Changes of natural frequencies of a short-span concrete skew bridge during construction (original) (raw)
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Vibration Study of Distressed Concrete Bridge
Sometimes problems come to bridges which are cracking, malfunctioning etc. and they arise due to various reasons. The distressed in bridges may be due to various deficiencies such as Geometry and material deficiency, loading deficiency, boundary conditions deficiency, etc. A research had been carried on to study the effect of deficiency in boundary conditions. For the purpose of identifying the critical locations for failure a PSC-I girder bridge, already casted at DHT laboratory, Ghaziabad, has been analyzed using ATENA-3D under simulated Traffic Load as per IRC18:2000. Accordingly, installation of various gauges and sensors at the critical locations has been done. The instrumentation and test set up has be carried out on the PSC-I Girder Bridge for checking behavior of bridge under deficiencies of bearings. The Experimental Vibration Study using LVDT had been carried out and recorded the various data from gauges by varying support conditions of PSC Bridge (deficiency in one roller support bearing, deficiencies in both roller support bearing). To investigate the change in behavior of deflection under free vibration at various locations of bridge under various boundary conditions, a PSC I-Girder bridge already casted at DHT (Dynamic Heavy Testing) laboratory situated at Ghaziabad was chosen. A stimulated Live Load (as per IRC 18:2000) of 40.1 tons at frequency 2.8 Hz that represent to a vehicle of 40.1 tons moving with the speed of 100 Km/hr. is applied as four point Load over the bridge to test the deflection after removal of load. The system is repeated for all the FOUR CASES:-CASE 1-When all bearings are working properly, CASE 2-When Left Roller Bearing is hinged, CASE 3-When Right Roller Bearing is hinged and CASE 4-When Both Roller Bearings are hinged. After experimental analysis it was found that the deflection pattern obtained in restricting the bearings is showing an increase in vertical deflections at the mid span and so this indicates that, if roller bearings experience some malfunctioning in longitudinal movement then the bridge is more unsafe and unreliable. This data will help in investigating the bearings of bridges that they are working perfectly or not.
Proceedings of the 4th International Symposium on Life-Cycle Civil Engineering IALCCE2014, Tokyo, Japan, November 16–19, 2014, pp. 1-7, 2014
Modal properties of structures (namely natural frequency and damping ratio) play critical roles in design and analysis of new and existing structures and are found to be closely related with the vibrational amplitude. This amplitude-dependent effect is not well characterized due to the relative lack of adequate data on the real behavior of full-scale structures. The paper focuses on the investigation into the amplitude-dependent modal properties of the Nelson St off-ramp bridge (part of the motorway network in Auckland’s CBD, New Zealand) by large shaker forced vibration testing. Different levels of steady-state sin-swept excitations were generated in the vicinity of the natural frequencies of the bridge. A series of normalized frequency response function curves under the condition of different loading scenarios were constructed, from which natural frequencies and damping ratios were identified. The obtained quantitative relationship between natural frequencies/damping and response amplitude was used to describe the amplitude-dependent dynamic behavior.
Dynamic testing of a modern concrete bridge
Canadian Journal of Civil Engineering, 1979
A posttensioned reinforced concrete bridge, slated for demolition, was tested to obtain its dynamic properties. The 10 year old bridge consisted of a continuous flat slab deck of variable thickness having a total width of 103 ft (31.39 m) and spans of 28 ft 6 in. (8.69 m), 71 ft 0 in. (21.64 m), and 42 ft 6 in. (12.95 m). The entire bridge was skewed 10°50′ and the deck was slightly curved in plan.The mode shapes, natural frequencies, and damping ratios for the lowest five natural modes of vibration were determined using sinusoidal forcing functions from an electrohydraulic shaker. These modes, located at 5.7, 6.4, 8.7, 12.0, and 17.4 Hz, were found to be highly dependent on the lateral properties of the bridge deck. Damping ratios were determined from the widths of resonance peaks. The modal properties from the steady state excitation were compared with those obtained from measurements of traffic-induced vibrations and good agreement was found between the two methods.
Ambient Vibration Test on Reinforced Concrete Bridges
MATEC Web of Conferences, 2016
An investigation was carried out to determine dynamic characteristic of reinforced concrete (RC) bridges by using ambient vibration test (AVT). The ambient vibration sources on bridges may come from traffic, wind, wave motion and seismic events. AVT describes the dynamic characteristics of the bridge and ground by measuring the natural frequencies using highly sensitive seismometer sensor. This test is beneficial due to light weight equipment and smaller number of operator required, cheap and easy to be handled. It is able to give a true picture of the bridge dynamic behavior without any artificial force excitation when vibration data is recorded. A three-span reinforced concrete bridge located in Sri Medan, Batu Pahat, Johor was measured by using microtremor equipment consist of three units of 1 Hz eigenfrequency passive sensors used in this test was performed in normal operating condition without excitation required from any active sources or short period noise perturbations. Ten measurements were conducted on the bridge deck and ten measurements on the ground surface in order to identify the natural frequencies of the bridge. Several peak frequencies were identified from three components of Fourier Amplitude Spectra (FAS) in transverse (North-South), longitudinal (East-West) and vertical (Up-Down) direction as well as squared average Horizontal to Vertical Spectral Ratio (HVSR) of ground response, computed by using Geopsy software. From the result, it was expected the bridge have five vibration modes frequencies in the range of 1.0 Hz and 7.0 Hz with the first two modes in the transverse and longitudinal direction having a frequency 1.0 Hz, the third mode is 2.2 Hz in transverse direction, fourth and fifth mode is 5.8 Hz and 7.0 Hz. For ground natural frequencies are in range 1.0 Hz to 1.3 Hz for North-South direction and 1.0 Hz to 1.6 Hz for East-West direction. Finally the results are compared with several empirical formulas for simple verification.
Ambient vibration based evaluation of a curved post-tensioned concrete box-girder bridge.
This paper describes ambient vibration based evaluation of a curved, post-tensioned, concrete, box-girder bridge, the Newmarket Viaduct. The procedure includes ambient vibration testing, system identification, finite element modelling and finite element model updating. Since the dynamic excitations were not measured in the ambient testing, two operational modal analysis methods, namely enhanced frequency domain decomposition and stochastic subspace identification, were applied to identify the experimental dynamic modal characteristics. A three dimensional finite element model of the bridge was created to determine the dynamic characteristics analytically. Analytical and experimental dynamic modal characteristic were compared with each other and the finite element model of the bridge was updated by changing the material properties and boundary conditions to reduce the differences between the experimental and analytical results. It is demonstrated that the proposed procedure can successfully identify the most significant modes of the bridge and the in-situ material properties and boundary conditions.
The vibrational behaviour of three composite beam-slab bridges
Engineering Structures, 1982
This paper describes field measurements of the vibrational frequencies of three bridges with prestressed concrete beams and in situ concrete deck slabs. In each bridge, the beams are simply supported over each span while the composite deck is continuous over three or four spans with short, full width, crumple slabs between the beam diaphragms over each pier. Analytical analyses were also carried out and compared with the field measurements. Values are also given for the damping determined from the tests.
Natural Frequencies of Concrete Bridges in the Pacific Northwest
Transportation Research Record, 1993
Analyses of field ambient vibration were performed on 50 concrete bridge spans along Interstate highways I-5 and I-405 in Washington State. These 50 spans included 21 pretensioned concrete beam (PCB) spans, 19 reinforced concrete box-girder (CBOX) spans, and 10 reinforced concrete slab (CS) spans. Eight measurement transducers were used to record ambient bridge vibrations at three locations on each span: midspan, one-quarter point, and one support. These records of bridge motion versus time were each subjected to a fast Fourier transformation, and plots of amplitude versus frequency were generated for each record. The plots of amplitude versus frequency were used to determine the fundamental vertical and lateral frequencies for the bridge spans measured. These fundamental frequencies were used with the bridge design parameters to derive empirical formulas that will be used to estimate the fundamental vertical and lateral frequencies of other PCB, CBOX, and CS bridge spans along I-5,...
Vibration of bridge structures induced by Traffic loads
Outline of the Paper- Objective- The objective of the study will be to analyse the different methods of analysing the vibrations due to traffic loads on bridge structures, study numerical modelling techniques and evaluate models/methods which can be utilised to control this type of vibration. Scope of the study- The study will be limited to analysing the effects of only traffic loads on bridge structures. Though there are other forces like wind, earthquake etc. which by themselves or in conjunction to each other cause deformations in bridge structures which are considerably high. Different types of bridges will be considered for the study. Effects of traffic vibrations on suspension bridges, steel bridges, concrete girder bridges etc. will be evaluated. Introduction The current standards accepted in design of bridge structures with respect to the loads due to traffic. Review the current AASHTO(American Association of State Highway and Transportation Officials) and OHBDC(Ontario Highway Bridge Design Code) requirements for design of bridges for dynamic effects of traffic induced vibration. Numerical modelling of a standard truck according to AASHTO guidelines. Come out with points where there can be improvements in the code. Brief historical perspective of designing bridge structures considering the vibration induced due to moving traffic loads. Methods of analysis of bridge structures and how they evolved over time. Methods of measurements of vibration over time. Analysis of bridge structures vibration induced due to traffic movement Methods of measurement of effects on bridge structures due to moving traffic. Strain gauges, Load cells and Accelerometers. Positioning of instruments to capture the effect on the entire structure due to different loading conditions. Taking into account volume and speed of traffic. Dynamic tests under controlled heavy traffic. Bridge-vehicle models. To analyse dynamic response of the structure. Effects of pavement roughness and vehicle speeds on the free vibration of the structure. Description of the problem in terms of different types of vibration induced due to traffic loads. Longitudinal Flexural(LF), Symmetric Torsional(TS), Transverse Flexural(TF), Distortion(DS) etc. Effects of each type of vibration on the life of the structure(fatigue stresses) and the comfort level of the drivers of vehicles. Numerical modelling of the bridge-vehicle system. Articulated lorry-AASHTO HS20-44 Truck Finite Element method-Discretization of the structure into number of discrete small elements. Calculating the DAF(Dynamic Amplification Factor). Analysing the problem of vibration due to traffic and zooming down on the concentration areas- Whether the problem is more with the bridge deck and isolating the deck from the piers will solve the problem. Or the axial stresses on the stay cables increase due to traffic movement. In case of suspension bridges-whether the effects of vibration are more on the suspended span. Methods to mitigate effects of vibration due to traffic loads Analyse various methods available presently to absorb the effects of vibration. Eg bearing pads under the deck system which isolate the deck from the piers, dampers placed strategically where the vibration amplitudes are maximum or using specially developed technologies like Tuned Vibration Absorbers. Summary and Conclusions From the study, coming up with methods of analysis best suited for the particular type of bridge. Suggest vibration mitigating measures suited to the type of bridge and vibration type.
MODELLING AND VIBRATION ANALYSIS OF REINFORCED CONCRETE BRIDGE
IRJMETS Publication, 2021
As catastrophic bridge collapse accidents not only cause significant loss of property, but also have a severe social impact. Therefore, the structural health monitoring of bridges for damage detection by vibration analysis gets more attention. Reinforced concrete bridges are the most common and extended structures present in the worldwide. These structures are often characterized by Piers, Abutments, deck slabs. This paper looks on the work of modelling and analysis of bridge in STAAD.Pro software, and the specific bridge model is taken of a particular span. It is subjected to vary Young's modulus (E) in the mid span of bridge deck slab to induce damage in order to obtain maximum bending moment, as the structural strength reduces. From the analysis Mu/bd 2 values from SP 16 code is used to identify the damage on the bridge deck slab, then natural frequency of the bridge, mode shapes, variation of the deflection and node displacements of bridge deck slab under the action of static and dynamic load at different aspect ratios with original design parameters and at failure is carried out in this project.