Increase of stress in unbonded tendons in prestressed concrete beams and slabs

1981 ◽  
Vol 8 (2) ◽  
pp. 262-268 ◽  
Author(s):  
Perumalsamy N. Balaguru
Keyword(s):  
Prestressed Concrete ◽  
Ultimate Load ◽  
Concrete Beams ◽  
Regression Equation ◽  
Prestressing Force ◽  
Unbonded Tendons ◽  
Stress Strain Relation ◽  
Stress Changes ◽  
Tendon Strain ◽  
Suggested Formula

In the case of prestressed concrete beams with unbonded tendons, in order to design for strength and serviceability, one has to evaluate the effective prestressing force in the tendon, which is beam dependent rather than section dependent, both at ultimate and working loads. The formulae available in the published literature deal only with ultimate load conditions. A simple equation to predict the tendon stress changes for the complete loading range is presented in this paper. The formula was developed using the basic theory of flexure to obtain the equation for the elastic curve, and numerical integration to obtain the curve lengths. Using the computer generated results of the increase in tendon strain for various span lengths, eccentricities, and maximum deflections, a regression equation was developed. This regression equation predicts the increase in tendon strains as a function of the span–eccentricity and eccentricity – maximum deflection ratios. The recently published stress–strain relation which seems to be very accurate is then used to predict the tendon stress. The results are compared with a set of experimental results. The suggested formula is also consistent with some of the available equations for the prediction of the tendon stress at ultimate load.

Ductility analysis of prestressed concrete beams with unbonded tendons

2008 ◽  
Vol 30 (1) ◽  
pp. 13-21 ◽  
Author(s):  
J.S. Du ◽  
Francis T.K. Au ◽  
Y.K. Cheung ◽  
Albert K.H. Kwan
Keyword(s):  
Prestressed Concrete ◽  
Concrete Beams ◽  
Unbonded Tendons

Flexural ductility of prestressed concrete beams with unbonded tendons

2009 ◽  
Vol 6 (6) ◽  
pp. 451-472 ◽  
Author(s):  
F.T.K. Au ◽  
K.H.E. Chan ◽  
A.K.H. Kwan ◽  
J.S. Du
Keyword(s):  
Prestressed Concrete ◽  
Concrete Beams ◽  
Unbonded Tendons ◽  
Flexural Ductility

Research on Stress Increase of Unbonded Tendons at Ultimate in Prestressed Concrete Continuous Beams

2012 ◽  
Vol 166-169 ◽  
pp. 1554-1557
Author(s):  
Xiao Dong Wang ◽  
Wen Zhong Zheng ◽  
Ying Wang
Keyword(s):  
Prestressed Concrete ◽  
Concrete Beams ◽  
Simulation Analysis ◽  
Analysis Method ◽  
Stress Increase ◽  
Continuous Beams ◽  
Unbonded Tendons ◽  
Index Ratio ◽  
Prestressed Reinforcement ◽  
Rational Evaluation

Rational evaluation for stress increase of unbonded tendon at ultimate is the basis to exactly compute flexural load bearing capacity of unbonded prestressed concrete beams. Moment-curvature nonlinear analysis method is adopted to compile programs for calculating stress increase at ultimate in unbonded prestressed continuous beams. The precision of the method is proved by comparing results of 16 experimental two-span unbonded prestressed continuous beams to the prediction value of stress increase at ultimate. Based on the simulation analysis, law of the influence of some basic factors to stress increase at ultimate in unbonded tendons in continuous beams is obtained, such as non-prestressed reinforcement index, prestressed reinforcement index, ratio of span to depth and loading type. Then formulas for calculating stress increase at ultimate in unbonded tendons in prestressed concrete continuous beams were established.

scholarly journals COMBINING EBR CFRP SHEET WITH PRESTRESSED NSM STEEL STRANDS TO ENHANCE THE STRUCTURAL BEHAVIOR OF PRESTRESSED CONCRETE BEAMS

2021 ◽  
Vol 27 (8) ◽  
pp. 637-650
Author(s):  
M. Obaydullah ◽  
Mohd Zamin Jumaat ◽  
U. Johnson Alengaram ◽  
Md. Humayun Kabir ◽  
Muhammad Harunur Rashid
Keyword(s):  
Prestressed Concrete ◽  
Failure Modes ◽  
Concrete Beams ◽  
Element Model ◽  
Control Specimen ◽  
Flexural Performance ◽  
Flexural Failure ◽  
Prestressing Force ◽  
Cfrp Sheet ◽  
Strengthening Technique

In this study, a combined strengthening technique is used to improve the flexural performance of prestressed concrete beams using CFRP sheets as EBR and prestressed steel strands as NSM. Seven prestressed beams were tested under four-point loading with one control specimen, one EBR CFRP sheet strengthened specimen, one NSM steel strand without prestress strengthened specimen and four specimens strengthened with a combination of EBR CFRP sheet and NSM steel strands prestressed from 0% to 70% of their tensile strength. The flexural responses and failure modes of the specimens were investigated and the variations due to the level of prestressing force in the PNSM steel strands were also assessed. A finite element model (FEM) was developed using ABAQUS to verify the flexural responses of the strengthened specimens. The test results revealed that the combined strengthening technique remarkably enhanced the flexural performance of the specimens. The serviceability, first crack, yield, and ultimate load capacities improved up to 44%, 49%, 55% and 70%, respectively when compared with the control specimen. The combined technique also ensured the flexural failure of the specimens with significant enhancement in stiffness and energy absorption. The results of the FEM model exhibited excellent agreement with the experimental results.

Beams prestressed with unbonded tendons at ultimate

1996 ◽  
Vol 23 (6) ◽  
pp. 1220-1230 ◽  
Author(s):  
Marco Andrea Pisani ◽  
Emilio Nicoli
Keyword(s):  
Numerical Analysis ◽  
Key Words ◽  
Prestressed Concrete ◽  
Concrete Beams ◽  
Experimental Tests ◽  
Safety Factors ◽  
Unbonded Tendons ◽  
External Tendons ◽  
Simplified Method ◽  
Good Agreement

This paper presents a numerical investigation on beams and slabs prestressed with either unbonded internal or external tendons. Twenty-three experimental tests (beams and slabs prestressed with unbonded internal tendons) were numerically simulated to verify the reliability of the numerical algorithm adopted. The good agreement established enables us to study the behaviour of these beams in depth and to compare it with the behaviour of similar beams prestressed with external tendons. The numerical analyses were then repeated after including the safety factors related to the materials. The outputs were then compared with the results adopted by making use of the simplified method suggested by Eurocode E.C.2 Part 1-5, to check the size of the error involved in the adoption of the latter. Key words: numerical analysis, unbonded internal tendons, external tendons, European Prestandard, prestressed concrete, beams, post-tensioned.

Theoretical Analysis of Natural Vibration Frequency for Unbonded Prestressed Concrete Beams

2012 ◽  
Vol 594-597 ◽  
pp. 882-885 ◽  
Author(s):  
Feng Ge Li ◽  
Rong Li
Keyword(s):  
Prestressed Concrete ◽  
Natural Frequencies ◽  
Concrete Beams ◽  
Flexural Rigidity ◽  
Variable Stiffness ◽  
Natural Vibration Frequency ◽  
Test Results ◽  
Unbonded Tendons ◽  
Proposed Model ◽  
Calculation Results

This papers deals with the study of the influence of prestress force on the natural frequencies for unbonded prestressed concrete beams. A total of 5 unbounded prestressed concrete simply support beams were constructed and tested. The test results show that the prestress force has little effect on the nature frequencies of unbonded prestressed concrete beams. A model of variable stiffness is proposed to calculate the natural frequencies of prestressed concrete beams with unbonded tendons, which assumed that the flexural rigidity of the beam is changing when beams vibrating. The calculate results show that the calculation results by the proposed model agree well with experimental ones.

scholarly journals Analysis of Prestressing in Precast Prestressed Concrete Beams

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jakub Kraľovanec ◽  
Martin Moravčík ◽  
Jozef Jošt
Keyword(s):  
Numerical Analysis ◽  
Service Life ◽  
Prestressed Concrete ◽  
Concrete Beams ◽  
Direct Methods ◽  
Actual State ◽  
Indirect Methods ◽  
Remaining Service Life ◽  
Prestressing Force ◽  
Precast Prestressed Concrete

Abstract Knowledge of prestressing force’s value is in the case of prestressed concrete structure the most important basis for defining load-carrying capacity and remaining service life. Numbers of prestressed concrete structures are about to reach their limit of service life and they are exhibiting signs of deterioration due to the conceptional errors, inadequate maintenance and environmental distress. All of these factors negatively influence the actual state of prestressing. Thus, it is essential to determine the value of prestressing force considering the degradation of materials, such as corrosion of prestressing strands or wires. While assessing structure in service, it is difficult to apply magnetoelastic sensors or use other direct methods for determining the state of prestressing. Hence, the indirect methods enable to analytically calculate the prestressing force based on the results of measurement, e.g. strain, stress, deflection, or width of the crack. The present paper focuses on numerical analysis of prestressing in a twosome of precast prestressed concrete beams. For the numerical analysis, two indirect methods are applied, specifically Saw-cut method and Crack initiation method. Finally, the results are discussed and recommendations for the experimental campaign are summarized.

Shear Capacity Research on Transversely Reinforced Concrete Beams

2015 ◽  
Vol 744-746 ◽  
pp. 283-287
Author(s):  
Can Liu
Keyword(s):  
Reinforced Concrete ◽  
Prestressed Concrete ◽  
Concrete Beam ◽  
Concrete Beams ◽  
Great Influence ◽  
Shear Capacity ◽  
Reinforced Concrete Beams ◽  
Force Level ◽  
Prestressed Concrete Beam ◽  
Prestressing Force

Inner transverse prestressed bars were used to enhance the shear capacity of concrete beams in this paper, which can be used in transformer beams to reduce the sectional size. Two transversely prestressed one ordinary concrete beams were tested and calculated by finite element method, and the following conclusions can be drawn: (a)The shear capacity of transversely prestressed concrete beam increase rapidly with the increase of the prestressing force level, which means that prestressing force level has a great influence on the shear capacity of transversely prestressed concrete beam. (b) The transverse prestressing bars can efficiently enhance the anti-crack performance of the reinforced concrete beams.

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