, cost will not be ignored). Your tutorial videos are always a pleasure to watch. This one is no exception. Thank you for the pedestrian bridge series and for the associated tangents covering pattern loading and influence lines. I am looking forward to the next adventure. Ps. I have a proposal for a possible future video tutorial for your consideration and I will write it up on a separate comment here. Have a great day, and I’ll see you in the next CEE video. Regards, DK

[@CivilEngineeringEssentials]

Hello Engr. DK, I guess you are kind of right. Somehow, wrapping everything up may give insights of what was done, and some food for thought for the future. I told the Editor to add the influence surfaces to the list of videos to be covered. Thanks for the suggestion, it really helps. Also, indeed, the WisDOT doc is an important doc. I guess this is the reason why the theory parts of those structures is equally important. That is the reason why in that instance, I just added me some loads. This is basically the first time Mr. Editor has his own "explanation of things". I guess his debut was well received. Now I do hope he does not have to jump with his own explanations often. But I guess that I missed the deflections so Mr. Editor came to the rescue. oooooooooooooooooooooooooooooooooooooooooh the immediate def. vs long term def... This is a really really really interesting topic. Now truth to be said, I usually heard stuff like (the long term deflection is 2.5 times the short term) But I want to personally dive into this and check out that thing. Indeed, here are the problems in the deflection you get from any FEM commercial software (Robot, SAP, ETABS, PROKON, STAAD, AxisVM, Dlubal RSTAB):::: 1) The deflections you get are under the elastic theory 2) The deflections you get do not account for cracked section Inertia 3) Even if you input the cracked section inertia, those deflections do not account for ANY long term effects. This is a topic definitely worth checking out. Ok now to your questions: Gimme a moment I will address them one by one

[@CivilEngineeringEssentials]

Continued: I just realized in Q1 that you are right. But I have an explanation for this: The current model does connect the slab with the beam with no release between the slab and the beam. This means that: whatever moment that is on the beam, would also result in rotations. Those rotations are then also affecting the slab (because no release between beam and slab). And those rotations would produce moments in the slab. Please note that: this is the reason why codes allow beams to take some parts of the slab into account as their upper flange. Now if you want to totally eliminate this, do not use offset, but use compatible nodes. It will take some time, as you might have to split the slab into 3 parts. For Q2: For a pedestrian bridge, I would immediately opt for a precast non prestressed PCI girder. Now those PCI girders have well-known application ranges that are already established. The document that is shared now is based on prestressed concrete, but could give an indication for non-prestressed members. drive.google.com/file/d/1T7NM02P8HG4D3JTCh8U6Njr6n9Grp2eP/view?usp=share_link Please note that the initial design of bridges is still the topic of research today. There are a million things that get into the mix: number of girders, stresses in girders, cost, deckslab, and so on. Here is a to a research profile having two research papers about it: scholar.google.com/citations?view_op=list_works&hl=en&hl=en&user=kOKFPw4AAAAJ Still, drawing from an actual experience I had, we do have constructed the girders and deck slab within 48 hours. In that case, we diverted one direction of traffic to the other direction for one day, to finish one span, then vice versa, we diverted the flow of the other direction to the first direction for 48 hours. The rest of course was finished in normal speeds. It was kind of a hassle and I had to be present there 16hours per day. But it was a success. I hope I did not miss any question you had. Regards, CEE

[@donaldkhanye9011]

@@CivilEngineeringEssentials Thank you for the feedback. Your deflections discussion is really really really 😊 enlightening. I am curious to see what the CEE may find from the possible stated dive on this topic. Your response have also pointed me to review the assumptions, limitations, and/or options which a software manufacturer may have published on this topic as it applies directly to the various structure types that are used on their software. Kind regards, DK

[@donaldkhanye9011]

@@CivilEngineeringEssentials For Question 1: a) I hear the explanation as to why there are relatively larger moments present on the deck slab in the direction parallel to the support beams. However, if one were to design the deck slab based on these moments results as they are, would it then make practical sense that there are more design (bending) reinforcements in the direction parallel to the span than there is (bending) reinforcements in the actual direction of the span itself? b) Regarding the flanged T or L concrete beams cast integral with a concrete slab; and the option to release the slab from the beam [if required] using compatible nodes is something that I will still have to try out and compare the results by using verifiable fundamental situations in order to see if I can figure out how it all works in RSAP. For Question 2: a) Thank you for the reference. From the design charts, it is quite clear that indeed extensive work have been done to establish certain products and their application ranges with confidence. It is amazing how far one [an experienced designer] can get with these by simply having just the span and the loading vehicle information in order to start [no analysis or calculations appear to be necessary at the initial design]. b) The G.O.A.T research profile, 😊: Ooooooh, what a treat. I will definitely browse and read through what I can; thank you so much for sharing Doc. c) 48hrs Construction: Wow…that was hectic, I am glad that it was a success. Yes, you have addressed all my questions that I had posed, and then some 😊. Thank you, and kind regards, DK

[@CivilEngineeringEssentials]

Hello dear Engr. DK, as for Q1, Indeed, there should be a way to eliminate the longitudinal moments in the slab to better fit the real construction circumstances. I personally do not think that for the slab discussed in this video, if the slab is constructed above the girders, and not cast together with the girders, I believe that the slab should not be designed for longitudinal reinforcements. It is kind of intriguing, because each modelling result has implications in the in-situ construction and structural detailing. This is what I love in structural engineering, and keep mentioning every now and then in my vids. Also, here is a good for thought that I have not yet mentioned in any video, in case you monolithically cast the girders and slab, an approach is to treat the entire bridge as ONE BIG GIRDER.. it is an amazing approach indeed, and you would see in the pdf (if I remember correctly) there is a double T section (just to get an idea how it would look like). I need to dig a little bit deeper about how to force RSAP to consider the case of slab on girders. I will check about it. As for the research profile, well, I am still not a professor, I mean, a 34 (almost 35) year old assistant prof. is still a "n00b" in the research realm of science. But I am doing my best. Oh just to clarify, the 48 hours was only the placement of the girders on the piers, the project itself, of course, needed more time. The planning for that day took a while, we erected the piers, brought the precast concrete, did all measurements and checks, and then lifted each span within a day. No slabs, nothing, just the precast girders. Then, we put 5cm concrete slabs that are gonna act as both formwork and part of the slab. those slabs had shear connectors and we had to basically put our steel meshes and cast concrete on top of those. The concrete cast could theoretically be done during day, but to limit danger, we had to rely on night concreting for the jobs. It was a kind of nice experience. Regards, CEE

[@ofodilemichael179]

I commend you for these great RSA tutorials. I would like to propose that you consider making videos on RC pile cap foundation/pile design. Looking forward to it, Thanks.

[@CivilEngineeringEssentials]

Hi there I am glad you like those vids. Indeed, I am thinking of starting the lecture series besides the RSA series, and definitely would consider those cool topics as viable to be done. Stay tuned for more content. Regards, CEE

[@jesuscandea512]

Thank you so much for the mention! , you have become my weekly checked channel 👌🏻 Btw you pronounced it correctly

[@CivilEngineeringEssentials]

Hi there, Great ^_^ most welcome. I am happy you like the channel and follow it. Stay tuned for more content. Regards, CEE

[@salaheddine6721]

thank you👋

[@CivilEngineeringEssentials]

Most welcome. Stay tuned for more content.

[@youyoutarikt7015]

Lot of benefits thank you so much brother

[@CivilEngineeringEssentials]

Most welcome, stay tuned for more content.

[@donaldkhanye9011]

Hello CEE, If I may, I would like to propose a future video tutorial idea for the CEE consideration as follows: • Modelling and Design of stiffened RC raft foundations for light structures (using finite element method in RSAP). • The particular foundation that I am referring to comprises of a RC floor slab that is cast monolithic with a grillage of RC rectangular downstand beams. • This type of foundation is mostly used in residential housing and in other light public or commercial structures founded in expansive (heaving clay) soil. • Some of the empirical and rational stiffened raft foundation design methods include Lytton Method, Lytton and Woodburn method, Walsh method, Mitchel method, Swinburne method, etc. • Follow on from the previous CEE tutorial video on the “…Modelling Mat (Raft) Foundations (Flexible Method)…” I have tried to model the above requested “stiffened RC raft foundation concept for light structures” by defining an “Orthotropic” floor thickness using RSAP pre-defined template of a floor with “one-sided, bidirectional ribs” Whilst this approach does “perfectly” allow one to model the stiffened RC raft geometric parameters that are required. RSAP help files (support and learning) noted and confirmed that for a slab that is defined in this way, the “…local change of rib stiffness is not recognized; the exact slab geometry is not visualized and it is not recognized during calculations of reinforcement….. Reinforcement calculations for this type of slab will not provide correct results. A new algorithm for slab reinforcement should be implemented that would recognize a T-section or an H-section. Therefore, the reinforcement calculations for this type of slab are carried out as if they were homogenous slabs with invariable cross-section….” knowledge.autodesk.com/support/robot-structural-analysis-professional/learn-explore/caas/CloudHelp/cloudhelp/2022/ENU/RSAPRO-UsersGuide/files/GUID-2000B438-5453-4C90-B658-E3DE6F8AF33A-htm.html • In practice, the beams (placed 2m to 4m centres) and the integrated floor slab (usually 100mm to 150mm thick or more) are each reinforced “separately”. The beams are reinforced as rectangular beams sections with both top and bottom rebars and the floor slab is reinforced with either a steel fabric mesh reinforcement or with normal top and bottom layers of slab reinforcements. “standardised” detailing of stiffened RC raft foundations containing mesh reinforcement in the floor slab was for example recently (2019) withdrawn from the New Zealand building code NZS3604 in favour of calculation methodologies and design by engineering principles. The mesh reinforced floor slab is (according to the ideas leading to the above withdrawal) viewed to be flawed in that “…the 100mm thick floor spanning between beams at 2.5m centres is unlikely to be sufficiently stiff and strong. The slab needs to be both capable of transferring soil expansive forces to the beams and spanning between the beams should the soil contract away from the underside….” • If one were to keep things “simple” 😊, what options are available in RSAP to determine the values of the Moments and Shear forces for which to design a) each of the beams in each of the perpendicular directions? b) the integrated floor slab required reinforcements as a two-way slab? • Could this problem be modelled or be approached in more than one way in RSAP? Can the CEE illustrate the various conceivable or available approaches side by side 😊 if possible? I know it’s a tall order but the CEE is the G.O.A.T that has proven capabilities and out-of-the box thinking beyond imaginations. Regards, DK

[@CivilEngineeringEssentials]

I see what you mean. Basically you have "inverted beams" that are on the raft foundation. I guess those inverted beams are also below the ground floor walls. Now I saw RC floor slab in your comment, but I guess you meant the raft, right? Indeed, whatever you use for the shell thickness (monolithic or not) will only affect the stiffness matrix, deflections and so on, but has 0 influence on the design. It will not design you those little things. I will take a look on that definitely, and also on your methods that you use. I am gonna prepare me smthn nice with that regard. It might not be in the next video, but definitely something worth to be checked. Thanks for being around, Regards, CEE

[@donaldkhanye9011]

@@CivilEngineeringEssentials To confirm. Yes, you are correct; basically, the system is comprised of “beams” and “a raft foundation slab”. The beams are however NOT inverted, they are located underneath the “raft foundation slab, which as you have correctly noted, I have also referred to this slab as a RC floor slab”. See attached typical layout of the beams under the slab. drive.google.com/file/d/1GdZ5vqNN0lF5Zmp8ZBWjpVSMnKXawfsC/view?usp=share_link The RC floor slab or the raft slab + the RC beams are together what I am referring to as the “Stiffened Raft Foundation” Additionally, this type of foundation can also be considered where the walls and floors of light structures such as residential houses are required to withstand a loss of support without collapse into sinkholes (for example) that may develop within the footprint of the structure. Thank you for considering this. There is definitely no rush from my side. I am just glad that the CEE will look at it. It feels really good to be around the CEE Channel 😊 Have a great day, DK

[@ofodilemichael179]

Thanks for these lecture series. I've gained a lot. 👍

[@CivilEngineeringEssentials]

I am really happy. Stay tuned for more content.