Yanyan Sha

Laboratory Tests and Numerical Simulations of CFRP Strengthened RC Pier Subjected to Barge Impact Load

Bridge piers are designed to withstand not only axial loads of superstructures and passing vehicles but also out-of-plane loads such as earthquake excitations and vessel impact loads. Vessel impact on bridge piers can lead to substantial damages or even collapse of bridge structures. An increasing number of vessel collision accidents have been reported in the past decade. A lot of researches have been conducted for predicting barge impact loads and calculating structural responses. However, in practice it is not possible to design bridge structures to resist all levels of barge impact loads. Moreover, with an increasing traffic volume and vessel payload in some waterways, the bridge piers designed according to previous specifications might not be sufficient to resist the current vessel impact loads. Therefore, strengthening existing bridge piers are sometimes necessary for protecting structures from barge impact. Carbon fiber reinforced polymer (CFRP) has been widely used in strengthening reinforced concrete structures under impulsive loadings. It is an effective material which has been proven to be able to increase the flexural strength of structures. In this study, CFRP composites are used to strengthen reinforced concrete piers against barge impact loads. Pendulum impact tests are conducted on scaled pier models. Impact force and pier response with and without CFRP strengthening are compared. The effectiveness of using CFRP strengthening the pier model is observed. In addition, numerical models of the bridge piers are developed and calibrated with experimental results. Parametric simulations of barge impacting on piers with or without CFRP strengthening are carried out. The results show that compared with unstrengthened pier, CFRP composite strengthened bridge pier has a higher impact resistance capacity and hence endures less structural damage under the same barge impact load. The effectiveness of CFRP strengthening with different CFRP thickness, CFRP strength and bond strength between the pier and the CFRP composite are also discussed.

Numerical simulation of barge impact on a continuous girder bridge and bridge damage detection

Vessel collisions on bridge piers have been frequently reported. As many bridges are vital in transportation networks and serve as lifelines, bridge damage might leads to catastrophic consequences to life and economy. Therefore it is of great importance to protect bridge structures, especially bridge piers, against vessel impacts. Many researches have been conducted to predict vessel impact loads on bridge piers, and to design bridge piers or additional protective structures to resist such impact loads. Studies on assessing the bridge conditions after a vessel impact are, however, very limited. Current practice basically uses visual inspections, which not only requires very experienced engineers to perform the inspection in order to obtain creditable assessment, but also is often very difficult to inspect the underwater pier conditions. Therefore it is necessary to develop methods to give efficient, quantitative and reliable assessment of bridge conditions under ambient conditions after a vessel impact. This study explores the feasibility of using vibration measurements to quickly detect bridge conditions after a vessel impact. The study consists of three parts. First, a detailed numerical model of an example bridge structure is developed to calculate the vibrations under ambient hydrodynamic force. Then the model is used to simulate vessel impact on bridge pier and predict the pier damage. The vibration response analysis of the damaged bridge model is performed again in the third step to simulate vibration responses of the damaged bridge under ambient conditions. Using the vibration data obtained before and after vessel impact, the bridge vibration parameters such as vibration frequencies and mode shapes are extracted by using the frequency domain decomposition method. The bridge condition will then be identified through the changes in bridge vibration parameters and compared with the damage observed in the impact simulation. It is found that this method is capable of estimating bridge damage condition after barge impact accident.

A Simplified Approach for Predicting Bridge Pier Responses Subjected to Barge Impact Loading

Bridge piers are often designed to resist barge impact loads according to empirical equations given in various design codes based primarily on equivalent static analyses. Although these analyses can give useful guidance in design practice, they neglect dynamic effects which can have significant influence on barge-bridge structure interactions. It is necessary to develop an efficient and accurate method that takes into consideration of dynamic effect, material nonlinearity and structural damage in predicting impact loads and structural responses. In this study, empirical equations based on intensive numerical simulation results proposed in a previous study are used to estimate dynamic impact loads on bridge piers. The bridge structure is simplified as a nonlinear single degree of freedom system to calculate its dynamic response. As compared to detailed finite element simulation, this simplified approach is straightforward and gives reasonably accurate prediction of bridge responses. It can be used in the preliminary analysis and design of bridge structures against barge impact.

Numerical investigations of the dynamic response of a floating bridge under environmental loadings

ABSTRACT Floating bridges across wide and deep fjords are subjected to the environmental wind and wave loadings. In this study, the dynamic response of floating bridges under such loadings is investigated. A floating bridge concept, which consists of two cable-stayed spans and 19 continuous spans, is selected. An eigenvalue analysis is first conducted and it is found that the period of the first mode is typically in the order of one minute or more. This implies that the amplified response effect should also be evaluated for the second-order wave load in addition to the first-order wave load. By performing a nonlinear time domain dynamic analysis, the bridge dynamic responses from wind and wave loadings are obtained. The effects of the wind load, first-order and second-order wave loads are studied considering different load combinations. Structural responses including girder displacements, accelerations and moments are investigated for each load combination.