Concept on positioning of Columns

Aim:-

Comment on the layout of the framing plan concerning earthquake resistance in the two horizontal directions X or Y Looks into aspects of symmetry, redundancy, and bi-directional stiffness and elasticity.

Comments on the above figure as shown below,

Investigation for symmetry in X and Y directions.

For X directions:- if we split the above figure in the vertical direction in the half part, then it looks lick a mirror. so, we can conclude that it is symmetrical in the x-direction.

For Y directions:- if we split the above figure in the horizontal direction in the half part, then it looks lick a mirror. so, we can conclude that it is symmetrical in the y-direction.

Investigation for redundancy in X and Y directions.

For X-direction:- Based on the above figure the columns in X-direction are evenly spaced. so, the structure is more redundant in the X-direction. except the bottom and top column rows are having longer spans.

For Y-direction: Based on the above figure the columns in the y-direction are fewer but evenly spaced. so, the structure is less redundant as compared to the x-direction.

Investigation for bi-directional stiffness in X and Y directions.

1. The columns in the horizontal direction are connected with straight-to-straight beams. if a lateral load passes from the right, then its path will be from the right to the left end of the building.
2. the columns are not connected to straight beams in the vertical direction. so, the lateral load passing from the south will be diverted to the east and west directions to reach the next bay i.e. north. major force diversion will take place in the y-direction during seismic forces. so, the framing plan is weak with respect to bi-directional stiffness in the y-direction.

Investigation for Ductility in X and Y directions.

1. the aspect ratio of the plan clearly hints at more columns in the x-direction compared to the y-direction. it will result in higher stiffness of the building in the x-direction, which would reduce ductility in the x-axis.
2. moreover, the x-force will pass easily from one bay to the next beam. whereas, the y-force will get struggle to reach the next bay due to the zig-zag arrangement of beams and columns. so, it leads to discontinuous bracing.
3. we can conclude that the given framing plan is more ductile in the y-direction than that in x-direction.

Q 2:-

Aim:-

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.

Conclusion:-

Based on the above figure, I observed that the different types of irregularity as shown below.

1. Soft Storeys
2. Flexible structures in Torsion

As per IS 1893: 2016 part 1 and IS 1893: 2002 part. we have different types of irregular structures as you can see below table.

Q 3:-

Aim:-

A 4-story hotel building has an open ground floor for the restaurant. Story 2 to 4 have one row of rooms along each long side in plan, separated by a corridor. The two short sides of the perimeter are fully in-filled in all stories, except for certain openings at the ends of the corridor at storeys 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 member no. in meters.

Comment on the features of the structural design and of the layout of infills which are important 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 plan).

Procedure:-

• The Building collapse occurred due to the Ground excitation in both Orthogonal horizontal directions and also due to the Torsional effects.
• In spite of being having Earthquake resistance for the two mentioned actions

The following are the responsible factors:

1. Open Ground Floor
2. Two short sides of the perimeter in-filled
3. Extreme left hand bay Staircase filled with the Concrete
4. Columns not in the same line

1. Open Ground Floor

1. The ground floor of the building is open, which may be a soft story (having long columns) due to this Ground floor excitation the columns could have been unable to resist the Earthquake and form collapse.
2. This is called as soft story mechanism.
3. This can be avoided by having a Strong column-weak beam mechanism.

1. Two short sides of the perimeter in-filled

1. The mass has been undistributed in all the sides of the Building in all storeys because it is given that the two sides of the perimeter of the building is in-filled (may be with the soil) which causes the Irregular distribution of mass called as Mass Irregularity.
2. This can be avoided by providing the shear walls in the directions of Two short sides of the perimeter which can resist the Lateral loads (soil due to Infill) by providing stiffness in the Building frame and helps to resist the Earthquake actions.
3. Also it adjusts the Mass Irregularity for the plan.

1. Extreme left hand bay Staircase filled with the Concrete

1. The extreme left hand bay has Staircases (made of concrete) due to this the mass got concentrated in the staircase area due to which torsional effects are formed having the base of the concentration of mass in the Staircase.
2. To avoid this type of failure the staircases should be kept in the centre of the Building which makes the Torsional effect as Zero by Uncoupling the moment. It also makes the Implications of the Irregularity in plan of the Building.

1. Columns not in the same line

1. It is observed that the columns in the Extreme left hand middle line columns has the deviation in the line of the Construction at the staircase which again a reason for the Irregularity in plan having the Torsional flexibility.
2. To avoid this the Eccentricity should be maintained for the deviation to be within the limits of Beam size and the Columns sizes.
3. Also the sizes of the Beams and Columns in the Plan should be redesigned in such a way that the line of the columns doesn't deviate even in the staircase area.