Chapter 19Protection Against Termite Attack in Buildings

19.1 Two groups of organisms which affect the mechanical and aesthetic properties of wood in houses

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

are fungi and insects. The most important wood destroying insects belong to termites and beetles. Of about 250 species of wood destroying termites recorded in India, not more than a dozen species attack building causing about 90 percent of the damage to timber and other cellulosic materials. Subterranean termites are the most destructive of the insects that infest wood in houses justifying prevention measures to be incorporated in the design and construction of buildings.

19.1.1 Control measures consist in isolating or sealing off the building from termites by chemical and non-chemical construction techniques. It is recognized that 95 percent damage is due to internal travel of the termites from ground upwards rather than external entry through entrance thus calling upon for appropriate control measures in accordance with good practices [6-3A(21)].

19.2 Chemical Methods

Termites live in soil in large colonies and damage the wooden structure in the buildings by eating up the wood or building nests in the wood. Poisoning the soil under and around the building is a normal recommended practice. Spraying of chemical solution in the trenches of foundations in and around walls, areas under floors before and after filling of earth, etc. In already constructed building the treatment can be given by digging trenches all around the building and then giving a liberal dose of chemicals and then closing the trenches.

Natural resistance against organisms of quite a few

wood species provides durability of timber without special protection measure. It is a property of heartwood while sapwood is normally always susceptible to attack by organisms. Preservatives should be well applied with sufficient penetration into timber. For engineers, architects and builders, the following are prime considerations for choice of preservatives:

a) Inflammability of treated timber is not increased and mechanical properties are not decreased;

b) Compatibility with the glue in laminated wood, plywood and board material;

c) Water repellent effect is preferred;

d) Possible suitability for priming coat;

e) Possibility of painting and other finishes;

f) Non-corrosive nature in case of metal fasteners; and

g) Influence on plastics, rubber, tiles and concrete.

Protection against potential problem of termite attack can simply be carried out by ordinary good construction which prevents a colony from gaining access by,

a) periodic visual observations on termite galleries to be broken off;

b) specially formed and properly installed metal shield at plinth level; and

c) continuous floor slabs, apron floors and termite grooves on periphery of buildings.

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

LIST OF STANDARDS

The following list records those standards which are acceptable as ‘good practice’ and ‘accepted standards’ in the fulfilment of the requirements of the Code. The latest version of a standard shall be adopted at the time of the 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 reference in this Subsection.

IS No. (1) 707 : 2011 Title Timber technology and utilization of wood, bamboo and cane — Glossary of terms (third revision)

(2) 1708 (Parts 1 to 18): 1986 Methods of testing small clear specimens of timber (second revision) 2408 : 1963 Methods of static tests of timbers in structural sizes 2455 : 1990 Methods of sampling of model trees and logs for timber testing and their conversion (second revision)

(3) 4970:1973 Key for identification of commercial timbers (first revision)

(4) 287 : 1993 Recommendations for maximum permissible moisture content of timber used for different purposes (third revision)

(5) 3629 : 1986 Specification for structural timber in building (first revision)

(6) 401 : 2001 Code of practice for preservation of timber (fourth revision)

(7) 2366 : 1983 Code of practice for nail-jointed timber construction (first revision)

(8) 4983 : 1968 Code of practice for design and construction of nail laminated timber beam (first revision)

(9) 11096:1984 Code of practice for design construction of bolt-jointed construction

(10) 4907 : 2004 Methods of testing timber connector joints (first revision)

IS No. Title

(11) 9188 : 1979 Performance requirements for adhesive for structural laminated wood products for use under exterior exposure condition

(12) 14616 : 1999 Specification for laminated veneer lumber

(13) 10701 : 2012 Specification for structural plywood (first revision) 4990 : 2011 Specification for plywood for concrete shuttering works (third revision)

(14) 4924 Method of test for nail-jointed timber trusses (Part 1): 1968 Destructive test (Part 2): 1968 Proof test

(15) 12120 : 1987 Code of practice for preservation of plywood and other panel products

(16) 4990 : 2011 Specification for plywood for concrete shuttering works (third revision)

(17) 9307 (Parts 1 to 7): 1979 Methods of test for wood based structural sandwich construction

(18) 723 : 1972 Specification for steel countersunk head wire nails (first revision)

(19) 451 : 1999 Technical supply conditions for wood screws (fourth revision)

6736 : 1972 Specification for slotted countersunk head wood screw

6739 : 1972 Specification for slotted round head wood screw

6760 : 1972 Specification for slotted countersunk head wood screws

(20) 1708 (Parts 1 to 18): 1986 Methods of testing small clear specimens of timber (second revision)

(21) 6313 Code of practice for anti-termite measures in buildings

(Part 1): 1981 Constructional measures (first revision)

(Part 2): 2013 Pre-constructional chemical treatment measures (third revision)

(Part 3): 2013 Treatment for existing buildings (third revision)

PART 6 STRUCTURAL DESIGN

Section 3 Timber and Bamboo: 3B Bamboo

BUREAU OF INDIAN STANDARDS

• FOREWORD
• ... 3
• 1 SCOPE
• ... 5
• 2 TERMINOLOGY
• ... 5
• 3 SYMBOLS
• ... 7
• 4 MATERIALS
• ... 7
• 5 PERMISSIBLE STRESSES
• ... 10
• 6 DESIGN CONSIDERATIONS
• ... 11
• 7 DESIGN, TECHNIQUES OF JOINTS AND CONSTRUCTION PRACTICES
• ... 14
• 8 BAMBOO AS REINFORCEMENT IN CONCRETE
• ... 19
• 9 WALLING, FLOORING, ROOFING, AND IN-FILL PANELS FOR WALL, AND COMMON ROOF COVERING/CLADDING
• ... 21
• ANNEX A SOURCE AND LOCAL NAMES OF SOME OF THE SPECIES OF BAMBOO
• ... 26
• ANNEX B RECOMMENDATIONS FOR BAMBOO STRUCTURES IN HIGH WIND/CYCLONE PRONE AREAS
• ... 28
• LIST OF STANDARDS
• ... 29

National Building Code Sectional Committee, CED 46

This Code (Part 6/Subsection 3B) covers the general principles involved in the design of structural bamboo in buildings with regard to mechanical resistance and durability of structures. Design of both bamboo (round bamboo, split bamboo, glued laminated bamboo) and bamboo-based panels joined together with adhesives or mechanical fasteners are covered in this Subsection. It also covers minimum strength data, dimensional stability, grading requirements and traditional bamboo joints for quality assurance. Constructional aspects using bamboo, such as, work on site, fabrication of components off-site and their erection on site is also covered to the extent necessary to indicate and ensure the quality of material and standard of workmanship to comply with the assumptions of the design rules and the limitations.

Bamboo is a versatile resource possessing high strength-to-weight ratio and cost ratio and offers considerable ease in working with simpler tools. It has a long and well established tradition as a building material. The application of bamboo as a constructional material is largely based on established traditions and intuitions of forefathers throughout the tropical and sub-tropical regions.

Resilience coupled with light weight makes bamboo an ideal material for housing in disaster prone/earthquake prone areas. It has the capacity to withstand repetitive loadings and absorb more energy and show larger deflections before collapse and as such is safer under earth tremors. As the design guidelines were inadequate, the application of bamboo as an engineering material was largely based on practical and engineering experience. A need was therefore felt to develop a Code for design and construction with bamboo so as to cater to a number of social and trade advantages, engineering recognition and the improved status of bamboo as an engineering material. This was achieved by adding a new chapter in the last revision of the Code, covering structural design with bamboo. Forest Research Institute, Dehradun and some other organizations were engaged in bamboo research to establish its silviculture, botanical, entomological and pathological aspects besides creating a utilization base. All these works were utilized in the preparation of the last version of this Subsection of the Code.

Some of the suitable species grown in India and neighbouring countries are enlisted in Annex A along with their local names and source, for general information.

The bamboo culm has a tubular structure consisting essentially of nodes and inter-nodes. In the inter-nodes the cells are axially oriented while the nodes provide the transverse inter-connection. The disposition of the nodes and the wall thickness are significant in imparting strength to bamboo against bending and crushing. In a circular cross-section, bamboo is generally hollow and for structural purposes this form is quite effective and advantageous. Each of the species of bamboo has widely different characteristics affecting its usefulness as constructional material. The strength of bamboo culms, their straightness, lightness combined with hardness, range and size of hollowness make them potentially suitable for a variety of applications both structural and non-structural. With good physical and mechanical properties, low shrinkage and good average density, bamboo is well suited to replace wood in several applications, especially in slats and panel form. Mass production of bamboo components, if required, may be integrated with treatment facilities near to the site of plantation or site of construction, for speed and economy in construction.

The Section on structural design with bamboo was first published in 2005 as Subsection 3B of Part 6. In the 1983 version of the Code, timber was covered under Section 3 of Part 6 ‘Structural Design’ under the title ‘Wood’, which did not cover bamboo. In the last version of 2005, the scope of Section 3 was enlarged as Section 3 ‘Timber and Bamboo’, which was subdivided into Subsection 3A ‘Timber’ and Subsection 3B ‘Bamboo’. This Subsection pertains to ‘Bamboo’.

As a result of experience gained in implementation of 2005 version of this Code and further research work done and feedback received as well as formulation of new standards in the field and revision/updation of some of the existing standards, a need to revise this Subsection was felt. This revision has, therefore, been brought out to take care of these aspects.

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

The significant changes incorporated in this revision include the following:

a) This Subsection now also covers construction practices with bamboo which were earlier covered in Part 7 ‘Construction Management, Practices and Safety’ of the Code.

b) Definitions of some existing terms have been modified as per the prevailing engineering practice and new terms relating to bamboo based panel products have been added.

c) Provisions on bamboo trusses have been further updated.

d) Some details about bamboo foundations have been included.

e) Use of bamboo as reinforcement in concrete has been included.

f) Provisions for use of bamboo based materials/panel products as walling, flooring and roofing, and in-in-fill panels for wall and common roof covering/cladding materials, have been included. Some provisions for reconstituted wood from destructured bamboo have also been included.

g) References to all the concerned Indian Standards have been updated.

With the standardization on design and construction aspects of bamboo in this Subsection of the Code, it is expected to ensure durable structures, however, some specific guidelines are required in the event of tropical cyclones in the sub-continent and the traditional non-engineered structures generally constructed. Keeping this in view, some recommendations are given in Annex B which may be followed in addition to provisions given in the main text of this Subsection.

The information contained in this Subsection is largely based on the works carried out at Forest Research Institute, Dehradun, Indian Plywood Industries Research and Training Institute, Bangalore, International Network for Bamboo and Rattan (INBAR) documents and Indian Standards given below. Assistance has also been derived from ISO 22156 : 2004 ‘Bamboo-Structural design’.

IS 9096 : 2006 Code of practice for preservation of bamboo for structural purpose (first revision)

IS 15912 : 2012 Code of practice for structural design using bamboo

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.