Reliability-based Load Factor Research Articles

Reliability-based load factors for airblast and structural reliability of reinforced concrete columns for protective structures

Reliability-based design allows the decision-maker to select the level of reliability for a specific explosive blast loading scenario. Important to this is an understanding of airblast and resistance uncertainty. Reliability-based load factors are calculated and are dependent on the variability of model error, explosive mass and range. Reliability-based design load factors (RBDFs) are estimated for explosive ordnance, terrorism, weaponeering and other scenarios. The effect of RBDFs on structural reliabilities for reinforced concrete (RC) columns is then calculated where resistance and loading are random variables, and compared to target values. It was found, for realistic combinations of range and explosive mass variabilities, that RC columns designed to existing standards have a significant margin of safety with a probability of failure of 1 × 10−3 to 1 × 10−5. However, if there is large airblast variability, then the application of RBDFs is necessary to ensure that safety levels are acceptable according to international standards.

Reliability-based load factor design model for explosive blast loading

The risk of damage to infrastructure and people is affected by airblast variability. Reliability-based design allows the decision-maker to select the level of reliability for a specific blast loading scenario. Reliability-based load factors are calculated where the nominal load is multiplied by the load factor to ensure that the actual load is equal to the reliability level. A design model for predicting reliability-based load factors is developed where model error, explosive mass and stand-off distance are random variables, and calculated reliability-based design load factors (RBDF) are independent of explosive mass, net equivalent quantity, angle of incidence, temperature or pressure. Hence, a design model describing reliability-based load factors are presented for reliability levels of 0.05 to 0.99, and for coefficients of variation of explosive mass and range each varying from 0.0 to 0.3. The paper then shows the significant effect that range and explosive mass variability have on RBDFs, and how this affects structural design and damage predictions for reinforced concrete columns and glazing.

Reliability-Based Design Load Factors for Explosive Blast Loading

AbstractReliability-based design allows the decision maker to select the level of reliability for a specific blast loading scenario and key to this is an understanding of airblast uncertainty. Hence, explosive field trials have been conducted in Australia that measured the variability of free-field blast loading caused by military standard plastic explosives. The results have revealed a high level of variability of peak incident pressure, impulse, and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The accuracy of predictive blast load models (model error) was also assessed. A probabilistic blast load computer model is revised to capture these observed variabilities. The effect of a 20% mass-increase safety factor typically applied to explosive mass on the probability of exceeding a design blast load is assessed. Reliability-based load factors are calculated where the nominal load is multiplied by the load factor to ensure that the actual load is e...

Reliability-based load factors for blast design

In this study the concepts of reliability are used to derive blast load factors. First, some objective criteria are proposed for the proper interpretation of pressure data gathered in arena tests. These criteria are applied to the pressure–time histories recorded during field tests involving live explosive detonated in contact with the ground. Three major shock wavefront parameters, including peak pressure, impulse, and positive phase duration are calculated. Next, statistical analysis is performed on these metrics to estimate their probability density functions and goodness-of-fit tests are carried out to gauge the appropriateness of each estimate. Using the best-fitting distribution for each wavefront metric, load factors are derived on the basis of two approaches. The first approach employs the percentiles of the three load metrics, each estimated using the pertinent probability distribution. The second approach uses concepts of reliability and presents load factors for low, medium, and high level of protection. The two sets of load factors are compared and the limitations of each approach are discussed.