Good day,
I would like to kindly query a few observations I have gathered from a shear wall model I am currently undertaking. The structure being modelled is an rectilinear shear wall system which comprises 4 walls, similar to an elevator core in a building. The structure will serve mainly as an elevated pedestrian bridge, where persons will access the elevated platform through the use of stairs protruding from the exterior of the walls and an elevator system, which is housed on the interior of the walls. The bridge comprises a suspended simply-supported beam spanning between two towers (the towers being the rectilinear shear wall system). The model I have developed was done using the parametric modelling tool in STAAD and includes the opening for the doors to access the elevator shaft. The queries I have relating to the system are as listed below, most of these are related to the results observed when I used the results along a line tool to see the plate forces:
1. For the walls along the x-axis, the in-plane seismic moment generated in the walls with the openings is shown as essentially the same under the results tab. This seems strange as one wall has a large opening at the base which would reduce the stiffness appreciably. This should result in the other wall 'attracting' additional seismic force. Why are the forces in both of these walls this similar despite the presence of the opening?
2. The wall that has the opening at the top represents the wall which offers primary support for the suspended beam. Based on my hand verification checks, this wall also has significantly larger gravity load when compared to the other walls. However, even though the beam point load is only assigned to this wall, the walls in the perpendicular direction have also the same amount of gravity loads. Why is this the case? Also, it must be noted that when the point load is located closer to the base then the gravity loads on the primary wall increase substantially as opposed to when the point load is located where the beam will the placed.
3. My hand verification checks indicate that the seismic in-plane moment should be within the range of 800-1000 kNm per a wall for each direction, however, from the model, this ranges from 220 - 305 kNm in the seismic load cases (Cases 1-8). Both my hand checks and the model have the same seismic weight and base shear. I used an equivalent lateral force method and assumed the forces acting at the same diaphragms I selected in the model. Is there something relating to the finite elements that causes the loads to be lowered?Model 1 - without staircase plates + Openings.STD
I have attached the model for reference. Any assistance granted would be highly appreciated.