Archimedes was a Greek mathematician and the first to understand the operation of the lever arm mechanism. He had said the familiar phrase to show the power of the lever arm (It was said by Archimedes (287-212 BC) and it means "Give me a place to stand and I will move the earth" And we come to the current state of construction, where the load-bearing structure of reinforced concrete consists of columns, walls and beams, extending in height and width, ie by huge lever mechanisms that multiply the great forces of the earthquake. These huge levers of height (columns) and width (beams) join at the nodes creating a galaxy of opposite moments raised by seismic displacements and multiplied by the mechanisms of the levers. These torque forces are called to pick up the cross sections of reinforced concrete around the joints. Of course it is impossible to ignore these stresses concentrated at one point of the cross section (the one that fails first, critical failure area) and civil engineers have devised some techniques to trick the cross section failure at this point of the shear failure. One of these tricks is called elasticity. When the displacement of the structure is small, within the limits of the elasticity of the columns and beams the construction does not present failures. That is, they design the construction so that it works like a spring which stores and releases energy in the opposite direction. But when the earthquake is big and the displacements increase and the elasticity of the elements is not enough, they start to show leaks (small cracks) Here begins the second trick used by civil engineers to trick the great failure of cross sections and is called plasticity. Basically what they want to avoid is the creation of a large crack, which predisposes the collapse of the structure. They prefer to create many but much smaller cracks so that the construction does not collapse. They achieve this by placing dense transverse reinforcement (hoops) placed near the ends of the elements where they frame the node. If the earthquake is very large and the elasticity and plasticity are not enough then they use another trick which is called satisfactory design. Basically what they do is design the columns and the walls to be stronger than the beams. So the first thing that fails is the beam. And they do this because when the beam fails it releases seismic energy without falling because it hangs on the steel reinforcement, while if the pillar fails first with an oblique / form of failure it takes it all and leaves. These are the three defenses of construction today (elasticity, ductility, good design) that do nothing but try to overflow the displacement so that it is greater than the displacement of the earthquake.
This is the concept of strong-column-weak-beam theory. Maximum RC beam-column joints which were designed before 1970, are not code conforming. Hence, in this case, there is need to retrofit or strengthen the beam column joint for resisting the lateral earthquake force.
Follow the below article
Article Quasi-static cyclic performance of RC exterior beam-column j...
Dear Subhrasmita Majumder
The reinforcement of the cross-sections at the nodes you are talking about is done by compacting the connecting reinforcement at the ends of the cross-sections. You call this plasticity and it does not negate the competent design of the nodes which is still valid and applied today. It is very difficult to further increase the strength of reinforced concrete without increasing its mass. Mass increases inertia loads. I used a force without mass, which comes from an external factor, that of the ground, which I carried with the help of unrelated tendons to the upper ends of the structure, to help the structure respond to seismic shifts. This design method takes the seismic intensities before they are transferred to the cross sections of the nodes, and changes their direction by deflecting them into the ground. This design method is my own patent and research and is not taught in universities. It is under investigation.
Article The Ultimate Anti-Seismic System
- Badges
- Science topic
- Similar topics
- Analytical Chemistry
- Column