Practice Periodical on Structural Design and Construction

The design and analysis of a bridge system is a complicated task. In order to simplify the design process, it is necessary to break the system into smaller, less complex, and more manageable subsystems. The AASHTO load-and-resistance factor design (LRFD) bridge design specifications provide the design methods and procedures to design the bridge components explicitly and on an individual basis. In particular, the AASHTO LRFD bridge design specifications employs the beam-line method or distribution factor method to reduce the spatial dimensionality of bridge structures into line elements. The distribution factor is used to modify the load effects determined from the beam-line analysis to account for the effects at other locations in the structure. The published vehicular design loads adopted by the AASHTO LRFD bridge design specifications are considered to be an “average design truck.” The average design truck loads exclude vehicles that are above the legal weight limits for the United States, but are regularly allowed to operate on the U.S. highway systems. These loads are short-haul vehicles such as solid waste trucks, aerial rescue fire trucks and concrete mixers. The most common type of bridge in the United States is the slab-girder bridge system. The principal function of the slab-girder bridge is to provide a roadway surface and transmit the applied loads of the roadway to the girder system supporting the roadway. This research examines the loading effects of the short-haul vehicular loads on a typical prestressed concrete open box beam (U-beam) bridge. This study consists of analytically determining the distribution factors of special vehicles such as, a concrete mixer, a solid waste truck, and an aerial fire rescue truck, and comparing the results to distribution factors recommended in the AASHTO LRFD bridge design specifications.

The Paderno Bridge along the Adda river in the northern part of Italy is a relevant arch-bridge connecting Milan and Bergamo province in the northern part of Italy: the bridge is part of the Monza-Bergamo line and is in service from 1889. A stepwise and practical approach for evaluating the structural integrity of historical and deteriorated steel bridges, incorporating analytical, mechanical, and structural characterizations, is presented. Critical regions of hot spot members were identified using structural finite-element analysis, and fatigue reliability assessment analysis has been performed along with traffic estimation, taking into account various scenarios of traffic increase, in order to assess the possible remaining fatigue life. This analysis has evidenced that the structure might be kept in service at least for other 10 years. Appropriate retrofitting interventions are also indicated.

Scour is one of the main causes of bridge failures. It accounts for about 60% of bridge failures in the United States. Scour failures tend to occur suddenly without prior warning and are very difficult to monitor during flood events. This paper presents a comprehensive review of the up-to-date work on scour at bridge piers and abutments. First, a general introduction of bridge scour including the current situation of bridge scour problems and different types of bridge scour is given. Then, different approaches developed for predicting bridge scour are reviewed. Numerical and laboratory models established for bridge scour studies are also presented. Moreover, laboratory experiments and field tests conducted for bridge scour are reviewed. Different techniques and instruments developed for bridge scour monitoring are also presented with their advantages, disadvantages, and relative cost summarized in a table. Finally, various mitigation countermeasures developed for bridge scour are discussed.

This is Part I of a three-part paper on the phenomena of explosions and effects of explosions on structures. The overall paper is intended to provide the reader with a practical overview of the various types of explosions and methods available to predict explosion effects with emphasis on air blast. The response of structures to air blast is discussed and methods of analysis are presented. Since the subject area is broad, reference sources for more in-depth information on many of the topics presented are provided. In this paper, Part I, the background is provided on explosion phenomena and the types of effects produced by explosions of various general types. Physical, chemical, electrical, and nuclear explosions are discussed. Explosion effects for external (outdoor) explosions presented include air blast characteristics of peak overpressure, positive phase impulse, time of arrival, and positive phase duration. The ranges of peak overpressure and event duration from different types of explosions are compared. Other effects discussed include thermal effects, projectiles, ground shock, and cratering.

This is Part II of a three-part paper on the phenomena of explosions and effects of explosions on structures. The overall paper is intended to provide the reader with a practical overview of the various types of explosions and methods available to predict explosion effects, with emphasis on air blast. The response of structures to air blast is discussed and methods of analysis are presented. Since the subject area is broad, reference sources for more in-depth information on many of the topics presented are provided. In this paper, Part II, calculation methods for predicting explosion effects are presented for different types of explosions, with emphasis on air blast. Logic diagrams are presented to aid in the prediction of air blast characteristics from different types of explosions. Then the analysis tools required are summarized. A dispersion analysis is required to characterize a combustible cloud in cases involving a dispersed fuel. For the prediction of air blast characteristics the following methods are discussed: experimental modeling, TNT (trinitrotoluene) equivalency, methods for pressure vessel explosions, methods for boiling liquid expanding vapor explosions, multienergy and Baker-Strehlow-Tang methods for vapor cloud explosions, and computational fluid dynamics. A prediction of overpressure inside buildings and equipment is included.

This is Part III of a three-part paper on the phenomena of explosions and effects of explosions on structures. The overall paper is intended to provide the reader with a practical overview of the various types of explosions and methods available to predict explosion effects, with emphasis on air blast. The response of structures to air blast is discussed and methods of analysis are presented. Since the subject area is broad, reference sources for more in-depth information on many of the topics presented are provided. In this paper, Part III, methods are presented for predicting the response of structures to explosion effects. The methods that are discussed include peak pressure as a criterion, lumped mass, pressure-impulse as criteria, and finite-element analysis. Some example cases are given. A comprehensive tabulation of damage produced by different peak pressure levels is provided in Appendices I and II. A discussion of the appropriate use of such peak pressure data in predicting structural response is presented, together with some cautions.

The intent of this technical paper is to present and document the seismic performance of three new structural glass systems, each of which was designed to accommodate the elastic and inelastic seismic displacement criteria for high displacement in areas with high seismic activity. These systems include a rail-supported seismic glazing system, a point-fixed seismic glazing system, and a point-fixed seismic fin glass system. These systems may be used for cladding facades of buildings in areas of high seismicity and in particular in the state of California Seismic Zone 4. The California Building Code is now the underlying design methodology for the design of building cladding systems in California As most point supported glazing systems that are commonly used are not able to accommodate large building drifts, there was a need for an alternate point supported cladding system to address the design criteria imposed by current building codes. The performance of these systems was verified by mock-up testing, demonstrating that the proposed glazing systems can be used for cladding facades of building structures in areas of high seismicity, such as the state of California. The mock-up testing verified that the glass would translate horizontally and distribute seismic drift evenly over the height of the glazing systems, without breaking any components or glass. The testing also demonstrated that the silicone would withstand the shear demand imposed without rupturing the seal. The authors of this paper contributed to these three new glazing systems in ways of system engineering, design development, component finite analysis, preparation of engineering reports, test procedures, mock-up test result analysis, and project management for the actual implementation on the three successful installations. After successful completion of the mock-up test structures, each of these individual systems was used in real project applications; these projects are currently completed with the glazing systems fully installed. Please refer to the actual technical paper for detailed analysis on these systems.

This note recalls the circumstances leading to the late introduction of the idea of a shear center (or flexural center). It presents several graphs allowing a direct determination of the position of the shear center and of the corresponding warping constant for thin-walled asymmetrical U sections found as compression elements of channels and of similar profiles.