02-Construction Stages and Column Shortening Analysis in Tall Buildings

Midas Gen – One Stop Solution for Building and General Structures

Construction Stage Stage Analysis An alysis and Column Shortening in Tall Buildings Midas IT Technical Seminar 17th February 2012

Ravi Kiran


Contents Construction Stage Analysis Column Shortening & Related Issues Effects of Column Shortening Procedure for Accounting Compensation at Site Useful Features for Construction Stage Analysis Project Applications Live Demonstration

Midas Gen – Technical Seminar

Construction Stage Analysis

One Stop Solution for Building and General Structures

Why Construction Stage (CS) Analysis Analysis •

In general structures are analyzed assuming that the structure struct ure is built and loaded in a moment.

•

Construction of structures is a time taking process process and during this period Material Material Properties, Loads and Boundaries conditions may change.

Dead Load + Live Load

LL,WL,EQ Acts

Wind

Other Dead Loads (Partions, Finishes)

Self weight of slab Earthquake

Construction Completed Structure Sequence




Conventional Analysis Analysis Vs. Construction Stage Analysis Analysis

Stage 1

Case 1 – Conventional Analysis

Stage 2

Case 2 – CS Analysis




Conventional Analysis Analysis Vs. Construction Stage Analysis Analysis

Case 1 – Conventional Analysis

Case 2 – CS Analysis




Where CS Analysis Analysis is Required Long Span Trusses

Long Span Slabs, Beams constructed in multiple stages Prestressed concrete Structures CS analysis should be performed for all structures where where there is a change in Support Conditions, Loading and varying material properties (Concrete).




Column Shortening


Column Shortening and Related Issue When any member is loaded with Axial Load, it undergoes axial deformation

σ

Why is this Important E = (σ / ε) ΔL = (PL/A E)


Column Shortening


Column Shortening and Related Issue P2, ΔL2

P1, ΔL1

The differential shortening happening between the vertical members may cause additional forces and stress in Beams and Slabs


Column Shortening


Column Shortening and Related Issue Steel Structures - Linear elastic Behavior

σ

Stress ∞ Strain Strain is constant for a given Str ess during loading & unloading

E = (σ / ε) ΔL = (PL/A E)

Column Shortening



Column Shortening and Related Issue Concrete Structures -

Nonlin Nonl inea earr Ine Inela last stic ic Beh Behav avio iorr But in in general general analy analysis sis and design design behav behavior ior of concr concrete ete is trea treated ted as Linear Linear Elas Elastic tic Mater Material ial Neither Stress

∞

Strain

Nor Strain is constant for a given Stress During loading & unloading

Elastic Strain + Inelastic Strain


Column Shortening


Column Shortening and Related Issues Concrete Structures Elastic Shortening

Inelastic Shortening

σ

Creep Shortening. Shrinkage Shortening.

σ Ei = (σ / ε) ΔL = (PL/A Ei)

Modulus of Elasticity changes with time.


Column Shortening


Column Shortening and Related Issue

With increased height of structures the effect of column shortening (Elastic & Inelastic) take on added significance and need special consideration in design and construction.

Elastic Shortening of 80 Storey Steel Structure Structure ~ 180 mm to 255 mm.

Elastic Shortening of 80 Storey Concrete Structure ~ 65 mm.

Total Shortening of 80 Storey Concrete Structure ~ 180 to 230 mm.

Inelastic Shortening ~ 1 to 3 times Elastic shortening.


Column Shortening


Column Shortening and Related Issue 



Two basic prerequisites for accurately and efficiently predicting these effects are 

Reliable Data for the creep and shrinkage characteristics of the particular concrete mix



Analytical procedures for the inclusion of these time effects in the design of structure.

Some of the popular predictive methods for predicting creep and shrinkage strains are 

ACI 209 -92



Bazant – Bewaja B3



CEB – FIP (1978, 1990)



PCA Method (Mark Fintel, S.K.Ghosh & Hal Iyengar)



GL 2000 (Gardner and Lockman)



Eurocode


Column Shortening



The total strain at any time t may be expressed as the sum of the instantaneous, instantan eous, creep and shrinkage components: com ponents:

Where, εe (t) = Instantan Instantaneous eous strain at time t, εc (t) = Creep strain at time t, εsh (t) = Shrinkage Shrinkage strain at time time t.


Column Shortening



The instantaneous strain in concrete at any time t is expressed by

Where, σ (t) = stress at time t, Ec(t) = Elastic modulus of concrete at time t, given by

fct = Compressive strength at any time t, given by

α & β are constants depending on Type of Cement & Type of Curing


Column Shortening


Column Shortening and Related Issue Inelastic Shortening = Creep + Shrinkage Creep

Shrinkage

Creep is time-dependent increment of strain under sustained stress.

Shrinkage is the time-dependant decrease in concrete volume compared with the original placement volume of concrete.

Basic creep

Drying Shrinkage is

occurs under the condition of no moisture movement movem ent to and from the environment. Drying creep

is the additional additi onal creep caused by drying.

Drying creep has its effect only during the initial period of load.

due to moisture loss in concrete.

Autogenous Shrinkage is

caused by hydration of

cement. Carbonation

shrinkage results as the t he various cement hydration products are carbonated in the presence of CO


Column Shortening


Column Shortening and Related Issue Factors affecting the Creep & Shrinkage of o f Concrete

Concrete Composition

Cement Paste Content Water – Cement ratio Mixture Proportions Aggregate Characteristics Degrees of Compaction

Initial Curing

Length of Initial Curing Curing Temperature Curing Humidity

Environment

Concrete Temperature Concrete Water Content

Geometry

Size and Shape

Loading History

Concrete age at load Application During load Period Duration of unloading Period Number of load Cycles

Stress Conditions

Type of Stress and distribution across the Section Stress/Strength Ratio

Concrete (Creep & Shrinkage)

Member Geometry and Environmen Environmentt (Creep & Shrinkage)

Loading (Creep Only)


Column Shortening


Column Shortening and Related Issue Inelastic Shortening = Creep + Shrinkage Creep

Shrinkage

As per ACI 209R-92 the creep coefficients are predicted

As per the ACI 209R-92, shrinkage can be predicted by

as =

After 7 days for moisture cured concrete

After 1-3 days for steam cured concrete Where, t = time in days after loading. vu = Ultimate creep coefficient = 2.35 c c = Product of applicable correction factors

Where, t = time in days after the end of Initial Curing (sh)u = Ultimate Shrinkage Coefficient = 780 sh x 10-6 m/m sh = Product of applicable correction factors




Column Shortening


Effects of Column Shortening



Absolute shortening is rarely of practical interest.



Differential shortening between adjacent vertical elements is the most important factor for engineer.



Axial Shortening of vertical elements will not effect those elements very much,

horizontal elements like beams and slabs and non structural elements are affected.


Column Shortening


Effects of Column Shortening Structural Effects   

Slabs may not be truly horizontal after some time. Beams could be subjected to higher bending moments. Load transfer.

Non Structural Effects      

Cracks in Partition Walls. Cracks in Staircases Deformation of Cladding. Mechanical Equipment. Architectural Finishes. Built in Furnishings.

These non structural elements are not intended to carry vertical loads and are therefore not subjected to shortening.


Column Shortening


Effects of Column Shortening

Deformation and breakage of Facades, windows & Parapet walls…

Deformation of Vertical Piping System

Reverse Inclination of Drainage Piping System

Deformation and breakage of internal partitions




Column Shortening


Movement Related to Construction Sequence •

Pre-slab installation shortenings – Shortenings taking place up to the time of slab installation i nstallation

•

Post-slab installation shortenings – Shortenings taking place after the time of slab installation

① :Compensation ② : Design Level ③: Pre-slab Installation shortening ④: Post-slab Installation shortening


Column Shortening

Procedure for Accounting Column Shortening



Column Shortening



Climatic Condition

Loading Condition Conditions

Construction Progress

Other Conditions

Pre-Analytical Prediction & Continuous Monitoring

?

Experimental Measurements & Construction Survey

Correctio n

Precise prediction of shortening


Column Shortening


Procedure for Accounting Column Shortening Analytical Measurement

Using Software or Manually (Manual calculation is almost impossible) Reflection of physical properties in calculation from material experiment: Young’s Modulus, Poisson’s Ratio, Mean Compressive strength, Volume to Surface ratio, Shapes, sizes etc.

Reflection of effects of Climate on shortening: Average Temperature Average Temperature , RH etc. Construction Sequence: Stage duration, Additional Steps, Member Age, Load activation age, Boundary activation age etc. Reflection of the above effects on site masterschedule.

Method has Limitation

Experimental Measurement

Field Measurements

Installation of sensors or gages in members for determining the actual shortening. Understanding and noting the following:

Curing procedure / Temperature, Actual Shortening, Change in Ambient Temperature (Important), Actual Humidity, Deviation from Defined Construction Stages, Manipulation of factors in analytical Calculation, Re- Analysis… Analysis…


Column Shortening



Field Measurements

Determination Determinatio n of Installation location

After Installation of Gauge Gauge

Installation of Gauge

After Casting of Concrete

After Installation

Field data collection


Column Shortening



Engineering Re-Analysis

Manipulation of the construction stage as per site condition

Perform 3D CS Analysis

Activation of Construction Construction stages

Construction stage of each group




Column Shortening


Compensation at Site 2nd correction 1st correction

1st correction

Column

Column


Column Shortening


Compensation at Site

CON'C Casting face

Height of correction

 The order of construction

installation of column forms SLAB THK.

insertion of FILLER Column Rebar

B (= Height of correction

insertion of correcting FILLER

f i l l e r

Installation of SLAB forms

securing the thickness of slab.




Useful Features for CS Analysis


Construction Stage Wizard for Building Strcuture  The

wizard readily allows us to define the timing of elements created and loadings applied in the construction

stages during the erection of a building. buildi ng.  You

may find it more convenient to first click the [Automatic Generation] button to define the basic

construction stages and modify them as necessary.




Construction Stage Analysis Analysis for Composite Members  Define

an analytical model for each construction stage by assigning activated or inactivated sections corresponding to

each construction stage of a composit composite e section.  By

using Composite Section for Construction Stage, we can consider the construction sequence with creep and

shrinkage effect. effect.




Material Stiffness Changes for Cracked Sections  Specific stiffness of specific member types may be reduced such as the

case where the flexural stiffness of lintel beams

and walls may require reduction to reflect cracked sections of concrete.  Section

stiffness scale factors can be included in boundary boundary groups for construction stage analysis. analysis. The scale factors are

also applied to composite sections for construction stages




Spring Supports For Soil Interaction  Point

Spring Support (Linear, Comp.-only, Tens.-only, and Multi-linear type)

 Surface

Spring Support (Nodal Spring, and Distributed Spring)

 Springs can be activated / deactivated during construction stage analysis. analysis.

[Nonlinear point spring support]

[Pile Spring Support]

[Surface Spring Support]

[Nodal Spring and Distributed Spring]



Tendon Loss

 Pre-stress  Tendon

load can be considered in construction stage analysis.

primary / secondary forces are provided with pre-stress loss graph





Project Applications


Burj Khalifa (Dubai, UAE) CS:1

CS:30

Height wNo. of floors e i Location v Function / Usage r e Designer v o Architect General Contractor

705 m 160 Dubai, United Arab Emirates Office Building & Residential Building Adrian D. Smith Skidmore, Owings & Merrill Samsung Development




SK S-Trenue (Seoul, Korea)

Area No. of floors w e i Location v Function / Usage r e Structure Type v o Foundation Type Lateral load resisting system

39,600 m2 36 Seoul, Korea Office Building Composite Structure Mat Foundation RC Core + Steel + RC Composite Frame




Keangnam Hanoi Landmark Tower (Hanoi, Vietnam)

Height wNo. of floors e i Location v Function / Usage r e Structure Type v o Architect Contractor

345m 70 fl., 49 fl. Hanoi, Vietnam Hotel, Office, and Residential building Reinforced Concrete Structure Heerim, Samoo, Aum & Lee, Hellmuth Obata + Kassabaum Keangnam




Live Demonstration


Structural Plan

Storey's :- 40 Storey Height :- 3.15 m Total Height :- 126.85 m

Typical Floor Plan


Live Demonstration


Material and Sectional Properties

Size Level

f ck

C1

C2

Wall Thk.

1st to 10th

50

1200 x 1200

900 x 900

500

11th to 20th

40

1000 x 1000

800 x 800

500

21st to 30th

35

800 x 800

700 x 700

500

31st to 40th

30

600 x 600

600 x 600

500

Girder

30

900 x 600

-

Link Beam

30

700 x 500

-


Live Demonstration


Construction Schedule Partition Load : 5 weeks after first slab casting. Finish Load : 5 Weeks after Partition Wall Construction.

Stage 1

Stage 4

Final Stage


Live Demonstration

Procedure Time Dependant Material Properties •Define Creep and Shrinkage Properties . •Define time Dependant Material Properties. •Define Time Dependant Material Link. •Change Element Dependant Material Property

Define Construction Construction Stage •Define Construction stages using Building Wizard for CS analysis •Create LL group and add LL to LL group. •Define CS for LL

Perform Analysis

Results •BMD’s and SFD’s for different CS. •Deformations for different CS. •Column Shortening Graph.



Q&A

02-Construction Stages and Column Shortening Analysis in Tall Buildings

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