Research works on both concrete shell and SCS sandwich shell structures are quite limited in public domain to deal with the curved geometry. Several published papers and PhD thesis on this topic were reviewed and summarized as below.
2.3.1 Curved reinforced concrete (RC) structure or RC shell structure
Concrete shells were proposed as the selective form of the ice-resistant structures (Birdy et al, 1985; Long, 1988; McLean et al., 1990). Birdy et al. (1985) proposed a concept of
‐ 23 - using concrete shells as the ice-resistant wall for the Arctic concrete platforms. The concrete shells in a cone shape around the platform resisted the ice contact pressure and provided protections. A typical segment of this protection cone was designed and tested under point load (shown in Fig. 2.5). All the tested concrete shells were designed with same dimensions for span and width of 2286 mm. The thickness was 152 mm. Concrete shells were designed with two types of curvature that the ratios of soffit radius-to- thickness were 12 and 36, respectively. All these concrete shells were compared with the flat ones. From the experimental studies, several conclusions were drawn as follows:
(1) The ratio of the shear reinforcement would significantly increase the punching shear capacity of the concrete shell. This influence was larger than the strength of the steel shear reinforcement; (2) Increasing curvature of the concrete shell, the punching shear strength would be significantly increased; (3) All the concrete shells failed in a ductile mode; (4) The predictions by ACI 318-77 greatly underestimated the test results.
The beam shear model gave the most satisfactory predictions.
Maclean et al. (1990) and Long (1988) investigated the punching shear behavior of the concrete shells with lightweight concrete. Nine concrete slabs and six concrete shells were tested under concentrated loading. All the tested concrete slabs and shells were designed with a span of 40 inches. The thicknesses for the slabs and shells were 5 and 7 inches, respectively. The investigated parameters were shear reinforcement ratio, loading area, radius-to-shell thickness ratio, prestressing of the flexural reinforcement and concrete strength. The test setup and dimensions of these lightweight concrete slabs and shells are shown in Fig. 2.6. Some conclusions were drawn from the experimental investigations and illustrated as follows:
(1) The curvature of the concrete shell led to increments in the punching shear resistance. However, the increasing rate of the strength would decrease as the curvature
‐ 24 - increased; (2) Using shear reinforcement significantly increased the punching shear strength for both flat concrete slabs and concrete shells. This influence was more significant on flat concrete slabs than shells. The increase in punching shear strength by the shear reinforcement was more significant to the shells with lesser curvature; (3) Larger loaded area led to lower strength due to the increasing interaction between punching shear and beam shear; (4) Strength of flat slab with single span was larger than the one with three-span slab; (5) Punching shear strength predicted by the ACI design code underestimated the test results especially for the specimens with shear reinforcements.
All these tested concrete covered both normal weight and lightweight concrete. The tested concrete shells were designed with or without shear reinforcements. Many exciting and beneficial observations were obtained from these tests on the scaled specimens. However, the specimens were only limited to the RC shells but not for the SCS sandwich composite shells. All these tested concrete shells were limited to one or several grade normal weight concrete or one particular lightweight concrete.
Sabnis and Shadid (1994) summarized and analyzed tests results on 68 concrete shells from different literatures. The modified the design formulae considered different parameters that influenced the punching shear strength of the concrete shells. Those analyzed parameters were concrete strength, flexural reinforcement content, thickness of the slab or shell, dimension and shape of the loaded area, interaction between shear and flexure, and curvature of the shell. Based on the regression analysis, a design formula was proposed to predict punching shear strength of the concrete shells. Compared with available design guidelines ACI, this proposed formula offered better predictions.
‐ 25 - 2.3.2 SCS sandwich shell structure
SCS sandwich composite shells without taking any bonding measures had been proposed as oil reservoirs laid on the seabed by Montague (1978). Considering the working state of the proposed shells, pressure of the sea water was the main concern for this type of shell structures. Therefore, behaviors of SCS sandwich composite shells under external pressure had been studied by Montague (1978a; 1978b; 1979; 1986), Goode and Fatheldin (1980). SCS sandwich composite shells subjected to external pressure and concentrated loading were investigated by Shukry (1986). The concrete and SCS sandwich shells subjected to external pressure had been studied by Nash (1987). The experimental works on punching shear strength on SCS sandwich shells were investigated by Shukry and Goode (1990). Besides experimental studies, the analytical method on strength of SCS sandwich shells under external pressures had been developed and verified against the test results. In the experimental studies on punching shear strength of the SCS sandwich composite shells (Shukry, 1986), the investigated parameters were thickness of the external face steel plate, size of the loading area, concrete strength, curvature of the shell, and total wall thickness of the shell. All the SCS sandwich shells were designed with the same span of 345 mm. The detailed dimensions are shown in Fig. 2.7. Based on test results of these SCS sandwich composite shells, some conclusions were drawn for the punching shear strength of these sandwich composite shells as below:
1) The thickness of the steel skin increased the punching shear capacity of the filler concrete. The external steel skin plates were an efficient method to resist ice loading; 2) Curvature of the shell would significantly influence the punching shear strength of the SCS sandwich shells; 3) Several used design codes including EC2, CEB-FIP and BS5950 underestimated the punching shear strength of the sandwich shell; 4) Deeper angles between the shear plane and concrete free surface were observed in the circumferential
‐ 26 - direction than that in longitudinal direction.
All the above research works are limited to the SCS sandwich composite shells without mechanical shear connectors. Moreover, only normal weight concrete was used for all the tested SCS sandwich shells. SCS sandwich shells with LWC have not been investigated.
Composite bonding measures such as cohesive material or mechanical connectors were not used in the sandwich shell structure.