scholarly journals DETERMINATION OF UNIT CHARACTERISTICS OF CONCRETE LINEAR CREEP/BETONO TIESINIO VALKŠNUMO VIENETINIŲ RODIKLIŲ NUSTATYMAS

2000 ◽  
Vol 6 (2) ◽  
pp. 87-96 ◽  
Author(s):  
Robertas Balevičius ◽  
Eugenijus Dulinskas
Keyword(s):  
Cement Paste ◽  
Coefficient Of Variation ◽  
Time Dependent ◽  
Prestress Loss ◽  
Concrete Creep ◽  
Creep Coefficient ◽  
Creep Characteristics ◽  
Creep Deformations

t is very important to take into account time-dependent non-elastic deformations and variation of concrete mechanical characteristics in analysis of concrete structures. In codes of many countries, such as ENV 1992-1-1 (Eurocode) [1], ACI 209–92 (USA), AS 3600–1988 (Australia), DIN 4227 (Germany) and others, variation of creep deformations and physical mechanical characteristics with time is specified. The Code acting in Lithuania SNiT (Russ. СНиП 2.03.01-84*) [2] does not describe these characteristics directly. Calculation of time-dependent processes in the code acting in Lithuania SNiT [2] is associated with specific creep characteristics (specific creep, coefficient of creep) and with regulation of creep deformations. Such integral characteristics as steel prestress losses due to concrete creep associated with these specific characteristics are determined by empirical formulas which are obtained by tests with verification of stress and strain state of individual members. There are many investigations for determination of concrete creep characteristics. In the investigation [3], different relationships for determining specific characteristics of „young” and „old” concrete are proposed to apply, in recommendations [4] characteristics are presented according to their authors only for design, relationships presented in monograph [5] describe very well the creep of „young” concrete, code [6] regulates only limit values of creep characteristics. Characteristics determined by Eurocode [1] depend on the main factors influencing creep deformations but their relationship with regulations of the code [2] used in Lithuania is not clear. Therefore in this investigation relationships of specific creep characteristics for various compression grades of normal weight concrete describing great area of long-term deformations and taking into account the main factors influencing concrete creep were proposed. The proposed relationships also comply with regulation area of the code [2]. Analysis of specific concrete creep deformations based on steel prestress loss due to concrete creep calculation method [2] is presented in Chapter 2. Relationships for pure concrete specific creep (20–21) and for creep coefficient (23) were obtained. Comparison of these expressions with specific creep calculated according to code EC-2 [1] and recommended in [4] methods is shown in Figs 1–2. In Chapter 3, mathematical description of pure specific concrete creep (21) and of pure creep coefficient (23) based on theory of elastic plastic body is presented. Comparison of specific concrete creep characteristics determined by (35) and (37) relationships with analogous characteristics applied in codes [1, 4] is shown in Figs 3–4. In Chapter 4–5, coefficients (40), (41) evaluating the influence of water-cement ratio and quantity of cement paste on concrete creep deformations are presented. Analysis of experimental results of investigations of specific creep characteristics shows that time-dependent deformation properties depend not only on factors by which concrete creep is specified in codes and discussed in Chapters 3–4, but also on quantity of cement paste and water-cement ratio. Conformity of specific creep values determined by relationships (35) proposed by us taking into account coefficients (40–41) with standard concrete [3] and experimental creep investigation results [18] are shown in Figs 4–5. Statistical analysis of experimental and theoretical concrete creep deformation values determined according to the method proposed by us and by the code [1] is presented in Table 2. Mean ratios κ = C eksp (t, t 0)/C(t, t 0), mean square deviations σκ and coefficient of variation δκ were calculated. It was determined that theoretical values of specific creep calculated by the proposed method comply better (coefficient of variation δκ=27.7%) with presented test results than code EC-2 [1] (coefficient of variation δκ=31.9%) (Table 2). Analysis of method of calculation of steel prestress loss due to concrete creep according to the acting code SNiT [2] was made and relationships for linear specific creep of concrete B15—B60 grade were proposed to satisfy the accuracy of practical calculations in the area of regulations of the code [2]. Specific creep relationships presented take into account the most important factors effecting creep deformations: concrete grade, times of loading and observation, scale and ambient humidity, quantity of cement and cement paste. These relationships of specific creep characteristics and the method of evaluation of variation of concrete characteristics can be applied for analysis of concrete structures under the action of long-term loads.

scholarly journals Experimental and Analytical Study on Creep Characteristics of Box Section Bamboo-Steel Composite Columns under Long-Term Loading

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 983
Author(s):  
Shixu Wu ◽  
Keting Tong ◽  
Jianmin Wang ◽  
Yushun Li
Keyword(s):  
Load Level ◽  
Experimental Results ◽  
Creep Model ◽  
Composite Column ◽  
Composite Columns ◽  
Creep Coefficient ◽  
Creep Characteristics ◽  
Section Size ◽  
Steel Composite

To expand the application of bamboo as a building material, a new type of box section composite column that combined bamboo and steel was considered in this paper. The creep characteristics of eight bamboo-steel composite columns with different parameters were tested to evaluate the effects of load level, section size and interface type under long-term loading. Then, the deformation development of the composite column under long-term loading was observed and analyzed. In addition, the creep-time relationship curve and the creep coefficient were created. Furthermore, the creep model of the composite column was proposed based on the relationship between the creep of the composite column and the creep of bamboo, and the calculated value of creep was compared with the experimental value. The experimental results showed that the creep development of the composite column was fast at first, and then became stable after about 90 days. The creep characteristics were mainly affected by long-term load level and section size. The creep coefficient was between 0.160 and 0.190. Moreover, the creep model proposed in this paper was applicable to predict the creep development of bamboo-steel composite columns. The calculation results were in good agreement with the experimental results.

scholarly journals EM-Based Monitoring and Probabilistic Analysis of Prestress Loss of Bonded Tendons in PSC Beams

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zheheng Chen ◽  
Shanwen Zhang
Keyword(s):  
Probabilistic Analysis ◽  
Prestressed Concrete ◽  
Monitoring Methods ◽  
Prestress Loss ◽  
External Tendons ◽  
Material Environment ◽  
Key Factor ◽  
One Year

The prestress level is a key factor of prestressed concrete (PSC) beams, affecting their long-term serviceability and safety. Existing monitoring methods, however, are not effective in obtaining the force or stress of embedded tendons. This paper investigates the feasibility of elastomagnetic (EM) sensors, which have been used for external tendons, in monitoring the long-term prestress loss of bonded tendons. The influence of ambient temperature, water, eccentricity ratio, plastic duct, and cement grouts on the test results of EM sensors is experimentally examined. Based on the calibrated EM sensors, prestress loss of a group of PSC beams was monitored for one year. In order to further consider the high randomness in material, environment, and construction, probabilistic analysis of prestress loss is conducted. Finally, the variation range of prestress loss with a certain confidence level is obtained and is compared with the monitored data, which provides a basis for the determination of prestress level in the design of PSC beams.

scholarly journals DETERMINATION OF CREEP PARAMETERS IN LAYERS OF BUILDING COMPOSITES/SLUOKSNIUOTŲJŲ STATYBINIŲ KOMPOZITŲ VALKŠNUMO PARAMETRŲ NUSTATYMAS

1998 ◽  
Vol 4 (2) ◽  
pp. 101-108 ◽  
Author(s):  
Gediminas Marčiukaitis
Keyword(s):  
Force Action ◽  
Building Product ◽  
Creep Coefficient ◽  
Deformation Properties ◽  
Linear Creep ◽  
Modulus Of Deformation ◽  
Composite Product ◽  
Properties Of Materials ◽  
Creep Deformations

Various composite building products consisting of layers of different physical-mechanical properties being tied rigidly together are manufactured and used in construction. In many cases such products curve, become flaky, crack and their thermo-insulating capability suffers. It occurs because deformation properties are not adjusted, different layers of such products deform differently under the load. And the deformation effects the behaviour of the whole structure. A correct adjustment of deformations can be achieved with allowance for creep of different layers and of the whole composite. Determination of creep parameters—creep coefficient and specific creep—depends on the orientation of layers in respect of the direction of force action. When layers are situated transverselly in respect of the direction of action of forces (stresses), creep parameters of composite depend on creep parameters of materials of separate layers and on relative volumes of these layers. Creep deformations of a composite can be described by equations describing creep of individual layers. Appropriate equations and formulas ((17)-(25)) are presented for determining such deformations. When layers are parallel to the direction of stresses, redistribution of these stresses between layers takes place. Compression stresses increase in a layer with higher modulus of deformation and decrease in that with lower modules. Proposed equations (37)-(42) enable to determine redistribution of stresses between layers, the main creep parameters of composite, their modulus of deformations and creep deformations themselves when strength of a composite product is reached, E(t0)=E(t)=const and stresses produce linear creep. Such loading of a composite product is the most common in practice. Presented formulas ((46), (52)) and diagrams show that it is possible to design a composite building product or material with creep parameters given in advance by means of appropriate distribution of product layers, selecting ratios between layers and properties of materials.

Analysis on Creep Characteristics of PC and RC Cylinders with Different Loading Ages

2014 ◽  
Vol 578-579 ◽  
pp. 631-636
Author(s):  
Guo Hui Cao ◽  
Yong Ming Chen ◽  
Jia Xing Hu
Keyword(s):  
Plain Concrete ◽  
Least Square ◽  
Correction Coefficient ◽  
Concrete Creep ◽  
Building Model ◽  
Creep Coefficient ◽  
Concrete Cylinders ◽  
Age Correction ◽  
Term Creep

Through a long time test for creep of 9 PC (plain concrete) and RC cylinders, obtained the long-term creep rule of PC and RC cylinders, the results show that the different loading ages of PC have a greater influence on the creep coefficient, the larger loading age of concrete cylinders, the smaller of concrete creep coefficient. The experiment indicates that the measured creep rule of creep coefficient is basically the same under different loading ages with the same reinforcement ratio of concrete cylinders, the loading age have smaller influence on long-term creep of reinforced concrete cylinders. Based on the measured long-term rule of concrete creep, using the least square method to nonlinear fitting of experimental data, obtained the final value of creep coefficient of the PC under different loading ages, compared the applicability of loading age correction coefficient in the China Institute of building model and CEB-FIP (1990) model for low intensity concrete (≤C40), the results show that the predicted results of loading age correction coefficient in the China Institute of building model are agree well with the measured values, and calculated values of loading age correction coefficient in CEB-FIP (1990) model is large, for low strong concrete (≤C40), the prediction values of loading age correction coefficient in the China Institute of building model should be adopted to linear interpolation.

Predicted and measured stresses and displacements around the Darlington Intake Tunnel

1984 ◽  
Vol 21 (1) ◽  
pp. 147-165 ◽  
Author(s):  
K. Y. Lo ◽  
B. Lukajic
Keyword(s):  
Field Measurements ◽  
Time Dependent ◽  
Long Term Conditions ◽  
Field Instrumentation ◽  
Deformation Properties ◽  
Strength And Deformation ◽  
Short And Long Term ◽  
Keywords Stress

The C.W. Intake Tunnel of the Darlington Nuclear Station is D-shaped in section with a span of 8 m and a length of 925 m beneath Lake Ontario. The tunnel is located in a horizontally bedded limestone with variable shaly interbeds.The geotechnical investigation including in-situ rock stress measurements, and laboratory determination of strength and deformation properties as well as time-dependent behaviour are reported. Design of the tunnel, in particular provisions for "rock squeeze," is described in detail.To verify the design approach adopted and the provisions made, field instrumentation was performed during excavation of the tunnel. The results of field measurements of stresses and displacements were compared with premonitoring analysis. Postmonitoring analyses were also performed using the as-constructed condition. It is shown that the performance of the tunnel is in general agreement with the predicted behaviour in both short and long term conditions. Keywords: stress, displacement, time-dependent deformation, stressmeter, tunnel, rock mechanics, rock squeeze.

scholarly journals Time-dependent Behaviour Analysis of Long-span Concrete Arch Bridge

2019 ◽  
Vol 14 (2) ◽  
pp. 227-248
Author(s):  
Yongbao Wang ◽  
Renda Zhao ◽  
Yi Jia ◽  
Ping Liao
Keyword(s):  
Concrete Structures ◽  
Time Dependent ◽  
Mean Deviation ◽  
Concrete Creep ◽  
Arch Bridge ◽  
Model Code ◽  
Time Dependent Behaviour ◽  
Creep And Shrinkage ◽  
Dependent Behaviour

This paper continues the previous study on clarifying the time-dependent behaviour of Beipanjiang Bridge ‒ a reinforced concrete arch bridge with concrete-filled steel tubular stiffened skeleton. The obtained prediction models and the Finite Element Models were used to simulate the long-term behaviour and stress redistribution of the concrete arch bridge. Three-dimensional beam elements simulated the stiffened skeleton and surrounding concrete. Then, a parameters study was carried out to analyse the time-dependent behaviour of the arch bridge influenced by different concrete creep and shrinkage models. The simulation results demonstrate that concrete creep and shrinkage have a significant influence on the time-dependent behaviour of the concrete arch bridge. After the bridge completion, the Comite Euro-International du Beton mean deviation of displacements obtained by 1990 CEBFIP Model Code: Design Code model and fib Model Code for Concrete Structures 2010 model are 3.4%, 31.9% larger than the results predicted by the modified fib Model Code for Concrete Structures 2010 model. The stresses between the steel and the concrete redistribute with time because of the concrete long-term effect. The steel will yield if the fib Model Code for Concrete Structures 2010 model is used in the analysis. The stresses in a different part of the surrounding concrete are non-uniformly distributed.

scholarly journals Problems in the strength and stability of inhomogeneous structures of rocket and space hardware with account for plasticity and creep

2021 ◽  
Vol 2021 (1) ◽  
pp. 3-15
Author(s):  
V.S. Hudramovich ◽  
◽  
V.N. Sirenko ◽  
E.L. Hart ◽  
D.V. Klimenko ◽  
...  
Keyword(s):  
High Cycle Fatigue ◽  
Physical Nonlinearity ◽  
Approximation Schemes ◽  
Stress And Strain ◽  
Structural Elements ◽  
Equilibrium Equations ◽  
Early Failure ◽  
Creep Deformations

Shell structures provide a compromise between strength and mass, which motivates their use in rocket and space hardware (RSH). High and long-term loads cause plastic and creep deformations in structural elements. RSH structures feature inhomogeneity: design inhomogeneity (polythickness, the presence of reinforcements, openings, etc.) and technological inhomogeneity (defects produced in manufacturing, operation, storage. and transportation, defects produced by unforeseen thermomechanical effects, etc.). These factors, which characterize structural inhomogeneity, are stress and strain concentrators and may be responsible for an early failure of structural elements and inadmissible shape imperfections. In inhomogeneous structures, different parts thereof are deformed by a program of their own and exhibit a different stress and strain level. In accounting for a physical nonlinearity, which is governed by plastic and creep deformations, the following approach to the determination of the stress and strain field is efficient: the calculation is divided into stages, and at each stage parameters that characterize the plastic and creep deformations developed are introduced: additional loads in the equilibrium equations or boundary conditions, additional deformations, or variable elasticity parameters (the modulus of elasticity and Poisson’s ratio). Successive approximation schemes are constructed: at each stage, an elasticity problem is solved with the introduction of the above parameters. Special consideration is given to the determination of the launch vehicle and launch complex life. This is due to damages caused by alternate high-intensity thermomechanical loads. The basic approach relies on the theory of low- and high-cycle fatigue. The plasticity and the creep of a material are the basic factors in the consideration of the above problems. This paper considers various aspects of the solution of RSH strength and stability problems with account for the effect of plastic and creep deformations.

scholarly journals EVALUATION OF CONCRETE LINEAR CREEP IN DETERMINATION OF STRESS STATE AND STEEL PRESTRESS LOSSES IN CONCRETE MEMBERS/BETONO TIESINIO VALKŠNUMO ĮVERTINIMAS, NUSTATANT GELŽBETONINIŲ ELEMENTŲ ĮTEMPIMŲ BŪVĮ IR ARMATŪROS IŠANKSTINIO ĮTEMPIMO NUOSTOLIUS

1999 ◽  
Vol 5 (6) ◽  
pp. 364-373 ◽  
Author(s):  
Robertas Balevičius ◽  
Eugedijus Dulinskas
Keyword(s):  
Prestressed Concrete ◽  
Strain State ◽  
Time Dependent ◽  
Prestress Loss ◽  
Stress Strain ◽  
Prestress Losses ◽  
Concrete Creep ◽  
Stress Strain State ◽  
Concrete Members ◽  
Linear Creep

Determination of stress-strain state imposed by concrete linear creep and specification of steel prestress losses in linear prestressed concrete member is discussed in this article. Particularities of regulations of the Code acting in Lithuania [1] and of Eurocode [2] are analysed and a modified method for calculation of steel prestress losses due to concrete linear creep in prestressed concrete linear members suitable for assessment of Code regulations is presented. Also, the method is used for analysis of results of long-term tests of reinforced concrete members. In Lithuania, a code based on investigations of prestressed concrete members is used for calculation of steel prestress losses due to concrete creep. Therefore calculation of losses is associated with stress-strain state of the member in time t in empirical way only and time dependent stress-strain state is adjusted by additional coefficients to take into consideration concrete creep. Analogous calculations of steel prestress losses by Eurocode are presented in a more general form and are based on creep theory. It is clear that in the first [1] and the second [2] cases the same change in stress-state is evaluated by different parameters. Therefore it is important to create a general method based on concrete creep characteristics. General case of eccentrically reinforced prestressed concrete linear member under the action of prestressing forces changing with time in relation to prestress losses due to concrete creep is analysed (Fig 1). Stress-strain time dependent state of such member with the changing concrete stress σ b (t) and σ′ b (t) is determined using well-known equations of equilibrium (1–4) and integral differential equations (7–8) for evaluation of concrete creep deformations [4–8]. These equations are solved by numerical method (9–10) dividing time period considered in intervals. In reference [9] a more particular solution method evaluating variation of interval magnitude in relation to accuracy of solution is presented. In such a way it is possible to assess reduction of concrete stress (13–14) at time moment t when loss of steel prestress due to concrete creep takes place (33–34). There are many experiments performed for investigating concrete creep and determinating time dependent stress-strain state of reinforced concrete members. Various methods are applied for analysis of these data. Assumptions of these methods influence the conclusions of the analysis. In this article there is presented a general method giving opportunity to assess creep of concrete members by the same characteristics, when specific creep (51) or coefficient of creep (52) is determined by tests on eccentrically prestressed linear members (the case of axially prestressed members is presented in [9]). Pure specific creep C* (t,t 0) values determined according to the method proposed in this article and results of experimental investigations [12] of prestress in steel of eccentrically prestressed concrete members and also according to data of analysis [11] of the Code [1] are presented in Fig 2. Using the same creep characteristics method of the Code EC-2 and proposed in this article losses of prestress in steel due to concrete creep were calculated according to EC-2 and the method proposed. Values of these losses and their ratio are presented in Fig 3 and 4. In Fig 5, losses of prestress in steel due to creep predicted after 70 years were calculated in accordance with data of the Code SNiP [1] analysis [11] and regulations of the Code EC-2 [2]. Relationships (62) including (63), (64) formulas are modified EC-2 method for regulation of steel prestress loss due to concrete creep calculation for doubly reinforced members are proposed in the article. Results of analysis of regulations of Eurocode EC-2 and the Code SNiP indicate that design according to Code [2] method for steel prestress loss due concrete creep calculation in all cases gives increased values of stiffness and crack resistance characteristics of the structure, but larger amount of steel is to be used in comparison with the design according to SNiP [1].

Preparation And elemental analysis of ancient fibers

1987 ◽  
Vol 45 ◽  
pp. 410-411
Author(s):  
Allen Angel ◽  
Kathryn A. Jakes
Keyword(s):  
Cross Sections ◽  
Physical Structure ◽  
Energy Dispersive ◽  
Archaeological Sites ◽  
X Ray ◽  
Long Term Storage ◽  
Backscattered Electron ◽  
Electron Imaging

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.

Masonry: the brittle or plastic material?

2019 ◽  
pp. 22-28
Keyword(s):  
Plastic Material ◽  
Experimental Studies ◽  
Point Of View ◽  
Plastic Properties ◽  
Plastic Deformations ◽  
Base Materials ◽  
Stress States ◽  
Creep Deformations ◽  
Structural Point

The results of experimental studies of masonry on the action of dynamic and static (short-term and long-term) loads are presented. The possibility of plastic deformations in the masonry is analyzed for different types of force effects. The falsity of the proposed approach to the estimation of the coefficient of plasticity of masonry, taking into account the ratio of elastic and total deformations of the masonry is noted. The study of the works of Soviet scientists revealed that the masonry under the action of seismic loads refers to brittle materials in the complete absence of plastic properties in it in the process of instantaneous application of forces. For the cases of uniaxial and plane stress states of the masonry, data on the coefficient of plasticity obtained from the experiment are presented. On the basis of experimental studies the influence of the strength of the so-called base materials (brick, mortar) on the bearing capacity of the masonry, regardless of the nature of the application of forces and the type of its stress state, is noted. The analysis of works of prof. S. V. Polyakov makes it possible to draw a conclusion that at the long application of the load, characteristic for the masonry are not plastic deformations, but creep deformations. It is shown that the proposals of some authors on the need to reduce the level of adhesion of the mortar to the brick for the masonry erected in earthquake-prone regions in order to improve its plastic properties are erroneous both from the structural point of view and from the point of view of ensuring the seismic resistance of structures. It is noted that the proposal to assess the plasticity of the masonry of ceramic brick walls and large-format ceramic stone with a voidness of more than 20% is incorrect, and does not meet the work of the masonry of hollow material. On the basis of the analysis of a large number of research works it is concluded about the fragile work of masonry.

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