Experimental Study of Three-Dimensional Flow Field around a Complex Bridge Pier

In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching boundary layer at the upstream of the pile cap separated in two vertical directions and induced an upward flow toward the column and a contracted downward flow below the pile cap and toward the piles. The contracted upward flow on the pile cap interacts with downflow in the front of the column and deflects toward the side of the pier, which in return produces a strong downflow along the side of the pile cap. The flow at the rear of the pile cap is very complex. The strong downward flow at the downstream and near the top of the pile cap in interaction with the reverse flow behind the column and upward flow near the bed produce two vortices close to the upper and lower corners of the pile cap with opposite direction of rotation. On the other hand, the back-flow from the wake of the pile cap is forced into the top region resulting in a secondary recirculation at the wake of the column. The contracted flow below the pile cap and toward the piles, a strong downflow along the sides of the pile cap at the upstream region, and a vortex flow behind the pile cap and an amplification of turbulence intensity along the sides of the pile cap at the downstream region are the main features of the flow responsible for the entrainment of bed sediments.     

Analytical Load Rating of an Open-Spandrel Arch Bridge: Case Study

The live load structural capacity of open-spandrel arch bridge structures is difficult to quantify. In addition to live and dead loads, geometric nonlinear effects, temperature effects, and material behavior play key roles in the design and load rating of such a structure. This paper is a case study that illustrates the effect these variables have on load rating a two-span shallow concrete arch bridge. Presented are load ratings of the structure’s arch ribs using a three-dimensional finite-element model with American Association of State Highway and Transportation Officials publications. As a result of this study, a refined analysis is recommended for load rating arch bridges.     

Rapid Bridge Replacement under Emergency Situation: Case Study

The terrorist attack on September 11, 2001, and subsequent potential threats to the United States transportation systems have presented an urgent need to elevate the security of the transportation infrastructure and to develop emergency response plans to quickly react to the possible consequences of an extreme event. Highway bridges, as critical components of the nation’s transportation network, have been brought to closer attention by government agencies. A research project was conducted to identify strategies and technologies to restore the use of a damaged bridge quickly. One of the tasks associated with the research was to perform several case studies of previous bridge replacements following extreme events. These events include explosion and fire caused by vehicle impact, vessel collision with a bridge, and damage caused by flood and earthquake. By studying the cases, the research team seeks to identify and expand on lessons learned and address which actions did and did not work well given the circumstances of the incident. These lessons have great value to the people who need to develop and implement an emergency response plan.     

Effects of Bed Roughness on Flow around Bed-Mounted Cylinders in Open Channels

This paper presents the results of an experimental study of flow around cylindrical objects on a rough bed in an open channel. This is an extension of a previous study of flow around cylinders on a smooth bed. The purpose of this study is to explore the effects of bed roughness on the characteristics of the deflected flow around cylindrical objects and the resulting bed-shear stress distributions. Similar to the previous study cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence. Bed shear stress and deflected flow velocities were measured by a thin yaw-type Preston probe after a set of flow visualization tests. Flow visualization tests showed that the horse-shoe vortex systems on the rough bed occupy a relatively greater width compared to the smooth bed. Unlike smooth bed observations, the flow separation point upstream of the cylinder was not dependent on the level of submergence as the separation points were found to appear within a short range of x = ?1D to ?1.2D. Bed shear stress has been found to increase significantly near the shoulder of the cylinders, and its ratio with respect to the approach bed-shear stress was twice as large compared to the smooth bed case. Mean velocity profiles were analyzed in terms of three-dimensional turbulent boundary layer theories. Bed roughness was found to oppose the effect of the lateral pressure gradient that causes skewing in the boundary layer. Perry and Joubert’s model has been found to be equally accurate on smooth and rough beds for predicting the deflected velocity magnitudes around cylinders. The present study will enhance the knowledge of hydraulics of flow around bed-mounted objects (e.g. fish-rocks) in natural streams.     

Case Study: Movable Bed Model Scaling for Bed Load Sediment Exclusion at Intake Structure on Rio Grande

Results of a laboratory modeling study are presented for excluding bed load sediment from a diversion/intake structure on the Rio Grande in Albuquerque, New Mexico. To achieve model similitude, crushed coal was used to model the prototype sediment in a 1:24 scaled model with an exaggerated slope such that shear force is adequately modeled. The Shields parameters and critical Shields parameters were matched between the prototype and the model, resulting in similar grain Reynolds numbers. Twenty-four tests, where guiding walls, submerged vanes, and/or the angle of the intake bay were altered, were conducted for a single river and diversion flow rate to develop the best performing sediment exclusion system at the intake structure. Independent vanes with 45° rotated intake bays were recommended for the most effective sediment exclusion at the intake structure.     

Construction and Testing of an Innovative Concrete Bridge Deck Totally Reinforced with Glass FRP Bars: Val-Alain Bridge on Highway 20 East

The Val-Alain Bridge, located in the Municipality of Val-Alain on Highway 20 East, crosses over Henri River in Québec, Canada. The bridge is a slab-on-girder type with a skew angle of 20° over a single span of 49.89?m and a total width of 12.57?m. The bridge has four simply supported steel girders spaced at 3,145?mm. The deck slab is a 225-mm-thick concrete slab, with semi-integral abutments, continuous over the steel girders with an overhang of 1,570?mm on each side. The concrete deck slab and the bridge barriers were reinforced with glass fiber reinforced polymer (GFRP) reinforcing bars utilizing high-performance concrete. The Val-Alain Bridge is the Canada’s first concrete bridge deck totally reinforced with GFRP reinforcing bars. Using such nonmetallic reinforcement in combination with high-performance concrete leads to an expected service life of more than 75?years. The bridge is well instrumented with electrical resistance strain gauges and fiber-optic sensors at critical locations to record internal strain data. Also, the bridge was tested for service performance using calibrated truckloads. Design concepts, construction details, and results of the first series of live load field tests are presented.     

Case Study: Retrofitting Large Bridge Piers on the Nakdong River, South Korea

The Gupo Bridge crosses the Nakdong River near the city of Busan, South Korea. During Typhoon Maemi in 2003, the old Gupo Bridge collapsed due to excessive pier scour. More recently, the highway construction on the left-bank floodplain required right-bank channel widening to restore the channel flood-carrying capacity. This 7?m deep floodplain excavation is expected to cause significant local scour around the 8–10?m wide and 3?m thick spread footings of Piers 11 and 12 of the Subway Bridge and Piers 15 and 16 of the Gupo Bridge. Three design options are examined for retrofitting floodplain bridge piers with massive spread footings. A solution with sheet piles and riprap was recommended in 2006 as the most appropriate design, but Plan III with a conical riprap structure around the footings was ultimately constructed in 2007 for economic reasons. Laboratory experiments also highlight the need to place gravel and synthetic filters under the designed riprap.     

Applicability of 4D CAD in Civil Engineering Construction: Case Study of a Cable-Stayed Bridge Project

Four-dimensional (4D) computer-aided design (CAD) has been credited with improving construction planning procedures. The integration of three-dimensional CAD with schedule information has enabled the effective detection of design and planning flaws in many construction projects. However, the benefit of 4D CAD has been centered on architectural constructions, as other areas such as civil infrastructure have seldom been the target of 4D CAD application. This paper presents a case study in which a cable-stayed bridge construction was analyzed and modeled using the 4D graphic simulation approach. The cable-stayed bridge was chosen for the case study because it suitably represents the complex nature of modern civil infrastructure. 4D CAD models were developed at three different levels of detail: activity, discrete operation, and continuous operation. The clear definitions of the three levels of detail of 4D CAD and their application results for the cable-stayed bridge are presented herein.     

Case Histories in Soil and Rock Erosion: Woodrow Wilson Bridge, Brazos River Meander, Normandy Cliffs, and New Orleans Levees

This lecture presents four case history examples of erosion processes. Because the topic of soil and rock erosion is relatively underdeveloped in geotechnical engineering, an introduction precedes the case histories to describe some fundamental aspects of erosion. Erosion involves the soil or rock through its erodibility, the water through its velocity, and the geometry of the obstacle through its size and shape. Knowledge of these three components is needed for any erosion problem to be studied and solved. A set of fundamental issues are addressed in the first part including an erodibility classification for soils and rocks, an explanation of the stresses imposed by the water on the soil-water or rock-water interface, and an explanation of how the geometry impacts the problem. The Woodrow Wilson Bridge case history outlines a new and less conservative method to compute the scour depth and gives examples of bridge scour calculations. The Brazos River meander case history outlines a new method to predict meander migration and gives an example of migration calculations. The Pointe du Hoc case history gives an explanation of a process of rock cliff erosion. The New Orleans levees case history gives an example of erosion of levees by overtopping and proposes an erosion design chart for levee overtopping. Whenever possible the results are presented in a probabilistic fashion. All case histories make use of the erosion function apparatus, an apparatus developed to quantify the erodibility of a soil or rock and to give the constitutive law for erosion problems: the erosion function. The power point slides for the lecture including many photos of the case histories are available at ?http://ceprofs.tamu.edu/briaud/? under “Lectures” and the video (DVD) of the lecture is available from the author, free of charge.     

Case Study of Application of FRP Composites in Strengthening the Reinforced Concrete Headstock of a Bridge Structure

Worldwide interest is being generated in the use of fiber-reinforced polymer composites (FRP) in the rehabilitation of aged or damaged reinforced concrete structures. As a replacement for the traditional steel plates or external posttensioning in strengthening applications, various types of FRP plates, with their high strength-to-weight ratio and good resistance to corrosion, represent a class of ideal material in externally retrofitting. This paper describes a solution proposed to strengthen the damaged reinforced concrete headstock of the Tenthill Creeks Bridge, Queensland, Australia, using FRP composites. A decision was made to consider strengthening the headstock using bonded carbon FRP laminates to increase the load carrying capacity of the headstock in shear and bending. The relevant guidelines and design recommendations were compared and adopted in accordance with AS 3600 and Austroads bridge design code to estimate the shear and flexural capacity of a rectangular cracked FRP reinforced concrete section.     

In-Service Diagnostics of a Highway Bridge from a Progressive Damage Case Study

Development of diagnostic and prognostic routines for application to in-service measurements from highway bridges necessitates analysis of experimental measurements from in-service highway bridges under natural or prescribed induced damage. This is generally limited to the unique opportunity of investigating end-of-service life bridges prior to reconstruction and consequently only a limited library of such case studies exist. This paper documents a field test of an end-of-service bridge span with prescribed progressive damage to a bearing as well as several diaphragm connections. Thirty dual-axis accelerometers were distributed across the bridge span with data acquisition and transmission facilitated by a real-time lossless wireless sensor network. A highway department service truck applied traffic excitation to the structure through routine passes on a consistent lane of traffic. Output-only system identification was applied to the baseline time history response to develop a state-space model of the bridge dynamics used for forward prediction in the form of a Kalman filter. Simple statistical evaluation of the prediction error in the model demonstrates the variance can be used to localize and generally quantify the degree of damage in the structure. The case study additionally illustrates the potential importance of monitoring lateral acceleration along the girders to permit identification of damage to elements, such as the diaphragms, that contributing primarily to the lateral and torsional response of primary structural members.     

Field Experiments and Numerical Models for the Condition Assessment of Historic Timber Bridges: Case Study

Covered wooden bridges and the principles of heavy timber framing by which they were built represent both a significant chapter in this country’s civil engineering heritage, and a subclass of bridges that are in immediate need of repair and rehabilitation. This work often falls on the shoulders of the municipalities who own the bridges or local consulting engineering companies, neither of which have the resources to perform state-of-the-art damage assessment analyses. This study presents two case studies in which a simplified approach to damage assessment is used. The writers explore the importance of proper condition assessments, including both field observations and load tests, to the creation of viable finite-element models that practicing engineers may use in their repair and rehabilitation of these unique structures. Experimental tests were performed on two covered bridges: Morgan Bridge in Belvidere, Vermont and Pine Grove Bridge, in Oxford, Pennsylvania, and comparisons were made to finite-element models created of those bridges. The combination of experimental and numerical tools led to the identification of several deteriorated components, including scarf joints, lapped brace joints, and retrofitted members within the bridges that may have otherwise gone undetected.     

Experimental Study of Particle Motion on a Smooth Bed under Shoaling Waves Using Particle Image Velocimetry

The motion of spherical particles (diameter 1.58 mm, specific gravity 2.5) on 2 and 3% plane slope was studied in a laboratory wave flume for shoaling wave conditions. The range of wave-height-to-water-depth ratio was 0.24相似文献   

标准物质稳定性考察及评价

对标准物质稳定性进行了系统的论述 ,对稳定性的作用及如何考察、评价作了详细的讨论     

Simplified Lateral Analysis of Deep Foundation Supported Bridge Bents: Driven Pile Case Studies

A simplified approach for modeling soil and foundation system supported bridge bents is applied to three bridges that represent three pile types and three superstructures. This point-of-fixity approach is applied by modeling the bridge bent substructure as an elastic frame. The models are compared with more refined analyses in FB-MultiPier, with SAP as an independent verification tool, using pile sections with nonlinear soil, pile, and pile cap material properties. The results for simple pile bents show that an equivalent frame model provides similar moment, shear, and displacement values as those obtained from both the SAP and MultiPier nonlinear analyses. Analysis results also indicated that the equivalent frame model parameters are particularly sensitive to the comparable selection of both axial and lateral loads. If lateral loads used to develop the equivalent model are higher than experienced, the axial and lateral deflections and moments will also be higher. For design purposes, this is conservative.     

Experimental Study of the XY-Friction Pendulum Bearing for Bridge Applications

The XY-friction pendulum (XY-FP) bearing is a modified Friction Pendulum (Earthquake Protection Systems, Inc., Vallejo, Calif.) bearing that consists of two perpendicular steel rails with opposing concave surfaces and a connector. The connector resists tensile forces, provides for independent sliding in the two principal directions of the isolators, and ideally, permits unhindered rotation about its vertical axis. Experimental studies on an XY-FP seismically isolated truss-bridge model were undertaken to study response under tridirectional excitations and to evaluate the use of XY-FP bearings for bridges. A truss bridge model was tested on a pair of earthquake simulators using acceleration orbits and near-field earthquake histories. The experimental results demonstrated the effectiveness of the XY-FP bearings as an uplift-prevention isolation system: the XY-FP bearings simultaneously resisted significant tensile loads and functioned as seismic isolators. The bidirectional horizontal response of the small-scale XY-FP isolation system was coupled due to the internal construction of the small-scale connectors that joined the two rails of each XY-FP bearing and the limited free-to-rotate capacity of the XY-FP bearings due to misalignment of the isolators during installation.     

Study of Passive Deck-Flaps Flutter Control System on Full Bridge Model. I: Theory

A passive aerodynamic control method for suppression of the wind-induced instabilities of a very long span bridge is presented in this paper. The control system consists of additional control flaps attached to the edges of the bridge deck. Control flap rotations are governed by prestressed springs and additional cables spanned between the control flaps and an auxiliary transverse beam supported by the main cables of the bridge. The rotational movement of the flaps is used to modify the aerodynamic forces acting on the deck and provides aerodynamic forces on the flaps used to stabilize the bridge. A time-domain formulation of self-excited forces for the whole three-dimensional suspension bridge model is obtained through a rational function approximation of the generalized Theodorsen function and implemented in the FEM formulation. This paper lays the theoretical groundwork for the one that follows.     

Study of Passive Deck-Flaps Flutter Control System on Full Bridge Model. II: Results

Using the analytical format set forth in the first of these two companion papers, numerical simulations of a passive aerodynamic control method for suppression of the wind-induced instabilities of a very long span bridge are presented in this paper. At first, the aerodynamic stability of the uncontrolled system is discussed using a sectional model and full bridge model, respectively. Next, the efficiency of the proposed asymmetric and symmetric cable connection control systems is studied. Both systems offer similar maximum improvements in critical wind speed. The asymmetric cable connection system turns out to be very sensitive to horizontal motions, which strongly degrade its effectiveness. On the contrary, the symmetric cable connection system is not sensitive to horizontal motions, but its efficiency is limited by divergence.     

Replacement of the Movable Span of the Thames River Bridge: How 19th Century Technology Impacted 21st Century Construction

The replacement of the Thames River Railroad Bridge between Groton and New London, Connecticut, was a challenging task on many levels, some of them anticipated, some of them not. The effort culminated with an outage that stopped the most heavily used passenger rail service in the United States for 4?days and blocked navigation for industrial and national defense waterway users. Unanticipated foundation problems added an additional set of challenges. All challenges were successfully overcome with a spirit of cooperation and innovation by all involved. Advances in information technology after completion of the project led to the discovery of lost information that could have warned the project team of problems to come had that knowledge been available at the start of the project.