Conceptual design of a building with columns and shear walls
Conceptual design of a building with columns and shear walls
Question 1:
The building shown, 20 × 35 m in plan, has columns on a 5 × 5 m grid and shear walls (with dimensions shown in m, 250 mm in thickness) in three alternative arrangements, (a), (b), (c), all with the same total cross-sectional area of the shear walls. Compare the three alternatives, taking into account the restraint of floor shrinkage, the lateral stiffness and the torsional one with respect to the vertical axis, the vertical reinforcement required for the same total flexural capacity at the base, the static eccentricity, the system’s redundancy, foundation systems, architectural constraints etc.
ANSWER:
- Restraint of floor shirnkage:
-case 1:
In this case the shear walls are provided at the four corners as show in the above figure. these shear walls are hold the postion of the floor it gives the result against the good resistant of shrinkage.therefore the shrinkage will be in controll.
-case 2:
In this case the shear walls are provided along the edges of the walls in all of four sides of the building as shown in figure above. the shear walls are provided in ths case to give better stability but coming to the corner of the buildiing is no stable and it should be shrinkage at the corner of the buildings.
-case 3:
In this case the places of shear walls are not symmetrically.the long shear provides at the left side edge of the wall and remainig short shear walls are provided right side of the plan.at the left side corner of floor and middle at right side of the floor there is no shear wall because occurance of floor shirnkage.
- Lateral stiffness:
-case 1:
In this case the shear walls are provided at the four corners as show in the above figure. the corners of the floor is not supported beacuse the seismic forces are tend to act along the edges of the floor.The placement of shear wall will be less lateral stiffness and have least stability.
-case 2:
In this case the shear walls are provided along the edges of the walls in all of four sides of the building as shown in figure above.The shearwalls are placed along the edges of the floor is in the same direction of the earthquake excitation.Then more lateral stifness along the principal planes.
-case 3:
In this case the places of shear walls are not symmetrically.the long shear provides at the left side edge of the wall and remainig short shear walls are provided right side of the plan. Along the x direction there are 12 shear walls are provided which reduces the stifness along the direction.While coming to the y direction there is only asingle shear wall provided. due to the shear wall instability and reducing of the lateral stiffness when eqrth quake excitation. - Torsional stiffness with respect to vertical axis:
-case 1:
Here the provided placement of shear walls are symeterical.hence there is no center of mass and center of stiffness between the eccinetricityand both are coinisdes.so there is less effect of torsion. finally the plan is torsionally stiff.
-case 2:
In this case also similarly like case1.Here the provided placement of shear walls are symeterical.hence there is no center of mass and center of stiffness between the eccinetricityand both are coinisdes.so there is less effect of torsion. finally the plan is torsionally stiff.
-case 3:
In this case along the direction is symmetrical. but coming to the y direction is unsymmetrical because the shear provided along the wall and left side of the plan. there is change in eccentricty between the change of mass and chnage of the Stiffness. the eccentricity move leftwards of the plan.which leads to the torisional instability of the structure. - The vertical reinforcement required at the base:
-case 1:
In this case the shear walls are placed at the corners of the building.these shear walls are taken the less lateral loads when compared to the other parts.as well as the reinforcement of the shear wall is provided less.
-case 2:
In the case the walls ar provided along the wallsand centres of it on the four sides of it. by these provide of shear walls are resise the lager lateral forces.so we need to provide the more reinforcement in theshear walls. to reduce the lateral force effects on the structure.and the shear walls are also provided symmetrical.
-case 3:
In this case the provide of shear walls are unsytmmetrical.there fore very larger amount of lateral forces are taken by sherrawalls . In order to resists that forces we have to provide the heavily reinforced into shear walls. - The static eccentricity:
-case 1:
In this case the shear wall are provided symmetricallay and corner of the structure.for this case their is no eccentricity occurs. because there is a coinside of center of mass and center of stiffness.
-case 2:
In this case the shear walls are provided along the edges of the walls and symmetrically. hence there is coincidence of center of mass and center of stiffness therefore there is no static eccentricity.
-case 3:
In this case there Are provided 3 shear walls . in that shear walls are symmetrical in x direction but coming to the y direction is un symmetrical.so there is no coincides of center of mass and and center of stiffness hence there is an eccentricity. which is move leftward to the plan. hence the eccentricity is to be arranged. - The system's redundancy:
-case 1:
in this case the shear wall are provided at the corners of the plan. In this plan their is no active of shearwalls in the case of lateral loads.so lateral loads are taking by the other structural parts.beacuse of it this case have less redundancy.
-case 2:
While coming to this case, the shear walls are provided along the edges of wall and center of it. The forces are equally shared among th structure.so this arrangement have good redundancy.
-case 3:
In this case, the arrangement of shear walls are unsymmetrical and also the concentric of loads acts to the left where the eccentricity.sothis for this structure also poor in redundany. - Foundation systems:
-case 1:
In this case the shear walls are provided at the corners of the structure.because for it an isolated footing With a tie beam can be provided a sfondation for this structure.
-case 2:
In this case the shear walls are provided along the edges of the walls in all of four sides of the building as shown in figure above.for this type pattern the matt or box type foundation are considered.
-case 3:
In this case 3 shear walls are there. in that 2 are provided along the walls on rightside for that combined footing can be provided. And for the remainig shear wall provide the isolated footing for it. - Architectural constraints:
-case 1:
In this case the arrangement of shear walls is visible from the architectural ponit of view. And doen't coincide with any other elemnts like doors, windows, etc..
-case 2:
In this case this arrangement is known as stable arrangement but the architectural point of view there is a chance of coiincide shear walls with the opening of the of the elements like doors, windows, etc.. So this arrangement is not suitable.
-case 3:
In this case, The two horizontal shear walls are provideded corners so it ok for the architectural point of view.Now coming to the vertical shear wall occupies the half of the portion so the shear may coincides with the opening of the architectural members like Doors, windows,etc..So, this case is also not suitable.
Question 2:
Discuss the suitability for earthquake resistance of the moment resisting framing plan of a three-storey building depicted here (cross-sectional dimensions in cm), the eccentricity of the centre of mass (as centroid of floor plan) to the centre of stiffness (from the moments of inertia of the columns) are shown. Suggest an alternative. Also, is there torsional flexibility? Are the two fundamental translational modes of vibration larger than the fundamental torsional mode of vibration. Discuss qualitatively.
ANSWER:
Above structure is an three storey building and plan the seems quite complicated in the transfering the loads at three locations where the absence of vertical mebers near the horizontal member. Due to providing this type of complex strctural plan the loads in x and y directiion may takes place long and indirect way. So we have rearrange the strctural plan.
The rearrangement of structural plan should be good load transfer mechanism and it should be short and direct.
-Alternative plan:
In the below figure the complixcity is elimated and good load transfer structure is created.
While coming to the alternative plan we arranged each horizontal members is providede in between the two vertical members that leads to effective lateral loads are transfered.Hence, the complixcity of the structure is removed.
And, Since there also a eccentricity betwwen the centre of mass and cenre of stiffness, trosional flexibility also exits.Since, the bnuilding will rotate about to axis.
Eccentricity is X direction-1.505m
Eccentricity is y direction-1.165m
Eccentricity in torsional direction(diagonal)-1.903m
Firslty the eccentricity in x direction is more then the y direction.and also the eccentricity of torsional direction is more than the two( x and y) directions.
Question 3:
A multi-storey building with basement, with a quadrilateral (non symmetrical floor plan) plan as, has interior columns in an irregular (not in a grid) pattern in plan that serves architectural and functional considerations. Partition walls and interior beams supporting the slab have different layout in different stories. However, there is no constraint to the type, location and size of the lateral force resisting components and sub-systems on the perimeter. Proposals are to be made and justified for the choice of the lateral-load-resisting system and its foundation.
ANSWER:
the above repersents the a multistoried building, with a quadrilateral (non symmetrical floor plan) plan as, has interior columns in an irregular (not in a grid) pattern in plan that serves architectural and functional considerations. For any structure the main lateral loading resisting .
- Moment resisting frame system:
For this structure consists of normal frame like beams, columns, rigid or semi rigid connections.So the stiffness adn strength are proportional to column spacing and height of the storey. - Shear wall or Rc wall system.
by providing the proper the shear walls to the structure. - duals systems of frames and walls.
As per the above structural plan it is in irregular shape of the floor plan.For this type of structures to better load resisting system is the shear wall system or Rc wall system.So we can provided at the corners of the structure. by providing the shear wall, torsional rigidity can also be maintained for the structure.
The placement of shear walls is given below in the figure.
now coming to the this of arrangement , type of foundation to be provide can be a box type foundation.For the box type foundation it will transfer the loads coming evenly from the columns and Shear walls.