02-Construction Stages and Column Shortening Analysis in Tall Buildings

Midas Gen – One Stop Solution for Building and General Structures

Construction Stage Analysis and Column Shortening in Tall Buildings

Midas IT Technical Seminar

17th February 2012

Ravi Kiran


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

Contents

One Stop Solution for Building and General Structures Midas Gen – Technical Seminar

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

• Construction of structures is a time taking process and during this period Material Properties,

Loads and Boundaries conditions may change.


Why Construction Stage (CS) Analysis

Construction Sequence

Self weight of slab

Other Dead Loads (Partions, Finishes)

Completed Structure

Dead Load + Live Load

Wind

Earthquake

LL,WL,EQ Acts

One Stop Solution for Building and General Structures Midas Gen – Technical Seminar Construction Stage Analysis

Conventional Analysis Vs. Construction Stage Analysis

Case 1 – Conventional Analysis Case 2 – CS Analysis

Stage 1 Stage 2


Conventional Analysis Vs. Construction Stage Analysis

Case 1 – Conventional Analysis Case 2 – CS Analysis


Where CS 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 there is a change in

Support Conditions, Loading and varying material properties (Concrete).









Live Demonstration

Contents


Column Shortening and Related Issue

σ

When any member is loaded with Axial Load, it undergoes axial deformation

E = (σ / ε)

ΔL = (PL/A E)

Why is

this

Important

Column Shortening


P1, ΔL1

P2, ΔL2

The differential shortening happening between the vertical members may cause

additional forces and stress in Beams and Slabs


Column Shortening


Steel Structures

- Linear elastic Behavior

Stress ∞ Strain

Strain is constant for a given Stress

during loading & unloading

E = (σ / ε)

ΔL = (PL/A E)

σ


Column Shortening


Concrete Structures - Nonlinear Inelastic Behavior

- But in general analysis and design behavior of concrete is treated as Linear Elastic Material

Neither Stress ∞ Strain

Nor Strain is constant for a given Stress

During loading & unloading

Elastic Strain + Inelastic Strain


Column Shortening


Concrete Structures

Elastic Shortening

Modulus of Elasticity changes with time.

Ei = (σ / ε)

ΔL = (PL/A Ei)

Inelastic Shortening

σ

σ

Creep Shortening.

Shrinkage Shortening.

Column Shortening and Related Issues

Column Shortening


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 ~ 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



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, creep and shrinkage components:

Where,

εe (t) = Instantaneous strain at time t,

εc (t) = Creep strain at time t,

εsh (t) = Shrinkage strain at 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



Inelastic Shortening = Creep + Shrinkage

Shrinkage Creep

Shrinkage is the time-dependant decrease in concrete

volume compared with the original placement volume

of concrete.

Drying Shrinkage is due to moisture loss in concrete.

Autogenous Shrinkage is caused by hydration of

cement.

Carbonation shrinkage results as the various cement

hydration products are carbonated in the presence of CO

Creep is time-dependent increment of strain under sustained

stress.

Basic creep occurs under the condition of no moisture

movement to and from the environment.

Drying creep is the additional creep caused by drying.

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

Column Shortening



Factors affecting the Creep & Shrinkage of Concrete

Concrete

(Creep & Shrinkage)

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

Member Geometry and Environment

(Creep & Shrinkage)

Environment Concrete Temperature

Concrete Water Content

Geometry Size and Shape

Loading

(Creep Only)

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

Column Shortening



Inelastic Shortening = Creep + Shrinkage

Shrinkage Creep

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

as =

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

Where,

t = time in days after loading.

vu = Ultimate creep coefficient = 2.35 c

c = Product of applicable correction factors

After 7 days for moisture cured concrete

After 1-3 days for steam cured concrete

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









Live Demonstration

Contents



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



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.

Slabs may not be truly horizontal after some time.

Beams could be subjected to higher bending moments.

Load transfer.

Structural Effects

Non Structural Effects

Column Shortening



Deformation and breakage of Facades, windows &

Parapet walls…

Reverse Inclination of Drainage Piping System

Deformation of Vertical Piping System

Deformation and breakage of internal partitions

Column Shortening









Live Demonstration

Contents


Movement Related to Construction Sequence

• Pre-slab installation shortenings

– Shortenings taking place up to the time of slab installation

• 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

Conditions

Loading Condition

Construction Progress

Other Conditions

Pre-Analytical

Prediction &

Continuous

Monitoring

Experimental

Measurements

&

Construction

Survey

Precise prediction of shortening

Correctio

n

Column Shortening



Analytical Measurement

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 , RH etc. Construction Sequence: Stage duration, Additional Steps, Member Age, Load activation age, Boundary activation age etc. Reflection of the above effects on site master-schedule.

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…

Experimental Measurement

Using Software or Manually

(Manual calculation is almost impossible)

Field Measurements

Method has Limitation

Column Shortening



Determination of Installation location Installation of Gauge After Installation

After Installation of Gauge

After Casting of Concrete Field data collection

Field Measurements

Column Shortening



Manipulation of the construction stage as per site condition

Construction stage of each group

Activation of Construction stages

Perform 3D CS Analysis

Engineering Re-Analysis

Column Shortening









Live Demonstration

Contents



Column Column

1st correction

2nd correction

1st correction

Column Shortening

One Stop Solution for Building and General Structures Midas Gen – Technical Seminar Column Shortening


SLAB THK.

B (= Height of correction

filler

Height of correction

Column Rebar

CON'C Casting face

The order of construction

installation of column forms

insertion of FILLER

insertion of correcting FILLER

Installation of SLAB forms

securing the thickness of slab.









Live Demonstration

Contents


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.

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

construction stages and modify them as necessary.

Useful Features for CS Analysis


Construction Stage 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 composite section.

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

shrinkage 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 groups for construction stage analysis. The scale factors are

also applied to composite sections for construction stages



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.

Spring Supports For Soil Interaction

[Nonlinear point spring support]

[Nodal Spring and Distributed Spring] [Surface Spring Support] [Pile Spring Support]



Pre-stress load can be considered in construction stage analysis.

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


Tendon Loss









Live Demonstration

Contents

One Stop Solution for Building and General Structures Midas Gen – Technical Seminar Project Applications

Burj Khalifa (Dubai, UAE)

Height 705 m

No. of floors 160

Location Dubai, United Arab Emirates

Function / Usage Office Building & Residential Building

Designer Adrian D. Smith

Architect Skidmore, Owings & Merrill

General Contractor Samsung Development

ove

rvie

w

CS:1

CS:30


SK S-Trenue (Seoul, Korea)

Area 39,600 m2

No. of floors 36

Location Seoul, Korea

Function / Usage Office Building

Structure Type Composite Structure

Foundation Type Mat Foundation

Lateral load resisting system RC Core + Steel + RC Composite Frame

ove

rvie

w


Keangnam Hanoi Landmark Tower (Hanoi, Vietnam)

Height 345m

No. of floors 70 fl., 49 fl.

Location Hanoi, Vietnam

Function / Usage Hotel, Office, and Residential building

Structure Type Reinforced Concrete Structure

Architect Heerim, Samoo, Aum & Lee, Hellmuth Obata + Kassabaum

Contractor Keangnam

ove

rvie

w









Live Demonstration

Contents

One Stop Solution for Building and General Structures Midas Gen – Technical Seminar Live Demonstration

Structural Plan

Typical Floor Plan

Storey's :- 40

Storey Height :- 3.15 m

Total Height :- 126.85 m


Material and Sectional Properties

Level fck

Size Wall Thk. C1 C2

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 -


Construction Schedule

Stage 1

Stage 4 Final Stage

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


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 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

Documents

general structures column

general analysis

construction of structures

differential shortening

stop solution

construction stage cs

times elastic shortening

effect of column