Effect of Podium Interferences on the shear force distribution

in RC walls supporting buildings

Mehair Yacoubian,

Department of Infrastructure Engineering, The University of Melbourne

Nelson Lam,

Department of Infrastructure Engineering , The University of Melbourne

Elisa Lumantarna,

Department of Infrastructure Engineering ,The University of Melbourne

John L. Wilson

Centre for Sustainable Infrastructure, Swinburne University of Technology

Podium-tower building configuration is an attractive alternative that is

widely used in contemporary constructions.

Wide podium structures can cater for multiple towers.

The seismic performance of podium-tower buildings has not been

widely covered in the literature

Few recommendations have been set-forth by the PEER/ATC in the

advent of performance-based earthquake engineering of tall buildings

𝐶𝑀𝑇𝑜𝑤𝑒𝑟

𝐶𝑅𝑃𝑜𝑑𝑖𝑢𝑚

Backstay effectResults in high shear reversals

at (and below) the interface level

High torsional moments imposed on the podium by towers

Other issues…..

Incompatible (unequal) wall displacement is the direct result of

the asymmetric podium restraint on the tower walls/cores

Displacement of tower walls (kinematic)

INT EXT INT EXT

Local increase in shear forces and

bending moments on tower walls

Incompatible wall

displacements

Generation of In-plane strutting

forces in the connecting

floors/beams

Analyses on 2D Planar Podium-Tower Sub assemblages

Significant shear force redistribution occurs when tower walls are offset from the centre of the

podium by virtue of the slab in-plane compatibility forces….

Offset-Case I

Centred-Case II

Effect of rigid-diaphragm constraint

Rigid diaphragm constraint: All

Horizontal displacement of nodes (at

a specific level) are Identical

Rigid diaphragm: Displacements of the

walls are compatible

Explicitly modelled connecting

diaphragms

Parametric studies on representative 2D sub-assemblage models

Podium-Building height ratio

Tower eccentricity

In-plane stiffness of the main back-stay slab

Relative stiffness of connected walls

e Podium-Building height ratio

Reduction in

the tower

flexibility

Validation-3D Case study buildings

With rigid diaphragm constraints

assigned at each level

Explicitly modelled slabs

≈ 40% 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒𝑖𝑛 𝑠ℎ𝑒𝑎𝑟 demands

Inelastic Response of Podium-Tower buildings

Floor slabs were modelled as inelastic beam elements with effective width

Influence of Rigid-diaphragm assumption on the inelastic response of the building

High shear concentrations in the interior core due

to slab-wall interaction

Wall drift [%}

Interaction between primary and secondary Lateral load resisting systems

Interior Core

Exterior CoreInterior Core

Discrete Modelling of Shear Failure in Interior Walls

Equivalent material

representing podium

stiffness

Inelastic (case-1)

Elastic (case-2)

Modelling Validation

Link elements representing in-plane stiffness of main backstay floors

𝐈 𝐈𝐈

𝐈𝐈𝐈 𝐈𝐕

Axial collapse proceeding shear failure of the interior wall

𝐈

𝐈𝐈

𝐈𝐕

𝐈𝐈𝐈

Several key recommendations for practitioners are summarised as follows:

1-Explicit modelling of the floor slabs in between these two height limits: (i) two

stories above the podium and (ii) 60% of the height of the podium.

2- Alternative design procedures to reduce podium restraints on the tower walls by

the use of properly detailed expansion or settlement joints at the podium-tower

interface.

3-Use of procedures stipulated in PEER/ATC 72-1for the design and detailing of

floor slabs in locations where high strutting forces are expected.

4- Consideration of interactions between primary and secondary gravity systems in

the lateral analysis of the type of buildings considered in this study.

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-5000 -3000 -1000

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Wall Shear Force [KN]

Interior-No ReleaseExterior-No ReleaseInterior-Expansion Joint-PartialExterior-Expansion Joint-PartialInterior-Expansion Joint-PartialExterior-Expansion Joint-Partial

𝑴𝒐𝒏𝒐𝒍𝒊𝒕𝒉𝒊𝒄𝒄𝒐𝒏𝒏𝒆𝒄𝒕𝒊𝒐𝒏𝑽𝒊𝒏𝒕𝑽𝒆𝒙𝒕

= 𝟏. 𝟓𝟏

𝑭𝒍𝒆𝒙𝒊𝒃𝒍𝒆𝒄𝒐𝒏𝒏𝒆𝒄𝒕𝒊𝒐𝒏𝑽𝒊𝒏𝒕𝑽𝒆𝒙𝒕

= 𝟏.𝟎𝟖

𝑰𝒏𝒕𝒆𝒓𝒎𝒆𝒅𝒊𝒂𝒕𝒄𝒐𝒏𝒏𝒆𝒄𝒕𝒊𝒐𝒏𝑽𝒊𝒏𝒕𝑽𝒆𝒙𝒕

= 𝟏. 𝟐𝟕

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Explicitly modelled slabs -All stories

Explicitly modelled slabs -2T +0.6Hp

𝐅𝐥𝐨𝐚𝐭𝐢𝐧𝐠 𝐁𝐚𝐲

Thank you

Questions?