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Assessing the stability of steel building frames exposed to fire conditions is challenging because of the need to consider the elevated temperature properties of steel, nonuniform heating o...

Since the devastating 2011 tornado season, there has been renewed interest in understanding tornado wind loads and developing methodologies to reduce the risk of tornado damage. This study ...

This paper describes a new method for fitting probability distributions for modeling annual maximum ground snow loads for use in structural design. These probability models are intended for...

This paper describes the development of reliability-targeted ground snow load maps for use in building (roof) design. The proposed procedures aim to ensure that structures designed achieve ...

Severe hurricanes in coastal areas have caused enormous human and economic losses. Furthermore, the intensity and frequency of future hurricanes may increase due to the potential impact of ...

This paper investigates the robustness of moment-resisting steel frames that are typical of building construction in seismic regions before the 1994 Northridge earthquake against progressive (disproportionate) collapse. Uncertainties in the collapse demands and the resisting capacities of the connections in the frames are modeled probabilistically. The dominant connection failure mode, which involves fracture of the weld connecting the beam and column flanges under scenarios involving sudden column loss, is developed using a J-integral formulation of fracture demand and is characterized probabilistically. The connection behavior model is validated using connection test data from the SAC Project on steel frames conducted following the Northridge earthquake. The robustness of two three-story steel frames designed in the SAC Project is assessed by utilizing (a) the requirements in the new Unified Facilities Criteria (UFC), and (b) a system reliability analysis. This analysis reveals that steel moment frames ...

Structural applications of carbon fiber-reinforced polymer (FRP) composites in civil infrastructure rehabilitation projects are receiving increasing interest due primarily to their high strength-weight ratio, resistance to aggressive environments, and other favorable properties that can be used to advantage in civil projects. Structural design and evaluation in civil engineering applications are distinguished by their reliance on codes of practice and on advanced analysis in lieu of component testing. The current lack of supporting codes, standards, and other regulatory guidance is a barrier to the implementation of high-performance FRP materials in civil construction. Experience over the past three decades in developing probability-based limit state design criteria for common construction materials points the way forward for making similar advances in guidelines for design and evaluation of structural components and systems that employ FRP composite materials. This paper summarizes some of the available tools and supporting databases that can be used to develop reliability-based guidelines for design and evaluation of FRP composites in civil construction and illustrates their application with several practical examples involving strengthening reinforced concrete flexural members.

The infrequent nature of earthquakes in the Central and Eastern United States (CEUS), and the fact that none with intensity comparable to the New Madrid sequence of 1811-12 has occurred in the past century, have caused the earthquake hazard in the CEUS to be neglected until quite recently. The performance of reinforced concrete (RC) frames in the CEUS may be deficient if they are subjected to earthquakes that are believed to be plausible in the New Madrid Seismic Zone (NMSZ). This study presents a set of probability-based tools for seismic vulnerability and risk assessment of such gravity load designed (GLD) RC frames, and uses these tools to evaluate the seismic vulnerability of RC frames that are representative of the building inventory in Memphis, Tenn.—the largest population center close to the NMSZ. This evaluation indicates that traditional GLD RC frames have a substantial probability of suffering life-threatening damage or collapse in the event that they are subjected to earthquake demands stipulat...

Site-built wood-frame (light-frame) construction is the most common form of construction for residential structures in the United States. Such structures have suffered significant damage in recent earthquakes, and wood-frame construction practices in the western United States (WUS) have improved considerably in the last 2 decades. On the other hand, little is understood about the expected performance of wood-frame structures located in the central and eastern United States (CEUS), where the seismicity is moderate compared to the WUS and construction practices seldom provide earthquake resistance. This paper examines the seismic performance of typical one- and two-story wood-frame structures in the CEUS. Six structures with two foundation types were considered, for which conditional limit state probabilities (fragilities) were evaluated considering three possible failure mechanisms: excessive interstory drift, wall uplift, and sill plate splitting. This examination shows that seismic damage to wood-frame structures in the CEUS under earthquakes of moderate intensity is unlikely to lead to loss of life, but may result in significant financial losses. An evaluation of two possible retrofit strategies illustrates how the expected seismic performance of the CEUS structures can be improved by adding more anchor bolts and perimeter sheathing nails to the shear walls.

Wood-frame residential construction represents a major investment in the United States, which, when exposed to hurricanes, earthquakes, and other natural hazards, may sustain substantial damage. Although in many parts of the country one natural hazard dominates, in certain areas multiple hazards may pose a significant threat to buildings. Building design and construction practices should address the overall risk to residential construction from multiple hazards to achieve design strategies and risk levels that are consistent with occupant expectations and social objectives. This paper presents a framework for multihazard risk assessment using hurricane and earthquake hazards as an example. Structural reliability-based methods that describe natural hazard and structural system response probabilistically are essential for quantifying expected losses from natural disasters and for developing appropriate strategies to manage risk. The framework permits the main sources of uncertainty that affect building performance to be identified, and provides insight on strategies for effective multihazard mitigation efforts.

The load combinations in ASCE Standard 7 for load and resistance factor design (LRFD) and for allowable stress design (ASD) differ in their treatment of counteracting loads, where the permanent gravity load (dead load) stabilizes the structural system against the effect of uplift or lateral loads. In LRFD, the loads are factored prior to the analysis, and the load factor on dead load is less than unity. In ASD, one factor of safety (the allowable stress factor) had been applied to the difference between the nominal load effects through the 1995 edition of ASCE Standard 7. Beginning with the 1998 edition, the load factor on nominal dead load in the ASD combination was increased to 0.6 to achieve consistency between ASD and LRFD. This particular ASD load requirement has been controversial and has drawn criticism from certain segments of the structural engineering community. This technical note examines the treatment of counteracting loads in ASCE Standard 7 from a reliability viewpoint, and shows that failure to reduce the gravity load for design may lead to inadequate safety.

The majority of single-family dwellings in the United States are light-frame wood construction. Residential construction practices have evolved gradually over the years, most light-frame wood structures have not been structurally engineered, and many residential buildings suffered significant damage in recent hurricane and earthquake disasters. As a result, new concepts and methodologies are evolving to better predict and evaluate the performance of wood frame structures exposed to natural hazards and to support improved residential building practices. This paper examines the behavior of typical light-frame wood structural systems in the central and eastern United States under earthquake hazards. Nonlinear structural analysis tools and stochastic methods are used to model the uncertainties in ground motion intensity and structural response. Fragility curves defining damage state probabilities as a function of ground motion intensity are developed for typical lateral force-resisting shear wall systems subjected to increasing levels of ground motion. A comparison of these fragilities with those embedded in HAZUS provides additional perspective on damage potential for residential construction in regions of low-to-moderate seismicity.

Steel structures may be vulnerable to fires; therefore, work is underway in several quarters to advance performance-based engineering (PBE) of steel frames for fire conditions. Both experimentation and finite-element simulations are necessary tools in PBE for assessing the behavior of structures under elevated temperatures. Numerical modeling of the overall structural system using line-element models fails to capture the localized behavior of connections due to the simplistic nature of such models. With advances in computation, attention is shifting to three-dimensional (3D) models, which are better able to capture the behavior of connections. Accurate predictions of structural response require the inclusion of realistic boundary conditions such that the interaction between the connections and the surrounding structure is properly captured. The study reported herein evaluates the response of steel frames with reduced beam section (RBS) connections under a typical compartment fire, with temperature...

During the 1999 SEI/ASCE Structures Congress, the Executive Committee of the Technical Activities Division of the Structural Engineering Institute approved a new technical committee for defining the “performance of a civil engineering facility.” The new committee’s purpose is as follows: “facilitating the development and adoption of realistic, effective, comprehensive and reliable performance-based design and evaluation techniques and procedures for civil engineering facilities, and helping to establish the foundations for specifications, model codes and commentaries for performance-based design and evaluation” ASCE 2000 . The Committee met four times from 2000 to 2003 and organized two technical sessions at the 2003 Structures Congress at Seattle. Its membership comprised approximately 30 individuals— representing academe, government and the consulting industry, and included individuals who are not engineers. The committee recognized that formulating and articulating a clear, comprehensive, and consistent consensus definition for the performance of a civil engineered facility is an important step and in fact a prerequisite for serving as an intellectual foundation before making any transition to a performance-based approach in civil engineering. This paper offers a synthesis of specification-based versus performance-based civil engineering and articulates the committee’s conclusions in framing and articulating the following questions: What is performance-based civil engineering? How can we objectively define performance? What are the issues that should be recognized along the way to performance-based engineering and their possible resolutions? While this report was being completed and circulated within the committee and Performance of Structures TAC members, steps were taken to merge the Performance-Based Design and Evaluation of Civil Engineering Facilities Committee with the Performance of Full-Scale Structures Committee. This merger took place during the 2004 Congress, and a critical mass of committee members from professional practice and academe continue

A consistent basis for statistically reducing fiber-reinforced polymer (FRP) composite material property test data for load and resistance factor design (LRFD) of composite structures is developed in this paper. A two-parameter Weibull probability distribution is recommended for modeling both strength and stiffness properties. Consistent with practice for other materials used in structural engineering applications, the 5-percentile value of strength of coupons and components, as well as modulus values, appropriately adjusted for the small size of typical data samples, is recommended for the nominal value of strength for LRFD applications. Statistical uncertainty due to small sample size in the data reduction process is accounted for through the use of a data confidence factor, which is the tolerance limit defined as the 80th percent lower confidence level of the 5-percentile value of the population. With the nominal values so determined, appropriate resistance factors for LRFD-based design codes can be de...

A fragility analysis methodology is developed for assessing the response of light-frame wood construction exposed to stipulated extreme windstorms and earthquakes. Performance goals and limit states (structural and nonstructural) are identified from a review of the performance of residential construction during recent hurricanes and earthquakes in the United States. Advanced numerical modeling tools provide a computational platform for risk analysis of light-frame wood building structural systems. The analysis is demonstrated for selected common building configurations and construction (defined, e.g., by roof sheathing, truss spacing, and roof or shear wall nailing patterns). Limit state probabilities of structural systems for the performance levels identified above are developed as a function of 3-s gust wind speed (hurricanes) and spectral acceleration (earthquakes), leading to a relation between limit state probabilities and the hazard stipulated in ASCE Standard 7, “Minimum design loads for buildings ...

Advanced fiber-reinforced polymer (FRP) composites, which have been favored for certain aerospace, military, marine, and automotive applications, now are starting to be introduced in buildings, bridges, and other civil construction, where their desirable properties can enhance performance. A load and resistance factor design (LRFD) standard for composites would facilitate their use in civil infrastructure, creating a market for new FRP building materials by providing a basis for structural design that is comparable with existing LRFD standards for other common construction materials. Such a specification must take into account the distinguishing features of FRP composites: Their orthotropic nature, sensitivity to moisture, temperature, and ultraviolet effects, dependence of strength and stiffness on the rate of application and duration of structural loads, and uncertainties in their mechanical and structural properties. The structural reliability tools needed to develop an LRFD standard are at hand. However, at present, only rudimentary statistical databases required to support this development are available. If such databases were to become available in the near future, practical LRFD design criteria could be implemented for civil construction.

Recent trends in building construction have highlighted the need for improved methodologies for engineering new light-frame structures for housing and techniques for condition assessment of existing structures. The aftermath of natural disasters during the past decade, the rapid evolution of design and construction methods, and heightened expectations on the part of the public and its scrutiny of perceived and actual deficiencies in codes and code enforcement have further underscored these needs. Among the high-priority areas identified at a 1997 ASCE workshop on wood engineering research needs were behavior and performance of wood structural systems; criteria for performance assessment; and methods for condition assessment of damaged systems following natural disasters. The development of appropriate and usable fragility models and system reliability analysis tools is necessary to meet these needs and to make meaningful advances in performance-based engineering of wood frame structures. This paper provid...

The Northridge earthquake of 1994 led to numerous weld fractures in beam-to-column connections in welded special moment-resisting frames. To address building performance issues raised by these failures and to support improvements in probability-based load resistance factor design for steel building structures, four welded special moment-resisting frames of different sizes and configurations that suffered connection damage during the earthquake are evaluated using both deterministic and stochastic approaches. The results of this investigation are presented in two companion papers. This paper focuses on deterministic dynamic modeling issues, using a new hysteretic model that incorporates the effects of connection weld fractures on building response and ground motions believed to be representative of the Northridge earthquake. The degraded connection model results in somewhat larger frame deformations, but its impact only becomes significant at spectral accelerations larger than those believed to have occurred. The agreement of predicted and surveyed damage was quite good for two of the frames, but not as good for the other two. Inherent randomness and modeling uncertainties limit the quality of the agreement that is possible from a single deterministic analysis. Thus, in the companion paper, the role of uncertainties in making such comparisons is investigated. Randomizing the strength and ground motion yields a probabilistic description of building performance that places such comparisons of predicted and observed damage in better perspective.

ASCE Standard 7, “Minimum Design Loads for Buildings and Other Structures,” has contained provisions for load combinations and load factors suitable for load and resistance factor design since its 1982 edition. Research in wind engineering in the intervening years has raised questions regarding the wind load factor 1.3 and load combinations in which the wind load appears in ASCE 7-95. This paper presents revised statistical models of wind load parameters based on more recent research and a Delphi, and reassesses the wind load combinations in ASCE Standard 7 probabilistically. The current approach to specifying wind loads in ASCE 7 does not lead to uniform reliability in inland and hurricane-prone regions of the country. It is recommended that the factor accounting for wind directionality effects should be separated from the load factor and presented in a separate table in the wind load section, that the wind load factor should be increased from 1.3 to approximately 1.5 or 1.6 to achieve reliability consis...

ASCE Standard 7, “Minimum Design Loads for Buildings and Other Structures,” and the “NEHRP/BSSC Recommended Provisions for Seismic Regulations for Buildings” both contain load requirements for earthquake-resistant structural design. Many of the NEHRP provisions are being implemented in building codes and are the basis for the seismic load provisions in Chapter 9 of ASCE 7. However, the treatment of combinations of earthquake and snow loads differs in the ASCE 7 and NEHRP documents. Concerns regarding these differences were raised during the balloting of both the ASCE 7-93 and ASCE 7-95 provisions. To address these concerns, the load combination requirements involving dead, snow and earthquake load in these two resource documents were examined using modern probabilistic load models and load combination techniques. It is found that approximately 20% of the nominal snow load should be considered in combining snow and earthquake loads.

A stochastic finite element method (SFEM) is developed to study the reliability of structures with material nonlinearities. Bilinear stress-strain relationships that involve two correlated random fields are used to model the material nonlinearities. Random fields are represented as continuous functions by using general orthogonal series expansions, and are incorporated directly into the nonlinear finite element analysis and first-order reliability formulation. The proposed method is illustrated by two examples involving a fixed-end beam and a frame. Random spatial fluctuations in the material properties or distributed loads may have a significant effect on reliability if correlation lengths of random fields are less than the lengths of members, meaning that local fluctuations in the fields are relatively high.

The effects of uncertain material properties on the elastic stability of structural members and frames are analyzed using a stochastic finite-element method. The uncertain material properties are modeled as continuous random fields by a series expansion involving orthogonal functions. The expanded random fields are incorporated into the finite-element formulation leading to an eigenvalue problem involving random parameters. A mean-centered second-order perturbation technique is used to find the probabilistic characteristics of the buckling load. Illustrations involving a simply supported beam, a simply supported beam on an elastic foundation, and a frame are presented. These illustrations demonstrate the impact on instability of characteristics of the random fields, including correlation length and coefficients of variation of random flexural rigidity and/or random elastic foundation modulus, finite-element mesh selection, and the interrelation between statistical and finite-element modeling. A comparison...

Reinforced concrete shells are structurally complex and closed-form models for their various limit states of serviceability and strength either are not available or may be based on approximations and idealizations of behavior. Nonlinear finite-element techniques have made it possible to account for the complexities of reinforced concrete behavior in the inelastic range, to identify these limit states more accurately, and to assess the safety and reliability of concrete shells. Traditional reliability analysis methods are more convenient to apply when closed-form mechanical models of limit states are available. In the absence of such models, the reliability analysis can be performed by response surface methods that approximate the limit states by polynomial surfaces obtained through finite-element analyses of the system at a set of predetermined experimental points. This paper presents the reliability analysis of a reinforced concrete containment structure by the response surface method. Axisymmetric nonli...

This is the second of two papers that describe the role of in‐service inspection/repair in maintaining the reliability of concrete structures taking into account the randomness of existing damage and damage detection. Since inspection and maintenance are costly, there are trade‐offs between the extent and accuracy of inspection, required level of reliability, and cost. The method to evaluate degradation in strength of a component described in part 1 is combined with the time‐dependent reliability analysis to devise optimum strategies for inspection and maintenance that minimize the expected future cost of structures and components, while maintaining their limit‐state probabilities at or below an established target failure probability. Optimum inspection/repair strategies are sensitive to the relative costs of inspection, repair, and failure as well as to the threshold value of damage detection. Inspection at approximately uniform intervals leads to near minimum costs for a wide variety of cases studied.

One major serviceability consideration in modern buildings is excessive floor vibrations due to occupant activities. Floor vibrations are becoming a more important design consideration with the use of high-strength, light-weight materials in building structures, longer floor spans, and more flexible framing systems. Floor systems in shopping malls, pedestrian walkways and concourses, and gymnasiums are relatively light and susceptible to vibration problems. Methods for accurate prediction of these vibrations and evalution of floor systems are not readily available to the design community. An investigation is made into the characteristics of crowd-induced loads. These characteristics include the density of the crowd, randomness of crowd movement, crowd activity, and temporal interaction between individuals. Analytical procedures are developed to determine the influence of each load characteristic on the dynamic response of floor systems. Design guidelines are developed for floors in malls, gymnasiums, and walkways subjected to crowd-induced loads.

Concrete structures may be affected by aging or changes in strength and stiffness beyond the baseline conditions assumed for design. These changes may impair the safety and serviceability of the structure, and should be considered as part of the process by which a structure is evaluated for continued future service. Methods are being developed using structural reliability principles to evaluate time-dependent reliability of reinforced or prestressed concrete structures. These methods enable the impact on safety and serviceability of uncertainties in loading conditions, structural strength, and strength degradation due to aggressive environmental stressors to be assessed qualitatively. Parametric analyses show that the reliability is sensitive to the choice of initial component strength and strength degradation models. Less sensitivity is found to correlate component strengths within a system. Identification of the critical components before performing system reliability analysis is important in reducing the size of the analysis. The role of periodic inspection and maintenance in enabling a target reliability level to be met over a period of continued service also is considered.

Strength and serviceability limit states are closely interrelated in wood construction. The design of wood beams is often governed by limits on deflection, and the resulting section is larger than that required for flexure or shear strength. Moreover, members used in light-frame construction are chosen from standard available dimension lumber sizes. Relatively few sizes are available for wood in comparison to the number of standard shapes available in steel construction. As a result, the sections selected in wood design may be significantly larger than what would otherwise be required by the design equations. This paper addresses the additional reliability gained with respect to ultimate strength by including the deflection limit state and by considering the availability of standard sections for individual wood members and parallel-member systems. The significance of system effects from load sharing in serviceability reliability is assessed. The implications that these effects have for the ongoing development of load and resistance factor design (LRFD) provisions for engineered wood construction is examined.

The results of a comprehensive three‐dimensional dynamic analysis of structurally asymmetric high‐rise buildings subjected to stochastic wind forces are summarized. Random vibration theory is used to obtain the response statistics that are important for checking the serviceability of the building. Surface pressures measured in wind‐tunnel tests are analyzed to determine the spectra and cross spectra among the force components. The effects on building response of eccentricities in centers of rigidity and/or mass' and of the correlation among the force components are examined. A simple approach is proposed that could be used at the preliminary design stage to assess potential building vibration problems and to identify situations that warrant a more comprehensive treatment.

The ASTM Standard E-119 specifies that when a structural component is fire-tested by exposing one surface to a standard fire exposure, the component fails if the temperature of the unexposed surface of the test component rises 250°F (130°C) or more during the rating period. The standard fire exposure usually is not representative of the compartment temperatures that develop during an actual fire, and the test results may not be indicative of how components might actually behave. In particular, the standard test may give an overly pessimistic appraisal of the behavior of concrete components greater than 76 mm (3 in.) thick and that have excellent insulating characteristics. Design economies might be achieved by allowing the use of natural fire exposures rather than one universal test in assigning fire ratings and in fire-resistant structural design.

This is a study of the load-sharing effects and their coupling with the duration-of-load effects in floor systems. A probabilistic analysis of wood structural systems was made under a random static load process utilizing the following: probabilistic descriptions of both strength and stiffness; a damage accumulation model; and a system behavior (member interaction) model. The floor systems studied were assumed to be subjected to a conbined dead-plus occupancy live-load process. The paper describes a reliability analysis of wood floor systems using simple structural models developed for use in DOL (duration of load) studies. These models were subjected to stochastic loads for which the structural action is static rather than dynamic in nature. The details of the study are described.

The wood industry is developing a load and resistance factor design (LRFD) specification for wood construction. This effort provides an opportunity to reevaluate and restructure the current bases for design with wood, and to develop a specification using concepts of probability-based limit-states design. Wood design must take into account the fact that wood is a natural material with large variations in mechanical properties, sensitive to the rate of application and duration of structural loads. These complications are addressed by modeling structural loads as random processes, rather than as random variables, and by postulating limit states that reflect the possibility of failure by either progressive damage accumulation or overload. Current treatment of duration of load effects in the national design specification is found to be inconsistent from a uniform reliability viewpoint. Practical LRFD criteria that are consistent with a desired reliability measure can be developed to reflect the time-dependent nature of wood behavior.

This paper describes the results of a research program to study the behavior of reinforced concrete beams exposed to severe fires. Data are presented from fire tests of six full-scale beams continuous over one support that were fabricated using normal-weight concrete. Four beams were exposed to the standard ASTM E119 fire, and two to a short-duration high-intensity (SDHI) fire developed using realistic fire-load and compartment-ventilation parameters. All six beams developed significant shear cracks near the continuous support rather early in the fire, but eventually failed from excessive flexural cracking and deformation. Mathematical models for predicting thermal and structural response of concrete beams exposed to natural fires, as well as the ASTM standard exposure, were also developed. These models predicted the experimental behavior with sufficient accuracy for purposes of limit-states design.

A random vibration‐based procedure is used to estimate the dynamic responses of symmetric tall buildings (coincident centers of mass, rigidity, and geometry) subjected to the effects of wind. The along‐wind, across‐wind, and torsional components of wind force were obtained from a time‐series analysis of surface pressures measured during a wind‐tunnel test of a rigid model. The structural response analysis takes the statistical correlation among these three components of aerodynamic force into account. The contributions of the first and second translational and torsional modes to the response are investigated. The across‐wind and torsional accelerations are the major contributors to building acceleration. A simple approach is developed for evaluating the response statistics that are important for building serviceability. This approach can be used in the preliminary design stage to assess the possibility of unserviceability and the need for more detailed and expensive wind‐tunnel model tests.

The reliability of structural systems often is analyzed under the assumption that the system limit states are not dependent on load path. Although brittle systems are known to be load-path dependent, limit states for ductile frames usually are assumed to be independent of the manner in which the loads are applied. In this study, the dependence of limit states of a single-story and multi-story ductile frame on load path is investigated. For certain cyclic load cases, the strength of the structure decreases significantly and load-path dependence is apparent. It is observed that this can be related to a ratcheting type phenomenon of the structure, and depends on the load sequencing and the degree of nonlinear behavior within each cycle. A load-path-independent lower bound limit state is formulated using shakedown theory. Reliability analyses of the different limit states are performed to determine the importance of load-path dependence on computed system reliability.

Structural engineers often must estimate wind or snow loads at a building site using data from weather stations some distance from the site. This paper describes how design loads at a site can be estimated using moving area-averaging rules that take into account inherent randomness in the data and the sparseness of the reporting stations. These rules provide load estimates or contour maps which are specified exactly by the given data.

The reliability of floor and roof deflections due to occupancy and snow loads, respectively, and of lateral frame deflections due to wind loads is examined. These deflections are determined for unfactored code‐specified loads, and they are not to exceed professionally established deflection limits. Firstorder, second‐moment probabilistic theory is used in the analysis. Values of the reliability index are calculated for eight‐ and one‐yr reference periods. Recommendations are made with regard to load levels to be used in the serviceability analysis of deflection‐sensitive and deflection‐insensitive structures.

Reliability measures for simple nonlinear structures subjected to seismic loading are investigated using dynamic analysis and damage‐related limit states. The nonlinear dynamic response and accompanying statistical analyses are computed using simulation for a vriety of single‐degree‐of‐freedom frames. These analyses provide benchmarks against which theoretical results may be compared. Reliability measures computed in this study are compared to those determined previously using equivalent static limit states, and the implications for probability‐based safety checking are described.

This paper summarizes the results of a research program conducted during 1980–1985 to develop probability‐based analysis and design procedures for structures in nuclear plants. Limit states of concrete containments and shear walls are formulated. Probabilistic models for static and dynamic loads and structural resistance variables are established. Reliability analysis methods are established for estimating limit state probabilities for nuclear plant structures subjected to combinations of static and dynamic loads. Practical probability‐based design criteria are developed for concrete containments and shear walls in a load and resistance factor design format. The load and resistance factors are illustrated for several limit states and target limit state probabilities.

Fluctuating wind forces on tall buildings can cause excessive building motion that may be disturbing to the occupants. A method to relate dynamic alongwind, acrosswind, and torsional forces acting on square isolated buildings to building accelerations is developed using random vibration theory. Wind tunnel test data are analyzed to determine the spectra of force components and correlations among the different components of force. The effects on building vibration of statistical correlations among components of force and mechanical coupling of components of motion introduced by eccentricities of the centers of mass and rigidity from the building centroid are examined. Comparison are made with more common building analyses, where the forces are assumed to be statistically uncorrelated and the components of motion are assumed to be uncoupled.

Basic climatological variables such as wind speed, ground snow and other environmental effects are needed to calculate structural design loads. The design loads are contingent on the selection of suitable probability distributions for these climatological variables. This note compares the probability plot correlation criteria as a tool for statistical analysis and testing of environmental data to other common methods as a tool for testing and analyzing environmental data.

Specifications for masonry and other construction materials are expected to move gradually over the next several years toward the adoption of probability based limit states criteria for design. This paper illustrates how such criteria might be developed for brick and concrete masonry construction using, as an example, masonry walls loaded in combinations of axial compression and out-of-plane flexure. The paper identifies the type of data and analyses that are necessary to develop probability-based resistance criteria.

A majority of structural failures and associated damage costs are due to errors in planning, design, construction, and utilization, rather than stochastic variability in construction material strengths and structural loads. Recently developed probability-based load and resistance factor design methods treat uncertainties due to inherent randomness and modeling more rationally than is possible with current design methods, but still do not take errors in design and construction into account. Any meaningful attempts to reduce failure rates will need to deal with this issue. This paper reviews the status of design and construction errors in structural safety studies, summarizes some simple mathematical tools for their analysis, and demonstrates why errors are so difficult to treat in codified design.

Snow loads for structural design are calculated as the product of the ground snow load and a snow load coefficient that transforms the ground load to a roof load. This paper presents a statistical analysis of annual extreme water‐equivalents (reported as inches of water) of ground snow measured at 76 weather stations in the northeast quadrant of the United States through the winter of 1979–1980. The analysis suggests that the lognormal distribution is preferable to a Type I distribution of extreme values for describing annual extreme ground snow loads at a majority of sites. Sampling errors and the selection of design loads from the statistical analysis are also described.