טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGrisaro Hezi
SubjectResponse of a Structural Element to Combined Loading of
Explosion and Fragmentation Impact
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Avraham Dancygier


Abstract

Detonation of a cylindrical cased charge generates one of the extreme loads on structures. After the detonation, the casing expands and ruptures into many fragments. On the one hand, the blast wave in this case has lower overpressure and impulse than the same explosive without a casing, because part of the energy is dissipated through the expansion and rupture of the casing. On the other hand, the fragments cause damage to the structure and load it by their impulse.  The characteristics of the combined loading (CL) of blast and fragments are functions of the charge properties and shape, and its distance from the structure. The decay in the fragmentation velocities is much lower than the decay of the blast wave velocities. Thus, from very close distances, the fragments arrive to the structure before the blast wave. Under this CL, structural elements may exhibit more severe damage and structural response than under bare charge detonations. This phenomenon was not well understood. The current work deals with various aspects regarding the structural response of reinforced concrete (RC) elements to the CL. The main aims are to first understand and delineate the loading characteristics, then to apply them in order to study their effects on the response of a RC structure, which is subjected to these loads, and finally to assess the structural response.

The first part of the work is presented in chapters 3-6, which deal with the characteristics  of the CL in various aspects. Numerical and analytical studies have been performed to assess the casing effect on the blast wave parameters, the fragmentation velocity distribution, the spatial mass distribution of the fragments, and the influence of the transmitted momentum due to the fragmentation impact, which is commonly neglected in design. The presented models and insights provide information for a more realistic evaluation of the CL.

The second part of the work deals with the structural behavior and response to CL. It starts with an experimental study, described in chapters 7 and 8. Field tests have been conducted, in which RC elements have been subjected to cased charge detonations to study the effects of the fragmentation damage on the structure and to experimentally validate models that have been developed in the first part of the work. These specimens have then been further examined in static laboratory tests to evaluate their residual structural behavior. In chapter 9, the static test results are further analyzed to develop a methodology for consideration of the fragmentation damage. The dynamic response of a structural element to CL is implemented in dynamic analysis in chapter 10, which shows a comparison between three design approaches.

Findings of this research, which are relevant for both strengthening of existing structures and for design guidelines of new structures, show that the damage due to the fragmentation impact plays a key role in the reduction of the stiffness and capacity of a protective structural element. Thus, consideration of the fragmentation damage is important in the design of a structural member, subjected to CL.