Response Of Girder Research Articles

Whipping response analysis by one way fluid structure interaction—A case study

Accurate prediction of whipping induced hull girder response is important for evaluation of hull girder stresses and fatigue life assessment of ships structure. Traditionally, strip theories and panel methods have been popularly used for seakeeping analyses of ships for evaluating the slamming loads. These loads are used for whipping response prediction by idealizing the ship’s hull as a free–free beam. In the present work, numerical seakeeping computations have been performed assuming ship’s hull as a rigid beam. Wave loads thus computed are applied on to the real flexible structure of the ship to obtain the bending moment response amidships. For this purpose, modal superposition technique is utilized. Interaction of fluid (water) with structure (ship) is accounted only once, i.e. while computing fluid forces the structure is considered as rigid. Whipping response is hence obtained considering one way Fluid Structure Interaction (FSI). The obtained peak values are quite close to the experimental values. It is concluded that added mass effect and damping due to the degree of coupling between fluid and structure plays a vital role in whipping response prediction. The present method being computationally efficient and reasonably accurate can be practically used for whipping response predictions at initial design stage.

Damage assessment of shear connectors with vibration measurements and power spectral density transmissibility

Shear connectors are generally used to link the slab and girders together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girders, which significantly reduces the load-carrying capacity of the bridge. Because shear connectors are buried inside the structure, routine visual inspection is not able to detect conditions of shear connectors. A few methods have been proposed in the literature to detect the condition of shear connectors based on vibration measurements. This paper proposes a different dynamic condition assessment approach to identify the damage of shear connectors in slab-on-girder bridge structures based on power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral densities of two responses in the frequency domain. It can be used to identify shear connector conditions with or without reference data of the undamaged structure (or the baseline). Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at sensor locations by experimental modal analysis. PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT vectors in the undamaged and damaged states can be compared to identify the damage of shear connectors. When the baseline is not available, as in most practical cases, PSDT vectors from the measured response at a reference sensor to those of the slab and girder in the damaged state can be used to detect the damage of shear connectors. Numerical and experimental studies on a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrate that damages of shear connectors are identified accurately and efficiently with and without the baseline. The proposed method is also used to evaluate the conditions of shear connectors in a real composite bridge with in-field testing data.

Progressive collapse evaluation of Murrah Federal Building following sudden loss of column G20

The Murrah Federal Building (MFB) was the main target of the Oklahoma City Bombing in 1995. Previous studies have concluded that the building would have collapsed even if exterior column G20 was statically removed. In this paper, the system-level response of the MFB due to the sudden loss of column G20 is analytically studied. It is demonstrated that the building would have resisted progressive collapse, even if the column was suddenly removed. Two important reasons have led to a different conclusion from those of the previous studies. First, the axial compressive force of the column above the lost column diminishes only a few milliseconds after column removal, thus, it does not continue to push the supporting girder down. Second, two collapse resisting mechanisms were not considered in the previous studies: (a) a beam’s tendency to grow as it cracks and yields under flexure and its effects on the axial–flexural response of the 3rd floor transfer girder, resulting in the enhancement of its gravity load carrying capacity and (b) the redistribution of the gravity loads through new load paths in both longitudinal and transverse directions through Vierendeel frame action. Given that the structure collapsed, the initial damage to the MFB must have been more severe than a sudden loss of column G20.

Behavior of steel bridge girders under fire conditions

This paper presents results from experimental and numerical studies on the fire performance of typical steel girders used in bridges. As part of experimental studies three steel–concrete composite girders were tested under simultaneous loading and fire exposure. Test variables included: load level, web slenderness, and spacing of stiffeners. Results from fire tests indicate that typical steel girders can experience failure under standard fire conditions in about 30–35min. The time to failure and mode of failure in fire exposed steel girders is highly influenced by web slenderness, spacing of stiffeners, and type of fire exposure. Steel bridge girders fail through flexural yielding when web slenderness is around 50; however failure mode changes to web shear buckling when web slenderness in girders exceed 100. Data from fire tests is utilized to validate a finite element based numerical model for tracing the response of steel bridge girders exposed to fire. Results from numerical analysis show that the proposed finite element model is capable of tracing the response of steel bridge girders under simultaneous loading and fire conditions.

Finite element modeling of the dynamic response of a composite reinforced concrete bridge for structural health monitoring

This paper describes three-dimensional (3D) finite element (FE) modeling of a composite steel stinger supported reinforced concrete (RC) deck highway bridge subjected to moving truck loads. FE models were validated using test data that were generated elsewhere for structural health monitoring. The FE models were established using a commercial FE analysis package called ABAQUS/standard. The case study bridge was discretized to a combination of shell and solid elements which represent the deck and piers, respectively. Numerous constrain interactions were defined to make the model suitable to obtain accurate results. Moving loads induced by two standard AASHTO trucks were developed through a specific load-time history, applied on 35 nodes on the superstructure. To study the dynamic behavior of the bridge under a moving load, a modal analysis followed by an implicit dynamic analysis was carried out. Acceptable agreement was found between the field measurements and FE simulation. Most concerned dynamic response was strains at different locations in bridge girders and columns, because it is the only critical parameter that can be measured with confidence during SHM at site. The range of strains determined in analysis was reasonably close to the measured strains at the site of the study bridge. Several parameters including damping, truck weight and speed, and material properties were studied. Truck speed had the highest effect on strain response of both girders and columns.

Influence of initial distortion of 3 mm thin superstructure decks on hull girder response for fatigue assessment

This paper investigates the influence of initial distortion of 3 mm thin superstructure decks on hull girder response and fatigue assessment. Part of the traditional superstructure of a prismatic passenger ship is replaced by thin decks with initial distortion amplitude of 0, 1 and 2 times the IACS limit value for thicker plates, i.e. 0, 6 and 12 mm. Both geometrically linear and nonlinear finite element (FE) analysis is used. For reference also traditional superstructure with 5 mm plate thickness is analyzed. Thin straight superstructure decks give 43% of weight reduction and carry approximately 30% less load than corresponding thick straight decks in traditional model. The load that is not carried by thin decks is divided between other traditional decks. The redistribution of forces also happens at the deck level between plates, stiffeners, girders and longitudinal bulkheads. The presence of initial distortion with the shape of one half wave between web frames and stiffeners causes an additional few percent-decrease in forces carried. The results and conclusions are similar for hogging and sagging loading conditions and differences between geometrically linear and nonlinear FE analysis are very small. This means time saving since the panel loading for fatigue assessment can be defined from geometrically linear hull girder response analysis without considering the initial distortions.

Accurate measurements of gross vehicle weight through bridge weigh-in-motion: a case study

In a bridge design code, the design live loads should be based on actual traffic loads. In the past, the information about the actual truck loads on highway bridges was obtained from truck surveys, in which the trucks are stopped for measurement and weighed on ‘static’ weighing scales. During the past few decades, however, the information about truck loads is collected either by pavement weigh-in-motion or bridge weigh-in-motion (BWIM) systems. This paper provides details of three BWIM methods, which were calibrated with extensive testing on a slab-on-girder bridge in Winnipeg, Canada. The first two methods are based on the assumption that truck loads could be represented by an equivalent uniformly distributed load. The first method uses the asymmetry in the shape of the bending moment diagram to calculate the gross vehicle weight (GVW), while the second method compares the girder response at two instrumented transverse sections. The third method calculates GVW using strain signal area as proposed by Ojio and Yamada in 2002. The results show that the first method was inconsistent in its accuracy; the second method’s accuracy reduced with the length of the vehicle. The third method proved consistent and accurate to within 5 % for the test trucks provided that the vehicle speeds could be estimated accurately. Accurate calculations of the truck speeds were achieved by using the time delay in the peak responses of the straps that confine the externally restrained deck slab of the bridge.

DAMAGE DETECTION OF SHEAR CONNECTORS IN BRIDGE STRUCTURES WITH TRANSMISSIBILITY IN FREQUENCY DOMAIN

Shear connectors are generally used to link the slab and girder together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girder, which significantly reduces the load-carrying capacity of bridges. A damage detection approach based on transmissibility in frequency domain is proposed in this paper to identify the damage of shear connectors in slab-on-girder bridge structures with or without reference data from the undamaged structure. The transmissibility, which is an inherent system characteristic, indicates the relationship between two sets of response vectors in frequency domain. Measured input force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at the slab and girder sensor locations by the experimental modal analysis. The transmissibility matrix that relates the slab response to the girder response is then derived. By comparing the transmissibility vectors in undamaged and damaged states, the damage level of shear connectors can be identified. When the measurement data from the undamaged structure are not available, a study with only the measured response data in the damaged state for the condition assessment of shear connectors is also conducted. Numerical and experimental studies on damage detection of shear connectors linking a concrete slab to two steel girders are conducted to validate the accuracy and efficiency of the proposed approach. The results demonstrate that the proposed method can be used to identify shear connector damages accurately and efficiently. The proposed method is also applied to the condition evaluation of shear connectors in a real composite bridge with in-field testing data.

Field Monitoring of Rebar Debonding in Concrete Bridge Decks under Traffic-Induced Vibrations

Concrete deck resurfacing is conducted through staged construction under active traffic conditions in lanes adjacent to the newly poured concrete. Many engineers are concerned about the potential of cracking and rebar debonding and other factors, such as shrinkage, thermal expansion and contraction, and live loads. There is a need to evaluate these detrimental effects with techniques that are reliable under field conditions. In this paper, results are presented from a field study that measured peak rebar velocities during concrete pours. The peak velocities were then compared with experimentally established limits for the cracking potential of the concrete surrounding the rebar. However, it is often more feasible to process accelerometer measurements to obtain velocity indirectly from common processing techniques, such as direct integration. A numerical approach was developed to mitigate the various sources of error in the integration and produce accurate estimates of velocities and displacements from raw accelerometer data. The comprehensive field testing of a rehabilitated bridge span was conducted to capture the dynamic response of the bridge girders, stringers, and deck reinforcement. The bridge was monitored during the pour of a simple span and for several hours after the initial concrete placement. The response predicted by the numerical analysis compared well with the field results: the time histories of velocity and displacement were accurately reconstructed. A comparison with the established limits of peak particle velocity suggested that vibrations induced by typical truck traffic during the initial concrete setting period should not pose any significant risk of debonding.

Damage Detection of Shear Connectors Based on Power Spectral Density Transmissibility

Damage of shear connectors in slab-on-girder structures will result in shear slippage between slab and girder, which significantly reduces the load-carrying capacity of the bridge. This paper proposes a dynamic damage detection approach to identify the damage of shear connectors in slab-on-girder bridges with power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral density functions of two responses. Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at the slab and girder sensor locations by experimental modal analysis. When measurement data from the undamaged structure are available, PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT matrices in the undamaged and damaged states are directly compared to identify the damage of shear connectors. When the measurement data from the undamaged structure are not available, PSDT matrices from measured response at a reference sensor response to those of the slab and girder in the damaged state can also be used to detect the damage of shear connectors. Experimental studies with a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrated that damage of shear connectors can be identified accurately and efficiently with and without measurement data from the undamaged structure.

Dynamic Response of Bridge Girder and Shear Keys Subjected to Pounding during Earthquakes

Shear keys have been widely used to control the damage in abutments and piles during earthquakes. To investigate the dynamic response of bridge girder and traverse shear keys subjected to pounding, a three dimensional model of continuous girder bridge is developed in this study. With the assistance of the finite element method program ANSYS and the package LS-DYNA, the pounding between bridge girder and shear keys is simulated. Subsequently, the stress and displacement responses of the model are analyzed, and the movement characteristics are presented.

Comparative Study on Nonlinear Earthquake Response of Girder Isolated Bridges with LRB and Model Shaking Table Test

Abstract: The thesis is aimed to study the characteristics nonlinear seismic response of the isolated continuous girder bridges with LRB. Inorder to achieve the aim, force- deformation properties of the LRB is considered as bilinear first, the bouc-wen model is adopted to imitate the force nonlinear deformation behavior of LRB, and by using Finite element method, the motion equation of the Isolation system of continuous girder bridge is established, then some shaking table tests towards the model of isolated continuous girder bridges with LRB is done. On this basis of it, by comparing the experimental results and calculation results, such as the acceleration and displacement of deck, vertical force of bearing, and the relationship between the Isolation layer displacement and the Level force displacement of the Bearing, we can see that the difference between the analytical results and the experimental results are very small. The results show that the calculation method can analyze Nonlinear Seismic Response of isolated continuous girder bridges with LRB efficiently. But when the vertical earthquake component is larger ,whether the results of the Vertical tension are produced or not, designing the Rubber bearings should be considered.

An approach for evaluating the residual strength of fire exposed bridge girders

This paper presents an approach for evaluating residual strength of fire exposed steel bridge girders. The approach involves three stages of analysis that is to be carried out at ambient conditions, during exposure to fire, and after cooling of the fire exposed bridge girder. In the first stage, load carrying capacity of the girder is evaluated at room temperature. In the second stage of analysis, thermal and structural response of the bridge girder is traced under specified fire exposure and loading conditions. In the third stage (after the bridge girder has cooled down), residual capacity of the girder is evaluated by incrementing load on the girder till failure occurs. The proposed approach is applied to carry out a set of numerical studies on a typical steel girder using finite element computer program ANSYS. Results from numerical studies indicate that the maximum fire temperature (and associated temperature in steel) is the most critical factor that influences residual strength of a fire exposed bridge girder. A girder exposed to typical “external” fire conditions, with maximum fire temperatures reaching to 600–700°C, retains about 70 to 80% of its strength on cooling. On the other hand, a steel bridge girder exposed to hydrocarbon fire, with a maximum temperature of about 1100°C, looses most of its strength during heating phase of the fire and experiences failure.

Seismic Response Analyses of the Yokohama Bay Cable-Stayed Bridge in the 2011 Great East Japan Earthquake

Yokohama Bay Bridge, with a total span length of 860 m, is the second longest span cable-stayed bridge in East Japan, and one of the most densely instrumented bridges in Japan. On March 11, 2011, the Great East Japan (Tohoku) Earthquake hit northeastern Japan with magnitude of MW 9.0, notably the largest earthquake in Japan’s modern history. Intensity 5+(PGA 1.4–2.5 m/s2) of the maximum scale 7 of Japan Meteorogical Agency’s seismic intensity was recorded on the bridge site. This paper describes seismic response analyses of the bridge, system identification, performance evaluation of link-bearing connections (a seismic isolation system), and postearthquake field observation. Response analyses show that transverse vibration dominated the response of girder and tower, with a maximum girder displacement of 62 cm. The large transverse vibrations induced pounding between tower and girder on the tower–girder connections as shown by the periodic impulses on acceleration records. Meanwhile, longitudinal accelerations indicate that the link-bearing connections functioned properly during the earthquake. System identification reveals nonlinearity of the response as evidenced by variations in natural frequencies and mode shapes during large excitation. Despite these conditions, the bridge did not suffer any structural damages, since the ground motions experienced during the earthquake were less than the design and seismic retrofit ground motions.

Deformation process of web girders in small-scale tanker double hull structures subjected to lateral impact

Experimental drop weight impact tests are performed to examine the dynamic response of web girders in a one-tenth scaled tanker double hull structure struck laterally by a knife edge indenter. The small stiffeners of the full-scale prototype are smeared in the small-scale specimen by increasing the thicknesses of the corresponding plates. The plastic response is evaluated at two impact velocities and the impact location is chosen between two web frames to assure damage to the outer shell plating and the stringers. The laboratory results are compared with numerical simulations performed by the LS-DYNA finite element solver. In the simulations, the strain hardening of the material is defined using experimental data of quasi-static tension tests and the strain rate sensitivity is evaluated using standard coefficients of the Cowper–Symonds constitutive model. The experimental permanent deflection and shape of the deformation show a good agreement with the collision simulations. It is found that the crushing resistance of the specimens is determined by the deformation mechanism of the stringers. Thus, the deformation process is described and compared with theoretical deformation modes for web girders subjected to large in-plane quasi-static loads. Additionally, the influence of the stiffeners on the shape of the deformation of the stringers is illustrated through simulations of stiffened structural elements.

Compartment level progressive collapse analysis of lightweight ship structures

The continued development of large high speed ships, often constructed from aluminium alloy, has raised important issues regarding the response of lightweight hull girders under primary hull girder bending. In particular, the response of lightly framed panels in compression may be influenced by overall panel buckling over several frame spaces. Therefore, to provide improved ultimate strength prediction for lightweight vessels, an extended progressive collapse methodology is proposed. The method has capabilities to predict the strength of a lightweight aluminium midship section including compartment level buckling modes. Nonlinear finite element analysis is used to validate the extended progressive collapse methodology.

Experimental study of the shear response of lean duplex stainless steel plate girders

An experimental and numerical study of the shear response of lean duplex stainless steel plate girders is described in this paper. A total of nine welded plate girders were tested. Lean duplex stainless steel, which is a low nickel variety of the material, has approximately twice the strength of the common austenitic grades and at approximately half the initial cost. It also possesses good corrosion resistance and high temperature properties, as well as adequate weldability and fracture toughness. Two web panel aspect ratios and a range of web slendernesses were considered. The results from the experiments, including the full load-deformation histories and failure models are reported. A numerical investigation was carried out in parallel with the testing. The models were first validated against the experimental results after which parametric studies were performed to generate data for a wider range of cross-sections. The generated experimental and numerical data were used to assess the shear resistance design equations given in Eurocode 3: Part 1.4. The current design provisions were shown to be safely applicable to lean duplex stainless steel, though improved guidance is sought in further ongoing research.

Behavior of Horizontally Curved I-Girders during Lifting

AbstractSeveral stages of performance need to be considered during the design of curved I-girders, including both the construction stage and the in-service conditions. Girder stability during the early stages of construction can be difficult to assess because the girders, at times, have little or no bracing present. One stage when there is no bracing present occurs when the girders are picked up from the ground or transport trucks by cranes and lifted into place. To better understand girder response during this critical stage, field studies were conducted on horizontally curved I-girders to measure rotations and stresses during the lifting process. This paper provides details of a semianalytical solution to predict the buckling and deformational responses of straight and curved girder segments during lifting. The deformations can be compared with rotational limits that were established to minimize problems with making connections to previously erected girder segments. The total rotational deformations of ...

Comparative Study on Buffeting Performance of Sutong Bridge Based on Design and Measured Spectrum

The recent development in structural health monitoring (SHM) technology enables the buffeting responses of bridges to be evaluated in a more realistic manner. In this paper, the buffeting responses of the cable-stayed Sutong Bridge with a main span of 1,088 m is analyzed with the wind spectra used in the design phase and those obtained experimentally from a long-term SHM system to compare the actual buffeting response with design predictions. The autospectra of longitudinal and vertical fluctuating wind components are derived from the in situ strong wind data recorded by the monitoring system. The buffeting analysis is accomplished in the time domain with the aeroelastic effect included. Compared with the buffeting responses obtained from the measured spectrum, the girder responses from the design spectrum are larger in the horizontal direction and smaller in other directions, whereas the tower responses are larger and thus relatively conservative.

Similarity research of anomalous dynamic response of ship girder subjected to near field underwater explosion

The final anomalous sag distortion of the ship girder subjected to the near field underwater explosion (undex) below the middle ship is studied. The sinking exercise of Spruance class destroyer DD973 sunk by one MK48 torpedo is first presented, and a simulation model is established. The exponential attenuation phase, the reciprocal attenuation phase, the post reciprocal attenuation phase, and the negative pressure phase of the undex load are precisely applied in this model. The fluid-solid interaction, the added water mass, the gravity, and the change of buoyancy are also taken into account. The similarity theory is then used to analyze the dynamic response of the ship girder. Similarity parameters and theory prediction formulae of the dynamic response of the ship girder are presented. The physical meaning and influences of these similarity parameters are analyzed.