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8/7/2019 ADOBE SYSTEMS INDIA PVT LTD

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ADOBE SYSTEMS INDIA PVT LTD

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POST- TENSIONED BEAM DESIGN REPORT

FOR

PROPOSED CONSTRUCTION OF CAMPUS FOR ADOBE SYSTEMS INDIA PVT LTD

HIG-20 Shivaji Nagar, Bhopal-462016(M.P.)

Tel: 0755-4058484, Fax: 0755-4058485

E-mail: [email protected]


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CONTENTS

1) GENERAL PROJECT DETAILS.

2) POST TENSIONED SLAB INTRODUCTION.

3) LIST OF REFERENCES

4) MATERIAL, WORKMANSHIP, INSPECTION AND TESTING

4.1Concrete

4.2Durability of concrete

4.3VSIL PT material.

4.4Reinforcement.

4.5Construction joint.

5) GENERAL PT SLAB & BEAM DESIGN CONSIDERATION

5.1Method of Design

5.2Loads and Forces

6) POST TENSIONED SLAB, BEAM ANALYSIS &DESIGN

7) ADAPT-PT Result sheet for Design strip

7.1 Input Data

7.2Output Data

7.3Graphical Result Data

8) PT Drawings.


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The structure is PROPOSED CONSTRUCTION OF CAMPUS FOR ADOBE SYSTEMS INDIA PVT LTD.

The document attempts to record all inputs assumed in design and will form the basis for all future detailed

structural work.

The report most importantly clarifies the load criteria assumed in the design and it is therefore expected that

all related consultants, including the architects, would go through the document and refer to it at every stage of

detailed design. Recommendations or revisions on assumed parameters are requested at this stage.

Besides this the report will also form the outline of the design criteria and methods of both analysis and

design to be adopted in this project with the aim of achieving a design that satisfies all sorts of seismic, and

serviceability requirements.(At preliminary stage pt slab design for DL+LL only).

1. GENERAL PROJECT DETAILS

Post-Tensioned Slab introduction:

1.1 Objective

One of the major advancements in bridge construction in the United States in the second half of the twentieth

century was the development and use of prestressed concrete. Prestressed concrete bridges, offer a broad range

of engineering solutions and a variety of aesthetic opportunities. The objective of this Manual is to provide

guidance to individuals involved in the installation or inspection of post-tensioning work for post tensioned

concrete bridges including post-tensioning systems, materials, installation and grouting of tendons.

1.1.1 Benefits of Post-Tensioning

The tensile strength of concrete is only about 10% of its compressive strength. As a result, plain concrete

members are likely to crack when loaded. In order to resist tensile stresses which plain concrete cannot resist, it

can be reinforced with steel reinforcing bars. Reinforcing is selected assuming that the tensile zone of the

concrete carries no load and that tensile stresses are resisted only by tensile forces in the reinforcing bars. The

resulting reinforced concrete member may crack, but it can effectively carry the design loads (Figure 1.1).

Figure 1.1 - Reinforced concrete beam under load

Although cracks occur in reinforced concrete, the cracks are normally very small and uniformly distributed.

However, cracks in reinforced concrete can reduce long-term durability. Introducing a means of precompressing

the tensile zones of concrete members to offset anticipated tensile stresses reduces or eliminates cracking toproduce more durable concrete bridges.


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1.1.2 Principle of Prestressing

The function of Prestressing is to place the concrete structure under compression in those regions where load

causes tensile stress. Tension caused by the load will first have to cancel the compression induced by the

prestressing before it can crack the concrete. Figure 1.2 (a) shows a plainly reinforced concrete simple-span

beam and fixed cantilever beam cracked under applied load. Figure 1.2(b) shows the same unloaded beams with

prestressing forces applied by stressing high strength tendons. By placing the prestressing low in the simple-spanbeam and high in the cantilever beam, compression is induced in the tension zones; creating upward camber.

Figure 1.2(c) shows the two prestressed beams after loads have been applied. The loads cause both the simple-

span beam and cantilever beam to deflect down, creating tensile stresses in the bottom of the simple-span beam

and top of the cantilever beam. The Bridge Designer balances the effects of load and prestressing in such a way

that tension from the loading is compensated by compression induced by the prestressing. Tension is eliminated

under the combination of the two and tension cracks are prevented. Also, construction materials (concrete and

steel) are used more efficiently; optimizing materials, construction effort and cost.

Figure 1.2 - Comparison of Reinforced and Prestressed Concrete Beams

Prestressing can be applied to concrete members in two ways, by pretensioning or post-tensioning. In pretension

members the prestressing strands are tensioned against restraining bulkheads before the concrete is cast. After

the concrete has been placed, allowed to harden and attain sufficient strength, the strands are released and their

force is transferred to the concrete member. Prestressing by post-tensioning involves installing and stressing

prestressing strand or bar tendons only after the concrete has been placed, hardened and attained a minimum

compressive strength for that transfer.

2) The Advantages of Post-Tensioned Slab can be summarized as follows

Early Post-Tensioning allows the formwork to be stripped and re-deployed quickly.

Significant saving on material, up to 30% on concrete alone with longer spans, fewer columns &

thinner slabs producing lighter overall structure and reducing foundation cost.


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Joint free ground slabs up to 10000 m and true & level floor ideal for automated ware housing and

super markets.

Water proof floors to eliminate unsightly staining of concrete fascias.

Thinner slabs give more head room.

flexibility- Internal layout flexibility is greatly increased, making it much easier to place or reposition

partitions

Spans up to 50% longer than those using RCC can be constructed with fewer support columns.

Offers resistance to cracking and water seepage due to limited deflection and highly compressive

characteristics of pre stressed concrete structure.

3) List of References:

4) Material, Workmanship, Inspection and Testing:

The proposed PT structure will consists of concrete, P.T Strands and steel reinforcement as the three main

materials used for construction of the structure. The specifications for these materials are discussed in this

chapter.

4.1 Concrete:

The concrete shall be in grades designated as per Table 2 IS 456-2000.

Recommended grades for the different members is as follows:

Columns M28

Beams/Slabs M35

In this case consider Characteristic concrete cube strength at 28 days= 35 N/mm2

Cube strength at transfer of prestress, days (7) = 28 N/mm2

Retaining Walls M30.

IS 456-2000

IS 1343-1980

Plain and reinforced concrete-code of practice

Indian Standard Code of Practice for Pre-stressed Concrete

ACI 318 Plain and reinforced concrete-code of practice American standard


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4.2 Durability of concrete

The structure is located in NOIDA, where the climatic conditions are considered as moderate. Concrete grade

of submerged structural elements will be a minimum of M35. Nominal covers shall not be less than 20mm from a

durability point of view.

The cover to the various structural elements is to be as follows,

Exposure : Moderate

Structural Element Clear Cover in mm

Slabs 20

Beams 40

4.3 VSIL Post-tensioning System.

VSIL multi-strand post tensioning system comprising a variable number of strands encased in ribbed

semi-rigid circular galvanized steel ducts of variable diameters

PT Strand

The P.T strands will be 12.7mm HTS low relaxation of ultimate stress capacity 1850N/mm2.

H.T. Strand Specification:

Nominal Diameter

Nominal Area 99 mm

Nominal Weight 0.778 kg/m

Min Ultimate Strength 1860 N/sq mm

Modulus of Elasticity 195 KN/sq mm

Min Breaking load per Strand 186KN


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Relaxation, low 2.5% at 0.70 UTS

Identification Metal Tag for each coil

Certificates Mill Certificate for each

Product Type Un-oiled

Strand quality in Accordance with IS 14268

Friction parameters () 0.25/m

(k) 0.0046/rad/m

Anchorage set


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4.4 Reinforcement:

The reinforcement shall be high strength deformed steel bars with yield strength of 415N/mm2

confirming to

IS 1786 2008.

4.5 Construction Joint

Construction, and shrinkage strips will be planned with the contractor and only be used at locations pre-

approved by consultants.

5) General Assumptions for PT slab and Beam design

1) Strength design of prestressed member for flexure and axial loads shall be based on assumptions given in

clause 18.3 (Chapter 18) ACI-318

2) Design moment strength of flexural members shall be computed by the strength design method of the code

ACI-318

3) Prestressed flexural members shall be classified as class U, Class T or Class C based on extreme fiber stress

(Ft) in tension in precompressed tensile zone calculated at service loads.

4) Serviceability Design Requirements are as per Clause 18.3 - ACI 3185) Deflection of prestressed flexural members shall be calculated in accordance with Clause 18.3.5-ACI 318

6) Permissible tensile stresses in flexural member are as per Class-C (Table 18.3.3-ACI-318).

7) Permissible stresses in prestressing steel shall not exceed the following

a) Due to prestressing steel jacking force---0.94 Fpy (specified yield strength of prestressing steel in psi) but not

greater than the lesser of 0.80(Fpu specified tensile strength of prestressing steel)and the maximum value

recommended by the manufacturer of prestressing steel or anchorage devices.

B) Immediate after prestress transfer -----0.82Fpy but not greater than 0.74 Fpu (specified tensile strength of

prestressing steel)

8) Minimum Bonded reinforcement shall be provided in all prestressed flexural members is as per clause 18.9-

ACI 318


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9) Minimum average effective prestress of 125 psi on the slab section tributary to the tendon or tendon group.

10) Required elongation shall be determined from average load-elongation curves for the prestressing steel used.

Generally 8% tolerance in prestressing steel force determined by gauge pressure and elongation measurements

for posttension construction.

5.1 Permissible Fiber Stresses Class 3 0.2 mm crack width

Transfer Service

Compression at support -10.0 N/mm - 14 N/mm

At mid span - 12.5 N/mm - 11.6 N/mm

Tension 1.5 N/mm 3.0 N/mm

(Tensile force taken as positive)

5.2 Loads and Forces

In structural design, account is taken of the dead and imposed loads.

5.2 A Dead Loads

The dead loads are calculated on the basis of unit weights of materials given in IS 875 (Part 1).

Reinforced Concrete

The data

provided by consultant and other service consultants will be used for the specific materials/equipments.

Unless otherwise specified the unit weight of materials will be used as follows.

25 kN/cum

Plain concrete 24 kN/cum

Brickwork 20 kN/cum

Concrete block work 24 kN/cum

Siporex Blocks 10 kN/cum

Stone cladding 25 kN/cum

Soil dry 16 kN/cum

Floor finishes 20 kN/cum


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5.1b Imposed Loads:

Imposed loads are assumed in accordance with IS 875 part 2

SR.NO

, as follows.

The table listed below is a summary of these loads.

FLOOR LOAD-KN/M

1 ALL FLOOR

LIVE LOAD 4.0

DEAD LOAD 3.0

Analysis:

For analysis purpose, the program converts each object into one or more elements.

A static analysis is carried out for the whole structure.

On analysis with any RCC software, we will be getting the moment contour in kNm/m for slab, kN.m for

beams, whereas in ADAPT-PT, the moment will be generated in kNm.

As per the moments contour, the bending moments in the slab/beam for a corresponding strip/beam is

taken and the same moment is generated in ADAPT-PT.

Comparing ADAPT_PT and R C C, Ultimate Design Moments.

Post tensioning Analysis & Design

Slabs and beams with associated columns are modeled as a two-dimensional plansframe. Along the slabs or beam, nodes are placed at column centerlines, column faces, and at any

changes of geometry. Supports are provided at the ends of columns.

Gross sections are used for the computation of I values.

Tendon Modeling

The tendon profiles in any span are described as parabolic.


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The loss factor immediate or deferred to the computed force profile.The loss factor is calculated as follows:

For each span, the level of prestress at mid-span is computed, along with the associated concretestress.

The corresponding elastic shortening is used to compute the loss in stress in the pre stressing steel,using a factor of .5 to allow for sequential stressing of the strands. The immediate loss factor isobtained by averaging over all spans.

Shrinkage loss is obtained by applying the % loss (based on the average tendon stress at transfer tothe mid span stress in each span. Stress loss due to creep is calculated from the creep strain atmid-span. The deferred loss factor is obtained by averaging over all spans and adding the relaxationloss.

Design strips

1 RCC Software moment contour:

:

Computation modules develop the design moments and forces for each strip by factoring the computed

bending moments using the moments factor specified during input, and then adding the effects of pre-

stress using results from the application pre-stress load case.

For cantilevers, the adjacent column factor applies to the entire cantilever span in addition to the column

region.

How to Read and Compare Analysis Result

2 Maximum Positive and Negative Moment for Dominant Load cases.

3 Bending moment contour about Y-axis

4 Bending moment contour about X-axis.

6) Post tensioned slab analysis and design:

PT slab designed for (DL+ LL) only. RCC Consultant provides reinforcement for earthquake.

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