MSc Viva Voce

An MSc viva voce was performed on 25/01/2018 at the department of civil engineering for the Master student thesis Nadia Abbod Swadi that is titled as “NONLINEAR DYNAMIC RESPONSE OF R.C. TALL BUILDING SUBJECTED TO VARIABLE BLAST STANDOFF DISTANCE AND HEIGHT“.

The viva committee members were assigned by the civil engineering department as follow:

Assist. Prof. Dr Riyadh Jwad Aziz (Chairman)

Assist. Prof. Dr Laith Khalid Kamel (Member)

Lec. Dr Ammar Abduljabbar (Member).

The student was supervised by Assist. Prof. Dr Hussam Kadhim Risen.

The research abstract:

Recently, threat of terrorist becomes very large and dangerous. When the building become tall
as the today’s trend, it will definitely attract more attention from enemies. When the explosion
take place at very short standoff distance nearby a building it can be cause a complete failure
to the building in addition to life loss or injures of its occupants. From the above, including
blast load as a new case in the analysis and design of multi-storey building becomes very
important. The aim of this research to carry out three-dimensional nonlinear dynamic
responses of forty five multi-storey R.C. building under blast loading. The influence on the
lateral building responses in terms of displacement, velocity and acceleration for three
quantities of charge weight in terms of TNT (115, 230 and 500 kg), three variable standoff
distances (10, 20 and 30 m), three variable explosion source heights (zero level, 11th storey
level and 23rd storey level) and three variable mass sources (uniform mass, mass concentrated
at floor level 23rd and 38th) were investigated. Firstly, the blast load parameters were
calculated based on both the India standard IS:4991 (1968) and American standard UFC-2008.
The result of both codes were compared and discussed. Secondly, the UFC-2008 was used to
complete the full dynamic analysis of the tall building under consideration. Both purely elastic
and elasto-plastic responses were conducted in this study for comparison purposes. Effect of
both only positive blast phase pressure and positive with negative blast phase pressure on the
total response of a structure was investigated. The comparison in term of blast load parameters
based on both IS and UFC revealed that the IS code use the same values of the blast load
parameter for both on ground explosion (hemispherical) and above ground explosion
(spherical) with very conservative values when the standoff distance becomes very short. It is
recommended to use the UFC for analysis and design of structure subjected to blast load due
to accurate and economic purposes. The comparison in term of both purely elastic and elastoplastic
responses proved that allowing small permanent plastic deformation or distortion in the
structure under very short duration dynamic load such as blast load results in a large reduction
in a structure resistance. A reduction in the structure strength of one-half resulted in an
increase in deflection of only about 25 percent. The results of the negative blast phase on the
response of the structure revealed that a slightly different in the maximum displacement
occurs with including the effect of negative phase pressure. It has been recommended to
neglect the negative blast phase pressure for such cases in order to simplified the problem and
save the run analysis time. In case of variable charge weight in term of TNT, standoff
distance, explosion source height and masses of the building, it has been observed that the
dynamic response of R.C. tall building is random and not necessarily the peak response occurs
at the top storey as in static analysis. In other words, the response is change with the run time
analysis. Such that for example at run analysis time equal to 0.42 second which represent 10%
of the fundamental periods, the building behaves as a simply supported structure. But when
the run analysis time becomes 1.0 second, the behavior of the building is change from the
simply supported become to cantilever action.

The committee decided to award the student an MSc degree in civil Engineering with an excellent classification grade.