Static load testing with temperature compensation for structural health monitoring of bridges

Abstract

Abstract:The paper presents a series of repeated static loading tests on a prestressed concrete beam, which was originally part of a real bridge and then subjected to stepwise artificial damage. The tests were done during a one-month period that four levels of damage were introduced by cutting tendons until visible cracking occurred. The deflection line was measured by means of several displacement sensors and the retrieved information is used in different ways for damage detection.At first, the sensor spacing requirement is analyzed with respect to measurement accuracy as well as necessary resolution for the numerical derivations of the deflection line to obtain the rotational angle and the curvature of the beam. These derived quantities may be used as damage indicators in addition to the deflection.Damage of concrete goes very often along with non-linear phenomena like cracking of concrete and plastic strain of reinforcement steel. These effects are discussed and their influence on the repeated loading tests as well the test procedure for condition monitoring is deployed. Progressive damage goes along with progressive sagging of the bridge due to gravity, which can also be used as damage indicator.Finally, the effect of varying outdoor temperatures are discussed and assessed. Though these effects can be reduced by choosing cloudy days without high temperature changes and without high solar irradiation, the outdoor temperature is never constant. Hence, a compensation algorithm is proposed which reflects the measured data according to a reference temperature. This compensation visibly improved the regularity of data.

Bridge Monitoring with Harmonic Excitation and Principal Component Analysis

“…Therefore, the UL had an opportunity to perform a series of tests in a piece of this bridge, as shown in Figure 2c. Good results of static loading tests were reported recently in Nguyen, Schommer, Maas, & Zürbes (2016) and . The current paper presents some results accordingly from the dynamic test, performed by the shaker shown in Figure 2b.…”

“…Their measurement is quite fast and often implemented simultaneously with static load testing. Measurements in several positions in a bridge give a direct global vision of the structure (Nguyen, Schommer, Maas, & Zürbes, 2016). Static load testing means generally charging with important weight, for example, some trucks or lorries/wagons, which are under or sometimes over the design load capacity of the structure.…”

Comparison of different excitation‐ and data sampling‐methods in structural health monitoring

“…Such a box can easily be used to determine the plot of any eigenfrequencies vs temperature df i /dT , wherefore the slope stays quite constant . Once this slope is provided, it can be used for temperature compensation . The idea of compensation can be also suitable for more precise and sophisticated excitation techniques as described before.…”

“…In addition, real bridge bearings, even if sliding, are not free of friction and may generate constraints. Modal features like eigenfrequencies are rather dependent on the temperature distribution T ( x,y,z,t ) of a bridge (also variations up to 15%), which has to be measured in the healthy reference state, thus enabling later temperature compensation . This correction of measured data is mandatory and can be done in a physical or statistical manner, for example, based on principal component analysis (PCA) .…”

Distributed Deformation Monitoring for a Single-Cell Box Girder Based on Distributed Long-Gage Fiber Bragg Grating (LFBG) Sensors

“…The main disadvantages of geodetic survey are possible obstruction to public traffic when the survey is ongoing and measurement error from manual observation. Recently, some automatic monitoring techniques, such as Global Positioning System [3,4], displacement sensors [5], hydrostatic leveling system [6] and laser measurements [7] are applied to gain bridge deformation. However, these sensors may be also disturbed by some environmental factors including bad weather, accidental vibration or satellite ephemeris error.…”