Numerical Analysis of Reverse Fault Rupture Hazards on Buildings

The destructions of earthquakes in Turkey and Taiwan (1999) have increased the interest of investigation on structures behavior in surface fault rupture propagation. Therefore, many studies have been accomplished to investigate the fault rupture and shallow foundations interaction. Based on the fact that a lot of structures are constructing and they have the possibility of facing fault emergence hazards due to the uncertainty in exact locating of surface fault emergence, the investigation on surface fault rupture hazards can give a better insight to explicit this issue and mitigate the damage to constructions adjacent or in active fault zones. In this research, numerical investigations on surface fault rupture hazards based on the evaluation of earthquake's field studies and seismic codes limitations for constructions in active fault zones have been employed.Based on field studies observations, four different fault zones withdifferent levels of hazard possibility for structures have been obtained. Some of the field studies results have been reviewed in this paper. For numerical studies, the two-dimensional, finite element software (Plaxis) was employed to study the surface fault rupture mechanism beneath the foundation in four different locations. In the mentioned Plaxis model, a rigid foundation with breadth,B=20and embedment depth, 𝐷=0𝑚was used. The model height was 25 m, and in order to model the bedrock, 5 m layer with Vs= 1000m/s was considered beneath the model. It should be mentioned that the fault has a dip angle,α=60°at the rock–soil interface, the length of fault propagation upward from the bedrock is 25 m and the fixed part of the model is 75 m.After locating the fault rupture trace on the ground in free-field condition, the foundation was located in four different positions in respect of free field and bearing pressure, q=90kpa(9-storey building) was imposed on all of them. Foundation rotations were calculated in these models and compared together. By moving the foundation toward the foot wall, the rotation amount decreased. In the following, to investigate the effect of load onreverse faulting, the bearing pressure was increased to 360 kpa for two foundation locations and the results discussed. Decreased foundation rotation and soil uplift in surrounding area were really noticeable. In order to investigate the seismic code limitations, two different models were made. The foundation was located in hanging wall at the distance of 15 m from free field location. In these models, bearing pressure of 90 and 360 kpa were examined. In this case, by increasing the bearing pressure, the amount of foundation rotation increased.The field studies results indicate, foundation location and structure weight have important impact on structure damages during surface fault ruptures. As mentioned, these results have been achieved in this paper. Briefly, the results of numerical models demonstrate that seismic codes limitations such as setback do not have necessarily safe construction outcome.