Crack Resistance of Steel–Concrete Hybrid Joint between Concrete Girder and Steel–Concrete Composite Girder in Long-Span Cable-Stayed Bridge under Hogging Moment
Abstracts:The steel–concrete hybrid joint (SCHJ) between a concrete girder and a steel–concrete composite girder in a cable-stayed bridge has a high risk of cracking under a hogging moment. This study investigated the crack resistance of the SCHJ. Based on a specific bridge, a half-scale SCHJ specimen was designed and tested. A particular loading setup was developed to reproduce the actual loading conditions of the SCHJ. The crack developments and strain distributions of the SCHJ specimen were observed. The SCHJ with fully infilled concrete cracked earlier than the composite girder. A numerical model was developed using the ABAQUS software version 6.14, and the results obtained by this model were in good agreement with the experimental results. The crack development laws of the concrete deck at typical sections in the SCHJ and composite girder in this bridge were derived. An analytical model was proposed to describe crack development in the SCHJ and composite girder. An SCHJ with partially infilled concrete was proposed to improve the crack resistance of the SCHJ compared with the composite girder, and design recommendations were provided for the novel SCHJ with partially infilled concrete in this bridge.
Performance-Based Retrofits of Long-Span Truss Bridges Based on the Alternate Load Path Redundancy Analysis
Abstracts:Existing long-span truss bridges typically undergo significant retrofits to improve their resistance against extreme load events, such as the seismic loads, for which the bridge may not have been designed or considered originally. However, the conventional seismic retrofit measures recommended in most existing codes and specifications may not be effective in providing sufficient alternative load path (ALP) redundancy to a bridge that is vulnerable to sudden member-loss scenarios because of the significantly different magnitude of demands. This paper proposed a performance-based retrofit (PBR) approach for long-span truss bridges that are vulnerable to sudden member-loss scenarios. The performance of the bridge has been evaluated by using the demand-to-capacity ratio (DCR) or strain ratio (SR) on the member/component level or the displacement factor on the bridge system level as indicators. Based on the analysis results, the argument is made that the proposed PBR approach allows bridge designers to meet the predetermined performance objectives for sudden member-loss loading conditions. Increase in weight of steel because of such the ALP retrofits is less than 10%. The retrofitted bridge would meet the desired performance levels in the event of sudden loss of any members on the primary trusses of the bridge.
Seismic Responses and Damage Control of Long-Span Continuous Rigid-Frame Bridges Considering the Longitudinal Pounding Effect under Strong Ground Motions
Abstracts:Continuous rigid-frame bridge (CRFB), a type of bridge adopting the unique form of pier-girder consolidation, combines a T-shaped rigid frame with a continuous girder. CRFBs located in western China are likely to suffer destructive earthquakes, which may result in serious damage to bridges. To study the longitudinal seismic responses and damage control of different structure types of the CRFB under strong ground motions, this work develops three nonlinear dynamic analysis models considering the initial internal force state and longitudinal girder-pier pounding effect based on the OpenSEES (version 3.3.0) platform. Moreover, the present study comparatively analyzes the displacement responses, internal force of piers, pounding force and times, and damage condition of the three models and investigates the effectiveness of tuned inerter-based dampers (TIBDs) in controlling seismic responses of the CRFB. The numerical results show that the longitudinal seismic responses of the main piers in the three models are obviously different, especially when subjected to near-fault ground motions. The peak pounding force at the abutments is much larger than at the transition piers, while the pounding times are the opposite. Under near-fault ground motions with a peak ground acceleration (PGA) of 0.4g, the main piers may be damaged moderately or even more seriously, and the bearings are completely destructive. The TIBDs can effectively control the maximum seismic responses and damage degree of the CRFB under pulse-like near-fault ground motions. Among them, both the tuned viscous mass damper and tuned inerter damper are ideal and useful devices. This study can provide useful references for the seismic design and performance analysis of CRFBs.
Early Warning of Abnormal Bridge Frequencies Based on a Local Correlation Model under Multiple Environmental Conditions
Abstracts:The accuracy of frequency prediction is markedly affected by the nonlinearity and model degradation caused by multiple environmental conditions, which may hinder the prediction accuracy and detectability of damage. Therefore, this paper proposes a local correlation model (LCM) between multiorder bridge frequencies and multiple environmental factors for early warning of abnormal frequencies. First, partial least-squares analysis was conducted to extract several environmental principal components sensitive to modal frequencies. The most relevant local data set for each online environmental sample was selected according to similarity measurements based on Euclidean distance metrics. On this basis, more accurate environment–frequency relation models were formed using relatively simple local linear regression models. To filter out the residual environmental variability not suppressed by the LCM and to enlarge slightly abnormal frequency variation, a warning index (i.e., the weighted Mahalanobis distance) was defined using the residual subspatial reconstruction of principal component analysis. Finally, the validity of the proposed method was verified on a cable-stayed bridge. The results show that in contrast to conventional methods, the proposed LCM can accurately describe complicated frequency variations under changing environmental conditions by considering both the nonlinearity of environmental conditions and the time-varying properties of relation models. The detectability of frequency anomalies induced by sudden events can be effectively improved.
Utilizing Kriging Metamodeling to Provide Practical and Effective Bridge Weigh-in-Motion
Abstracts:Emerging technologies are a strategic ally in the efficient management and preservation of pavements and bridges. Toward this end, different methodologies, such as weigh-in-motion (WIM), have been developed for the detection of overweight vehicles and traffic monitoring. Bridge weigh-in-motion (BWIM) systems can be installed and serviced without interrupting traffic flow. This paper presents a new approach for processing traditional strain response data. This proposal extends the BWIM concept of influence area from response time-histories. The dimensionality of the strain response waves is reduced by the calculation of the centroid and the area under the curve. Subsequently, these two dimensions are used as inputs to an ordinary Kriging (OK) metamodel to predict the gross vehicle weight (GVW) of the passing traffic. The OK methodology allows for the strategic selection of vehicles to train the BWIM metamodel. An example of the application of Kriging metamodeling (KM) to BWIM through the instrumentation of an in-service highway bridge located in Costa Rica is presented. Experimental horizontal strain data along with corresponding weight measurements from a static permanent weigh station were available for 90 trucks to validate the proposed enhanced BWIM methodology.
Early Warning for Abnormal Cable Forces of Cable-Stayed Bridges Considering Structural Temperature Changes
Abstracts:The deterioration or damage of stay cables can threaten the safety of bridges. It is difficult to judge whether a stay cable is deteriorated only by the variation in cable force because cable force also varies with temperature. Therefore, an early warning method for abnormal cable forces of cable-stayed bridges considering structural temperature changes is proposed in this paper. In the proposed method, a baseline model is established to characterize the normal relationship between the healthy cable force and structural temperatures, so the abnormal cable force can be detected by inspecting the residual between the identified cable force to be detected and the cable force predicted by the baseline model. First, the frequency–temperature relationship (FTR) model obeyed by a healthy cable is established by analyzing the mechanism of cable force change caused by structural temperature changes in bridge components from the perspective of deformation coordination. Then, the prediction error is inspected by constructing a mean value control chart of the modeling error generated from the baseline FTR model. An early warning will be triggered when the prediction error exceeds the control limits. Finally, the proposed method is applied to an actual cable-stayed bridge to verify its effectiveness. The results show that the modeling and prediction capabilities of the established FTR model are satisfactory and that the abnormal changes in cable forces can be detected by the proposed early warning method with satisfactory accuracy.