Jianren Zhang

Bridge Remaining Strength Prediction Integrated with Bayesian Network and In Situ Load Testing

This paper proposes a new framework for predicting remaining bridge strength that integrates a Bayesian network and in situ load testing. It discusses the uncertainty of important factors on corrosion damage and develops a stiffness degradation model for corroded beams based on experimental investigations. Following this, the authors develop a Bayesian network that includes corrosion damage, stiffness degradation, load-deflection response, and other factors to predict structural strength degradation. A numerical example using an existing RC bridge demonstrates the general procedures. The comparison between the theoretical and the experimental deflections from load testing shows that the proposed methodology can efficiently improve prediction accuracy and reduce prediction uncertainty.

Field Study of Overload Behavior of an Existing Reinforced Concrete Bridge under Simulated Vehicle Loads

Overload attributable to increased vehicle loads is becoming an increasingly serious issue in highway transportation. Overload results in damages to bridge structures, degradation of their load-carrying capacities, and even collapse of bridges, which may cause loss of lives and properties. Hence, the actual load-carrying capacity of existing bridges with many years of service and obvious damages is becom- ing an important concern for researchers and engineers. In this paper, field experiments were conducted on a simply supported concrete girder bridge located at Province Road 209 of Hunan Province, China. Test loads were applied to the bridge through a group of hydraulic jacks to simulate the heavy vehicle loads of 196 and 294 kN on single-lane loaded and two-lane loaded cases. The results showed that at the deflection limit, the measured load-carrying capacity of the tested bridge was much higher than the designed value. During experiments, the transverse connection stiffness of the bridge varied insignificantly. Cumulative damage of the structure was observed when the simulated cyclic loads were increased to three times the weight of the 294 kN truck on a two-lane loaded case. DOI: 10.1061/(ASCE)BE.1943-5592.0000140.

Model for Flexural Strength Calculation of Corroded RC Beams Considering Bond–Slip Behavior

AbstractAn analytical model is proposed in this paper to evaluate the residual flexural strength for corroded RC beams. The steel slipping caused by bond degradation is included in the proposed model. Various failure modes of beams caused by different types of steel bar anchorage are also incorporated in the model. The bond degradation is considered as a function of the corrosion rate of steel. Bond degradation transfers prematurely the effective bond force, resulting in incompatible strain within the slipping region. A new method is developed to quantify the slipping region based on the transfer theory of effective bond force. Next, a new strain-incompatibility analysis method is proposed to determine the deteriorated flexural strength. The accuracy of the model is validated by experimental observations on the beams with different steel anchorage under corrosive environments. Results show that the proposed model can provide a reasonable prediction for the flexural strength and failure modes. The strain i...

Probabilistic Analysis of Corrosion of Reinforcement in RC Bridges Considering Fuzziness and Randomness

AbstractA general methodology for probabilistic corrosion analysis of reinforcing bar in RC bridges is proposed in this paper. Uncertainties due to limited number of experimental data, incomplete inspection information, as well as the intrinsic randomness of random variables affect the prognostics of corrosion damage. The proposed study includes both fuzziness and randomness to consider different types of uncertainties. First, the chloride-induced corrosion initiation and propagation model are developed for reinforcement in RC bridge. The relationship between the area corrosion rate and the yield strength degradation is proposed on the basis of experimental investigation from accelerated corrosion testing. Following this, the randomness and fuzziness are included using fuzzy random variables to consider the uncertainties of the degradation under corrosive environments. The probabilistic modeling of the mean and the SD of reinforcement yield strength is discussed in detail. Finally, the proposed methodolog...

Simplified model for corrosion-induced bond degradation between steel strand and concrete

AbstractThe corrosion-induced bond degradation between corroded steel strands and concrete is investigated in the present study. Ten pull-out specimens with different corrosion levels were tested t...

Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products

The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent.

Recent Highway Bridge Collapses in China: Review and Discussion

AbstractThe data of 302 highway bridge catastrophic collapses occurring in China between 2000 and 2014 due to human causes were collected and statistical analyses were conducted from various viewpoints including accident stages (during construction or service), casualties (death or injury), location, time, life span, bridge type, and primary causes behind the accidents. Six representative collapse cases were expounded on to find out their individual peculiarities. These cases encapsulated serious problems in Chinese highway bridge engineering, including design, construction, maintenance, and management, among others. A concise review of highway bridge collapses due to human causes in China was presented. Some typical abnormal phenomena, such as those concerning entities involved in the Chinese highway bridge engineering industry, were analyzed and highlighted. Suggestions were put forward to urge all related parties to obey rules and laws to reduce and avoid bridge collapse accidents. The lessons from the...

Static and Fatigue Behavior Investigation of Artificial Notched Steel Reinforcement

Pitting corrosion is one of the most common forms of localized corrosion. Corrosion pit results in a stress concentration and fatigue cracks usually initiate and propagate from these corrosion pits. Aging structures may fracture when the fatigue crack reaches a critical size. This paper experimentally simulates the effects of pitting morphologies on the static and fatigue behavior of steel bars. Four artificial notch shapes are considered: radial ellipse, axial ellipse, triangle and length-variable triangle. Each shape notch includes six sizes to simulate a variety of pitting corrosion morphologies. The stress-strain curves of steel bars with different notch shape and depth are obtained based on static tensile testing, and the stress concentration coefficients for various conditions are determined. It was determined that the triangular notch has the highest stress concentration coefficient, followed by length-variable triangle, radial ellipse and axial ellipse shaped notches. Subsequently, the effects of notch depth and notch aspect ratios on the fatigue life under three stress levels are investigated by fatigue testing, and the equations for stress range-fatigue life-notch depth are obtained. Several conclusions are drawn based on the proposed study. The established relationships provide an experimental reference for evaluating the fatigue life of concrete bridges.

Curvilinear Fatigue Crack Growth Simulation and Validation under Constant Amplitude and Overload Loadings

AbstractA concurrent simulation and experimental validation for curvilinear fatigue crack growth (FCG) analysis under both constant amplitude and overload spectrums is proposed in this paper. The simulation methodology is based on a small time-scale fatigue crack growth model and the extended finite element method (XFEM) to calculate the stress intensity factor solution of an arbitrary curvilinear crack. Parametric studies are used to determine the algorithm parameters in the numerical fatigue crack growth simulation. Following this, experimental testing on modified compact specimens is performed under both constant amplitude and overload loadings for model validation. Experimentally measured crack growth orientations and lengths are compared with numerical simulations. Both the experimental and simulation results show the overload retardation behavior for curvilinear cracks under overload loadings. The investigated periodic overload loading has no significant impact on the crack growth orientations. Seve...

Effects of stress ratio and banded microstructure on fatigue crack growth behavior of HRB400 steel bar

AbstractThis paper investigates the effects of stress ratio and microstructure on the fatigue crack growth (FCG) behavior of HRB400 steel bars widely used in concrete bridges. A constant stress–con...