Figure 3: Pressures due to incident and reflected shock wave
Figure 3: Tee dimensions
blast wave interaction with the building floors and walls within
the building. The scale models were tested at different angles of
incidence of the blast to determine the variation in the reflected
pressure as a function of the angle of incidence. The results were
also used to assess the accuracy of analytical equations used for
calculating blast action and for providing guidance on numerical
(computational fluid dynamics) modelling of blast actions.
Response of building components and whole building
Large scale blast tests were also performed on building elements
and sub-assemblies including masonry and composite cladding,
simple beam-column connections and composite floors.
The purpose of these tests was to study the transfer of blast
actions from the envelope to the frame of the building and the
performance under blast action of building elements such as
floors and connections. The results were used to validate detailed
numerical models and carry out numerical parametric studies.
Based on this work, sub-models (a component connection model
and a 2D flat shell element for the composite slab) were calibrated
and used in whole building finite element models. The whole
building model enabled the behaviour of the reference building
under a series of explosion scenarios to be studied, identified
failure modes and was used to propose retrofitting strategies.
New SCI design guide
The project led to the development of a new SCI design guide
which provides recommendations and advice for the structural
design of low to medium rise steel-framed buildings (typically
two to five storeys high) subjected to blast action due to external
explosions. Step-by-step methods are given for the calculation of
the resultant blast action on a building as a result of the interaction
of the blast wave with the building elevations.
Guidance is given on the calculation of material properties to
be used in the design of members. Yield stress design values are
increased by a static increase factor to account of the fact that the
actual yield strength of the common grades of steel (up to S355)
is frequently greater than its guaranteed minimum value by more
than 25%. This reduces conservatism in a design situation which
involves an accidental combination of actions and ensures that the
forces and moments transmitted from members to connections
are not underestimated. To avoid failure of the connections, the
static increase factor is not applied to the connection components.
This is similar to the approach adopted in BS EN1998-1 for capacity
The mechanical properties of structural steels are affected by
the rate of load application. The guide therefore recommends
values to account for the increase in yield and ultimate strength
due to the dynamic nature of the blast action.
In blast response analysis, the calculation of forces, moments
and deformations requires the use of dynamic analysis of
the building structure. Simplified analysis software (www.
blastresponse.com) was developed comprising three modules: (i)
an advanced single degree of freedom (SDOF) model capable of
accounting for generalised boundary conditions and loading of
a structural element, (ii) SDOF composite floor model and (iii) a
multi-degree of freedom (MDOF) model capable of analysing 3D
building structures with general grid layouts. The software was
validated using advanced finite element analysis.
The response of the building frame members is verified by
reference to deformation limits (both deflection and rotation)
which correspond to different damage levels. These depend on
member type and slenderness and on the nature of loading acting