More and more cars changed routes and the robbers discovered that the control keys had been taken.
Shu said: "Didn't you say they didn't take away the control keys? Why did so many vehicles change their routes?"
Pi said: "I didn't notice this problem at first. I just received signals from the keys in these vehicles and I quickly went to one of the vehicles to have a look."
He came back after a while and said: "It turns out that the control key here is a fake key. Although it emits signals outward, it cannot be controlled by us. The real control key is probably taken away by them."
"We still need to regain control of these vehicles," Shui said.
Pi said: "Then let's grab them one by one?"
Gui said: "These vehicles are too scattered, and they pass one by one, which takes too long. Maybe if you go to one vehicle, the other vehicle will run away."
"Moreover, you snatched one car back, and then when you tried to snatch another car, the original car was snatched back again."
Pi said: "What should we do? We have to find a way, or surround them."
In the end, they planned to rush to the front mountain pass and block the intersection so that they could intercept other vehicles and force them to hand over their control keys.
A huge ravine appeared ahead. They thought, "These cars will definitely not be able to pass, so we'd better take a detour."
Dai Zhao and others also arrived at this gully, which looked like a natural chasm. Looking around, we are surrounded by vast, desolate grasslands, with hills and ravines in between from time to time. The fallen stones slid along the paths, leaving traces.
Zheng Xiling stared at the deep ravine and said to Dai Zhao, "How about looking for another way?"
It would be relatively easy if there were just a few people walking together through open fields, short bushes, and deep ravines.
Dai Zhao stared at the dark ravines under the valley, wondering what else was in these deep valleys with staggered rocks and few trees. I don’t know if a car can drive underneath.
Dai Zhao said: "We used our method to get there, using two of the cars, first going down the ramp, and then forming pillars to support the upper track. The ends of the two cars extended to the left and right to form a simple track , and then we use a car to extend the track and lay it, forming a stronger track above this simple track, and other vehicles can pass on this track, which is equivalent to making a simple bridge first."
The slope leading from the mountain to the top of the mountain is relatively steep. There are many braking devices under the car to prevent the vehicle from sliding down the hillside, so that the vehicle can slowly reach the bottom of the ravine step by step. Another car also slowly reached the bottom of the gully. The support pillars on the front of the car slowly unfolded, supporting the body like a camera frame. The rear door of the car opened, and then two flat panels stretched out. The flat panels opened like a flower, but here there were only two petals on the left and right. On the edge of the ravine. The construction vehicle, which is composed of multiple construction machines, opens the door and stretches out the bridge.
Of course, this was still very unstable, so two more arch bridges were built above. There are hooks on the arch bridge above that connect to the bridge below.
Next, we need to analyze the stress at each point of the bridge. Some optical fiber sensors are laid inside to detect force.
Dai Zhao explained, “Bending deformation of beams is also the most common simple deformation.”
The most commonly encountered bending deformation in engineering practice is the plane bending of the beam, that is, the cross section of the beam has at least one center line of symmetry, the whole beam has a longitudinal center plane of symmetry, and all external forces act in the longitudinal center plane, and the axis of the beam It is bent into a plane curve in the longitudinal center plane of symmetry. The internal force that causes the beam sections to slide relative to each other is shear force, which is equal in magnitude to the reaction force and opposite in direction.
The direction of the shear force is specified as follows: the shear force takes a moment at any point in the separation body, which is positive when going clockwise and negative when going counterclockwise. The internal force that causes the beam to bend is called the bending moment. In engineering practice, when slender rods are often encountered and bent under load, the bending moment is the main factor in the beam's damage, and the possibility of shearing is very small. Therefore, when calculating the bending internal force, only the bending moment is considered and ignored. shear force. The bending moment of a certain section is numerically equal to the algebraic sum of all external forces on one side of the section, including loads and reactions, and the centroidal moment of the section. Using this rule, the bending moment equation of any section can be written directly.
According to the phenomenon of beam bending, it can be assumed that: 1) The cross section of the beam is still flat after deformation, but it is just rotated at an angle. The cross section rotates about an axis, which is called the neutral axis. The plane formed by the axis of the beam and the neutral axis is called the neutral layer, and the fiber length on it remains unchanged. 2) All longitudinal fibers parallel to the axis are axially stretched or shortened.
In summary, the characteristics of bending deformation are as follows: the cross section rotates around the neutral axis, the fibers above the neutral layer shorten, and the fibers below the neutral layer elongate. In the same way, the compressive stress is above the stress neutral layer on the cross section, and the tensile stress is below the neutral layer.
Qi Yanliang said that these are general qualitative analyses. Is there any specific quantitative analysis? Dai Zhao thought, it seems that he is very studious and always wants to break the casserole and get to the bottom of it. So he continued:
"To solve the normal stress at any point on the beam, you can first use the deformation geometry equation. At the point where the beam bends, look at the distance between this analyzed point and the middle layer along the direction of the curvature radius. Based on its radius and the turned The arc length can be obtained from the angle. The relative change in the arc length is the strain. Then look at its stress according to the physical equations. The beam is stretched or compressed along the axial direction. Within the elastic range, there is a gap between stress and strain. According to Hooke’s law, stress equals elastic modulus times strain.”
"Then the stress is obtained according to the static relationship. Take a micro-area on the cross section, perform an integral calculation on this micro area, and obtain the total bending moment of this interface. It can be obtained that the stress is equal to the bending moment multiplied by the distance divided by the moment of inertia. The maximum stress of the beam occurs on the section with maximum bending, at the point farthest from the intermediate layer. The stress is equal to the bending moment divided by the bending resistance. The section coefficients are different, and the cross-section size and shape have different bending section coefficients. The bending resistance increases. The section coefficient can reduce stress and increase the strength of the beam."
After passing the force test, Dai Zhao then directed each construction vehicle to pass. The young man also sat on this construction truck, bumping along slowly. The speed of the car was relatively slow, and the boy was worried that he might fall under the bridge or into the valley if he was not careful.
One construction truck was so heavy that it began to tip over. The support column below also fell sideways. Dai Zhao ordered the car behind him to use a wire rope to tightly grab the bridge and pull it outward to prevent the pillars below from tilting. In this way, the car slowly moved over and crossed the bridge.
