The accuracy of bridge system safety evaluations and reliability assessments obtained through refined structural analysis procedures depends on the proper modeling of traffic load effects. While the live-load models specified in AASHTO procedures were calibrated for use in combination with approximate analysis methods and load-distribution factors commonly used in the United States, these existing models may not produce accurate results when used in association with advanced finite-element analyses of bridge structures. This paper proposes a procedure for calibrating appropriate live-load models that can be used for advanced analyses of multigirder bridges. The calibration procedure is demonstrated using actual truck data collected at a representative set of weigh-in-motion (WIM) stations in New York State. Extreme value theory was used to project traffic-load effects to different service periods. The results are presented as live-load models developed for a 5-year typical rating interval and for a 75-year design life. The outcome of the calibration indicates that maximum traffic-load effects can be calculated using finite-element models with the help of a single truck for short to medium one-lane multigirder bridges and two side-by-side truck configurations for multilane bridges. The proposed analysis trucks have axle configurations of the standard AASHTO 3-S2 and Type 3 legal rating trucks with appropriate factors to amplify their nominal weights. The amplification factors reflected the presence of overweight trucks in the traffic stream and the probability of multiple presence. The proposed live-load models are readily implementable for deterministic refined analyses of highway bridges and for evaluating the reliability of bridges at ultimate limit states considering the system’s behavior.
Diaz de Teran, J. R.; Haach, V.; Turmo, J.; Jorquera, J. ASCE. Journal of bridge engineering Vol. 21, num. 9, p. 04016050-1-04016050-11 DOI: 10.1061/(ASCE)BE.1943-5592.0000831 Data de publicació: 2016-09 Article en revista
The current paper relates the state of the art of construction of viaducts with a movable scaffolding system (MSS). Two different procedures are introduced: the traditional sequence and the new sequence applied to some viaducts in Spain. The traditional sequence consists of two phases: first, concreting the bottom slab and webs, and then concreting the top slab of the deck. Once the first and second casting phases are completed, the total prestressing force is introduced. The new sequence consists of concreting a self-supporting core (i.e., the bottom slab, webs, and only a portion of the top slab). Once the self-supporting core has hardened, a partial prestressing force is introduced so that the scaffolding can be advanced to the next span; the central zone of the top slab is cast in a second phase. Both sequences are described here with their constructive peculiarities and issues.
This paper investigates the near-fault (NF) seismic performance of a novel isolation system, referred to as the roll-n-cage (RNC) isolator, considering the cable-stayed Bill Emerson Memorial Bridge in Missouri. The RNC isolator is designed to achieve a balance in controlling bridge displacement demands, structural accelerations, and internal forces in the tower attributable to horizontal seismic forces. It provides in a single unit all the necessary functions of rigid support, horizontal flexibility with enhanced stability, and energy-dissipation characteristics. Moreover, it has two unique features that are built-in: energy-absorbing buffer and linear recentering mechanisms. Through a nonlinear time history analysis under three recorded NF earthquakes and three synthetic ground accelerations, the results show that the RNC isolator is a convenient isolation system in protecting cable-stayed bridges against NF earthquakes.
In this paper, current and proposed methodologies for assessing the robustness and redundancy of bridge structures are discussed and an overview of the latest advances in research is presented along with proposals for implementation in bridge design and evaluation codes. In particular, European and North American standard codes and guidelines, including the Eurocode, AASHTO, and the Canadian Standards Association (CSA), as well as some national European codes and related guidelines, are compared. Research projects, including those of the European Cooperation of Science and Technology (COST) and the U.S. National Cooperative Highway Research Program (NCHRP), represent key links between research activities and the need for implementing concepts of structural redundancy and robustness into the codes. The activities undertaken by COST and NCHRP constitute attempts to synthetize, simplify, and implement theoretical concepts that have been discussed over many years. This review shows that the U.S. approach concentrates on developing tools and criteria for the numerical evaluation of the capability of a bridge structure to continue to carry load after the failure of a member, whereas the European approach, still in a more
theoretical phase, lacks specific guidelines for bridges and uses available building recommendations. This paper also presents a critical
assessment of the state of the art and argues that criteria implementable in future generations of bridge codes should be based on quantifiable measures of risk, which is a subject still in its very early stages of development.
Villalba, S.; Casas, J.; Aparicio, A.; Villalba, V. ASCE. Journal of bridge engineering Vol. 18, num. 11, p. 1174-1188 DOI: 10.1061/(ASCE)BE.1943-5592.0000450 Data de publicació: 2013-11 Article en revista
The objective of this research has been to design, develop, and evaluate experimentally 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 purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, 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. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were 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 was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.
Advances in the production of optical fibers made possible the recent development of innovative sensing systems for the health monitoring of civil structures. The main reasons for this development are the reduced weight and dimensions of fiber optic sensors, the strong immunity to electromagnetic interference, the improved environmental resistance and the scale flexibility for small-gauge and long-gauge measurements. These systems can provide high-resolution and measurement capabilities that are not feasible with conventional technologies. In addition, they can be manufactured at a low cost and they offer a number of key advantages, including the ability to multiplex an appreciable number of sensors along a single fiber and interrogate such systems over large distances. For these reasons, it is evident that fiber optic sensors will change the instrumentation industry in the same way fiber optics has revolutionized communications. This paper provides an overview of the intensity modulated and spectrometric fiber optic sensors and techniques to assess the condition of existing structures in order to enhance the durability of the new bridges, increasing lifetime and reliability and decreasing maintenance activities. Application of these sensors to monitoring strain, temperature, inclination, acceleration, load measurements, ice detection, vehicles speeds and weights, and corrosion and cracking of reinforced and prestressed concrete structures will be described.
Linzhong, D.; Ghosn, M.; Znidaric, A.; Casas, J. ASCE. Journal of bridge engineering Vol. 6, num. 4, p. 276-284 DOI: 10.1061/(ASCE)1084-0702(2001)6:4(276) Data de publicació: 2001-08 Article en revista
This paper presents a procedure to improve the accuracy of the classical grillage method for the nonlinear analysis of concrete girder bridges. The procedure uses equivalent element plastic hinge lengths that account for the actual mesh size instead of using a mesh-independent global plastic hinge length. A thorough review of the results of tests conducted on two 1/3-model prestressed concrete girders and a 1/3-model prestressed concrete girder bridge is undertaken in order to model the nonlinear properties of prestressed concrete girder bridges. The purpose of this review is to study the extent of plastification and plastic hinge length development as well as the evaluation of the validity of the grillage method for the nonlinear analysis of girder bridges. An Lp transfer model is used to calculate the plastic hinge length for every beam element of the grillage based on the results from the experiments and other empirical models. The Lp transfer model allows the use of empirical data obtained from tests on individual girders to model the response of a variety of bridge configurations subjected to different loading conditions. The equivalent grillage element plastic hinge length Lgp is calculated as a function of the grillage mesh size. A number of examples are presented to demonstrate the validity of the proposed method by comparing the analytical results of grillage analysis using the Lp transfer model with those of laboratory and in situ tests on full-scale and model-scale prestressed concrete bridges. The proposed approach has a high potential for use in engineering practice because of the simple input requirement and improved accuracy.
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.