Structural performance evaluation of arch type long span highway bridge

188-202This paper describes an arch type long span highway bridge, its finite element modeling, experimental measurements, finite element model updating using some uncertain parameters, and structural performance evaluation before and after model updating. For this purpose, Birecik Highway Bridge located on the 81st km of Şanlıurfa-Gaziantep state highway over Fırat River in Turkey is selected as a numerical example. The bridge consist of five arches, each of arch has a 55 m main span. The total bridge length is 300 m and width of bridge is 10 m.The initial finite element model of the arch type long span highway bridge is modelled using SAP2000 program to extract the analytical dynamic characteristics. Operational modal analysis method is used to extract dynamic characteristics using enhanced frequency domain decomposition method. Obtained dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from 49.1% to 0.6% by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, axial forces, bending moments and compressive stresses are reduced 35.7%, 38.9%, 47.05%, and 29.6%, respectively

Operational modal analysis of a scaled bridge model using EFDD and SSI methods

320-330In this study, dynamic characteristics of a laboratory bridge model are determined by operational modal analysis using frequency and time domain methods. For this purpose, a reinforced box girder concrete bridge model is constructed in laboratory conditions. The bridge deck consists of a main span of 3 m and two side span of 1.5 m each. The structural system of the model bridge consists of deck, piers and foundation. The total length of bridge deck is 6 m and width of bridge deck is 60 cm. Ambient vibration tests are conducted to the model bridge to identify its natural frequencies, mode shapes and damping ratios. Natural excitations such as wind and impact hammer are used to vibrate the model bridge. Vibration data is gathered from bridge deck. Measurement time, frequency span and effective mode number are determined by consider similar studies in literature. Sensitivity accelerometers are placed to collect signals from the measurements. The signals collected from the tests are processed by operational modal analysis; and the dynamic characteristics of the bridge model are estimated using enhanced frequency domain decomposition (EFDD) method in the frequency domain and stochastic subspace identification (SSI) method in the time domain. The dynamic characteristics obtained from both methods are found to be close to each other. Maximum 2.68% differences are obtained between natural frequencies for the first mode. Modal assurance criteria values are between 0.85-1.00. This shows that EFDD and SSI results are almost overlapped. It can be concluded that the both of enhanced frequency domain decomposition and stochastic subspace identification methods are very useful to identify the dynamic characteristics of the bridge model. </span

Performance-based fire assessment of a fully automated multi-storey steel parking structure: A computational approach

Conducting a structural fire analysis for automated steel parking structures present a complex challenge due to the vulnerability of steel structures to high-temperature exposure, the unpredictability of fire source locations, and the enhanced thermal loading due to high concentration of vehicles in a compact area. This study conducted a performance-based assessment (PBA) of a fully automated multi-storey steel parking structure under various fire scenarios. The assessment employed Fire Dynamic Simulator (FDS) to simulate the fire behavior in different scenarios and record the temperature developments within the structure. OpenSees was utilized to perform the subsequent thermo-mechanical analysis and obtain the fire responses of the parking structure. The fire analyses demonstrated that the ignition location and ventilation conditions within the structure considerably affects fire propagation and structural responses. Fire cases initiated on the first floor led to a slightly higher drift ratio than those initiated on the 9th floor. The PBA based on strain and drift ratio led to different results. Cases 1, 2, 4, and 6 maintained life safety based on drift ratios, and strain results indicated a collapse prevention level. For centrally located fire cases, the drift ratios were at collapse prevention level while based on strain values, the elements already exceeded the collapse prevention limit. Under all fire cases, the ultimate performance level of the structure has exceeded the collapse prevention level. The findings highlight the necessity of employing fire safety measures in multi-storey parking structures and enhancing their fire resilience

Vibration Characteristics of Kömürhan Highway Bridge Constructed with Balanced Cantilever Method

Kömürhan Highway Bridge is a reinforced concrete box girder bridge located on the 51st km of Elazığ-Malatya highway over Fırat River. Because of the fact that Kömürhan Bridge is the sole in this part of Fırat, it has a major logistical importance. So, in this paper it is aimed to determine dynamic characteristics such as natural frequencies, mode shapes and damping ratios of the bridge using experimental measurements to evaluate current behaviour. The experimental measurements are carried out by ambient vibration tests under traffic loads. Due to the expansion joint in the middle of the bridge, special measurement points are selected while experimental test setups constitute. Vibration data are gathered from both box girder and bridge deck. Measurement time, frequency span and effective mode number are determined by consider similar studies and literature. Peak Picking method in the frequency domain is used for the output-only modal identification. At the end of the study, dynamic characteristics of the Elazığ and Malatya part of bridge are compared with each other and torsional effects on the bridge are determined. Good agreement is found between dynamic characteristics in the all measurement test setups performed on box girder and bridge deck