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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

RESEARCH PROGRAM DEVELOPMENT

Technology Areas

The CMS and its working groups—the Materials Work Group and the Design Work Group—recommend a multiyear plan that introduces new, long-range performance concerns. Long-range research guidance comes from:

  • the working groups' thrust-development sessions held in June 1994;

  • SSC report recommendations;

  • the annual joint meeting of the CMS and the SSSC;

  • the SSC fall meeting; and

  • the expertise of the working groups, whose members were selected for their broad experience in the areas of concern.

The working groups' specific concerns, activities, and common interest in structural reliability are as follows.

Design Work Group—extreme wave loads, higher-order forces, and responses; ice, groundings, and collisions; large-scale structural tests; operations-oriented monitoring systems; modeling errors in loads and responses; procedures for fatigue stress computations; design process improvement; producibility; and reliability-based design codes.

Materials Work Group—new marine structural materials; fracture mechanics; fatigue (including corrosion fatigue); corrosion and its prevention; welding; inspection; and deep-ocean inspection and repair.

To varying degrees, these specific activities and recommendations contribute knowledge and data needed for the SSC's overall objective of improving the structural reliability of vessels and other marine structures.

The proposed multiyear plan addresses five technology areas that provide the underlying technical support for the thrust areas. The technology areas are

  1. materials criteria;

  2. loads and response;

  3. design methods;

  4. fabrication and maintenance techniques; and

  5. reliability.

The research program that has been developed represents the collective judgement of the CMS. Individual projects were developed by the Design Work Group and the Materials Work Group at their meeting in June 1994 when the two groups met jointly and separately. Projects were prioritized as high, medium, or low priority. All these projects were discussed at the joint meeting of the SSSC and the CMS in September 1994. All these projects were then evaluated by the CMS at their September

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

1994 meeting. Factors taken into account during discussions were the interest shown by the agencies for individual projects, the cost and time for accomplishment, technical feasibility, timeliness of the project with respect to ongoing work, and current needs. The projects were originally proposed by the work groups on the basis of technology areas. The CMS considered their own thrust areas and the national goals of the strategic plan of the SSC but maintained an independent attitude based upon their own professional experience. Based on these considerations, the CMS determined an initial prioritization by ballot vote. Further discussions were then held to consider the balance of the entire program, and revised priorities were assigned.

At the November 1994 meeting of the CMS, project priorities were again discussed based upon the factors listed above. Final priorities for accomplishment were then assigned and are indicated by the assigned project numbers. Therefore, Project 96-1 represents the highest priority of the CMS.

Relationships Among Strategic Plan, Technology Areas, and Thrust Areas

The Table 1 relationships between CMS-recommended projects and thrust areas are further expanded in Table 2 and Figure 1. Table 2 relates the goals of the strategic plan to thrust areas of the CMS and to the technology areas of the multiyear research program. Table 2 identifies all technology area descriptions of this report in which the particular project is discussed. As Table 2 reflects, the research projects recommended for FY 1996–97 are heavily oriented toward the CMS's traditional emphasis on safety and integrity of structures with diverse technology areas required for performing these projects. Figure 1 outlines a multiyear research program. The CMS recommendations are organized on the basis of the four thrust areas (producibility/competitiveness, reliability, inspection/maintenance, and composites). They are further organized on the basis of their primary technology area. The proposed later-year projects (see Appendix A) are included for completeness, without indicating estimates of initiation dates. Again, the CMS recognizes that many recommended research projects are related to more than one strategic goal and objective.

The following sections of this chapter describe the technology areas of the 5-year program plan development and the programmatic argument for the recommended FY 1995 projects. The project descriptions identify the objectives, benefits, SSC nationals goals, and SSC strategies that the individual projects address. In most cases, these are complementary, such as the fulfillment of a SSC strategy representing a benefit.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

TABLE 2 Relationships Among the Strategic Plan, Thrust Areas, and Technology Areas in the Research Plan. Sheet 1.

 

Research Projects

STRATEGIC PLAN: NATIONAL GOALS

THRUST AREA

TECHNOLOGY AREAS

96-1

Evaluation of Effect of Construction Tolerances on Vessel Strength

Maritime Industry Support

Safety and Integrity

Producibility/Competitiveness

Design

96-2

A Predictive Methodology for the Evaluation of Residual Stress and Distortion in Double Hull Ship Structures

Environmental Risk Reduction

Safety and Integrity

Producibility/Competitiveness

Fabrication and Maintenance

96-3

Failure Definition for Structural Reliability Assessment

Safety and Integrity

Reliability

Reliability

96-4

Probability-Based Design (Phase 5): Load and Resistance Factor Design (LRFD) Methods for Ship Structures

Safety and Integrity

Environmental Risk Reduction

Reliability

Reliability

96-5

In Situ Nondestructive Evaluation of Fatigue and Fracture Properties for Aging Ship Structures (95M-H)

Maritime Industry Support

Environmental Risk Reduction

Safety and Integrity

Inspection/Maintenance

Materials Criteria

96-6

Methodology for Systematic Collection of Corrosion Data Using Ultrasonic Thickness Measurements of Ship Structures (95TC-B Revised)

Safety and Integrity

Inspection/Maintenance

Fabrication and Maintenance

96-7

Workshop on Industry Standards for Integrated Ship Design Software Interfaces

Maritime Industry Support

Safety and Integrity

Producibility/Competitiveness

Design

96-8

Alternative Stiffening Systems for Double-Skin Tankers

Maritime Industry Support

Safety and Integrity

Producibility/Competitiveness

Design

Fabrication and Maintenance

96-9

Rupture Resistance of Cargo Tanks of Double Hull Tankers to Low Energy Impacts (95-12)

Environmental Risk Reduction

Safety and Integrity

Producibility/Competitiveness

Design

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

96-10

Fatigue and Fracture Criteria for Assessing Safety in Double-Hulled Ships (95-8)

Environmental Risk Reduction

Reliability

Materials Criteria

96-11

Evaluation and Assesssment of Fillet Welding of Double Bottom Structure to Resist Pollution in Groundings

Maritime Industry Support

Safety and Integrity

Producibility/Competitiveness

Design

96-12

Environmental Risk Assessment Associated with the Use of Polymer Matrix Composites in Marine Environments (95-14)

Environmental Risk Reduction

Safety and Integrity

Composites

Materials Criteria

96-13

Durability of Polymer-Based Composites in Marine Environments (95M-S)

Safety and Integrity

Environmental Risk Reduction

Composites

Materials Criteria

96-14

Crack-Arrest Toughness of Steel Weldments

Safety and Integrity

Reliability

Materials Criteria

96-15

Ship Bow Structural Guidance

Maritime Industry Support

Producibility/Competitiveness

Design

96-16

Weldable Primers for Ship Construction (95M-V)

Maritime Industry Support

Producibility/Competitiveness

Fabrication and Maintenance

96-17

Sea-Operational Profile for Structural Reliability Assessment

Safety and Integrity

Reliability

Reliability

96-18

Condition Assessment and Optimal Maintenance of Existing Surface Coating System for Tankers

Safety and Integrity

Maritime Industry Support

Inspection/Maintenance

Fabrication and Maintenance

96-19

Development of a Sensor for Evaluating Corrosion in Areas Not Easily Accessed for Inspection (95M-D)

Safety and Integrity

Inspection/Maintenance

Fabrication and Maintenance

Materials Criteria

96-20

Experiments on Stiffened Panel Collapse and Estimation of Modeling Bias

Safety and Integrity

Maritime Industry Support

Reliability

Reliability

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 1.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 2.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 3.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 4.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 5.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 6.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 7.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

FIGURE 1 Recommendations of the Committee on Marine Structures for the Ship Structure Committee's research program. Sheet 8.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

Materials Criteria Technology Area

Marine structures operate under varied conditions; therefore, they must meet many requirements. The need to design marine structures that are more efficient presents challenges with regard to the selection and use of materials. These challenges are being met in two ways: improvements to established materials technology are being sought, and new concepts and materials are being introduced. Of special interest to the CMS is materials research that introduces new analytical approaches; reviews progress in other industries that is transferable to the marine industry; increases productivity of marine structures; and, most importantly, increases life and integrity.

The CMS has identified key areas of materials research as:

  • novel marine materials;

  • fracture; and

  • corrosion and corrosion fatigue.

Novel Marine Materials

Composites. Composites have been identified by the CMS as a thrust area upon which special attention should be focused. Recommended for FYs 1996 –97 is a program that identifies applications for composite use in ship structure and develops a plan to incorporate these materials into new and existing ship structures, Project 96M-K, “Implementation Plan for Use of Polymer-Based Composites in Ship Structures.” Parallel efforts that focus on structural safety and integrity have been recommended for FYs 1996–97. One such effort is Project 96-13, “Durability of Polymer-Based Composites in Marine Environments. ” In the area of materials and design, a program is recommended to develop the analytical tools and design methods needed to achieve the full benefits of using composite materials. The program includes Project 96M-W, “Analysis and Design Technology Development for Marine Composite Structures,” and Project 96-12, “Environmental Risk Assessment Associated with the Use of Polymer Composite Matrix Composites in Marine Environments. ”

Use of Newer High-Performance Steels. Thermomechanical controlled process (TMCP) steels are becoming the material of choice for ship and marine structures because they possess a very attractive combination of high strength, excellent weldability, and relatively low cost. Available data demonstrate that TMCP-welded joints can have better fracture resistance than conventional steel joints of the same static strength. To develop proper design criteria that will facilitate more-effective utilization of high-strength TMCP steels, as well as maintaining ruggedness of structure, it is necessary to

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

document available information on fatigue, crack growth, and fracture data. To do so, Project SR-1358, “Optimized Design Parameters for Welded TMCP Steels,” has been initiated.

Incorporation of these new high-strength, high-performance steels into ship designs offers the potential for increased productivity. Unfortunately, using these steels to allow higher design stresses has resulted in shortening of useful fatigue life. Project SR-1379, “Weld Detail Fatigue Life Improvement Techniques,” will evaluate techniques that promise to improve the fatigue life of critical structural details. These procedures may be useful both in original construction and in life-extension or repair procedures.

Fracture

The recent failures of bulk carriers, weld cracking of structural members of Trans-Alaska Pipeline Service trade tankers, and the large number of SSC projects related to reliability of marine structures are cause for the CMS to recommend a hands-on workshop addressing fracture assessments and the application of reliability methods to real design problems. Project SR-1363, “Symposium and Workshop on the Prevention of Fracture in Ship Structure,” is a 2-day session that brought together experts in the field to rationally discuss causes and remedies for the rash of failures occurring in ships.

The major fracture technology activities are (1) incorporation of elastic-plastic fracture models in the durability assessment of marine structures, (2) development of a guide for damage tolerance assessment of marine structures, (3) evaluation of a crack arrest methodology, and (4) exploitation of nondestructive techniques for evaluating durability of aging ship structures.

To provide a more technological basis for the evaluation of the potential for failure in double-hulled ships, Project 96-10, “Fatigue and Fracture Criteria for Assessing Safety in Double-Hulled Ships,” will use current approaches to fracture and fatigue prediction to evaluate that potential and will incorporate those approaches into the design process for double-hulled ships.

Evaluation of ship-structure reliability can be based on ductile fracture methodologies, which are now well enough developed to be applied to complex structures. These methodologies generally employ laboratory test specimens with a simple geometry and loading mode, but are applied to complex structural details. Elastic-plastic fracture analysis methodologies will be put into a usable format in Project SR-1374, “A Guide to Damage Tolerance Analysis of Marine Structures. ” Evaluation of how these methods apply to some of the more complicated details found in ship structures is being conducted in Project SR-1349, “Evaluation of Ductile Fracture Models for the Prediction of Fracture Behavior of Ship Details,” where predictions from various ductile fracture methodologies are compared with test results from complex model components. These experiments will serve as benchmark tests for evaluating the methodologies. To streamline the development of ductile fracture toughness data, a project, 96M-D, “Specification of Toughness for High Performance Steels in Designs Requiring Ductile Fractures,” is proposed to develop correlations between toughness tests like the Charpy V-Notch impact test and the more sophisticated elastic-plastic

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

toughness tests. These projects on elastic-plastic fracture will help develop a more complete ductile fracture methodology for ship structure evaluation and design.

Most fracture problems originate in the weldment area; hence, prevention of fracture of weldments has become an important issue for ensuring safety and reliability in ship structures. Project 96-14, “Crack Arrest Toughness of Steel Weldments,” proposes to evaluate fracture potential based on a crack arrest methodology. To look at potential for life extension, Project 96-5, “In-Service Nondestructive Evaluation of Fatigue and Fracture Properties for Aging Ship Structures,” will examine a new technology for assuring the continued safe life for aging ships.

Corrosion and Corrosion Fatigue

Prevention of corrosion of marine structures is important because of the increased cost associated with the maintenance and repair of corroded structure. Emerging technology presents the opportunity to reduce these costs and to increase reliability of marine structures.

Cathodic protection is the most important active corrosion-mitigation technique for structural steels in submerged marine service. This approach has typically been designed for the anticipated life of the structure. Because of increased emphasis upon life extension, structures are, after appropriate repairs or structural augmentations, being retained in service after the cathodic protection system has required retrofit or replacement. The possibility of performing this replacement with new systems that require a fraction of the initially needed current is the subject of recommended Project 96M-S, “Retrofit of Marine Cathodic Protection Systems.”

Knowledge has been gained in the area of design for the minimization of corrosion, and this knowledge is slowly being implemented. However, corrosion detection and corrosion rate determinations for existing structures remain a problem. One access-limited area where corrosion rate information would be especially useful is in interhull spaces in new and existing ships. Project 96-19, “Development of a Sensor for Evaluating Corrosion in Areas not Easily Accessed for Inspection, ” proposes to address development of a corrosion monitor for these areas.

For structures receiving many cycles during life, most of the fatigue life is in initiation of a crack or propagation at very low growth rates (10-6–10-7 mm/cycle), which is labeled the near-threshold regime. Fatigue test data are difficult to acquire even under ambient exposure conditions, but the problem becomes even more formidable when concurrent corrosion is involved. This difficulty occurs because the corrosion fatigue damage under low frequency in service conditions is not adequately predicted by the higher–frequency laboratory tests. The project “Threshold Corrosion Fatigue of Welded Marine Steels” (SSC-366) evaluated different approaches to developing realistic, near-threshold fatigue data more rapidly, under conditions relevant to offshore structures. As a part of this activity, a new test specimen and accompanying procedure were proposed that reduced by a factor of about two the time required to develop data for near-threshold fatigue crack growth. Project 96M-U, “Threshold and Near-Threshold Corrosion Fatigue Testing of Marine Steels,” proposes to further investigate laboratory

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

testing in the near threshold regime, comparing these new approaches with standard ones.

Loads and Response Technology Area

The development of sound and rational analysis procedures for marine structures requires accurate estimates of the statistical representation of wave characteristics, wave loads, and the structural response of individual ships. In addition, a thorough understanding of reliability-based design methodologies is essential to incorporate the analysis results in practical design.

Sea characteristics in terms of operational profiles are needed to determine wave loads that can be used in designing ship structures. Profiles consist of wave heading, sea state, and ship speed and are mission based. These profiles are essential for a good reliability-based design. Proposed Project 96-17, “Sea-Operational Profile for Structural Reliability Assessment,” will address this area and will develop a standardized, systematic method to determine the profiles for selected classes of vessels and missions.

Large waves frequently result in extremely high hydrodynamic impact forces on marine structures (e.g., the ship's forebody and the underdecks of small-waterplane-area twin-hull ships or semisubmersibles). This impact phenomenon is highly nonlinear. Advanced techniques are needed to quantify extreme wave kinematics and hydrodynamic impact forces, so that a time-domain simulation technique can be developed for design applications. Project SR-1342, “Hydrodynamic Impact on Displacement Hulls,” initiated in 1991, will assess the state of the art in estimating forebody hydrodynamic impact loadings on ship structures and will identify weaknesses in current technology. The project will be completed this year.

Design Methods Technology Area

The need to maintain a pipeline of well-trained structural designers, versed in the principles of structural integrity, requires support for the technical education community. Accordingly, Project SR-1372, “Evaluation of Marine Structures Education in North America,” has been initiated. The thrust of this project is to evaluate the status of the current education system in naval architecture in North America and to get more schools and students interested in naval architecture, structural design, and marine engineering. The proposed Project 96D-P, “Student Design Competition for Innovative Producible Marine Structures,” is intended to foster interest among students of naval architectural schools in the design of ship structures. The project will provide opportunities for several undergraduate students to obtain grants to perform structural designs for a practical marine structure.

One of the SSC's strategies is to develop better design tools. One project, Project 96-15, “Ship Bow Structural Design Guidance,” proposed to provide guidance in designing ship forebody structures. The current state-of-the-art of ship bow design involves somewhat empirical rules, such as the required thickness of the stem plate in the

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

American Bureau of Shipping Rules being based only on the length of the ship and the somewhat arbitrary placement of intercostal transverse stiffeners in the bow of U.S. Navy combatants. Completion of this recommended project will provide more analytic means of structural design.

Adequate Strength in Service

Fatigue is a primary source of in-service structural damage in most types of ships and platforms, thus, it remains a key research topic. The recently completed project, “Fatigue Design Procedures” (SSC-367), summarizes fatigue design methodologies for ship applications and reviews their relative merits. Details with similar endurance characteristics have been combined in the recently completed project, “Reduction, Classification, and Application of S-N Curves for Ship Details” (SSC-369). In addition, the fact that in-service fatigue often involves complex stress conditions was addressed by another recently completed project, “Fatigue Performance under Multiaxial Loading” (SSC-356).

Several projects have been proposed to study the strength characteristics of ship structures. Project 96-1, “Evaluation of Effect of Construction Tolerances to Vessel Strength,” will study the effect of structural imperfections during construction on ship structural behavior and strength. The CMS is also recommending a project to perform a statistical evaluation of the metal strength properties of ships. This project, 96D-U, “Statistical Characteristics of Strength Properties of Currently Used Steel in Marine Structures,” will benefit load and resistance factor design. In an associated proposed project (96D-V), “Statistical Characteristics of Geometric Properties of Currently Used Plates and Structural Shapes in Marine Structures,” the geometric properties of plates and structural shapes of marine structures will be examined statistically.

Ship-Hull Structural Design

The tools for the design of ship structure are varied and sometimes fragmented. The output of one computer program cannot be used directly as part of the input to another, and the input and output data do not relate to the database used in ship construction. The status of current software development should be more widely known, and guidelines for common interfaces should be established. To accomplish this, the CMS proposes Project 96-7, “Workshop in Industry Standards for Integrated Ship Design Software Interfaces,” as a first step.

National and international concern for environmental pollution from tanker collisions and groundings led to passage of the Oil Pollution Act of 1990, which includes a requirement for double hulls on tankers. In addition, the International Maritime Organisation has established similar requirements. The law mandates double hulls, but the structural behavior of double hulls in collisions and groundings is not well understood. The consequences of low-energy impact in double-hull tankers and the effect of rupture of the outer hull on the inner hull is not known. In addition, a wide variety of configurations of stiffening systems are being used or proposed in double-hull designs that are being developed to comply with these new regulations. Aspects of these

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

configurations are being studied extensively through the Advanced Double Hull Program at the Carderock Division of the Naval Surface Warfare Center,1 and the Lehigh University Fleet of the Future Program.2 In consultation with the managers of those programs, the CMS has developed research needs to cover gaps in the research.

The influence of the structural configuration of the double-hull structure on the damage caused by low-energy impacts is unknown. Current double-hull tankers under construction worldwide have structural details that closely resemble those used in single-skin design. Project 93-3, “Double-Hull Vessel Assessment Methods for Collision and Grounding Protection,” proposed in the FY 1993 recommendations, was therefore combined into a joint industry project under Project SR-1354, “Grounding Protection of Tankers.” To expand this work to include the effect of collisions, the CMS recommends Project 96-9, “Rupture Resistance of Cargo Tanks of Double Hull Tankers to Low-Energy Impact.” In addition, Project 96-8, “Alternative Stiffening Systems for Double Skin Tankers, ” should produce concepts that will reduce the cost of these ships. Yet another project on the double-bottom structure, Project 96-11, “Evaluation and Assessment of Fillet Welding of Double Bottom Structure to Resist Pollution in Groundings,” would specifically investigate fillet weld design not covered by the Massachusetts Institute of Technology program on Tanker Safety.

To enhance the performance of ship structure, Project SR-1346, “Improved Ship Hull Structural Details Relative to Fatigue,” began in 1992; Project SR-1350, “Reexamination of Design Criteria for Stiffened Plate Panels,” began in 1993. Generally, openings in primary structural members are compensated for in accordance with guidelines based on past experience. Improperly placed and inadequately compensated openings can result in cracking and associated problems. Project SR-1368, “Compensation for Openings for Primary Structural Members of Ships,” began in 1994 to establish rational guidelines for such design features. Project SR-1373, “Hull Response Monitoring System,” is intended to improve the design of ship-hull structure and should provide the ship operator with real-time reliable data on hull-girder stresses and external loads, such as ice loadings, and other data necessary for reliable design.

Human Error and Its Impact on Design

It has been estimated that 75 percent to 90 percent of all structural failures are due to nonphysical factors: errors in calculations, poor judgment, incomplete professional understanding, inadequate design review, poor workmanship, improper inspection, and abuse by the operator. Human error is a departure from acceptable or desirable practice on the part on an individual that results in unacceptable or undesirable

1  

Department of the Navy. 1994. Proceedings of the Advanced Double-Hull Symposium held October 25–26, 1994, at the National Institute of Standards and Technology, Gaithersburg, Maryland.

2  

Lehigh University. 1993. Fleet of the Future: Phase One February 1991–March 1993. Bethlehem, Pennsylvania, Lehigh University.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

results. Human errors can also develop as a result of influences from organizations or groups of individuals. The third aspect of human errors regards the physical systems with which individuals and organizations interface. These systems can be prone to, and encouraging of, errors. Structural design procedures and codes do not recognize this aspect of the design process but assume that methods will be applied unerringly. Some structural failures can be attributed to errors in the design procedures themselves, such as the failure to require fatigue analysis when higher operating stresses were permitted through the use of higher-strength steel, reduced corrosion allowances, or both.

Physical uncertainty, the probability of modeling error, and statistical uncertainty can be quantified and explicitly included in a probability-based code or ad hoc assessment of reliability. Human error, a nonphysical factor, is difficult to quantify relative to its influence on design and is not ordinarily considered in formal design procedures. Human error is, however, an important component of uncertainty that is not yet introduced explicitly in the probabilistic mathematics leading to probability-based code requirements.

Project SR-1353, “The Role of Human Error in the Design, Construction, and Reliability of Marine Structures,” was initiated to assess the impact of human error on the safety of marine structures. It was a first step to reduce the risk of failures due to human error and to establish procedures and guidelines for considering the effects of human errors in design and the appropriate reformulation of structural design criteria. Similar attention should be focused on developing methods to integrate human and organizational error into ship structure construction and maintenance. Hence, the CMS proposes Project 96D-Q, “Integrate HOE Consideration into Ship Structure Construction and Maintenance.”

The SSC has chosen the subject “quality and human/organizational errors in marine structures” for their joint SSC/Society of Naval and Marine Engineers symposium to be held in 1996.

Fabrication and Maintenance Techniques Technology Area

The U.S. ship design and shipbuilding community is aware of the paramount need for improving fabrication methods which will lead to greater producibility and maintainability. It supports the use, whenever possible, of the concepts of zone construction, parts and systems standardization, parts and systems interchangeability, and international/commercial standards. Attention must also be focused on environmental awareness and safety in decisions relating to new construction and repair and maintenance. Improvements in fabrication and maintenance directly benefit competitiveness in the global marketplace, safety and integrity of marine structures, and risks to the marine environment. These benefits, plus reduced costs, also accrue to owners/operators.

Increasing productivity, however, requires an interdisciplinary approach involving concurrent engineering, where the design of the product occurs simultaneously with design of the production process and consideration of maintenance procedures. Projects based upon this approach should be emphasized. Keeping this in mind, the CMS has

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

initiated Project SR-1368, “Compensation for Openings in Primary Structural Members of Ships. ” This effort is intended to establish rational methodologies and guidelines for determining appropriate compensation for openings small and large in the primary structural members of ships. The benefit should include improvement in the efficiency, reliability, and producibility of openings.

There has been growing interest in the issue of maintaining integrity in aging marine structures. A large number of papers have been published on this topic in recent years. Stated simply, inspection is expensive. Therefore, there is a strong motivation to develop strategies for minimizing the cost of inspection without impacting the quality of the maintenance program. Project SR-1365, “Optimal Strategies for Inspection of Ships for Fatigue and/or Corrosion Damage,” has been initiated to rationalize the inspection process. The result should be improvement in the system, with optimization of the cost factors to force a reduction of maintenance costs of ships and possibly an improvement in structural quality. Inspection for shipbuilding is predominantly performed visually, with varying levels of volumetric nondestructive evaluation required for different applications. Visual inspection for surface profile and flaws is qualitative in nature, and the meaning of results is often questioned. Consequently, the probability of detecting surface defects visually will be investigated in Project SR-1375, “Detection Probability Assessment of Visual Inspection of Ships.” This project is intended to provide guidance as to the effectiveness of visual inspection. Once the reliability of visual inspection to determine surface quality is quantified, the impact of surface quality on weld integrity would be addressed in proposed Project 96M-H, “Effect of Weld Surface Quality on Hull Structural Integrity.” Finally, there are instances in which it is necessary to augment visual inspection by ultrasonic testing or radiographic testing. Ultrasonic testing is much less expensive to perform and should detect more damaging linear indications than radiographic testing. However, some concern is being directed toward ultrasonic testing inspection for commercial tankers as a result of failures in vessels inspected using this type of testing. Proposed Project 96M-I, “Ultrasonic/ Radiographic Inspection of Hull Structures,” is intended to clarify the advantages and disadvantages of each process and result in recommendations for the most reliable and cost-effective approach.

Corrosion of marine structures can produce significant damage and result in extensive repair costs. The existence and extent of corrosion damage can often be difficult to determine nondestructively, particularly under paint and in hard to reach areas. In recognition of that concern, Project SR-1377, “Commercial Ship Design and Fabrication for Corrosion Control,” was initiated in 1993. This project is intended to identify corrosion-control methodologies that will improve life-cycle maintenance costs and enhance the safety and integrity of marine structures. Two proposed projects to evaluate alternative approaches to corrosion detection are proposed, Project 96-19, “Development of a Sensor for Evaluating Corrosion in Areas not Easily Accessed for Inspection, ” and Project 96M-J, “Development of Smart Coatings for Early Detection of Underfilm Corrosion. ” The first would examine the use of novel nondestructive sensors, and the second would evaluate paints that would change colors or otherwise indicate the presence of corrosion.

Design and fabrication of U.S.–built ships require a higher number of labor hours than is customary in foreign practice. In an attempt to reduce labor hours in design and

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

construction, a project has been proposed to improve the efficiency of the ship design process by developing alternatives that are more structurally efficient and producible and that will be available to structural designers prior to beginning a specific ship design. Project 96-8, “Alternative Stiffening Systems for Double-Skin Tankers, ” proposes to evaluate and develop alternative stiffening systems for the double-side and double-bottom structures of tanks to enhance pollution prevention, fatigue strength, and producibility of the structure. This project supplements work being done at the Carderock Division of the Naval Surface Warfare Center and concentrates on the double-hull design in an effort to provide U.S. designers and builders with the information necessary to compete successfully in the important new market (created in part by U.S. legislation) for tankers entering U.S. ports in the future.

The proposed Project 96-2, “A Predictive Methodology for the Evaluation of Residual Stress and Distortion in Double Hull Ship Structures,” should help in identifying means for minimizing the deleterious effects of residual stresses on ship structures and, thus, also add to the abilities of U.S. designers and builders of double-hull ships.

Most existing tankers with combined cargo and ballast tanks experience serious pitting of their bottom plates. This threatens to add to environmental pollution. Project 96D-L, “Strategies for Control of Bottom Pitting Corrosion in Tankers and Evaluation of Optimum Inspection Frequency,” is intended to develop recommendations for an optimum control strategy for corrosion and optimum inspection intervals. For the control to be effective, accurate data on corrosion must be available, and a standard methodology for collection and analysis must be in hand; the latter is lacking. The proposed Project 96-6, “Methodology for Systematic Collection of Corrosion Data Using Ultrasonic Thickness Measurements of Ship Structures,” is intended to investigate this problem.

Another area important to tanker maintenance is the tanker surface coating system. There is increased need to assess the integrity of coatings to ensure proper maintenance of ballast tanks and guard against pollution. The proposed Project 96-18, “Condition Assessment and Optimal Maintenance of Existing Surface Coating Systems for Tankers, ” is intended to address this problem and develop guidelines and methodology for coating maintenance.

Weldability

Weldability and welding clearly play a significant role in the economics of shipbuilding. Fabrication issues focus on development of improved weld consumables, weld process control, understanding of inspection requirements and impact of inspection results, and concurrent engineering approaches to shipbuilding. In the maintenance area, primary focus is on weld repair methods and adequacy of repairs.

Successful incorporation of new steels and procedures requires a thorough understanding of their effects on weldability. Although much development has been performed over the past few years for welding high-strength steels (80–100 ksi) without pre-heat, there are still no commercially available tubular or flux-cored wire consumables.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Project 96M-G, “Development of High Performance Tubular/Flux-Cored Weld Filler Metal, ” has been proposed to unite a developer to a commercialization source to develop these materials and ultimately to make them commercially available.

As overall toughness increases with better steels, isolated low toughness attributable to local brittle zones becomes more of a problem. Recognizing the significance of local brittle zones, the offshore marine structures industry has established criteria for the preproduction qualification of steel plates to be welded. However, there is not complete agreement among researchers as to the mechanism(s) involved in the creation of these zones. The CMS recommends that Project 96M-B, “The Definition of Local Brittle Zones in the Heat-Affected Zones of Low Alloy High-Strength Steel Weldments,” be undertaken to define the nature and causes of local brittle zones. The results of this project would lead to improved understanding of the nature of the zones and their causes, resulting in more-realistic criteria for weldable steels and welding processes in marine structures.

One area identified as promising for enhanced producibility involves weld-over-primer technology. It is generally necessary to remove primers prior to welding because of their adverse effects (porosity in particular) on weld-metal properties. Development of weld through primer technology would eliminate grinding before welding and would result in a major saving in weld-surface preparation. An SP-7 project funded by the National Shipbuilding Research Program will develop and evaluate improved weldable primers. However, there is no agreed-upon standard method for acceptance criteria to guide paint manufacturers or shipyards in testing these coatings and comparing their weldability. The industry needs such methods and criteria to evaluate their acceptability, based on weld properties and engineering analysis. The industry also needs to verify that the current porosity criterion for acceptance is sufficient for new paint systems. The CMS, therefore, proposes Project 96-16, “Weldable Primers for Ship Construction,” to better facilitate development and use of primers that can be applied to structural steel for the purpose of minimizing weld preparation costs.

When developing procedures for manufacturing and repair of welded ships, it is necessary to predict or estimate the properties of welded alloys. Currently, information is pieced together from various sources, and, in many instances, insufficient information is available for a given application. One single source of information does not exist for many of the important materials used by the maritime industry. The CMS recommends Project 96M-N, “Atlas of Welding Properties and Procedures,” to develop an atlas to be used for design and manufacturing of critical components.

The domestic steel industry will soon produce high performance TMCP steels produced with new accelerated cooling (AC) and/or direct quenching (DQ) methods. These steels will have higher strengths, better toughness, and lower costs than conventional 50-ksi steels. Weight and cost savings, as well as better toughness, could be realized by the substitution of 65-ksi TMCP steels, for example, for conventional 50-ksi steels in hull structural applications. Key to successful implementation, however, is verifying that current welding procedures, used for lower-strength steels, can also be used for these new steels. Thus, the CMS recommends Project 96M-Q, “Performance and Optimized Weld Metal Properties of Domestically Produced AC/DQ Steels,” to facilitate introduction of these steels in shipbuilding. The evaluation of consumables for 65-ksi

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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yield steel in this project would follow Project SR-1343 “Optimized Weld Metal Properties for Ship Structures,” which is establishing the viability of slightly undermatched consumables for 100-ksi-yield steels.

Improved fabrication technologies of many kinds are necessary to enhance shipyard productivity. These technologies cannot be implemented in isolation but rather require an interdisciplinary approach involving design, material delivery, cutting and forming operations, joining, assembly, inspection, and coating methods. As domestic shipyards focus on commercial new-ship construction as a sequel to the decline of military business, opportunities will increase for utilizing more automated and robotic processes. One of these is extremely efficient higher-deposition welding processes. It is essential, however, that the toughness criteria for the heat-affected zone and weld metal of very high heat input weldments be well established for specific ship applications.

Welding technology also needs to be improved so that more-productive welding of high-strength steels can be done without compromising structural integrity. The steel industry is introducing new high-strength, less-crack-sensitive steels that offer lower fabrication costs, principally by reducing or eliminating weld preheat requirements. The first generation of these steels, the high-strength, low-alloy grades, has lower carbon and lower carbon equivalent, which provides less sensitivity to hydrogen-assisted cracking and improved weldability. These steels may ultimately be produced at lower alloy costs if the domestic steel industry builds TMCP facilities either under a Department of Defense Title III program (which is currently in jeopardy for lack of funding) or with their own funds. The industry has also developed a new sense of awareness of the problem of weld-metal hydrogen-assisted cracking and the strong effect that welding process parameters have on the properties of those welds. As a result, Project SR-1357, “Retention of Weld Metal Properties and Hydrogen Cracking,” is contributing to the capability of the shipbuilding industry to incorporate the new, high-strength steels that are easier to weld.

Economic and reliable methods for performing repair welding of ships ' structure are also major concerns. Project SR-1376, “Methodology to Establish the Adequacy of Weld Repairs,” will be initiated soon and is intended to provide guidance as to whether the repair should be performed. This will improve the safety and reduce the costs of maintenance procedures. Another proposal, Project 96 M-M, “Underwater Weld Repair Using Solid State Welding, ” would evaluate methods to repair corrosion and other damage. This research is intended to evaluate a novel method to perform wet-weld repairs with potential for better properties, minimum porosity, and lower operator skills than conventional wet-arc welding.

Inspection and Integrity

Marine structural integrity during construction and service is a continuing concern of the CMS, especially with the extended service life of existing structures. Predictability of structural integrity has been improved by improved understanding as to how specific defects contribute to structural failure. Approaches and methodologies of inspection for these defects are being further improved. Nondestructive examination is becoming more quantitative with new analytical approaches to the assessment of structural integrity. The

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

possibility of using imbedded sensors and interpretation analysis to monitor in-service structural behavior also exists. The capability to identify a significant defect by such means is a potentially useful engineering tool, since knowledge of defect shape, orientation, and distribution can be translated into a statement of integrity and residual service life through fracture mechanics. For these reasons, and to evaluate the adequacy of inspection methods, Project 96M-I, “Ultrasonic/Radiographic Inspection of Hull Structure,” is proposed.

Visual inspection remains the most popular and extensively used method for assessing the status of ship hulls, but questions concerning accuracy, reliability, and repeatability remain. To address these questions, Project SR-1375, “Detection Probability Assessment of Visual Inspection of Ships,” is being initiated.

The CMS has promoted new analytical techniques for evaluating defective structure in the marine structures industry, by completing two relevant projects, “Relationship Between Inspection Findings and Fatigue Reliability ” (SSC-355) and “Influence of Weld Porosity on the Integrity of Marine Structures” (SSC-334).

Innovative methodologies are needed to reduce the amount and frequency of nondestructive testing. One such method is addressed in Proposed Project 96M-J, “Development of Smart Coatings for Early Detection of Underfilm Corrosion.” The petroleum production industry will be relying increasingly on remote inspection techniques for deepwater structures, for example, by using remotely operated vehicles with nondestructive test packages. Standards for such testing need to be established. In addition, failure research needs to be consistent with advanced reliability theory. The CMS will continue to recommend research that introduces new analytical approaches to the marine industry through research and technology transfer.

A broad conceptual examination of redundancy, as it relates to residual and reserve strength, was undertaken in the project “Structural Redundancy for Discrete and Continuous Systems” (SSC-354). Initially the project defined structural redundancy, residual strength, and reserve capacity relative to framed structures (offshore platforms), monocoque structures (ships), and other structures (e.g., guyed-tower mooring systems and tension-leg platforms). Criteria defining structural stability for simple discrete systems were used to illustrate applicability to more-complex systems.

Repair of Marine Structures

Routine maintenance and repair intervals for marine structures affect service life and operating costs. However, the lack of adequate repair techniques can reduce structural integrity, shorten service life, or require costly replacements. The scheduling of inspection and routine maintenance needs to be more analytically determined.

As regards weld repairs, it is, unfortunately, often difficult to determine whether a proposed repair will be an improvement. The decision whether to repair or to operate without specific repairs should be made on a technical basis. Project SR-1376, “Methodology to Establish the Adequacy of Weld Repairs,” will be initiated to provide guidelines that are intended to both improve safety and reduce costs of maintenance procedures.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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A major component of the structural maintenance process is inspection. Decisions on design and maintenance of ship structures hinge on the effectiveness and cost of inspection. Project SR-1355, “Inspection of Marine Structures,” was initiated to quantify inspection performance and address inspection cost. This program will supplement Project SR-1340, “Structural Maintenance for New and Existing Ships,” which addresses structural maintenance and life extension for aging tankers.

Another program objective involves development of new underwater repair methods for ship hulls, semisubmersibles, and fixed platforms. A combination of temporary wet welds and permanent dry welds may ultimately be approved for permanent repairs, and, at a minimum, they could extend ship usefulness until a scheduled dry-docking. The recently completed project “Permanent In-Service Repair Procedures for Underwater Damage to Ship Hulls,” (SSC-370), reviewed present practices and recommended procedures for permanent in-service underwater repair of structural damage. Project SR-1356, “Strength Assessment of Pitted Plate Panels,” has been initiated and relates to this.

Frequently weld repairs are required on materials that are crack sensitive and require a postweld heat treatment. However, postweld treatment is often impractical for these structures. A temper-bead technique is one method of performing sound repairs in crack-sensitive materials without postweld heat treatment. Since there are no definitive guidelines for using this technique, the CMS is considering defining a project on recent developments, applications, and guidelines for temper-bead techniques. Establishment of this project, and the proposal of any specific new research in this area awaits completion of a joint industry project from an independent source.

Reliability Technology Area

Reliability technology is the application of probability and statistics to engineering analysis and design. Incorporating modern reliability technology into decision making for marine structural engineering promises to improve quality and performance. The results will ensure production of a structure that has an improved balance of risk relative to that produced by current procedures. The implication is a more efficient, balanced design and has possible structural weight savings compared with current design procedures.

The design of any structure depends on predicted loads and on the structure's calculated capacity to resist them. There is always some element of uncertainty in determining either. Engineering design has compensated for these uncertainties by experience and subjective judgment. With reliability technology, these uncertainties can be considered quantitatively.

The development and implementation of probability-based structural design procedures have been under way in other areas since the early 1960s. In addition to the existing design procedure that is based on the concept of a working stress, a probability-based load and resistance factor design procedure was issued by the American Institute for Steel Construction in 1986, with a second edition published in 1993. Further, the American Petroleum Institute has recommended this technology for offshore structures

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

with their publication RP2A, “Recommended Practice for Design, Fabrication, and Installation of Fixed Offshore Structures.”

The development of probability-based design codes in other areas appears to have stimulated important advances in structural design. In addition, the codes become a living document that can be revised to include new sources of information and to reflect additional statistical data on loads and load effects. It is a top-down approach that actively encourages the collection of better data.

Final design decisions about materials, sizes, and arrangements should be based on experience, regardless of the overall approach. The main advantage of a probabilistic approach as a design method is that it provides a mechanism for taking advantage of all relevant information. Probabilistic methods allow engineers to make decisions based on a quantitative description of uncertainty, in addition to reaching a consensus in structural design based on experience and judgment. The process of developing reliability technology for marine structures unifies the thrusts of many other active and recommended projects that had appeared to be unrelated in earlier times.

The advantages of new probabilistic design strategies are expected to produce a more balanced design and allow use of different safety levels (or safety factors) that depend on the predicted accuracy of various loads and structural capabilities.

To kick off the program, the SSC cosponsored a symposium and funded a tutorial on structural reliability to inform the marine community of this new technology. Sponsored by the SSC and the Society of Naval Architects and Marine Engineers, the Marine Structural Reliability Symposium was held in Arlington, Virginia, in October 1987.3 It attracted experts from around the world and provided a forum for assessing the state of the art in reliability methods. The report “Application of Reliability Methods to Analysis and Design of Marine Structures” (SSC-351) is a tutorial on applying reliability to marine structures. A 1-week seminar, in which the draft document was presented to SSC participants and colleagues, was held in San Francisco in January 1988 and repeated in Washington, D.C., in October 1990.

A multiyear research program is under way to apply reliability technology and develop probability-based design criteria for ship structures. The program represents a major sustained effort that will make significant changes in structural design, improve the reliability of ship structures, and permit the results of research to be more easily incorporated into future designs. The program consists of the following projects recommended by the CMS.

Probability-Based Design Approach for Ship Structures

Phase 1: Demonstration Project A demonstration project, “Probability-Based Ship Design Procedures: A Demonstration” (SSC-368), was completed in 1993. The study compares a hull girder designed by present conventional American Bureau of Shipping rules with a design that uses probability-based procedures, illustrating the applications of

3  

Ship Structure Committee and the Society of Naval Architects and Marine Engineers. Proceedings of the Marine Structural Reliability Symposium, October 5-6, 1987. New York: Society of Naval Architects and Marine Engineers, 1987.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×

this approach and identifying its advantages and problems. The project report will be useful for information, instruction, and future reference.

Phase 2: Loads and Load Combinations The Phase 2 project “Probability-Based Ship Design: Loads and Load Combinations” (SSC-373), which defines ship design loads suitable for use in reliability analysis, was completed in 1993. This study includes statistical distributions of extreme wave loads, fatigue loads, and modeling errors. Load-combination issues that require further investigation are addressed in this project.

Modeling errors were addressed in the project “Uncertainties in Stress Analysis on Marine Structures” (SSC-363), which was completed in 1991. The project's materials counterpart, “Uncertainty in Strength Models for Marine Structures” (SSC-375), was completed in 1993.

Phase 3: Implementation The third phase of probability-based design approaches is Project SR-1345, “Probability-Based Design: Implementation of Design Guidelines for Ships,” which will develop a more detailed probability-based design procedure for ships. Load models provided by the Phase 2 project will be combined with strength formulations from the supporting project, “Uncertainty in Strength Models for Marine Structures” (SSC-375). This Phase 2 project will develop design procedures based on reliability considerations similar to reliability-based design procedures used for other structural applications worldwide. The procedures will include provisions for ultimate strength of hull girders; design of stiffened panels; fatigue of details (typically connections); and buckling, which will require further investigation for marine structures.

The first part of Project SR-1344, “Assessment of Reliability of Existing Ship Structures (Phase 1),” is now complete, and it will be useful for the Phase 3 reliability project. Phase 2 of Project SR-1344 began in 1994.

Phase 4: Synthesis of the Reliability Thrust Area The fourth phase will provide a summary and synthesis of the various projects in the reliability thrust area, including the complementary projects in design methods and load uncertainties. There have been several programs and several investigators, and there is now a need to put all of the pieces together. The synthesis will provide a summary of reliability technology for specific application to (1) design code development, (2) failure analysis, and (3) reliability assessment of existing designs. Project SR-1362, “Probability-Based Design: Synthesis of the Reliability Thrust Area,” has been initiated by the CMS.

Phase 5: LRFD Design Practice Several SSC projects have introduced load and resistance factor design. It is time now to put this design procedure into practice. Proposed Project 96-4, “Probability-Based Design (Phase 5): Load and Resistance Factor Design (LRFD) Methods for Ship Structures, ” will include a rigorous and complete code calibration for the design of ship structure. The resulting load and resistance factor design criteria, including all failure modes, will be written in a code style that is suitable for the direct use of practicing engineers. This phase should have higher priority than the phase for novel hull-form design, but the two research projects may be performed concurrently.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Phase 6: Novel Hull Forms and Environments The sixth phase will address reliability-based design processes for novel structures. Project 96D-O, “Probability-Based Design (Phase 6): Novel Hull Forms and Environments,” is proposed for Phase 6. The term “novel” in this project applies to unconventional hull forms or structures subject to uncommon environments. The premise of the project is that in novel situations, first principles must be applied, because these designs cannot be based on extrapolation or interpolation of current practice or existing structures, as implied in the third phase. This project will determine whether the current data base, existing structural reliability literature, and practice contain the necessary elements to probabilistically assess the performance and safety of ship structures that have unusual forms or are subject to uncommon environments.

Reliability of Existing Ship Structures

Knowledge of the probabilistic characteristics of important failure modes would be useful in developing rational probability-based design criteria. This information could be used on an ad hoc basis to review or revise present procedures or to develop an entire design-criteria document. For successful implementation of a load and resistance factor design code, an estimation of modeling bias is required. In support of efforts to develop this information, the CMS recommends Project 96-20, “Experiments on Stiffened Panel Collapse and Estimation of Modeling Bias.” This research should provide, for example, the much needed uncertainty data on stiffened panel collapse. In order to develop a method for the kind of failure definition needed to calculate structural reliability, Project 96-3, “Failure Definition for Structural Reliability Assessment,” has been proposed. In support of this effort, Project SR-1380, “Post Yield Strength Of Structural Members,” is intended to provide additional means to verify the load-carrying capacity of structural components.

Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Page 36
Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
Page 37
Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
Page 38
Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
×
Page 39
Suggested Citation:"RESEARCH PROGRAM DEVELOPMENT." National Research Council. 1995. Marine Structures Research Recommendations: Recommendations for the Interagency Ship Structure Committee's FY 1995 and Later-Years Research Program. Washington, DC: The National Academies Press. doi: 10.17226/9152.
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Page 40
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