Construction Stage Seismic Vulnerability Evaluation of a Continuous Girder Bridge with the Cast-in-Place Cantilever Construction Method

To evaluate the vulnerability of bridges at various construction stages under the action of strong earthquakes, the incremental dynamic analysis (IDA) method is applied, and the vulnerabilities of a continuous girder case study bridge with the cast-in-place cantilever construction method, which owns five main construction stages, are evaluated and compared. The results show the following: With the increase in the peak ground acceleration (PGA), the vulnerabilities of bridges at different construction stages all increase. The fragility and vulnerability are mainly determined by the structural mechanical system condition and the mode shapes but not the modal frequency. For the working condition of seismic PGA of 0.4 g, (1) the bridge at the substructure construction stage may only experience slight or moderate damage with the exceedance probability of 8% to 5% and the mean loss ratio being only about 5%; (2) the vulnerabilities of bridges at the middle cantilever construction stage and the long cantilever construction stage are similar, the collapse damage exceedance probability is about 80%, and the mean loss ratio is about 65%; and (3) the vulnerabilities of bridges at the middle span closure construction stage and the bridge completion construction stage are nearly the same, the collapse damage exceedance probability is about 98%, and the mean loss ratio can reach 80%. The research results explore a new method for evaluating the vulnerability of bridges at different construction stages, which can provide suggestions for seismic damage defense and seismic insurance risk evaluation.

Key Construction Monitoring Technology for Long-Span Continuous Girder Bridge

This paper integrates a monitoring practice for the construction of a long-span continuous girder bridge to explore strain measurement and geometric shape control technology. In doing so, the actual stress of the bridge in the cantilever-construction stage is identified, and the influence of ambient temperature on the geometric shape control of the main girder is eliminated. According to linear creep theory, a strain correction method based on the superposition principle is proposed to remove the strain induced by concrete shrinkage and creep. By identifying the pattern of the solar thermal effect on the main girder geometry, a double in-situ measurement interpolation method is proposed to predict the adjusted value of formwork erection elevation. The results show that the deviation between the measured and corrected stress values on the root section of the main girder under the maximum cantilever state of the main girder is 16%–23%, which verifies the necessity of strain correction. The corrected values of measured stress on each controlled section are essentially identical to the calculated values, and both have consistent change patterns throughout the construction process, which verifies the validity of the strain correction method. During the cantilever-construction stage, the vertical deformation of the main girder owing to the solar thermal effect is parabolic and significant; hence, the main girder geometry should be measured prior to sunrise. The double in-situ measurement interpolation method can effectively eliminate the adverse effects of solar thermal when lofting the vertical formwork elevation in a non-ideal period.

Analysis on the Influence Factors of Construction Linear Control of Continuous Rigid Structure Bridge

In order to study the influence of prestress on cantilever deflection and construction linear control of continuous rigid frame bridge in construction stage, this paper introduces the significance of continuous rigid frame bridge’s linear control, the calculation principle and deflection influence analysis of vertical formwork elevation in cantilever construction. According to a specific continuous rigid frame bridge, this paper use the finite element software to simulate and calculate the deflection of prestress to the cantilever construction of continuous rigid frame bridge. The influence of friction coefficient between prestressed steel bundle and bellows and prestress loss on cantilever deflection and construction line control of continuous rigid frame bridge is also analyzed, furtherly brings out the solution to deal with the problems due to the change of prestress.

Thermo-Hydro-Mechanical Combined Effect Analysis Model for Early-Age Concrete Bridges and Its Application

The early cracking of concrete beam bridges remains a concern in civil engineering. An analytical model considering the combined effect of thermo-hydro-mechanical processes forms the basis for assessing the cracking risk of girders during construction. Based on the equivalent hydration theory, the temperature and moisture conduction processes and the evolution of the mechanical properties of concrete were modeled as a function of the equivalent age. A coupling model for the temperature and moisture fields was established, and a theoretical framework for analyzing the thermo-hydro-mechanical combined effect was presented. Based on this, a numerical analysis method was proposed and implemented into ABAQUS; the results were validated with some typical tests. Finally, a long-span prestressed concrete (PC) box girder bridge with balanced cantilever construction was taken as an example, and the causes of web cracking and its impact degree were analyzed. The results show that the rate of moisture conduction is significantly lower than the rate of temperature conduction; even for thin-walled components, there exists a significant humidity gradient on the surface layer. The humidity-induced shrinkage and restraint of the precast members are the main causes of web cracking.

Time-varying Reliability Analysis of Long-span Continuous Rigid Frame bridge under Cantilever Construction Stage based on the Monitored Strain Data

In general, the material properties, loads, resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying. So, it is essential to monitor the internal force state when the bridge is in construction. Among them, how to assess the safety is one of the challenges. As the continuous monitoring over a long-term period can increase the reliability of the assessment, so, based on a large number of monitored strain data collected from the structural health monitoring system (SHMS) during construction, a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory. At the same time, the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed. This method can provide basis and direction for the internal force control of this type bridge in construction process. So, it can reduce the bridge safety and quality accidents in construction stages.