What Is a Structural Load?

Load, pronunciation: hè zài. ("Load" has the meaning of "bearing", so four sounds)) refers to external forces and other factors that cause internal forces and deformation of structures or components. Or customarily refers to the various direct effects that are applied to the engineering structure to make the engineering structure or component effect, common are: structural dead weight, floor live load, roof live load, roof area gray load, vehicle load, crane load, equipment Dynamic loads, as well as natural loads such as wind, snow, ice, and waves.

Chinese name: Load
Explanation: Other factors that cause internal forces and deformation

Common are: Structural dead weight floor live load roof live load
Action direction: Vertical load horizontal load

Load Introduction

The external effects that cause the structure to lose balance or damage are: various forces directly applied to the structure, which are customarily called loads, such as the dead weight of the structure (constant load), live load, ash deposit load, snow load, wind load; Class is indirect action, which refers to other effects that cause additional deformation and restraint deformation on the structure, such as concrete shrinkage, temperature change, welding deformation, foundation settlement, etc. ^[1]

The purpose of paying attention to loads is to meet the needs of building structure design, in order to meet the requirements of safety, applicable, economical and reasonable.

The design range of load is applicable to the structural design of various projects

The reference standard is GB50068 load statistical parameter, and the design base period is 50 years.

Load classification method

Load classification

Load time classification

1 Permanent load (constant load), whose value does not change with time; or a load whose change is negligible compared to the average. Such as structural dead weight, earth pressure, prestressed foundation settlement, concrete shrinkage, welding deformation, etc. Dead load, also called permanent load, is a load that is invariant (or whose changes are negligible compared to the average value) applied to the engineering structure. Such as the weight of the structure, plus the permanent load, the weight of non-load-bearing structural components and building decorative components, earth pressure, etc. Because the dead load is constantly applied to the structure throughout its life, the long-term effects must be considered when designing the structure. The dead weight of the structure is generally determined according to the standard value (also called the nominal value) of the geometric size of the structure and the material bulk weight.

The house is composed of some heavy structural members such as foundation, wall (column), beam and slab. They must first bear their own weight, which is called dead load. In addition, the floors, roofs, ceilings, plaster layers on the walls, doors and windows are all loads.

2 Variable load (live load). A load whose value changes with time during the design basis period, and whose value is not negligible compared to the average value. For example, floor live load, roof live load and ash load, crane load, wind load, snow load, etc.

Live load, also called variable load, is the use or occupation load and the naturally occurring natural load imposed on the structure caused by crowds, materials and vehicles. Such as industrial building floor live load, civil building floor live load, roof live load, roof area gray load, vehicle load, crane load, wind load, snow load, ice-wrapped load, wave load, etc. are all.

3 Occasional load (special load or accidental effect) may or may not occur during the design basis period. Once it occurs, its value is large and its duration is short. Such as explosive force, impact force, typhoon avalanche and so on.

Note: Dead weight refers to the load (gravity) caused by the weight of the material itself.

Classification of load structure

1. Static action does not cause acceleration or negligible acceleration of the structure or structural components. For example, floor load of a house or office building, etc.

2.Dynamic action causes non-negligible acceleration to the structure and structural parts. For example, vibration of crane equipment; impact of falling objects at high altitude, etc.

Classification of load surface size

1. Uniformly distributed load Uniformly distributed load on the building floor, such as the load caused by the weight of the wooden floor, floor tiles, granite, marble, etc. Severity y is multiplied by the thickness d of the surface material to obtain an increased uniform cloth load value, Q = yd.

2. Line load Various surface loads on the original floor or layer of the building are transmitted to the beam or strip foundation, which can be simplified as a distributed load per unit length, called a line load

3. When the distribution area of the concentrated load is much smaller than that of the structure, in order to simplify the calculation, the load can be regarded as acting on one point. For example, the load transmitted from the secondary beam to the main beam can be approximately regarded as a concentrated load. The pressure transmitted from the roof truss to the column and the pressure of the crane wheel to the crane beam are concentrated loads.

Load direction

1. Vertical loads such as structural dead weight, snow load, etc.

2. Horizontal loads such as wind loads, horizontal earthquakes, etc.

The difference between load and action

Due to direct or indirect action on the structure, internal forces (such as axial forces, bending moments, shear forces, torques, etc.) and deformations (such as corners, cracks) within the structure are called "structural effects", which is what we say Role. When the action is a direct action, its effect is also called a "load effect", which is the load.

Load application

Load industrial building

During the production, use, maintenance and installation of industrial building floors, the loads generated by the weight of equipment, transportation vehicles, raw materials, finished products and the weight of operators. Industrial equipment and other heavy objects are usually local or concentrated loads, which should be determined based on actual data. However, in order to facilitate the design, an equivalent uniformly distributed live load that causes the same effect on the structural members can generally be used instead.

Load civil building

During the use of civil buildings, loads generated by people, objects, furniture, equipment, etc. For common residential, office, hotel, hospital, school, auditorium, movie theater, gymnasium, exhibition hall, shop, station hall, waiting room, library, bathroom, balcony and other civil buildings, the live load value is uniformly distributed by the national load specification Regulations.

Load roof

Loads generated by the roof, during construction, use and maintenance, by crowds, tools and appropriate piles. For rainy areas, the live roof load also includes the stagnant water load due to possible water in the roof area.

Roof area gray load For a factory building with a large amount of ash discharge, the roof load specified for the safety of the roof structure. For example, foundry workshop, steelmaking workshop, sintering workshop, blast furnace, cement plant, etc. and its adjacent buildings should consider the gray load of the house area. The standard value of the load can be specified according to conditions such as the nature of the ash source, the distance between the building and the ash source, the shape of the roof and the ash cleaning system.

Vehicle load

Live loads on houses, docks and bridges by vehicles carrying people and cargo. Floors of multi-story industrial plants, warehouses, and garages sometimes require loads such as cars and forklifts. Highway bridges are required to withstand loads such as cars, flatbed trailers, tracked vehicles, and road rollers. Railway bridges are required to withstand the loads of trains. Due to the different models and grades of vehicles, the loads on the structure are also different. The most representative and controllable vehicle loads must be considered when designing. For example, highways and bridges select cars that appear frequently and in large numbers as a team to calculate the load; tracked vehicles and flatbed trailers that are less likely to appear are used as the calculated load. Cars and trains travel on the bridge surface, which causes the bridge to be impacted. The vehicle load should be multiplied by the dynamic coefficient during the design. In addition, the braking force of the vehicle when braking, the centrifugal force of the vehicle on the curve, the lateral swaying force of the train, and the additional lateral pressure of the soil caused by the vehicle load (see bridge load) must also be considered.

Load crane load

Vertical and horizontal forces on the structure caused by crane operations. In order to lift materials and finished products in production in industrial plants, various types of cranes such as bridge cranes, suspension cranes, and cantilever cranes are often installed during the installation and maintenance of lifting equipment. The vertical force of the crane is the maximum vertical wheel pressure of the crane. For bridge cranes, it can be determined by the weight of the large bridge, the weight of the trolley, the weight of the driver's operating room and the rated maximum lifting weight. Generally available in accordance with the provisions of the crane product catalog. The horizontal force of the crane is the braking force transmitted through the track when the wheels of the crane are braking. For bridge cranes, the horizontal force is generated when the large car is braked; the horizontal force is generated when the small car is braked. Due to the non-straight, non-parallel track, insufficient rigidity of the crane bridge, and incorrect or non-parallel installation of the crane wheels, the crane moves in a serpentine shape when traveling in the longitudinal direction, causing the wheel's wheel to squeeze the track. Rail force. Due to the vertical impact of the crane due to the height difference of the rail joints, the workpiece turning over, etc., generally different dynamic coefficients can be considered according to the crane type, structural component type and location, and crane weight.

Wind load

The dynamic pressure of the wind is the effect of air flow on the engineering structure, including two effects of stable wind and pulsating wind. It is called aerostatic effect and aerodynamic effect on the engineering structure. In windy areas and when designing towering structures or long-span bridges, special attention must be paid.

Snow load

The general snow load is one of the control loads for the tensile membrane structure design in China (except South China). The combined value is 0.7, the frequency value is 0.6, and the quasi-permanent coefficient is 0.5, 0.2 respectively according to snow load zones I, II, and III , 0.0.
Basic snow pressure generally refers to specifications or local meteorological records. The standard gives basic snow pressure in some large and medium-sized urban areas in China for 10, 50, and 100 years. The general structure takes 50 years of basic snow pressure, landscape sketches, temporary buildings, storage, unimportant structures, etc., which can be taken as values for 10 or 30 years, or adjusted appropriately. ^[2]

Load representative value

When designing the building structure, different representative values should be adopted for different loads.

For permanent loads, standard values shall be used as representative values.

For the variable load, the standard value, combination value, frequency value or quasi-permanent value shall be adopted as the representative value according to the design requirements.

Occasional loads should be determined according to the characteristics of the building structure.

Partial load factor

The load partial coefficient is a partial coefficient that reflects the load uncertainty and the structural reliability in the design calculation. The partial load factor can be adopted as follows:

Partial coefficient of permanent load

When the effect is unfavorable to the structure, the combination controlled by the variable load effect shall be 1.2; the combination controlled by the permanent load effect shall be 1.35.

When the effect is good for the structure, 1.0 should be taken, and 0.9 for overturning, slipping or floating check calculation.

2.Variable load partial coefficient

Generally, 1.4 should be taken. ^[3] But for live load of industrial building floor structure with standard value greater than 4KN / , 1.3 should be taken.

Load design value

The value of the load representative value multiplied by the load partial coefficient is called the load design value. ^[3]

Load combination

When designing the ultimate state of load-carrying capacity or designing the ultimate state of normal use according to the standard combination, the variable value shall adopt the standard value or the combination value as the representative value according to the combination regulations.

The variable load combination value shall be the variable load standard value multiplied by the load combination value coefficient.

When designing the limit state of normal use according to the frequency combination, the frequency value and quasi-permanent value should be used as the representative value of the variable load; when the quasi-permanent combination design is used, the quasi-permanent value should be used as the representative value of the variable load.

The variable load frequency value shall be the variable load standard value multiplied by the load frequency value coefficient.

The variable load quasi-permanent value shall be the variable load standard value multiplied by the load quasi-permanent value coefficient.

Load basic value

Standard values of loads The basic representative values of loads used in the design of the structure, that is, the standard loads listed in the load specification. The standard load generally refers to the maximum load value that a structure or component may occur under normal use conditions, so it should be higher than the frequently occurring load value. From a statistical point of view, the standard value of the load is the load value whose probability of overrun is less than a specified value within the specified design basis period, also known as the characteristic value, which is the maximum value acceptable for engineering design. In some cases, a load can have two standard values, upper and lower limits. When the reduction of load has a more dangerous effect on the structure, the lower unfavorable lower limit value should be taken as the standard value; on the contrary, when the increase of load makes the structure have more dangerous effects, the upper limit value is taken as the standard value. As for various live loads, when there are sufficient observation data, they should be statistically determined according to the definition of the above-mentioned standard values; when there are not enough observation data, the standard values of the loads can be determined in combination with design experience according to the above-mentioned concept agreement.

ansys Load ansys

In ansys, loads include boundary conditions and excitations. Corresponding to different analysis types, the loads can be divided into the following different types: loads commonly used in structural analysis: forces, pressures, gravity, displacement boundary conditions, etc .; loads commonly used in thermal analysis: temperature, heat flow rate, convection boundary conditions, etc .; Common loads in magnetic field analysis: magnetic potential, magnetic flux boundary conditions, etc .; Common loads in electric field analysis: potential (voltage), current, charge, and charge density; etc. Common loads in flow field analysis: velocity and pressure.

Accidental load

Occasional loads refer to loads that occur occasionally (or not) during the design life of a structure, and whose values are large and of short duration, such as explosive forces, seismic forces, and impact forces of ships or floating objects.

Load other

1. The functions involved in the design of building structures include direct effects (loads) and indirect effects (such as those caused by ground deformation, concrete shrinkage, welding deformation, temperature changes, or earthquakes). This entry only explains the relevant loads.

2. The functions or loads involved in the design of the building structure, in addition to the implementation in accordance with this code, shall also comply with the provisions of other current national standards.

3, other special loads must be used after investigation and demonstration in accordance with the norms

Load other information

Snow load The weight of snow applied to the roof of a building or other exposed surface of a structure. The snow load value S is determined by the ground area snow weight, that is, the basic snow pressure So times the house area snow distribution coefficient r:

S = rSo

The basic snow pressure stipulated by China is the annual maximum snow volume (average of a certain quantile value of the maximum snow weight distribution in the reference period for a certain number of years) calculated on a generally flat and flat ground based on a certain recurrence period. According to statistics, the statistical distribution of annual maximum ground snow pressure can also be considered as extreme value type I. Compared with the snow-covered Soviet Union, Japan, Northern Europe, Canada and other countries in the world, the snow cover in China is not large and the snow cover period is short. Northeast China and northern Xinjiang are China's two high snow pressure regions. In addition, the middle and lower reaches of the Yangtze River is also a region of high snow pressure, but the snow period is extremely short. For most areas in southern China, the snow on the roof is not considered in the design. Severe snow in the area can also cause a house collapse. Due to the influence of roof form, orientation, wind, and indoor heating or heat dissipation of buildings, the area snow is generally different from the snow measured by a weather station on a flat ground in the wild.

Ice-wrapped loads surround the icing weight on the tower members, cables, and wires. In the winter or early spring season, under certain climatic conditions, in some areas, it is formed by freezing rain, freezing drizzle, fog, clouds or snow melting below 0 ° C, and its value can be determined according to the thickness of the ice and the weight of the ice .

Ice-wrapped loads are often an important load for structures such as transmission towers and lines. Because ice wrap increases the cross section of rods and cables, or closes certain lattice gaps, not only increases the weight of the structure or components, but also increases the wind load significantly due to the increase in the area of wind resistance of the structure. Make the structure more unfavorable.

Wave load, also called wave force, is the effect of waves on structures such as ports, docks and offshore platforms. According to diffraction theory, the effect of waves on structures is composed of four parts: frictional resistance caused by the viscosity of water flow (which is proportional to the square of the velocity of the water mass point); The additional mass force generated by the motion (which is proportional to the acceleration of the water mass point in the wave); the pressure caused by the presence of the structure on the incident wave flow field and the pressure caused by the movement of the structure on the incident wave flow field . The wave force theory including all the effects mentioned above is called diffraction theory. In actual work, the semi-empirical and semi-theoretical Morrison's equation, which only considers the structure affected by wave friction resistance and mass force, is often used to analyze wave force.

Loads in mechanical engineering

Load refers to the external force to which a part or component is subjected during operation.

Classification of loads:

According to different load properties, it can be divided into two types: static load and variable load.

· Loads that do not change with time or change slowly are called static loads, such as gravity, pressure in the boiler, and the tensile force received after the bolts are tightened;

· The load that changes with time is called variable load, such as the force on the piston rod of an internal combustion engine and the force on the gears in a machine.

In the calculation, the load is divided into a nominal load and a calculated load.

· The load acting on mechanical parts calculated based on the rated power (or resistance, drag torque) of the prime mover is called the nominal load. Generally, F is used to indicate force, and T is used to indicate torque.

· Consider the impact, vibration and uneven load distribution of mechanical parts caused by various factors during work. The load that is used to calculate the part after the nominal load is corrected is called the calculated load, and it is expressed by F _c and T _c .

The relationship between the calculated load and the nominal load is: F _c = K F T _c = K T

In the formula, K is the load coefficient, and K is generally taken as 1.

Determination of the calculated load:

The main failure form of engineering machinery drive train parts is fatigue failure. Parts often work at full load, and the impact load is large, so the smaller of the maximum static torque transmitted by the engine and the torque determined by the attachment conditions should be used as the calculated torque.

In fact, the adhesion coefficient is a value that varies with the ground conditions in a large range. Therefore, the calculation is mainly based on the torque transmitted from the engine. The calculation of the adhesion situation is only used for verification when necessary.

The calculation of the torque of each component can be determined as follows:

Gearbox: M _j = M _f (or M _T )

Where M _{j is the} calculated moment;

M _f rated torque of the engine;

M _T output torque of torque converter.

Main drive: M _j = M _f i _{b 1} _{b 1} (or M _T i _{b 1} _{b 1} )

Where _{b 1} transmission efficiency of the first gear of the gearbox.

Final drive: M _j = 0.5 M _f i _{b 1} _{b 1} i _{z c} _{z c}

Where _{z c} the transmission efficiency of the main drive.

After determining the distribution of the transmission ratio and the transmission diagram, you can design and calculate the components of the drive train, such as gears, shafts, bearings, etc.

Load example:

Examples of loads in different disciplines are described below.

Structural analysis: displacement, force, pressure, temperature (thermal stress) and gravity.
Thermal analysis: temperature, heat flow velocity, convection, internal heat generation, infinite surface.
Magnetic field analysis: magnetic potential, magnetic flux, magnetic field segment, source current density, infinite surface.
Electric field analysis: potential (voltage), current, charge, charge density, infinite surface.
Fluid analysis; speed, pressure.