Showing papers in "Journal of Performance of Constructed Facilities in 2004"

Progressive Analysis Procedure for Progressive Collapse

Abstract: Following the collapse of the World Trade Center towers in September 2001, there has been heightened interest among building owners and government entities in evaluating the progressive collapse potential of existing buildings and in designing new buildings to resist this type of collapse. The General Services Administration and Department of Defense have issued general guidelines for evaluating a building’s progressive collapse potential. However, little detailed information is available to enable engineers to confidently perform a systematic progressive collapse analysis satisfying these guidelines. In this paper, we present four successively more sophisticated analysis procedures for evaluating the progressive collapse hazard: linear-elastic static; nonlinear static; linear-elastic dynamic; and nonlinear dynamic. We discuss the advantages and disadvantages of each method. We conclude that the most effective analysis procedure for progressive collapse evaluation incorporates the advantageous parts of al...

Explosive Testing of Polymer Retrofit Masonry Walls

Abstract: The most widely used terrorist tactic is the improvised explosive device, which can range in size from hand-held to truck-size. Most casualties and injuries sustained in such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of walls, the shattering of windows, and by nonsecured objects propelled at high velocities by the blast. Since 1995, the Air Force Research Laboratory at Tyndall Air Force Base has investigated methods of retrofitting wall structures to better resist blast loads from external explosions. This paper summarizes results from recent tests that involve an innovative use of a sprayed-on polymer to increase blast resistance of unreinforced concrete masonry walls. Test methodology, retrofit materials considered, material properties, mechanisms of effectiveness, and research challenges are discussed.

Collapse of 2000 Commonwealth Avenue: Punching Shear Case Study

Abstract: On January 25, 1971, two thirds of a 16-story apartment building collapsed while under construction at 2000 Commonwealth Avenue, Boston, Massachusetts Four workers died after a failure on the roof instigated a progressive collapse all the way to the basement, where the men were found Fortunately, the collapse occurred slowly enough for most of the other workers to run to safety An investigation, conducted by a commission assembled by the Mayor of Boston, painted a picture of a troubled project, with considerable confusion about responsibility for structural safety The surviving workers' descriptions of the failure provide a textbook definition of punching shear Low concrete strength due to inadequate protection against cold weather contributed to low punching shear strength of the flat slab Inspection, quality control, planning, and supervision were for all practical purposes absent from the project This paper investigates the numerous causes and lessons learned of this structural failure Two similar cases are also reviewed

Seismic Effect on Highway Bridges in Chi Chi Earthquake

Abstract: This paper reports the bridge damage in the Chi Chi earthquake. Damage to bridge structures may occur in the superstructure, the substructure, or the approaches. Typical types of damage are discussed and illustrated in this paper. A review of the design specifications in Taiwan is also presented to give the background on the seismic design of highway bridges in Taiwan.

Performance and Seismic Vulnerability of Masonry Housing Types Used in Chile

Abstract: Masonry is the most used construction material, especially for residential dwellings built in all regions of Chile, up to four stories high. The masonry wall's reinforcement of these buildings can be classified into three types: confined, reinforced and hybrid. Although buildings with confined masonry walls have limited shear strength and ductility, they have demonstrated acceptable seismic behavior. Experience for buildings with the other two types of reinforcement has been different; during the 1985 Llolleo earthquake several buildings had severe damage due to design and construction deficiencies. In this paper a description of key structural features, construction process, seismic resilient features and deficiencies of masonry housing types used in government-subsidized low-income dwellings is provided. In addition, various seismic vulnerability indices that characterize their seismic behavior are calculated. The evolution over time of such indices shows that nowadays a large amount of buildings are likely to be damaged after a severe earthquake.

Lessons Learned on Improving Resistance of Buildings to Terrorist Attacks

Abstract: This paper presents some findings of the FEMA and SEI/ASCE sponsored studies of structural performance of New York’s World Trade Center (WTC) following the attacks of September 11, 2001, and the Murrah Building following the April 19, 1995, Oklahoma City bombing. The WTC collapses were caused not by aircraft impact alone but by the combination of impact and the resulting fire that weakened structural members and connections. On the other hand, the Murrah Building collapsed as a direct result of the blast. Although these studies call for further research in a number of areas, this report summarizes some of the lessons learned.

Performance of campus parking garages in preventing crime

Abstract: The Ohio State University ~OSU! initiated this study in response to campus parking garage crime that persisted at an unacceptably high level in spite of campus-wide efforts to reduce crime. The writers combined crime statistics gathered by the OSU Police Department with results of an on-site survey to model parking using Crime Prevention Through Environmental Design ~CPTED! principles. The goal of the study was a group of CPTED-based design changes intended to create an environment that would deter parking garage crime. The analysis included factors such as lighting, visibility, garage color, location of entrances and exits, and design of elevators and stairways. The evaluation showed that lighting was the most significant factors in users' perception of parking garage safety. As a result of this study, OSU implemented the recommended CPTED improvements. In the 2 years following the implementation of CPTED improvements, the average annual incidence of crime in the parking garage where the CPTED improvements had been made fell by more than half of the average annual incidence of crime in that same garage for the four years before the improvements were made.

Laser-based instrumentation for bridge load testing

Abstract: This paper describes the developments and application of a laser-based instrument used to experimentally load test bridges. The instrument is used to quickly and unobtrusively measure bridge girder deflections under static loading. The system can be set up in the median or shoulder of the roadway under the bridge without altering traffic. Data can be collected on multiple girders from one measurement location without requiring access to the girders, and no special targets are required on the girders. As a result, this type of a system can greatly speedup the process of load testing a bridge. In fact, the system can allow bridges to be load tested that would be difficult or impossible under other circumstances. To help understand the way the instrument is used, a description of the basic system operation is given followed by a detailed explanation of the main instrument features. Details of the procedure used to measure vertical deflection of bridge girders are discussed. Finally, an overview of the experimental local tests performed with the NDEVC laser system is presented.

Survey of Window Retrofit Solutions for Blast Mitigation

Abstract: Explosive attacks on buildings create a rapid release of energy in the form of a shock wave. Window glass is often the weakest part of a building, breaking at low pressures compared to other building components. Explosion-related injuries caused by glass breakage include eardrum damage, lung collapse, and penetration- or laceration-type injuries from airborne glass fragments which may lead to fatalities. As glass breakage may extend for miles for a large external explosion, reducing glass hazard is an important aspect of blast-mitigation for buildings. Blast-mitigating window products are in their infancy in the United States. Categories of available window retrofit solutions include: window film technologies, mullion and frame upgrades, catch systems, window replacement systems, installa- tion of secondary windows, and/or a combination of these technologies. Installation of daylight film is the least costly but provides the lowest level of protection, while replacing windows is the most costly with the greatest gain in blast protection. Selection of the best window retrofit solution is usually based on a number of design constraints including blast criteria, building constraints—which can be broken down into type of building, maintenance and operability requirements, interior finishes, energy conservation requirements, lifecycle—and finally the retrofit cost.

Human Error and Reliability of Multistory Reinforced-Concrete Building Construction

Abstract: This paper develops probabilistic and human reliability models to estimate the probability of structural collapse (system risk) during the construction of typical multistory reinforced-concrete buildings in the presence of human error. Results obtained from the human reliability analysis suggest that errors related to concrete cover and concreting workmanship are more detrimental to system risk than any other errors. Errors related to reinforcement area have a minor effect on system risk, provided that the existing effectiveness of engineering inspections is maintained. The results also show that errors related to installation of steel shores/reshores do not significantly affect the system risk.

Nondestructive Evaluation of the I-40 Bridge over the Rio Grande River

Abstract: A nondestructive strength evaluation of the I-40 Bridge over the Rio Grande River in Albuquerque, N.M. was completed for the New Mexico Department of Transportation (NMDOT). The I-40 Bridge is a pr...

Retrofitting Existing Masonry Buildings to Resist Explosions

Abstract: In recent years, many buildings around the world have had their windows protected or strengthened to resist the effects of explosions in an attempt to reduce the level of casualties associated with terrorist bomb attacks. While the windows form the most vulnerable parts of a building, occasionally it becomes necessary to strengthen the walls as well—particularly in older and weaker historical structures or where the blast loads are high. This paper highlights a number of different techniques available to the structural engineer and security specialist that can be employed to make existing masonry walls stronger and more capable of safely resisting the effects of explosions.

Contribution of Intermediate Diaphragms in Enhancing Precast Bridge Girder Performance

Abstract: The objective of this study was to determine the effect of intermediate diaphragms on the stiffness of precast prestressed AASHTO type bridge girders, combined with the actual bearing stiffness and thermal changes. Some of the parameters studied include the presence of intermediate diaphragms, bridge skewness, temperature change, and an increase in bearing stiffness due to cold temperature or aging. A finite element model of a bridge superstructure containing Florida Bulb Tee 78 girders was created. This model was subjected to an HL93 truck load as suggested by the AASHTO LRFD. Results indicate that intermediate diaphragms have a modest positive effect of reducing the maximum deflections for the chosen girder, with the effect varying with skewness and thermal change.

Field Performance of an Independent Full-Height Facing Reinforced Soil Wall

Abstract: An innovative retaining wall system was adopted for the construction of a ramp connecting Interstate-25 and Interstate-70 in Colorado. The retaining wall system, known as the independent full-height facing (IFF) reinforced soil wall, has a full-height concrete facing panel in front of a soil mass that is reinforced with layers of tensile inclusion. The use of this retaining wall system allowed the highway to remain open to traffic during the construction operation and alleviate the need to deal with the excavation and disposal of the subsoil that had been contaminated in the past. Two sections of the retaining wall, locally known as the Fox wall, were instrumented to monitor the performance during and after construction. A study was undertaken to synthesize the measured data and to evaluate the performance and design assumptions of the retaining wall. This paper describes the IFF reinforced soil wall system and the Fox wall project, presents the measured data, and discusses the wall performance. Design implications concerning the initial setback of facing panels, reinforcement strength requirement, and lateral forces on facing panels are also addressed.

Budget Allocation for Steel Bridge Paint Maintenance

Abstract: Government authorities are responsible for managing their available budget so that they gain maximum benefit. Therefore, they must make intelligent decisions as to which projects will be funded and the degree of funding. Dynamic programming (DP), integer programming (IP), and greedy heuristic (GH) approaches have been applied to optimize a two-year budget allocation for repainting steel bridges in Indiana. The optimal solution and the objective function values resulting from application of DP, IP, and GH are similar. The Indiana Department of Transportation (INDOT) divides Indiana into six districts. The results show that District 1 has the highest budget allocation percentage (28%). It has the lowest percent in the first year and the highest percent in the second year. District 2 has the lowest percentage (11%). A sensitivity analysis has been completed to show the potential alternative solutions that assist INDOT decision makers in solving their budget allocation problems.

Evaluation of In-Service Performance of Tom's Creek Bridge Fiber-Reinforced Polymer Superstructure

Abstract: The Tom's Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load carrying members. It is a simply supported, short-span bridge located along Tom's Creek Road in Blacksburg, Virginia. As a result of discussions among Virginia Tech, Strongwell, the Virginia Department of Transportation, and the Town of Blacksburg, the existing deteriorated superstructure of the Tom's Creek Bridge was replaced with a glue-laminated timber deck on 8 in. (20.3 cm) deep pultruded FRP beams. The project was intended to address two issues. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution and deflections under service loading, the Tom's Creek Bridge will aid in modifying current AASHTO bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after being exposed to controlled laboratory and service conditions, the project will begin to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. A dynamic load allowance, IM, of 0.90 is recommended for the Tom's Creek Bridge. This value is the largest average IM observed and is therefore conservative. This value is significantly higher than those set forth in the AASHTO standards of 0.33 (AASHTO, 1998) and 0.30 (AASHTO, 1996). It is recommended to use a value of L/425 (LRFD Specification) or L/500 (Standard Specification). This value is consistent with AASHTO deflection control criteria for an all timber bridge. It is recommended to use the AASHTO wheel load distribution factors for a glulam timber deck on steel stringer bridge. There is no indication of loss of FRP girder ultimate strength after 15 months of service. Given the low service loads (no more than 10% of the ultimate capacity) and traffic volume the fatigue life prediction model suggests that fatigue will not be a major concern during the life of service (10 to 15 years).

Corrosion response of a decommissioned deteriorated bridge deck

Abstract: This paper summarizes the results of field tests on the decommissioned Montreal Dickson Bridge, undertaken over a grid of 0.25 by 0.25 m on four randomly selected 5 by 6 m deck patches, and the associated laboratory tests as part of a detailed research program aimed at determining why the bridge deteriorated so rapidly. The basic cause of deterioration was determined to be the lack of quality control (concrete mix composition, placing, compaction, and curing) and the resulting higher permeability of the concrete cover and the associated chloride ion ingress. As a consequence, the resistivity of the concrete was low and reflected in a high steel bar mass loss due to corrosion at several locations on the bridge after a period of only 35 years.

Nondestructive Assessment of Damage in Concrete Bridge Decks

Abstract: Impact-echo tests were performed on a precast, reinforced concrete bridge slab that was removed from a maintenance bridge built in 1953 in South Carolina. Impact-echo tests were first performed to nondestructively assess the initial condition and the distribution of damage throughout the slab by analyzing the variation in propagation wave velocity. It was found that the velocity varied by as much as 900 m/s throughout the slab. After the in-service condition was assessed, the slab was subjected to a full-scale static load test in the laboratory and impact-echo tests were again performed, this time to evaluate the initiation and progression of damage (stiffness loss and crack development) within the slab. After structural failure of the slab, a reduction in propagation wave velocity up to 6% was observed correlating to a reduction in slab stiffness. Cracks were detected within the concrete slab that were not visible from the surface. Areas with preexisting damage experienced more crack growth when subjected to the load test than those that were initially intact. Locations exhibiting stiffness loss, crack propagation, and localized damage can be differentiated such that the method can be used to make decisions between rehabilitating and replacing concrete bridge decks depending upon the severity of damage.

Workmanship Factors Influencing Quality of Installed Parking Garage Waterproofing Membranes

Abstract: Elastomeric waterproofing membrane performance is dependent not only on material properties, but also on the quality of the installation. Currently marketed products are cold, liquid applied, self-adhering elastomers that vary in chemical composition and method of application. Material properties are governed by the response of each material to many site factors encountered in the installation. Application problems can result from a variation of ambient weather conditions, the quality of workmanship, and the surface preparation of the substrate. The influence of workmanship factors and surface preparation on the performance of five elastomeric membranes was investigated. The results show that poor on-site practice and a lack of quality control during installation often produce a final product of low durability.

Safety Evaluation for Campus Parking Garage Performance Using Fuzzy Logic

Abstract: Crime has been plaguing parking garages in the United States. At The Ohio State University, (OSU) crime on campus, in general, has decreased in recent years; however, crime in OSU parking garages has remained stable in spite of campus-wide efforts to reduce crime. When assessing and evaluating parking garages, occupants employ experience-based judgment that is subjective and imprecise, yet extremely useful. When designers employ the principles of crime prevention through environmental design, they also use subjective variables. An approach that captures the imprecise information in noncrisp expressions reflecting subjective and experience-based variables is the fuzzy logic concept. This concept allows the use of mathematical operations to manipulate and operate on imprecise information or knowledge. Variables such as garage illumination and wall height were collected, fuzzified, and treated as the knowledge base of a model presented in this paper. In addition, numerous experience-based implication rules were developed and employed to evaluate subjective variables. A computer program was developed to illustrate implementation of the model.

Assessment of retrofit dowel benefits in cracked portland cement concrete pavements

Abstract: A parametric study was conducted using the finite-element rigid pavement program ISLAB2000. For cracks that utilize aggregate interlock as the sole means of load transfer, the integrity of the cracks was initially modeled using the aggregate interlock factor. A subsequent analysis was then performed on the same cracks for the case where both dowel bars and aggregate interlock were available for load transfer purposes. The latter scenario represents the case where dowel bar retrofitting (DBR) has been performed on the cracks. In both cases, the deflection load transfer efficiency and critical slab tensile stresses were computed in order to examine the immediate theoretical benefits of the dowel bars. The validity of these theoretical benefits was tested using data from falling-weight deflectometer testing on DBR sites in both Michigan and Washington. It was found that installation of dowel bars did not increase the load transfer efficiency for cracks that had levels greater than 89–95%, depending on paveme...

Splitting Failures in Trapezoidal Steel Roof Cladding

Abstract: High wind events such as hurricanes and storms often cause severe damage to crest-fixed thin steel roof claddings. Past research on wind damage has shown that low cycle fatigue cracking of steel roof sheeting around the fastener holes has been the reason for the premature pull-through failures of roof claddings under fluctuating wind forces. Such a situation will be at its worst if the roof sheeting is already split at the fastener holes. An inspection of trapezoidal steel roofs has shown that roofing has been split in the transverse direction due to overtightening of screw fasteners accidental or caused by poor workmanship. Once split, even slightly, the roofing can survive only a few cycles of wind uplift loading. Therefore an investigation using laboratory experiments and finite element analyses was carried out to study the splitting behavior of two commonly used high tensile steel trapezoidal roof claddings. The analytical and experimental results agree reasonably well and present a good understanding of the splitting behavior of trapezoidal roof claddings. This paper presents the details of this investigation and the results.

Investigation of permeability on indiana sr-38

Abstract: In 1999, a 9.5 mm nominal maximum size hot-mix asphalt mixture, designed according to the Superpave mixture design method, was placed as an overlay on Indiana State Road 38. Within one year of construction, the pavement showed signs of significant distress, including aggregate pop-outs and degradation, the presence of free water (weeping) on the driving surface, and longitudinal and fatigue cracking. At the request of the District, an investigation was undertaken to determine the cause of the pavement distress. As part of the investigation, core samples were taken from the roadway surface and tested for compliance with material properties and volumetrics, and to determine the mixture permeability. The mixture met all applicable materials and volumetric specifications, but had a low in-place density and was permeable. The results indicate that the mixture was too coarsely graded to achieve compaction in the relatively thin lift specified by the Department of Transportation. The resulting recommendations were that the mixture be removed and replaced, and that the mixture specifications be revised to more closely control gradation and increase mixture lift thickness.

Condition assessment of the eastbound 6th Avenue Viaduct using strain gauges

Abstract: This paper presents the procedure and results of a strain gauge study completed on the eastbound 6th Avenue Viaduct in Denver. The 6th Avenue Viaduct was modified in a 1997–1998 rehabilitation, making the entire superstructure continuous. New sliding bearing pads failed to properly accommodate expansion and contraction of the bridge superstructure due to temperature changes. Visible damage due to contraction of the superstructure in the winter of 1999–2000 prompted a study of substructure elements to determine the short-term safety and long-term viability of the bridge. Substructure elements were instrumented with a total of 62 strain gauges and two concrete crack gauges. Data were taken for a period of 3 months. Analysis of the data suggests that the bridge is safe for short-term use, but that the long-term viability of the structure has been compromised. Repair or replacement of substructure elements is recommended, along with frequent monitoring during the interim period.

Laboratory Testing for Building Failure Investigations

Abstract: Failure of a building or its components usually means that it is performing in an unsatisfactory way. Investigation of such a failure often uncovers deterioration or other problems with the building or component materials. Deterioration can mean loss of strength, disintegration, or corrosion of some part of the structure. Discovering the cause of such deterioration may involve removing representative samples or complete systems and testing them in the laboratory. There are a wide variety of laboratory tests available to the investigator. This forum summarizes some of the more common ones used as part of a failure investigation.

Protecting People in Buildings from Terrorist Attack

Abstract: Richard G. Little is Director of the Board on Infrastructure and the Constructed Environment of the National Research Council ~NRC! where he develops and directs a program of studies in building and infrastructure research and maintains outreach and liaison with federal agencies, the legislative branch, and affiliated organizations. He has directed NRC study activities, participated in workshops and panels, and written several papers dealing with physical security and critical infrastructure protection. He served as the Study Director for several NRC reports including Protecting Buildings from Bomb Damage in 1995, Protecting People and Buildings from Terrorism: Technology Transfer for Blast-Effects Mitigation in 2001, a review of the Interagency Security Committee ~ISC! security criteria issued in 2002, and the recently completed report Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering. Little has over 30 years experience in planning, management, and policy development relating to public facilities, including 15 years with local government. He is a member of the American Institute of Certified Planners and the Federal Planning Division of the American Planning Association. Little holds a BS in Geology and an MS in UrbanEnvironmental Studies, both from Rensselaer Polytechnic Institute. The events of September 11, 2001, made it clear that there are no safe havens from terrorism. Tragedy can strike anyone— anywhere—at any time. But as we move beyond those events, it is important that we do everything reasonable to protect the nation’s buildings and the people they shelter from possible future attacks. Despite the terrible loss of life, the World Trade Center towers and the Pentagon actually performed extremely well under circumstances far more severe than anything anticipated when they were designed. This proved that buildings can make a real difference in saving lives, and, clearly, we can and should design and construct our buildings to do the best possible job of protecting the people that live and work inside them. Experience over the past 25 years has demonstrated that the primary causes of injuries and death in vehicle-bomb attacks against buildings are glass fragmentation, the impact of other debris, and building collapse. Resistance to these vulnerabilities is generally provided by passive features such as additional reinforcement and special connections in the structural frame for increased ductility, composite fiber wraps and other coatings to prevent shattering of columns and slabs, and high-performance glazing materials that resist blast pressures. As demonstrated by the attack on the Pentagon, these measures can be quite effective in reducing damage and casualties. In 2001, shortly after the attacks, the National Research Council released a report, Protecting People and Buildings from Ter-

Performance simulation of nuclear containments for security

Abstract: Under blast loading, nuclear containment structures are subjected to cyclic flexural, axial, and shear forces. Less attention has been paid to modeling the cyclic behavior of reinforced concrete elements in which shear deformations are significant, such as in nuclear containments. Research has demonstrated that the strength of concrete in the principal compression direction is softened by tension in the lateral direction. This interaction has been considered for monotonic loading for many years. To consider this interaction for cyclic loading, the material laws recently derived by Mansour et al. in 2001 for the cyclic softened membrane model (CSMM) can be used. Both fire and explosion effects resulting from blast loading can also be incorporated into the constitutive models of concrete and reinforcing bars. This paper presents a method to implement the CSMM model, so that it can be used to simulate the performance of nuclear containments for security by the design communities.

Bridge Evaluations Using Nondestructive Techniques

Abstract: In the fall of 2002, I had the privilege of moderating a half-day seminar on nondestructive evaluation (NDE) techniques at ASCE’s 150th Anniversary Conference, in Washington, D.C. Eight speakers addressed a wide range of established and developing technologies that allow us to learn how a building is put together, without taking it apart. At that seminar, Ken Carper, editor of this Journal, suggested devoting one or more special topic issues to NDE techniques and technologies. This is the first of what we hope will be a recurring series of journal issues focused on NDE. The six papers presented here all address the critical issue of bridge evaluation, with particular attention given to the implementation and standardization of NDE techniques. There are more than a half-million bridges in the United States. Many are well-known and receive the special care and attention commensurate with their celebrity status. My esteemed New York neighbor, the Brooklyn Bridge, frequently carries my feet to and from my home across the East River, and is no less inspiring or serviceable than the day it opened more than 120 years ago. The vast majority of our bridges, however, labor in relative obscurity, but have equal importance. On a highway drive of any length we may unknowingly entrust our safety to dozens of utilitarian bridges. Despite their lowly status, these structures perform in an environment far more challenging than most buildings ever experience. In addition to lateral forces (wind and seismic), foundation settlement, and materials deterioration, bridges are subjected to constant dynamic loading and associated fatigue, aggressive erosive forces from flowing water, the corrosive impact of road salts, and cyclic freezing. Sadly, from time to time we have been reminded of the reality of the forces that affect bridge performance. The wind-driven failure of the Tacoma Narrows bridge, an image that often graces the cover of this journal, is the most widely known, but numerous other failures have imparted equally tough lessons to the profession. For example, the 1987 failure of the Schoharie Creek Bridge was one of several caused by scour, but in a broader sense it represented a failure of the inspection and evaluation program. Numerous observations of the bridge before the fatal collapse failed to detect critical weaknesses. Because of the importance of our bridges and the aggressive environments in which they serve, mandatory periodic bridgeinspection programs exist throughout the United States, and indeed throughout much of the world. These programs and the professionals who execute them serve a continuing vital role in protecting the safety and welfare of the public. The work of bridge inspectors has undoubtedly averted countless potential failures. Nevertheless, even an occasional failure is one too many, and we continue to strive to improve the accuracy, consistency, and