Site: Rolling Traffic Test Simulator
Osaka University
Osaka, Japan
Date Visited: October 1996
Host: Professor S. Matsui, Associate Professor of Civil Engineering, Osaka University
Summary: Simulation of wheel loads on a carbon fabric strengthened concrete deck.

ACTIVITIES OF INTEREST

As part of an ongoing research project on the deterioration of reinforced concrete deck slabs of highway bridges, Professor Matsui has developed a test machine that simulates wheel loads while duplicating crack pattern development as seen in the field. The development was initiated by observations that laboratory simulated cracking of reinforced concrete (RC) slabs did not follow crack development patterns seen in the field (Fig. B.7). In the field, deterioration is initiated by cracks in the transverse (load-carrying) direction. These subsequently limit the tributary width of the transverse deck span, resulting in cracking in the longitudinal direction. It eventually leads to an orthotropic crack pattern (Fig. B.8), which has a tendency to result in local punching shear failures.


Fig. B.7. Comparison of cracking patterns on slabs.


Fig. B.8. Stages of crack growth.

The running wheel load machine (Figs. B.9 and B.10) permits the development of realistic crack patterns and deterioration under laboratory conditions while simultaneously simulating running wheel loads. In a research project being conducted for the Public Works Research Institutes (PWRI) and Tonen Corporation, the machine is being used to assess the efficiency of the use of external strengthening of RC bridge decks through the application of carbon fiber sheets. Fatigue testing is conducted on a slab that has tow sheet layers on the bottom and is instrumented with linear potentiometers and strain gages. Testing was still in progress at the time of this WTEC visit.


Fig. B.9. Schematic of the running wheel load machine.


Fig. B.10. View of the load roller on top of the strengthened slab.


Fig. B.11. Close-up showing tow sheet on the bottom surface of the slab, and instrumentation.

After the establishment of criteria by the Ministry of Construction for the raising of load levels from 20 tons (T-20) to 25 tons (T-25), tests were conducted using the machine and a slab configuration as shown in Fig. B.12.


Fig. B.12. Configuration of slab.

Three slabs were subjected to 100,000 cycles of initial loading at a wheel load of 10 tons. Then the performance was measured for stiffness and initial deflection. The first slab was then subjected to further cyclic loading at 15 tons until fracture. The second slab was retrofitted with carbon fiber sheet of grade FTS-C5-30, which has properties as listed in Table B.1, and was then subjected to 100,000 cycles at 10 tons and 1,000,000 cycles at 15 tons. The third slab was likewise retrofitted and subjected to 1,000,000 cycles at 10 tons, then further reinforced with a layer of concrete (60 mm thickness) on the top face. Next, it was loaded to 60,000 cycles at 10 tons, 560,000 cycles at 15 tons and 440,000 cycles at 18 tons. For each configuration, static tests were conducted at intervals to assess degradation through visual examination and through measurements of slab deflection and strains in the reinforcing bars (which were also continuously monitored during the test). Overall results are shown in Fig. B.13 and B.14.

Characteristic

Value

Fiber Density

Areal Weight

Thickness (per layer)

Tensile Strength (103 kg/cm2)

Tensile Modulus (106 kg/cm2)

Ultimate Elongation

1.82 g/cm2

300 g/cm2

0.165 mm

30

3.8 - 4.1

0.8%


Fig. B.13. Comparison of deflections under live load (10 tons).


Fig. B.14. Comparison of deflections under live load (15 tons). Based on its experience with the current machine, PWRI is installing two such machines (Figs. B.15 and B.16) with extensive monitoring instrumentation for 24 hour continuous testing. It is expected that further testing on composite retrofit strategies for the assessment of long-term deterioration will be conducted once these machines are operational.


Fig. B.15. Dual test setup of running wheel machine at PWRI.


Fig. B.16. Overall view of the machine.


Published: October 1998; WTEC Hyper-Librarian