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ABSTRACT The corrosion of steel rebar negatively affects the serviceability and capacity of RC bridges and increases their vulnerability in earthquakes. Most of existing numerical models rely on either solid [...]

The dynamic interaction between the vehicle, rail, and bridges presents a huge computational challenge, especially for reliability analysis based on Monte Carlo simulations. In this study, an integrated algorithm is proposed for the vehicle–rail–bridge dynamic interaction problem. This algorithm divides the system into two subdomains, i.e. the vehicle–rail subdomain and the bridge subdomain. The vehicle–rail subdomain and the bridge subdomain are integrated by the Zhai algorithm and the Newmark-β algorithm, respectively. The integrated algorithm allows different time steps (or multitime steps) to be used for the two domains: a large time step for the bridge subdomain and a smaller one for the vehicle–rail subdomain. The stability region of the proposed algorithm was found through the two-degree-of-freedom model problem, when a single time step is used in both subdomains. The accuracy of the algorithm was numerically investigated through the two-degree-of-freedom model. The vehicle–rail–bridge vibration excited by rail irregularities and earthquakes was simulated using the multitime step algorithm. The effect of the time step ratio (ratio of the large time step to the small time step) on the accuracy of the vehicle–rail–bridge responses was investigated. It has been shown that the time step ratio of less than 50 produces vehicle–rail–bridge responses in an accurate manner for engineering purposes. The multitime step algorithm can solve the vehicle–rail–bridge problem 20 times faster than the single time step algorithms that are conventionally used in the vehicle–rail–bridge simulations. This multitime step algorithm provides an efficient alternative for solving the dynamic interaction between vehicle–rail and large-scale civil structures.

ABSTRACTThe vibration of railway bridges induced by moving vehicles was conventionally evaluated through time domain simulations, which are computationally expensive in probabilistic analyses that require Monte Carlo simulation. A frequency domain solution to the random vibration of railway bridges is derived in this paper where the random wheel-rail force is represented by its power spectral density. As a frequency domain approach, the proposed method is naturally suitable for the random analysis of the vehicle-induced bridge vibration, and the method is highly efficient since it only involves the Fast Fourier Transform (FFT). Numerical examples showed that the simply supported bridge may resonate in several natural modes due to the coincidence of dominant frequencies of hunting forces to the natural frequencies of the bridge. For long-span bridges with low natural frequencies out of which the dominant hunting frequencies fall, resonances are unlikely to occur.

In order to investigate the fatigue behavior of perforated shear connection in steel-concrete composite bridges, 24 connection specimens with different geometric configurations were subjected to static and fatigue testing protocols. Using the design shear resistance of perforated shear connectors obtained from static push-out tests as a reference load level, numbers of fatigue cycles under different cyclic load levels were determined. Accumulated relative slip between steel and concrete components was used to characterize and track fatigue damage accumulation. The relationship between cycle numbers and accumulated relative slip between steel and concrete was established. Test results revealed that the fatigue damage of perforated shear connectors can be divided into three stages, and fatigue life of perforated shear connectors can be evaluated by the accumulated slip, which depends on the maximum shear stress and stress range.

Increased freight activities on Interstate highways escalate the risk of collision between trucks and overpass bridges. Although such events are rare, the consequences of such a collision may be catastrophic. Many overpass bridges were designed and constructed in the early years of development of the Interstate highway system and therefore did not meet the requirements specified in AASHTO's Load and Resistance Factor Design Bridge Design Specifications. In this study, 5-year truck run-off-the-road crash data, information on Interstate highway geometric characteristics, and traffic information were collected to develop crash prediction models for bridge bents. The bent-based predictive methods improved the collision risk estimate by evaluating the individual bents of a bridge on the basis of roadway geometrics and traffic conditions. The detour costs subsequently measured on the basis of the additional road user costs caused by the failure of a bridge were used to assess the importance of a bridge quantitatively. As a result of this study, a bridge index was developed from both the collision risk and detour costs. This study could provide guidance to departments of transportation to develop mitigation plans for bridges with high collision risk indexes.

In 2009, the British Columbia Building Code was amended to increase the allowable height of wood-frame residential buildings to six stories from four stories. This paper presents the details of a numerical study undertaken to understand the seismic performance of six-story wood-frame buildings designed in accordance with the 2006 British Columbia Building Code. To investigate the seismic behavior, a four-story building was used to represent the benchmark seismic performance prior to the amendment. Two independent analyses using computer programs DRAIN-3DX and SAPWood were carried out on representative buildings located in the city of Vancouver, BC, using a suite of 20 earthquake records scaled to the design seismic hazard level for the site. The analyses showed that six-story wood-frame buildings had similar performance to four-story wood-frame buildings.

Light frame wood structures make up the vast majority of the residential building stock in the United States. Because of this, earthquake-induced losses for this category of building from a significant earthquake would have a substantial financial impact on the regional economy, as well as on the building owner. Current wood-framed structural design philosophy focuses only on life safety and only limits damage through implicit assumptions. The concept of loss-based seismic design is introduced in this paper with typical loss-based design statements explicitly formulated with the intent of addressing the concerns, e.g., financial loss, of the building end-user. The loss-based design procedure was established based on a loss estimation framework that relied on the existing concept of assembly-based vulnerability (ABV). With the help of an automated dynamic and loss analysis package developed for wood-framed structures (SAPWood™) at Colorado State University, loss-based seismic design for a typical North American single family residential building was conducted for several different explicitly stated loss targets. The results from the numerical examples showed that loss-based seismic design for wood-framed structures is a viable concept that can serve as an important step in the evolution of end-user oriented, performance-based seismic design (PBSD).