FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS USING SHAPE MEMORY ALLOYS

Transcription

1 FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS USING SHAPE MEMORY ALLOYS Osman E. Ozbulut Assistant Professor Muhammad Sherif Ph.D. Student Department of Civil and Environmental Engineering University of Virginia Reginald Hamilton Associate Professor Asheesh Lanba Ph.D. Candidate Department of Engineering Science and Mechanics The Pennsylvania State University 6 th World Conference on Structural Control and Monitoring (6WCSCM) July 16, 2014 Barcelona, Spain

2 Shape memory alloys (SMAs) are a smart class of metals that exhibit several extraordinary properties STRESS Detwinned STRESS Detwinned LOADING UNLOADING LOADING Twinned STRAIN Austenite UNLOADING Austenite HEATING Detwinned STRAIN COOLING Austenite M d No transformation Full recovery Austenite LOADING Detwinned TEMPERATURE A f A s M s Twinned LOADING COOLING Detwinned UNLOADING HEATING Detwinned TEMPERATURE A f A s UNLOADING Partial recovery M s M f Shape memory effect (Heat- ac1vated SMAs) M f Superelas1city (Superelas1c SMAs)

3 Advantageous of SMA tendons: ü The use SMA tendons, which possess high fa1gue and corrosion resistance, as post- tensioning elements in concrete girders will increase the service life and provide life- cycle cost savings for concrete bridges. ü The replacement of steel tendons with SMA prestressing tendons will prevent corrosion- induced deteriora1on of tendons in concrete structures. ü The use of heat of hydra1on of grout to ac1vate the shape memory effect of SMA tendons will provide self- stressing capability. ü This will greatly simplify the tendon installa1on. ü The need for jacking equipment or electrical source will be eliminated. ü This will also enable to form the reinforcement in any shape in two or three- dimensional space without special devices. ü The use of SMA tendons will lead to befer control of the prestress and higher levels of effec1ve prestress. During the service life of a bridge, heat- triggering the SMA tendons can repair possible damage observed in girders and reduce excessive deflec1ons.

4 This study investigates self-post-tensioned beams by activating the SME of NiTiNb using the heat of hydration of grout Twinned Detwinned! Austenite Self- post- tensioning process

5 The conditions on the phase transformation temperatures and the required temperature window for self-stressing application are shown below fraction Should be over maximum ambient temperature 100% M f Twinned A s Austenite 0% M s A f Should be below minimum ambient temperature Service Temperature Temperature Should be close to the A s Phase transforma1on temperatures of SMAs

6 The relationship between processing, microstructure, and transformation temperatures were studied processed

7 Systematic experiments were conducted to characterize the shape memory effect recovery at different levels of pre-strain Load Cell Induction Heating Coil Specimens cooled in liquid nitrogen prior to tes1ng in order to try and stabilize martensite in the matrix at RT

8 The material was loaded to 5.0, 8.9, 12.5, and 16.9 percent pre-strain levels and was heated to recover the residual strain

9 The recovery ratio and reverse transformation temperatures A s and A f are plotted as a function of prestrain level Recovery Ra1o (%): heat ε recov unl *100% ε res

10 In order to gain insight into the transformation morphology, strain localization is characterized via DIC % % DIC Ext. 0% ε (%) 20% % % 0% ε (%) 15%

11 The constrained recovery stress were conducted on two types of specimens! Type A is a dog- bone specimen whose gage sec1on is 57.2 mm long and 4.2 mm wide, and strained to 14% strain Type B is a flat specimen which is 241 mm long, and strained to 15%.

12 In order to determine the temperature increase during grouting post-tensioning ducts, four commercially available tendon grouts were tested (1) Euco Cable Grout PTX (Euco), produced by Euclid Chemical; (2) SikaGrout 300 PT (Sika), produced by Sika Corp.; (3) Five Star Special Grout 400 (Five Star), produced by Five Star Products, Inc.; (4) MasterFlow 1205 Grout (MasterFlow), produced by BASF Chemical.

13 Temperature ( C) Euco S1 S2 S3 S1 Ambient S2 Ambient S3 Ambient Temperature ( C) Sika S4 S5 S6 S4 Ambient S5 Ambient S6 Ambient Time (hour) Time (hour) Temperature measured in different commercially available grouts during curing

14 Temperature ( C) Five Star S7 S8 S7/8 Ambient Temperature ( C) MasterFlow S9 S10 S11 S12 S9/10/11/12 Ambient Time (hour) Time (hour) Temperature measured in different commercially available grouts during curing

15 SUMMARY OF GROUT TEMPERATURE TEST RESULTS

16 To investigate the bond behavior of SMA bars with grout, pull-out tests were conducted!! τ = T πd b l b T = the tensile load on the SMA bar d b = the nominal bar diameter l b = the embedment length of the bar

17 Bond Stress (MPa) Loaded End Bond Stress (MPa) Free End Bond stress- slip rela1onship for SMA bars at free end and loaded end for Slip (mm) Slip (mm) (a) Specimen Bond Stress (MPa) Loaded End Bond Stress (MPa) Free End (b) Specimen Slip (mm) Slip (mm)

18 Beam tests will be conducted in Fall

19 ! Material characterization tests were conducted on two types of NiTiNb SMAs. It was shown that a recovery stress more than 500 MPa could be achieved after cooling to ambient temperature. The increase in temperature during the hydration of four commercially available grouts was evaluated. At three different tests of Sika grout, an average of 28 C temperature increase was observed. Temperature ( C) Sika S4 S5 S6 S4 Ambient S5 Ambient S6 Ambient 20 Pullout tests were conducted on cylindrical specimens to investigate the bond between the grout and SMA bar Time (hour)

20 ACKNOWLEDGEMENTS This study has been supported by the Mid-Atlantic Universities Transportation Center (MAUTC) Pooled Research Program issued by the Research and Innovative Technology Administration of the US DOT (Grant No. DTRT12-G-UTC03).

21 FEASIBILITY OF SELF-POST-TENSIONED CONCRETE BRIDGE GIRDERS USING SHAPE MEMORY ALLOYS Osman E. Ozbulut Assistant Professor Muhammad Sherif Ph.D. Student Reginald Hamilton Associate Professor Asheesh Lanba Ph.D. Candidate THANK YOU! 6 th World Conference on Structural Control and Monitoring (6WCSCM) July 16, 2014 Barcelona, Spain