A Probabilistic Study Of Safety Criteria For Design

National Science Foundation Under Grant GK-1812

Performance-based engineering for multiple hazards: the role of structural reliability and risk assessment

Buildings, bridges and other civil infrastructure facilities are designed by current codes and standards using provisions that invariably are prescriptive in nature. While facilities so designed usually possess adequate levels of safety under design-basis events, other environmental or man-made events may cause them to suffer damage or loss of function, leading to economic losses, with uncertain impacts on the building occupants, owners and the community that they serve. The new paradigm of performance-based engineering enables structural engineers to achieve more reliable and informative prediction of civil infrastructure behavior and control of performance across a range of hazards. When supported by a risk-informed decision framework founded on structural reliability principles, performance-based engineering provides stakeholders with a structured framework for thinking about performance objectives, uncertainty, and how public safety and socio-economic well-being may be threatened by the failure of civil infrastructure to perform under a spectrum of hazards

Reliability of Wood Systems Subjected to Stochastic Live Loads

Multiple-member wood structural systems are designed using the current National Design Specification with an increase in allowable bending stress of 15% to account for load sharing and partially composite action. Efforts are underway to develop Load and Resistance Factor Design (LRFD) procedures for engineered wood construction to enable design of wood structures to be performed in a similar fashion as design of steel or reinforced concrete structures. The proposed LRFD methodology includes a system factor derived by probabilistic analysis to account explicitly for load sharing among members in a wood structural system. Available statistical data on mechanical properties of individual pieces of lumber along with structural system and stochastic damage accumulation models can be utilized to evaluate system reliability and to develop LRFD design criteria that are consistent with a desired reliability

Challenges and alternative approaches for simulating the response of steel structures exposed to fire

Although structurally significant building fires are rare events, their occurrence can cause substantial damage and may lead to partial or complete system collapse. While fireproofing has proven to be effective in mitigating the effect of severe fires, it is rated for only a certain time and will eventually fail to provide adequate protection during a large or extended fire event. Furthermore, fireproofing typically is rated using a standard fire exposure, such as ISO 834 or ASTM E119, neither of which represent realistic fire exposures in an actual building. With the worldwide move toward performance-based fire protection engineering, understanding and quantifying system behavior through advanced numerical simulations, especially during the heating and cooling phases of realistic fire exposures, is essential for establishing proper performance-based provisions for fire engineering that ensure both safe and economical design. This paper highlights current challenges in simulating the effect of fire on steel components and frames, including proper representation of loading and boundary conditions, geometrical nonlinearities, material inelasticity, and numerical instabilities. The structural models considered include 2-D line elements, 3-D continuum elements, and multi-resolution models. In addition, the advantages and drawbacks of these models are highlighted and the implication of their features is discussed. The highlighted modeling approaches and the corresponding results shown can be used by engineers for selecting the most economical and effective techniques for simulating the response of components and structural systems to scenario fire hazards accurately

An approximate dynamic programming approach to food security of communities following hazards

Food security can be threatened by extreme natural hazard events for households of all social classes within a community. To address food security issues following a natural disaster, the recovery of several elements of the built environment within a community, including its building portfolio, must be considered. Building portfolio restoration is one of the most challenging elements of recovery owing to the complexity and dimensionality of the problem. This study introduces a stochastic scheduling algorithm for the identification of optimal building portfolio recovery strategies. The proposed approach provides a computationally tractable formulation to manage multi-state, large-scale infrastructure systems. A testbed community modeled after Gilroy, California, is used to illustrate how the proposed approach can be implemented efficiently and accurately to find the near-optimal decisions related to building recovery following a severe earthquake.Comment: As opposed to the preemptive scheduling problem, which was addressed in multiple works by us, we deal with a non-preemptive stochastic scheduling problem in this work. Submitted to 13th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP13 Seoul, South Korea, May 26-30, 201

Load Duration and Probability Based Design of Wood Structural Members

Methods are presented for calculating limit state probabilities of engineered wood structural members, considering load duration effects due to stochastic dead and snow load. These methods are used to conduct reliability studies of existing wood design criteria. When realistic load processes are considered, it is found that the importance of load duration and gradual damage accumulation has been somewhat overstated. One possible probability-based design method that should be useful in future code development work also is presented