Conceptual design of a building with columns and shear walls

1)

Aim:

To compare the three alternative arrangements provided in the question, taking into account the restraint of floor shrinkage, the lateral stiffness and the torsional 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.

GIVEN ARRANGEMENTS OF A BUILDING:

PROCEDURE:

• Let us discuss and compare all the three alternative arrangements of the building shown in the above figure as per the required properties.

• S.NO.	PROPERTIES TO BE CHECKED UPON:	1ST ARRANGEMENT	2ND ARRANGEMENT	3RD ARRANGEMENT	CONCLUSIONS
  1)	Restraint of floor shrinkage	Full Restraints at all corners	Corners are left free but there are restraints along the edge	Non-uniform restraints	1st one will have higher restraint to shrinkage, thus leads to cracks in the floor. 2nd one is average. 3rd one will not effectively restrain the shrinkage, so possibly less cracks
  2)	Lateral Stiffness	Comparatively lower lateral stiffness in both X and Y directions	Uniform and comparatively high lateral stiffness in both X and Y directions	Non uniform lateral stiffness in both X and Y directions	2nd one will provide higher lateral stiffness for a pure seismic acceleration in both X and Y directions.
  3)	Torsion with respect to the vertical axis	Corner walls provides more resistance	Edge walls provides good resistance to twisting moment	Irregular walls provide very poor resistance to twisting moment	1st one will be best option with respect to Torsional Resistance whereas 3rd one is the worst one.
  4)	Vertical reinforcement required for the same total flexural capacity at the base	Walls are subjected to nominal flexural moment and heavy twisting moment	Walls are subjected to nominal twisting moment	Walls are subjected to heavy flexural moment and twisting moment.	3rd one require higher vertical reinforcementand 2nd one requires the list.
  5)	Static Eccentricity	Structurally symmetric	Structurally symmetric	Unsymmetric	Only 3rd one will have static eccentricity and it is significant
  6)	System’s redundancy	Uniform placement of lateral load supports in both the axes	Uniform placement of lateral load supports in both the axes	Concentrated lateral load supports in both the axes.	1st one and 2nd one are more redundant than 3rd one.
  7)	Foundation systems	Due to L-shaped walls, the geometry of foundation and its design will be critical	Walls are in line. Easy to fix the geometry and design of foundaton.	Walls are in line and concentrated. Easy to fix the geometry of foundation but critical in design.	2nd and 3rd one shall be incorporated with isolated footings/strip footings.1st one is recommended to have a peripheral box foundation.
  8)	Architectural constraints	Walls obstruct only corners	Walls obstruct faces of building	Vertical wall will not allow any passage	Architecturally speaking, 1st one is the preffered one. 2nd one is subjected to discussion.3rd one will not be accepted both architecturally and economically.

Result:

For all the three alternative arrangements given ,observations and comments are passed with proper justification.

2)

AIM:

To discuss the suitability for earthquake resistance of the moment resisting framing plan of a three-storey building depicted here.

PROCEDURE:

• Issues in the given framing plan are discussed below :
• Indirect Lateral Load Transfer in both X and Y directions: The beams are connecting to other beams which is ineffective during the lateral load transfer. In such conditions, the primary beam is prone to shear failure.

Incomplete lateral load transfer in X-direction :

Incomplete lateral load transfer in Y-direction :

• Strong Beam Weak Column Possibility: The size of Columns are mentioned as 25cm X 25cm. But all the beams have much deeper section ( i.e., 50cm). Inertia of beam is visually higher than the column. If column reinforcement is adequately greater than that of the beams, we are okay and since we do not have the reinforcement details, this is doubtful. It is recommended to have slightly bigger sizes for column.

SUGGESTED ALTERNATIVE SCHEME:

• Eccentricity: The longer the distance between the center of mass and center of stiffness, the higher is the torsional moment of the building. As per the given plan, eccentricity of the building is subjected to higher torsional moment in both X and Y directions.

Result:

All the possible issues have been discussed and an alternative scheme has also been given to overcome the existing issue in the given framing plan.

3)

AIM:

To make the proposals and also to justify for the choice of the lateral-load-resisting system and its foundation.

PROCEDURE:

Observations from the given framing plan are:

• Floor Plan: The floor plan of the building is neither uniform nor symmetric. So any lateral load induced on the floor will not have 100% influence in the same direction. Therefore a special lateral resisting system for these torsional moments should be accommodated to make the framing plan stable.
• Internal Columns: Since the internal columns are random in the given plan, they are unable to transfer lateral loads efficiently hence they can not achieve desirable building response. So we have to assume and design those columns for only gravity loads.
• Floor to floor variations in both the partition walls and the beams: Partition walls provide an important mass control in a building and beams play key role in shear transfer from floor to the beam. As all these elements are not in order in the given plan there will be a chance for heavy distortion and distribution of lateral laods to happen.

Suggestions on the Lateral load system and its foundation:

• Heavy torsional forces should be controlled by respective lateral load system. So Corner Shear Walls are suggested.
• The proportion of floor area is greater on the left side than the right side . So, corner shear walls on the left side should be heavier than the right side one.
• Corner Shear walls are preferably supported over a box foundation. Shear walls should be connected by Link Beams to transfer shear from one to the other.
• The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams.

Proposed Schematic Plan of Lateral Load System:

Result:

Appropriate Proposal has been made for the given framing plan as per the need and suggestion on the lateral load system has been given.