CCL Engineering CCL Gulf

Project : B-971–1178 Lilian Tower

Status: For Approval B-1178-BD-01

Name Signature Date

Prepared by: MB 30-10-2013

Checked for CCL Eng.

SK 31-10-2013

CCL Eng. Approved: SK 31-10-2013

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Table of Content

1 INTRODUCTION ........................................................................................................................... 3

1.1 Purpose ........................................................................................................................................ 3

1.2 Scope ............................................................................................................................................ 3

2 SOURCES OF INFORMATION .................................................................................................... 3

2.1 Codes and Standards .............................................................................................................. 3

2.2 Incoming Drawings .................................................................................................................. 3

2.3 Loadings and load combination ............................................................................................. 3

3 DESIGN SOFTWARE USED ........................................................................................................ 4

3.1 RAM Concept ........................................................................................................................... 4

3.2 DECON STDesign 3.1 ............................................................................................................... 4

4 General Design Considerations ................................................................................................. 5

4.1 Construction Materials ............................................................................................................ 5 (i) Concrete .................................................................................................................................................. 5 (ii) Passive reinforcement and Shear links ............................................................................................... 5 (iii) Tendons ................................................................................................................................................... 5 (iv) Anchors ................................................................................................................................................... 5 (v) Ducts ........................................................................................................................................................ 5

4.2 Calculation of post-tensioning losses and extensions ......................................................... 5

4.3 Concrete cover ......................................................................................................................... 6

4.4 Tendon and Reinforcement Layering ..................................................................................... 6

4.5 Tendon Stressing ..................................................................................................................... 7

4.6 Restrain To Elastic Shortening ............................................................................................... 7

4.7 Construction Sequence and Temporary Works Design ........................................................ 8

4.8 MEP Openings General Restrictions ...................................................................................... 8

4.9 Fire Rating ................................................................................................................................ 8

4.10 Non structural cracks .............................................................................................................. 8

4.11 Limit states and limiting stresses ........................................................................................... 9

4.12 Long-term deflection ............................................................................................................... 9

ANNEX A ............................................................................................................................................. 11

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1 INTRODUCTION

1.1 Purpose

This document provides general background to the design philosophy used for the design of post-

tensioned slabs and beams for CCL Gulf. It outlines the key design assumptions, general theoretical

approach and the technical standards and design software used.

1.2 Scope

This document is intended for use for post-tension design work undertaken for CCL Gulf on Lilian

Tower, Business Bay, Dubai, UAE. All information is based on the bonded CCL system and is limited

to suspended slabs and beams.

CCL Engineering assumes that all columns and walls are adequately designed in order to accept the loading transferred from the PT slabs

The scope of the post-tension design is designed to the gravity design loads as shown on the

provided drawings and the combined action for gravity, Lateral (wind & seismic), creep, shrinkage

and thermal effect as provided by the ETABS model submitted by the Main Consultant.

A minimum bottom mesh of T10@200 will be provided as requested by the main consultant as note

no. 20 on drawings S002.

2 SOURCES OF INFORMATION

2.1 Codes and Standards

All post-tension design, and associated reinforced concrete design, is carried out in accordance with

the requirements of ACI318-08. Two way PT slab system will be designed to class U while one-way

slabs and beams will follow class T.

2.2 Incoming Drawings

The post-tension design will be carried out in accordance with the supplied fully coordinated

drawings. CCL Gulf will not take responsibility for the coordination of the drawings or for identifying

inconsistencies; however where obvious inconsistencies are found between architectural, structural

and MEP drawings, we will bring the matter to the attention of the Main Contractor to resolve.

2.3 Loadings and load combination

The loading for the post tensioned slab design are provided in drawing S000, general arrangement plan

drawings and K&A Design Criteria (via letter ref. DU1112/DU/19352/2013 dated 01st October 2013)

issued to CCL Gulf at start of the project.

Cladding load will be considered as (Height x 1.0) kN/m. For block wall, the peripheral load will be

considered as (Height x 3.6) kN/m.

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Lateral (wind & seismic), creep, shrinkage and thermal effect are as provided by the ETABS model

submitted by the Main Consultant to CCL Gulf at start of the project.

3 DESIGN SOFTWARE USED

3.1 RAM Concept

RAM Concept V8i r4.1.3 is the primary tool for the design of the PT slabs and beams and RC slabs.

RAM Concept is a Finite Element based design and analysis tool which enables efficient modelling

of both regular and irregular post-tension floor arrangements.

The software represents the floor plate geometry with shell elements capable of modelling both in-

plane (membrane) and out-of-plane (plate bending) effects. The ability to define the vertical

eccentricity of structural members enables the software to represent steps in slab levels, beams

(up-stands and down-stands) and recesses and consider the interaction of in-plane and out-of-

plane effects. All significant openings are included the analysis to accurately establish load paths

and force concentrations.

Loads are applied either as point loads, line loads or areas loads and can be superimposed on plan

to develop the cumulative loading arrangement for any particular load case. Serviceability and

Ultimate Limit State load combinations are created by the software in accordance with code

requirements.

Column and wall supports are represented with either as point or line supports with vertical and

rotational stiffness calculated based on the column/wall dimensions and concrete properties.

Post-tension tendons are represented explicitly by the user and the equivalent forces are

automatically calculated and applied to the finite element model as a separate load case including

the appropriate post-tension losses. Both the in-plane and out-of plane effects of post-tensioning

are modelled (i.e. pre-compression and equivalent load). Secondary (or parasitic) moments are

automatically calculated by RAM Concept and are considered in the Ultimate Limit State design

calculations. Both short-term and long-term pre-stressing losses are automatically calculated along

the tendon profile based on the user defined parameters based on the post-tensioning system.

Design checks are carried out by the software based on concrete cross-sections defined by ‘design

strips’ or ‘design sections’ predefined by the user on plan. Design checks are carried out for the

transfer, serviceability and strength (Ultimate Limit State) conditions in accordance with ACI318-08.

All reinforcement requirements are detailed by the software graphically on plan output.

The mesh of the finite element is generally generated with size of (0.8 x 0.8 m). Ram Concept generates the mesh before performing the analysis.

3.2 DECON STDesign 3.1

“Decon STDesign 3.1 ‘’ is a program developed by DECON which enables the checking of concrete

shear stresses and the design of punching shear reinforcement. Using the vertical reaction and

moment output from RAM Concept, the program carries out calculations in accordance with ACI

318-08 for internal, edge and corner columns.

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4 General Design Considerations

4.1 Construction Materials

(i) Concrete

F’c = 45 N/mm2 (Cylinder) for slabs and beams, after 28 days for P1, P2, 4

th,4A & 5

Th Floors.

F’c = 40 N/mm2 (Cylinder) for slabs and beams, after 28 days for 6

Th to Roof Floors.

F’ci = 28 N/ mm2 (Cylinder) at Transfer for all floors.

(ii) Passive reinforcement and Shear links

The Yield strength for all reinforcement bars is 420 N/mm2 as stated in drawing S000.

(iii) Tendons

This document is intended for use with the bonded CCL post-tensioning system. Below summarizes the relevant tendon design properties for all the anchors and strand combinations 12.9 mm diameter for PT slabs and 15.7mm diameter for transfer beams bonded strands using CCL anchors.

- GUTS = 186 kN for 12.9 and 279 kN for 15.7 - Tensile strength = 1860 N/mm

2

- Area 12.9mm = 100 mm2

- Area 15.7mm = 150 mm2

- Modulus of Elasticity Es = 195 kN/mm2

- Jacking force = 78% GUTS (145 kN for 12.9 and 218 kN for 15.7)

(iv) Anchors

CCL Flat anchorages types XF10 3/13 and XF20 5/13 for the PT slabs and XM40 12/15 and XM60 19/15 for transfer beams will be used. XF anchors can accommodate up to 3 and 5 12.9 strands and XM anchors can accommodate up to 12 and 19 15.7 strands. Further details on the CCL Anchors will be provided in the material submittals.

(v) Ducts

Flat corrugated galvanized ducts of 45 X 20mm for XF10 3/13 and 70 X 20 mm for XF20 are used in the PT slab. Round corrugated galvanized ducts of 80mm dia for XM40 12/15 and 100mm dia for XM60 19/15 are used in the PT transfer beams.

4.2 Calculation of post-tensioning losses and extensions

Post-tension losses are calculated automatically by RAM Concept based on the tendon profiles and the CCL system parameters, resulting in a force profile along the length of the tendon. The CCL system parameters for short-term losses are as follows:

Wobble friction coefficient, K = 0.0017 /meter Angular friction coefficient, µ = 0.2 /radian Anchor Friction = 0.02 Wedge draw-in = 6 mm.

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The total long-term losses are input manually in RAM Concept and are included in the automatically calculated tendon force profile for the final condition. The long-term losses include consideration of strand relaxation, creep and long-term shrinkage. A value of 100 N/mm

2 is suitable for most post-

tension slabs in Gulf region.

4.3 Concrete cover

For passive reinforcement: - Top & Bottom cover for slab = 25mm (to reinforcement) minimum - Side cover for slab = 25mm (to reinforcement) minimum - Top & Bottom cover for beam = 40mm (to reinforcement) minimum - Side cover for beam = 40mm (to reinforcement) minimum For Post tensioning duct: - Minimum Top cover to the duct = 30mm (to duct) - Minimum Bottom cover to the duct = 30mm (to duct)

4.4 Tendon and Reinforcement Layering

In order to facilitate consistent design and to assist with site installation, tendon and reinforcement

layering system should ensures that tendons can be installed without any obstruction from passive

reinforcement that may prevent the assumed design profile being achieved. This is particularly

relevant at internal columns where heavy flexure and punching shear reinforcement may be

specified. The minimum cover to duct is always no less than 30mm.

The design of the PT slabs and beams takes into consideration the following tolerance:

• Vertically at high and low points: +/- 5 mm

• Vertically and intermediate points: +/- 10 mm (where tendons clashes)

• Horizontally: +/- 200 mm ( taken into consideration in the design)

• Visually smooth deviation in horizontal spacing and location of slab tendons are permitted when required.

• Maintain a minimum clearance of 150 mm between tendons and openings.

The layering system is detailed in Figure 1.

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Figure 1. Tendon and reinforcement layering used in flat slab design

4.5 Tendon Stressing

• Measure elongation to closest 3.2 mm

• If difference between measured and calculated elongations exceed plus or minus 7 percent, PT designer will review these elongation and issue his approval or recommendations.

• For tendons that are shorter than 8 m (calculated elongation of about 5 cm), the tolerance can be up to 6.5 mm instead of in percept, as even a small discrepancy will exceed the allowable 7 percept.

4.6 Restrain To Elastic Shortening

Consideration of release for elastic shortening due to post-tension forces is included in the design

and, where agreed with the Main Contractor, infill strips and release details are specified. These

details are indicated on the post-tension design drawings.

It is usually recommended that, where temporary release is proposed, it remains for a minimum of

21 days following casting and stressing of the last adjacent horizontal element.

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4.7 Construction Sequence and Temporary Works Design

CCL Gulf is not responsible for temporary works design and do not consider temporary works in the design process. We will however indicate stressing sequences or extraordinary propping where critical to safety. The effect of release details and pour strips is not usually critical to the design and does not significantly influence the forces and moments in the permanent condition provided that the infill strip locations are sensibly located and adequate propping is provided to all affected spans. Infill strips to be cast from same slab concrete strength a minimum 21 days after adjacent slabs have been cast, and all stressing and grouting operations have been completed. Side faces of completed slabs should be suitably prepared to achieve aggregate interlock. Edges of infill strips are to remain propped until concrete has reached full design strength. Special care should be taken in the design of the propping system at pour strips in order to account for the upper slabs loads.

4.8 MEP Openings General Restrictions

• All MEP cut out opening should be issued to CCL Gulf prior to the start of the design.

• Maximum slab opening dimensions of 300mm can be accommodated without design checking if

they are at least 10h away from column supports, where “h” is the slab thickness.

• Minimum clear distance between the sleeves and the PT Tendons should be 100mm.

• Maximum diameter of 0.25b for horizontal sleeves in PT/RC beams and 0.2L away from columns

and at mid beams’ depth. Adjacent sleeves in the beams should be a minimum 3 sleeve

diameter. All need to be checked by CCL Gulf before implementation on site. Typical

reinforcement for sleeves in beams will be issued in detailed design stage and should be followed

on site.

• If one of the above restrictions is not fulfilled, a design verification should be carried out by CCL

Gulf. (See Annex A)

4.9 Fire Rating

The fire rating for this project is as Main Consultant design specification

4.10 Non structural cracks

There are no specific requirements for crack widths limitation for class T in ACI 318-08 cl. R18.4 Table R18.3.3. CCL Gulf design will be limited uncracked section for 2 way PT slabs. Minor non-structural cracks may appear in the PT Slab due to restraint of the vertical elements even before stressing. Any such cracks can be closed to prevent water seepage.

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4.11 Limit states and limiting stresses

The standard CCL Gulf approach is to use average stresses from the finite element model and compare these stresses with those in Table R18.3.3 for class U & T (ACI318-08). Design sections are placed where parts of the slab are normal reinforced concrete.

4.12 Long-term deflection

Deflection to be considered That part of the total deflection occurring after attachment of non-structural elements (Summation of the long-term deflection due to all sustained loads and the immediate deflection due to any additional live load). Also refer to table 9.5(b)

Allowable stresses at Transfer Allowable stresses at service Section

Properties

for stress

calculation

at service

Deflection

calculation

basis Structural

Elements Class Compression Tension Compression Tension

Two-way

PT slab U

< 0.6f’ci < 0.25 PT + sustained

loads < 0.45f’c

<0.5 Cross section

un-cracked

Gross section

un-cracked

refer to ACI

318-08-9.5.4.1 Ends of simply

supported members

< 0.7f’ci

Ends of simply

supported members

< 0.5

PT + total loads

< 0.6f’c

PT Beams

&

One- way

PT slab

U

< 0.6f’ci < 0.25 PT + sustained

loads < 0.45f’c

ft< 0.625 Cross section

un-cracked

Gross section

un-cracked

refer to ACI

318-08-9.5.4.1

Ends of simply

supported members

< 0.7f’ci

Ends of simply

supported members

< 0.5

PT + total

<0.6f’c

PT Beams

&

One- way

PT slab

T

< 0.6f’ci < 0.25 PT + sustained

loads < 0.45f’c

0.625 <ft <

Cross section

in transition

between un-

cracked and

cracked

Cracked

section refer to

ACI 318-08-

9.5.4.2 Ends of simply

supported members

< 0.7f’ci

Ends of simply

supported members

< 0.5

PT + total loads

<0.6f’c

PT Beams

&

One- way

PT slab

C

< 0.6f’ci < 0.25 No

requirement

ft > Cross section

cracked

Cracked

section refer to

ACI 318-08-

9.5.4.2 Ends of simply

supported members

< 0.7f’ci

Ends of simply

supported members

< 0.5

No

requirement

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The following deflections are calculated based on ‘Design Criteria’:

− Instantaneous Deflection (at t=0): These are the deflections, which occur after completion of the slab. They included the superimposed dead loads. The prestressing effects are taken at time=0, i.e. without long-term losses. Sinst = SDL + SSDL + SPT at t=0

− Long-term gross deflections (at t=∞): These are deflections occurring at t=∞. To account for the long-term losses due to the creep, shrinkage and relaxation the prestressing forces are reduced by computed value from stressing time. The elastic deflections are usually multiplied by an assumed factor of to be provided on a case by case basis (superstructure and substructure) or considered as 2.5 to allow for the effect of creep. Calculations to be submitted justifying the assumed creep factor value. S∞,gross = 3.0 SDL + 3.0 SSDL + 1.25 SLL + 3.0 SPT at t=0

− Net Deflections (gross-instant): These are the deflections, which occur after all fitting out operations and at final (t=∞). This is also the more critical deflection, as it will affect partitions below the slab. Snet = S∞,gross – Sinst. = 2.0 SDL + 2.5 SSDL + 1. 25 SLL + 2.0 SPT at t=0

For the floor slabs and beams the maximum deflections are maintained below the following values with the understanding that the floor structure is not supporting or attached to non-structural elements likely to be damaged by large deflections of the floors: Member Long Term Deflection Limitation Slabs L/360

Beams L/360 Note that the incremental deflections of the slab & beam after the installation of partitions and finishes are limited to the least of span/480. (refer to table 9.5(b))

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ANNEX A

0.2L 0.25b