This article discusses different types of bridge loads. Correct identification of the load to be considered during design and construction is very important.
There are very bad experiences around the world that result in bridges collapsing or where modifications have subsequently been made to make them suitable for use. The Millennium Bridge in London is one example where changes were required after construction due to vibration issues.
First, we will briefly discuss the types of bridges before discussing the types of loading on bridges.
- Arch bridge
- Suspension bridges
- Truss bridges
- Girder bridges
- Cantilever bridge
And there are many other types of bridges.
Let's discuss the types of loads on bridges.
Types of loads on bridges
Different Types of Loads on Bridges are discussed in detail. Live loads, dead loads and other applicable load types are covered.
We focus on the loads that need to be considered when driving on the bridge in accordance with BS 5400.
own weight
This is a burden we know well. It is the dead weight of the structure. In addition to the structure's own weight, there are other types of loads, such as: B. superimposed loads.
Weights other than the self-weight of the bridge components can be considered as superimposed dead loads.
Filling concrete, thin concrete, compensation concrete, etc. can be considered as superimposed permanent loads.
payloads
According to BS 5400 Part 2 there are two main types of payloads considered.
- HA loads (equal load and tip load)
- HB Rates
High availability charges
HA loads are uniformly distributed loads on the bridge deck. These types of loads on bridges must be taken into account and are an essential type of load that we must consider in the design.
The HA loads to be applied depend on the bridge span. To calculate the uniformly distributed load, the following procedure can be used.
- If the bridge span is less than 30 m, the UDL is considered 30kN per meter of length per dummy lane.
- If the loaded length exceeds 30m, the load can be calculated from the equation B = 151 (1/L) 0.475 However, the value should not be less than 9 kN/mm. 2 L is the loaded length.
- For ease of reference, the following table can also be used.
Furthermore, the following figure shows the variation of HA-UDL with the bridge span.
In addition to the UDL, an HA point load and a knife edge load (KEL) must be applied simultaneously on the same dummy track.
KEL is considered 120 kN For maximum bending moment it must be applied in the middle of the torsion track and for maximum shear force it must be applied close to the support.
HB Fees
This is the load applied taking into account the vehicle's axles. It also depends on the length of the vehicle, the impact on the bridge varies. Furthermore, the axle load also varies depending on the number of HB units considered.
The following figure shows the HB vehicle considered in the project.
The HB vehicle is positioned so that the critical load case occurs.
Furthermore, the number of HB units is determined based on the design intent of the project. One HB unit corresponds to 10 kN (2.5 kN per axle).
Longitudinal loads
Longitudinal loads caused by traction or braking forces are taken into account in the design.
There are longitudinal loads of the HA and HB types.
Rated load type HA = 8 kN/mx load length + 200 kN ≤ 700 kN
Nominal load type HB = 25% of nominal load HB
Assessments are based on BS 5400 Part 2: 1978. Values from newer standards may vary slightly.
Slip loads – Horizontal loads – Unexpected loads
This load must be taken into account in the HA loads.
Nominal sliding load = 250kN
This load must be applied parallel to the road surface and in any direction.
Furthermore, it can only be used on a dummy track.
Water Flow – Horizontal Load
This is a type of loading that must be taken into consideration during design. The values to be taken into account may correspond to local guidelines.
Centrifugal load
This load is generally not taken into account in bridge design.
For many reasons, bridges are widely avoided.
Centrifugal load can be calculated using the following equation.
F C = 30,000 / (r + 150) Force in kN
Where F C is the centrifugal force and r is the radius of the track.
Vehicle collision load
Road vehicle crash loads can be found in the following table from BS 5400.
Collision load is a special load case and is not included in all load cases.
wind loads
Equations for calculating wind loads are given in BS 5400 Part 2.
In addition to BS 5400 or in accordance with local regulations, wind loads on the bridge can be calculated.
Temperature loads
The effects of temperature on the bridge must be considered in accordance with clause 5.4 of BS 5400 Part 2: 1978.
Shrinking and crawling
Prestressing concrete beams leads to shrinkage and creep. These deformations can affect the bridge structure.
If we consider the adhesion effect of bridges, the in situ concrete is placed on a precise support and subject to shrinkage.
This leads to additional tension. To avoid this effect, the necessary reinforcements must be described in detail.
Earth pressure
Applying earth pressure to the bridge can be done in a conventional manner.
Depending on the location, any additional loads that may arise must be taken into account in the design.
The pressure coefficients for active pressure, resting pressure, and passive pressure can be calculated using the Coulomb method or another applicable method.
Another settlement
If the foundation of the pillars and pillars is Pile foundation there could be no other way settlement .
However, with shallow foundations there is the possibility of different settlements due to different loads and soil conditions.
Erection loads
The type of construction has a significant influence on the loads to be considered as assembly loads.
Furthermore, the construction sequence is also an important factor that must be taken into consideration during planning.
Additionally, see BS 5400 Part 2, Section 5.9 for more information.
boost
If the water table level is above the foundation or any part of the structure, a buoyant force acts on the structure.
This must be taken into account in planning, as it can significantly influence the design of the structure.
