Bond Strength and Development Length Models for Straight Plain Longitudinal Reinforcement in Tension

Previous experimental and analytical studies have shown that state-of-practice provisions for evaluating the bond strength and development length of plain bars are not appropriate. Existing provisions tend to provide overconservative estimates of the required development length of plain bars. Using a database of 518 development and 35 splice test specimens, this study proposes simple models for evaluating the bond strength and development length of plain round and square bars. The study demonstrates that the bond strength of a plain bar depends on the casting position, concrete strength, and the ratio of concrete cover to bar diameter. The study also shows that the influence of the loading rate and stirrup confinement level on the bond strength of plain bars may be insignificant. Furthermore, it is shown that the bar size factor in ACI 318 for deformed bars is not justified for plain bars. Using the proposed model, it is concluded that the required development length of a bottom-cast plain bar is 1.33 times that of a bottom-cast deformed bar. Also, the required development length of a top-cast plain bar is two times that of a top-cast deformed bar. The proposed model in this paper is recommended for incorporation into assessment standards

Seismic fragility assessment of bridges with as-built and retrofitted splice-deficient columns

A significant proportion of existing bridges in high seismic regions were constructed prior to the 1970s. As a result of poor reinforcement detailing, pre-1970s bridge columns are susceptible to lap-splice or shear failure in the plastic region. Given the high economic impact of retrofitting all pre-1970s reinforced concrete (RC) bridges, it is essential to identify the most vulnerable bridges for retrofit prioritisation. Analytical fragility functions are useful for quantifying the seismic vulnerability of existing bridge stock. However, the accuracy of these fragility functions relies on the adequacy of the adopted modelling approach. This paper presents a hinge-type modelling approach for capturing the seismic response of as-built splice-deficient and retrofitted RC bridge columns. Fragility analysis is carried out for typical seat and diaphragm abutment two-span bridges using the proposed hinge-type modelling approach. The results showed that the vulnerability of the bridges depends on the column failure mode and the limit state under consideration. Also, the common notion that the column is the most vulnerable component may not necessarily be true. The study underscored that retrofitting columns without retrofitting other components may not effectively mitigate the damage and associated risk

A Probabilistic Framework for Post-Disaster Recovery Modeling of Buildings and Electric Power Networks in Developing Countries

Post-disaster recovery is a significant challenge, especially in developing countries. Various technical, environmental, socioeconomic, political, and cultural factors substantially influence post-disaster recovery. As a result, methodologies relevant in developed nations may not be directly applicable in Global South contexts. This study introduces a probabilistic framework for modeling the post-disaster recovery of buildings and electric power networks (EPN) in developing countries. The proposed framework combines a building-level assessment of individual assets with a community-level assessment of EPNs to evaluate a building portfolio's post-event functionality state. As part of the framework, a stochastic network analysis approach is proposed to estimate the recovery time of damaged buildings while accounting for technical, environmental, socioeconomic, political, and cultural factors, quantified using data gathered from past events. Similarly, a probabilistic modeling approach is proposed to quantify the EPN's initial post-event outage levels. Specifically, empirical formulations for estimating the recovery time of an EPN as a function of its initial post- event outage levels are calibrated using post-event data from developing countries. A case study is presented to illustrate the application of the proposed framework to model the post-earthquake recovery of a synthetic low-income residential community. The analysis showed that negative technical, environmental, socioeconomic, political, and cultural factors could amplify the reconstruction time of damaged buildings by a factor of almost three. The proposed framework can support decision-makers in disaster planning and management strategies for vulnerable low-income communities