Tipos de cargas em pontes (16 tipos diferentes)

Types of loads on bridges (16 different types)

June 5, 2024 Roberto Magalhães

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.