Analysis of concrete structures subjected to sustained temperature gradients

1984 ◽  
Vol 11 (3) ◽  
pp. 404-410
Author(s):  
K. S. Sivakumaran ◽  
Walter H. Dilger
Keyword(s):  
Prestressed Concrete ◽  
Structural Engineering ◽  
Elevated Temperatures ◽  
Computing Time ◽  
Temperature Gradients ◽  
Time Dependent ◽  
Simple Method ◽  
Concrete Members ◽  
Continuous Beams ◽  
Sustained Loads

A simple method using aging coefficients and “creep-transformed” section properties is presented for computing time-dependent effects in uncracked concrete members subjected to sustained loads and sustained temperature gradients. The creep coefficients at elevated temperatures are determined using a normalizing function for temperature. The method is applied to prestressed continuous beams and the results are compared with experimental data. Key words: analysis, concrete (prestressed). concrete (reinforced), creep, loads (forces), shrinkage, structural engineering, temperature.

Time‐Dependent Analysis of Cracked Partially Prestressed Concrete Members

1993 ◽  
Vol 119 (12) ◽  
pp. 3571-3589 ◽  
Author(s):  
S. V. Krishna Mohan Rao ◽  
A. S. Prasada Rao ◽  
Walter H. Dilger
Keyword(s):  
Prestressed Concrete ◽  
Time Dependent ◽  
Concrete Members ◽  
Time Dependent Analysis

Time-dependent prestress loss and deflection in prestressed concrete members

PCI Journal ◽  
1975 ◽  
Vol 20 (3) ◽  
pp. 86-98 ◽  
Author(s):  
Maher K. Tadros ◽  
Amin Ghali ◽  
Walter H. Dilger
Keyword(s):  
Prestressed Concrete ◽  
Time Dependent ◽  
Prestress Loss ◽  
Concrete Members

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].

Experimental Study on the Stress Increment of Prestressed Tendons of Retard-Bonded Prestressed Concrete Continuous Beams

2010 ◽  
Vol 163-167 ◽  
pp. 1431-1435 ◽  
Author(s):  
Qiang Fu ◽  
Xia Cao ◽  
Ling Zhi Jin ◽  
Wan Xu Zhu ◽  
Hui Xian Yang ◽  
...  
Keyword(s):  
Experimental Study ◽  
Prestressed Concrete ◽  
Technical Specification ◽  
Continuous Beam ◽  
Stress Increment ◽  
Concrete Members ◽  
Continuous Beams ◽  
Unbonded Tendons ◽  
Working Performance ◽  
Made In

Based on the bending experiment for two-span continuous beams of retard-bonded prestress concrete, the analysis of the stress increment of prestressed tendons is made in the loading process. The theory that the working performance of retard-bonded prestressed concrete members is as same as unbonded prestressed concrete members during the retarding period is demonstrated. It is feasible to use the formulas for the reference (Technical specification for concrete structures prestressed with unbonded tendons) to calculate σputhe ultimate stress and Δσp the Stress increment of the retard-bonded prestressed tendons and the recommended formulas are advised to use. It is also demonstrated that retard-bonded prestressed concrete members have the same working performance as bonded prestressed concrete members after the retarding period. The conclusion of this paper can provide the reference date for the design of retard-bonded prestressed concrete continuous beam.

Flexural design of precast, prestressed ultra-high-performance concrete members

PCI Journal ◽  
2020 ◽  
Vol 65 (6) ◽  
pp. 35-61
Author(s):  
Chungwook Sim ◽  
Maher Tadros ◽  
David Gee ◽  
Micheal Asaad
Keyword(s):  
Prestressed Concrete ◽  
High Performance ◽  
High Performance Concrete ◽  
Limit State ◽  
Design Guidelines ◽  
Design Tool ◽  
Supplementary Cementitious Materials ◽  
Ultra High Performance Concrete ◽  
Concrete Members ◽  
Cylinder Strength

Ultra-high-performance concrete (UHPC) is a special concrete mixture with outstanding mechanical and durability characteristics. It is a mixture of portland cement, supplementary cementitious materials, sand, and high-strength, high-aspect-ratio microfibers. In this paper, the authors propose flexural design guidelines for precast, prestressed concrete members made with concrete mixtures developed by precasters to meet minimum specific characteristics qualifying it to be called PCI-UHPC. Minimum specified cylinder strength is 10 ksi (69 MPa) at prestress release and 18 ksi (124 MPa) at the time the member is placed in service, typically 28 days. Minimum flexural cracking and tensile strengths of 1.5 and 2 ksi (10 and 14 MPa), respectively, according to ASTM C1609 testing specifications are required. In addition, strain-hardening and ductility requirements are specified. Tensile properties are shown to be more important for structural optimization than cylinder strength. Both building and bridge products are considered because the paper is focused on capacity rather than demand. Both service limit state and strength limit state are covered. When the contribution of fibers to capacity should be included and when they may be ignored is shown. It is further shown that the traditional equivalent rectangular stress block in compression can still be used to produce satisfactory results in prestressed concrete members. A spreadsheet workbook is offered online as a design tool. It is valid for multilayers of concrete of different strengths, rows of reinforcing bars of different grades, and prestressing strands. It produces moment-curvature diagrams and flexural capacity at ultimate strain. A fully worked-out example of a 250 ft (76.2 m) span decked I-beam of optimized shape is given.

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