Load1. refers to the external force and other factors that cause internal force and deformation of the structure or component.
2. Customarily refers to the various direct effects exerted on the engineering structure to cause the engineering structure or components to have an effect. Common ones include: structural self-weight, floor live load, roof live load, and roof dust load. , vehicle load, crane load, equipment dynamic load, and natural loads such as wind, snow, ice, waves, etc.
Load standard value is the basic representative value of load used in structural design, which is the standard load listed in the load specification. Conceptually, standard load generally refers to the maximum load value that may occur on a structure or component under normal use conditions, so it should be higher than the load value that often occurs. From a statistical point of view, the standard value of the load is the load value whose exceeding probability is less than a certain specified value within the specified design reference period, also called the characteristic value, which is the maximum acceptable value for engineering design. In some cases, a load may have upper and lower standard values. When the load decreases and produces more dangerous effects on the structure, the less favorable lower limit value should be used as the standard value; conversely, when the load increases and the structure produces more dangerous effects, the upper limit value should be used as the standard value. For example, when there is sufficient observation data for various live loads, they should be statistically determined according to the definition of the above standard value; when there is not enough observation data, the standard value of the load can be determined based on the above conceptual agreement based on design experience.
Dead load, also called permanent load, is a load that is constant (or the change is negligible compared to the average value) applied to the engineering structure. Such as the self-weight of the structure, plus the weight of permanent load-bearing, non-load-bearing structural components and building decoration components, earth pressure, etc. Because dead loads are continuously exerted on a structure throughout its service life, its long-term effects must be considered when designing the structure. The self-weight of a structure is generally determined based on the geometric dimensions of the structure and the standard value (also called the nominal value) of the material bulk density.
Live load, also known as variable load, is the use or occupancy load and naturally occurring natural load imposed on the structure caused by people, materials and vehicles. Such as industrial building floor live load, civil building floor live load, roof live load, roof dust load, vehicle load, crane load, wind load, snow load, ice load, wave load, etc.
Industrial building floor live load refers to the load generated by the weight of equipment, transportation tools, raw materials, finished products, etc. and the weight of operators during the production, use, maintenance and installation of industrial building floors. Heavy objects such as industrial equipment are usually local loads or concentrated loads, which should be determined based on actual data. However, in order to facilitate design, an equivalent uniformly distributed live load that causes the same effect on structural members can generally be used instead.
Civil building floor live load refers to the load generated by people, objects, furniture, equipment, etc. during the use of civil buildings. For common residential buildings, offices, hotels, hospitals, schools, auditoriums, theaters, gymnasiums, exhibition halls, shops, station halls, waiting rooms, library, bathrooms, balconies and other civil buildings, the floor uniform live load value is determined by the national load code Regulation.
Roof live load refers to the load generated by people, tools and appropriate piles of materials during the construction, use and maintenance of the roof. For rainy areas, the roof live load also includes the water load caused by possible roof water accumulation.
Roof area ash load For factories with a large amount of ash discharge during production, the roof load is specified to consider the safety of the roof structure. For example, foundry workshops, steelmaking workshops, sintering workshops, blast furnaces, cement plants, etc. and their adjacent buildings, the roof area dust load should be considered. The standard value of this load can be specified based on the nature of the ash source, the distance between the building and the ash source, the shape of the roof, and the cleaning system.
Vehicle Loading The live load exerted on building floors, docks and bridges by vehicles carrying people and goods. Floors of multi-story industrial plants, warehouses and garages are sometimes required to withstand loads such as cars and forklifts. Highway bridges are required to withstand loads such as cars, flatbed trailers, crawlers and road rollers. Railway bridges are required to withstand the load of trains.
Since the types and grades of vehicles are different, the loads exerted on the structure are also different. The most representative and controllable vehicle loads must be considered during design. For example, highway bridges use vehicles that appear frequently and in large numbers in formation as calculation loads; crawlers and flatbed trailers that are less likely to appear are used as verification loads. Cars and trains run on the bridge deck, causing the bridge to be impacted by impact. The vehicle load should be multiplied by the dynamic coefficient during design. In addition, the braking force when the vehicle is braking, the centrifugal force of the vehicle traveling on the curve, the lateral sway force of the train when traveling, and the additional lateral pressure of the soil caused by the vehicle load (see bridge load) must also be considered.
Crane load refers to the vertical and horizontal forces caused to the structure during crane operations. In order to lift materials and finished products during production and lift equipment during installation and maintenance, industrial plants often set up various cranes, such as bridge cranes, suspension cranes, cantilever cranes, etc. The vertical force of the crane is the maximum vertical wheel pressure of the crane. For an overhead crane, it can be determined by the weight of the bridge frame of the large vehicle, the self-weight of the small vehicle, the weight of the driver's operating room and the rated maximum lifting weight. Generally, it can be obtained according to the provisions of the crane product catalog. The horizontal force of the crane is the braking force transmitted through the track when the crane wheels are braking. For bridge cranes, the longitudinal horizontal force is generated when the crane is braking; the transverse horizontal force is generated when the trolley is braking. Due to reasons such as the track is not straight and parallel, the crane bridge frame is not rigid enough, and the installation position of the crane wheels is incorrect and non-parallel, the crane moves in a serpentine shape when traveling longitudinally, causing the squeezing force of the cart wheels against the track, which is called jamming. rail force. The vertical impact of the crane due to the height difference of the track joints, the turning of the workpiece, etc. can generally be considered by using different dynamic coefficients based on factors such as the type of crane, the type and location of the structural components, and the weight of the crane.
Wind load, also known as wind dynamic pressure, is the effect of air flow on engineering structures, including steady wind and pulsating wind. In engineering structures, it is called aerostatic effect and aerodynamic force. effect. Special care is required in windy areas and when designing tall structures or long-span bridges.
Snow load The weight of snow exerted on the exposed surface of a building roof or other structure. The snow load value S is determined by multiplying the ground snow weight, that is, the basic snow pressure So, by the roof snow distribution coefficient μr:
S=μrSo
The basic snow pressure specified in China is generally open The annual maximum snow accumulation on flat ground calculated based on a certain return period (equivalent to a certain quantile value of the maximum snow accumulation weight distribution in the base period of a certain number of years). According to statistics, the statistical distribution of annual maximum ground snow pressure can also be considered as extreme value type I. Compared with the Soviet Union, Japan, Northern Europe, Canada and other countries with severe snow accumulation in the world, China's snow cover situation is not large and the snow cover period is also short. Northeast China and northern Xinjiang are two areas with high snow pressure in China. In addition, the middle and lower reaches of the Yangtze River are also areas with high snow pressure, but the snow cover period is extremely short. For most areas in southern China, snow accumulation on roofs is not considered in the design. Severe snow accumulation on roofs can also cause house collapse accidents. The snow accumulation on the roof is affected by the roof form, orientation, wind force, and the dissipation of indoor heating or production heat of the building. It is generally different from the snow accumulation measured by the weather station on flat ground in the field.
Ice load is the weight of ice surrounding the surface of tower members, cables, and wires. In winter or early spring, under specific climatic conditions, it is formed in some areas by freezing rain, freezing drizzle, fog, clouds or melting snow with temperatures below 0°C. Its value can be determined based on the ice thickness and ice density. .
Ice load is often an important load for structures such as transmission towers and lines. Because the ice coating increases the cross-section of rods and cables, or closes the gaps in some lattice structures, it not only increases the weight of the structure or components, but also significantly increases the wind load due to the increase in the windshield area of ??the structure. Make the structure more unfavorable.
Wave load, also called wave force, is the effect of waves on structures such as port terminals and offshore platforms. The current analysis is based on diffraction theory.
The effect of waves on structures consists of four parts: the friction caused by the viscosity of the water flow (proportional to the square of the water point velocity); the inertia of the unsteady water flow or the additional mass force generated by the variable speed movement of the structure in the water flow. (Proportional to the acceleration of the water point in the wave); the pressure caused by the radiation effect of the structure on the incident wave flow field and the pressure caused by the radiation effect of the movement of the structure on the incident wave flow field. The wave force theory that includes all the above effects is called diffraction theory. In current practical work, the semi-empirical and semi-theoretical Morrison equation, which only considers the influence of wave friction and mass forces on the structure, is commonly used to analyze wave forces.