Journal of Bridge Engineering

Cable-stayed bridges are flexible structures, and control of their vibrations is an important consideration and a challenging problem. In this paper, the wavelet-hybrid feedback least mean squared algorithm recently developed by the writers is used for vibration control of cable-stayed bridges under various seismic excitations. The effectiveness of the algorithm is investigated through numerical simulation using a benchmark control problem created based on an actual semifan-type cable-stayed bridge design. The performance of the algorithm is compared with that of a sample linear quadratic Gaussian (LQG) controller using three different earthquake records: the El Centro (California, 1940), Mexico City (Mexico, 1985), and Gebze (Turkey, 1999) earthquakes. Simulation results demonstrate that the new algorithm is consistently more effective than the sample LQG controller for all three earthquake records. Additional numerical simulations are performed to evaluate the sensitivity of the new control algorithm. It is concluded that the algorithm is robust against the uncertainties existing in modeling structures.

A new highway system is being constructed in Chile including many bridges. Due to the high seismic risk in the country, high damping rubber bearings, friction bearings, and passive energy dissipation devices have been considered in the design of the majority of the new moderate and large span bridges. Their design follows American Association of State Highway guidelines and technical specifications from the Chilean Ministry of Public Works. Experimental and analytical studies have been performed in three of these structures: (1) a 383 m long continuous beam bridge supported on high damping rubber bearings; (2) a 268 m long continuous beam bridge supported on friction bearing with additional viscous dampers; and (3) a five-span simply supported beam bridge resting on neoprene bearings. Predominant periods and damping characteristics for small amplitude vibrations have been determined from output-only nonparametric analyses. Comparison with standard analytical structural models indicates that the models normally used for analysis yield comparable predominant periods and mode shapes but the damping values typically recommended are larger than the ones observed from ambient vibrations, even when additional energy dissipation elements are present.

The objective of this paper is to present the results of an investigation of the dynamic and impact characteristics of half-through arch bridges with rough decks caused by vehicles moving across them. Seven arch bridges modeled as three-dimensional structures with overall span lengths ranging from $20\text{to}200\mathrm{m}$ $\left(65.5\text{to}656.2\mathrm{ft}\right)$ are analyzed. The American Association of State Highway and Transportation Officials Specifications HS20-44 truck is the applied vehicle loading used in the analysis and is simulated as a three-dimensional, nonlinear vehicle model with 11 degrees of freedom. Truck components include the body, suspension, and tires. The bridge deck surface is assumed to have a “good” surface roughness and is simulated using a stochastic process (power spectral density function). The effect on impact factors of span length, rise-to-span ratio, and vehicle speed is discussed. The results of the analyses show that the impact factors of bending moment and axial force will not exceed 0.4 and 0.25, respectively. The proposed impact equations are simple and conservative and can be used in the design of half-through arch bridges.

The paper considers nonlinear (autoparametric) resonance in footbridges as a reason for excessive lateral vibrations induced by walking pedestrians. To describe the above-mentioned phenomenon, a physical model (an elastic pendulum) is proposed. Under the special frequency conditions (the ratio between frequencies of vertical and lateral beam modes is about 2, or 2:1), nonlinear resonance becomes possible if a vertically excited mode is near a primary resonance and a load parameter (a static displacement caused by pedestrians) is equal or more than its critical value. When the increasing load parameter passes through the critical value, a jump phenomenon is observed for the lateral mode and the vertical mode is saturated. Swaying of pedestrian bridges can be treated as a two-step process. The first step (achievement of the jump phenomenon), described in the paper, is the condition for the beginning of the second step—the process of interaction between applied forces and the lateral mode of vibration.

An in-depth analysis of the deterioration mechanisms in high-strength wires of suspension bridge cables is presented. Accelerated cyclic corrosion tests were conducted to assess the relative effect of corrosion on galvanized and ungalvanized wires. Samples were corroded under various levels of sustained loads in a cabinet that cyclically applied an acidic salt spray, dry conditions, and 100% relative humidity at elevated temperature, and mass loss, hydrogen concentration, ultimate load, and elongation at failure were measured. Elongation measurements indicated a significant embrittlement of the wires that could not be explained solely by the presence of absorbed hydrogen (hydrogen embrittlement). The main cause of reduction of wire elongation was found to be the surface irregularities induced by the corrosion process. The experimental results were validated through a numerical analysis using a finite-element method model of the corroded steel wire and through a series of scanning electron microscope analyses of the fracture surfaces.

A real-time kinematic (RTK) global positioning system (GPS) has been developed and installed on the Humen Bridge (China) for on-line monitoring of bridge deck movement, which may occur as a result of seismic activity, traffic load, and such environmental elements as temperature and wind. This paper presents the main features of the on-line GPS RTK system and its value for on-line safety monitoring.

Impact modal testing combined with finite element (FE) analyses is currently being used to evaluate the condition of steel bridges in the state of Ohio. Using modal testing techniques, it is relatively easy to measure the dynamic response of bridges, including mode shapes, frequencies, and modal scaling factors. These responses are compared to the results of the FE analyses and the model is iteratively updated until a good agreement is obtained. After a good agreement between experimental and analytical results has been achieved, the FE model is used to obtain stresses that are used to load rate the bridge. During the iterative calibration process, several quantities, including the fundamental mode shapes and frequencies, are used to evaluate the accuracy of the FE model. Since each mode shape plays a different role in the dynamic behavior of the structure, a more efficient calibration routine can be achieved if more emphasis is placed on obtaining good matches for the modes that are most influential. The aim of this paper is to develop a quantitative measure of the contribution of different modes to the overall dynamic response of a structure. The proposed measure, a series of contribution coefficients, is used to identify which modes are most critical in the process of modal testing and FE model calibration. Several applications of the contribution coefficients are identified.

The behavior of double-angle stringer-to-floor-beam connections in riveted railway bridges is examined experimentally. A series of static and fatigue tests were performed on three full-scale bridge parts taken from an old riveted railway bridge. The results of the static tests reveal that the amount of end moment developed in these connections as a result of their rotational stiffness could be considerable. As a result of the cyclic variation in this moment, fatigue damage might develop in these connections. This damage was, however, observed to have a fairly low propagation rate and did not immediately reduce the load-carrying function of the connections.

The monitoring of a precast, prestressed girder bridge during fabrication and service provided the opportunity to observe temperature variations and to evaluate the accuracy of calculated strains and cambers. The use of high curing temperatures during fabrication affects the level of prestress because the strand length is fixed during the heating, the coefficients of thermal expansion of steel and concrete differ, and the concrete temperature distribution may not be uniform. For the girders discussed here, these effects combined to reduce the calculated prestressing stress from the original design values at release by 3 to 7%, to reduce the initial camber by 26 to 40%, and to increase the bottom tension stress in service by 12 to 27%. The main effect of applying the standard service temperature profiles to the bridge was to increase the bottom stress by 60% of the allowable tension stress. These effects can be compensated for by increasing the amount of prestressing steel, but in highly stressed girders, such an increase leads to increased prestress losses (requiring yet more strands) and higher concrete strength requirements at release.

After years in service, many steel girders have deteriorated to the point where fatigue cracks have initiated in the girders. In girders having cover plates that do not terminate in a compression region, a common type of crack initiates at the weld toe at the ends of the cover plate after being subjected to cyclic tensile loads due to traffic. The use of precured carbon-fiber-reinforced polymer (CFRP) laminates, adhered to the inside face of the girder tension flange, is one proposed method for repairing these cracked bridge girders. The main advantages of using CFRP laminates are their light weight and their durability, which result in ease of handling and maintenance. For the application of this rehabilitation method, it is important to determine the effective bond length for CFRP laminates adhered to the inside face of a cracked steel girder flange. Experimental tests using a new type of effective bond length test specimen were conducted in this research on several types of adhesives and precured CFRP laminates, in addition to several different bonding configurations. The minimum bond length required to achieve the maximum strength of the rehabilitation scheme for the materials investigated in this research was determined. The experimental results also indicated that an adhesive with relatively large ductility is required to redistribute the stresses successfully within the adhesive layer during increased loading. A simple analytical solution for the shear strain distribution in the adhesive layer was proposed for estimating the effective bond length, and the results were verified with computational analyses. Good agreement was found among the computational, analytical, and experimental results.

Secondary elements such as barriers, sidewalks, and diaphragms may affect the distribution of live load to bridge girders. The objective of this study is to evaluate their effect on girder reliability if these elements are designed to be sufficiently attached to the bridge so as not to detach under traffic live loads. Simple-span, two-lane structures are considered, with composite steel girders supporting a reinforced concrete deck. Several representative structures are selected, with various configurations of barriers, sidewalks, and diaphragms. Bridge analysis is performed using a finite-element procedure. Load and resistance parameters are treated as random variables. Random variables considered are composite girder flexural strength, secondary element stiffness, load magnitude (dead load and truck traffic live load), and live load position. It was found that typical combinations of secondary elements have a varying influence on girder reliability, depending on secondary element stiffness and bridge geometry. Suggestions are presented that can account for secondary elements and that provide a uniform level of reliability to bridge girders.

Typical rehabilitation procedures for posttensioned slab bridges involve removing concrete from the top surface of the bridge, replacing corroded reinforcement, and resurfacing with new concrete. These permanently change primary and thus secondary prestressing moments. Continuous posttensioned bridges often rely on secondary prestressing moments to counteract dead and live load moments over interior supports and thus changes caused by rehabilitation impact serviceability and, particularly, ultimate limit states. An analysis procedure is derived for computing the changes in prestressing moments caused by rehabilitation. The impact of rehabilitation on a two-span continuous voided-slab bridge is evaluated considering rehabilitation schemes where both spans are rehabilitated simultaneously, or where one span is completely rehabilitated before work commences on the other. Rehabilitation creates concentrated primary prestressing moments at the exterior supports and at interfaces between solid and voided regions that reduce or even reverse the secondary moment at the interior support. The two-span scheme virtually eliminates secondary prestressing moments and, contrary to intuition, the span-by-span scheme has a markedly greater impact.

A large number of pile-supported bridge approach slabs in southeastern Louisiana were examined to identify the factors that affect their long-term performance. Design drawings and subsoil conditions at these sites as well as their traffic and maintenance records were compiled, and seven representative test sites were selected for thorough field investigation that included inspection of the approach slabs, bridge decks, bridge abutments, and roadway pavement. Field evaluation included walking profiler, falling-weight deflectometer (FWD), laser profiler, geodetic survey, soil borings, cone penetrometer, and nondestructive testing. Measurements made with the walking profiler agreed well with the geodetic survey. The FWD and nondestructive testing were effectively used to detect voids under the approach slab. Results of the study indicated that the current empirical methodology used by the Louisiana Department of Transportation and Development for design of pile-supported approach slabs yields inconsistent field performance. It was concluded that this inconsistent performance is primarily due to the differences in roadway embankment design and construction and in subsoil conditions, which in turn affect the negative skin friction (downdrag) loads imparted on the piles. Impact of other variables such as ramp type, speed limit, traffic volume, and so on was found to be insignificant. Results of the field study were used to develop a new rating system for approach slabs (IRIS) based on International Roughness Index (IRI) measurements obtained with the laser profiler.