Damage detection of gusset plate condtion in truss bridges based on wavelet packet energy percentage

This paper investigates the possibility and effectiveness of using a recently developed relative displacement sensor for the damage detection of gusset plate conditions in steel truss bridges. The developed sensor is an innovative design offering some advantages and unique features, and is a much easier and cheaper method of structural health monitoring due to the simplicity of its direct measurement of relative displacement without the need for a stable reference point. To investigate the potential applications of the developed sensor to the damage detection of joint conditions, a steel truss bridge model is fabricated in the laboratory and installed with the developed sensors to detect the loosen bolt damage in the gusset plates by using measured relative displacements. Those measured relative displacement measurements from the free vibration tests of both the undamaged and damaged truss models are analyzed, and a damage index based on the wavelet packet energy percentage change is used to detect the existence of the loosen bolt damage in steel truss bridges. Experimental studies demonstrate that the developed relative displacement sensor has a sensitive performance to indicate the joint conditions in steel truss bridges

Concrete spall damage of UHPC slabs under contact detonation - An experimental investigation

Concrete spallation is a typical brittle damage mode under close-in or contact explosions. Upon concrete spallation, a large number of fragments displace from the concrete surface with high speed and these fragments endanger the personnel and equipment shielded by the concrete member. It is therefore important to have a better understanding on the concrete spall phenomena. In the present study, contact explosion tests are carried out on concrete slabs. Four slabs including two made of normal strength concrete (NRC) and two ultra-high performance concrete (UHPC) slabs are tested. Different size of contact explosives are used in the tests. Test observations are compared with the predictions made by available empirical methods

Fragility curves for corrugated structural panel subjected to windborne debris impact

With the climate change, more and more extreme wind events such as cyclone take place around Australia and the world, which cause tremendous loss and damage. The wind speed has been reported constantly increasing with the climate change, which imposes more threats to building environments. The building envelopes are vulnerable to the windborne debris impact in a form of creating an opening in wall, roof, door, windows and screens, which leads to internal pressure increase and results in roof lifting up. The capacity requirements of wall or roof panels to resist windborne debris impact in cyclonic regions has been substantially increased in the 2011 Australian Wind Loading Code (AS/NZS 1170.2:2011) as compared to its previous version. The performance of commonly used structural panels in Australian Building Industry under the increased design wind speed needs be evaluated. Intensive laboratory tests and intensive numerical simulations on performances of typical structural panels subjected to windborne debris impacts have been carried out. This paper presents the results of one panel type, i.e., corrugated panel. The vulnerability curves of the corrugated panel with respect to the debris mass and impact speed are simulated. These results can be used in probabilistic loss estimations of structural panels in extreme wind events

Improved damage identification in bridge structures subject to moving loads: Numerical and experimental studies

This paper proposes a damage identification approach in bridge structures under moving vehicular loads without knowledge of the vehicle properties and the time-histories of moving interaction forces. The dynamic response reconstruction technique in wavelet domain is developed for a structure subject to moving vehicular loads. The transmissibility matrix between two sets of time-domain response vectors from the structure is formulated using the unit impulse response function in the wavelet domain with the moving loads at different locations. Measured acceleration responses of the structure in the damaged state are required for the identification, and the damage identification procedure is conducted without knowledge of the time-histories of the moving loads. A dynamic response sensitivity-based method is used for the structural damage identification, and local damage is modeled as a change in the elemental stiffness factors. The adaptive Tikhonov regularization technique is adopted to improve the identification results when noise effect is included in the measurements. Numerical studies on a three-dimensional box-section girder are conducted to illustrate the effectiveness and performance of the proposed approach, and the simulated damage can be effectively identified even with 10% noise in the measurements. The proposed method is also found capable to identify the damage zone with an approximate estimation of the damage extent when under the influence of initial model errors of the structure. Experimental studies on a Tee-section prestressed concrete beam subject to a moving vehicle are preformed to validate the proposed approach. Identification results from the experimental test data show that the damage locations can be identified with a reasonable estimate of the damage extent

Differential measurement of atmospheric refraction with a telescope with double fields of view

For the sake of complete theoretical research of atmospheric refraction, the atmospheric refraction under the condition of lower angles of elevation is still worthy to be analyzed and explored. In some engineering applications, the objects with larger zenith distance must be observed sometimes. Carrying out observational research of the atmospheric refraction at lower angles of elevation has an important significance. It has been considered difficult to measure the atmospheric refraction at lower angles of elevation. A new idea for determining atmospheric refraction by utilizing differential measurement with double fields of view is proposed. Taking the observational principle of HIPPARCOS satellite as a reference, a schematic prototype with double fields of view was developed. In August of 2013, experimental observations were carried out and the atmospheric refractions at lower angles of elevation can be obtained by the schematic prototype. The measured value of the atmospheric refraction at the zenith distance of 78.8 degree is $240.23"\pm0.27"$, and the feasibility of differential measurement of atmospheric refraction with double fields of view was justified. The limitations of the schematic prototype such as inadequate ability of gathering light, lack of accurate meteorological data recording and lower automatic level of observation and data processing were also pointed out, which need to be improved in subsequent work.Comment: 10 pages, 6 figure

Dynamical Computation on Coefficients of Electroweak Chiral Lagrangian from One-doublet and Topcolor-assisted Technicolor Models

Based on previous studies deriving the chiral Lagrangian for pseudo scalar mesons from the first principle of QCD, we derive the electroweak chiral Lagrangian and build up a formulation for computing its coefficients from one-doublet technicolor model and a schematic topcolor-assisted technicolor model. We find that the coefficients of the electroweak chiral Lagrangian for the topcolor-assisted technicolor model are divided into three parts: direct TC2 interaction part, TC1 and TC2 induced effective Z' particle contribution part, and ordinary quarks contribution part. The first two parts are computed in this paper and we show that the direct TC2 interaction part is the same as that in the one-doublet technicolor model, while effective Z' contributions are at least proportional to the p^2 order parameter \beta_1 in the electroweak chiral Lagrangian and typical features of topcolor-assisted technicolor model are that it only allows positive T and U parameters and the T parameter varies in the range 0\sim 1/(25\alpha), the upper bound of T parameter will decrease as long as Z' mass become large. The S parameter can be either positive or negative depending on whether the Z' mass is large or small. The Z' mass is also bounded above and the upper bound depend on value of T parameter. We obtain the values for all the coefficients of the electroweak chiral Lagrangian up to order of p^4.Comment: 52 pages, 15 figure