COMPUTATIONAL STUDY OF STRUCTURAL INSULATED POLYSTYRENE REINFORCED CONCRETE SANDWICH PANEL FOR ENERGY EFFICIENT BUILDING CONSTRUCTION Presented by : Anubhav Roy

Proposed sandwich panel seems to be a sustainable approach towards building constructionNatural vibration parameters are quite fundamental for a structural judgement of any composite structure Damage detection analysis is necessary for a composite structure at every intervalsEffect of various type of damage to various components of the proposed composite panel on the modal parameters of the same is enumerated by a forward problem This forward problem is explained in the proposed work

Thermal resistance (exhibiting poor conductivity)Acoustic impedanceLower mass-stiffness ratio proving to be an effective compositeResistance to earthquake Largely economic efficient for a country like India

Reference: INDUSTRIAL BUILDING SYSTEM--Operators Handbook by Subham Resources Ltd.

Polystyrene used as coreSteel-reinforced concrete used as face-sheets Steel bars used as shear connectors through the entire thickness of the plate

Foam polystyrene core should be non-toxic, self-extinguishing and chemically inertThe reinforcement is electro welded steel wire meshes made of galvanized drawn steel wires placed on both sides of the polystyrene sheetFace-sheet reinforcements connected to through-thickness shear connectors by spot welded steel wiresFoam polystyrene panels sandwiched between welded steel wire meshes and installedSubsequent spraying of M25 grade concrete

Generation of a numerical model in ABAQUS platform of Finite Element frameworkExtraction of its modal parameters in undamaged situation for different support situationsInduction of various types, degrees and locations of damage in its modelExtraction of modal parameters in damaged state

Evaluation of effect of damage on modal parametersIdentification of active damage responsible for affecting modal parametersAn approximate identification of sensitive modal parameters most prone to be affected by damage induction

A numerical model of 1.0 m x 1.0 m x 0.13 m dimensions is generated Polystyrene thickness is kept 60 mmRCC thickness is kept 35 mm on both sides of the polystyrene coreThe steel main bars were of 3 mm diameter with 100 mm c/c reinforcementsThe shear connectors were also 3 mm diameter and c/c distance in both directions

The analysis is carried out for different support conditions : Panel fixed on one thickness face Panel simply-supported on two edges of bottom face-sheetPanel simply-supported on four edges of bottom face-sheetPanel fixed on all thickness faces

Concrete face-sheetThis part is modelled by 3D-solid-homogenous modellingGeometrically the created part having planar dimensions as 1.0 m x 1.0 m and extruded through 35mm which is the thickness of the part

Polystyrene coreThis part is modelled by 3D-solid-homogenous modellingGeometrically the created part having planar dimensions of 1.0 m x 1.0 m and extruded through 60 mm which is the thickness of the core.

Steel reinforcement barsDue to much lower thickness-length ratio of the bars, the cylindrical bars are assumed to be behaving axially instead of behaving in flexural pattern for simplification of our analysesHence the steel re-bars are modelled by 2D-planar-wire modellingThe re-bars are created with length 1.0 m as the total length of reinforcement bars

Steel shear connectorsAs of previous assumption, the shear connector member was also modelled by 2D-planar-wireThe length of the shear connector member was the distance between the face-sheet inter rebar connections and hence taken as 80 mm through core from one face-sheet to the other

The following material properties as given are assigned to create the corresponding sections of the generated parts

For the steel section 7.07 sq.mm c/s area as the main bar as well as shear connectors are of 3mm diameter.

The parts are assembled in correct positions and orientationsThe concrete face-sheets are assembled on either sides of the polystyrene core as shown in the right figure

The main bars and shear connectors are oriented and assembled as mesh shown in the left figure

The interaction properties are modeled at junctions of the assembledmodelCoreface-sheet surf-surf ROUGH interaction with finite-slidingInter-wire junction tie constraint is provided Main reinforcing bars embedded within the concreteMain reinforcing bars embedded within the concrete and polystyrene

The boundary conditions are imposed on the model forfour support restraint casesOne thickness face is fixedSimply supported on two edgesSimply supported on four edgesAll four thickness faces fixed

abcd

Natural frequencies : The extracted natural frequency of the undamaged panel model are shown below

Mode shapes : The extracted 1st mode shapes for fixing one thickness face, simply supporting at two edges, simply supporting at four edges and fixing all faces respectively are shown in figs below

Three types of damages are induced in the modeled panel in which the degrees and locations are variedFace-sheet damage (DF)Reinforcement bars and shear connectors damage (DB)Multiple damage involving both of the above damage situations (DM)

Damage was induced in various degrees and locations by reducing the stiffness of the damaged region

DF1 :

DF2 :

Natural Frequency : The variation of extracted natural frequency with induction of various degrees and locations of face-sheet damage is shown This face-sheet damage seems to be an active one to affect the natural frequency of the panelThe first mode natural frequency seems to bequite sensitive in detection of this type of damage as the other two modes remains dormant over little change from DF1 to DF2

Mode shape : The critical mode shapes of the panel for this type of damage those deserve discussions are presented below

DF1DF2DF3DF4

For DF1 and DF2 the damage induction is done on both the face-sheets, the former being more symmetric one, undisturbing the stiffness distribution on the plate exhibiting a LOCAL deformation or vibration propagation in the stiffer face-sheet due to higher frequencyFor DF3 the phenomenon turns to be a GLOBAL one for hampering the stiffness distribution affecting an abrupt asymmetric damage on the plateFor DF4 as many circular regions of bottom face-sheet are damaged, LOCAL behavior is observed in lower modes followed by GLOBAL in higher modes. For the lower ones, the local propagations gradually shift from one region to other

Damage was induced in various degrees and locations of bar mesh by reducing the stiffness

DB1DB2DB3DB4DB5DB7DB8

Natural Frequency : The extracted natural frequencies of panel with induction of various degrees and locations of bar and shear connector damage is shown

The damage at reinforcement bars and shear connectors dosnt seem to be an active one for affecting the natural frequency of the proposed panel until all the shear connectors are damaged i.e. of DB7 caseNatural frequency is not a sensitive parameter prone to the damage at bars and shear connectors

Mode shapes : The mode shapes of the panel for this type of damage those deserve discussions are presented below

UDDB1DB5DB7

The through-thickness propagation of the natural wave in the proposed panel seems to be independent on shear connectorsThe slight change in natural frequency may be attributed to greater frictional resistance between the laminatesMore over until DB6 the existing undamaged shear connectors prove to be steady enough to resist the global change in shape from the undamaged one (UD)For DB7 induction a global collapse between the laminates has been observe in 1st mode shape So neither this damage proves to be an active one nor any modal parameters can be identified to be sensitive to these kind of damages

Damage is induced both in face-sheets as well as in bars and shear connectorsDM1 Face-sheet damaged as DF2 and main bars damaged as DB1DM2 - Face-sheet damaged as DF2 and shear connectors as DB6DM3 Face-sheet damaged as DF2, main bar as DB1 and shear connectors as DB7

Natural Frequency : The variation of natural frequency with induction of various degrees and locations of multiple damage is shown The multiple damage scenario seems to be quite active for affecting the natural frequencies of the panelThe first mode seems distinctive and sensitive that is approximately prone to be affected by induction of damage

Mode shape : The second mode shapes of the panel for this type of damage those deserve discussions are presented below UDDM1DM2DM3

For DM2 induction, the natural frequency curve goes up from that of DM1 due to the fact that the undamaged shear connectors present, offer stiffnessDM3 is an easily identifiable case of damage from the mode shapes Thus Multiple damage DM seems to be an active damage fopr affecting the modal parameters fascilitating the forward problemModal parameters are quite sensitive to detect the above mentioned multiple damage scenario

The proposed panel seemed to be an energy efficient approach for building construction now a days in IndiaA forward problem is presented that may help I damage detection of these type of sandwich panelThe proposed forward problem helps to determine the active damages affecting the modal parameters of the panel and also the sensitive modal parameters prone to induction of damage

More studies are to be done varying the inter-laminar bond strength to correctly enumerate the effect of shear-connector damage on modal parametersThis forward problem needs to be experimentally performed and a convergence study is to be made to reach to the desired data and more studies are required with different model parameters for better understanding of various phenomenon This dynamic problem may be utilized in developing an inverse approach formulation for damage detection in the proposed panel that may help in structural health monitoring in future

[1] Fabrizio Gara, Laura Ragni, Davide Roia, Luigino Dezi, Experimental behaviour and numerical analysis of floor sandwich panel, Journal of Engineering Structures, (2012) Vol. 36, pp 258-269. [2] A. Benayoune , A.A.A. Samad , A.A. Abang Ali , D.N. Trikha, Response of pre-cast reinforced composite sandwich panels to axial loading , Journal of Construction and Building Materials, (2007) Vol. 21,pp 677-68.