Reliability-based calibration of main Brazilian structural design codes

Given the tendency of risk-targeted seismic design maps worldwide, it is important that Brazil is inserted in this context as well. This study aims to apply the risk-targeting methodology for Northeastern Brazil, more specifically the region within Zone 1 of the Brazilian earthquake-resistant design code ABNT NBR 15421:2006. Different inputs for the methodology are explored and combined with existing hazard studies for the region, and their impact in the final map are evaluated. The results outline that, depending on the safety level required, the provisioned design accelerations could be lower than the commonly used in codes, but may as well be much higher. The results are also compared with the current code provisions and their differences are discussed, providing insights on the code provisioned level of safety.

Section: Risk-targeting Methodologysupporting

confidence: 85%

Prospective study on risk-targeted seismic hazard maps for Northeastern Brazil: case study in Zone 1 of ABNT NBR 15421:2006

Pereira

Cavalcante

Andrade

et al. 2022

“…where Φ(•) is the cumulative distribution function of the standard normal distribution; 𝛼𝛼 𝑆𝑆 is the FORM sensitivity factor for the action effects, and 𝛽𝛽 𝑇𝑇 is the target reliability index. In Section 3.6, the reliability-based calibration of partial safety factors employed in Brazilian design codes for steel [45] and concrete [46] structures -originally performed by Santiago et al [47] -is re-processed using the live load statistics developed herein, and the mean reliability index using current NBRs 8681, 8800 and 6118 factors is found to be equal to 3.17 for a period of 50 years. Hence, a target reliability index of 𝛽𝛽 𝑇𝑇 = 3.17 is considered herein.…”

Section: Partial Safety Factor For Uls Verificationmentioning

confidence: 99%

Probabilistic models for live loads in buildings: critical review, comparison to Brazilian design standards and calibration of partial safety factors

Costa

Santiago

Beck

2023

Self Cite

Nowadays, structural “limit state” design is made using characteristic or nominal values of actions, partial safety factors and load combination factors. The actual loading that a structure will be subjected to throughout its life is not known at the design phase. Yet, probabilistic models of such loadings are useful for the rational determination of partial safety factors and load combination factors. The probabilistic model leading to nominal live loads of NBR 6120:2019 (Design Loads for Structures) has never been openly discussed. Herein a simple probabilistic model describing spatial and temporal variabilities of live loads in buildings is presented and discussed. The model is built as a sum of two stochastic processes representing the sustained and intermittent parts of the live load. Model parameters are the ones recommended by the Joint Committee on Structural Safety (JCSS), based on extensive surveys done in several countries. By way of Monte Carlo simulations, sample values of live load actions are obtained for buildings of different occupancy types. These values are compared with those recommended by international standards, and those recommended in NBR 6120:2019 and NBR 8681:2003 (Actions and Safety of Structures). The corresponding statistics for the fifty-year extreme and arbitrary point-in-time distributions of live loads are presented; these statistics are very relevant for reliability analyses and for reliability-based code calibration. The stochastic live load model is also employed in a reliability-based calibration to obtain partial safety factors and load combination factors to be used in Brazilian design codes, for ultimate and serviceability limit state verifications.

“…Yet, the analysis is justified as we are more interested in the variation of reliability indexes for different points of the structure. Moreover, the recent study on reliability-based calibration of Brazilian design codes [49] has suggested that the partial load factor for dead load should be reduced (to ). These values are somewhat closer to the values given by ASCE 7, as reported below.…”

Section: Load Combinations and Designmentioning

confidence: 99%

Distribution of load effects and reliability of reinforced concrete frames: intact and with columns removed

Facholli

Beck

2022

Self Cite

The design of reinforced concrete (RC) frames is made on a member-by-member basis. Similarly, in the literature, the reliability of RC beams and columns is often studied in isolation from the rest of the structure. Yet, in the construction of regular frames, symmetry and regularity are often exploited, resulting in the same design for each element type. This is despite of different load effects on different parts of the structure, which leads to significant variations in the failure probability of the elements. Hence, in this paper, we investigate the reliability of members and the distribution of load effects in regular RC frame buildings, considering intact and column loss cases, where symmetry is lost. Results show that the ratios of normal-to-bending loads change significantly along building height, and this has a significant impact on reliability of individual columns.