Experimental Monitoring of Long-Term Structural Behaviour and Prestress Losses of BFRP Pretensioned Beams Under Sustained Loading

The proper distribution of prestressing force (PF) is the basis for the design of prestressed concrete (PSC) structures. However, the PF distribution obtained by predictive equations of prestress losses has not been sufficiently validated by comparison with measured data due to the poor reliability and durability of conventional sensing technologies. Therefore, the Smart Strand with embedded fiber optic sensors was developed and applied to PSC structures to investigate the long-term characteristics of PF distribution as affected by concrete creep and shrinkage. The data measured in a 20 m-long full-scale specimen and a 60 m-long PSC girder bridge were analyzed by comparing them with the theoretical estimation obtained from several design equations. Although the long-term decreasing trend of the PF distribution was similar in the measurement and theory, the equation of Eurocode 2 for estimating the long-term prestress losses showed better agreement with the measurement than ACI 209R and ACI 423.10R did. This can be attributed to the more refined form of the predictive equation of Eurocode 2 in dealing with the time-dependency of the PF. The study results also confirmed the need to compensate for the temperature variation in the long-term monitoring to derive the actual mechanical strain related to the PF. We expect our developed Smart Strand to be applied practically in PF measurement for the reasonable safety assessment and maintenance of PSC structures by improving several of the existing drawbacks of conventional sensors.

Download Full-text

Flexural behaviour of concrete beams strengthened with prestressed carbon fibre reinforced polymer sheets subjected to sustained loading and low temperature

Canadian Journal of Civil Engineering ◽

10.1139/l03-091 ◽

2004 ◽

Vol 31 (2) ◽

pp. 239-252 ◽

Cited By ~ 13

Author(s):

Raafat El-Hacha ◽

Mark F Green ◽

R Gordon Wight

Keyword(s):

Low Temperature ◽

Carbon Fibre ◽

Flexural Behaviour ◽

Prestress Losses ◽

Cfrp Sheets ◽

Reinforced Polymer ◽

Carbon Fibre Reinforced Polymer ◽

Fibre Reinforced Polymer ◽

Prestressed Cfrp Sheets

This paper presents results of an experimental investigation that examined concrete beams post-tensioned with bonded carbon fibre reinforced polymer (CFRP) sheets and then exposed to either room (+22 °C) or low (-28 °C) temperatures. The primary objective of this investigation was to assess the flexural behaviour of the strengthened beams after sustained loadings at both room and low temperatures. The strengthened beams showed significant increases in flexural stiffness and ultimate capacity as compared with the control-unstrengthened beams. Failure of the strengthened beams was by tensile rupture of the prestressed CFRP sheets. Test results showed that the long-term and low temperature effects did not adversely affect the strength of the beams. Long-term loading and low temperature exposure caused prestress losses in the CFRP sheets. The loaddeflection behaviour of the long-term beams was predicted accurately by an analytical model. These results suggest that bonded prestressed CFRP sheets could be used to increase the strength of damaged prestressed concrete girders under extreme environmental conditions.Key words: strengthening, anchorage, low temperature, long-term, prestress losses, sustained load, carbon fibre reinforced polymer sheet.

Download Full-text

Conical Acrylic Windows Under Long-Term Hydrostatic Pressure of 10,000 psi

Journal of Engineering for Industry ◽

10.1115/1.3428292 ◽

1972 ◽

Vol 94 (4) ◽

pp. 1053-1059 ◽

Cited By ~ 1

Author(s):

J. D. Stachiw

Keyword(s):

Hydrostatic Pressure ◽

Deep Ocean ◽

Diameter Ratio ◽

Conical Cavity ◽

Ambient Temperatures ◽

Hydrostatic Loading ◽

Pressure Application ◽

Sustained Loading ◽

General Service

Over 150 conical frustum acrylic plastic windows were subjected to 10,000 psi hydrostatic loading of up to 1000-hr duration in deep ocean simulators maintained at 65–75 deg F ambient temperature. Axial displacements of the windows under hydrostatic loading through the conical cavity in the flange were recorded and plotted as a function of time, thickness to minor diameter ratio (t/D), and included conical angle α. Data indicate that only windows with α ≥ 90 deg and t/D ≥ 0.75 are satisfactory for sustained long-term hydrostatic loading of 1000-hr duration at 10,000 psi in ambient temperatures ≤80 deg F. For general service, which includes also cyclic pressurizations to 10,000 psi, an included angle α ≥ 90 deg and t/D ratio of ≥ 1.0 are recommended. The axial displacement of windows recommended for 10,000 psi service is approximately 0.04D after 1000 hr of sustained loading. Approximately 75 percent of this displacement takes place during the first hour of pressure application.

Download Full-text

Long-Term Reliability of Historical Monuments Built with Low Quality Sandstone

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.133-134.331 ◽

2010 ◽

Vol 133-134 ◽

pp. 331-336 ◽

Cited By ~ 1

Author(s):

Els Verstrynge ◽

Luc Schueremans ◽

Dionys Van Gemert ◽

Evert Bourel

Keyword(s):

Compressive Strength ◽

Creep Model ◽

Original Material ◽

Dead Load ◽

Test Program ◽

Long Term Stability ◽

Sustained Loading ◽

Historical Monuments ◽

Set Up

The presented research concerns the long-term stability of a series of historical monuments, which were constructed with low-strength, ferrous sandstone. The main issues are the overall low compressive strength of the sandstone, the large scatter on these strength values, the sensitivity of its characteristics to water absorption and the lack of new original sandstone to replace the damaged zones. The sandstone reacts poorly under sustained high load levels, a situation which typically occurs at the base of bell towers and medieval city towers, as the dead load is considerably high compared to the compressive strength of the sandstone material. To assess the long-term behaviour of the sandstone, a test program has been set up to obtain information on its strength characteristics under monotonic and sustained loading. Therefore, test specimens were taken from the original material of a collapsed church tower. The results of these laboratory tests were used to adapt the parameters of an existing creep model to simulate the long-term behaviour of the sandstone under specific stress levels. Additionally, a number of strengthening solutions are discussed.

Download Full-text

Structural behaviour of CFRP reinforced concrete members under monotonic and cyclic long-term loading

Materials and Structures ◽

10.1617/s11527-021-01728-4 ◽

2021 ◽

Vol 54 (4) ◽

Author(s):

Redouan El Ghadioui ◽

Dominik Hiesch ◽

Lukas Bujotzek ◽

Tilo Proske ◽

Carl-Alexander Graubner

Keyword(s):

Experimental Data ◽

Reinforced Concrete ◽

Structural Engineering ◽

Creep Behaviour ◽

Time Dependent ◽

Experimental Investigations ◽

Structural Behaviour ◽

Displacement Sensors ◽

Precise Knowledge

AbstractA large percentage of the damages to reinforced concrete structures is caused by corrosion of the reinforcement steel, which often leads to expensive repairs or new construction of existing structures. Due to their high strength and resistance to corrosion, reinforcements made of carbon fibre-reinforced polymers (CFRP) are becoming more and more important in structural engineering. It is expected, that the service life of CFRP reinforced concrete (RC) members can be significantly increased as the strength-reduction due to corrosion is negligible compared to conventional RC members. Therefore, precise knowledge of the long-term behaviour of CFRP RC members is required in order to ensure safe and economic design. This paper presents experimental investigations on the long-term behaviour of CFRP RC members as well as steel-reinforced RC members under monotonic and cyclic long-term loading with varying load levels, different cross-sectional shapes and shear slendernesses. Accompanying experiments on the concrete creep behaviour that were conducted within the investigations are shown. Within the scope of the experiments, the deflections as well as the strains on the top and bottom side of the RC members were measured using displacement sensors and strain gauges. The experimental data is evaluated, especially with regard to the time-dependent deflections. The data is compared to existing mechanical and empirical models, which are usually derived for steel-reinforced RC members. Based on the experimental data, the time-dependent reduction of stiffness and conclusions for the calculation of deflections are shown.

Download Full-text

RC slabs strengthened with externally bonded CFRP strips under long-term environmental exposure and sustained loading. Part 2: Laboratory experiments

Composites Part C: Open Access ◽

10.1016/j.jcomc.2021.100210 ◽

2021 ◽

pp. 100210

Author(s):

Matteo Breveglieri ◽

Christoph Czaderski

Keyword(s):

Environmental Exposure ◽

Laboratory Experiments ◽

Sustained Loading ◽

Externally Bonded ◽

Rc Slabs

Download Full-text

Performance of Linear Mixed Models to Assess the Effect of Sustained Loading and Variable Temperature on Concrete Beams Strengthened with NSM-FRP

Sensors ◽

10.3390/s21155046 ◽

2021 ◽

Vol 21 (15) ◽

pp. 5046

Author(s):

Ricardo Perera ◽

Lluis Torres ◽

Francisco J. Díaz ◽

Cristina Barris ◽

Marta Baena

Keyword(s):

Failure Modes ◽

Experimental Testing ◽

Variable Temperature ◽

Local Level ◽

Impedance Method ◽

Electromechanical Impedance ◽

Sustained Loading ◽

Long Term Performance ◽

Term Performance

Although some extended studies about the short-term behavior of NSM FRP strengthened beams have been carried out, there is a lack of knowledge about the behavior of this kind of strengthening under sustained loads and high service temperatures. Electromechanical impedance method formulated from measurements obtained from PZT patches gives the ability for monitoring the performance and changes experienced by these strengthened beams at a local level, which is a key aspect considering its possible premature debonding failure modes. This paper presents an experimental testing program aimed at investigating the long-term performance of a concrete beam strengthened with a NSM CFRP laminate. Long term performance under different levels of sustained loading and temperature conditions is correlated with EMI signatures processed using Linear Mixed-effects models. These models are very powerful to process datasets that have a multilevel or hierarchical structure as those yielded by our tests. Results have demonstrated the potential of these techniques as health monitoring methodology under different conditions in an especially complex problem such as NSM-FRP strengthened concrete structures.

Download Full-text