Viduriniojo sluoksnio supleišėjimo įtaka lenkiamųjų trisluoksnių gelžbetoninių konstrukcijų elgsenai ; Influence of cracking of internal layer on behaviour of flexural three-layer reinforced concrete structures

Linas Juknevièius

Description

LinasJUKNEVIČIUSINFLUENCEOFCRACKINGOFINTERNALLAYERONBEHAVIOUROFFLEXURALTHREELAYERREINFORCEDCONCRETESTRUCTURESSummaryofDoctoralDissertationTechnologicalSciences,CivilEngineering(02T)1327Vilnius 2006 VILNIUSGEDIMINASTECHNICALUNIVERSITYLinasJUKNEVIČIUSINFLUENCEOFCRACKINGOFINTERNALLAYERONBEHAVIOUROFFLEXURALTHREELAYERREINFORCEDCONCRETESTRUCTURESSummaryofDoctoralDissertationTechnologicalSciences,CivilEngineering(02T)Vilnius 2006 DoctoraldissertationwaspreparedatVilniusGediminasTechnicalUniversityin1999–2006ThedissertationisdefendedasanexternalworkScientificSupervisorProfDrHabilJonasGediminasMARČIUKAITIS(VilniusGediminasTechnicalUniversity,TechnologicalSciences,CivilEngineering–02T)ThedissertationisbeingdefendedattheCouncilofScientificFieldofCivilEngineeringatVilniusGediminasTechnicalUniversity:ChairmanProfDrHabilGintarisKAKLAUSKAS(VilniusGediminasTechnicalUniversity,TechnologicalSciences,CivilEngineering–02T)Members:Dr Darius BAČINSKAS (Vilnius Gediminas Technical University,TechnologicalSciences,CivilEngineering–02T)Prof Dr Habil Gintautas DZEMYDA (Institute of Mathematics andInformatics,TechnologicalSciences,InformaticsEngineering–07T)ProfDrHabilAudronisKazimierasKVEDARAS(Vilnius

Sujets

• Reinforced concrete

Informations

• Publié par: vilnius_gediminas_technical_university
• Publié le: 01 janvier 2007
• Nombre de lectures: 48

Extrait

 

        Linas JUKNEVIČIUS         INFLUENCE OF CRACKING OF INTERNAL LAYER ON BEHAVIOUR OF FLEXURAL THREELAYER REINFORCED CONCRETE STRUCTURES         Summary of Doctoral Dissertation Technological Sciences, Civil Engineering (02T)          

 

Vilnius

2006

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VILNIUS GEDIMINAS TECHNICAL UNIVERSITY                   Linas JUKNEVIČIUS         INFLUENCE OF CRACKING OF INTERNAL LAYER ON BEHAVIOUR OF FLEXURAL THREELAYER REINFORCED CONCRETE STRUCTURES           Summary of Doctoral Dissertation Technological Sciences, Civil Engineering (02T)        

 

Vilnius

2006

 

Doctoral dissertation was prepared at Vilnius Gediminas Technical University in 1999–2006 The dissertation is defended as an external work   Scientific Supervisor Prof Dr Habil Jonas Gediminas MARČIUKAITIS (Vilnius Gediminas Technical University, Technological Sciences, Civil Engineering – 02T)   The dissertation is being defended at the Council of Scientific Field of Civil Engineering at Vilnius Gediminas Technical University: Chairman Prof Dr Habil Gintaris KAKLAUSKAS (Vilnius Gediminas Technical University, Technological Sciences, Civil Engineering – 02T)   Members: Dr Darius BAČINSKAS Gediminas Technical University, (Vilnius Technological Sciences, Civil Engineering – 02T)   Prof Dr Habil Gintautas DZEMYDA (Institute of Mathematics and Informatics, Technological Sciences, Informatics Engineering – 07T) Prof Dr Habil Audronis Kazimieras KVEDARAS (Vilnius Gediminas Technical University, Technological Sciences, Civil Engineering – 02T)   Prof Dr Habil Vytautas STANKEVIČIUS (Kaunas University of Technology, Technological Sciences, Civil Engineering – 02T)   Opponents: Prof Dr Habil Jonas BAREIŠIS University of Technology, (Kaunas Technological Sciences, Mechanical Engineering – 09T) Assoc Prof Dr Bronius JONAITIS(Vilnius Gediminas Technical University, Technological Sciences, Civil Engineering – 02T)   The dissertation will be defended at the public meeting of the Council of Scientific Field of Civil Engineering in the Senate Hall of Vilnius Gediminas Technical University at 10 a. m. on 2 February 2007. Address: Saul÷tekio al. 11, LT–10223 Vilnius–40, Lithuania Tel. [phone]; fax [phone]; e>mail [e-mail]   The summary of the doctoral dissertation was   distributed on 2 January 2007 A copy of the doctoral dissertation is available for review at the Library of Vilnius Gediminas Technical University (Saul÷tekio al. 14, Vilnius, Lithuania)   © Linas Juknevičius, 2006

 

 

VILNIAUS GEDIMINO TECHNIKOS UNIVERSITETAS                   Linas JUKNEVIČIUS       VIDURINIOJO SLUOKSNIO SUPLEIŠöJIMO ĮTAKA LENKIAMŲJŲ TRISLUOKSNIŲ GELŽBETONINIŲ KONSTRUKCIJŲ ELGSENAI           Daktaro disertacijos santrauka Technologijos mokslai, statybos inžinerija (02T)            

 

Vilnius

2006 

 

Disertacija   rengta   1999–2006   metais   Vilniaus   Gedimino   technikos universitete. Disertacija ginama eksternu.   Mokslinis vadovas prof. habil. dr. Jonas Gediminas MARČIUKAITIS(Vilniaus Gedimino technikos universitetas, technologijos mokslai, statybos inžinerija – 02T).   Disertacija ginama Vilniaus Gedimino technikos universiteto Statybos inžinerijos mokslo krypties taryboje: Pirmininkas prof. habil. dr. Gintaris KAKLAUSKAS(Vilniaus Gedimino technikos universitetas, technologijos mokslai, statybos inžinerija 02T). – Nariai: dr. Darius BAČINSKAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, statybos inžinerija – 02T), prof. habil. dr. Gintautas DZEMYDA ir informatikos (Matematikos institutas, technologijos mokslai, informatikos inžinerija – 07T),   prof. habil. dr. Audronis Kazimieras KVEDARAS(Vilniaus Gedimino technikos universitetas, technologijos mokslai, statybos inžinerija – 02T), prof. habil. dr. Vytautas STANKEVIČIUS technologijos (Kauno universitetas, technologijos mokslai, statybos inžinerija – 02T). Oponentai: prof. habil. dr. Jonas BAREIŠIS technologijos universitetas, (Kauno technologijos mokslai, mechanikos inžinerija – 09T), doc. dr. Bronius JONAITIS(Vilniaus Gedimino technikos universitetas, technologijos mokslai, statybos inžinerija – 02T).   Disertacija bus ginama viešame Statybos inžinerijos mokslo krypties tarybos pos÷dyje 2007 m. vasario 2 d. 10 val. Vilniaus Gedimino technikos universiteto senato pos÷džių sal÷je. Adresas: Saul÷tekio al. 11, LT–10223 Vilnius–40, Lietuva. Tel. [phone]; faksas [phone]; el. paštas [e-mail]   Disertacijos santrauka išsiuntin÷ta 2007 m. sausio 2 d. Disertaciją galima peržiūr÷ti Vilniaus Gedimino technikos universiteto bibliotekoje (Saul÷tekio al. 14, Vilnius, Lietuva) VGTU leidyklos „Technika“ 1327 mokslo literatūros knyga   © Linas Juknevičius, 2006

 

 

GENERAL CHARACTERISTIC OF THE DISSERTATION Topicality of the research.The application of layered structures increases in Lithuanian construction industry and in the rest of the world. Due to the worldwide increase of price of all kinds of fuel – the development of the efficient building structure elements that have a low thermal conductivity is one of the most important tasks in nowadays building industry. Moreover, the building codes in many countries constantly introduce higher and higher requirements concerning the thermal insulation properties of the building elements. According to the thermal insulation requirements in current European building codes – the use of the single layer structures is not efficient. All mechanical properties of the material cannot always be utilised while using the single layer structures. For instance, the stress in the middle of the eccentrically compressed or flexural elements is significantly lower than the stress in the edges of the same elements. This example shows that the middle part of the section could be made of materials that have less strength but are significantly cheaper. The purpose of such middle layer is to join the external layers and redistribute stress within the section depth. The structures consist of two or more layers that are made of different materials. Each layer is designed in the way that most of its best properties could be utilised. The carrying capacity is ensured by the reinforcement and plain or modified heavy concrete. The thermal insulation is ensured by the internal layer or layers made of lightweight concrete, gaseous silicate, foamed concrete, etc. The most popular structures of such type are the hollow slabs which internal layer is made of a cheaper fine aggregate concrete or lightweight concrete type materials. There are many calculation methods for layered structures in scientific literature, but in most cases these calculation methods are complicated and inapplicable for layered structures made of reinforced concrete. Moreover, most of the calculation methods do not estimate the possibility of appearance of the cracks in the internal layers before the cracks in external layer in which the tensile stresses are higher. The internal layers could be made of lightweight concrete type materials (e.g. foamed concrete) which shrinkage deformations are several times higher if compared to the external layers. Therefore, the cracks in the internal layer may appear even before actual loading of the structure. The flexural layered members may have very complex state of stress and strain. Such state of stress and strain should be estimated when designing the effective and reliable building structures. The proposed method for the calculation of carrying capacity and cracking moment of the external layer of flexural layered reinforced concrete structures estimates the cracking of the internal layer, concrete shrinkage deformations and the physical and mechanical properties of used materials.

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Main objective of this work are the flexural three>layer reinforced members made of concrete type materials. Methodology of research.The analysis of the calculation methods given in the scientific literature was done. There was done an experimental research on the three>layer reinforced concrete beams, which internal layer was made of lightweight concrete type materials. Also the experimental research on the physical and mechanical properties and shrinkage deformations of various concrete type materials was done.   Main task was to propose the method for the calculation of the carrying capacity and cracking moment of the flexural three>layer reinforced concrete members taking into account the influence of different shrinkage deformations and cracking in the internal layer. In order to achieve this task the following research was done: •Analysis of the existing methods for the calculation of cracking and   carrying capacity of flexural layered reinforced concrete members.   •   Analysis of the state of stress and strain within the section of flexural three>layer reinforced concrete members.   •   Analysis of the influence of shrinkage deformations on the state of stress and strain within the section of flexural three>layer reinforced concrete member.   •   Estimation of the influence of various physical and mechanical characteristics on the carrying capacity and cracking moment of the flexural three>layer reinforced concrete members.   Scientific novelty   •   The method for the calculation of carrying capacity and cracking moment of external tensile layer of flexural three>layer reinforced concrete members taking into account the cracking of internal layer and different concrete shrinkage deformations is proposed. •   The new experimental data concerning the influence of cracks in the internal layers on the deformations of external layers of flexural three> layer reinforced concrete members are presented. •   The new experimental data concerning the influence of poly>prophylen fibre admixture on deformational properties and shrinkage deformations of the concrete are presented. •   Quantifiable estimation of the influence of various concrete deformational properties on the carrying capacity and cracking moment of flexural three> layer reinforced concrete members is presented. Approbation and publications. main results of this work were The presented in four scientific conferences. Five articles were published on the

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topic of the dissertation and two of them were published in the reviewed scientific periodical magazines (see p. 17). The scope of the scientific work.The thesis written in Lithuanian consists of the general characteristics, 4 main chapters, general conclusions, 59 pictures, 10 tables and the list of references. The total scope of the dissertation is 131 pages.   CONTENT OF THE WORK   1. Review of methods for calculation of cracking and carrying capacity of flexural layered members In this chapter the existing methods for calculation of cracking and carrying capacity of flexural layered reinforced concrete members and the methods for estimation of concrete shrinkage influence were reviewed. The analysis of methods for the calculation of cracking and carrying capacity of flexural layered reinforced concrete members has shown that most of the methods are based on transformed sections method. Such methods are simple and easy applicable but they have several disadvantages. By using such methods it is impossible to estimate all the deformational properties of materials. The possible cracking of the internal layer also can not be estimated. The more advanced calculation methods (based on elasticity theory, finite element modelling, etc) could be found in the scientific literature, but they are hardly applicable for layered reinforced concrete members. There are many methods for the calculation of unrestrained concrete shrinkage deformations. Although these methods can not be directly applied to the estimation of initial state of stress and strain in the layered reinforced member made of different concrete type materials.   2. Method for calculation of carrying capacity and cracking moment of flexural threelayer reinforced concrete member In this chapter the method for calculation of carrying capacity and cracking moment of flexural three>layer reinforced concrete member is proposed. The four most possible cases of state of stress and strain within the depth of three>layer section are analysed (see Fig 1, a, b, c, d). These cases represent all the possible states of internal layer performance: when internal layer is not cracked, when internal layer is partly cracked in the tensile zone, when internal layer is completely cracked and when the cracks shuts in the compressive zone due to the flexure of three>layer member. The proposed method for calculation of cracking moment and carrying capacity of three>layer reinforced concrete

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members allows the estimation of initial stresses and cracks caused by different shrinkage deformations of different layers (see Fig 2, a).  

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  Fig 1.Analyzed cases of state of stress and strain within the depth of the section of flexural three>layer reinforced concrete member: a – case when internal layer is not cracked; b – case when internal layer is partially cracked; c – case when internal layer is completely cracked; d – case when crack in internal layer shuts during the flexure of the member, e – strain distribution within the section   The initial state of stress and strain is represented as the total sum of stresses caused by the reinforcement resistance to the shrinkage of external layer concrete (see Fig 2, b) and the stresses caused by the different shrinkage deformations of neighbouring layers (see Fig 2, c). Due to the different geometrical and deformational properties of different layers – the initial state of stress and strain within the depth of the section could take various shapes.   ε ,,3 ε ,0,3 ε ,0,2 ε ,,1 ε ,0,1 σ , σ , σ , σ ,   Fig 2.Initial state of stress and strain caused by the different concrete shrinkage deformations of three>layer reinforced concrete member: a – different concrete shrinkage deformations in different layers; b – stresses in external layers caused by reinforcement resistance to concrete shrinkage; c – stresses in three>layer section caused by greater shrinkage deformation of lightweight internal layer; d, e – total initial stresses, caused by concrete shrinkage deformations  

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The stresses of concrete in the external layers could be tensile or compressive or both (see Fig 2, d, e). The shrinkage deformation of the internal layer could be expressed as the difference between the unrestrained shrinkage deformation of external layer and the restrained shrinkage deformation of external layer:      ε ,,2 = ε ,0,2 − ε ,,1 , (1) here ε ,0,2  – unrestrained shrinkage deformation of internal layer; ε ,,1  – deformation of external layer (restrained by reinforcement). Formulas (2) and (3) could be used for the calculation of deformation and stress in the bottom edge of the internal layer:      ε    ,2 ⋅ α ,1 ⋅ κ ,1   ε ,,2 = 1 ,   , (2) + α ,1 ⋅ κ ,1 ε  ⋅⋅ κ    ,,2,1,1   σ ,,2 = ε ,,2 ⋅ ,2 ⋅ ν 2 = 1+ α ,1 ⋅ κ 1 , (3) , ⋅ here α ,1 =  ,  2 , ⋅ 1 2 ; κ ,1 = 2  ,  2 ,1 ; , ,   – modulus of elasticity and elasticity coefficient of concrete respectively; , , ,  – effective area and real area of layer cross>section respectively; layer index (counting from – most tensile bottom layer). When calculating the cracking moment of the external tensile layer, the position of neutral axis should be calculated according to the cracking of the internal layer:   [ ,2 ⋅ 2 ⋅ (1− ν 2 ) ]⋅ . 2 . + [2⋅(− ,3 ⋅ 3 ⋅ 3 − ,2 ⋅ 2 ⋅ 1 ⋅ (1− ν 2 ) + 2 − ,2 ⋅ ν 2 −    ,1 ⋅ 1 ⋅ 1 ⋅ ν 1 − ,1 ⋅ ,1 − ,2 ⋅ ,2 )]⋅ .. + (4) [ ,3  3 ⋅ 3 ⋅ ( 2⋅ 1 +2⋅ 2 + 3 ) + ,2 ⋅ 2 ⋅ (  1 + 2 ) 2 − ν 2 ⋅ 1 +  2 2, +  ,1 ⋅ 12 ⋅ 1 ⋅ ν 1 +2⋅ ,1 ⋅ ,1 ⋅ 1 +2⋅ ,2 ⋅ ,2 ⋅ (  1 + 2 + 3 − 2 ) ]=0, here  ,   width and thickness of layer respectively; – ..  distance from – neutral axis to the most tensile edge of three>layer section.  

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Here the depth of the crack in the tensile zone of the internal layer is calculated using the strain distribution diagram:      2 = .. − 1 − ε ,2, ⋅ .. , , ε ,1,  (5) here ε ,, – ultimate tensile deformations of layer concrete.  There are four different formulas for the four different cases of stress and strain as shown in Fig 1. Formula (4) is used for the estimation of neutral axis position in case when the internal layer is partially cracked in the tensile zone (Fig 1, b). Formulas (4) and (5) are dependent on each other and should be calculated by using the iteration method. Due to the different state of stress and strain, the depth of compressive zone could be calculated by using the formula (6) when calculating the carrying capacity of three>layer reinforced concrete member:   ,1 + σ ,,1 ⋅ ,3 ⋅ (  1 + 2 + 3 ) + ,3 − σ   ,,3 ⋅ ,1 ⋅ 1      =  , (6) . .  ,1 + σ ,,1 ⋅ ,3 + ,3 − σ ,,3 ⋅ ,1 here , , , – strength of reinforcement and concrete respectively;σ  – ,,   initial stresses in concrete or reinforcement caused by concrete shrinkage; – index of material: reinforcement steel ( ) or layer concrete (). The stress and strain diagrams used for the calculation of cracking moment and carrying capacity of three>layer reinforced concrete members are shown in Fig 3.     2  ,3  ,3 , ,2  ,2  2  3    3 , ,3 ,3   ,2  ,2  ,3 ,2  ,2  2    ,  2 ,2 ε ,2, ,2  ,2  ,2   ,2 ..    ,  1 ,1  ,1  ,1  ,1 ,1  1  1 ,1   Fig 3.Diagrams for calculation of cracking moment and carrying capacity of flexural three>layer reinforced concrete member with cracked internal layer: a – stress diagram for calculation of cracking moment; b – stress diagram for calculation of carrying capacity; c – strain diagram

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