Lakshmikandhan Pkn - Academia.edu (original) (raw)

Papers by Lakshmikandhan Pkn

Rectangular RC beams were tested before and after retrofitting by external Prestressing. RC beams... more Rectangular RC beams were tested before and after retrofitting by external Prestressing. RC beams of 150 mm x 275 mm section and 4 m length were subjected to monotonically increasing static two-point load and the cracks were induced to a limit such that the strain in reinforcing steel was around 85 % of the yield strain. Retrofitting by external Prestressing using trapezoidal tendons was done while the member was subjected to superimposed dead weight of a bridge girder, equivalent to 25 % of the ultimate load of the beam. Retrofitted beams were tested by monotonically increasing two-point load. It was observed that ultimate flexural capacity of the beam is increased by 59 %. Around 10 % of loss was observed due to the friction between tendon and deviators. An analytical model is developed and compared with experimental results.

Precast segmental construction technique integrates all the advantages of prestressing, precast c... more Precast segmental construction technique integrates all the advantages of prestressing, precast concrete and external
prestressing. It is widely practised for longer spans with straight or curved alignments and facilitate fast and flexible construction
with high quality and economy. The segments of segmental beam are intact and behave as a monolithic one and maintain the
structure in concrete compression state within the serviceability limit. In this study, the response of an externally prestressed
segmental prestressed box beams with flat, dry joints subjected to two-point loading is analytically calculated using existing
formulas and numerically investigated using a popular software. The numerical simulation satisfactorily predicts the behaviour
of the segmental beam up to ultimate. The effectiveness and accuracy of the contact elements in transferring forces between
the jointed segments of the beam was proved to be more accurate. The results can be used for structural design of precast
segmental bridge.

— Reinforced concrete shells and folded plates are the structural systems, widely used to cover t... more — Reinforced concrete shells and folded plates are the structural systems, widely used to cover the small to large area with more aesthetics at minimum cost. Shell structures are stressed skin structures, has unique character in which the curved shape of the shell carries load rather than material strength. Funicular shells are special type of shells for both flooring and roofing systems. The efficiency of funicular shell is mainly due to its shape which formed from both positive (synclastic) and Negative (anticlastic) curvatures. Funicular shells are mainly subject to compression and concrete is most appropriate material for construction. Concrete has the flexibility to form into any shape and size which permits to explore numerous alternatives to arrive efficient funicular shell geometry. In view of above, Present work aimed to investigates funicular shells of different spans with varying rises and thickness. The grid beams are generally used for supporting funicular shells which increase the cost. The present study also proposed to explore the applicability of funicular shells for one-way slab action to avoid the two-way grid beam. The shell spans between 1 m and 3 m with different span to rise ratio between 5 and 40 are investigated analytically. Both material and geometrical nonlinearities were considered in the finite element analysis of concrete shells and the results are comparable with the experimental results. The results indicate that the span to rise ratio between 5 and 12.5 has better performance. The result also infers that the reinforcements are not required at the shell surface. The reduction in shell thickness is more advantageous in lifting handling and placing of precast shells and present investigation showcased about 30% of weight reduction of shell. Further, the funicular shells performed better in one-way action and the results concludes that the funicular shells are favorable for one-way slab action to avoid two-way grid beams.

With the recent developments in the non-destructive testing methods, the possibility to assess th... more With the recent developments in the non-destructive testing methods, the possibility to assess the changes in material characteristics caused by the addition of admixtures, influence of temperature, and other parameters are gaining significance. Towards this, the present work focuses on using the resonance test method for the experimental investigation. In the case of transient dynamic analysis which involves vibrations at higher frequencies, the understanding obtained from finite element simulations is relatively higher to that gained by conducting experiments. Hence, the present work mainly aims to analytically model the concrete specimens as it matures during the first 28 days after concreting. Towards this, the modelling of the specimens and the adaptation of the appropriate boundary conditions to simulate the resonance test method becomes significant. The results of the experimental and finite element analysis are compared and found to be in good agreement.

Non-destructive evaluation is an area of focussed research around the world. Through non-destruct... more Non-destructive evaluation is an area of focussed research around the world. Through non-destructive evaluation it is aimed at evaluating the integrity of concrete and identify the location of defects like voids and honeycombs. While most of these methods rely on wave propagation, the infrared thermography technique uses heat conduction principles to identify defects at shallow depth. The infrared thermography technique is a non-contact non-destructive testing technique which makes it possible to evaluate the test medium independent of its surface characteristics. Also, the ability of the infrared thermography camera to capture and assess a surface area at every time instant makes it an interesting technique to pursue research on. In the present work, it is proposed to examine the possibility of defect identification using the infrared thermography technique by employing the finite element analysis. For this study, two case studies have been carried out. For the analysis a standard commercial FEM package has been used and the heat transfer analysis is carried out using ten node tetrahedron elements by incorporating the thermal properties. Heat is applied from one surface and the evaluation is carried out from the same surface. Encouraging results have been obtained on the application of the thermography method. In the present study, it has been observed that the thermography method could be effectively applied for large defect identification up to a depth of 90mm from the investigating surface.

The population growth and urbanization have resulted in demand for shelters and construction mate... more The population growth and urbanization have resulted in demand for shelters and construction materials. There is equal challenge to develop new techniques and technologies to cope up with the demand. Further the natural and manmade disasters are the huge threat in current scenario which needs development of structural components or system to manage the post disaster requirements such as speedy and mass construction of buildings. The advancement in research made wider alternatives with many options to overcome these demands. In view of this, the present investigation aims at developing affordable technologies, particularly for the rural and poor urban population. The novel light weight ferrocement wall panel with required stiffness and strength is investigated. This technology reduces the usage of conventional building materials and overall structural weight and cost. The wall panel is proposed with ferrocement skin with appropriate ribs to achieve the structural adequacy and constructability. The analytical parametric study is carried out using the nonlinear finite element analysis. The material nonlinearity is modeled using damaged plasticity model. The ferrocement panels of various sizes with window opening and with door opening are examined. The analytical study showed that the ferrocement panel with proposed ribs performs well. Further a 25 mm thick ferrocement wall panel with 1m width and 2m height is experimentally investigated and the results were compared. The conventional method of precasting of ferrocement panel is long, tedious and labour intensive construction methods in practice. To make it simple and cost effective, the single vertical casting is proposed using self-compacting concrete. Several mix trails were carried out and the suitable mix is obtained. The supporting systems and mould were developed to cast the wall panel within a few minutes. The panel is found to be more uniform and better quality. The panel is tested for in-plane compression loading. The strain and deflections were measured and plotted for comparison. Both the analytical and experimental results are found comparable. The present study found that the novel ferrocement wall panel is more appropriate for the light weight and affordable building construction.

The steel space frame structures are popular in covering the large areas with or without intermit... more The steel space frame structures are popular in covering the large areas with or without intermittent supports. Steel space structures are more advantageous in lower weight to usage ratio. The space structures are frequently reported for their catastrophic nature of failure. The catastrophic failure is generally initiated from one or few critical compression chord member nearer to truss support. The initial stresses developed in the space structure due to the uncertainties causes the over stressing of members. The space structures have about 25% of indeterminate members which redistribute these initial stresses and generate the secondary effects. All these are finally affects the critical compression member behaviour and leads to catastrophic failure. This catastrophic nature of failure should necessarily be reduced by altering member force of members at specific location by using new technological advents. In the present study, numerous papers were reviewed and presented a better review on the active and passive control mechanisms, which are investigated to improve the performance of space structure. The present study aimed to make use of this member imperfection to improve the space truss capacity. A novel double sleeve system is developed to alter the member force of critical compression member using lack of fit concept. This performs as a passive force control device by manually adjusted member post-stress developing system. The passive control device changes the member length and introduces the prestressing force. Three numbers of three-bar space truss system and one four-bar space truss structure are investigated experimentally and verified analytically. The study showed evidence for altering about 20 to 25 percent of compression force in the critical compression member. Also, the experimental study showed its efficiency in shifting the brittle compression member failure to ductile tension member failure.

Concrete is strong in compression but weak in tension. Reinforced concrete, in which steel rods a... more Concrete is strong in compression but weak in tension. Reinforced concrete, in which steel rods are provided to resist tensile stresses, however, does not meet the satisfactory structural demands. The concept of prestressing was introduced to generate compressive stresses in concrete prior to loading, by means of prestressing tendons inserted in the member. These compressive stresses resist the tensile forces, thereby effectively increasing the tensile strength of the concrete member. In this study, reinforced and pre-tensioned concrete beams are analysed for their nonlinear behaviour under external loading using the finite element method of analysis. ANSYS 12.0, an efficient finite element software package, is used for the analysis of the concrete members. Load-deflection responses, variations of stresses in concrete and steel and the crack patterns at critical stages of loading are studied. The numerical predictions are compared to the data obtained using the theories of structural analysis. In comparison to the theoretically predicted data, the numerical method of analysis using ANSYS was seen to satisfactorily predict the behavioural responses of the beams up to ultimate, but was not as effective in predicting the strain variation in the prestressing tendons.

The space structures are popular and well accepted in the steel construction industry for many st... more The space structures are popular and well accepted in the steel construction industry for many structural applications
and also compete successfully with conventional structures. The space structures offer an effective solution to cover
the large open areas with or without any intermediate supports. Earlier research on space structures has identified
the tendency to collapse in a catastrophic brittle manner, caused by the successive buckling of a series of critical
compression members. The present study deals with an attempt to alter the brittle characteristics of truss top chord
members by introducing concrete slab, which acts compositely with the truss. The truss top chord members and
concrete slab are interconnected with shear connectors, which improve the behaviour of the compression members and
the overall space truss behaviour. An analytical study based on the finite element method is carried out on composite
and non-composite space frames and the details of the study are presented in the paper. Further the results obtained
from the grouping of the truss members are compared with the results obtained from the truss optimization.

The repair and rehabilitation of concrete structures has become a necessary measure for deficient... more The repair and rehabilitation of concrete structures has become a necessary measure for deficient structures. The deficiency of structure is generally due to the unexpected loads, corrosion and upgradation of load standards. Concrete structures are generally subjected to very light to severe damage due to seismic and wind loads. The visual damages can be comfortably observed during visual inspection, but the damages occurred internally needs examination through experimental and/or analytical investigation. These methods also have their own limitations. The present study was carried out to arrive at the percentage of damage in reinforced concrete beam from its stiffness degradation. A repair mechanism for concrete beam with a particular percentage of damage has been attempted. CFRP which is a well accepted and efficient material for repair and rehabilitation is used in this study. The reinforced concrete beam has been tested and the performance under cyclic load has been observed. The stiffness degradation in each cycle has been observed for an equivalent damage assessment. The information on damage level from the results is used to predict the loading required to simulate the required percentage of damage. A guideline for simulation of required percentage damage has been arrived. In a set of experiments, beams were subjected to different levels of loading to create varying percentage damage and then the damaged beams were repaired with CFRP. The undamaged control beam has been strengthened with CFRP laminates and the repaired/strengthened beams were tested under monotonic load for comparison. The study has confirmed the applicability of cyclic loading method to evolve the stiffness degradation and damage assessment. The bonding strength of CFRP governs the strength of the repaired beams in most cases. The bonding of CFRP is better in the cracked beams than in the un-cracked beam. The results have also shown that the repaired damaged beams outperformed than the undamaged control beam strengthened with CFRP.

In order to enhance the income and to improve the quality of life of the poor people, cost effect... more In order to enhance the income and to improve the quality of life of the poor people, cost effective, innovative and environment-friendly housing technologies have been adopted to construct houses at affordable cost.

Space frame structures are efficient solution to cover large area with minimum material and cost.... more Space frame structures are efficient solution to cover large area with minimum material and cost. Space frame structures are formed with number of truss members connected together by means of nodes, which are specially made to transfer load from individual member to the whole system. these structures are built up from simple prefabricated units of standard size and shape in the factory and assure quality and time saving. the mass production of prefabricated units can easily be handled, transported and assembled. Space structures allow great flexibility in deciding different layout and positioning of columns. the last three decades saw the emergence of a new generation of space structures developed considering the parameters to address the usual high cost problem of this type of structure. the economy and performance of the space structures depends on many parameters including topology, span, support conditions, external loading (heavy, moderate, light), span to depth ratio, support locations etc. the degree of indeterminacy of space structures generally have about 25 percent of its total number of members which is most considered factor for the uncertainties 1 . the space structures are more sensitive to the imperfection, which introduces the initial forces and these forces in the members are distributed uniformly and effectively. the failure of one or few critical compression members of Space structures leads to adjacent member failure and frequently reported the catastrophic failure total structure. a number of research works have been carried out to improve the performance of the individual chord members and the overall space structure behavior, using numerical, analytical and experimental means. space structures are common in covering large area with few or no intermittent supports. The catastrophic failures of space structures are frequently reported and it urges to develop suitable techniques to prevent such failures. The composite space structures are found to be an efficient solution, in which the forces in the critical compression members are redistributed and safe guarded with concrete slabs. In this study, numerical studies were conducted using a standard finite element analysis package. Effect of shear connectors with varying heights on the behaviour of the space structure is studied. results are compared with the steel space structure and composite space structure with full shear interaction. The maximum deflection observed in the steel space structure for the service load is less than span/300 and the maximum deflection observed in the steel concrete composite space structure for the service load is less than span/360, which ensures the serviceability conditions. The results show about 20 to 30 percent of reduction in deflection with about 250 percent increase in stiffness due to the composite action for the service load. The results substantiate that the length of shear connector should be equal to the concrete depth for more efficient composite interaction. The composite action is more effective and efficient in composite space structure for larger spans compared to shorter spans.

Man's desire to cover large area with minimum materials and cost resulted in a space frame system... more Man's desire to cover large area with minimum materials and cost resulted in a space frame system. a Space frame structure is formed by a number of truss members which are joined together at their ends to form a three dimensional array. these truss members are connected together by means of nodes which are specially made to transfer load from individual member to the whole three dimensional system. these structures have high integrity and indeterminacy. Due to this, the forces in the members are distributed uniformly and effectively redistributed during any failure of adjacent members of these steel space structures. these structures are built up from simple prefabricated units of standard size and shape in the factory, assures the product quality and savings in time. these mass produced simple prefabricated units can easily be handled, transported and assembled. Space structures allow great flexibility in deciding different layout and positioning of columns. a space structure eliminates the expensive and complicated temporary supports during erection and it is offers higher percentage of reusability. These structures are more beneficial to provide the service accessories such as lighting, air conditioning and etc. Depending upon the connecting The steel space frame structures are popular in covering the large areas with or without intermittent supports. steel space structures are more advantageous in lower weight to usage ratio. The space structures are frequently reported for their catastrophic nature of failure. The catastrophic failure is generally initiated from one or few critical compression chord member nearer to truss support. The initial stresses developed in the space structure due to the uncertainties causes the over stressing of members. The space structures have about 25% of indeterminate members which redistribute these initial stresses and generate the secondary effects. All these are finally affects the critical compression member behaviour and leads to catastrophic failure. This catastrophic nature of failure should necessarily be reduced by altering member force of members at specific location by using new technological advents. In the present study, numerous papers were reviewed and presented a better review on the active and passive control mechanisms, which are investigated to improve the performance of space structure. The present study aimed to make use of this member imperfection to improve the space truss capacity. A novel double sleeve system is developed to alter the member force of critical compression member using lack of fit concept. This performs as a passive force control device by manually adjusted member post-stress developing system. The passive control device changes the member length and introduces the prestressing force. Three numbers of three-bar space truss system and one four-bar space truss structure are investigated experimentally and verified analytically. The study showed evidence for altering about 20 to 25 percent of compression force in the critical compression member. Also, the experimental study showed its efficiency in shifting the brittle compression member failure to ductile tension member failure.

Double layered grid space structures are well known in the building industry for their ability to... more Double layered grid space structures are well known in the building industry for their ability to cover large areas. This paper presents the results of a parametric study on the various factors affecting the flexural behavior of double layered grid space structures, considering (i) various support arrangement (ii) concrete slab at the top and (iii) an experimental investigation on a full scale space grid. Based on the study it was concluded that top concrete slab enhances not only the strength of top chord compression members but also increase the strength and stiffness of the system with a fail safe system. It was found from the study that atleast 20% saving in steel is possible with a mid edge supported system.

Experimental investigations have been carried out on five specimens, out of which three were of s... more Experimental investigations have been carried out on five specimens, out of which three were of single-draped tendon profile and two were of straight tendon profile. Rectangular RC beams of section size 150 mm X 275 mm with 4 m length were used for investigation. Crack was induced in RC beams to a limit in which strain in reinforcing steel was around 85 % of the yield strain by monotonically increased static two-point load at flexural zone. Strengthening by external prestressing was done while the member was subjected to superimposed dead load of a bridge girder, equivalent to 25 % of the calculated ultimate load of the specimen. Strengthened members were tested by monotonically increased two-point load. Role of the reinforcing steel were observed from electrical strain gauges, which were fixed throughout the length of the beams. It was observed that the ultimate load carrying capacity of strengthened members have increased 48 % and 17 % for single-draped tendon profile and straight tendon profile respectively.

The strength of the composite deck slab depends mainly on the longitudinal shear transfer mechani... more The strength of the composite deck slab depends mainly on the longitudinal shear transfer mechanism at the interface between steel and concrete. The bond strength developed by the cement paste is weak and causes premature failure of composite deck slab. This deficiency is effectively overcame by a shear transferring mechanism in the form of mechanical interlock through indentations, embossments, or fastening studs. Development of embossment patterns requires an advanced technology which makes the deck profile expensive. Fastening studs by welding weakens the joint strength and also escalates the cost. The present investigation is attempted to arrive at a better, simple interface mechanism. Three types of mechanical connector schemes are identified and investigated experimentally. All of the three shear connector schemes exhibited full shear interaction with negligible slip. The strength and stiffness of the composite slabs with shear connectors are superior about one and half time compared to these of the conventional reinforced concrete slabs and about twice compared to these of composite slabs without mechanical shear connectors. The scheme2 and scheme3 shear connector mechanisms integrate deck webs and improve strength and stiffness of the deck, which can effectively reduce the cost of formworks and supports efficiently.