Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

El Damatty, Ashraf

Abstract

Observations of post-hurricane events indicate that light-frame wood houses are vulnerable to failure

Observations of post-hurricane events indicate that light-frame wood houses are vulnerable to failure due to the inability of their connections to provide sufficient transfer of uplift wind loads from the roof of the house to the foundation. One of these connections is the roof-to-wall connection (RTWC), which connects roof trusses to the top plate members of the walls. This issue has been investigated through full-scale testing at the Insurance Research Lab for Better Homes. This thesis describes the detailed finite element modelling performed for this full-scale testing and provides a comparison of the numerical predictions with the experimental results. The comparison revealed the ability of the sophisticated finite element modelling to predict the nonlinear response of the roof under uplift wind loads that vary both in time and space. A semi-analytical solution for analyzing the full-scale test is also introduced. With the use of statically indeterminate slope deflection equations that include shear deformation, the new model simulates an entire roof truss as a beam on an elastic foundation. The solution model was validated first against a finite element model with respect to the RTWC reactions and then by comparison with the experimental results. A further component of the study was an evaluation of the reliability of the roof system using Monte Carlo simulations and appropriate probabilistic models. Beta and normal distributions were designed for generating both RTWC stiffness values and uplift wind loads, respectively. It was found that beyond a mean wind velocity of 30 m/sec, the probability of roof failure increases rapidly. The study proceeds by considering a previously prepared external retrofitting that can reduce possible toe-nail failure and create an additional load path. For use only in the case of warnings of highly intense winds, the external retrofitting consists of bearing cables, external cables, and rigid bars. A small-scale house was previously tested at the Wind Engineering, Energy and Environment Research Institute (WindEEE) facility in order to assess the performance of the retrofitting system. In the current study, the semi-analytical solution model was extended to analyze the retrofitting system. The results reveal that the retrofitting system increases the possible wind velocity threshold prior to failure by 36.4%.

due to the inability of their connections to provide sufficient transfer of uplift wind loads from the roof of the house to the foundation. One of these connections is the roof-to-wall connection (RTWC), which connects roof trusses to the top plate members of the walls. This issue has been investigated through full-scale testing at the Insurance Research Lab for Better Homes. This thesis describes the detailed finite element modelling performed for this full-scale testing and provides a comparison of the numerical predictions with the experimental results. The comparison revealed the ability of the sophisticated finite element modelling to predict the nonlinear response of the roof under uplift wind loads that vary both in time and space. A semi-analytical solution for analyzing the full-scale test is also introduced. With the use of statically indeterminate slope deflection equations that include shear deformation, the new model simulates an entire roof truss as a rigid beam on an elastic foundation. The solution model was validated first against a finite element model with respect to the RTWC reactions and then by comparison with the experimental results. A further component of the study was an evaluation of the reliability of the roof system using Monte Carlo simulations and appropriate probabilistic models. Beta and normal distributions were designed for generating both RTWC stiffness values and uplift wind loads, respectively. It was found that beyond a mean wind velocity of 30 m/sec, the probability of roof failure increases rapidly. The study proceeds by considering a previously prepared external retrofitting that can reduce possible toe-nail failure and create an additional load path. For use only in the case of warnings of highly intense winds, the external retrofitting consists of bearing cables, external cables, and rigid bars. A small-scale house was previously tested at the Wind Engineering, Energy and Environment Research Institute (WindEEE) facility in order to assess the performance of the retrofitting system. In the current study, the semi-analytical solution model was extended to analyze the retrofitting system. The results reveal that the retrofitting system increases the possible wind velocity threshold prior to failure by 36.4%.

Summary for Lay Audience

Observations of post-hurricane events indicate that light-frame wood houses are vulnerable to failure due to the inability of their connections to provide sufficient transfer of uplift wind loads from the roof of the house to the foundation. One of these connections is the roof-to-wall connection (RTWC), which connects roof trusses to the top plate members of the walls. This thesis describes a detailed analysis of this problem. A simplified solution for analyzing this problem is also introduced. A further component of the study was evaluating the probability of failure for these connections using Monte Carlo simulations. It was found that beyond a mean wind velocity of 30 m/sec, the probability of roof failure increases rapidly. The study proceeds by considering a previously prepared external retrofitting that can reduce possible connections failure and create an additional load path. For use only in the case of warnings of highly intense winds, the external retrofitting consists of bearing cables, external cables, and rigid bars. The bearing cables are installed on the roof and attached to rigid bars in the roof edge, which are, in turn, connected to external cables supported by micropiles permanently embedded in the ground. The retrofit system would be designed so that the cables could be kept folded during normal wind conditions, thus avoiding distortion of the style and aesthetics of the house. The installation of the retrofit system would take place when advance hurricane warnings are issued. In the current study, the simplified model was extended to analyze the retrofitting system. The results reveal that the retrofitting system increases the possible wind velocity threshold prior to failure by 36.4%.

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