Whether it is a warehouse, factory or commercial building, how to reasonably consider the load when building design is the key to ensuring the safety and durability of the structure.
We will explore in depth the types, calculation methods and design points of steel structure loads to help you better understand this complex engineering problem and provide strong guidance for practical design. Whether you are a novice in the industry or a senior engineer, this article will bring you specific practical suggestions and technical points.
Types of Loads in Steel Structures
In steel structure design, loads are the core factor that determines the safety and stability of a building. Different types of loads have different effects on the structure, so it is important to understand the characteristics of these loads and their design significance. The following are common types of loads in steel structure design and their brief descriptions.
1. Dead Load
The dead load encompasses the static weight of the rigid frame, as well as the weights of components such as the roof panel, purlins, insulation cotton, and others. Below are some typical dead load values:
- Purlin + roof panel (0.5mm thickness): 0.10 KN/m²
- Purlin + roof panel (0.5mm thickness) + roof lining board (0.5mm thickness): 0.15 KN/m²
- Purlin + sandwich panel: 0.15 KN/m²
The precise dead load calculation must be tailored to the specific circumstances. In cases where numerous hanging devices are installed on the roof, the weight of the beams used to connect and support these devices cannot be overlooked and should be incorporated into the roof’s dead load assessment.
2. Live load and roof hanging load
Roof live load: When using corrugated steel sheet light roof, the standard value of roof vertical live load should be 0.5KN/m2 (Note: When the rigid frame or purlin has only one variable and the load-bearing area exceeds 60m2, the live load for the steel frame can be 0.3KN/m2).
Roof hanging load: Including sprinklers, pipes, lamps, etc., roof hanging load can be included in the roof live load.
Commonly used roof suspension load values can be referred to as follows:
- Gypsum ceiling 0.15 KN/m2
- Air conditioning duct 0.05 KN/m2
- Lighting 0.05 KN/m2
- Sprinkler 0.15 KN/m2
It should be pointed out that since the light steel structure roof system is very light, when using design software such as STS (the software does not allow users to add suspension load conditions), it is more appropriate to merge the roof suspension core load into the live load. If the roof suspension load is considered in the dead load, the design is unsafe when the dead load + wind load combination is combined.
3. Snow load
When considering snow load, please note:
- It is necessary to consider μr—roof snow distribution coefficient according to Code 50009-2001. The basic snow pressure multiplied by the snow accumulation coefficient is the standard value of snow load;
- When designing the load-bearing components of the building structure and roof, the distribution of snow accumulation can be adopted according to the following provisions:
- Roof panels and purlins are adopted according to the most unfavorable situation of uneven snow distribution;
- Roof trusses and arch shells can be adopted according to the uniform distribution of snow accumulation in the entire span, the uneven distribution of snow accumulation, and the uniform distribution of snow accumulation in half a span respectively;
- Frames and columns can be adopted according to the uniform distribution of snow accumulation in the entire span.
4. Wind load
The wind load shape coefficient of the portal frame can be taken according to the “Building Structure Load Code” (GB50009-2001) or the “Technical Code for Lightweight Steel Structure of Portal Frame” (CECS102:2002). Please note the following:
- The basic wind pressure should be adopted according to the 50-year wind pressure given in Appendix D.4 of the load code, but it must not be less than 0.3kN/m2.
- Not all portal frames can be used according to CECS. The portal code is only applicable to: roof slope α≤10, average roof height ≤18m, house height-to-width ratio ≤1, and eaves height ≤the minimum horizontal size of the house;
- When the column foot is hinged and the l/h of the frame is less than 2.3 and the column foot is rigidly connected and the l/h is less than 3.0, it is safer to use the wind load body shape coefficient specified in GB50009 for frame design, while using the value of GB50009 in other cases will lead to unsafe design;
- In any case, the algebraic sum of the wall shape coefficients on both sides of the horizontal frame should not be less than 1.2.
5. Crane load
The vertical load of bridge (beam) crane or suspension crane should be taken according to the unfavorable position of the crane; The horizontal load can be ignored for manual crane and electric hoist.
6. Earthquake load
When the seismic fortification intensity is high and the building span is large, the height is high, or there are many sway columns in the width direction, the horizontal earthquake effect can be verified according to the “Building Seismic Design Code” under the rigid frame earthquake left and right combination. When calculating, the damping ratio can be taken as 0.05.
4. Other loads
7. Other loads
In addition to the common loads mentioned above, steel structures may also be affected by some special loads.
Thermal loads: Expansion and contraction of materials caused by temperature changes may cause stress in the structure. The effects of thermal loads can be mitigated by setting expansion joints or using flexible connectors.
Explosion load: The impact force generated by the explosion, usually used in the design of high-safety buildings.
Construction load: Temporary load generated during the construction process, such as construction equipment, material stacking, etc.
Vibration load: Load caused by mechanical equipment, traffic or other external vibration sources.
Corrosion load: Material performance degradation due to environmental corrosion, indirectly increasing the structural load.
In steel structure design, load analysis is a key step to ensure the safety and stability of the building. Whether it is dead load, live load, environmental load or other special loads, we will provide you with comprehensive analysis and design solutions. Should you have any inquiries regarding load analysis or design, please do not hesitate to reach out to us; we are committed to serving you with all our hearts!
Steel Structure Load combination
Why do we need a load combination?
In actual engineering, structures are often subjected to multiple loads at the same time. The design under a single load cannot fully reflect the complex situation in actual use. Therefore, the load combination is to consider the synergistic effect of different loads and ensure the safety and stability of steel structures under various possible conditions.
Common load combinations
- Dead load + live load: This is the most common load combination, which is used to consider the static load and dynamic load of the structure under normal use conditions.
- Wind load + snow load: Commonly used in high-rise buildings or open-air facilities, considering the superposition of wind and snow weight.
- Earthquake load + dead load: In earthquake-prone areas, consider the stability of the structure under earthquake action and the combined effect of constant load.
These load combinations can not only improve the safety factor of the design, but also reasonably predict the performance of the structure under complex working conditions.
The design of load combinations must follow local building codes (such as ASCE, European codes, etc.). These codes have formulated specific load combination requirements based on regional characteristics to ensure that the design is both safe and economical. Following the code can not only improve the safety of the structure, but also avoid overdesign and save costs.
Load Analysis and Design of Steel Structures
Finite Element Analysis (FEA)
Finite Element Analysis (FEA) serves as a valuable tool for analyzing steel structures, enabling engineers to visualize the stress distribution within the structure under various complex loads (including dead load, live load, wind load, earthquake load, etc.) and identify potential issues.
Beam and column design
Beams and columns are the most important parts of steel structures, responsible for supporting and transferring loads.
Load is transferred from beams to columns:
- The function of beams is to bear loads (such as the weight of the floor, the weight of people or furniture), and then transfer the loads to columns. Columns subsequently transmit the loads to the foundation. When designing, ensure that the load can be transferred smoothly to avoid structural imbalance.
Selection of beam and column size:
- The size of beams and columns should be determined according to the load size. If the size is too small, it may not provide adequate support, whereas if it is too large, it will result in material wastage. Engineers need to choose the right size based on the load and the code.
For example, a factory beam will need to support heavier equipment, so it needs to be larger or stronger steel, while a residential beam can be smaller.
Foundation Design
The foundation’s primary objective is to safely transfer the structural load to the ground. When designing the foundation, it is crucial to ensure its strength to prevent any issues.
Load Transfer to the Ground:
- The foundation must be able to evenly distribute the load to the soil. When designing, consider the bearing capacity of the soil and make sure the foundation can support the weight of the entire structure.
Prevent Uneven Settlement:
- If different parts of the foundation sink at different rates, it can cause the house to tilt or even collapse. To mitigate this, engineers design the foundation considering soil conditions and load distribution. For example, in areas with soft soil, pile foundations can be used to transfer the load to deeper, more stable soil layers.
Through finite element analysis, proper beam and column design, and a solid foundation design, engineers can ensure that steel structures are safe and reliable in a variety of situations.
Challenges of Load Calculation for Steel Structures
Uncertainty of Load Estimation
Live loads and environmental loads, including wind, snow, and earthquakes, exhibit significant variability and pose challenges in accurate prediction. For example, the density of people or wind speed in an office building may fluctuate. Therefore, safety factors need to be used in the design to ensure that the structure is safe under various conditions.
Complexity of Load Combinations
In actual projects, multiple loads (such as dead loads, live loads, wind loads, and snow loads) may act at the same time or even superimpose. For example, strong winds and earthquakes occurring at the same time will increase horizontal forces. Engineers need to make reasonable combinations according to the specifications to ensure that the structure is still safe under the most unfavorable conditions.
Software Limitations
Load calculations rely on software, but the accuracy of the results depends on the input data. Incorrect data (such as material properties and load conditions) will lead to deviations in the results. In addition, it is difficult for software to fully simulate real complex situations. Therefore, engineers need to carefully check the data and combine experience to make judgments.
How did we overcome these difficulties?
As a professional steel structure supplier, we are well aware of the challenges in load calculations.
To this end, we combine advanced design software and rich engineering experience to accurately estimate loads and combine them reasonably; at the same time, we strictly follow the design specifications and set appropriate safety factors to ensure that the structure is safe and reliable under various circumstances.
In addition, the team will review the data many times to ensure that every step is accurate, and ultimately provide customers with safe and economical steel structure solutions.
FAQs
What is the difference between dead load and live load?
Dead load refers to the permanent weight of the structure itself, including beams, columns, and floor slabs, which remains constant. Live load, on the other hand, represents the variable weight that may change during use, such as the weight of people, furniture, and equipment. In simpler terms, dead load is the “fixed weight,” while live load is the “changing weight.”
How does wind load affect high-rise steel structure buildings?
The impact of wind load on high-rise buildings is mainly reflected in horizontal forces. Strong winds will produce pressure or suction on the surface of the building, which may cause the structure to shake or even deform. Therefore, wind loads must be specially considered when designing high-rise steel structures to ensure the stability and comfort of the building under strong winds.
How to calculate seismic loads on steel structures?
The calculation of seismic loads needs to take into account the seismic area, building weight, and structural design. The formula usually used is: seismic load = building weight × seismic acceleration × structural coefficient. The specific calculation must follow the local seismic design specifications to ensure the safety of the structure in an earthquake.
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