Cable Stay Graphic Static Analysis

[@PandaJerk007]

It's such a good idea to record instructional videos like this! I really appreciate it because there's almost no better resource you can access 24/7

[@professordeb]

Thanks...glad it's helpful. 😊

[@glennfelpel9785]

Your presentations on this and graphical truss analyses is excellent. There is much more understanding in this solution technique than in finite element solutions for the engineer. I still remember descriptive geometry studies.

[@mohammadzainmakhdoomi2ndd290]

Lovely graphic static videos please post more. Great work

[@professordeb]

Thanks...happy it helps.

[@SUKUMARVMST]

I would like to know more about graphic static analysis and Force Polygons.

[@alf3071]

How do you calculate this for a curver deck bridge?

[@郭秋浩]

Hi Professordeb, thanks for sharing this awesome knowledge. Just have a quick question, would you consider the self-weight of the mast? If the mast is made of reinforced concrete and inclined with some angle, would it will impact the forces within the cables?🤣

[@professordeb]

Yes, that's absolutely correct! This is a simplified analysis that is not considering the weight of the mast. In fact, Calatrava's Alamillo bridge in Sevilla, Spain, does not even have back stays because the inclination and weight of the mast is the basis for stabilizing the cables.

[@conorgallagher2096]

Hey professordeb, I am stuck on a similar problem to this. If there were no back stay and a rigid joint at the tower base, how would I work out vertical, horizontal and moments at the base? The horizontal force is especially tricky to understand. Any help would be greatly appreciated!

[@professordeb]

If I'm understanding right, you'd like to have a moment connected base rather than cable stayed, similar to the Alamillo Bridge by Calatrava. If that's the case, then you can still carry out the graphic analysis to find the stay cable forces, and then these would be applied to a secondary analysis of the cantilevered mast, using the horizontal and vertical cable forces and their respective moment arms from the base of the mast. A moment connection, though, would lead to a *very* large member to keep stresses down, unless the structure is smallish like a short footbridge. In the case of the Calatrava bridge, the moment is substantially balanced by the dead counterweight of the concrete mast itself, producing a HUGE balancing moment. I think it's one of his finer works.

[@conorgallagher2096]

Hey @@professordeb, thanks for the reply! The bridge is similar to the Alamillo Bridge apart from I am accepting a permanent large resisting moment in the foundation. However, would I also have to consider horizontal forces? I've attached a link to the problem for clarity. Thanks very much for the help! docs.google.com/drawings/d/1k3YNL4gm6w4usUEctmdPSWvAc8Z1g-RK2ssgb8xAhaA/edit?usp=sharing

[@professordeb]

@@conorgallagher2096 I see. Yes, that's pretty much the Alamillo concept, except using moment resistance. You asked about the horizontal forces...the horizontal components from the stays are what generate the moment on the mast. Interestingly, though, the vertical components from the stays will create a stabilizing moment that works with the weight of the mast, although the moment arms for the vertical components will be lower. The sum of all of the moments from each stay will be the total. The horizontals also accumulate in the bridge deck itself, so become large compressive forces that need to be resisted. The Alamillo has an orthotropic box section that effectively works as a horizontal column to resist that compression.The mast size, though, will be VERY large to accept that much bending moment, so an appropriate solution would be to use a tapered section that gets increasingly large from the top to the base where the moment is highest. From an aesthetic standpoint, I would think that parallel harped stays might be a little more attractive than the semi-fan as it is now. Overall, it looks like you're on the right track though!

[@conorgallagher2096]

@@professordeb thanks very much!

[@Souliee]

Very good video! But.. these imperial units tho.

[@professordeb]

Thanks. Yes, here in the US we still archaically use Imperial units in the construction industry. Nothing changes in the process using SI as the unit base. When I was a kid I was told the country would be fully metric by 1980. We're a little behind that...