Civil Engineering Reference
In-Depth Information
Serviceability issues, other than beam deflection, may also
be missed. This may lead to inadequate provision for items
such
at interconnecting walls or floors may not be tied into walls
where expected. The process of structural inspection, part
demolition, and removal of existing, possibly load-bearing
walls requires careful assessment during the design phase and
adequate planning by the engineer.
Stability of the structure is paramount during these works as
there have been numerous unplanned collapses over the years.
Propping should be planned and installed prior to removal of
structural elements thereby ensuring loads are supported and
transferred to ground level.
Where load paths are revised - leading to increased loads
on existing elements such as walls and structural framing of
beams and columns - they should have their capacity assessed
for the proposed loads. In older buildings care should be taken
to ensure that the steel strength used in assessment calcula-
tions is correct with reference to the
Historic Structural Steel
Handbook
(Bates, 1984) which provides properties of UK and
European cast iron, wrought iron and steel sections and stress
data since the mid-nineteenth century. However, in the absence
of any existing building information, materials testing may be
required in order to assess the material quality and strength
characteristics.
Care should also be taken when dealing with brittle materi-
als such as cast iron in refurbishment projects. Cast iron can
be present in the form of beams and columns and is regularly
found within masonry jack arch construction. In general, many
cast iron elements continue to be reliable; however, care should
be taken when assessing their residual strength to accommo-
date a change of loading situation. As with most structural ele-
ments, long-standing ingress of water into the construction can
lead to corrosion, deterioration of any infill around the beam
and ultimately loss of composite action.
It should always be remembered that it is normal for over-
stressed cast iron beams to fail without warning.
Additional loading on to load-bearing walls and subse-
quently their foundations requires proper assessment and suit-
able site investigation. If the existing foundations are found to
unsuitable then underpinning in the form of mass concrete to
suitable depth or mini-piling may be required to transmit the
increased loads to suitable strata.
In all these cases, it is expected that the engineer responsi-
ble for the assessment and design of such projects is an expe-
rienced, preferably Chartered engineer. Unfortunately where
failures have occurred in the past, the work has been under-
taken by designers without the proper training or experience to
undertake this type of work.
as
thermal
movements/restraints,
shrinkage/creep,
groundwater or differential settlements.
There may also be a lack of knowledge when specifying
construction materials, their use, grades and isolation require-
ments from other materials. For instance, the instigation of
bi-metallic corrosion between steel and stainless steel material
requires adequate separation with gaskets and steel has differ-
ent grades to accommodate the required stress under many dif-
ferent environmental conditions.
Communication between the design engineer and the draw-
ing office is also of paramount importance to ensure that the
structural drawings are produced according to the designer's
calculations and there is no lack of detail. After all, the draw-
ings communicate the design requirements to the contractor
for construction and should therefore be checked to ensure the
structure is buildable and that the drawing indicates all the nec-
essary safety issues for the contractor.
Construction stage instability should be considered at the
design stage especially if the structural form is elaborate and
the design requires special analysis. Any non-standard struc-
tural frame that the contractor or subcontract designer (fabri-
cator) may not have experience of should be either annotated
fully on drawings or be undertaken by the engineer responsible
for the structure, working alongside the contractor to ensure
structural safety during construction. Items such as erection
sequencing, temporary bracing and connection forces should
be detailed, as applicable.
Many errors or altercations at construction stage are due to
lack of information or split responsibilities, where one party
expects the other to provide additional input, in order to finalise
the construction method. Temporary bracing is typical of this,
as it usually falls to the steelwork subcontractor. However, as
previously mentioned, the engineer responsible for the overall
building should ensure that any subcontractor design is com-
patible with the building design and the construction method
of the building.
The engineer should also ensure that the details provided
on the construction drawings are thoroughly checked prior
to issue. Critical items such as adequate reinforcement, lap
lengths anchorages and curtailment, reinforcement conges-
tion, correct material grades (masonry/steel/concrete/timber),
embedded items, etc., are all to be reviewed.
One of the most critical areas of construction is that re-
quiring refurbishment of existing buildings. Refurbishment
projects can include demolition, foundation improvements,
reuse of existing materials and, most importantly, increases in
load and changes to the original building load path. In add-
ition, the method of construction may require additional re-
search as such methods have changed considerably over the
years. Thick stone walls may be loose rubble filled between the
outer stone faces, lintels may be missing with support relying
on door/window frames. There may be unbonded brick skins
9.7 Analysis
As buildings become more complex with increased heights,
layouts and other architectural requirements, the engineering
design standards that are used have also developed requiring
in-depth analysis. As such, commercial design software has
been developed to enable the engineer to both analyse the
structure and design the structural elements for both static
