SSI and SSSI effects in seismic analysis of twin buildings: discrete model concept

This paper presents a numerical study of soil-structure interaction (SSI) and structure-soil-structure interaction (SSSI) effects on response of twin buildings during earthquake excitations. The buildings are modeled as shear buildings and the soil is simulated by a discrete model representing a visco-elastic half-space subjected to earthquake acceleration. Equation of motion of twin buildings with different conditions, fixed based (FB), SSI and SSSI, are developed via an analytical procedure and solved numerically. Buildings responses are evaluated for aforementioned three conditions considering various soil types and compared together. One must say that soil causes change in distribution of responses throughout the buildings while ignoring soil interaction may lead to detrimental effects on buildings. Anyway, interaction between twin buildings with SSSI condition slightly mitigates soil unfavorable effects compare to one building with SSI condition. In addition, it is found that influence of soil is very significant for soft to stiff soils whereas negligible for hard soils

Separation gap, a critical factor in earthquake induced pounding between adjacent buildings

In this paper it is attempted to study seismic responses of adjacent buildings subjected to earthquake induced pounding and to clarify pounding effects for various separation gaps. An analytical model of adjacent buildings resting on a half-space is provided whilst the buildings are connected by visco-elastic contact force model. Results show that with same separation gap, adjacent buildings with structure-soil-structure interaction (SSSI) are more likely to pound together than buildings with fixed-based (FB) condition. Also, building condition gets worse due to pounding because the seismic responses of buildings are unfavourably increased and the condition becomes more critical if the separation gap becomes narrower

Pounding between adjacent buildings in consideration of soil structure interaction

Earthquake is known as one of the most devastating natural disasters to human and their environment that causes catastrophic failure of their life and belongings particularly buildings. The main cause of numerous building failures is collision of adjacent buildings during the earthquake which is called building pounding. It occurs when the separation gap between adjacent buildings is less than minimum distant required for them to vibrate freely. As consequence of building pounding, seismic responses of buildings are altered and in some occasions it produces larger forces and displacements than the design limits which causes building damage. The aim of this research project is to numerically investigate seismic responses of two adjacent buildings due to earthquake induced building pounding. As the buildings are usually constructed on the soil; interaction between building and soil and further interaction between two buildings through the soil are considered in this research project. Other parameters affecting building pounding such as separation gap, dynamic property of building and earthquake excitation are studied too. In order to achieve the aim of this research project, a new analytical model of building pounding considering soil effect is developed. The proposed model consists of two adjacent shear buildings connected with linear visco-elastic contact force model during pounding constructed on a homogenous half-space soil. This model is then implemented into a computer program and calibrated and validated. It is found that the proposed model is efficient and accurate to evaluate seismic responses of buildings with soil effect considerations due to building pounding. A comprehensive number of analyses are then performed and results are explained and interpreted graphically in terms of building displacement and story shear. When a tall and flexible building is pounded to an adjacent short and stiff building,displacements of tall and flexible building are reduced but displacements of short and stiff building are increased. Considering soil effect (structure-soil-structure interaction, SSSI), produced displacements in both buildings due to pounding are greater than fixed-based (FB) buildings. On the other hand, building pounding causes increment of story shears of both buildings and this increment is pronounced if SSSI condition is considered. In conclusion, building pounding worsens buildings conditions and underlying soil amplifies this detrimental effect. Further analyses are performed to clarify effects of separation gap, dynamic property of building and earthquake excitation in building pounding. Separation gap between two adjacent buildings is found to be very critical. Number of collisions and intensity of pounding forces are increased due to reduction of separation gap. Therefore, wider separation gap is necessary to prevent building pounding when the soil is considered,particularly if the soil is soft. In addition, evaluation of variation of buildings dynamic properties (building height) indicates more intense building pounding for tall and flexible building when the period ratio of the buildings is about half. While for short and stiff building, the most critical condition is referred to the least period ratio. Finally, the results show that each earthquake produces unique effect for different buildings and underlying soils. Thus seismic responses of adjacent buildings due to earthquake induced pounding should be analyzed in case by case basis and soil effects, particularly soft soils must be taken into consideration

Pounding between adjacent buildings of varying height coupled through soil

Pounding between adjacent buildings is a significant challenge in metropolitan areas because buildings of different heights collide during earthquake excitations due to varying dynamic properties and narrow separation gaps. The seismic responses of adjacent buildings of varying height, coupled through soil subjected to earthquake-induced pounding, are evaluated in this paper. The lumped mass model is used to simulate the buildings and soil, while the linear visco-elastic contact force model is used to simulate pounding forces. The results indicate while the taller building is almost unaffected when the shorter building is very short, it suffers more from pounding with increasing height of the shorter building. The shorter building suffers more from the pounding with decreasing height and when its height differs substantially from that of the taller building. The minimum required separation gap to prevent pounding is increased with increasing height of the shorter building until the buildings become almost in-phase. Considering the soil effect; pounding forces are reduced, displacements and story shears are increased after pounding, and also, minimum separation gap required to prevent pounding is increased

Computational modelling of hip resurfacing arthroplasty investigating the effect of femoral version on hip biomechanics.

AimHow reduced femoral neck anteversion alters the distribution of pressure and contact area in Hip Resurfacing Arthroplasty (HRA) remains unclear. The purpose of this study was to quantitatively describe the biomechanical implication of different femoral neck version angles on HRA using a finite element analysis.Materials and methodsA total of sixty models were constructed to assess the effect of different femoral neck version angles on three different functional loads: 0°of hip flexion, 45°of hip flexion, and 90° of hip flexion. Femoral version was varied between 30° of anteversion to 30° of retroversion. All models were tested with the acetabular cup in four different positions: (1) 40°/15° (inclination/version), (2) 40°/25°, (3) 50°/15°, and (4) 50°/25°. Differences in range of motion due to presence of impingement, joint contact pressure, and joint contact area with different femoral versions and acetabular cup positions were calculated.ResultsImpingement was found to be most significant with the femur in 30° of retroversion, regardless of acetabular cup position. Anterior hip impingement occurred earlier during hip flexion as the femur was progressively retroverted. Impingement was reduced in all models by increasing acetabular cup inclination and anteversion, yet this consequentially led to higher contact pressures. At 90° of hip flexion, contact pressures and contact areas were inversely related and showed most notable change with 30° of femoral retroversion. In this model, the contact area migrated towards the anterior implant-bone interface along the femoral neck.ConclusionFemoral retroversion in HRA influences impingement and increases joint contact pressure most when the hip is loaded in flexion. Increasing acetabular inclination decreases the area of impingement but doing so causes a reciprocal increase in joint contact pressure. It may be advisable to study femoral neck version pre-operatively to better choose hip resurfacing arthroplasty candidates