Stresses in armour units
This research was undertaken by Dr. Jiansheng Xiang at Imperial College under the supervision of Dr. J-P Latham.
Real Concrete Units:
 AccropodeTM Units, Le Havre, France |
 Accropode IITM Units, S Korea (Courtesy CLI) |
Stress development at instant during a drop test collision of Accropode IITM Unit simulated with VGeST FEMDEM tools
For faceted and angular concrete units and rock blocks used in armour layers, FEMDEM provides excellent shape representation and deformability for static and dynamic problems. It also provides a powerful tool for examining stress chains within granular packs of armour units, e.g. showing where units in the toe of a structure are carrying excessively high stresses while other units are carrying very little.
Virtual Concrete Units:
 Vcross |
 VRcross |
Two virtual units were designed with the purpose of providing a non -commercial test case. They are termed the Vcross (33 tonnes) and VRcross units (42 tonnes) the latter having the corners substantially reinforced and a greater mass but the same square cross section for the base of the cross arms.
Cut plane showing maximum tensile stress of 3.89 MPa at instant of maximum stress 4.6 ms after drop test collision of Vcross Units, Vcrossmovie (see Latham et al. 2009). Total destruction of unit arms due to tensile failure would be expected.
| Vcross | VRcross |
Maximum tensile stress of 3.49 MPa at instant of maximum stress 4.8 ms after drop test collision of Vcross Units. Same impact velocity, greater mass, local spalling and crushing damage only to the VRcross unit.
The drop test simulation continues with the block bouncing off the anvil into the air. The FEMDEM method has been extended to multibody systems such as realistic rock dumping and packing relevant to armour layers.
Settlement and Transient Stress Development in ACCROPODETM units
A loose pack of 8m3 concrete units is subjected to a shake test on a smooth slope at full-scale using the FEMDEM code Y3D.
Results of simulations examining dynamic and static stress levels, settlement and factors of safety for CORELOC and ACCROPODE units were described in two conference papers presented in Yokohama, Oct 2011, at Coastal Structures ‘11.
References
Xiang, J., Munjiza, A. and Latham, J.-P., 2009. Finite strain, finite rotation quadratic tetrahedral element for the combined finite-discrete element method. International Journal for Numerical Methods in Engineering. 79(8), 946-978. doi: 10.1002/nme.2599
Latham, J.-P., Xiang, J. and Baird, W.F. 2011 A numerical investigation of the influence of friction and vibration on laboratory scale armour unit layers. Proceedings of International Conference on Coastal Structures, Yokohama, Japan. September 6-8, 2011.
Xiang J., Latham J.-P., Zimmer, D., Baird, W.F., Fons, M. 2011. Modelling breakwater armour layers and the dynamic response of armour units. Proceedings of International Conference on Coastal Structures, Yokohama, Japan. September 6-8, 2011.
Latham, J.-P., Mindel, J., Xiang, J., Guises, R., Garcia, X., Pain. C.,Gorman, G., Piggott, M., Munjiza, A., 2009. Coupled FEMDEM/Fluids for coastal engineers with special reference to armour stability and breakage. Geomechanics and Geoengineering, Volume 4, Issue 1, 797-805. dx.doi.org/10.1080/17486020902767362