Paul A. Bosela

Application of Nondestructive Evaluation to Subway Tunnel Systems

Subway tunnel condition assessment presents significant challenges for engineers and managers and is becoming increasingly important as the systems continue to age. Tunnels are in constant heavy use in an aggressive environment. Tunnel systems are vast, dark, and noisy. The national investment in subway tunnels is enormous, and careful maintenance and management are necessary to protect this investment. Technologies that can rapidly and accurately access the condition of subway tunnels without interfering with the normal operation of the system were studied. First, issues and problems in subway tunnel maintenance were reviewed through the literature and by interviewing transit agency managers and engineers. Next, different nondestructive evaluation (NDE) methods including spectral analysis of surface waves, impact echo, ground-penetrating radar, and impulse response were evaluated to determine the advantages and limitations of these methods on different problems like water leakage, corrosion, and cracks in subway tunnel systems. Issues of data and infrastructure management were also considered. NDE technologies have considerable potential for improving the maintenance and management of transit infrastructure. However, to fully realize that potential, further development is needed. It is necessary to distinguish between methods that require interruption of subway traffic from those that do not. Rapid screening NDE methods must be researched to develop clear signals of delamination, moisture-related damage, and other issues of concern. It is also necessary to develop automated procedures to process the vast amounts of data generated during extensive NDE testing. Case studies and demonstration projects must be developed and documented to convince managers of the utility of this approach.

Steel Slag Aggregate Used in Portland Cement Concrete: U.S. and International Perspectives

The issue of sustainability in the built environment is increasingly important, particularly in the transportation sector. In some cases slags from the iron and steel industries can be used to replace natural aggregates in construction. In this research, laboratory investigations of the use of steel slag as a portland cement concrete (PCC) aggregate were reviewed. Much of this research took place outside the United States. Some limited field cases of the use of steel slag in pavements were found. In at least two cases dramatic pavement failure resulted, but it is not known whether the slag used in the applications had been properly aged as required by modern specifications. Research on the use of steel slag aggregate in PCC has been carried out in Spain, Germany, Canada, Italy, India, and Saudi Arabia. Despite some limited field applications, virtually all research has been done in the laboratory. Much of this work shows that properly aged steel slag can be nonexpansive when used in PCC. When these research results are evaluated, it is important to consider the properties of the slags used because they may differ from the slags produced in the United States due to differences in sources or industrial processes. Several state department of transportation specifications were reviewed, and they generally do not permit the use of steel slag as a PCC aggregate. Steel slag represents a small part of the total aggregates currently used, but it is an alternative material that should be considered where it makes economic sense.

Geometric stiffness effects on data recovery of an idealized mast/blanket model

Abstract The photovoltaic arrays for the international space station consist of a pre-tensioned blanket of solar collectors and a deployable mast. NASA uses the MSC/NASTRAN finite element program for modeling the dynamic response of the structure due to various loading conditions, such as plume impingement during shuttle docking. This finite element program uses the updated stiffness matrix (elastic plus geometric, or initial stress stiffness matrix) in determining the natural frequencies and mode shapes, as well as the dynamic response, of a pre-loaded structure. However, during the data recovery phase, when the moment and shear at the supports, and internal stresses are determined, geometric stiffness effects are neglected, and only the elastic stiffness is used in the calculation. The purpose of this study was to determine whether using the actual displacements, calculated based upon both elastic and geometric stiffness effects, would produce acceptable results in predicting shear and moment if the geometric stiffness effects were later omitted during data recovery. In this study, the PV array was idealized as a cantilever beam with an attached pre-tensioned cable. Static and dynamic analysis were performed, both using and neglecting the geometric stiffness matrix during data recovery. When considering the idealized mast/blanket model, neglecting the geometric stiffness contribution during data recovery led to a 32.2% difference in the vertical (shear) load at the fixed support, and an 8.8% difference in shear at the free end of the beam (compared to the inclusion of geometric stiffness effects in the analysis). The static analysis provided similar results and supported the “reasonableness” of the dynamic analysis. Due to the large discrepancies in the predicted stresses which can ocur when geometric stiffness contributions are neglected during data recovery, it should be imperative that when a structure contains pre-loaded elements, the geometric stiffness effects must be fully considered both in the determination of the natural frequencies and mode shapes, as well as in the subsequent calculation of nodal reactions and stresses.

Another Look at the Collapse of Skyline Plaza at Bailey's Crossroads, Virginia

AbstractOn March 2, 1973, the Skyline Plaza apartment building in Bailey’s Crossroads, Virginia collapsed while under construction. The Occupational Health and Safety Administration (OSHA) requested an investigation from the National Bureau of Standards [(NBS); now the National Institute of Standards and Technology (NIST)]. The NBS team concluded that the most likely cause of the collapse was a punching shear failure of the 23rd floor slab. The two factors that contributed to this were premature removal of shores below the 23rd floor slab, and the low strength of the 23rd floor concrete in the area supporting the weight of the 24th floor slab. The engineer’s structural drawings required 2 full stories of shoring and 1 story of reshoring while a concrete slab was cast. The project architect and structural engineer were sued and held responsible, although their specific shoring instructions had been ignored. This case study reviews the available published information on the case to determine what lessons ca...

A new pre-loaded beam geometric stiffness matrix with full rigid body capabilities

Abstract Space structures, due to economic considerations, must be light-weight. Accurate prediction of the natural frequencies and mode shapes is critical for determining the structural adequacy of components, and designing a control system. The total stiffness of a member, in many cases, includes both the elastic stiffness of the material as well as additional geometric stiffness due to pre-load (initial stress stiffness). The pre-load causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as “grounding”, or false stiffening, of the stiffness matrix occurs during rigid body rotation. The author has previously shown that that the grounding of a beam element is caused by a lack of rigid body rotational capability, and is typical of beam geometric stiffness matrices formulated by others, including those with higher-order effects. Having identified the source of the problem as the force imbalance inherent in the formulations, the author developed a beam stiffness matrix from a directed force perspective, and showed that the resultant global stiffness matrix contained complete rigid body mode capability, and performed well in the diagonalization methodology customarily used in dynamic analysis. In this paper, the authors investigate the “grounding” of membrane elements, and develop a new membrane element with rigid body rotational capabilities.

Grounding of space structures

Abstract Space structures, such as the Space Station solar arrays, must be extremely light-weight, flexible structures. Accurate prediction of the natural frequencies and mode shapes is essential for determining the structural adequacy of components, and designing a controls system. The tension pre-load in the ‘blanket’ of photovoltaic solar collectors, and the free/free boundary conditions of a structure in space, causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as ‘grounding’, or false stiffening, of the stiffness matrix occurs during rigid body rotation. This paper examines the grounding phenomenon in detail. Numerous stiffness matrices developed by others are examined for rigid body rotation capability, and found lacking. A force imbalance inherent in the formulations examined is the likely cause of the grounding problem, suggesting the need for a directed force formulation.

Dynamic analysis of space-related linear and non-linear structures

Abstract In order to be cost-effective, space structures must be extremely light-weight, and subsequently, very flexible structures. The power system for Space Station ‘Freedom’ is such a structure. Each array consists of a deployable truss mast and a split ‘blanket’ of photo-voltaic solar collectors. The solar arrays are deployed in orbit, and the blanket is stretched into position as the mast is extended. Geometric stiffness due to the preload make this an interesting non-linear problem. The space station will be subjected to various dynamic loads, during shuttle docking, solar tracking, attitude adjustment, etc. Accurate prediction of the natural frequencies and mode shapes of the space station components, including the solar arrays, is critical for determining the structural adequacy of the components, and for designing a dynamic controls system. This paper chronicles the process used in developing and verifying the finite element dynamic model of the photo-voltaic arrays. Various problems were identified in the investigation, such as grounding effects due to geometric stiffness, large displacement effects, and pseudo-stiffness (grounding) due to lack of required rigid body modes. Various analysis techniques, such as development of rigorous solutions using continuum mechanics, finite element solution sequence altering, equivalent systems using a curvature basis, Craig-Bampton superelement approach, and modal ordering schemes were utilized. This paper emphasizes the grounding problems associated with the geometric stiffness.

Implementation and Assessment of Failure Case Studies in the Engineering Curriculum

The history of the development of practice in many engineering disciplines is, in large part, the story of failures, both imminent and actual, and of the changes to designs, standards and procedures made as the result of timely interventions or forensic analyses. In addition to technical issues, concepts such as professional and ethical responsibility are highlighted by failure cases. Pilot studies have been carried out over several semesters to assess the use of failure case studies in civil engineering and engineering mechanics courses at Cleveland State University under an earlier NSF project. Student learning has been assessed through surveys as well as focus groups, led by researchers from the Cleveland State University College of Education and Human Services. Students were asked specifically about the technical lessons learned, as well as their response to the case studies. Case study questions were included on homework assignments and examinations. Survey questions linked student achievement to learning outcomes. The focus groups identified additional benefits to the use of case studies. Students observed that the cases helped build engineering identity, and provided historical understanding. The cases made the technical information relevant and linked theory to practice. The project described in this paper will extend the work of implementing and assessing case studies from Cleveland State University to eleven other university partners, including using case studies in an Introduction to Engineering course for first year students, as well as the NSF Materials Digital Library for a total of thirteen universities participating in the project. The project is a work in progress, starting in the fall of 2009.

1976 Montreal Olympics: Case Study of Project Management Failure

AbstractA successful engineering project must include its timely and economic completion. A project management failure can lead to delays and cost overruns. One example of a project that greatly exceeded its projected budget is the construction of the multiple facilities for the 1976 Olympic Games in Montreal. These included the Olympic Stadium, a velodrome for bicycle events, and the Olympic Village to house the athletes. This case study reviews the circumstances of the cost increases and the design decisions and other circumstances that led to them. The difficulties were brought on by an unrealistic schedule to complete the facilities before the fixed start date of the Games, combined with an unusually cavalier attitude toward project costs, exacerbated by political tensions. Although the original cost estimate for the facilities was

Use of failure case studies in a construction management course

120 million, the final cost was