Hossein Ataei

Finite Element Analysis of Cable-Stayed Strands’ Failure Due to Fire

The failure of one structural element may lead to the failure of the other structural components where ultimately result in the collapse of the large sections or the entire structure. The progressive collapse of the structures have been mainly investigated for buildings. However, cable failure in cable-stayed bridges may cause catastrophic consequences due to the progressive collapse. This is also crucial in part given the importance of bridge infrastructure in transporting people and the goods across the country and the key role that they play in contributing towards the nation’s economy. In design process of the cable-stayed bridges, the possibility that the loss of one cable might be leading to the collapse of the entire structure is often overlooked. This is particularly due to the structural redundancy considerations and the high safety factors in design of the structural components for these bridges. In this paper, the effects of a hypothetical fire and the thermal gradient propagation along a pre-stressed cable is studied using non-linear finite element modeling and analyses. For this purpose, the possible fire intensities and durations are studied in order to determine their effects on the strength losses in pre-stressed cables using finite element method. Results of this research could be used as basis for investigation of structural failure of cable-stayed/suspended systems.

Stochastic evaluation of mortgage default losses resulting from flood damages and different mortgage arrangements for post-Katrina Louisiana houses

Purpose - – The purpose of this paper is to investigate the total number of mortgage default occurrence possibilities and monetary damage amounts to the sampled properties due to the excessive flooding caused by natural disasters. Mortgage default loss assessments due to natural catastrophic events are of great interest to lenders, insurance firms, forensic engineering professionals, inspecting agencies and the federal and state government planning officials and risk-mitigating teams. Design/methodology/approach - – In this study, a stochastic methodology is used to address the risk of mortgage default losses and the homeowners’ investment returns, given: damage severity levels of hurricane floods and the mortgage types and arrangements on selected properties. Nine different houses, with various mortgage arrangements, located in different flood damage zones were investigated three years after Hurricane Katrina. To quantify the flood damage risk values which are compared with exceeding damage probabilities, the Poisson’s distribution is used through performing random variable analysis walks for each property during each house’s mortgage life cycle. Findings - – Henceforth, through introduction and constructing the “Zonal Damage Matrix” for the investigated houses, the total number of mortgage default occurrence possibilities and monetary damage amounts to the properties are calculated for each exceeding flood. Thereafter, the homeowners’ net equity values and the investment returns are estimated for risk identification and evaluation purposes. Originality/value - – For each of the sampled houses, the probability of mortgage defaults and the homeowners’ net equity values are estimated using Poisson’s distribution based on 60,000 randomly generated numbers to construct ten different hazard-related default scenarios for each property over the 30-year mortgage life cycle. The investment returns are therefore estimated for risk identification and evaluation purposes.

Effect of Window Sizes and Glazing Panel Aspect Ratios on Mitigating the Injuries from Flying Glass due to Air Blast

When subjected to an air blast, conventional window glasses of different sizes break into numerous flying shards which account for most injuries ranging from minor cuts to severe wounds and, in many cases, to death. A successful blast-resistant glazing design considers the principles of reasonable degree of protection against explosive threats based on the proposed level of security and previous lessons learned. It also requires balancing of the safety and security of the window panels with physical appearance and cost-effectiveness. In an air blast event, reducing the injuries from flying glass and protecting the occupants shall always remain a top design priority. For such, having more accurate glazing models is inevitable and thus, it is necessary to have a better understanding of the glass panel responses to different window parameters and blast load characteristics. For this purpose, we have modeled conventional annealed glass window panels of different sizes using explicit finite element analysis. The results show that the response of the window panels to different blast loadings is highly dependent upon the window pane sizes. Therefore, we have studied the window size effects and panel aspect ratios on window fragmentation patterns using brittle failure theories and crack propagation micromechanics of structural glazing subjected to air blast. These results will help developing a more comprehensive flying glass injury model that eventually enables the decision makers to bring the appropriate structural, architectural and building perimeter choices to better address the threats facing the safety of the residents during an air blast.