All buildings have to serve two important functions.They
have to carry the loads(structural requirement) and provide livable environment
to the occupants to enable them to be comfortable in the use of the building (functional
requirement).
The building has to carry its own weight and external
occupancy loads and those caused by the environment such as those caused due to
wind or earthquake.The elements that bear these loads and transmit them to the
foundation are termed as "structural elements".
A good performance of the structural elements such as
beams and columns is of vital importance from the safety and stability points of
view. Hence, they are designed and constructed with prescribed safety margins
as per requirements specified in the Bureau of Indian Standard specifications. Their
failure will cause cracking, yielding of steel and even ultimate collapse of
the building.
The serviceability of a building depends on the good performance of the structural and the functional elements such as flooring, doors
and windows, glass panels and partition walls.The functional elements are generally
not intended to carry structural loads. Their failure to perform will only affect
the use of the building and not its strength or stability. Their good
performance is also equally important.
In a metropolitan city such as Chennai, most apartment buildings
are made of reinforced concrete frames. In this type of construction,the
structural elements comprise beams and columns which carry the loads. The
partition walls and infill walls in these buildings are treated as non-structural
and hence are not generally designed and constructed to carry structural loads.
In such buildings, for good performance it
is necessary to detail the junction structural and non-structural members with
proper care.The defonnation of the structural members under load should not be
restricted by non-structural partitions or in-fills.
For good performance of both beams and partitions, a proper
sequence of construction is essential. First building the infill or partition and
that casting the concrete beam on top will make the dead weight of the concrete
beam load the partition which is not correct.The partition is not supposed to
carry the weight of the beam.Moreover, when the additional live load comes on
the floor the deflection of the beam will crack the brick infill or partition.
To avoid this problem, first the frame should be completed.This should be followed
by the erection of partitions and in-fills.Care should be taken to see that a
structural gap exists between the frame and the in-fill.For functional convenience
this gap can be filled by inert flexible material such as thermocol or pith.
Under no circumstance a structural member should be cut
or chased or damaged in any way for any purpose including for taking services like
electrical conduits, concealed wiring etc.This will weaken the element and may
cause its collapse leading to the collapse of the whole building.However the services
may be taken through the non-structural partitions or infill.
Bearing walls: This type of construction is undertaken in
semi-urban and rural areas. All the main walls carry loads and also serve to provide
functional requirement.In these buildings, though the partition walls do not
carry structural loads, they cannot be either built or demolished without due
consideration for overall stability of the building. Some times their weight
may be required to provide stability against overturning failure. The main
walls invariably provide the structural stability and carry loads. Hence, they
cannot be damaged or dismantled for carrying conduits for electricity, etc.
Bearing wall buildings though safe for vertical loads are
weak under lateral loads.They are vulnerable for failure under out of plane
bending during lateral loading. Therefore, to make the building act as one integral
unit, they should be constructed with continuous plinth and continuous lintel
beams. No brick pillar should be less than 600 mm in width. All openings should
be reinforced on all sides.These simple precautions will ensure good
performance of bearing wall buildings under lateral loads caused by wind or
earthquakes.
Construction defects
In many sites the brick wall is first raised and then
used as shuttering to cast the column or beam adjoining it.This will make the column
or beam weak because the pores in brickwork will absorb the moisture from wet
concrete making the wlc ration in the beam and column uncertain. The
weakness will manifest in the cover concrete of the beam or column, leading to
early onset of corrosion in the rebars.
The cracking in the walls of the buildings are many times attributed to following wrong constructions practices. It is important to pay attention
to the details at the site of construction to ensure long and trouble free
service of the infrastructure created. A conscious distinction should be made
between the structural and non-structural items in a building and their requirements
and performance. These defects when permitted during construction are difficult
and costly to rectify later.
For more details,
No comments:
Post a Comment