Dynamic behavior of pile-supported wharves by slope failure during earthquake via centrifuge tests

The effects of earthquakes on pile-supported wharves include damage to piles by inertial forces acting on the superstructure, and damage caused by horizontal displacement of retaining walls. Piles can also be damaged through kinematic forces generated by slope failure. Such forces are significant but it is difficult to clearly explain pile damage during slope failure since the inertial force of superstructure and the kinematic force by slope failure can occur simultaneously during an earthquake. In this study, dynamic centrifuge model tests were performed to evaluate the effect of the kinematic force of the ground due to slope failure during earthquake on the behavior of a pile-supported wharf structure. Experimental results indicate that the slope failure in the inclined-ground model caused the deck plate acceleration and pile moment to be up to 24% and 31% respectively greater than those in the horizontal-ground model due to the kinematic force of the ground.

Welding-induced Residual Stresses in U-Ribs of a Steel Bridge Deck

To calculate the welding-induced residual stresses in U-ribs of the steel deck plate and conduct quantitative analysis of influential factors, the U-ribs of steel deck plate of Xinghai Bay Bridge was taken as the research object. In the ABAQUS finite element software, the local models of U-ribs of steel deck plate were established. Nodal body force loads, i.e., heat generation rate, of the double ellipsoidal heat source models were applied via the compiled subsidiary Dflux program. The welding process of the v-groove welds was simulated, to obtain the residual stresses distribution in the top plate and U-rib plates. The influence of thickness of top plate and angle of welding groove on the residual stresses in the U-ribs were studied. The results show that the welding-induced residual stresses calculated by the numerical method proposed in this paper agree well with the experimental data. The maximum residual stresses in the top plates and the U-rib plates all occur near the welds, which exceeds the yielding limitation of the material. As the thickness of top plate increases, the maximum values of residual stresses in the top plates and U-ribs increase. However, with the increase of groove angle, the maximum values of residual stresses in the top plates and U-rib plates decrease.

Analytical and Measured Effects of Short and Heavy Rail Cars on Railway Bridges in the USA

The overall number of railcars recorded in the North American railcar fleet from 2010 to 2015 increased about 5%; the number of all 130 tonne (286,000 lb) gross weight railcars (heavy axle load (HAL) railcars) increased 19%. The increase in shipments in short railcars increases the loading on railway bridges, especially the 12.8-m railcars, commonly used to ship sand and cement, which is approximately a 25% increase in load per unit length compared to 16.2-m coal cars. Significant differences between maximum effects of shorter railcars and common 16.2-m railcars were predicted in analysis for bridge spans longer than 18.3 m. The differences were more prominent on spans 24.4 m and longer. This study presents analytical and measured effects of freight railcars on a two-span truss bridge, with spans of 61 m and 33.5 m, and a 35-m riveted steel deck plate girder (DPG) bridge. The investigation confirmed that short railcars cause higher load effects on main bridge components: the 35-m riveted steel DPG has 28% higher stresses at mid-span, while in the truss, the difference in stresses depends on the location of the member and ranges from 15 to 35%.

Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete

In this research, flexural performance was evaluated using macro-synthetic fiber-reinforced concrete (MFRC) in structural deck plates. Material tests were performed to evaluate the mechanical properties of the MFRC, and the flexural strength evaluation was conducted in two experiments, positive and negative moment tests. In the material test results, compressive strength and modulus of elasticity of the MFRC were increased compared with normal concrete. Flexural tensile tests showed that, after achieving maximum strength, the deck plates had sufficient residual strength until fracture. Structural tests showed that flexural strength and cracking load of all specimens increased according to macro synthetic fiber dosage. According to the experimental results, we proposed a flexural strength model of a steel deck plate containing macro synthetic fiber. The model showed greater accuracy than the current standard compared with the experimental results. In addition, since it was confirmed that the MFRC steel decks had greater flexural stiffness until yielding, it will be necessary to quantitatively evaluate the effect of MFRC on the effective flexural stiffness of steel decking in future studies.

A Numerical Evaluation of Structural Hot-Spot Stress Methods in Rib-To-Deck Joint of Orthotropic Steel Deck

This study numerically investigates the limitations of structural hot-spot stress (SHSS) methods and proposes a guideline for the calculation of hot-spot stresses, which can be used for the better evaluation of fatigue-related problems. Four different SHSS evaluation methods have been applied to the rib-to-deck (RD) welded joint in orthotropic steel deck (OSD). These methods are used to calculate SHSS at this critical joint utilizing finite element analyses (FEA) based software Siemens NX.12. The limitations and the accuracy of these methods have been observed under different element types and meshing techniques. Moreover, the effect of the nodal-averaging feature is being studied. Two types of governing stresses are produced by the application of Eurocode fatigue load model-4. Essentially, the bending in deck-plate produces highly non-linear stress at the deck-toe, and the membrane effect in rib-plate generates linear stress at the rib-toe. Guidelines are proposed considering different parameters on these two stress states by applying SHSS evaluation methods. In comparison to other SHSS approaches, the International Institute of Welding (IIW) quadratic stress extrapolation (QSE) method shows better results for solid single-element, and the American Society of Mechanical Engineers (ASME) through thickness stress linearization (TTSL) method stands out in solid cubic-mesh technique. In general, shell elements have more consistent SHSS results as compared to solid elements for both stress states.

Nonlinear Optimization of Orthotropic Steel Deck System Based on Response Surface Methodology

The steel bridge deck system, directly subjected to the vehicle load, is an important component to be considered in the optimization design of the bridges. Due to its complex structure, the design parameters are coupled with each other, and many fatigue details in the system result in time-consuming calculation during structure optimization. In view of this, a nonlinear optimization method based on the response surface methodology (RSM) is proposed in this study to simplify the design process and to reduce the amount of calculations during optimization. The optimization design of the steel bridge deck system with two-layer pavement on the top of the steel deck plate is taken as an example, the influence of eight structural parameters is considered. The Box-Behnken design is used to construct a sample space in which the eight structural parameters can be distributed evenly to reduce the calculation workload. The finite element method is used to model the mechanical responses of the steel bridge deck system. From the regression analysis by the RSM, the explicit relationships between the fatigue details and the design parameters can be obtained, based on which the nonlinear optimization design of the bridge deck system is conducted. The influence of constraint functions, objective functions, and optimization algorithms is also analyzed. The method proposed in this study is capable of considering the influence of different structural parameters and different optimization objectives according to the actual needs, which will effectively simplify the optimization design of the steel bridge deck system.

Railroad Tie Lateral Resistance on Open-Deck Plate Girder Bridges

On open-deck railroad bridges, the crossties (sleepers) are directly supported by the bridge superstructure and anchored with deck tie fasteners such as hook bolts. These fasteners provide lateral resistance for the bridge ties, and in railroad bridge design, their spacing is controlled by the required lateral resistance of the ties. Currently there are no provisions to assist in the calculation of lateral resistance provided by railroad ties on open-deck bridges, and as a result there are no specific requirements for the spacing of deck tie fasteners. This has led to different design practices specific to each railroad, and inconsistent fastener spacing in existing railroad bridges. A research plan was conducted to experimentally quantify the lateral resistance of timber crossties on open-deck plate girder bridges using different wood species and types of fasteners. Experimental tests were conducted on four different species of timber crossties (Beech, Sycamore, Southern Pine, and Oak) with three different types of fasteners (square body hook bolt, forged hook bolt, and Quick-Set Anchors). A structural test setup simulated one half of an open-deck bridge with a smooth-top steel plate girder, and hydraulic actuators to apply both vertical and horizontal load to a railroad tie specimen. The three main contributions to lateral resistance on open-deck bridges were identified as friction resistance between tie and girder due to vertical load from a truck axle, resistance from the fastener, and resistance from dapped ties bearing against the girder flange. Initial testing conducted at Virginia Tech isolated each component of lateral resistance to determine the friction coefficient between tie and girder as well as resistance from just the fastener itself. Results indicate that friction resistance varies based on the magnitude of vertical truck axle load, species of wood, and quantity of creosote preservative on the tie, while fastener resistance varies based on type of fastener and displacement of the tie. With the experimental results, a preliminary equation for calculating the overall resistance of open-deck timber crossties is developed, which allows for a recommendation of fastener spacing based on the type of fastener, wood species, and anticipated lateral loads on the structure.

In Situ Experimental Study on the Behavior of UHPC Composite Orthotropic Steel Bridge Deck

A novel ultra high performance concrete (UHPC) layer composite orthotropic steel deck was adopted in the construction of a new bridge in China to improve the fatigue performance of the orthotropic steel deck plate and reduce the disease of surface wearing layer. In situ experiments were conducted to study the UHPC layer’s impact on the behavior of the orthotropic steel deck. The test vehicle loads were applied on the deck plate before and after UHPC layer paving, the stresses where fatigue cracks usually occur and the deflections of critical sections were measured. The test results verified that the UHPC composite steel deck system could significantly reduce the stress of the rib-to-deck connection region and the stress at the bottom toe of rib-to-diaphragm weld. In addition, it slightly influenced the performance of U shape rib, girder web-to-deck and diaphragm cutout.

Online Monitoring of Flexural Damage Index of a Cable-Stayed Bridge

This work introduces a recent application of the online nondestructive damage assessment system into a cable-stayed bridge. A set of ambient modal parameters are automatically extracted every 20 minutes using real-time signal data collected from a total of 26 accelerometers attached on the deck plate of the bridge. Then, a set of modal flexibilities are reconstructed by the combination of the extracted modal parameters with the approximated modal mass of the girder. Next, the curvature of the modal flexibility is approximated by a central difference formula. Finally, the set of flexural damage index equations is constructed by comparing the modal curvature of the damaged state to that of the undamaged state. Solving the overdetermined flexural damage index equations, the desired damage index is finally quantified. The resulting index clearly indicates the location and severity of the potential structural damage on the girder. Based on the overall performance of the implemented health monitoring system, the bridge operator’s damage index control criteria are set to ±20% of the undamaged state.