*Student: Abdukhamidov Jasurbek* *Group: E94-21-Arch* *Teacher: Sobit Akhtambaev*
Independent work from
” Theoretical mechanics“
Forces that cause acceleration in building masses are called dynamic forces. Forces applied slowly to parts of a structure are static forces. Stresses, deformations and displacements generated in the structure by dynamic forces change over time. Such changes do not occur under the influence of static forces.
There are the following types of dynamic forces:
- Excitation periodic forces. Such forces arise under the influence of mechanisms with an unbalanced mass in the rotating part, installed somewhere in the structure. If periodic forces act continuously according to the law of sine or cosine, then such forces are called vibrational or harmonic forces.
- 2. Combat power. An example of such a force is the load falling on the structure, the impact mechanisms.
Short-term impact forces (impulses). Such forces appear suddenly and disappear suddenly. The force generated by the explosion provides a short burst of force. 4. Driving forces. The traffic moving on the structure creates the driving forces. 5. Seismic forces. They are the forces that affect the building and the result during the earthquake.
The ability to correctly determine the magnitude of seismic forces has a great impact on ensuring seismicity. Dynamic forces are by their nature somewhat more complex than static forces, because such forces are characterized not only by their magnitude, direction, and location, but also by time. 1 The maximum deformation that occurs in the structure under the influence of dynamic forces and their production; 2. It deals with the issue of geometric dimensions that determine the formation of sufficiently small deformation and formation in the structure.`
Types of vibration.
There are many types of vibration, such as the beating of the human heart, the breathing of the lungs, shivering from the cold, light and sound waves, our steps, the ringing of an electric bell, the movement of a car, the earth. All phenomena such as motion are living examples of vibration. If an external force is applied to a stationary mechanical system (for example, a hammer or a mathematical pendulum) and is immediately removed, the system vibrates. Such oscillation of the system is called free or natural oscillation.
If the oscillating system is always under the influence of a driving force, such oscillation of the system is called forced oscillation. The free oscillation of the system is influenced by restoring (elastic) forces as well as resisting (dissipative) forces. Dissipative forces cause the vibration to decay. Such oscillations of systems are called damped oscillations. Resistance of the environment, internal friction forces, dry friction on the supports are dissipative.
Oscillations that repeat continuously over a period of time are called periodic oscillations. The time taken for a complete oscillation is called the oscillation period (T).
Dissipative forces are not taken into account when solving some problems. This type of vibration is called undamped free vibration. Degrees of freedom of the system
Degree of freedom of the system. In the dynamics of structures as well as in the statics, the term "system" refers to systems with a steering wheel, i.e., structures. In the process of dynamic calculation, the structure's dynamic calculation scheme is used. In dynamic calculation schemes, the mass of the structure is considered to be concentrated at certain points or distributed throughout the system. Depending on how the masses are obtained, the system has different degrees of freedom.
The number of geometric parameters determining the position (position) of all masses when the system is deformed is called the degree of freedom of the system. The degree of freedom of mass m hanging on a weightless spring is equal to one, because its position can be determined by only one parameter (y coordinate). Similarly, the degrees of freedom of a single-mass hammer are equal to one. , y and g describe systems with two degrees of freedom.
If the mass unit is located on an infinitely large rod, the state of the system is determined by the position of the rod. Therefore, there will be an infinite number of parameters determining the state of masses. Accordingly, when it comes to real constructions, their degree of freedom is said to be infinite. However, the higher the degree of freedom of the system, the more complicated the calculations. For this reason, in most technical calculations, the degree of freedom of the system is taken to be limited, allowing a small error. In this case, materials are collected at some points of the system, for example, at the places where heavy loads are located in the structure.
Methods of solving problems of dynamics of structures. Static and energy methods are widely used in solving problems of dynamics of structures. The essence of the static method is that dynamic problems are reduced to static problems on the basis of Dalamber's principle, that is, dynamic equations are reduced to static equations.
Natural loads depend on the changing environment, and they, in turn, are divided into three:
Meteorological;
Gravitational;
Seismic.
Depending on the impact of SHIPPING, it may be as follows:
permanent and temporary;
constant - natural (weight of the main parts of the building);
earth pressure;
Temporary loads are divided into long-term, short-term and specific loads.
Long-term loads: technical equipment inside the building.
Short-term loads: people, weight, stored cargo, traffic in motion, snow and ice coverage, wind force.
Specific loads: depending on the deformation of the ground structure.
Snow load. the snow load in many cases causes the constructions to fail. Snow loads are determined in advance in mountainous regions and rough places with the help of the hydrometeor service.
In our republic, snow and rain depend on certain conditions, and their impact on buildings is listed in normative indicators. Their effects are mainly
it is considered as a separate load in the design and calculation of constructions of buildings and structures.
Effect of wind. Hurricane winds cause the destruction of many engineering installations. Aerodynamic efficiency varies depending on the shape of buildings and structures - their height. If the roof of the building has two slopes, the windward side can rise. When the roof of the building is covered with the lightest material, the force of the blowing wind can lift it with a force greater than its weight. Builders should always consider this.
Earthquake power. Effects of vibration on buildings during an earthquake. An earthquake causes a lot of damage. For this reason, it is necessary to take special measures in earthquake-prone areas, information about this is given in the last chapters of the manual.
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