Journal of Bridge Engineering

In these days of bridge design by large national and international teams, it is easy to forget those days in the late nineteenth and early twentieth centuries when one man undertook the design and construction of a major bridge. This paper covers Leffert Lefferts Buck's career from 1868 to 1909. In 1872, when he built the famous Verrugas Viaduct in Peru, up to the construction of the Williamsburg Bridge over the East River in New York, he was one of the premier bridge builders of all time. Yet in spite of his acknowledged leadership, very few current bridge engineers are aware of his work.

Past research has been conducted on the behavior of horizontally curved girders by testing scaled models and full-scale laboratory bridges and by analyzing numerical models. Current design specifications are based on this past research; however, little field data of in-service bridges exist to support the findings of the past research on which the current design criteria are based. The purpose of the present study was to gather field response data from three in-service, curved, steel I-girder bridges to determine behavior when subjected to a test truck and normal truck traffic. Transverse bending distribution factors and dynamic load allowance were calculated from the data collected. Numerical grillage models of the three bridges were developed to determine if a simple numerical model will accurately predict actual field measured transverse bending distribution, deflections, and cross-frame and diaphragm shear forces. The present study found that AASHTO specifications are conservative for both dynamic load allowance and transverse bending moment distribution. The grillage models were found to predict with reasonable accuracy the behavior of a curved I-girder bridge.

Historically, truck regulations have maintained controls on axle and gross weights with legal load formulas based on limiting allowable stresses in certain types of bridges. These stress limitations do not usually lead to consistent or defensible safety levels and also ignore the cost impact of the weight regulation on the national bridge network. This paper illustrates how new truck weight regulations can be developed to provide acceptable safety levels. Target safety levels are derived from existing AASHTO bridge evaluation and rating procedures applied to structures showing adequate performance levels. Reliability indices are used to relate the statistics of bridge load effects, based on either existing or proposed truck weight regulations, to the dynamic behavior and resistance variables of existing bridges. The sensitivity of the results to various assumptions and errors in the database is also analyzed. An accompanying paper reviews the consequences of adapting such a formula on the safety of existing bridges. The deterministic analysis as well as a reliability assessment are performed in the accompanying paper to review the consequences of adapting such regulations on the U.S. bridge network using the National Bridge Inventory files.

Historically, truck weight regulations have maintained controls on axle and gross weights with legal load formulas based on limiting allowable stresses in certain types of bridges. These stress limitations do not usually lead to consistent or defensible reliability levels and also ignore the impact of the weight regulation on the existing highway bridge network. This paper is the second part of a two-paper series. The companion paper by the first writer illustrated how new truck weight regulations can be developed to provide an acceptable reliability level. The target reliability level was derived from bridge structures designed to satisfy AASHTO standard design specifications that showed safe and adequate performance levels under current truck loading conditions. In this part of the two-paper series, a deterministic load capacity evaluation as well as a reliability assessment are performed to review the consequences of adapting such regulations on the existing U.S. bridge network. A sensitivity analysis shows how changes in the safety criteria used to develop the truck weight regulations would affect the existing bridge network. Detailed load capacity evaluations and reliability analyses also are performed on a representative sample of bridges to provide specific examples of expected changes in rating and safety levels if the proposed truck weight regulation is to be adopted.

Concrete overlay cracking and delamination were noticed on a concrete segmental box-girder bridge. Analytical investigation and field and laboratory examinations were conducted to identify the major factors causing the defects. The time-dependent stress distribution and its change in the overlay and along the interface between the overlay and the bridge deck were modeled through the finite-element method with the consideration of concrete age, shrinkage, and critical temperature gradients. Appropriate interpretation of the modeling results were verified through field and laboratory examinations. The primary factors causing the defects were identified and discussed. It was concluded that conventional concrete is applicable for a thin bonded overlay construction on concrete segmental box-girder bridges. Removal and replacement were recommended to repair the delaminations through a field test program. Low shrink conventional concrete with a maximum aggregate size of 25.4 mm (1.0 in.) was used without the application of bonding grout. The base deck surface was roughened (by hydroblasting) to a macrotexture of 2.0–2.8 mm (0.08–0.11 in.) on average. The substrata was not presoaked and was surface dry before placing of plastic concrete. Curing consisted of moist curing for 7 days, followed by chemical (curing compound) curing for 21 days. The successful experience gained can be applied to other similar projects.

This paper presents a procedure for the evaluation of the expected seismic damage to bridges and highway systems in Memphis and Shelby County, Tenn. Data pertinent to 452 bridges and major arterial routes were collected and implemented as a geographic information system database. The bridges were classified into several bridge types using a bridge classification system modified from the NBIS/Federal Highway Administration coding guidelines. The bridge damage states considered are no/minor damage, repairable damage, and significant damage. The fragility curves corresponding to these damage states were established for various bridge types. Given an earthquake with a moment magnitude of 7.0 occurring at Marked Tree, Ark., the intensity of ground shaking and liquefaction-induced permanent ground deformation in Memphis and Shelby County were estimated, and then the expected damage to bridges and highway systems was determined. The results can be used to prioritize bridges for retrofitting, to prepare a pre-earthquake preparedness plan, to develop a postearthquake emergency response plan, and to assess the regional economic impact from the damage to highway transportation systems.

Bridge management systems focus on optimizing the life-cycle cost of preservation and improvement activities in a network of structures. Pontis, the predominant bridge management system currently implemented in the United States, considers load-carrying capacity as static during an incremental benefit-cost approach. Including consideration of load-carrying capacity, deterioration may enhance this model. To accomplish this goal, a method to relate load-carrying capacity to physical bridge deterioration using a combination of regression analysis and Markov chains is presented. The method is applied to historic bridge data from the United States and Hungary.

This paper presents an externally prestressed high strength concrete viaduct designed and erected in Spain. This viaduct, a three-span (41 + 50 + 41 m) continuous beam, has been designed and built with a 60-MPa strength concrete and a fully external replaceable prestressing. The paper describes the bridge, the erection procedure, the ultimate analysis performed with a nonlinear finite-element numerical model, and the thermal stresses measured and calculated at the anchorage diaphragms due to the hydration heat of the concrete. The results of the static tests carried out on the bridge also are commented upon.

This paper focuses on improving the efficiency and aesthetics of standard highway bridges with attention to cast-in-place substructure design. Standard short- and moderate-span bridges are predominantly functional and nondescript. Recent developments in superstructure design have led to improved efficiency of construction and material use, with a resulting slender, attractive appearance. However, typical substructure design remains a component where creativity can be played out for considerable improvements to the overall bridge appearance. A review of current cast-in-place substructure systems is presented including individual, wall, hammerhead, and multicolumn bents. Design recommendations for improving overall bridge appearance and the efficiency of the substructure are presented. Attention is given to integrating aesthetics with material and construction efficiency and with economic considerations. Recommendations include addressing structural expression, visibility through the bridge, shaping of the substructure, integration of substructure and superstructure, and enhancing substructure form with nonstructural details. Issues of coherence for large-scale projects and suggestions for standardization also are discussed. Economic implications of the design recommendations are presented.