Active Scour Monitoring using Ultrasonic Time Domain Reflectometry of Buried Slender Sensors

Local scour is a growing cause of bridge failure in the United States and around the world. In the next century, the effects of climate changes will make more bridges susceptible to scour failure more than ever before. This study aims to harness the spatially continuous monitoring capabilities of ultrasonic time-domain reflectometry to detect a soil interface for the purposes of scour monitoring. In this study, a long, slender plate is coupled with two flexible piezoelectric devices that propagate Lamb waves along the length of the plate to form the scour sensor. The sensor was tested for sensitivity to external pressure using metal weights, and was able to detect the position of the pressure up at a length of up to ~ 20 feet. The sensor was tested under simulated scour conditions, being buried in sand at various depths. The results show that the Lamb wave scour sensor is capable of reliably detecting a soil interface at 1 ft intervals. The scour sensor was also able to detect uncompacted soil interfaces, which is important considering the issue of scour hole refill following an extreme event.

Dentist’s Perspective Regarding Usage of Different Fixed Prosthesis Removal Systems in Islamabad and Rawalpindi

Background: Crowns and multi-unit fixed partial dentures have a limited lifetime. They fail for a number of reasons. The removal of provisional crowns and bridges is generally simple, however for permanent crowns, it becomes more challenging. Careful removal of FPD can help a dentist simplify a resto or endo procedure. The aim of this article was to analyze the different methods available for the removal of crowns and bridges and their awareness among dental practitioners Study Design & location: This was a cross-sectional study based on a questionnaire. The questionnaire was filled by a total of 250 general and specialist dentists who were practicing in various individual and group-based dental practices as well as private and government setups of Islamabad and Rawalpindi. Methodology: The questionnaire comprised a total of 13 questions to find out dentists' views about the usage of different system’s available for dental crowns and FPD removal. Participants were selected by random sampling. The results were then analyzed using SPSS version 23. Frequencies, percentages of different variables used in the study were calculated to identify the co-relation among different attributes. P-value of less than or equal to 0.05 was considered statistically significant. Results: The study reflected that out of those who answered, 247 dental professionals (98.5 %) preferred using hemostats or Morrell sliding hammer or a combination of both as they offered better control of force. A small percentage (approx 2%) of dentists used diamond or carbide burs as their first preference to trim off old crowns. Clinicians rarely used laser due to its high cost and less availability and its effectiveness primarily related to Porcelain jacket/ Zirconium crowns. Conclusion: It was concluded from this study that the majority of dentists preferred Morrell type crown remover with sliding hammer due to its ease of availability, universal acceptance, simple to use and because as it offered better control of force as opposed to spring-lock type Keywords: Crown and bridge removal, Crown and bridge disassembly, Crown and bridge failure.

Bridge Failure and Public Perception of Safety: Managing Situations the Public See as Dangerous

<p>Occasionally, bridge projects present a challenge to the general public in terms of how they look or feel. This can happen during construction, demolition or even through the working operational lifespan. Concern can understandably arise if a structure looks or feels unstable or unsafe, for any reason. Some bridges seem ‘wrong’ even when they are quite safe.</p><p>The question of safety, and more particularly the perception of safety, are areas where structural engineering, the commercial realities of bridge ownership/operation, human psychology and public relations meet. When a bridge looks or feel unsafe, despite it being quite stable and without danger, the public may deem such a scenario unacceptable, and this can create friction with what is desirable from the point of view of the bridge owner or operator.</p><p>When the above occurs, the interface with the public and clients must be carefully managed. Clear, concise information is vital, communicated in non-jargon language. To persuade the uninitiated that something is safe, despite it looking the opposite, requires skills that bridge professionals sometimes lack. Identifying, understanding, and practicing these skills will sometimes feel counterintuitive to bridge practioners, but they are skills which nonetheless are sometimes essential.</p>

Bridge failures, forensic structural engineering and recommendations for design of robust structures

A review of forensic structural engineering, which is a strategy that follows after bridge failure, is presented in the paper. A detailed statistical analysis, and worldwide systematisation of available bridge failure data for the 1966-2020 period, are given. More than six hundred cases of partial or full collapse of bridges are analysed in detail, and causes that have led to their failure are examined. Failure of each of these bridges was in most cases not caused by a single factor, i.e. the main cause was most often just a trigger in the cause-and-effect sequence of events that contributed to such failure. Consequently, in addition to main causes, the influence of human factor, as a precondition leading to failure, is considered in each of the analysed cases. Types of progressive collapse, being a critical structural failure mechanism, are described in the second part of the paper, with an emphasis on bridges. An overview of the theory of structural robustness is also given. Design guidelines and approaches, aimed at preventing catastrophic failure and creating more robust structures, are presented. Methods for achieving robustness in the design of new bridges and in the strengthening of the existing ones are also described, and practical real-life examples are provided.

Categorization of Bridges by Failure Consequences

Categorization of bridge constructions by the failure consequences due to loss of ultimate capacity or serviceability is a difficult task that can be resolved using two different approaches: elementary method using currently valid standards advanced method based on risk assessment. The elementary method is grounded on subjective assessment of bridge malfunctioning or collapse. The bridge is classified into an appropriate category (consequence class) in accordance with the most severe consequence. It is a simple procedure that may be applied without the need of demanding mathematical procedures. However, the resulting categorization may be affected by uncertainties in the assessment of consequences. The advanced method is based on a comprehensive analysis of bridge malfunctioning using a procedure of risk assessment. This method takes account of the occurrence probability of unfavourable events and the significance of individual consequences. Classification of a bridge construction into an appropriate category depends on the resulting risk of the bridge failure. This more laborious approach provides credible results without excessive uncertainties. The most adverse difficulty of the method is a combination of some consequences like the loss of life and economic costs. Both the above-mentioned approaches to the categorization of bridges by failure consequences can be effectively used depending on the type of bridge, on the intensity of exploitation, on expected consequences, and on social impacts of bridge malfunctioning.

Review on the Service Safety Assessment of Main Cable of Long Span Multi-Tower Suspension Bridge

The long-span multi-tower suspension bridge is widely used in the construction of river and sea crossing bridges. The load-bearing safety and anti-sliding safety of its main cable are directly related to the structural safety of a suspension bridge. Failure mechanisms of the main cable of a long-span multi-tower suspension bridge are discussed. Meanwhile, the tribo-corrosion-fatigue of main cable, contact, and slip behaviors of the saddle and service safety assessment of the main cable are reviewed. Finally, research trends in service safety assessment of main cable are proposed. It is of great significance to improve the service safety of the main cable and thereby to ensure the structural safety of long-span multi-tower suspension bridges.

The Impact of Fracture Persistence and Intact Rock Bridge Failure on the In Situ Block Area Distribution

The in situ block size distribution is an essential characteristic of fractured rock masses and impacts the assessment of rockfall hazards and other fields of rock mechanics. The block size distribution can be estimated rather easily for fully persistent fractures, but it is a challenge to determine this parameter when non-persistent fractures in a rock mass should be considered. In many approaches, the block size distribution is estimated by assuming that the fractures are fully persistent, resulting in an underestimation of the block sizes for many fracture geometries. In addition, the block size distribution is influenced by intact rock bridge failure, especially in rock masses with non-persistent fractures, either in a short-term perspective during a slope failure event when the rock mass increasingly disintegrates or in a long-term view when the rock mass progressively weakens. The quantification of intact rock bridge failure in a rock mass is highly complex, comprising fracture coalescence and crack growth driven by time-dependent changes of the in situ stresses due to thermal, freezing-thawing, and pore water pressure fluctuations. This contribution presents stochastic analyses of the two-dimensional in situ block area distribution and the mean block area of non-persistent fracture networks. The applied 2D discrete fracture network approach takes into account the potential failure of intact rock bridges based on a pre-defined threshold length and relies on input parameters that can be easily measured in the field by classical discontinuity mapping methods (e.g., scanline mapping). In addition, on the basis of these discrete fracture network analyses, an empirical relationship was determined between (i) the mean block area for persistent fractures, (ii) the mean block area for non-persistent fractures, and (iii) the mean interconnectivity factor. The further adaptation of this 2D approach to 3D block geometries is discussed on the basis of general considerations. The calculations carried out in this contribution highlight the large impact of non-persistent fractures and intact rock bridge failure for rock mass characterization, e.g., rockfall assessment.

Cascade effect of rock bridge failure in planar rock slides: numerical test with a distinct element code

Plane failure along inclined joints is a classical mechanism involved in rock slope movements. It is known that the number, size and position of rock bridges along the potential failure plane are of prime importance when assessing slope stability. However, the rock bridge failure phenomenology itself has not been comprehensively understood up to now. In this study, the propagation cascade effect of rock bridge failure leading to catastrophic block sliding is studied and the influence of rock bridge position in regard to the rockfall failure mode (shear or tension) is highlighted. Numerical modelling using the distinct element method (UDEC, Itasca) is undertaken in order to assess the stability of a 10 m3 rock block lying on an inclined joint with a dip angle of 40 or 80∘. The progressive failure of rock bridges is simulated assuming a Mohr–Coulomb failure criterion and considering stress transfers from a failed bridge to the surrounding ones. Two phases of the failure process are described: (1) a stable propagation of the rock bridge failures along the joint and (2) an unstable propagation (cascade effect) of rock bridge failures until the block slides down. Additionally, the most critical position of rock bridges has been identified. It corresponds to the top of the rock block for a dip angle of 40∘ and to its bottom for an angle of 80∘.