Journal of Bridge Engineering

Integral abutment bridges (IABs) are prevalent in the US due to their lower maintenance and construction costs, as well as longer service life. However, approach slabs at IABs experience complex demands owing to the fact that there are no expansion joints between the ends of a bridge and its approach slabs. To provide comprehensive field data on the response of IAB approach slabs, a four-lane IAB cast-in-place approach slab and a three-lane IAB precast approach slab were instrumented during construction to elucidate approach slab structural behavior due to live load and thermal effects. Static truck load tests were conducted at various traffic lanes and shoulder locations on each of the instrumented approach slabs. Finite-element analysis (FEA) models were developed to simulate slab behavior under controlled live loading and thermal effects. Numerical modeling of slabs subjected to truck loads is used to estimate the modulus of subbase support under the approach slab. The strain and stress results from numerical modeling are consistent with the truck-induced behavior measured in the field, validating key assumptions of approach slab boundary conditions. A nonlinear thermal gradient profile is proposed to improve the ability of the FEA models to properly capture slab behavior under thermal effects. Solar radiation is found to introduce peak stresses greater than the live load stresses. It is also observed that simplified structural analysis in practice (neglecting parapets) can significantly underestimate stresses in approach slab edge regions.

Effective maintenance planning for bridges is crucial for maintaining their performance, safety, and minimizing maintenance costs. Timely implementation of interventions can improve the performance of bridges and avoid the need for costly interventions. However, bridge maintenance is often delayed because of inadequate planning and budget allocation, as well as resource constraints such as funding. With the availability of historical condition data of bridges in databases such as the National Bridge Inventory (NBI) and National Bridge Elements (NBE), there is an opportunity to use data-driven methods to predict deterioration of bridge elements and optimize their maintenance interventions to maximize the performance of bridges. This paper presents the development of a novel system that uses machine learning (ML) techniques, to predict the condition of concrete bridge elements, and binary linear programming optimization method, to identify the optimal selection of maintenance interventions and their timing, to maximize the performance of bridges while complying with available annual budgets. Four ML methods are explored: decision tree, random forest, gradient boosting, and support vector machines. The results of the ML evaluation show that, while the values of the predictive performance metrics varied for different elements, random forest method had the best performance for all elements. A case study of a concrete bridge is analyzed to evaluate the performance of the system and demonstrate its new capabilities. The case study results show that the developed model identifies optimal maintenance interventions for various annual budgets over a 50-year study period. The primary contributions of this research to the body of knowledge are as follows: (1) the development of a novel system that integrates machine learning techniques and linear programming for predicting bridge element conditions and optimizing maintenance interventions; (2) modeling and predicting the deterioration of bridge elements based on health index metric; and (3) generating long-term maintenance plans for each of the bridge elements to maximize the performance of bridges within available annual budgets. The present system is expected to support decision makers, such as highway agencies, in allocating the limited financial resources for bridge maintenance more efficiently and cost-effectively.

This study aims to investigate the effectiveness of grout and the mechanism of force transfer in socket connections. In doing so, it proposes a new transfer mode called integral transfer mode (ITM), as opposed to the conventional separate transfer mode (STM). The proposed ITM suggests that, in a reinforced concrete socket connection, if there is a strong bond between the column, grouting material, and receiving member, the socket connection will function as an integral structure, deforming together as a whole rather than as separate components. Consequently, the grouting material does not need to provide a significant lateral bearing force, and the interface shear stresses become the key focus in designing a socket connection. To explore this concept, quasi-static tests and numerical analyses using solid elements were conducted on three half-scale specimens with varying grout strengths. The results demonstrated that the performance of specimens with normal-strength grout was comparable to that of the specimen with high-strength grout. And the proposed ITM was better than STM at predicting failure modes, force–displacement relationships, the stress states of reinforcements, and grout stresses.

Seven-wire prestressing strands are commonly used to pretension concrete bridge members. While the industry standard is 12.7-mm (0.5-in.) or 15.2-mm (0.6-in.) diameter strand, interest in developing greater pretensioning forces has resulted in the proposed use of 17.8-mm (0.7-in.) strands. This paper reports an experimental program aimed at characterizing the bond properties of 17.8-mm seven-wire prestressing strand and contrasting these with 9.5-mm (3/8-in.), 12.7-mm (1/2-in.), and 15.2-mm (−0.6-in) strands. The geometric and material properties of the strands are reported, and the evaluation of bond performance is assessed by standard test methods. Beam-end bond tests of both straight and 90° hooked strands are presented. The results of in situ transfer length determined from full-scale girders are also presented. Finally, finite-element analyses aimed at evaluating the influence of the Hoyer effect and strand spacing are presented. In all the tests, bond performance of 17.8-mm strand was found to be adequate and appropriately represented by existing AASHTO transfer and development length equations. The potential for utilizing the embedment of hooked strands into cast-in-place end diaphragms to increase the strand stress that may be developed near girder ends is proposed. From the in situ determination of transfer length, the mean and fifth percentile transfer lengths (determined with 95% confidence) of 0.7-in. strands were determined to be 30.4d_b (d_b is the strand diameter) and 53.4d_b, respectively, both less than the 60d_b prescribed by AASHTO. Additionally, the conventional 51-mm (2-in.) minimum center-to-center strand spacing appears to be adequate for 17.8-mm strands in terms of release stresses. No local cracking or other deleterious effects associated with strand spacing were observed. It is shown numerically that the lower Hoyer effect strand dilation and larger circumference result in marginally lower crack-inducing circumferential stresses. Although the current AASHTO determination of transfer and development length appears to overestimate these values for all strand diameters including 17.8-mm strands, the overestimation of transfer length underestimates concrete tensile stresses at prestress transfer in the area affected by the transfer length. This may result in unanticipated cracking. To address this, a two-tier approach is proposed: (1) using a reduced transfer length—40d_b is proposed—to check tensile stresses at prestress release; and (2) using the longer development length—using a transfer length component of 60d_b—to determine the load-carrying capacity of a prestressed concrete member.

Abstract

Low-damped lightweight footbridges usually present excessive human-induced vibrations. Hence, several experimental and numerical studies have been conducted over the years to propose easy-to-apply load models to represent pedestrian actions for vibration serviceability studies. In this sense, an experimental campaign of an in-service cable-stayed footbridge subjected to different pedestrian-stream scenarios has been carried out. The experimental results have been compared with numerical results involving direct time-integration analyses with and without considering human–structure interaction (HSI). As the application of interacting load models is time consuming and difficult to apply in practical engineering, a simplified frequency-domain interacting model based on the two degree-of-freedom equivalent coupled crowd–structure system is proposed and validated with the time-domain results. Furthermore, the effects of synchronization between pedestrians through the consideration of several statistical distributions for the synchronization angle is evaluated using direct time-integration with HSI and compared with the results of the simplified frequency-domain model in which the interpedestrian synchronization is considered by the equivalent number of pedestrians. Finally, showing the advantages of using the equivalent crowd–structure system, a parametric study of the influence of pedestrian dynamic properties on the structure response is carried out.

Practical Applications

Nowadays, footbridges tend to be slender and are designed using lighter materials than in the past. When footbridges are lightweight, the coupling vertical effect of pedestrians and the structure, called the human–structure interaction phenomenon that causes a reduction in the structure accelerations, is very significant. Therefore, it is of crucial importance to consider this in the design process of new footbridges. However, these models are complex and not geared to engineering practice. In this paper, a simplified method that allows for this phenomenon to be considered is proposed. It is based on simple algebraic operations between transfer functions which are obtained in the frequency-domain in a straightforward manner. The model is compared with another more complex model formulated in the time-domain and with experimental tests yielding very similar results. Furthermore, it is also compared with the noninteracting models proposed in guidelines. These models clearly overestimate acceleration response in lightweight footbridges, leading to a structural oversizing in the design stage.