in this beautiful flyover there are a few high- tension steel tendons protected in conduit Unfortunately they are corroding can you guess the impact of this on the flyover after 3 to 4 months why is this happening you may not believe this but modern flyovers use these kinds of empty box girs for construction interestingly the smart engineering of these girs allows male to female interlock of many such segments now let's insert a steel tendon via the holes in these box girs suppose you tightened the cable how will the cable's intention affect the load carrying capacity of the flyover to answer this question we need to First understand how a flyover transfers weight the weight of the entire superstructure including the vehicle is first transferred to the bridge bearing then to the Pier from there to the pile C app and finally to the piles the very first stage of flyover construction the engineers are searching for a hard strata layer here if the entire weight of the vehicles and the flyover is borne by the hard strata such a structure will be super stable once they find the hard strata the workers begin to insert the reinforcement bars then pour concrete after a 14-day curing period the pile Foundation is ready you can transmit a tremendous amount of force to these piles and the strong hard strata will make sure that the pile structure is stable you can easily guess what will happen to the flyover if the piles do not reach the hard strata this is why the piles are super important in a flyover all these piles are connected to a single concrete structure called a pile cap now the construction of the peers begins peers end with the construction of these beautifully curved Pier canopies obviously to pump the concrete at this height you need powerful concrete pumps it's an impressive sight to see all these well aligned and beautiful peers standing waiting to invite their next component the hero of the project the Box girs the Box gerss are pre-fabricated welcome to the Box girder fabrication site this bottom formwork and the inside form are the key components in the girder fabrication look at how they're able to move with the help of hydraulic power the steel structure is placed inside the form first the concrete is poured and allowed to cure first the inside formwork is removed now it's time to remove the bottom formwork you can see a lot of protruding shapes and holes in the Box girder why do we need them we'll explore that soon the segmental launching Gantry the biggest machine used in this project is almost a robot a robot with four legs yes this machine can move to the next segment once it's done with the Assembly of one segment this is how it does it initially the launching Gantry is supported on these support brackets the LG now starts the lifting and assembly work of the Box [Music] gutters the girder assembly between one pair of Pier is now complete to do the gerder Assembly of the next section the LG should reach this position to achieve this the launching Gantry has to make use of all its four legs first the rear leg is supported on the deck now even if you remove the rear middle leg there's no issue the LG is still stable next the rear middle leg is supported on the road deck now the launching Gantry can move forward the front leg gets supported on the next perer cap now the rear middle leg moves forward and gets supported on the front of the deck it's time to move the support bracket forward and support it on the next Pier next the rear leg is retracted and the entire launching Gantry is moved forward again if You observe the position of the LG now it's the same as the position of the LG just before the Assembly of the previous segment the main legs are in the center of the Gantry and the Gantry is properly centered from this position the Gantry can start the new launching process and this cycle is repeated now let's see some details of box girder assembly workers apply epoxy resin on the faces of the girs you can see how the male and female protrusions perfectly fit together after the assembly of one segment is over there will be a small Gap left between them this is deliberate if the engineers had planned to complete the segment perfectly with the girds there would be no way to fit the last girder the small Gap left is closed with reinforcement bars and concrete Engineers are now doing the most crucial operation insertion of super strong steel tendon wires via the holes of the box girs they're even tightening the wires at this stage even if the Gantry crane removes the support the segment will be strong and stable the segment can even carry the weight of at least 20 cars here's the big question are the steel tendons that the workers inserted and tightened just for bonding the box girs together even if the workers had not inserted the tendon wires the girs would be stable however after a few months of operation cracks will initiate from the bottom of the girs and finally lead to tragedy welcome to the brilliant engineering of concrete post stressing here are the concrete fryover we made Let's attach these end caps Also let's insert this re bars inside the fry overs in one of the gers I'm tightening the re bars and uh keeping it at extreme tension the other G has re bars but not under [Music] distress now let's test the weight carrying capacity of these two flyovers with the help of a car this is a gerer without post stressing as the car transfer some amount of weight it unen a sudden failure the gut with the Titan rars is able to survive more weight this one also failed but this time the failure was more gradual with increased load [Music] capacity that's the advantage of post stressing of concrete when you keep the steel tendons in tension and when they're not allowed to go back to their original length the concrete gets compressed what's the advantage of this when the concrete segment is supported from its two ends the segment bends as shown due to this the bottom portion of the segment will be in tension and the top portion will be in compression concrete is good in compression and bad in tension this means the bottom section Which experiences tensile stress will easily develop cracks the remedy for this is to keep the ENT ire concrete block in good compression well before the bridge construction is over in this case tensile stress may get produced on the bottom region due to the live load but much lower than the previous case this way the engineers make sure that the bridge will last for decades without developing cracks these powerful hydraulic jacks do the difficult job of tensioning the steel tendons the high pressure fluid moves the piston and the cables get tightened you can see that after tensioning the cable the workers release the pressure remove the machine and cut off the extra wire then why don't these cables which are in high tension contract and go back to their original length to understand this logically we 3D printed a simplified model of the hydraulic jack and the entire post stressing mechanism using a bamboo lab printer you can control this 3D printer from your mobile phone or computer and even watch the printing process live remotely this A1 C 3D printer from bamboo lab is perfect for your Innovative product development and educational 3D printing for your kids it's pocket friendly as well the interface of the A1C bamboo lab is quite intuitive and I don't have to say anything about the quality of the print just compare these two pieces now the hydraulic jack and the post stressing mechanism are accurately reproduced you won't believe this these simple wedges do the tricky job of keeping the tensioned cables in place even after the hydraulic jack is removed the clever engineering of the wedges makes sure that the cable can be stretched outward but once stretched outward it will not go inward even if you remove all other accessories here's how it works one thing we should keep in mind is that the wedges are not strongly connected with the tendon wires what will happen if the block surrounding the wedges moves like this the block will close the gaps in the wedges and the wedges will form a strong connection with the tendon wire obviously the cable will be stretched towards the right now what about this situation here somebody is pulling the cable from the right here the wedges won't form any strong connection with the tendon and the tendon wire will stretch toward the right freely keeping these two tricky Concepts in mind we're going to explore the clever engineering of post tensioning when the Jack moves from left to right the outer wedges are tight tightened and the cable moves from left to right it is undergoing a tension operation the inner wedges cannot block this cable movement since these wedges are not getting tight with the cable after achieving sufficient tension in the cable the engineers release the pressure on the Piston here obviously the cable wants to retract inward however as soon as it moves a little the inner wedges will get tight with the cable and further motion of the cable will be arrested in short these wedges will ensure that the cables remain in tension forever what a clever engineering feat to keep the cables always in tension simplicity at its best now you may remove the accessories and cut the cable from here the cable inside the flyover will remain in tension in reality a hydraulic jack is able to stretch more than a dozen tendons in one go we had planned for a three cable stretching initially since our plastic components were not able to carry this load we settled with a single cable stretching it's remarkable how just a few high- tension steel cables can dramatically increase the strength of a concrete flyover the structure that connects the ground and the flyover deck is called an abutment the angle of the abutment is crucial for the smooth entry of vehicles onto the flyover the abutments are filled with soil now the vehicles can enjoy a smooth ride over the flyovers ever wondered how Engineers come up with these clever and complicated interchange designs let's now skim through the basics of interchange designs the three-way interchange design is commonly used when one road terminates at another road facilitating movements in and out of a through route this design minimizes the use of land and construction costs and most importantly minimizes the need for Lane weaving it is commonly found at the ends of expressways or as a transition the Cloverleaf interchange might be the most beautiful innovation of civil engineering this design which resembles a clover leaf is used when two highways intersect the design allows free flowing movements without the need for traffic signals in a Cloverleaf design anyone can move to any road without any hassles just observe these line animations to understand how this design achieves this however the Cloverleaf design requires a significant amount of space this design also causes weaving issues as Vehicles enter and exit the loops the diamond interchange is a popular solution when a highway intersects a secondary Road its design consists of four ramps forming a diamond shape hence the the name this type of interchange is efficient in areas of moderate traffic volume offering easy and direct access between the roads with minimal land use it supports high traffic volumes and speeds but can be limited by traffic signals that may cause delays during peak times a modification of the full Clover Leaf the partial Clover Leaf interchange eliminates some of the loops to reduce space requirements the most important Advantage is that it minim IES weaving problems found in traditional Cloverleaf designs this interchange type combines the features of a Cloverleaf and a diamond interchange parkl interchanges are particularly effective in Suburban Traffic Engineers either grout the post tensioning cables or they just keep them inside a conduit in the first case the post tensioning cables are bonded to the grout in the second case they are not bonded in the case of the unbonded post tensioning greas should be added to the conduit to avoid corrosion bonded post tensioning produces greater resistance to corrosion however bonded post tensioning needs more cables in order to achieve the same compression level as the unbonded method you might have notice these kinds of gaps and strange Arrangements in flyovers if you delve into the details you'll be amazed at the intricacies of engineering these are Expansion Joints in civil engineering it's common practice to leave a gap in lengthy concrete structures materials expand or contract during temperature changes and these gaps allow for this motion if you constrain the structure too much it will crack during temperature change however we cannot simply leave a gap in the road Expansion Joints allow for the movement of the road deck while simultaneously preventing gaps this green member is the main support of the expansion joint interestingly this member is not fixed to the Rope it just floats on two bearings this means this support member won't block the movement of the road decks in any way the support boxes of the expansion joint are free to slide along the green member the portion you see on the flyover is a collection of lamelas with rubber strips between them now you may observe this animation and understand the entire working of the Expansion Joints let's watch the working of the expansion joint one more time this time from the perspective of a pedestrian this also means that the road deck must be resting on bearings thanks to these bearings and Expansion Joints flyovers can accommodate changes in environmental temperature the flyover we discussed so far is known as a concrete-based flyover which is the most popular choice however if you check the flyover in San Antonio Texas you'll be able to see a lot of Steel girds underneath these are steel structure flyovers the details of Steel structure flyovers are Illustrated in this visual they're mainly used when the situation Demands a shorter construction period they're lighter and stronger compared to concrete flyovers the main shortcoming of Steel flyovers is that they are more costly compared to concrete flyovers I thank bambula for extending the technical support for this video the 3D PR the A1C machine was super accurate allowing us to demonstrate the posten jacking DET if you like to explore the big world of 3D printers please check out their website thank you for watching the video take care bye-bye