Concept on positioning of Columns

1. Comment on the layout of the framing plan concerning earthquakes resistance in the two horizontal directions X or Y ( dots are columns, lines are depict beams). Look into aspects of symmetry, redundancy, and bi-directional stiffness and Ductility.

AIM

To describe the aspects of Symmetry, Redundancy and bi-directional stiffness and Ductility about given layout of the framing plan.

ANSWER

SYMMETRY

• For this Layout of the framing is symmetric in structure.
• This symmetrical structure have well distribution of load resistance framing throughout the entire structure.
• In symmetric structure with respect to an axis of symmetry in its plane if the reflection of the structure about the axis is identical in geometry, supports and material properties to the structure itself.
• This structure having on exact matching of form and arrangement of parts on opposite sides of boundary at X and Y direction.
• For this frame also to achieve uniformity.

REDUNDANCY

• For this structure have perfect redundant that is the structure becomes more reliable to resists any lateral forces acting on the structure.
• And more it tends to prevent any extend of degradation the structure can suffer without losing some specified elements of its functionality.

BI-DIRECTIONAL STIFFNESS

• The Horizontal seismic motion will cause the direction of horizontal axis of X and Y through entire framing of layout.
• For this structure can distributed the seismic forces is by nature of Bi-directional phenomenon, so it can withstand and able to resist any horizontal motion of forces.
• The given plan is in orthogonal layout in both X and Y directions, so it can transfers the forces through evenly, then its structure will able resist direct action of seismic forces.

2. What are the possible sources of irregularity in the building shown here? Explain how, as an engineer, each of these irregularities should be dealt with.

• For this structure of building may possible cause due to seismic forces under the category of soft storey, vertical geometry irregularities, floating columns, mass irregularities, inconsistent seismic forces.

Soft story failure

• The ground floor of the building is mostly consider to soft stories, because of their provided the short column, not provided to any shear wall and any much of mass properties.
• The damage may also occur like a collapse, buckling of column.., etc..

Floating columns

• The column is considered as a vertical member of resisting lateral forces of the structure.
• If anywhere, the horizontal forces acting about the structure, it may transfer through the vertical member and to the base shear foundation.
• Therefore, the column are at discontinuity of the structure, it does not taken to withstand the lateral forces during earthquakes, because of there is not possible to transfer the load to foundation.

Mass irregularity

• The structure at may possible to cause due to mass irregularity of the structure.
• The mass irregularity of the structure at any floor their should not consider the seismic response.
• At irregular frame to seismic excitation has been found to decrease when mass irregular floor moves towards the top of the building.
• In structural system, if there is a variation of more than 150 % of mass between the adjacent story then it is considered as mass irregularity.

3. A 4-storey hotel building has an open ground floor for the restaurant. Story 2-4 have one row of rooms along each long side in plan, separated by a corridor. The two short side of the perimeter are fully in-filled in all storeys, except for certain openings at the ends of the corridors at 2 to 4 and along the right-hand side of the ground floor. There is a staircase near the upper left-hand corner, with straight flights between landings at floor levels and in-between floors. Cross-section dimensions are written next to the members no. in meters.

Comment on the features of the structural designs and of the layout to infills which are omportant for earthquake resistance and seismic performance. How do they relate to the almost full collapse of this building (the extreme left-hand bay with the staircase survived, as well as one long-side façade in the rear end, and the frame along the right-hand side in plane.

ANSWER

• The frame of structure is not symmetric.
• In this structure, the columns are not in a proper alignments in a symmetrical plane, then there is may cause due to any lateral forces.
• There is no proper placement of masonry infill wall.
• In this building, Redundancy in the vertical direction is not provided properly.
• If framed structure can able to transfer the loaf from one direction to another direction of the structure of the foundation.
• In this layout we can see that the columns are closely placed, which results in the formation of short paths for the transfer of stresses, which is also an important factor in resisting eartquakes.
• The interaction between the staircase and other parts of the three dimensional structure., that is the interaction with beam, column and shear wall, results to pattern of deformation that are not usually studied during the design process.
• For example, the increased strength and stiffness of the structure in the stairway region will influence the seismic torsional distress of the structure and may lead to shear failure of the staircase itself or of other elements of the structure.