Nishant Rai
B. Tech. Civil Engineering.
M.Tech. Foundation Engineering
Ph.D. Structural Dynamics
Address: Hyderabad, Telangana, India
M.Tech. Foundation Engineering
Ph.D. Structural Dynamics
Address: Hyderabad, Telangana, India
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Papers by Nishant Rai
Constructions of such facilities are different from conventional buildings due to its environmental, health, commercial and strategic importance. Such constructions involve micrometer level accuracy and almost zero tolerances. These issues are to be addressed in totality covering planning, material selection, construction methodology with a focus on final utility.
Leak tight, corrosion free with minimal contamination probability construction of radio active zones is an area of concern, for which special lining methodology and site specific quality assurance measures have to be developed and adopted. Construction of hot cell and radio-activity related areas are a key activity in such facilities. The main construction material, in normal structures, is reinforced concrete and the same has to be utilised for making technology affordable. The needs for accurately positioning many special embedded parts and through pipes at various locations, with adequate radiation shielding provisions are challenges to be addressed.
The construction methodologies, techniques, special formwork systems etc. need special attention. The site specific measures and innovations to cope up the challenges encountered such as heat of hydration during concreting, and void-less dense concrete around fixtures also merit attention. The strict quality control measures adopted for a fail safe construction output and after construction serviceability of utility is of vital importance.
This paper briefly describes a recently constructed project in the light of prevailing guidelines for such structures. Planning, safety, quality and construction methodologies and innovations used at site with reference to better adoptability of the project has also been highlighted.
Water for domestic consumption is an essential right of society, which must be over-secured. However cost of such water infra-structure can be optimally reduced by combining it with other infrastructure projects.
Water for achieving food security, is another major concern. This goal may be achieved through an alternative methodology. It in-volves re-grading of cultivation fields and creating a formation to retain major part of monsoon rainfall in the field itself. This will make availability of captive water to the farmer for longer duration resulting in increased farm utilization and crop yield.
This paper tries to substantiate the above mentioned points with the help of statistical data and mathematical calculations for three agro-climatic zones - Madhya Pradesh, Vidarbha, and Gujarat. A solution for Water problem of Delhi has also been suggested.
frequency harmonic excitation and earthquake excitation. An execution scheme of MTSWD retrofitting system for ES has also been proposed.
The central to the TSWD based retrofitting, of RC frame masonry infilled structures, is to reduce the displacement of the ES and avoidance of masonry failure during earthquake. The concept has been explained by example of an existing four story residential building. The structure has been discretised for three structural contribution conditions of masonry, i.e full contribution, no contribution and intermediate state where some part of masonry is contributing as diagonal compressive struts. The retrofitting propositions for all these three conditions have been made, analytically, with TSWD systems. It has been explained that for well-defined system subjected to harmonic excitations single frequency TSWDs (STSWD) may be optimally devised. For approximately assessed systems subjected to broad band excitations multiple frequency TSWDs (MTSWD) systems more robust.
The existing procedure for design of retrofitting system is iterative and cumbersome due to involvement of many approximately assessed parameters. Design charts for effectiveness of retrofitting system have been developed to obtain a quick estimate of mass ratio required for desired response reduction. Two simplified non-iterative methods have been developed one for accurately assessed and another for approximately assessed structures. These methods give a quick estimate of required mass ratio for desired performance.
The analytically made retrofitting propositions have been verified experimentally through the shake table tests on scaled model of the ES in coupling with TSWDs. The main feature of the experimental study is that ES has been scaled down dimensionally such that SM≡ES, but dynamic parameters of the structure have not been scaled and SM is equal to ES. The TSWD, tested with SMs in laboratory, is proposed for actual field execution.
The process of experimental validations of SM-TSWD interaction has been accomplished through 157 test runs. The interpretation of these experimental observations has led to simplified empirical correlations between relevant dynamic parameters of TSWD and ES. These empirical relations are valid for harmonic excitations only. However for broad band earthquake excitation the analytically devised propositions are only trend indicative and not valid. The robustness of the MTSWD system over STSWD system against earthquake excitations has been substantiated. An adequate factor of safety may be incorporated for applying the inferences from harmonic excitations to broad band excitations for MTSWD based retrofitting system. This study proposes a factor of safety 3.
Two non-dimensional parameters, as effectiveness ratio quantifying percentage response reduction and specific mass ratio defined as mass ratio required for one percentage effectiveness of the retrofitting system, for evaluating the performance of TSWD based retrofitting system have been introduced.
Since the analytical proposals are not valid for broad band excitations, it is proposed that for real life situations, the TSWD based retrofitting systems, should be designed on the basis of experimental evidence. A Hardware interactive soft path methodology for design of TSWD retrofitting system has been devised. As there is no scaling of dynamic properties between SM and ES and the TSWD used in coupling with SM has to be installed at ES, hence the experimental inferences of SM-TSWD coupling can be extrapolated to retrofitting of the ES, as ES-TSWD coupling. Thus a TSWD based retrofitting system may be designed for desired response reduction of ES.
The required sloshing water mass is to be accommodated in multiple TSWDs with their frequencies distributed around the frequency of ES. The system as a whole behaves as a robust multiple TSWD retrofitting regime with assurance of replicating laboratory performance in real life seismic eventuality.
From experimental observations for 25% effectiveness of TSWD system against broad band excitation the required mass ratio is 2.59% for SM and same is valid for ES also, accordingly an execution scheme has been proposed.
This research presents a simple and non-invasive retrofit scheme utilising tuned sloshing water dampers in RC frame masonry infilled structures. The design approach utilises the theoretical knowledge in conjunction with experimental verifications for TSWD based retrofitting system. The retrofitting with TSWDs may be accomplished by modifying the existing overhead tank and installing additional tanks of optimally tuned geometry for desired response reduction. The installation of TSWD based retrofitting system provides all time preparedness against earthquake, without interfering with the structural, architectural and occupancy requirements. The proposed TSWD based retrofitting system essentially a technique of absorbing seismic energy through sloshing action of water.
retrofitting measure for the existing structures (ES).The water tanks of designed geometry rigidly attached with the
ES at strategic locations behave as TSWD. Response reduction during earthquake is affected by energy dissipated
through sloshing of water mass.
The energy dissipation is dependent on mutual tuning of ES and TSWD, mass ratio, damping ratio of
TSWD and damping ratio of ES. Larger the mass ratio more will be the response reduction. Mutual dependency and
uncertainties involved with the assessment of dynamic properties of ES make the design process of retrofitting
system iterative and cumbersome.
Multiple dampers, with their frequencies distributed around the first mode frequency of ES, shall perform
more robustly. The desired mass ratio may be accommodated in multiple tanks. The geometry of these tanks may be
moderated in such a way that it behaves as multiple dampers. The multiple TSWD system will overcome the errors
due to assessment approximations of dynamic properties of ES and TSWD.
The performance of the retrofitting system is assessed by reduction in maximum structural displacement
affected. Design charts in the form of effectiveness ratio, depicting the performance of TSWDs, have been presented
which reduces iterative computational effort. The retrofitting methodology is explained by example of an existing
four story structure. The effectiveness and robust performance of multiple TSWD has been demonstrated. The
method ensures all time preparedness of the ES, without occupancy and structural interference, against earthquake.
construction practices along with affordability.
In Indian reference the housing problem has been compounded by the fact that 59% area of our country is
disaster prone, to one or other kind of natural calamity. Of all the natural calamities earth quake does not give
any reaction time what so ever for hazard avoidance and mitigation. The suddenness makes earth quake most
feared natural disaster.
Settlements housing weaker sections of society are more vulnerable to such disasters as their houses are
poorly engineered and constructed with locally available material and technology, having very low score on
disaster resistance and sustainability count. A general feature of low cost housing concepts is maximum
replacement of cement and steel with locally available materials and vernacular technology. Avoidance of steel
and concrete increases the construction mass which increases the amount of seismic impact on such structures.
In Indian socio-economic context, low cost housing proposals do not get acceptability with common man, due to
lack of durability.
In the present paper a pre-engineered pre-cast design for rural mass housing, utilising most versatile and
durable building materials, concrete and steel as main constituent is proposed. This is less massive but
technology and labour intensive. The design and construction methodology adopted, results in light and quick
construction.
The proposed design incorporates base isolation through horizontal decoupling and seismic energy
dissipation through friction, flexibility. A collapse proof failure mode has been devised, which can avoid loss of
life and property. This design may be used with great advantage in aftermath of a seismic calamity, when after
shocks are still being experienced, by virtue of being light, quick to construct, disaster resistant, and
economical. The design is superior on sustainability parameters also.
under earthquake loading by structural response control methodology, with tuned sloshing water
damper (TSWD). The retrofitting may be accomplished by modifying the existing over head tank
and installing additional tanks of tuned geometry for required response reduction.
The required water mass is provided in multiple TSWDs with their frequencies distributed
around the frequency of ES. The system as a whole behaves as multiple TSWD retrofitting regime
with robustness and reliability. This system takes care of the assessment approximations in dynamic
properties of the ES.
The retrofitting method aims for reduced displacement during earthquake. The efficiency of the
retrofitting system may be quantified by effectiveness ratio. Design charts have been developed
which reduces iterative computational efforts.
The simplicity of design and execution of the proposed retrofitting regime is explained by
example of an existing four story structure.
have little resistance for lateral loads caused by earthquake and wind. Even for adequately designed structures
also, due to permissible deformation beyond elastic limits, failure of masonry causes severe loss of life and
property. In the case of structures designed to sustain excessive deformation such as of defence establishments,
functioning and serviceability of machines and equipment installed therein are adversely affected. This co-lateral
damage may be reduced by adopting another design philosophy of structure response control. In this methodology,
a supplementary damping device is incorporated in the primary structure, which absorbs most of the seismic
energy imparted to it, restricting the structural response within serviceable limits. These devices may be passive,
active, semi-active or hybrid types. Other than passive all options are technology-intensive and dependent on
external energy source, not a favourable proposition for developing nations. Among all the passive devices, tuned
liquid dampers (TLDs) promise to be most suitable. Here, existing overhead water tanks (OHWT) may be used
as TLD with slight adjustment and modification. This method will be able to control the structural response
without putting any extra load on the existing or newly-designed buildings. This paper reviews various types of
dampers and discusses evolution of tuned liquid dampers. A method has also been proposed for incorporating
TLDs in existing and new structures. This methodology may be very useful for structures of defence establishment
which are scattered and remotely placed by location, housing important equipments sensitive to vibrations, as it
is free from external power dependence and regular maintenance.
Constructions of such facilities are different from conventional buildings due to its environmental, health, commercial and strategic importance. Such constructions involve micrometer level accuracy and almost zero tolerances. These issues are to be addressed in totality covering planning, material selection, construction methodology with a focus on final utility.
Leak tight, corrosion free with minimal contamination probability construction of radio active zones is an area of concern, for which special lining methodology and site specific quality assurance measures have to be developed and adopted. Construction of hot cell and radio-activity related areas are a key activity in such facilities. The main construction material, in normal structures, is reinforced concrete and the same has to be utilised for making technology affordable. The needs for accurately positioning many special embedded parts and through pipes at various locations, with adequate radiation shielding provisions are challenges to be addressed.
The construction methodologies, techniques, special formwork systems etc. need special attention. The site specific measures and innovations to cope up the challenges encountered such as heat of hydration during concreting, and void-less dense concrete around fixtures also merit attention. The strict quality control measures adopted for a fail safe construction output and after construction serviceability of utility is of vital importance.
This paper briefly describes a recently constructed project in the light of prevailing guidelines for such structures. Planning, safety, quality and construction methodologies and innovations used at site with reference to better adoptability of the project has also been highlighted.
Water for domestic consumption is an essential right of society, which must be over-secured. However cost of such water infra-structure can be optimally reduced by combining it with other infrastructure projects.
Water for achieving food security, is another major concern. This goal may be achieved through an alternative methodology. It in-volves re-grading of cultivation fields and creating a formation to retain major part of monsoon rainfall in the field itself. This will make availability of captive water to the farmer for longer duration resulting in increased farm utilization and crop yield.
This paper tries to substantiate the above mentioned points with the help of statistical data and mathematical calculations for three agro-climatic zones - Madhya Pradesh, Vidarbha, and Gujarat. A solution for Water problem of Delhi has also been suggested.
frequency harmonic excitation and earthquake excitation. An execution scheme of MTSWD retrofitting system for ES has also been proposed.
The central to the TSWD based retrofitting, of RC frame masonry infilled structures, is to reduce the displacement of the ES and avoidance of masonry failure during earthquake. The concept has been explained by example of an existing four story residential building. The structure has been discretised for three structural contribution conditions of masonry, i.e full contribution, no contribution and intermediate state where some part of masonry is contributing as diagonal compressive struts. The retrofitting propositions for all these three conditions have been made, analytically, with TSWD systems. It has been explained that for well-defined system subjected to harmonic excitations single frequency TSWDs (STSWD) may be optimally devised. For approximately assessed systems subjected to broad band excitations multiple frequency TSWDs (MTSWD) systems more robust.
The existing procedure for design of retrofitting system is iterative and cumbersome due to involvement of many approximately assessed parameters. Design charts for effectiveness of retrofitting system have been developed to obtain a quick estimate of mass ratio required for desired response reduction. Two simplified non-iterative methods have been developed one for accurately assessed and another for approximately assessed structures. These methods give a quick estimate of required mass ratio for desired performance.
The analytically made retrofitting propositions have been verified experimentally through the shake table tests on scaled model of the ES in coupling with TSWDs. The main feature of the experimental study is that ES has been scaled down dimensionally such that SM≡ES, but dynamic parameters of the structure have not been scaled and SM is equal to ES. The TSWD, tested with SMs in laboratory, is proposed for actual field execution.
The process of experimental validations of SM-TSWD interaction has been accomplished through 157 test runs. The interpretation of these experimental observations has led to simplified empirical correlations between relevant dynamic parameters of TSWD and ES. These empirical relations are valid for harmonic excitations only. However for broad band earthquake excitation the analytically devised propositions are only trend indicative and not valid. The robustness of the MTSWD system over STSWD system against earthquake excitations has been substantiated. An adequate factor of safety may be incorporated for applying the inferences from harmonic excitations to broad band excitations for MTSWD based retrofitting system. This study proposes a factor of safety 3.
Two non-dimensional parameters, as effectiveness ratio quantifying percentage response reduction and specific mass ratio defined as mass ratio required for one percentage effectiveness of the retrofitting system, for evaluating the performance of TSWD based retrofitting system have been introduced.
Since the analytical proposals are not valid for broad band excitations, it is proposed that for real life situations, the TSWD based retrofitting systems, should be designed on the basis of experimental evidence. A Hardware interactive soft path methodology for design of TSWD retrofitting system has been devised. As there is no scaling of dynamic properties between SM and ES and the TSWD used in coupling with SM has to be installed at ES, hence the experimental inferences of SM-TSWD coupling can be extrapolated to retrofitting of the ES, as ES-TSWD coupling. Thus a TSWD based retrofitting system may be designed for desired response reduction of ES.
The required sloshing water mass is to be accommodated in multiple TSWDs with their frequencies distributed around the frequency of ES. The system as a whole behaves as a robust multiple TSWD retrofitting regime with assurance of replicating laboratory performance in real life seismic eventuality.
From experimental observations for 25% effectiveness of TSWD system against broad band excitation the required mass ratio is 2.59% for SM and same is valid for ES also, accordingly an execution scheme has been proposed.
This research presents a simple and non-invasive retrofit scheme utilising tuned sloshing water dampers in RC frame masonry infilled structures. The design approach utilises the theoretical knowledge in conjunction with experimental verifications for TSWD based retrofitting system. The retrofitting with TSWDs may be accomplished by modifying the existing overhead tank and installing additional tanks of optimally tuned geometry for desired response reduction. The installation of TSWD based retrofitting system provides all time preparedness against earthquake, without interfering with the structural, architectural and occupancy requirements. The proposed TSWD based retrofitting system essentially a technique of absorbing seismic energy through sloshing action of water.
retrofitting measure for the existing structures (ES).The water tanks of designed geometry rigidly attached with the
ES at strategic locations behave as TSWD. Response reduction during earthquake is affected by energy dissipated
through sloshing of water mass.
The energy dissipation is dependent on mutual tuning of ES and TSWD, mass ratio, damping ratio of
TSWD and damping ratio of ES. Larger the mass ratio more will be the response reduction. Mutual dependency and
uncertainties involved with the assessment of dynamic properties of ES make the design process of retrofitting
system iterative and cumbersome.
Multiple dampers, with their frequencies distributed around the first mode frequency of ES, shall perform
more robustly. The desired mass ratio may be accommodated in multiple tanks. The geometry of these tanks may be
moderated in such a way that it behaves as multiple dampers. The multiple TSWD system will overcome the errors
due to assessment approximations of dynamic properties of ES and TSWD.
The performance of the retrofitting system is assessed by reduction in maximum structural displacement
affected. Design charts in the form of effectiveness ratio, depicting the performance of TSWDs, have been presented
which reduces iterative computational effort. The retrofitting methodology is explained by example of an existing
four story structure. The effectiveness and robust performance of multiple TSWD has been demonstrated. The
method ensures all time preparedness of the ES, without occupancy and structural interference, against earthquake.
construction practices along with affordability.
In Indian reference the housing problem has been compounded by the fact that 59% area of our country is
disaster prone, to one or other kind of natural calamity. Of all the natural calamities earth quake does not give
any reaction time what so ever for hazard avoidance and mitigation. The suddenness makes earth quake most
feared natural disaster.
Settlements housing weaker sections of society are more vulnerable to such disasters as their houses are
poorly engineered and constructed with locally available material and technology, having very low score on
disaster resistance and sustainability count. A general feature of low cost housing concepts is maximum
replacement of cement and steel with locally available materials and vernacular technology. Avoidance of steel
and concrete increases the construction mass which increases the amount of seismic impact on such structures.
In Indian socio-economic context, low cost housing proposals do not get acceptability with common man, due to
lack of durability.
In the present paper a pre-engineered pre-cast design for rural mass housing, utilising most versatile and
durable building materials, concrete and steel as main constituent is proposed. This is less massive but
technology and labour intensive. The design and construction methodology adopted, results in light and quick
construction.
The proposed design incorporates base isolation through horizontal decoupling and seismic energy
dissipation through friction, flexibility. A collapse proof failure mode has been devised, which can avoid loss of
life and property. This design may be used with great advantage in aftermath of a seismic calamity, when after
shocks are still being experienced, by virtue of being light, quick to construct, disaster resistant, and
economical. The design is superior on sustainability parameters also.
under earthquake loading by structural response control methodology, with tuned sloshing water
damper (TSWD). The retrofitting may be accomplished by modifying the existing over head tank
and installing additional tanks of tuned geometry for required response reduction.
The required water mass is provided in multiple TSWDs with their frequencies distributed
around the frequency of ES. The system as a whole behaves as multiple TSWD retrofitting regime
with robustness and reliability. This system takes care of the assessment approximations in dynamic
properties of the ES.
The retrofitting method aims for reduced displacement during earthquake. The efficiency of the
retrofitting system may be quantified by effectiveness ratio. Design charts have been developed
which reduces iterative computational efforts.
The simplicity of design and execution of the proposed retrofitting regime is explained by
example of an existing four story structure.
have little resistance for lateral loads caused by earthquake and wind. Even for adequately designed structures
also, due to permissible deformation beyond elastic limits, failure of masonry causes severe loss of life and
property. In the case of structures designed to sustain excessive deformation such as of defence establishments,
functioning and serviceability of machines and equipment installed therein are adversely affected. This co-lateral
damage may be reduced by adopting another design philosophy of structure response control. In this methodology,
a supplementary damping device is incorporated in the primary structure, which absorbs most of the seismic
energy imparted to it, restricting the structural response within serviceable limits. These devices may be passive,
active, semi-active or hybrid types. Other than passive all options are technology-intensive and dependent on
external energy source, not a favourable proposition for developing nations. Among all the passive devices, tuned
liquid dampers (TLDs) promise to be most suitable. Here, existing overhead water tanks (OHWT) may be used
as TLD with slight adjustment and modification. This method will be able to control the structural response
without putting any extra load on the existing or newly-designed buildings. This paper reviews various types of
dampers and discusses evolution of tuned liquid dampers. A method has also been proposed for incorporating
TLDs in existing and new structures. This methodology may be very useful for structures of defence establishment
which are scattered and remotely placed by location, housing important equipments sensitive to vibrations, as it
is free from external power dependence and regular maintenance.