Introduction
In India
there are many old buildings which have reduced strength in due course of time.
If further use of such deteriorated structure is continued it may endanger the
lives of the occupants and surrounding habitation. Appropriate actions should
then be implemented to improve the performance of structures and restore the
desired function of structures. Thus, it is utmost important to perform
structural audit of existing buildings and to implement maintenance/ repair
work timely which will lead to prolonged life of the building and safety of the
occupant. To act more responsible and preemptive towards the dilapidated
buildings, the municipal corporation must issue notices to the buildings and
co-operative societies which are more than 30 years old to carry out mandatory
structural audit and submit the audit report. Structural audit should highlight
and investigate all critical areas and recommend immediate remedial and
preventive measures. It should cover the structural analysis of existing frame
and find critical elements for all types of loadings. It also helps in
delivering a strong building structure with cost effective solutions and
appropriate maintenance program. This paper deals with study of different
parameter of structural audit including visual inspection, non-destructive
testing, core sampling and testing. It also emphasizes on different repairs and
retrofitting measures to be used for buildings after structural audit.
Structural Audit :-
What
is Structural Audit?
Structural Audit is an overall health and
performance checkup of a building like a doctor examines a patient. It ensures
that the building and its premises are safe and have no risk. It analyses and
suggests appropriate repairs and retrofitting measures required for the
buildings to perform better in its service life. Structural audit is done by an
experienced and licensed structural consultant.
Purpose of Structural Audit
· To save human life and buildings
· To understand the condition of building
· To find critical areas to repair immediately
· To comply with statutory requirements
· To enhance life cycle of building by suggesting
preventive and corrective measures like repairs and retrofitting Structural
Audit of Buildings
Bye-Laws
As
per clause No.77 of revised Bye-Laws of Cooperative Housing Societies: “The
Society shall cause the ‘Structural Audit’ of the building as follows:
· For building aging between 15 to 30 years once in 5
years
· For building aging above 30 years Once in 3 years
Stages in Carrying Out Structural
Audit
1
Study of architectural and structural drawings, design criteria, design
calculations, structural stability certificate of existing structures
2
If architectural and structural drawings are not available, as built drawings
can be prepared by an engineer
3
Visual Inspection
3.1
Need of visual inspection
· to recognize the types of structural defects
· to identify any signs of material deterioration
· to identify any signs of structural distress and
deformation
· to identify any alteration and addition in the
structure, misuse which may result in overloading
Scope of visual inspection
The
inspection report should reveal the following listings along with photographs
and sketches.
General information of the building
· Name and address of the building
· Number of stories in each block of building
· Description of main usage of building viz.
Residential, commercial, institutional
· Maintenance history of the building
Structural System of the building
· Sub structure: Settlement of columns or
foundations, Settlement of walls and floors, Deflection and cracks in Retaining
wall, Soil bearing capacity through trial pits or from adjacent soil data
· Super structure: Materials used and framing system
of structure, identification of the critical structural members like floating
columns, transfer beams, slender members, rusting of exposed steel and its
extent.
· Mention the status of all building elements like
beams, slabs, columns, balconies, canopy, false ceiling, chajja, parapet and
railings with respect to parameters deflection, cracks, leakages and spalling
of concrete. A.B. Mahadik & M.H. Jaiswal
· Likewise, verify the status of water tank,
staircase, lift and lift machine room.
Addition or Alterations in the
building
· Identification of change of occupancy
· Alteration or addition of partition walls
· Alteration or addition in loadings- stacking
· Alteration or addition of toilets, water tank
· Alteration or addition of balcony
Dampness and leakages
· Detect the dampness in walls
· Identify the leakages in Terrace, toilets, plumbing
lines, drainage lines and overhead tanks.
Non Destructive and Destructive
Testing
In
addition to visual inspection, the real strength and quality of a concrete
structure need to be checked with non-destructive tests. A number of
non-destructive tests (NDT) for concrete members are available to determine
present strength and quality of concrete. Some of these tests are very useful
in assessment of damage to RCC structures subjected to corrosion, chemical
attack, fire and due to other reasons. These tests have been put under four
categories depending on the purpose of test as under.
Concrete Strength
· Rebound Hammer Test: To measure surface hardness of
concrete
· Ultrasonic Pulse Velocity Test: To assess
homogeneity of concrete, to assess strength of concrete qualitatively, to
determine structural integrity
· Core Sampling and Testing: To measure strength,
permeability, density of concrete.
Chemical Attack
· Carbonation Test: To assess depth of carbonation
and pH of concrete
· Chloride Test: To assess total water/acid soluble
chloride contents
· Sulphate Test: To assess total water/water soluble
sulphate contents of concrete
Corrosion Potential Assessment
· Cover Meter: To measure cover of reinforcement,
diameter of reinforcement and spacing of reinforcement
· Half Cell Method: To assess probability of
corrosion in the embedded steel
· Permeability Test: To assess permeability of
concrete due to water and air Structural Audit of Buildings
Homogeneity and integrity
Assessment
· Ultrasonic pulse velocity for determination of
cracks and discontinuities
Core Testing
This
is direct method of assessing strength of concrete. In this method cylindrical
core samples are taken from existing structures. The cores are visually
inspected and tested in laboratory to check its compressive strength.
Pushover Analysis
Generally
Push over analysis is used to understand the existing capacity of structure for
seismic and gravity loading which will show different occupancy levels like
immediate occupancy, life safety and collapse prevention. The seismic
evaluation of existing buildings compares their capacity against earthquake
demand at specific site and concerns the potential earthquake-caused risk to
building systems and elements that are closely related to human life safety.
Identification of critical areas in
building
Based
on the above inspection, analysis and test results, the report should conclude
the critical areas that need immediate repairs and retrofitting. For example:
number of columns requiring immediate repair and strengthening, repair of
critical slab and beams, water proofing of terrace, toilet blocks, cracks in
walls or structural elements etc.
Post Structural Audit
Repairs
Based
on the audit findings and recommendations different measures of repairs and
strengthening are carried out. According to ACI 546R-04, to repair is to
replace or correct deteriorated, damaged, or faulty materials, components, or
elements of a structural system. From this point of view, repair may be divided
into structural repair and serviceability repair. The former refers to the
restoration of lost sectional or monolithic properties of damaged members,
while the later refers to the restoration of structural surfaces to a
satisfactory operational standard.
Obviously, poor design, poor construction, poor
maintenance, incorrect usage, new environmental influences or an intended
increase of the loading or extension of the structure’s lifespan can make repair
and/or strengthening necessary.
Excluding technical considerations, the ultimate
choice of method of repair and strengthening of a concrete structure may also
be influenced by factors like overall quality of repairs and the size of
individual repairs, access for repair, relative cost, ease of application,
available labor skills and equipment and client requirements including future
maintenance and economic considerations
Strengthening and Retrofitting
Strengthening is the process of restoring the
capacity of damaged components of structural concrete to its original design
capacity, or increasing the strength of structural concrete. Strengthening of a
concrete structure may be required due to several reasons:
· Change of usage which may cause over-stress in the
structural member.
· Serious materials and structural deteriorations
which cause structural members to be no longer able to carry the imposed loads
with an adequate factor of safety
· To increase the capacity for seismic resistance if
the building is not designed for it or the structure does not fulfill current
design requirement corresponding to seismic zones, R factor or so.
Strengthening of structural members can be achieved
by replacing poor quality or defective material with better quality material,
by attaching additional load-bearing material, such as high quality concrete,
additional steel, thin steel plates, various types of fiber reinforced polymer
sheets, and so on, and by the redistribution of the load such as by adding a
steel supporting system. The purpose of strengthening is to increase the
load-carrying capacity or stability of a structure with respect to its previous
condition.
Preparation of Budget
1.
Circulation of format and orders by Director (Finance), CPWD to field
formations,
2.
Divisional heads fill the format online and submit to Circle office
3.
Circle office scrutinize and take the approval of Chief Engineer and forwards
the same to Director (Finance),
4.
Director (Finance) finalizes the Budget in consultation with Financial Advisor,
Mohua and submits to Mohua for inclusion in total demands of Mohua.
Addition of New Instruments of
Services/ Works in the mid of Financial Year
1.
Circulation of format and orders by Director (Finance), CPWD to field
formations for demand of NS/ NIS/ New Works for inclusion in the PINK BOOK,
2.
Concern Chief Engineer prepares the item and forwards the same to Director
(Finance) with fund requirement plan,
3.
Director (Finance) finalizes the item in consultation with Financial Advisor, Mohua
and submits to MoHUA for inclusion of item in work annexure and fund demands of
Mohua. This may require to get supplementary demands approved by the Parliament
Submission of PE/ RE for grant of
A/A and E/S for Capital Works of GPRA/ GPOA Scheme funded through Mohua Grant
1.
PE is prepared by Division and submitted to DDG (Works)/ ADG (TD), CPWD in
prescribed format.
2.
After technical scrutiny it is forwarded to Director (Finance), CPWD for
Financial Scrutiny and observations on all technical matters which have
financial implications or as per guidelines of the Ministry.
3.
If estimate is below Rs. 5.0 Cr concurrence of Director (Fin) and approval of
DG, CPWD is sufficient,
4.
If estimate is above Rs. 5.0 cr and below Rs. 20.0 Cr concurrence of IFD, Mohua
through Director (Fin) would be obtained and approval of DG, CPWD is
sufficient,
5.
If estimate is above Rs. 20.0 cr concurrence of IFD, Mohua through Director
(Fin) would be necessary and approval of competent authority i.e. Secretary
(HUA)/ Honourable Minister HUA/ EFC/ SFC/ DIB would be required.
Re-appropriation proposal in CPWD
under Rules prescribed in DFPR
1.
Demands of additional budget or NIS/ NS is submitted by Chief Engineer to
Director (Finance), CPWD,
2.
Director Finance will examine the demands, if it can be funded directly or need
Re-appropriation.
3.
Director Finance will examine the demand if it can be funded by
re-appropriation within Ministry or it needs Mof approval or it needs to be
converted into Supplementary Demands,
4.
As per requirement Re-appropriation/ supplementary demands are prepared by
Director (Finance) and submitted to DG, CPWD for approval and onward submission
to Mohua.
5.
Financial Advisor, Mohua finalizes the demands and with the approval of
Secretary HUA it is submitted to Mof for inclusion in total demands of Mohua.
6.
After approval of Re-appropriation or supplementary funds will be provided to
the field formation by Director (Finance).
Conclusion
The structural diagnosis is vast, important and
highly responsible job which is connected with lives of human beings. It is
mandatory and advisable to carry out the periodical structural audit of the
buildings by professional experts and act immediately through recommendations
provided in audit report. The success of repairs and restoration is always
based on thorough knowledge, correct diagnosis and in-depth studies of problems
in building, proper repair practices and finally socio-economic considerations.
The effective implementation of auditing enhances the life span of structure,
prevents deterioration of building leading to sustainability.
References
[1]
M. J. Monteiro and N. J. Pathak (2011), Article in International Journal of
Earth Sciences and Engineering, ISSN 0974-5904,
[2]
Volume 04, No 06 SPL, October 2011, pp. 677-680.
[3]
J. J. Shah (2008), Article in The Indian Concrete Journal, pp. 17-26.
[4]
Indian Standard: 13311:1992 (Part 1) NDT methods of Test- Ultrasonic Pulse
Velocity.
[5]
Indian Standard: 13311:1992 (Part 2) NDT methods of Test- Rebound Hammer.
[6]
ACI 546R-04 – Concrete repair guide.
[7]
ACI 562-12 - Code Requirements for Evaluation, Repair, and Rehabilitation of
Concrete Buildings.
[8]
Indian Standard: 456: 2000- Plain and Reinforced Concrete – Code of Practice
(Fourth Revision).
[9]
Indian Standard: 516: 1959- Method of test for strength of concrete.
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