Concept on positioning of Columns
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.
A.Investigation of framing plan with respect to symmentry in x direction:
we can see the all columns are packed at the even spaces in the xdirection which contributes more stifness to the building.
if we split the plan vertically half it will look mirrored ,so we can conclude the given plan is symmentric in x direction.
if the plan is symmetric it resist the torsional action when the lateral force acts on the building.
top and bottom framings are not well distributed because less columns are provided and spacing is more when compared to the others.
if the lateral force acts in x- direction these two portion may get more deformed compared to middled portion.
Investigation of framing plan with respect to symmentry in ydirection:
we can see the all columns are packed at even spaces in ydirection but less framing is provided which contributes less stiffness when compared to x direction.
if we split the plan horizontally half it will look mirrored , so we can conclude the given plan is symmentry in ydirection.
if the plan is symmetric it resist the torsional action when the lateral force acts on the building. But in the ydirection we can see the space when compared to x direction it is more.
top and bottom framings are not well distributed because less columns are provided.
if the lateral force acts in y-direction it gets more deformed when compared to x direction.
Investigation of framing plan with respect to redundancy in x direction:
redunduncy is more when the framing elements are well distributed.
if we split the plan vertically half it will look mirrored ,so we can conclude the given plan is redundancy in x direction.
the columns in xdirection are comparivetly more and evenly spaced so the structure is more redundant .except the top and bottom columns rows are having quite longer span.
redunducy helps the structure to dissipate energy and increase the more ductility not to get failure.
Investigation of framing plan with respect to redundancy in ydirection:
redunducy is less when the framing elements are not well distributed.
if we spilt the plan horizontally half it will look mirrored, but the elements are not well distributed so that it is non redundancy.
redunducy helps the structure to dissipate energy and increase the more ductility not to get failure.
Investigation of framing plan with respect to bidirection stiffness:(xdirection)
The columns in horizontal direction are connected with straight to straight beams this means any lateral load passing from the left end of the building will have its path straight till reaches right end of the building so there is less possibility of force diversion takes place.
The structural elements should be arrranged in an in-plan orthogonal pattern,so that the building can resist the seismic forces.
y-direction
The column is in vertical direction are not connected straight to straight end beam so the lateral load passing from bottom side to top side of building will get diverted to right and left side direction to reach next bay.
there will be major force diversion takes place with seismic force in ydirection.The framing plan is weak with respect to bi-direction stiffness in ydirection.
Investigation of framing plan with respect to ductility:(x-direction)
As i said in the symmentry x direction the columns are more a placed in even so there is more stiffness are there in that direction.
when there is more stiffness the deformation is low that means ductility.
in the x-direction there are more column so more stiffness we would reduce ductility in this direction.
Investigation of framing plan with respect to ductility:(y-direction)
in this direction there are less column and less connection leads to low stiffness.
when there is less stiffness we can see more deformation (ductilty)
so we can say that more ductility can see it in the y-direction.
ductilty demand is more in the ydirection.
ductility demand is less in the x-direction.
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.
A.
1.stiffness irregularities
2.verical geomentric irregularity
3.mass irregularity
4.setback
5.in plane irregularity.
stiffness irregularity:
we can in the elevation of the building one of the storey has open with out having infills .this storey may leads to soft storey mechanism because when lateral force acting in the x(or)y-direction these floor columns get more deformation addition support is not there.
we can there is discontuation of column if it is architectural purpose then ok but it acts as the structural elements there is deformation may occur some floor in that building.
2.verical geomentric irregularity
The building plan area is large in the bottom stories ; the floor area is reduced increasing in level.
as per is 1893 2016 a/l> 0.25.
distance between top of the storey facade to the ground storey facade indicate as A in the above figure.
that should be 25%of the length of the building.
cross check the seismic prone zone.
mass irregularity
offset in building leads to mass variation.
each floor may gets different experience when undergoes lateral force act on it.
in this building the plastic hinge formation can see it.
best example for the irregularity.
slopy bay
the building is constructed on a sloping ground at one side this will lead to significant variation in the stiffness
few levels may get subjected to soft storey mechanism.
in plane irregularity
i cant be sure that there is offset in the plane because the building having setbacks in the front side.
this type of model have to do 3d model response spectrum analysis either linear (or) non linear system adaption.
when is seismic motion occur in the y direction in plan front portion get vunerable deformation at the below levels.
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).
A.
if the seismic exitation x-axis direction this much affect couldnot happened .
more stiffness in one side
we see it plan top left corner having more stiffnes when seismic force in y-direction the torsional flexibility happened.
when we provide one side has more stiffness remaining other portion get large defornation.
but in the plan there is no support is provided in y-direction the strcture hardly transfer those forces to the floor.
open ground floor
this denotes soft storey mechanism acting in the building.
rooms along 2 bays separated by an open corridor
the bays filled with rooms will have higher mass compared to the middle bay left open for cooridor .this indues mass irregularities along height uniformity.
the middle portion had high scope to resist but the floor is imbalace at the outer two bays so total floor get collapse.
two short sides covered with infill walls
this means the buildings left and right side have more stiffness at the periphery to resist the seismic forces.
so that portion doesnot get damage.
staircase portionat the left top corner
usually staircase and lift portion are stiffer than other parts because of concentated concrete elements.so the staircase portion contains more stiffness in the building ploan.
no framing connection along y-direction
we could see no structural beams are provided along the vertical direction between columns .this makes the building fragility during y-direction seismic force.
beams connected along columns minor axis
the columns are having longer dimension in y-direction .This means they are more stiffer along y-direction but the beams running only xdirection which would attract much less lateralo forces and hardly tranfer it.
variation in column sizes
the internal columns are having higher sizes comparedto exterior columns this leads to significant difference in lateral deformation of columns .so the concrete floor might have softenede heavy out of plane shear which would leads to collapse.