Column Shortening in Tall Buildings

Theory Validation and Designing Precepts

Thesis Presentation by Rishabh Lala

Phenomena• Column Shortening

• Time Dependent Effects

• Axial Shortening, Creep, Shrinkage

• Construction Stage

Objectives IEstimation of Indian Scenario:

• In regards to provisions for column shortening, in Indian Standard Codes, and provisions that Indian Structural Designers are providing to accommodate this phenomena, in tall buildings.

Objectives IITheory Validation:

• Comparing the available theory as per Indian Codes (creep, shrinkage, elastic shortening), with results of column shortening obtained after detailed software analysis.

Theory ValidationThis is done in four steps:

Ds = Shortening between two columns

Ps1 and Ps2 = load coming on these columns

D1 and D2 Deflection manually calculated based on

available theory, due to Ps1 and Ps2

l D1 - D2 l = Ds=> Software Calculated Deflection = Manually Calculated Deflection• Theory Verified

Objectives IIIDeflection Permissible:

– Permissible deflection (Dp) comes from ‘permissible slope’, which is obtained from literature review, especially Indian Standard Codes

– To estimate, Permissible deflection (Dp) for Indian Scenario, using typical value of column spacing (L)

– Using typical value of (L), Permissible loads (P1 and P2) to be determined, for typical column section.

OBJECTIVE IVRelevant Height:

– Height at which this phenomena becomes relevant, taking base as Indian Standard Provisions.

– A height, for typical value of column spacing, in structure, after which it becomes compulsory to consider column shortening phenomena as a design consideration; is to be determined

RELEVANT HEIGHTBuilding Model : 20 m, 40m, 60m, 80m, 100m, with typical column spacing

Loads : Dead, Live, Construction with FOS as per literature review

Analysis Type : Non Linear, construction Stage Analysis (Sequential Analysis)

Analysis Software• MIDAS GEN 2015

• One of the best software available for the analysis of column shortening, and construction stage analysis.

MIDAS GEN: 2015Features:

• Manual Construction Stage Analysis• Enter Construction Stage specific Data• Check Results for Each Construction Stage• Check Column Shortening• Time Dependent Material Properties can be

taken into account like Creep and Shrinkage• Burj Khalfa’s construction stage analysis

was also done in Midas Gen 2010.