Yongming Tu

Sensitivity-based model updating for structural damage identification using total variation regularization

Abstract Sensitivity-based Finite Element Model Updating (FEMU) is one of the widely accepted techniques used for damage identification in structures. FEMU can be formulated as a numerical optimization problem and solved iteratively making automatic updating of the unknown model parameters by minimizing the difference between measured and analytical structural properties. However, in the presence of noise in the measurements, the updating results are usually prone to errors. This is mathematically described as instability of the damage identification as an inverse problem. One way to resolve this problem is by using regularization. In this paper, we compare a well established interpolation-based regularization method against methods based on the minimization of the total variation of the unknown model parameters. These are new regularization methods for structural damage identification. We investigate how using Huber and pseudo Huber functions in the definition of total variation affects important properties of the methods. For instance, for well-localized damages the results show a clear advantage of the total variation based regularization in terms of the identified location and severity of damage compared with the interpolation-based solution. For a practical test of the proposed method we use a reinforced concrete plate. Measurements and analysis were performed first on an undamaged plate, and then repeated after applying four different degrees of damage.

Study on the flexural behaviors of RC beams after freeze-thaw cycles

order to investigate the flexural behaviors of RC beams after freeze-thaw cycles, compressive strength test of concrete cubes after 0, 50, 100, 125 freeze-thaw cycles were made, and static flexural ...

Loading to failure of a 55 year old prestressed concrete bridge

In order to provide relevant data for calibration and development of methods for assessment ofexisting bridges, a 55 year old posttensioned concrete bridge has been subjected to non-destructiveand ...

Study on the Flexural Capacity of Concrete Beam Hybrid Reinforced with FRP Bars and Steel Bars

Two Nominal reinforcement ratios and three failure modes were put forward according to the characteristic of FRP bar and the criterion of appropriate hybrid reinforcement beam was given. Flexural capacity of appropriate hybrid reinforcement beam was analyzed according to the theory of reinforcement concrete and flexural capacities simplified calculate formula of appropriate hybrid reinforcement beam was proposed. three different area ratio of FRP bar to steel bar hybrid reinforced concrete beams, one FRP reinforced concrete beam and one reinforced concrete beam static flexural test were made and the tested results show that the flexural capacities calculate by proposed simplified formula was close to the tested value.

Experimental Study on the Flexural Behavior of Concrete Beam Hybrid Reinforced with FRP Bars and Steel Bars

The hybrid reinforced concrete structure combine the advantages of reinforced concrete structure and FRP structure together, it could resolve the problem of the durability of RC structure and brittle failure of FRP structure. In order to investigate the flexural behavior of concrete beam hybrid reinforced with FRP bars and steel bars, three different area ratio of FRP bar to steel bar hybrid reinforced concrete beams, one FRP reinforced concrete beam and one reinforced concrete beam static flexural test were made. Mechanics characteristic, flexural capacity of normal section and deflection of hybrid reinforced beams were analyzed. The results show that the average concrete strains of different height keep plane, the flexural capacities calculate by proposed formula was close to the tested value. The load-deflection curve decreased gradually after steel bars yielded.

Protecting a five span prestressed bridge against ground deformations

A 50 year-old, 121.5 m long, five span prestressed bridge was situated in the deformation zone close to a mine in Kiruna in northern Sweden. There was a risk for uneven ground deformations so the bridge was analyzed and monitored. Results and measures taken to ascertain the robustness of the bridge are presented. The analysis resulted in an estimate that the bridge could sustain 24 mm in uneven horizontal and 83 mm in uneven vertical displacement of the two supports of a span. To be able to sustain larger deformations, the columns of the bridge were provided with joints, where shims could be inserted to counteract the settlements. To accomplish this, each one of the 18 columns of the bridge was unloaded by help of provisional steel supports. The column was then cut and a new foot was mounted to it. This made it possible to lift each individual column with two jacks, when needed, and to adjust its height by inserting or taking away shim plates. The deformations of the bridge and the surrounding ground were monitored. The eigenmodes of the bridge were studied with accelerometers and by analysis with finite elements (FE) models. Comparison indicated good agreement between the model and the actual bridge, with calculated eigenfrequencies of 2.17, 4.15 and 4.67 Hz, for the first transversal, vertical and torsional modes, respectively. Measurements during winter resulted in higher values due to increased stiffness caused by frozen materials.

Finite element analysis of shear deformation in reinforced concrete shear-critical beams

Abstract The objective of this paper was to study the contribution of shear deformation in reinforced concrete (RC) shear-critical beams. A 2D concrete material model based on smeared fixed crack was presented and incorporated into a commercial finite element (FE) software. A method of calculating shear and flexure deformation separately out of total deformation in the shear span was presented and implemented into the FE analysis. Several experiments of RC shear-critical beams were simulated and good agreement between the experimental and numerical results was obtained in terms of total deformation, flexure deformation, shear deformation and crack patterns. The results show that after shear cracking, the contribution of shear deformation to total deformation increases rapidly. The shear span-to-depth ratio, the longitudinal reinforcement, the shear reinforcement and the load level could be the critical factor to influence the contribution of shear deformation. It appears that for RC shear-critical beams without shear reinforcement, the deformational behaviour is governed by flexure deformation. However, for RC beams with shear reinforcement, the contribution of shear deformation is not negligible after shear cracks develop. Moreover, the measuring method could also affect the measured shear deformation. Finally, future work on experimental investigation into this topic is recommended.

Extend the life of existing railway bridges – Results from EU FP7 project MAINLINE

There is a need to extend the life and capacity of many existing bridges. One of the objects of the EU FP7 Project MAINLINE, 2011-2014, was to facilitate this. Guidelines for assessment and strengt ...