Search Results (5)

While building the steel–concrete composite girder bridge by means of the incremental launching method, the steel box is directly in the sunlight, and the temperature impact should not be neglected. However, the existing specifications fail to offer the temperature gradient pattern applicable to the steel box featuring a significant height–width ratio and straight web. This paper, relying on the Fenshui River Bridge situated in the southwest region of China, carried out a temperature test. By analyzing the experimental data, the rules of temperature changes at the measuring points in various positions of the steel box were studied, and the temperature disparities of the steel box across different seasons were contrasted. Through the analysis of the test data, the rule governing temperature distribution across the height dimension of the cross-section and its change with time were studied, and a model designed to represent the temperature gradient within the steel box was put forward. By utilizing the numerical model, the effect of the temperature gradient on the force acting on the structure in the process of incremental launching was analyzed. The findings indicate that the temperature of the top plate of the steel box is the highest from 14:00 to 16:00. There is a lag phenomenon in the temperature rise in the bottom plate. The greatest temperature disparity between the upper and lower plates of the steel box is not always present in the season when the temperature is comparatively high. The curve of temperature gradient change exhibits nonlinear features, and the variation in temperature is considerable within the scope of 1 m. In this article, a double-broken line temperature gradient model is put forward, with the corresponding temperature gradient of 17.8 °C. The temperature gradient obviously affects the structural stress, changing the stress distribution, and it notably impacts the deformation. The deformation generated on the guide beam due to the temperature gradient makes up 39% of the total deformation. The temperature gradient is not a fixed value. When the steel box girder is under the jacking process, especially while the structure remains in its maximum cantilever condition and is about to cross the pier, the time should be avoided when the temperature gradient is at its highest. Full article

To investigate the dynamic characteristics of a PC beam–steel box arch composite bridge when the number of loading lanes for autonomous vehicles changes, the vehicle–bridge coupling motion equation was derived and solved iteratively via the Newmark-β method. Joint simulation software based on ANSYS 17.0 and Easy Language was developed to analyze vehicle–bridge coupling and driving comfort. The results showed that the dynamic response is the largest under single-lane conditions, with suspected vehicle–bridge resonance. For multilane conditions, eccentricity is the main factor when the vehicle weight is low, whereas the vehicle weight dominates when it is large. The dynamic response is positively correlated with eccentricity and vehicle weight. With respect to the dynamic amplification factor (DAF), single-lane conditions yield high DAF values for the main beam, main arch, and boom, whereas the main pier has a greater DAF under multilane conditions. Driving comfort is best under single-lane conditions, followed by dual-lane conditions, and worst under three-lane conditions. Speed is the primary influencer of comfort under single-lane conditions, with comfort reduced at higher speeds. Under multilane conditions, both speed and eccentricity affect comfort, with speed being the dominant factor. The calculated impact coefficient significantly exceeds the standard values, suggesting that separate impact coefficients should be set for each load-bearing component. These findings, combined with driving comfort analysis, provide valuable references for the setting of speed limits and the design and maintenance of such bridges under autonomous vehicle loads. Full article

In order to address the difficulty in determining the seismic damage probability of continuous girder bridges under construction, the seismic vulnerability analysis method of the construction state is proposed in this study. Firstly, taking a long-span prestressed concrete composite box girder bridge with corrugated steel webs (OSW) as an example, the finite element models (FEMs) of dynamic calculation in different phases of cantilever construction are simulated by OpenSEES. Secondly, by selecting reasonable seismic waves and seismic intensity measures, the non-linear time-history analysis is carried out, followed by the demand parameters and damage indexes suitable for the construction state proposed. Finally, the probabilistic seismic demand model (PSDA) of the continuous box girder bridge during the construction stage is constructed by using the “cloud method”, and the seismic vulnerability curves of the piers and temporary bearings are established to evaluate the seismic performance during the construction stage. The results indicate that the damage probability of piers and temporary bearings increases with the progress of construction. The initial formation of the cantilever structure and the sudden change in the size of the construction segmental girder correspond to a high probability of damage, and seismic protection measures should be strengthened during this construction state. Moreover, significantly higher damage probability of the components under construction compared to the completed bridge after it is built. Full article

Continuous rigid-frame bridges across valleys are often at risk of rockfalls caused by heavy rainfalls, earthquakes, and debris flow in a mountainous environment. Hollow thin-walled bridge piers (HTWBP) in valleys are exposed to the threat of impact from accidental rockfalls. In the current research, ANSYS/LS-DYNA is used to establish a high-precision rockfall-HTWBP model. The rockfall-HTWBP model is verified against a scaled impact test performed in previously published research. A mesh independence test is also performed to obtain an appropriate mesh size. Based on the rockfall-HTWBP model, the impact force, damage, and dynamic response characteristics of HTWBP under a rockfall impact are studied. In addition, a damage assessment criterion is proposed, based on the response surface model, combined with the central composite design method and Box–Behnken design method. The main conclusions are as follows: (1) the impact force of the rockfall has a substantial impulse characteristic, and the duration of the impulse load is approximately 0.01 s. (2) The impacted surface of the pier is dominated by the final elliptic damage, with conical and strip damage areas as the symmetry axis. The cross-sectional damage mode is from compression failure in the impact area and shear failure at the corner. (3) The maximum displacement occurs in the middle height of the pier. The maximum displacement increases with impact height, impact velocity, and rockfall diameter and decreases with the uniaxial compressive strength of the concrete. (4) The initial impact velocity and diameter of the rockfall are the most significant parameters affecting the damage indices. In addition, a damage assessment method, with a damage zoning diagram based on the response surface method, is established for the fast assessment of the damage level of impacted HTWBP. Full article

Currently, the seismic designs of reinforced concrete (RC) bridges with tall piers are often accomplished following the ductility-based seismic design method. Though the collapses of the RC bridges with tall piers can be avoided, they are likely to experience major damage and loss of functionality when subjected to strong near-fault ground motions. The objectives of this study are to put forward an innovative design concept of a tall-pier system and its application in tall-pier bridges. The concept of the innovative tall-pier system is derived from the principle of earthquake-resilient structures, and is to improve the seismic performances of the tall-pier bridges under strong near-fault ground motions. The proposed tall-pier system has a box section and is composed of four concrete-filled steel tubular (CFST) columns and energy dissipating mild steel plates (EDMSPs). Trial design of a bridge with the new composite tall-pier system is performed based on a typical continuous rigid frame highway bridge with conventional RC box section tall piers. Both static analysis and nonlinear time history analysis of both the bridges with the new composite tall piers and conventional RC tall piers under the near-fault velocity pulse-type ground motions were conducted in Midas Civil2019 and ABAQUS. The results show that: under the design-based earthquake (DBE), the CFST columns and connecting steel beams remain elastic in the bridge with the new composite tall piers, while the damage is found in the replaceable EDMSPs which help dissipate the seismic input energy. The displacement responses of the new bridge are significantly smaller than those of the conventional bridge under DBE. It is concluded that the bridge with the new composite tall piers is seismic resilient under near-fault ground motions. Full article