Annex B(Foreword)

NBC 2016 (SP 7:2016) Volume 1

2016 · PDF page 695

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Recommendations for Bamboo Structures in High Wind/cyclone Prone Areas

B-1 Given below are some recommendations for bamboo structures in high wind/cyclone prone areas, which are based on Rapid Visual Screening (RVS) of the damages of past events:

a) Prefer a square plan of the building symmetrical to the arrangement of partitions and openings for balanced distribution of forces within the structure. Window positioning be planned in such a way that wind entering through window could pass through similar opening on opposite wall in order to reduce built-up pressure, and incorporate ridge vents.

b) A hip-shaped, pyramidal or a conical roofing be preferred to gable end or mono-pitch ones for least wind resistance.

c) Wide mono-pitched Verandas abutting the entrance to residence should be structurally separated from the main building.

d) Roof overhangs be limited to 450 mm as they contribute to higher negative suction. Large

overhangs should be properly tied back to wall frame-work.

Roof structure shall be properly secured with vertical load-bearing members (wooden or bamboo columns, brick piers or walling) for eliminating the chances of being blown away from the building. A continuous beam connecting all the columns would increase the framing action.

f) Roof cladding (G. I. sheets, clay tiles or thatch) be properly connected with holding down U-bolts, or sturdy anchorages to ensure safety. Thatch roof be tied by nylon ropes in diagonal pattern.

g) Sufficient depth for anchorage be provided; columns be embedded in pits within the foundation and secured by poured concrete. Wetting of column base be checked by raising it from the floor level.

h) Highest importance be given to strengthening the junctions between structural elements at

different levels, that is, foundation, eaves and roof. Walls be linked together suitably by a continued collar beam at floor, sill, lintel and roof level.

j) Fastening any two mutually perpendicular load bearing members should be done in accordance with good practice of spacing the

connecting bolts with reference to loads direction and the centre of stiffness. This will increase the moment-resisting capacity of the joint and prevent hinge formation. A minimum of two bolts be provided to prevent rotation of members at a joint.

The following list records those standards which are acceptable as ‘good practice’ and ‘accepted standards’ in the fulfillment of the requirements of this Code. The latest version of the 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) 9096 : 2006 Code of practice for preservation of bamboo for structural purposes (first revision)

(2) 6874 : 2008 Method of tests for bamboo (first revision)

(3) 1902 : 2006 Code of practice for preservation of bamboo and cane for non-structural purposes (second revision)

(4) 8242 : 1976 Method of tests for split bamboo

(5) 2366 : 1983 Code of practice for nail-jointed timber construction (first revision)

IS No. Title

(6) 4924 Method of test for nail-jointed timber trusses (Part 1): 1968 Destructive test (Part 2): 1968 Proof test

(7) 13958 : 1994 Specification for bamboo mat board for general purposes

(8) 14588 : 1999 Specification for bamboo mat veneer composite for general purposes

(9) 15476 : 2004 Specification for bamboo mat corrugated sheets

(10) 15972 : 2012 Specification for bamboo-jute composite corrugated and semi-corrugated sheets

(11) 1734 (Parts 1 Methods of test for plywood to 20): 1983 (second revision)

(12) 1708 (Parts 1 to 18): 1986 Methods of testing of small clear specimens of timber (second revision)

(13) 848 : 2006 Specification for synthetic resin adhesives for plywood (phenolic and aminoplastic) (second revision)

PART 6 STRUCTURAL DESIGN — SECTION 3 TIMBER AND BAMBOO: 3B BAMBOO

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PART 6 STRUCTURAL DESIGN

Section 4 Masonry

BUREAU OF INDIAN STANDARDS

FOREWORD
... 3
1 SCOPE
... 5
2 TERMINOLOGY
... 5
3 MATERIALS
... 7
4 DESIGN CONSIDERATIONS
... 9
5 STRUCTURAL DESIGN
... 18
6 GENERAL REQUIREMENTS
... 22
7 REINFORCED BRICK AND REINFORCED BRICK CONCRETE FLOORS AND ROOFS
... 23
8 SPECIAL CONSIDERATION FROM EARTHQUAKE POINT OF VIEW
... 23
9 GUIDELINES FOR IMPROVING EARTHQUAKE RESISTANCE OF LOW STRENGTH MASONRY BUILDINGS
... 48
10 REINFORCED MASONRY
... 54
11 MASONRY WALLS USING RAT-TRAP BOND TECHNOLOGY
... 62
12 NOTATIONS AND SYMBOLS
... 62
ANNEX A SOME GUIDELINES FOR ASSESSMENT OF ECCENTRICITY OF LOADING ON WALLS
... 63
ANNEX B CALCULATION OF BASIC COMPRESSIVE STRESS OF MASONRY BY PRISM TEST
... 63
ANNEX C GUIDELINES FOR DESIGN OF MASONRY SUBJECTED TO CONCENTRATED LOADS
... 64
ANNEX D GUIDELINES FOR APPROXIMATE DESIGN OF NON-LOAD BEARING WALL
... 65
ANNEX E CONFINED MASONRY BUILDING CONSTRUCTION
... 66
ANNEX F TYPICAL ITERATIVE METHOD FOR WALLS SUBJECTED TO FLEXURE AND AXIAL LOAD
... 72
ANNEX G DISTRIBUTION OF LATERAL FORCES IN THE PIERS OF A MASONRY WALL
... 75
ANNEX H MASONRY WALLS USING RAT-TRAP BOND
... 78
ANNEX J NOTATIONS, SYMBOLS AND ABBREVIATIONS
... 83
LIST OF STANDARDS
... 83

National Building Code Sectional Committee, CED 46

This Code (Part 6/Section 4) covers the structural design of unreinforced and reinforced masonry elements in buildings. Provisions on reinforced brick and reinforced brick concrete floors and roofs have also been dealt with.

This Section was first published in 1970 and subsequently revised in 1983. The first revision of this Section was modified in 1987 through Amendment No. 2 to bring this Section in line with the latest revised masonry code. In the amendment, certain provisions were updated following the revision of IS 1905 'Code of practice for structural use of unreinforced masonry' on which the earlier version was based. In the amendment, requirements of masonry element for stability were modified; in the design of free standing wall, provisions were made for taking advantage of the tensile resistance in masonry under certain conditions; provision regarding effective height of masonry wall between openings was modified; method of working out effective height of wall with a membrane type DPC was modified; the criteria for working out effective length of wall having openings was modified; some general guidelines for dealing with concentrated loads for design of walls were included; and provision of cutting and chases in walls were amplified. The Section was thereafter revised in 2005.

In the second revision of this Section in 2005, the provisions of special considerations in earthquake zones were aligned in line with the revised Indian Standard, IS 4326 : 1993 ‘Code of practice for earthquake resistant design and construction of buildings’; a new clause covering guidelines for improving earthquake resistance of low strength masonry buildings was added; and reference to design of reinforced brick and reinforced brick concrete floors and roofs was included.

As a result of experience gained in the implementation of this Section and feedback received, as well as in view of revision of IS 4326, a need to revise this Section was again felt. This Section has, therefore, been revised to incorporate the following significant changes:

a) Detailed provisions relating to reinforced masonry have been included.

b) The provisions of special considerations in earthquake zones have been updated including by incorporation of suitable provisions relating to ‘Confined masonry building construction’.

c) A separate table on compressive strength for different grades of mortar has been included for clarity.

d) Mix proportions and strength of mortars for masonry have been updated to be based on proportioning by mass (instead of by volume) to reflect sound engineering practices; and 28 day strength values of cement-sand mortar with cement having compressive strength of $43\mathrm{MPa}$ and above.

e) Provisions related to durability criteria for selection of masonry mortars have been included.

f) Use of one and a half brick thick wall up to ground level from foundation level has been suggested to reduce the slenderness ratio of the wall above it for ground floor walls.

g) Stabilized soil blocks have been included as masonry unit.

h) Number of storeys of masonry construction has been limited to 4, in line with the seismic design standards.

j) Masonry wall construction using rat-trap bond has been included.

k) Reference to all the concerned Indian Standards has been updated.

Structural design requirements of this section are largely based on following Indian Standards:

a) IS 1905:1987 'Code of practice for structural use of unreinforced masonry (third revision)',

b) IS 4326:2013 ‘Earthquake resistant design and construction of buildings — Code of practice (third revision)

c) IS 10440:1983 Code of practice for construction of RB and RBC floors and roofs, and

d) IS 13828:1993 ‘Improving earthquake resistance of low strength masonry buildings — Guidelines’.

Until further research material is available on rat-trap bond masonry, its usage is proposed to be limited up to two storeys.

PART 6 STRUCTURAL DESIGN — SECTION 4 MASONRY

A reference to SP 20 : 1991 ‘Handbook on masonry design and construction (first revision)’, may be useful. In the formulation of this Section, inputs were also derived from the IITK-GSDMA’s publication, ‘Guidelines for structural use of reinforced masonry’.

All standards, whether given herein above or cross-referred to in the main text of this section, are subject to revision. The parties to agreement based on this section 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 Section 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 Section.