Annex H(Clause 37.1)

Moments of Resistance for Rectangular and T-sections

H-0 The moments of resistance of rectangular and T-sections based on the assumption of 37.1 are given in this annex.

H-1 Rectangular Sections

The moment of resistance of rectangular sections without compression reinforcement should be obtained as follows:

a) Determine the depth of neutral axis from the following equation:

b) If the value of $x_{u}/d$ is less than the limiting value (see Note below 37.1), calculate the moment of resistance by the following expression:

c) If the value of $x_{u}/d$ is equal to the limiting value, the moment of resistance of the section is given by the following expression:

d) If $x_{\mathrm{u}} / d$ is greater than the limiting value, the section should be redesigned.

In the above equations,

$f_{ck}$ = characteristic compressive strength of concrete,

$b =$ width of the compression face,

$M_{u,\lim} = \text{limiting moment of resistance of a section without compression reinforcement, and}$

$x_{\mathrm{u,max}} =$ limiting value of $x_{\mathrm{u}}$ from 37.1.

Where the ultimate moment of resistance of section exceeds the limiting value, $M_{\mathrm{u,lim}}$ compression

reinforcement may be obtained from the following equation:

where

$d' = \text{depth of compression reinforcement from compression face.}$

The total area of tension reinforcement shall be obtained from the following equation:

where

$A_{\mathrm{st}} =$ area of the total tensile reinforcement,

$A_{st1}$ = area of the tensile reinforcement for a singly reinforced section for $M_{u,lim}$ , and

H-2.1 For $x_{\mathrm{u}} < D_{\mathrm{f}}$, the moment of resistance may be calculated from the equation given in H-1.1.

H-2.2 The limiting value of the moment of resistance of the section may be obtained by the following equation when the ratio $D_{\mathrm{f}} / \mathrm{d}$ does not exceed 0.2:

where

$M_{\mathrm{u}}, x_{\mathrm{u,max}}, d$ and $f_{\mathrm{ck}}$ are same as in H-1.1,

$b_{\mathrm{f}} =$ breadth of the compression face/flange,

$b_{\mathrm{w}} =$ breadth of the web,

$D_{\mathrm{f}} =$ thickness of the flange.

H-2.2.1 When the ratio $D_{\mathrm{f}} / d$ exceeds 0.2, the moment of resistance of the section may be calculated by the following equation:

PART 6 STRUCTURAL DESIGN — SECTION 5 CONCRETE: 5A PLAIN AND REINFORCED CONCRETE

where $y_{\mathrm{f}} = (0.15x_{\mathrm{u}} + 0.65D_{\mathrm{f}})$, but not greater than and the other symbols are same as in H-1.1 and H-2.2.

H-2.3 For $x_{\mathrm{u,max}} > x_{\mathrm{u}} > D_{\mathrm{f}}$, the moment of resistance may be calculated by the equations given in H-2.2 when does not exceed 0.43 and H-2.2.1 when exceeds 0.43; in both cases substituting by .

The following list records those standards which are acceptable as ‘good practice’ and ‘accepted standards’ in the fulfillment of the requirements of the Code. The latest version of a standard shall be adopted at the time of enforcement of the Code. The standards listed may be used by the Authority for conformance with the requirements of the referred clauses in the Code.

In the following list, the number appearing in the first column within parentheses indicates the number of the reference in this Subsection.

IS No. Title

(1) 3370 Concrete structures for the storage of liquids — Code of practice

(Part 1): 2009 General requirements (first revision)

(Part 2): 2009 Reinforced concrete structures (first revision)

2210 : 1988 Criteria for design of reinforced concrete shell structures and folded plates (first revision)

3201 : 1988 Criteria for design and construction of precast-trusses and purlins (first revision)

4090 : 1967 Criteria for design of reinforced concrete arches

4991 : 1968 Criteria for blast resistant design of structures for explosions above ground 4995 Criteria for design of reinforced concrete bins for storage of granular and powdery materials

(Part 1): 1974 General requirements and bin loads

(Part 2): 1974 Design criteria

4998 : 2015 Criteria for design of reinforced concrete chimneys (third revision)

6922 : 1973 Criteria for safety and design of structures subject to underground blasts

IS No. Title

(2) 4845 : 1968 Definitions and terminology relating to hydraulic cement 6461 Glossary of terms relating to cement: (Part 1) : 1972 Concrete aggregates (Part 2) : 1972 Materials (Part 3) : 1972 Concrete reinforcement (Part 4) : 1972 Types of concrete (Part 5) : 1972 Formwork for concrete (Part 6) : 1972 Equipment, tool and plant (Part 7) : 1973 Mixing, laying, compaction, curing and other construction aspect (Part 8) : 1973 Properties of concrete (Part 9) : 1973 Structural aspects (Part 10) : 1973 Tests and testing apparatus (Part 11) : 1973 Prestressed concrete (Part 12) : 1973 Miscellaneous

(3) 269 : 2015 Ordinary Portland cement — Specification (sixth revision) 8041 : 1990 Specification for rapid hardening Portland cement (second revision) 455 : 2015 Specification for Portland slag cement (fifth revision) 1489 Specification for Portland pozzolana cement: (Part 1) : 2015 Fly ash based (fourth revision)

(Part 2): 2015 Calcined clay based (fourth revision)

8043 : 1991 Specification for hydrophobic Portland cement (second revision)

12600 : 1989 Specification for low heat Portland cement

12330 : 1988 Specification for sulphate resisting Portland cement

(4) 12600 : 1989 Specification for low heat Portland cement

PART 6 STRUCTURAL DESIGN — SECTION 5 CONCRETE: 5A PLAIN AND REINFORCED CONCRETE

PART 6 STRUCTURAL DESIGN

Section 5 Concrete: 5B Prestressed Concrete

BUREAU OF INDIAN STANDARDS

Section 5B (a) General

• SCOPE
• TERMINOLOGY
• SYMBOLS

Section 5B (B) Materials, Workmanship, Inspection and Testing

• 4 MATERIALS ... 6
• 5 CONCRETE ... 8
• 6 WORKABILITY OF CONCRETE ... 11
• 7 DURABILITY OF CONCRETE ... 11
• 8 CONCRETE MIX PROPORTIONING ... 15
• 9 PRODUCTION OF CONCRETE ... 15
• 10 FORMWORK ... 17
• 11 ASSEMBLY OF PRESTRESSING AND REINFORCING STEEL ... 17
• 12 PRESTRESSING ... 19
• 13 TRANSPORTING, PLACING, COMPACTING AND CURING ... 25
• 14 CONCRETING UNDER SPECIAL CONDITIONS ... 25
• 15 SAMPLING AND STRENGTH TEST OF DESIGN CONCRETE MIX ... 25
• 16 ACCEPTANCE CRITERIA ... 25
• 17 INSPECTION AND TESTING OF STRUCTURES ... 25

Section 5B (C) General Design Requirements

• 18 GENERAL DESIGN REQUIREMENTS ... 26

• 19 SAFETY AND SERVICEABILITY REQUIREMENTS ... 30
• 20 CHARACTERISTIC AND DESIGN VALUES AND PARTIAL SAFETY FACTORS ... 31
• 21 ANALYSIS ... 32
• 22 LIMIT STATE OF COLLAPSE ... 32
• 23 LIMIT STATE OF SERVICEABILITY ... 37
• ANNEX A SHEATHING DUCTS FOR PRESTRESSING ... 39
• ANNEX B TESTING OF SYSTEMS WITH MECHANICAL ANCHORAGES ... 45
• ANNEX C MOMENTS OF RESISTANCE FOR RECTANGULAR AND T-SECTIONS ... 49
• LIST OF STANDARDS ... 50

National Building Code Sectional Committee, CED 46

This Code (Part 6/Subsection 5B) covers the structural design aspects of prestressed concrete.

The Section 5 of Part 6 of the Code covers plain and reinforced concrete and also the prestressed concrete. The Section has been subdivided into the following subsections:

5A Plain and Reinforced Concrete 5B Prestressed Concrete

Provisions related to prestressed concrete are covered in the following format: Section 5B (A) General Section 5B (B) Materials, workmanship, inspection and testing Section 5B (C) General design requirements Section 5B (D) Structural design: Limit state method

In some clauses, the Code recommends reference to specialist literature, since the current knowledge on some aspects of design had not yet crystallized. This had also been done in order to avoid burdening the Code with a lot of details which may not be required for the design of great majority of structures.

While deciding on the symbols used in the Code, the recommendations on ISO 3898 : 2013 ‘Bases for design of structures — Names and symbols of physical quantities and generic quantities’ had been taken into consideration. However, considering the convenience of the users of the Code, the familiar symbols of the old version were retained to the extent possible.

IS 456 was revised in the year 2000 as IS 456 : 2000 ‘Code of practice for plain and reinforced concrete (fourth revision)’, to which 4 amendments were subsequently issued. In IS 456, major changes were incorporated in provisions relating to materials, workmanship, inspection and testing, and general design requirements. In view of the attempt at unification between provisions of reinforced concrete and prestressed concrete codes, these changes are relevant to prestressed concrete code also. Considering this aspect as also the need for a complete review of the provision of the Code in light of the latest international developments and the improved practices being followed now, a full scale revision of IS 1343 was done, bringing out IS 1343 : 2012 ‘Code of practice for prestress concrete (second revision)’.

In this second revision of this Subsection, the provisions have been brought in line with IS 1343 : 2012, along with the following further modifications incorporated with a view to keeping abreast with the rapid development in the field of prestressed concrete technology and also to bring in further clarifications and modifications in the light of experience gained, as follows:

a) It has been clarified that the Section/Code does not cover the specific requirements for bridges.

b) Clause on terminology has been reviewed and some new definitions such as anchorage device, cable, relaxation and sheathing have been added apart from modifications in other definitions such as on tendon.

c) Section on materials, workmanship, inspection and testing has been completely modified in line with IS 456 as applicable to prestressing and other changes have been incorporated as follows:

1. All the references to materials for making prestressed concrete have been updated.

2. Precautions to be made while using Portland slag cement and Portland pozzolana cement or mineral admixture to account for modified de-shuttering time, curing period and the time of prestressing have been included.

3. Provisions relating to maximum water cement ratio, minimum grade of concrete and minimum cement concrete have been clarified vis-à-vis concrete exposed to sulphate attack.

4. Uncoated stress relieved low relaxation seven ply strand has also been converted as prestressing steel.

PART 6 STRUCTURAL DESIGN — SECTION 5 CONCRETE: 5B PRESTRESSED CONCRETE

5. Provisions on modulus of elasticity have been modified.

6. Grades of concrete have been specified up to M 80 from the existing M 30 to M 60.

7. Provisions on creep and shrinkage of concrete have been revised.

8. Durability requirements have been covered exhaustively in line with IS 456 as applicable to prestressed concrete; the maximum cement content has been specified as $450\mathrm{kg / m^3}$.

9. Assumed standard deviation has been specified as $5.0\mathrm{N} / \mathrm{mm}^2$ for concrete mix proportioning.

10. Provisions on assembly of prestressing and reinforcing steel and on prestressing have been thoroughly revised in line with the present improved practices, and details on protection of prestressing steel, sheathing and anchorages have been incorporated.

11. Sampling and strength test of designed concrete mix has been modified in line with IS 456.

d) The Sections on General Design Requirement and Structural Design (Limit State) have been modified as follows:

1. Provisions are in line with IS 456 as applicable.

2. Design provisions are updated in line with the latest practices.

e) Provisions related to bearing stress in the end zone in post-tensioned members have been updated.

f) Provisions related to ultimate shear resistance of a section uncracked in flexure have been updated.

g) Provisions related to ultimate shear resistance of a section cracked in flexure have been updated.

h) Test on wall thickness of the duct of corrugated HDPE sheathing duct has been updated.

In this Code, it has been assumed that the design of prestressed concrete structures is entrusted to a qualified engineer, and that the execution of the work is carried out under the direction of an experienced supervisor.

All standards, whether given herein above or cross-referred to in the main text of this Subsection, are subject to revision. The parties to agreement based on this Subsection are encouraged to investigate the possibility of applying the most recent editions of the standards.

For the purpose of deciding whether a particular requirement of this Subsection is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded off value should be the same as that of the specified value in this Subsection.