CHAPTER 6 Experimetnal study on steel-concrete-steel sandwich composite shell
6.3 Static tests on SCS sandwich composite shells
6.3.3 Test setup and instrumentation
In order to measure the deformed shapes of the SCS sandwich composite shell, LVDTs were installed on both inner and outer steel shell surface to record the displacements at different loading levels.
6.3.3.1 Test setup for SA1 and SA2
Nominal wall thickness of the SCS sandwich shell takes average thicknesses at different locations. These locations are at the haunch, one and three quarters of the arch, and mid-
‐ 238 - span. For SA1 and SA2, the layout of the transducers is shown in Fig. 6.5(a). Four LVDTs are separately installed on top and bottom steel shells along the arch strip at the middle width. All these installed transducers were linked to a data logger TDS-530 that was controlled by software VISUAL LOG TDS7130 on the linked PC.
Three directional strain gauges-rosettes and single direction linear strain gauges were used to measure the strains in the inner and outer steel shells. The locations of these strain gauges are shown in Figs. 6.5(b), 6.6(b)~(e), and 6.6(g)~(h).
In order to provide the thrust forces to the curved SCS sandwich composite shells, two triangular beams were used to support the specimen. These two triangular supporting beams were bolted to the underneath four linking I-beams to provide horizontal restraints on movement. There was a reserved gap of 20 mm between the specimen and the support that was designed to tolerate the fabrication errors. After connecting the shell specimens to the two triangular beams by 10 bolts on each beam, high strength concrete with a 3 days’ compressive strength of 60 MPa was used to fill the gap between the support and specimen (shown in Fig. 6.7). All these measures were taken to overcome the ‘soft support’ problem during the test.
SA1 and SA2 were loaded by the INSTRON 200 tons servo-hydraulic actuator.
Displacement type of loading with a rate of 0.05mm/min was applied to the steel block that was put on the top of the specimen. The test setup is as shown in Fig. 6.7. The reaction forces and corresponding measured deflections and strains at different locations were recorded by the data logger at different loading stages.
Eccentric loading was applied to the specimen is that the eccentric ice-contact pressure will produce the horizontal push forces and produce the stability problems that is more harmful to the structure (Marshall, 2009).
‐ 239 - The specimens were preloaded to check the readings of all the measurements prior to the test. The loading procedures were as following:
1) Load to 110 kN-0.5 times the ISO load, recorded data then unloaded; 2) loaded to 220 kN-1.0 times the ISO load, recorded data then unloaded; 3) loaded to 330 kN-1.5 times the ISO load, recorded data then unloaded; 4) ten cycles of load from 0 to 440 kN (2 times the ISO load); 5) loaded to fail.
6.3.3.2 Test setup for SB1~SB7
For SB1~SB7, the LVDTs were installed on both outer and inner steel shells to measure the deformed shape at different loading levels (shown in Fig. 6.6(a)). All these transducers were linked to a data logger TDS-530 that was controlled by a software Visual Log TDS7130 running on the linked PC. Rosettes and linear strain gauges were installed on both inner and outer steel shells to measure the strains developed in the steel shells during the loading. The locations of them are shown in Fig. 6.6. The same supports for SA1 and SA2 were also used for SB1~SB7. The specimens were bolted to triangular beams that were connected to the underneath I-beam support. This apparatus could provide enough thrust to specimens when they were tested.
The test setup for SB1~SB7 is shown in Fig. 6.8. All the specimens SB1~SB7 were tested by 1000 tons INSTRON servo-hydraulic actuator. Displacement controlled type of loading with a rate of 0.05 mm/min was applied at the center of the shell. All the measured displacements and strains by LVDTs and strain gauges were recorded by the data logger controlled by the connected PC.
Preloading was also carried out to the specimens to fit them to the support and check the readings of the measurements by transducers and strain gauges. The same loading progress was used as that was used for SA1 and SA2 in section 6.3.3.1. Moreover,
‐ 240 - cameras were also used to take the photos of the deformed shapes of the SCS sandwich composite shell at different loading levels.
6.3.3.3 Test on core material and the steel face plates
As aforementioned in the progress of the casting SCS sandwich composite shell, cylinders and cubes were prepared and tested at the same day of the test on corresponding shell. Through the compressive test and splitting test on the cylinders, the average compressive strength and splitting tensile strength were obtained for the core material.
The compressive and splitting tests on the core material are shown in Fig. 6.8 (b) and (c), respectively.
Three pieces of coupons were prepared for each type of steel plate. Tension tests on these steel coupons were carried out to obtain the stress-strain curves (Test setup is shown in Fig. 6.8(d)). The stress-strain curve of the reinforcement that was used to fabricate the J- hook connectors were obtained through tension tests on the 30 cm long steel bars (Test setup is shown in Fig. 6.8(e)).