Tospol Pinkaew

Effectiveness of semi-active tuned mass dampers under harmonic excitation

The control effectiveness of a semi-active tuned mass damper (STMD) with variable damping under harmonic excitation is studied. An optimal control law governing the variation of damping of the damper is derived using the optimal control theory. A situation in which the damping can be varied within a certain range is included. Employing the numerical technique, the responses of a single-degree-of-freedom (SDOF) structure coupled with an STMD are investigated. The control effectiveness of the STMD is evaluated by comparing the structures transient and steady-state responses with those of the structure coupled with a tuned mass damper (TMD). It is found that, under harmonic excitation, the vibration suppression by an STMD is significantly superior to that of a conventional passive TMD in both transient and steady-state responses. This improvement is equivalent to an increase of the TMDs mass by about four times.

Modelling of liquid sloshing in rectangular tanks with flow-dampening devices

For the purpose of damper application, a new mathematical model of liquid sloshing in rectangular tanks, which includes the effects of flow-dampening devices, is developed. The devices used here are for increasing the dissipation rate of sloshing energy, such that the sloshing can be utilized as an effective vibration absorbing mechanism. The theoretical study is focused on the first sloshing mode. It is found that the devices introduce non-linear damping to the sloshing mode and also reduce the modal frequency slightly by added mass effect. The findings are confirmed by free sloshing experiments. After closely checking the performance of various devices, a wire-mesh screen device is chosen for further investigation. Forced vibration responses, as well as free sloshing characteristics, are elaborately examined by shaking table experiments and theoretical analysis. Reasonable agreement is obtained, and the validity of the model is confirmed.

Seismic effectiveness of tuned mass dampers for damage reduction of structures

The effectiveness of tuned mass dampers (TMD) for control of structures under seismic ground motion is investigated. Since describing the effectiveness of TMD using displacement reduction of the structure is found to be insufficient after yielding of the structure, damage reduction of the structure is proposed instead. Numerical simulations of a 20-storey reinforced concrete building modeled as an equivalent inelastic single-degree-of-freedom (SDOF) system subjected to both harmonic and the 1985 Mexico City (SCT) ground motions are considered. It is demonstrated that although TMD cannot reduce the peak displacement of the controlled structure after yielding, it can significantly reduce damage to the structure. In addition, certain degrees of damage protection and collapse prevention can also be gained from the application of TMD. This is of particular significance in view of the current trend toward performance-based design in which TMD may be installed to achieve the target performance of buildings designed for seismic loads.

Effectiveness of Vehicle Weight Estimation from Bridge Weigh-in-Motion

The effectiveness of vehicle weight estimations from bridge weigh-in-motion system is studied. The measured bending moments of the instrumented bridge under a passage of vehicle are numerically simulated and are used as the input for the vehicle weight estimations. Two weight estimation methods assuming constant magnitudes and time-varying magnitudes of vehicle axle loads are investigated. The appropriate number of bridge elements and sampling frequency are considered. The effectiveness in term of the estimation accuracy is evaluated and compared under various parameters of vehicle-bridge system. The effects of vehicle speed, vehicle configuration, vehicle weight and bridge surface roughness on the accuracy of the estimated vehicle weights are intensively investigated. Based on the obtained results, vehicle speed, surface roughness level and measurement error seem to have stronger effects on the weight estimation accuracy than other parameters. In general, both methods can provide quite accurate weight estimation of the vehicle. Comparing between them, although the weight estimation method assuming constant magnitudes of axle loads is faster, the method assuming time-varying magnitudes of axle loads can provide axle load histories and exhibits more accurate weight estimations of the vehicle for almost of the considered cases.

Evaluation of effectiveness of vehicle weight estimations using bridge weigh-in-motion

The effectiveness of two estimation methods of vehicle weight using bridge weigh-in-motion data is evaluated. The measured bending moments of a bridge under a moving vehicle are numerically simulated and are used as the input for weight estimations. Two axle weight estimation methods assuming constant magnitudes (Method I) and time-varying magnitudes (Method II) of axle loads are investigated and compared. One thousand cases of random values of vehicle-bridge parameters are considered. It is found that the weight estimation errors from both methods become larger as the vehicle speed becomes faster. The combined effect of closely spaced axles with high vehicle speeds is clearly observed. In general, both methods can provide rather accurate weight estimation, i.e. gross weight estimation errors are within ±10%. Comparing the two methods, although Method I exhibits a faster computational speed, Method II can provide axle load histories and exhibits more accurate weight estimations for almost all the considered cases.

Fatigue Damage Evaluation of Railway Truss Bridges from Field Strain Measurement

This paper is concerned with fatigue damage evaluation of railway truss bridges in Thailand, which have been in service for more than 60 years by using the deterministic approach. The dynamic strain measuring system was installed on selected bridge members to record the actual strain histories induced by the passing trains. The fatigue damages of all bridge members are evaluated based on Palmgren-Miner damage rule and the S-N curves of the stress ranges from field strain measurement of daily train traffic. For the members that their field strains were directly not monitored, the finite element analysis has been employed to estimate their stress ranges. The finite element models of the bridges are verified with the stress data obtained from the field load test of a locomotive. It is found that the vertical and diagonal members of the railway bridges appear to have the most fatigue damage risk whereas the lower chord and floor beams have the lowest estimated fatigue damage potential.

Field Investigation on Slab-on-Girder Steel Bridges over Intersections in Thailand

This paper overviews the recent project launched by the Bangkok Metropolitan Administration (BMA) as a part of the maintenance program to investigate the safety, remaining fatigue life, and serviceability of steel bridges over many intersections in Bangkok. A total of eleven steel bridges, which belong to the slab-on-girder type, were inspected and a full-scale nondestructive load test was conducted to investigate the bridge actual behaviors and validate the three dimensional finite element modeling. The remaining service life is based on the fatigue life assessment which consists of continuous measurement of traffic and strain data for about one week.

Axle Load Monitoring of Multiple Vehicles Using Dynamic Bridge Responses

A practical approach of axle load identification of multiple vehicles using continuous bridge bending moment is presented. Axle loads are identified using least squares regularization method via the updated static component (USC) technique in order to improve solution accuracy and calculation robustness. A parametric study considering effects of various characteristics of vehicles bridge system including vehicle mass, moving speed, axle spacing, axle weight ratio, vehicle type and bridge surface roughness is performed. The experimental verification is carried out through a scaled model of vehicles/bridge system. Comparison on different schemes of moving characteristic including following movement and overtaking movement is also considered and discussed. The obtained results indicate that identification of vehicle axle load of multiple vehicles is very effective and robust for all moving schemes of multiple vehicle travel when the USC technique is applied.