BRIMOS bridge dynamic monitoring technology

The analysis can determine its modal parameters, that is, the natural frequency, vibration mode and damping coefficient of the structure. These parameters reflect the true state of the structure and can be used to update the mathematical model of the structure or to compare with reference data obtained from previous tests. These test results are very accurate, can provide reference data for each future evaluation method, and have qualitative value.

BRIMOS® 3 × 3 outline

The "BRIMOS® 3 × 3 Outline" below illustrates the simplicity and convenience of the BRIMOS® method for structural evaluation:

Three structural parameters determine the dynamic performance:

Geometry (dimension, shape, moment of inertia ...) Material properties (specific gravity, damping coefficient ...) Boundary state (support condition, load ...)

Three modal parameters describe the inherent dynamic performance:

Natural frequency mode damping coefficient

3 main advantages (environmental vibration test AVM):

The test saves time and is more economical. The test does not interfere with the normal use of the structure. The response obtained by the test reflects the real operating state.

Why monitor?

The infrastructure network includes a large number of aging civil engineering structural systems. The performance of many of these in-service structures has been degraded, and their inherent safety level is insufficient compared to their existing design documents. After years of maintenance-free use, owners and competent authorities need rational decision-making principles and methods to arrange budgets for maintenance and repair. Due to the rapid increase in maintenance costs and reduced investment, the budget has become very tight.

Economists and engineers use structural vibration monitoring methods based on continuous vibration as a very promising solution to overcome the gap between long-term monitoring of structures and short-term budgets when doing maintenance planning.

Current maintenance is generally reactive (passive). When it is found that maintenance is needed, the structure has been damaged to a very serious later stage. A timely and targeted repair measure can not only reduce the current maintenance cost, but also have a significant positive impact on the lifetime performance of the structure. BRIMOS® has proven to be a new and very competitive life cycle management tool. In fact, it has become the leading tool covering structural assessment and interactive maintenance planning. Not only that, the implementation of life cycle management has improved the survival status of human beings, such as safety, health and comfort.

Bridges are very important for transportation facilities in any country. The 1960s and 1970s were the peak times for bridge construction in Europe. The owners of the bridge realized that after 30 years of use, the structure had reached a "critical age". In order to ensure safe and unrestricted use, time-consuming, costly repairs and even renovations must be carried out on the bridge.

Considering the above construction and development cycle of European bridges, large-scale repair and renovation investment peak is expected to start in 2005. In order to accurately arrange budget planning, early loss diagnosis and problem areas must be searched to avoid higher costs of accumulated damage.

classification

BRIMOS® provides a clearly defined grading system for the structure tested. Based on modal parameters, visual inspection, FE model update and data reference, this set of classification methods not only provides the corresponding risk level, but also provides rapid identification of structural integrity.

A detailed expert report includes status assessment and recommendations to customers.

SHM needs to return

The questions answered are: Detection-Is there any damage? Location-Where is the damage? Quantification – can it continue to be used? Prediction-User's safety level

Although facilities management methods vary from country to country, each administration and bridge owner is interested in the following:

Cost-effective testing

Reliable structural assessment

Expert reports to prioritize

Cost savings through timely and targeted renovation projects

RAMS integration (reliability, effectiveness, maintainability, and security)

Theory of structural health monitoring based on vibration

Each structure has its typical dynamic characteristics, also known as "vibration tags". A structural change, such as a variety of damages resulting in a reduction in its bearing capacity, will affect its dynamic performance. This shows that the integrity of the structure can be evaluated by testing and monitoring the dynamic response characteristics.

There are many different types of bridge vibration tests: one is to use heavy vibrators or drop weights (forced vibration test) to excite the bridge, and the other is to use environmental excitation (environmental vibration test, wind, traffic ...) . BRIMOS® technology uses the latter method (AVM), which has the advantage that it does not require expensive equipment to energize the bridge and will not interrupt traffic.

System identification includes extracting the dynamic characteristics of bridges and other civil engineering structures from vibration data. These dynamic characteristics are the input signals for damage identification and modal update. The main dynamic parameters to be determined for system identification are as follows:

Frequency and mode

The natural frequency of a structure is determined by the parameters of the structure itself and is called the natural frequency. These structural parameters are geometry (dimension, shape, damping coefficient ...) and boundary conditions (support state, load ...).

However, its size is also related to the vibration mode of the structure, called the vibration mode. For example, a bridge can perform vertical bending vibration, horizontal bending vibration or torsional vibration. Even in the vertical bending mode alone, the bridge may have the largest dynamic deflection in the span, or it may not have any deflection in the span, and a significant displacement occurs at the 1/4 span point. Each vibration mode has its corresponding natural frequency.

The natural frequency is usually evaluated in the standard design state, at which time the structure has no live load and extreme temperature effects. Since the instantaneous mass and stiffness of the actual structure may be different from the design assumptions, the natural frequency of the bridge in use may also be different from the value calculated earlier.

Mode 1BT (first bend along the transverse axis) Mode 2BT (second bend along the transverse axis) Mode 1TL (first twist along the longitudinal axis)

Damping

Damping refers to the ability of a structure to consume energy applied by external forces.

Dynamic energy consumption in vibration comes from multiple sources, such as incomplete elasticity, internal friction of structural materials, friction between structural members at nodes and supports, aerodynamic and hydraulic damping caused by the surrounding environment, nonlinear structural characteristics Energy dissipation and damage caused by foundation and substructure.

Although the formation mechanism of damping is diverse, its total impact on vibration is usually expressed by considering an equivalent viscous damping, specifically expressed as the damping ratio (z).

For example, if the overall damping of the system is 1% of the limit value, then after 11 cycles, the amplitude of the free vibration is reduced by half. If the damping is 10%, then after each cycle, the amplitude will be reduced by half. If the damping reaches a critical value, no vibration will occur.

Vibration intensity

The possible vibration of a structure usually needs to consider its effect on the structure itself. Therefore, in order to maintain the integrity of the structure, it becomes more and more important to consider the vibration limit. It is important to realize this: even when users think that the vibration level of the structure is already unbearable, the risk of structural damage caused by continuous vibration is actually very small. Vibration limits for specific damage risks can be classified based on vibration intensity levels.

If you need more detailed information, please click Brimos bridge dynamic monitoring system, or call us to obtain (contact number).

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