Concept on positioning of Columns

AIM:- To undersstand the  Concept on positioning of Columns

INTRODUCTION:- There are some of the basic principles in determining the positions of columns. Some of them are:

. Columns should be preferred to be positioned at the corners of the building and at the intersection of beams.

. They should be placed in such a way that the bending moments will be reduced in the beams.

. Avoid larger spans of beams.

. Avoid larger centre to centre distance between columns.

. Columns on property line. In this project we also try to understand the positioning of the structural elements to avoid siesmic calamities i.e earthquake destruction of the structure 

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

AIM: To comment on the layout of the framing plan concerning earthquake resistance in the two horizontal directions X or Y looking into aspects of symmetry, redundancy and bi-directional stiffness and ductility.

INTRODUCTION:- Layout of the framing plan which is shown in figure above concerning earthquake in the two horizontal directions is going to be explained with step by step procedure.

ANSWER:- (a) Symmetry:- i. Symmetry in the X-direction:-

. If we see carefully into the above given plan and split it into two equal portion in the horizontal direction then we can tell just by seeing the above plan that the plan looks mirrored,if we split the given above plan into equal parts.

. This will conclude that the given above plan in the X-direction is symmetric.

ii. Symmetry in the Y-direction:

. If we see carefully at the given above plan and then if we will cut the given plan from the middle or we can say that if we split the plan into two equal parts in the Y-direction horizontally i.e, Section 1 and Section 2 as we can see in the above plan then we will be able to understand that the give above plan looked mirrored in the give plan plan after we split them into two.

. So here we can conclude that the given above plan in the Y-direction is also symmetric.

(b) Redundancy: i. Checking the redundancy in the X-direction:                                      

. In the above given plan there are multiple dots and the lines.

. So these dots represents the columns and the line represents the beams.

. So if we observe the above given plan then we can see that the columns in the X-directions are more and evenly spread in the middle of the plan.

. So we can say that the structure is redundant in the X-direction.

. But if we observe the above plan then we can see that the colums in the top and the bottom there are less number of columns as compared to the middle portion of the plan but these columns are evenly spread so we can say the the structure in the X-direction is redundant in nature.

ii. Checking the redundancy in the Y-direction:

. In the above given plan there are multiple dots and the lines.

. So these dots represents the columns and the line represents the beams.

. So if we observe the above given plan then we can see that the columns in the Y-directions are evenly spread but they are lesser in number if we observe the above plan in the Y-direction.

. So we can conclude that the redundancy in the Y-direction is lesser.

C) Bi-directional stiffness

. In the horizontal(x) direction, the width is more compared to vertical(y) direction and as such distribution of structural elements is also more in x direction, hence the stiffness is more. . That is, the stiffness is more in X direction as compared to Y direction.

d) Ductility

. The ductility is always, inversely proportional to stiffness. If the structure is more stiffer, it will be less ductile and vice versa.

. So if we compare the ductility in both the direction i.e, X and Y direction then we can say that the frame in the X-direction is more ductile and the frame in the Y-direction is not ductile due to the lesser number of beams in the Y-direction.

Question 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.

AIM: To analyze the possible sources of irregularity in the building shown and to explain how, as an engineer, each of these irregularities should be dealt with.

INTRODUCTION: Irregular configuration either in plan or in elevation is recognized as one of the major causes of failure during earthquakes. Thus irregular structures, especially the ones located in seismic zones are a matter of concern. Structures generally possess combination of irregularities and consideration of a single irregularity may not result in accurate prediction of seismic response. The choice of type, degree and location of irregularities in the design of structures is important as it helps in improving the utility as well as aesthetics of structures. Hence, the present study addresses the seismic response of reinforced concrete structures possessing various combinations of irregularities. 

ANSWER:- a) Vertical Irregularity:-

. If we observe the above given plan carefully then we will be able to see that the buiding plan area is bigger in the bottom section and the building plan area keeps reducing as it goes up. In short it means that the building plan area reduces with the increase in the height as we can see clearly in the above image.

. The area in the green rectangle has bigger plan area than that of the area that are in the yellow rectangle.\

. The building offset has to be checked out with the reference of IS 1893-2016 table no.6 .

b) Soft Storey:- As we can see in the above given image that this building at the 6th floor has a soft storey because it has uncovered opening. As we can see that there is no partition wall or no occupancy or any other shear wall or any other type of support elements etc nothing is there to support the upper blocks of the building during the earthquake and this will also cause plastic hinge at the colums. According to the reference IS 1983-2016 Figure 4A, this has to be checked and we have to design the building accordingly. So that there will be no mistake in designing the buiding.

c)  Sloppy Base:-

. In the right side of the building, there is an embankment. It means the building is constructed over a sloping ground and this will lead to a significant variation in the stiffness (with reference to IS-1893-2016 Figure 5E). So, few levels may be subjected to soft Storey mechanism.

Question 3: A 4-storey 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 storeys, 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).

AIM: To 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).

INTRODUCTION: A soft story building is a multi-story building in which one or more floors have windows, wide doors, large unobstructed commercial spaces, or other openings in places where a shear wall would normally be required for stability as a matter of earthquake engineering design. A typical soft story building is an apartment building of three or more stories located over a ground level with large openings, such as a parking garage or series of retail businesses with large windows.

ANSWER:- Structure failure reasons for the given figure are; 

. Improper arrangement and placement of structural elements 

. Structure is not symmetric Which must required for standard structure

. Larger strength is provided hence low ductility.

. No proper placement of masonry infill walls.

. Redundancy in the vertical direction of this building is not provided properly.

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

2. Rooms along two bay separated by an open space:- The bay that are filled with the rooms will have higher mass than the middle bay whic is opened for the corridor. So this will cause mass mass irregularity along the height uniformity

. As we can see at the above image that the upper portion and the bottom portion is for the rooms and because of that rooms these portions have higher mass because of the various furniture load,live loads etc.

. And the middle portion they left for the corridor as we can see in the above given image.

 3. Two short sides coveres with the infill walls:   As we can see that the two shorter sides of the perimeter are not in filled in all the storeys,except for the certain openings at the ends of the corridor at the 2nd and the 4th floor and along the right-hand side of the ground floor. This means that the building at the left and the right of the given building is more stiffer during the earthquake. And they have built non structural wall.

4. Staircase portion at the left top corner:

.  As we can see that the staircase and the lift portion of the building is not affected with the seismic force. These are the only elements that are not affected during the earthquake force.

. This is because the usually the staircase and the lift portion are more stiff than the other members of the building. It m eans it does not bend easily with the external forces and that is the reason that the staircase and the lift is intact in the polsition with much harm.

5. Columns not in the same line :- 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 flexibilty. To avoid this the Eccentricity should be maintained for the deviation to be with in the limits of Beam size and the Columns sizes. 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.

6. Variation in column sizes:

. As we can see in the above given image that the sizes of the columns are different. We can say that the size of the interior column is big in size and the size of the exterior column is smaller as wecan see in the above image. And because of the difference in the size of the columns the structure collapse because it may suffered heavy out of plan shear.

7. Beams connected along column minor axis:- As we can see in the above image that the columns have the longer direction in the Y-direction. But there is no direct connection or frame in the Y-direction which may connects the beam in the Y-direction. There are columns that are connected in the X-direction but the large side of the column is in the Y-direction which means that they are more stiffer in that direction whic can attract more lesser lateral force and this is one of the reason for the collpase of this building.

RESULT:- we are understnad the concepts of column positioning