Papers in This Issue

This November 2013 issue of the Journal features 10 technical papers and one case study. Four technical papers are related to dynamic behavior of bridges. In the paper “Approximate Method for Transverse Response Analysis of Partially Isolated Bridges,” Della Corte et al. investigate an approximate linearized approach for the analysis of partially isolated continuous bridges, that is, bridges with isolation devices at piers and pinned supports at abutments. The role and effect of higher modes of vibration on the system response are discussed, and an approximate method is proposed to account for such effects. An improvement of the classical Jacobsen’s approximation for the effective viscous damping ratio is also proposed using the results of response history analyses. The latter is carried out on two-dimensional numerical models of five case studies, generated from a real existing bridge, which is supposed to be isolated with friction pendulum devices. Comparison of approximate predictions with response history analysis results is presented and discussed. Nonlinear dynamic analyses of a three-dimensional numerical model of the existing bridge are also carried out for comparison purposes. In the paper “Seismic Fragility of a Highway Bridge in Quebec,” Tavares et al. investigate the seismic vulnerability of the Chemin des Dalles Bridge over Highway 55 in Trois-Rivières, Quebec, Canada, through fragility analysis using field- and laboratory-validated models. This approach offers an effective means to capture the uncertainties in ground-motion realizations, the demands placed on key structural components, and the capacity of the components to resist various levels of seismic excitation. A series of 180 synthetic ground-motion time histories (GMTHs) compatible with Eastern Canada was used to capture the uncertainties related to the seismic hazard. Nonlinear time-history analyses were performed with these GMTHs and statistically analyzed to define the probabilistic seismic-demand model for the abutments, bearings, and columns, which are the critical components. Data from the literature, coupled with sectional and damage-mechanics analyses, are used to define the limit states for these components. Bridge components and system fragility curves are used to evaluate the likely failure modes of the bridge and potential targets for retrofit, while accounting for key sources of uncertainty in the performance assessment. The results reveal the seismic vulnerability of this specific bridge and even offer insight into the seismic vulnerability of a typical multispan girder-type concrete bridge in Quebec. In the paper “Finite-Element and Simplified Models for Collision Simulation between Overheight Trucks and Bridge Superstructures,” Xu et al. investigate the impact of overheight trucks on bridge superstructures through finite-element (FE) simulation. Simulation results indicate that collisions between overheight trucks and bridge superstructures induce two types of failure modes: global damage and local damage, which are necessary to be incorporated into bridge design guidelines. The numerical results also reveal that the collision forces are mainly influenced by the parameters associated with overheight trucks. To reduce computational costs and facilitate engineering applications, a simplified model for calculating the collision forces is also proposed. The predictions of the simplified model, although slightly conservative, are in good agreement with the FE results. In the paper “Blast Loading Effects on an RC Slab-on-Girder Bridge Superstructure Using the Multi-Euler Domain Method,” Pan et al. develop a multi-Euler domain method to simulate blast load effects on long-span bridges. Accuracy and efficiency of the method have been demonstrated through application to a RC composite slab-on-girder bridge. The blast-resistant capacities of three different detonation scenarios have been investigated, including one above-deck detonation and two underdeck detonations, with different trinitrotoluene (TNT) equivalent charge weights. The study establishes the dynamic performance and the damage mechanisms of the whole bridge and identifies the critical blast event for this typical slab-on-girder bridge. The results and observations provide a global understanding of protection strategies for highway bridges.

Two technical papers in this issue focus on fatigue behavior of bridges. In the paper “Improved Assessment Methods for Static and Fatigue Resistance of Old Metallic Railway Bridges,” Cremona et al. present a summary of different recommendations and advice proposed in Guideline for Load and Resistance Assessment of Existing European Railway Bridges of the European Union–funded Sustainable Bridges project for assessing old metal railway bridges. The knowledge of the material properties of existing metal bridges is essential for resistance assessment and determination of the remaining lifetime of old metallic bridges. Furthermore, old bridges require more exact and efficient assessment methods that call for a precise description of the material. Fatigue has been identified as the most common cause of failure of metal bridges. To make accurate assessments of existing bridges, it is important to know the behavior of bridges exposed to fatigue and the behavior of old metals subjected to cyclic loads. The possible traffic load on steel rail bridges is usually limited by the fatigue resistance, but for certain situations the static resistance also has to be checked. Most design rules for steel structures, for instance those in Eurocode 3, are also applicable to riveted structures. However, some information is missing on how to deal with the special case when elements are intermittently connected in contrast to welded structures that are connected continuously. Because the traditional methods for assessing the resistance of steel bridges are based on elastic analysis, a method for utilizing a limited redistribution of bending moments based on beam theory is proposed. In the paper “New Structural Joint by Rebar Looping Applied to Segmental Bridge Construction: Fatigue Strength Tests,” Villalba et al. experimentally investigate the design of a modified type of construction joint of limited length between concrete slab segments. The design concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The authors investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, and which often leads to serviceability problems, such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading, such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. This paper experimentally investigates the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results are compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints is confirmed to be similar to the slabs without joints. The experimental loop joint design is found to perform correctly under fatigue loads.

Two technical papers in this issue are related to barriers made of fiber-reinforced polymer (FRP) in bridges. In the paper “Steel Post-and-Beam Barrier with GFRP-Reinforced Concrete Curb and Bridge Deck Connection,” Ahmed et al. investigate the crashworthiness of prototype steel post-and-beam barriers (MTQ Type 210), whose concrete curb-to-bridge deck connection is reinforced with corrosion resistant glass fiber-reinforced polymer (GFRP) reinforcement. Experimental evidence is obtained from proof tests on five full-scale barrier and overhang subassemblies. The test matrix includes three GFRP RC specimens and two steel RC specimens, where the steel RC benchmark system is currently used, as specified in the Canadian Highway Bridge Design Code (CHBDC). The objective is to verify whether (1) the resistance to out-of-plane quasi-static loads and the associated transverse deflection of the GFRP RC curb and steel barrier system is comparable with those of the steel RC counterparts; (2) the transverse strength exceeds the CHBDC equivalent static load demand; and (3) failure at the curb-deck connection is attained at safe transverse loads, and premature failure at the curb-deck connection is prevented. The GFRP and steel RC systems exhibit comparable strength, with the former undergoing greater deformations. For both systems, premature brittle failure of the curb-deck connection is prevented, and the equivalent static load requirements are satisfied. A larger capacity is attained when closed GFRP stirrup connectors are used at the curb-deck connection in lieu of C-shaped stirrups. An analytical model is used to predict the lower-bound strength of the GFRP RC curb-deck connection, and relevant design implications are discussed. It is recommended that the adoption of the proposed GFRP RC design relies on conclusive evidence from crash testing to verify safety against vehicle rollover because of the greater deformations compared with steel RC systems having the same amount of reinforcement. In the paper “Design and Testing of a Concrete Safety Barrier for Use on a Temporary FRP Composite Bridge Deck,” Mongiardini et al. investigate the development of a crashworthy concrete barrier system for use with temporary FRP composite bridge decks. Upon failure of a full-scale crash test with a New Jersey safety shape barrier, an accurate analysis of the potential problems led to a series of design modifications to the barrier and to the attachment between the composite deck and both the bridge structure and the barrier. The second design, which used a vertical-faced barrier, was successfully crash tested according to TL-3 impact safety standards set forth in the AASHTO Manual for Assessing Safety Hardware.

Two technical papers are in different areas of bridge engineering. In the paper “Development Length Tests of Full-Scale Prestressed Self-Consolidating Concrete Box and I-Girders,” Andrawes et al. present the findings of a study investigating the development length of steel strands in self-consolidating concrete (SCC) full-scale prestressed bridge girders. Flexural tests were conducted on two 8.5-m-long box girders and two 14.6-m-long I-girders cast with SCC to determine the development length of their 12.7-mm-diameter prestressing steel strands. Experimental results are compared with requirements of the American Concrete Institute and the AASHTO. Results are also compared with analytical expressions for the development length proposed in literature. In the paper entitled “New Methodology for Calculation of Required Prestressing Levels in Continuous Precast Bridge Decks,” Sousa et al. present a feasible methodology for quantification of the minimum required prestress forces for different critical cross sections of continuous bridges, avoiding the use of iterative procedures. A methodology for taking into account the variability of the structure response because of the uncertainty associated with the quantification of creep, shrinkage, and construction timings is also presented. Monte Carlo simulations, based on the Latin hypercube sampling method, are used in the calculation of the statistical distribution of the long-term structure response. Two case studies are presented to show the relevance of the aforementioned variability and its consequences in terms of minimum required prestressing levels.

In the case study “Field Validation of a Statistical-Based Bridge Damage-Detection Algorithm,” Phares et al. present a field validation of a second-generation, statistical-based damage-detection algorithm and its ability to detect actual damage in bridges accurately. The algorithm had been theoretically validated previously. For the field tests, in lieu of introducing damage to a public bridge, two sacrificial specimens that simulated damage-sensitive locations of the bridge were mounted on the bridge, and different types and levels of damage in the form of cracks and simulated corrosion were induced in the specimens. Using strain data collected from sensors on the sacrificial specimens and on the bridge, the algorithm correctly identifies the damage. Analysis of data from sensors far away from the damaged area reveals a relatively high false-positive rate.