Structural Use of Unreinforced Masonry
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Document No. :: IITK-GSDMA-EQ12-V4.0 :: IITK-GSDMA-EQ19-V2.0 ::IITK-GSDMA-EQ25-V2.0 Final Report :: A - Earthquake Codes IITK-GSDMA Project on Building Codes Structural Use of Unreinforced Masonry by Dr. Durgesh C. Rai Department of Civil Engineering Indian Institute of Technology Kanpur Kanpur With assistance from Mr. Sandeep Pal Ms. Ami Patwa Mr. Samaresh Paikara Mr. Ashish Narayan Department of Civil Engineering Indian Institute of Technology Kanpur Kanpur Code &Commentary IS:1905 • This document has been made available as a “Draft for Comment” and is not ready for use. It is still in development stage as a part of ongoing project on Building Codes sponsored by Gujarat State Disaster Management Authority, Gandhinagar at Indian Institute of Technology Kanpur. • The views and opinions expressed are those of the authors and not necessarily of the GSDMA, the World Bank, IIT Kanpur, or the Bureau of Indian Standards. • Comments and feedbacks may please be forwarded to: Prof. Sudhir K Jain, Dept. of Civil Engineering, IIT Kanpur, Kanpur 208016, email: [email protected]; [email protected] Page ii Code &Commentary IS:1905 CONTENTS PART 1: CODE AND COMMENTARY 0. – FOREWORD .........................................1 5.6 – Permissible Stresses 59 5.6.1 – Basic Compressive stress 59 1. – SCOPE ..................................................5 5.6.2 – Permissible Compressive 1.1 – ..........................................................5 Stress……………………………….60 1.2 – ..........................................................5 5.7 – Combined Permissible Axial and Flexural Compressive 2. – TERMINOLOGY....................................6 Stresses…………2066 5.7.1 – …………………………………..66 3. – MATERIALS ........................................16 5.8 – Permissible Tensile Stress.........2067 3.1 – Masonry Units................................16 5.9 – Permissible Shear Stress...............70 3.1.1 – .................................................17 5.10 – Design Criteria .............................70 3.1.2 – .................................................17 3.2 – Mortar.............................................17 6. – GENERAL REQUIREMENTS .........2077 3.2.1 – .................................................18 6.1 –Methods of construction..............2078 3.2.2 – Selection of Mortar ..................19 6.2 – Minimum Thickness of Walls from 3.3 – Material Properties.....................2021 Consideration other than Structural2078 3.3.1 – General................................2021 6.3 – Workmanship.............................2081 3.3.2 - Elastic modulus....................2021 6.3.1 – General ...............................2081 3.3.3 – Shear modulus ....................2022 6.3.2 – Bedding of Masonry unit .....2081 6.3.3 – Bond....................................2081 4. – DESIGN CONSIDERATIONS .........2023 6.3.4 – Verticality and alingnment...2081 4.1 – General ......................................2023 6.4 – Joints to control deformation and 4.2 – Lateral Supports and Stability....2023 cracking ..........................................2086 4.3 – Effective Height..........................2033 6.5 – Chases, Recesses and Holes ...2081 4.3.1 –Wall ......................................2033 6.6 – Corbelling...................................2086 4.3.2 – Column ................................2034 7. – Seismic Design RequirementsError! Bookmark not define 4.3.3 – Openings in Walls ...............2035 7.1 –ScopeError! Bookmark not defined.Error! Bookmark 4.4 – Effective Length .........................2038 7.2 – Different Performance Levels of 4.5 – Effective Thickness....................2038 Masonry Shear WallsError! Bookmark not defined.Error 4.6 – Effective Length .........................2038 4.7 – Slenderness Ratio......................2042 8. – NOTATIONS AND SYMBOLS ....208889 4.8 –Minimum Design Dimention........2044 Appendix A .........................................208990 5. – STRUCTURAL DESIGN......................46 (Clause 4.8) ....................................208990 5.1 – General ..........................................46 Appendix B .........................................209091 5.2 – Design loads ..................................51 Appendix C.........................................209091 5.2.1 – Dead Loads………………........52 Appendix D.........................................209192 5.2.2 – Live Loads and Wind Loads….52 Appendix E .........................................209192 5.2.3 – Seismic Loads……………...….52 5.2.4 – Load Combinations……………52 5.2.5 – Permissible Stresses and Loads……………………………. 52 5.3 – Vertical Load Dispersion............2053 5.3.1 – General................................2053 5.3.2 – Arching Action .....................2053 5.3.3 – Lintels ..................................2055 5.4 – Lateral Load Distribution............2058 5.5 – Basic Compressive Strength of Masonry..........................................2059 5.5.1 – Unit Strength Method ..........2059 5.5.2 – Prism Test Method ..............2059 Page iii Code &Commentary IS:1905 CONTENTS PART 2: EXPLANATORY EXAMPLES Ex. Title Design Issue Page No. No. 1. Design of a hall subjected to Check for in-plane flexural and shear 99-103 wind load stresses due to gravity and wind loads, Determination of grade of mortar for long wall and cross wall 2. Design of a diaphragm type Determination of permissible height of 104-105 free standing wall diaphragm wall for specified masonry type (grade of mortar and brick units) 3. Design of wall of a room with Check for in-plane flexural and shear 106-108 opening stresses for a clay brick masonry wall with door opening, Determination of grade of mortar 4. Design of a unreinforced Check for in-plane flexural tensile and 109-111 cross wall for wind load shear stresses, Determination of grade of mortar for cross wall 5 Design of unreinforced shear Check for tensile and shear stresses for 112-113 wall for in-plane shear and masonry wall subjected to wind and flexure earthquake load Page iii Code &Commentary IS:1905 PART 1: CODE AND COMMENTARY Page iv Code &Commentary IS:1905 PROVISIONS COMMENTARY 0. – Foreword C0. – Foreword 0.1 – This Indian Standard (Third Revision) was adopted by the Bureau of Indian Standards on 30 August 1987, after the draft finalized by the Structural Safety Sectional Committee had been approved by the Civil Engineering Division Council. This draft revision of IS: 1905 is prepared as a project entitled “Review of building codes and Handbook” awarded to IIT Kanpur by GSDMA, Gandhinagar through World Bank Finances. 0.2 – Structural adequacy of masonry walls depends upon a number of factors, among which mention may be made of quality and strength of masonry units and mortars, workmanship, methods of bonding, unsupported height of walls, eccentricity in the loading, position and size of openings in walls: location of cross walls and the combination of various external loads to which walls are subjected. 0.3 – This code was first published in 1961. In its revision in 1969, basic compressive stresses and stress factors for slenderness were modified resulting in increased permissible stresses in load bearing brick and block walls. Subsequently two more revisions were published in 1980 & 1987. The following major changes were made in its second revision: a) Use of stones (in regular sized units), concrete blocks, lime based blocks and hollow blocks were included as masonry units; b) Mix proportions and compressive strengths of mortars used in masonry were revised; c) Optimum mortar mixes for maximum strength of masonry for units of various strengths were indicated; d) Provisions for lateral supports to walls had been amplified so as to include stability requirements; e) Conditions of support for calculation of effective height of masonry walls and columns, and effective length of masonry walls were spelt out more clearly; f) Maximum allowable slenderness ratio for load bearing walls was increased; g) In case of free-standing walls, height to Page 1 Code &Commentary IS:1905 PROVISIONS COMMENTARY thickness ratios were indicated for different wind pressures, based upon requirements for stability; h) Basic compressive stresses for masonry members were modified so that strength of masonry units correspond to revised values of brick crushing strength specified in IS:1077-1986*; i) Formula for calculating area reduction factor was modified; j) Angle of dispersion of concentrated loads, from the direction of such loads was changed from 45° to 30°; k) Provisions relating to shape modification factors for masonry units other than common bricks were amplified; l) Values of permissible shear stress was related to the actual compressive stresses in masonry due to dead loads; m) Provisions on ‘corbelling’ were amplified. *Specification for common burnt clay building bricks (Fourth Revision). 0.4 – The present revision is intended to further modify certain provisions as a result of experience gained with the use of the second revision of the standard. The following major changes have been made in this revision. (i) The requirements of a masonry element for stability have been modified. (ii) In the design of a free standing wall, provision has been made for taking advantage of the tensile resistance in masonry under certain conditions. (iii)Provision regarding effective height of a masonry wall between openings has been modified. (iv)Method of working out effective height of a wall with a membrane type DPC has been modified, (v)Criteria for working out effective length of wall having openings have been modified. (vi)Some